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1
Burrell, Geoffrey Scott. "Distortional buckling in steel I-girders." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 143 p, 2007. http://proquest.umi.com/pqdweb?did=1338867451&sid=1&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Arizou, Ramin. "Distortional Lateral Torsional Buckling of Doubly Symmetric Wide Flange Beams." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/41574.
Full textAbstract:
Distortional lateral-torsional buckling theories assume that the flanges remain undistorted, while the web is free to distort as a thin plate. Most theories adopt a cubic polynomial distribution along the web height to relate the lateral displacement of the web to the displacements and angles of twist both flanges. The present study develops a family of finite element solutions for the distortional buckling of wide flange beams in which the flanges are assumed to remain undistorted. In contrast to past theories, the lateral displacement distribution along the web height is characterized by superposing (a) two linear modes intended to capture the classical non-distortional lateral-torsional behavior and (b) any number of user-specified Fourier terms intended to capture additional web distortion. In the longitudinal direction, all displacement fields characterizing the lateral displacements are taken to follow a cubic distribution.
The first contribution of the thesis develops a finite element formulation that is able to replicate the classical non-distortional lateral torsional buckling solutions when the distortional modes are suppressed while enabling more accurate predictions for distortional lateral torsional buckling compared to those solutions based on the conventional cubic interpolation of the lateral displacement. The formulation is used to conduct an extensive parametric study to quantify the reduction in critical moments due to web distortion relative to the classical non-distortional predictions in the case of simply-supported beams, cantilevers, and beams with an overhang. The solution is then used to generate interaction curves for beams with an overhang subjected to various proportions of uniformly distributed and point loads.
The second contribution of the thesis adds two additional features to the formulation (a) to capture the destabilizing effect due to the load height relative to the shear center and (b) a module that incorporates any number of user-defined multi-point kinematic constraints. The additional features are employed to investigate the effect of load height, bracing height, and combined effects thereof in practical design problems. A distortional indicator is then introduced to characterize the distribution of web distortion along the beam span as the beam undergoes distortional lateral buckling. A systematic design optimization technique is then devised to identify the location(s) along the span at which the addition of transverse stiffeners would maximize the critical moment capacity.
3
Ho, Teck Tuak. "Analysis of distortional buckling in continuous composite beams." Thesis, University of Nottingham, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275729.
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Pezeshky, Payam. "Distortional Static and Buckling Analysis of Wide Flange Steel Beams." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36074.
Full textAbstract:
Existing design provisions in design standards and conventional analysis methods for structural steel members are based on the simplifying kinematic Vlasov assumption that neglects cross-sectional distortional effects. While the non-distortional assumption can lead to reasonable predictions of beam static response and buckling strength in common situations, past work has shown the inadequacy of such assumption in a number of situations where it may lead to over-predicting the strength of the members. The present study thus develops a series of generalized theories/solutions for the static analysis and buckling analysis of steel members with wide flange cross-sections that capture distortional effects of the web. Rather than adopting the classical Vlasov assumption that postulates the cross-section to move and rotate in its own plane as a rigid disk, the present theories assume the web to be flexible in the plane of the cross-section and thus able to bend laterally, while both flanges to move as rigid plates within the plane of the cross-section to be treated as Euler-Bernouilli beams. The theories capture shear deformation effects in the web, as well as local and global warping effects.
Based on the principle of minimum potential energy, a distortional theory is developed for the static analysis of wide flange steel beams with mono-symmetric cross-sections. The theory leads to two systems of differential equations of equilibrium. The first system consists of three coupled equilibrium differential equations that characterize the longitudinal-transverse response of the beam and the second system involves four coupled equilibrium differential equations of equilibrium and characterizes the lateral-torsional response of the beam. Closed form solutions are developed for both systems for general loading. Based on the kinematics of the new theory, two distortional finite elements are then developed. In the first element, linear and cubic Hermitian polynomials are employed to interpolate displacement fields while in the second element, the closed-form solutions developed are adopted to formulate special shape functions. For longitudinal-transverse response the elements consist of two nodes with four degree of freedom per node for longitudinal-transverse response and for lateral-torsional response, the elements consist of two nodes with eight degrees of freedom per node. The solution is able to predict the distortional deformation and stresses in a manner similar to shell solutions while keeping the modeling and computational effort to a minimum.
Applications of the new beam theory include (1) providing new insights on the response of steel beams under torsion whereby the top and bottom flanges may exhibit different angles of twist, (2) capturing the response of steel beams with a single restrained flange as may be the case when a concrete slab provides lateral and/or torsional restraint to the top flange of a steel beam, and (3) modelling the beneficial effect of transverse stiffeners in reducing distortional effects in the web.
The second part of the study develops a unified lateral torsional buckling finite element formulation for the analysis of beams with wide flange doubly symmetric cross-sections. The solution captures several non-conventional features. These include the softening effect due to web distortion, the stiffening effect induced by pre-buckling deformations, the pre-buckling nonlinear interaction between strong axis moments and axial forces, the contribution of pre-buckling shear deformation effects within the plane of the web, the destabilizing effects due to transverse loads being offset from the shear centre, and the presence of transverse stiffeners on web distortion. Within the framework of the present theory, it is possible to evoke or suppress any combination of the features and thus isolate the individual contribution of each effect or quantify the combined contributions of multiple effects on the member lateral torsional capacity. The new solution is then applied to investigate the influence of the ratios of beam span-to-depth, flange width-to-thickness, web height-to-thickness, and flange width-to-web height on the lateral torsional buckling strength of simply supported beams and cantilevers. Comparisons with conventional lateral torsional buckling solutions that omit distortional and pre-buckling effects quantify the influence of distortional and/or pre-buckling deformation effects. The theory is also used to investigate the influence of P-delta effects of beam-columns subjected to transverse and axial forces on their lateral torsional buckling resistance. The theory is used to investigate the load height effect relative to the shear centre. Comparisons are made with load height effects as predicted by non-distortional buckling theories. The solution is adopted to quantify the beneficial effect of transverse stiffeners in controlling/suppressing web distortion in beams and increasing their buckling resistance.
5
Ng, Maurice Loong-Hon. "Use of Fourier series in examining the distortional buckling of beams /." St. Lucia, Qld, 2003. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe17264.pdf.
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6
Chung, Kwok Fai. "The elastic distortional and local plate buckling of slender web beam." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/7860.
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7
Poon, Chou Ping. "Advanced finite element models for the distortional buckling analysis of I-beams." St. Lucia, Qld., :, 2003. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe17278.pdf.
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8
Hassan, Rusul. "Distortional Lateral Torsional Buckling Analysis for Beams of Wide Flange Cross-sections." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24008.
Full textAbstract:
Structural steel design standards recognize lateral torsional buckling as a failure mode governing the capacity of long span unsupported beams with wide flange cross-sections. Standard solutions start with the closed form solution of the Vlasov thin-walled beam theory for the case of a simply supported beam under uniform moments, and modify the solution to accommodate various moment distributions through moment gradient expressions. The Vlasov theory solution is based on the assumption that cross-sectional distortional effects have a negligible effect on the predicted elastic critical moment. The present study systematically examines the validity of the Vlasov assumption related to cross-section distortion through a parametric study.
A series of elastic shell finite element eigen-value buckling analyses is conducted on simply supported beams subject to uniform moments, linear moments and mid span point loads as well as cantilevers subject to top flange loading acting at the tip. Cross-sectional dimensions are selected to represent structural steel cross-section geometries used in practice. Particular attention is paid to model end connection details commonly used in practice involving moment connections with two pairs of stiffeners, simply supported ends with a pair of transverse stiffeners, simply supported ends with cleat angle details, and built in fixation at cantilever roots.
The critical moments obtained from the FEA are compared to those based on conventional critical moment equations in various Standards and published solutions. The effects of web slenderness, flange slenderness, web height to flange width ratio, and span to height ratios on the critical moment ratio are systematically quantified. For some combinations of section geometries and connection details, it is shown that present solutions derived from the Vlasov theory can overestimate the lateral torsional buckling resistance for beams.
9
Haidarali, Mohammad Reza. "Local and distortional buckling behaviour of cold-formed steel Z section beams." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/6992.
Full textAbstract:
The economic use of cold-formed steel members means that buckling and the possible loss of effectiveness it produces are important features of design. Cross-sectional instabilities in laterally-restrained cold-formed steel beams include local and distortional buckling. The prediction of the true buckling behaviour of cold-formed steel beams accounting for all governing features such as geometrical imperfections, spread of yielding, postbuckling etc. has been possible with the development of advanced numerical modelling. In this thesis, the finite element (FE) method (ABAQUS) has been used to develop numerical analyses to study the buckling behaviour of laterally-restrained cold-formed steel lipped Z-section beams. The FE models were verified against a series of four-point bending tests available from previous research, with special references to material and geometrical nonlinearities. Two sets of analyses have been conducted: FE analyses allowing for both local and distortional buckling and ones allowing for local buckling while distortional buckling is restrained using appropriate boundary conditions. For the former, the controlling buckling mode (local, distortional or combined) at different stages of loading (up to, at and beyond maximum load) has been realized. Comparing the results of two sets of analyses, the effect of distortional buckling on performance for different geometric proportions has been studied. The effect of the lip size, flange width, angle of inclination of the edge stiffener (lip), size and position of the intermediate stiffener and material strength as well as the interaction between them on both the ultimate strength and the buckling of cold-formed Z-section beams has been investigated. Limits for optimum design of the section were proposed. Depending on the geometric properties and material strength of the section, transitions between local, distortional and combined local/distortional buckling were observed. The lip/flange interaction including the interaction between the edge stiffener (lip) and the intermediate stiffener was the key governing feature of behaviour. The effect of the linear moment gradient and sharply varying bending moment on both the ultimate strength and the buckling of cold-formed Z sections was investigated. The latter occurred in two-span continuous beams subject to uniformly distributed loading. The results of moment gradient cases were compared with those of pure bending cases. The suitability of the design treatments available in Eurocode 3 (EC3) for local, combined local/distortional and distortional buckling of cold-formed Z-section beams was assessed. Overall, the EC3 predictions for cross-sectional bending resistances were unconservative. Shortcomings were identified and some suggestions for improvements were made. This included improvements in plate buckling factors for edge-stiffened compression flanges.
10
Ranawaka, Thanuja. "Distortional buckling behaviour of cold-formed steel compression members at elevated temperatures." Thesis, Queensland University of Technology, 2006. https://eprints.qut.edu.au/16417/6/Thanuja_Ranawaka_Thesis.pdf.
Full textAbstract:
In recent times, light gauge cold-formed steel sections have been used extensively in
residential, industrial and commercial buildings as primary load bearing structural
components. This is because cold-formed steel sections have a very high strength to
weight ratio compared with thicker hot-rolled steel sections, and their manufacturing
process is simple and cost-effective. However, these members are susceptible to
various buckling modes including local and distortional buckling and their ultimate
strength behaviour is governed by these buckling modes. Fire safety design of
building structures has received greater attention in recent times due to continuing
loss of properties and lives during fires. Hence, there is a need to fully evaluate the
performance of light gauge cold-formed steel structures under fire conditions. Past
fire research has focused heavily on heavier, hot-rolled steel members. The buckling
behaviour of light gauge cold-formed steel members under fire conditions is not well
understood. The buckling effects associated with thin steels are significant and have
to be taken into account in fire safety design. Therefore, a research project based on
extensive experimental and numerical studies was undertaken at the Queensland
University of Technology to investigate the distortional buckling behaviour of light
gauge cold-formed steel compression members under simulated fire conditions.
As the first phase of this research program more than 115 tensile coupon tests of
light gauge cold-formed steels including two steel grades and five thicknesses were
conducted at elevated temperatures. Accurate mechanical properties including the
yield strength, elasticity modulus and stress-strain curves were all determined at
elevated temperatures since the deterioration of the mechanical properties is one of
the major parameters in the structural design under fire conditions. An appropriate
stress-strain model was also developed by considering the inelastic characteristics.
The results obtained from the tensile coupon tests were then used to predict the
ultimate strength of cold-formed steel compression members.
In the second phase of this research more than 170 laboratory experiments were
undertaken to investigate the distortional buckling behaviour of light gauge coldformed steel compression members at ambient and elevated temperatures. Two types of cross sections were selected with various thicknesses (nominal thicknesses are
0.6, 0.8, and 0.95 mm) and both low and high strength steels (G250 and G550 steels
with minimum yield strengths of 250 and 550 MPa). The experiments were
conducted at six different temperatures in the range of 20 to 800°C. A finite element
model of the tested compression members was then developed and validated with the
help of experimental results. The degradation of mechanical properties with
increasing temperatures was included in finite element analyses.
An extensive series of parametric analyses was undertaken using the validated finite
element model to investigate the effect of all the influential parameters such as
section geometry, steel thickness and grade, mechanical properties and temperature.
The resulting large data base of ultimate loads of compression members subject to
distortional buckling was then used to review the adequacy of the current design
rules at ambient temperature. The current design rules were reasonably accurate in
general, but in order to improve the accuracy further, this research has developed
new design equations to determine the ultimate loads of compression members at
ambient temperature. The developed equation was then simply modified by
including the relevant mechanical properties at elevated temperatures. It was found
that this simple modification based on reduced mechanical properties gave
reasonable results, but not at higher temperatures. Therefore, they were further
modified to obtain a more accurate design equation at elevated temperatures. The
accuracy of new design rules was then verified by comparing their predictions with
the results obtained from the parametric study.
This thesis presents a description of the experimental and numerical studies
undertaken in this research and the results including comparison with simply
modified current design rules. It describes the laboratory experiments at ambient and
elevated temperatures. It also describes the finite element models of cold-formed
steel compression members developed in this research that included the appropriate
mechanical properties, initial geometric imperfections and residual stresses. Finally,
it presents the details of the new design equations proposed for the light gauge coldformed
steel compression members subjected to distortional buckling effects at
elevated temperatures.
11
Ranawaka, Thanuja. "Distortional buckling behaviour of cold-formed steel compression members at elevated temperatures." Queensland University of Technology, 2006. http://eprints.qut.edu.au/16417/.
Full textAbstract:
In recent times, light gauge cold-formed steel sections have been used extensively in residential, industrial and commercial buildings as primary load bearing structural components. This is because cold-formed steel sections have a very high strength to weight ratio compared with thicker hot-rolled steel sections, and their manufacturing process is simple and cost-effective. However, these members are susceptible to various buckling modes including local and distortional buckling and their ultimate strength behaviour is governed by these buckling modes. Fire safety design of building structures has received greater attention in recent times due to continuing loss of properties and lives during fires. Hence, there is a need to fully evaluate the performance of light gauge cold-formed steel structures under fire conditions. Past fire research has focused heavily on heavier, hot-rolled steel members. The buckling behaviour of light gauge cold-formed steel members under fire conditions is not well understood. The buckling effects associated with thin steels are significant and have to be taken into account in fire safety design. Therefore, a research project based on extensive experimental and numerical studies was undertaken at the Queensland University of Technology to investigate the distortional buckling behaviour of light gauge cold-formed steel compression members under simulated fire conditions. As the first phase of this research program more than 115 tensile coupon tests of light gauge cold-formed steels including two steel grades and five thicknesses were conducted at elevated temperatures. Accurate mechanical properties including the yield strength, elasticity modulus and stress-strain curves were all determined at elevated temperatures since the deterioration of the mechanical properties is one of the major parameters in the structural design under fire conditions. An appropriate stress-strain model was also developed by considering the inelastic characteristics. The results obtained from the tensile coupon tests were then used to predict the ultimate strength of cold-formed steel compression members. In the second phase of this research more than 170 laboratory experiments were undertaken to investigate the distortional buckling behaviour of light gauge coldformed steel compression members at ambient and elevated temperatures. Two types of cross sections were selected with various thicknesses (nominal thicknesses are 0.6, 0.8, and 0.95 mm) and both low and high strength steels (G250 and G550 steels with minimum yield strengths of 250 and 550 MPa). The experiments were conducted at six different temperatures in the range of 20 to 800°C. A finite element model of the tested compression members was then developed and validated with the help of experimental results. The degradation of mechanical properties with increasing temperatures was included in finite element analyses. An extensive series of parametric analyses was undertaken using the validated finite element model to investigate the effect of all the influential parameters such as section geometry, steel thickness and grade, mechanical properties and temperature. The resulting large data base of ultimate loads of compression members subject to distortional buckling was then used to review the adequacy of the current design rules at ambient temperature. The current design rules were reasonably accurate in general, but in order to improve the accuracy further, this research has developed new design equations to determine the ultimate loads of compression members at ambient temperature. The developed equation was then simply modified by including the relevant mechanical properties at elevated temperatures. It was found that this simple modification based on reduced mechanical properties gave reasonable results, but not at higher temperatures. Therefore, they were further modified to obtain a more accurate design equation at elevated temperatures. The accuracy of new design rules was then verified by comparing their predictions with the results obtained from the parametric study. This thesis presents a description of the experimental and numerical studies undertaken in this research and the results including comparison with simply modified current design rules. It describes the laboratory experiments at ambient and elevated temperatures. It also describes the finite element models of cold-formed steel compression members developed in this research that included the appropriate mechanical properties, initial geometric imperfections and residual stresses. Finally, it presents the details of the new design equations proposed for the light gauge coldformed steel compression members subjected to distortional buckling effects at elevated temperatures.
12
Yap, Derrick. "Interaction of local and distortional buckling of high strength cold-formed steel columns." Thesis, The University of Sydney, 2008. https://hdl.handle.net/2123/28965.
Full textAbstract:
Thin—walled high strength cold—formed steel sections, when subjected to axial
compression, generally fail in a local, distortional and/or flexural—torsional buckling
mode. The sections can have a complex shape and can be fabricated from high strength
cold-formed steel with thickness as low as 0.42 mm. Such complex section designs
may lead to the interaction of local and distortional buckling modes when subjected to
axial compression.
The objective of the thesis is to investigate both theoretically and experimentally the
interaction of the local and distortional buckling modes of cold—formed steel channel
section columns in the post-distortional buckling range.
A theoretical study was carried out using the Finite Element Method (FEM) by
analysing the stress distributions in a simple-lipped channel section under compression.
A range of section thicknesses was analysed to observe sections failing in purely
distortional buckling modes and with interaction of local and distortional buckling
modes. Stress redistribution around the section in the postbuckling range was
observed in a method similar to von Karman’s approach. From the stress distributions
of the different sections, it was observed that when local and distortional buckling
interacts in the postbuckling range, the effect of the post—distortional buckling on the
post-local buckling stress is to push the stress higher at the flange-web junctions. This
observation explains the mechanics of a section subjected to interaction of local and
distortional buckling modes and why it may fail prematurely.
The thesis describes two series of tests performed on Stiffened-Web Channel (SWC)
section columns and Stiffened Cross-shaped (SCR) channel section columns fabricated
from high strength cold-formed steel sheets with thicknesses of 1 mm and 0.42 mm
respectively and a nominal yield stress of 550 MPa.
For the SWC section, a total of 14 fixed—ended columns were tested in compression to
study the local buckling failure of the short columns and the effect of the interaction of
local and distortional buckling on the intermediate and long columns. For the SCR
section, a total of 14 fixed-ended columns were tested to study the effect of the
interaction of local and multiple distortional buckling modes on the failure loads. The
effect of the inward and outward deflections in the distortional mode on failure was also
observed.
The test results are compared with structural design codes of the Australian Standard
AS/NZS 4600:2005 and the North American Specification (NAS) for cold—formed steel
structures. Both the Effective Width Method (EWM) and the Direct Strength Method
(DSM) were found to predict unconservatively for sections failing in the local buckling
mode. Further, the DSM predicts very unconservatively for sections failing in the
distortional mode when the interaction of local and distortional buckling modes occur.
Four new design methods are proposed to improve the local/overall and distortional
DSM strength curves. Conclusions on the most appropriate of the four methods and the
range of applicability are given.
13
Cortese, Scott D. "Investigation of Single Span Z-Section Purlins Supporting Standing Seam Roof Systems Considering Distortional Buckling." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/34198.
Full textAbstract:
Presently, the industry accepted method for the determination of the governing buckling strength for cold-formed purlins supporting a standing seam metal roof system is the 1996 AISI Specification for the Design of Cold-Formed Steel Structural Members, which contains provisions for local and lateral buckling. Previous research has determined that the AISI provisions for local buckling strength predictions of cold-formed purlins are highly unconservative and that the AISI provisions for lateral buckling strength predictions of cold-formed purlins are overly conservative. Therefore, a more accurate "hand" method is needed to predict the buckling strengths of cold-formed purlins supporting standing seam roof systems. The primary objective of this study is to investigate the accuracy of the Hancock Method, which predicts distortional buckling strengths, as compared to the 1996 AISI Specification provisions for local and lateral buckling.
This study used the experimental results of 62 third point laterally braced tests and 12 laterally unbraced tests. All tests were simple span, cold-formed Z-section supported standing seam roof systems. The local, lateral, and distortional buckling strengths were predicted for each test using the aforementioned methods. These results were compared to the experimentally obtained data and then to each other to determine the most accurate strength prediction method.
Based on the results of this study, the Hancock Method for the prediction of distortional buckling strength was the most accurate method for third point braced purlins supporting standing seam roof systems. In addition, a resistance factor was developed to account for the variation between the experimental and the Hancock Method's predicted strengths.Master of Science
14
Smith, Frank Harrison. "Elastic buckling solutions for thin-walled metal columns with perforation patterns." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/23680.
Full textAbstract:
Presented are approximate finite strip methods for use in predicting elastic buckling strength of cold-formed steel columns. These methods were developed by examining elemental behavior of cross-sections in eigen-buckling analyses and validated using a large database of finite element rack-type columns with perforation patterns. The influence of perforations is accounted by reduced thicknesses related to the plate buckling coefficient and transverse web rotational stiffness in the prediction of local and distortional buckling respectively. Global buckling prediction including the influence of perforations uses critical elastic loads of an unperforated section multiplied by the ratio of weighted to gross cross-sectional moment of inertia for flexural buckling and the ratios of weighted to gross cross-sectional warping torsion constant and weighted to gross St. Venant torsional constant for flexural-torsional buckling. Concern for end-user was given and methods are presented in a way for incorporation into governing design standards. Data to support these findings are available at http://hdl.handle.net/10919/23797Master of Science
15
Grey, Christopher Norton. "Cold-Formed Steel Behavior: Elastic Buckling Simplified Methods for Structural Members with Edge-Stiffened Holes and Purlin Distortional Buckling Strength Under Gravity Loading." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/32829.
Full textAbstract:
Elastic Buckling Simplified Methods for Structural Members with Edge-Stiffened Holes:
Presently, the current design methods available to engineers to predict the strength of cold-formed steel members with edge-stiffened holes remains largely unaddressed in the North American Specification for the Design of Cold-Formed Steel Structural Members (NAS). Research was conducted to explore and develop a further understanding of the effects of stiffened edge holes on the elastic buckling parameters for local, distortional, and global buckling. Elastic buckling parameter studies have been conducted on a suite of cold-formed members including recently developed DeltaSTUDs manufactured by Steelform Building Products, Inc. and a series of common Steel Stud Manufacturers Association (SSMA) members. Furthermore, a suite of simplified methods for determining elastic buckling parameters used to predict capacity with the Direct Strength Method (DSM) for members with edge stiffened holes were developed and validated. The elastic buckling studies are used to validate the simplified methods presented in this thesis. All simplified methods are further validated with thin shell finite element eigen-buckling parameter studies where the edge-stiffened holes are explicitly modeled.
Purlin Distortional Buckling Strength Under Gravity Loading:
Laterally braced cold-formed steel beams generally fail due to local and/or distortional buckling in combination with yielding. For many members, distortional buckling is the dominant buckling mode and is addressed in the current North American Specification for the Design of Cold-formed Steel Structural Members. The current main code equation, AISI C3.1.4-10 for calculating the available distortional buckling stress was derived experimentally based on a series of four-point bending tests at John Hopkins University. Where this provides a good basis for determining capacity, in most loading conditions purlins are subjected to a downward uniform loading that provides additional resistance to distortional buckling in the top flange beyond the resistance of the steel roofing panel. This research describes an experimental study to explore and quantify the difference in distortional buckling flexural capacity of metal building Z-purlins treated as isolated components and Z-purlins loaded with a constant pressure applied to metal roof panels. A series of three different types of tests have been developed to quantify the system effect provided by the metal roof panels as well as downward pressure on distortional buckling. Results are also extended to validate the Direct Strength Method when predicting flexural capacity of purlins in a roof system.Master of Science
16
Huynh, Le Anh Thi. "Strength and Behaviour of Cold-rolled Aluminium Sections." Thesis, The University of Sydney, 2019. https://hdl.handle.net/2123/21549.
Full textAbstract:
This thesis presents a comprehensive study on the strength and the behaviour of cold-rolled aluminium sections in compression and bending. The first step of the research project focused on the investigation of mechanical properties and residual stresses in cold-rolled aluminium channel sections. Subsequently, both experimental and numerical investigations were performed to investigate the behaviour and sectional capacities. Finally, design rules based on the Direct Strength Method for cold-rolled aluminium columns and beams were proposed in this thesis. The experimental study encompassed three test series including mechanical property, column and beam experiments. All specimens chosen for the experimental program were roll-formed and supplied by BlueScope Permalite, Australia using aluminium alloy 5052-H36 coils. Thorough investigations of the distributions of mechanical properties and residual stresses in the cross-sections were carried out from three different cold-rolled aluminium C-sections. A total number of 227 coupon tests including 198 flat tension coupon tests, 20 corner tension coupon tests and 9 flat compression coupon tests were conducted. The residual stresses were measured from a total number of 9 cold-rolled aluminium channel sections of three different cross-sections. For section capacity experiments, the test series for columns was conducted on 21 column specimens, which consisted of 12 stub columns subjected to local buckling and 9 intermediate-length columns subjected to distortional buckling of three different cross-sections. The test series for beams comprised 18 bending tests undergoing local buckling and 18 bending tests undergoing distortional buckling of four different cross-section types including channel, down-lip channel, zed and down-lip zed section. Three different channel cross-sections, which were selected in column tests, also were used in beam test to further understand the behaviour of this aluminium members. The local and overall geometric imperfections for all specimens were measured prior to test. For numerical non-linear simulation, the finite element program ABAQUS was used to simulate the behaviour of cold-rolled aluminium sections in both compression and bending. Detailed finite element (FE) models were developed including non-linear material behaviour, actual initial geometric imperfections and forming-induced residual stresses. The simulation results were compared and validated against the four experimental series. The FE models were subsequently used for a parametric study to extend the database of cross-section geometries of columns and beams undergoing local and distortional buckling. In design section, the experiment and FE results were compared with the current design codes from American, Australian/New Zealand and European Standards/ Specifications for aluminium structures. Additionally, the Direct Strength Method (DSM), which has been developed for cold-formed steel structures and stainless steel, was used in this study for predicting cold-rolled aluminium alloy section capacities of columns and beams. Finally, the revised format Direct Strength Method formulae were derived and proposed to better fit the data and give more accurate predictions. The proposed formulae offered simple design solutions, which fit within the current Load and Resistance Factor Design (LRFD) framework. The reliability of the current and proposed design rules was evaluated using reliability analysis.
17
Nuttayasakul, Nuthaporn. "Experimental and Analytical Studies of the Behavior of Cold-Formed Steel Roof Truss Elements." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29765.
Full textAbstract:
Cold-formed steel roof truss systems that use complex stiffener patterns in existing hat shape members for both top and bottom chord elements are a growing trend in the North American steel framing industry. When designing cold-formed steel sections, a structural engineer typically tries to improve the local buckling behavior of the cold-formed steel elements. The complex hat shape has proved to limit the negative influence of local buckling, however, distortional buckling can be the controlling mode of failure in the design of chord members with intermediate unbraced lengths. The chord member may be subjected to both bending and compression because of the continuity of the top and bottom chords. These members are not typically braced between panel points in a truss.
Current 2001 North American Specifications (NAS 2001) do not provide an explicit check for distortional buckling. This dissertation focuses on the behavior of complex hat shape members commonly used for both the top and bottom chord elements of a cold-formed steel truss. The results of flexural tests of complex hat shape members are described. In addition, stub column tests of nested C-sections used as web members and full scale cold-formed steel roof truss tests are reported.
Numerical analyses using finite strip and finite element procedures were developed for the complex hat shape chord member in bending to compare with experimental results. Both elastic buckling and inelastic postbuckling finite element analyses were performed. A parametric study was also conducted to investigate the factors that affect the ultimate strength behavior of a particular complex hat shape.
The experimental results and numerical analyses confirmed that modifications to the 2001 North American Specification are necessary to better predict the flexural strength of complex hat shape members, especially those members subjected to distortional buckling. Either finite strip or finite element analysis can be used to better predict the flexural strength of complex hat shape members. Better understanding of the flexural behavior of these complex hat shapes is necessary to obtain efficient, safe design of a truss system. The results of these analyses will be presented in the dissertation.Ph. D.
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Mahenthirarasa, Rokilan. "Cold-formed steel compression members exposed to extreme temperature environments." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/226125/1/Rokilan_Mahenthirarasa_Thesis.pdf.
Full textAbstract:
This thesis investigated the behaviour of cold-formed steel compression members under extreme temperature environments using experimental and numerical studies. It proposed both new and improved design models for (1) the elevated and sub-zero temperature mechanical properties of cold-formed steels and (2) the compression capacities of cold-formed steel members exposed to uniform and non-uniform elevated temperatures and uniform sub-zero temperatures. The proposed design models are likely to be adopted by the Australian and American cold-formed steel structures standards, while the new knowledge will enable increased applications of cold-formed steel members in the building industry.
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YANG, Demao. "Compression Stability of High Strength Steel Sections with Low Strain-Hardening." University of Sydney. School of Civil Engineering, 2003. http://hdl.handle.net/2123/561.
Full textAbstract:
Thin-walled steel sections made from high strength thin cold-reduced G550 steel to Australian Standard AS 1397-1993 under compression are investigated experimentally and theoretically in this thesis. This thesis describes three series of compression tests performed on box-section stub columns, box-section long columns and lipped channel section columns cold-formed from high strength steel plates in 0.42 mm or 0.60 mm thickness with nominal yield stress of 550 MPa. The tests presented in this thesis formed part of an Australian Research Council research project entitled: Compression Stability of High Strength Steel Sections with Low Strain-Hardening. For the fix-ended stub column tests, a total of 94 lipped-square and hexagonal section stub columns were tested to study the influence of low strain hardening of G550 steel on the compressive section capacities of the column members. For the pin-ended long column tests, a total of 28 box-section columns were tested to study the stability of members with sections which undergo local instability at loads significantly less than the ultimate loads. For the fix-ended lipped channel section columns, a total of 21 stub and long columns were tested to study the failure resulting from local and distortional buckling with interaction between the modes. A numerical simulation on the three series of tests using the commercial finite element computer program ABAQUS is also presented as part of this thesis. The post-buckling behaviour of thin-walled compression members is investigated. The effect of changing variables, such as geometric imperfections and end boundary conditions is also investigated. The ABAQUS analysis gives accurate simulations of the tests and is in good agreement to the experimental results. Theoretical studies using finite strip methods are presented in this thesis to investigate the buckling behaviour of cold-formed members in compression. The theoretical studies provide valuable information on the local and distortional buckling stresses for use in the interaction buckling studies. The finite strip models used are the semi-analytical and spline models. As expected for the stub columns tests, the greatest effect of low strain hardening was for the stockier sections where material properties play an important role. For the more slender sections where elastic local buckling and post-local buckling are more important, the effect of low strain hardening does not appear to be as significant. The pin-ended and fix-ended long column tests show that interaction, which is between local and overall buckling in the box sections, and between local and distortional buckling in the open channel sections, has a significant effect on their member capacities. The results of the successful column tests and ABAQUS simulation have been compared with the design procedures in the Australian & New Zealand Standard for Cold-Formed Steel Structures AS&NZS 4600 and the North American Specification for Cold-Formed Steel Structural Members prepared by the American Iron and Steel Institute. The stub column tests show that the current design rules give too conservative predictions on the compressive section capacities of the column members; whereas the long column tests show that the current column design rules are unconservative if used in their current form for G550 steel. Three design proposals are presented in this thesis to account for the effects of high strength thin steels on the section and member capacities.
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Wanniarachchi, Somadasa. "Flexural behaviour and design of cold-formed steel beams with rectangular hollow flanges." Thesis, Queensland University of Technology, 2005. https://eprints.qut.edu.au/29810/1/Somadasa_Wanniarachchi_Thesis.pdf.
Full textAbstract:
Until recently, the hot-rolled steel members have been recognized as the most popular and widely used steel group, but in recent times, the use of cold-formed high strength steel members has rapidly increased. However, the structural behavior of light gauge high strength cold-formed steel members characterized by various buckling modes is not yet fully understood. The current cold-formed steel sections such as C- and Z-sections are commonly used because of their simple forming procedures and easy connections, but they suffer from certain buckling modes. It is therefore important that these buckling modes are either delayed or eliminated to increase the ultimate capacity of these members. This research is therefore aimed at developing a new cold-formed steel beam with two torsionally rigid rectangular hollow flanges and a slender web formed using intermittent screw fastening to enhance the flexural capacity while maintaining a minimum fabrication cost. This thesis describes a detailed investigation into the structural behavior of this new Rectangular Hollow Flange Beam (RHFB), subjected to flexural action The first phase of this research included experimental investigations using thirty full scale lateral buckling tests and twenty two section moment capacity tests using specially designed test rigs to simulate the required loading and support conditions. A detailed description of the experimental methods, RHFB failure modes including local, lateral distortional and lateral torsional buckling modes, and moment capacity results is presented. A comparison of experimental results with the predictions from the current design rules and other design methods is also given. The second phase of this research involved a methodical and comprehensive investigation aimed at widening the scope of finite element analysis to investigate the buckling and ultimate failure behaviours of RHFBs subjected to flexural actions. Accurate finite element models simulating the physical conditions of both lateral buckling and section moment capacity tests were developed. Comparison of experimental and finite element analysis results showed that the buckling and ultimate failure behaviour of RHFBs can be simulated well using appropriate finite element models. Finite element models simulating ideal simply supported boundary conditions and a uniform moment loading were also developed in order to use in a detailed parametric study. The parametric study results were used to review the current design rules and to develop new design formulae for RHFBs subjected to local, lateral distortional and lateral torsional buckling effects. Finite element analysis results indicate that the discontinuity due to screw fastening has a noticeable influence only for members in the intermediate slenderness region. Investigations into different combinations of thicknesses in the flange and web indicate that increasing the flange thickness is more effective than web thickness in enhancing the flexural capacity of RHFBs. The current steel design standards, AS 4100 (1998) and AS/NZS 4600 (1996) are found sufficient to predict the section moment capacity of RHFBs. However, the results indicate that the AS/NZS 4600 is more accurate for slender sections whereas AS 4100 is more accurate for compact sections. The finite element analysis results further indicate that the current design rules given in AS/NZS 4600 is adequate in predicting the member moment capacity of RHFBs subject to lateral torsional buckling effects. However, they were inadequate in predicting the capacities of RHFBs subject to lateral distortional buckling effects. This thesis has therefore developed a new design formula to predict the lateral distortional buckling strength of RHFBs. Overall, this thesis has demonstrated that the innovative RHFB sections can perform well as economically and structurally efficient flexural members. Structural engineers and designers should make use of the new design rules and the validated existing design rules to design the most optimum RHFB sections depending on the type of applications. Intermittent screw fastening method has also been shown to be structurally adequate that also minimises the fabrication cost. Product manufacturers and builders should be able to make use of this in their applications.
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Wanniarachchi, Somadasa. "Flexural behaviour and design of cold-formed steel beams with rectangular hollow flanges." Queensland University of Technology, 2005. http://eprints.qut.edu.au/29810/.
Full textAbstract:
Until recently, the hot-rolled steel members have been recognized as the most popular and widely used steel group, but in recent times, the use of cold-formed high strength steel members has rapidly increased. However, the structural behavior of light gauge high strength cold-formed steel members characterized by various buckling modes is not yet fully understood. The current cold-formed steel sections such as C- and Z-sections are commonly used because of their simple forming procedures and easy connections, but they suffer from certain buckling modes. It is therefore important that these buckling modes are either delayed or eliminated to increase the ultimate capacity of these members. This research is therefore aimed at developing a new cold-formed steel beam with two torsionally rigid rectangular hollow flanges and a slender web formed using intermittent screw fastening to enhance the flexural capacity while maintaining a minimum fabrication cost. This thesis describes a detailed investigation into the structural behavior of this new Rectangular Hollow Flange Beam (RHFB), subjected to flexural action The first phase of this research included experimental investigations using thirty full scale lateral buckling tests and twenty two section moment capacity tests using specially designed test rigs to simulate the required loading and support conditions. A detailed description of the experimental methods, RHFB failure modes including local, lateral distortional and lateral torsional buckling modes, and moment capacity results is presented. A comparison of experimental results with the predictions from the current design rules and other design methods is also given. The second phase of this research involved a methodical and comprehensive investigation aimed at widening the scope of finite element analysis to investigate the buckling and ultimate failure behaviours of RHFBs subjected to flexural actions. Accurate finite element models simulating the physical conditions of both lateral buckling and section moment capacity tests were developed. Comparison of experimental and finite element analysis results showed that the buckling and ultimate failure behaviour of RHFBs can be simulated well using appropriate finite element models. Finite element models simulating ideal simply supported boundary conditions and a uniform moment loading were also developed in order to use in a detailed parametric study. The parametric study results were used to review the current design rules and to develop new design formulae for RHFBs subjected to local, lateral distortional and lateral torsional buckling effects. Finite element analysis results indicate that the discontinuity due to screw fastening has a noticeable influence only for members in the intermediate slenderness region. Investigations into different combinations of thicknesses in the flange and web indicate that increasing the flange thickness is more effective than web thickness in enhancing the flexural capacity of RHFBs. The current steel design standards, AS 4100 (1998) and AS/NZS 4600 (1996) are found sufficient to predict the section moment capacity of RHFBs. However, the results indicate that the AS/NZS 4600 is more accurate for slender sections whereas AS 4100 is more accurate for compact sections. The finite element analysis results further indicate that the current design rules given in AS/NZS 4600 is adequate in predicting the member moment capacity of RHFBs subject to lateral torsional buckling effects. However, they were inadequate in predicting the capacities of RHFBs subject to lateral distortional buckling effects. This thesis has therefore developed a new design formula to predict the lateral distortional buckling strength of RHFBs. Overall, this thesis has demonstrated that the innovative RHFB sections can perform well as economically and structurally efficient flexural members. Structural engineers and designers should make use of the new design rules and the validated existing design rules to design the most optimum RHFB sections depending on the type of applications. Intermittent screw fastening method has also been shown to be structurally adequate that also minimises the fabrication cost. Product manufacturers and builders should be able to make use of this in their applications.
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Zhang, Xi. "Steel Portal Frames with Locally Unstable Members." Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/10452.
Full textAbstract:
The advanced analysis based design has an advantage over conventional member based design methods because it is most capable of capturing the limit state strength and stability of a real structure, taking into account system effects explicitly such as the load redistribution subsequent to first yielding. While being considered as the next generation's design method, the advanced analysis based design is still restricted to steel frames comprising only members with compact cross-sections in AS4100, partly because modelling local instability requires discretisation of the cross-section which makes analysis more complicated, and thus is not suitable for practicing engineers. This thesis presents a beam-element-based advanced analysis method which accounts for the occurrence of local/distortional buckling by incorporating the reduced tangent rigidities to replace the full rigidities of the section. The Open System for Earthquake Engineering Simulation (OpenSees) package is selected as the research tool. It was re-developed based on derived theory and two elements, which are Elastic Beam-Column Warping Element and Displacement Based Beam-Column Warping Element, were introduced. The proposed method was validated by comparison with shell finite element analysis in ABAQUS as well as full-scale portal frame experiments. Modelling techniques of frame structures in both shell element and beam element models, including semi-rigid joints, were introduced, and the effects of joint stiffness and initial geometric imperfections were studied. The author also proposed simple expressions for the reduction of section rigidities in frame analyses in a similar way to the b factors currently specified in AISC-360 to account for the reduction in rigidity caused by yielding. This allows the effect of cross-sectional instability to be considered by simple reduction factors, thus making the method feasible for the use of practicing design engineers.
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Cheng, Shanshan. "Fire performance of cold-formed steel sections." Thesis, University of Plymouth, 2015. http://hdl.handle.net/10026.1/3316.
Full textAbstract:
Thin-walled cold-formed steel (CFS) has exhibited inherent structural and architectural advantages over other constructional materials, for example, high strength-to-weight ratio, ease of fabrication, economy in transportation and the flexibility of sectional profiles, which make CFS ideal for modern residential and industrial buildings. They have been increasingly used as purlins as the intermediate members in a roof system, or load-bearing components in low- and mid-rise buildings. However, using CFS members in building structures has been facing challenges due to the lack of knowledge to the fire performance of CFS at elevated temperatures and the lack of fire design guidelines. Among all available design specifications of CFS, EN1993-1-2 is the only one which provided design guidelines for CFS at elevated temperatures, which, however, is based on the same theory and material properties of hot-rolled steel. Since the material properties of CFS are found to be considerably different from those of hot-rolled steel, the applicability of hot-rolled steel design guidelines into CFS needs to be verified. Besides, the effect of non-uniform temperature distribution on the failure of CFS members is not properly addressed in literature and has not been specified in the existing design guidelines. Therefore, a better understanding of fire performance of CFS members is of great significance to further explore the potential application of CFS. Since CFS members are always with thin thickness (normally from 0.9 to 8 mm), open cross-section, and great flexural rigidity about one axis at the expense of low flexural rigidity about a perpendicular axis, the members are usually susceptible to various buckling modes which often govern the ultimate failure of CFS members. When CFS members are exposed to a fire, not only the reduced mechanical properties will influence the buckling capacity of CFS members, but also the thermal strains which can lead additional stresses in loaded members. The buckling behaviour of the member can be analysed based on uniformly reduced material properties when the member is unprotected or uniformly protected surrounded by a fire that the temperature distribution within the member is uniform. However if the temperature distribution in a member is not uniform, which usually happens in walls and/or roof panels when CFS members are protected by plaster boards and exposed to fire on one side, the analysis of the member becomes very complicated since the mechanical properties such as Young’s modulus and yield strength and thermal strains vary within the member. This project has the aim of providing better understanding of the buckling performance of CFS channel members under non-uniform temperatures. The primary objective is to investigate the fire performance of plasterboard protected CFS members exposed to fire on one side, in the aspects of pre-buckling stress distribution, elastic buckling behaviour and nonlinear failure models. Heat transfer analyses of one-side protected CFS members have been conducted firstly to investigate the temperature distributions within the cross-section, which have been applied to the analytical study for the prediction of flexural buckling loads of CFS columns at elevated temperatures. A simplified numerical method based on the second order elastic – plastic analysis has also been proposed for the calculation of the flexural buckling load of CFS columns under non-uniform temperature distributions. The effects of temperature distributions and stress-strain relationships on the flexure buckling of CFS columns are discussed. Afterwards a modified finite strip method combined with the classical Fourier series solutions have been presented to investigate the elastic buckling behaviour of CFS members at elevated temperatures, in which the effects of temperatures on both strain and mechanical properties have been considered. The variations of the elastic buckling loads/moments, buckling modes and slenderness of CFS columns/beams with increasing temperatures have been examined. The finite element method is also used to carry out the failure analysis of one-side protected beams at elevated temperatures. The effects of geometric imperfection, stress-strain relationships and temperature distributions on the ultimate moment capacities of CFS beams under uniform and non-uniform temperature distributions are examined. At the end the direct strength method based design methods have been discussed and corresponding recommendations for the designing of CFS beams at elevated temperatures are presented. This thesis has contributed to improve the knowledge of the buckling and failure behaviour of CFS members at elevated temperatures, and the essential data provided in the numerical studies has laid the foundation for further design-oriented studies.
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Kurniawan, Cyrilus Winatama. "Flexural behaviour and design of the new LiteSteel beams." Thesis, Queensland University of Technology, 2007. https://eprints.qut.edu.au/16674/1/Cyrilus_Kurniawan_Thesis.pdf.
Full textAbstract:
The flexural capacity of the new hollow flange steel section known as LiteSteel beam (LSB) is limited by lateral distortional buckling for intermediate spans, which is characterised by simultaneous lateral deflection, twist and web distortion. Recent research based on finite element analysis and testing has developed design rules for the member capacity of LiteSteel beams subject to this unique lateral distortional buckling. These design rules are limited to a uniform bending moment distribution. However, uniform bending moment conditions rarely exist in practice despite being considered as the worst case due to uniform yielding across the span. Loading position or load height is also known to have significant effects on the lateral buckling strength of beams. Therefore it is important to include the effects of these loading conditions in the assessment of LSB member capacities.
Many steel design codes have adopted equivalent uniform moment distribution and load height factors for this purpose. But they were derived mostly based on data for conventional hot-rolled, doubly symmetric I-beams subject to lateral torsional buckling. In contrast LSBs are made of high strength steel and have a unique crosssection with specific residual stresses and geometrical imperfections along with a unique lateral distortional buckling mode. The moment distribution and load height effects for LSBs, and the suitability of the current steel design code methods to accommodate these effects for LSBs are not yet known. The research study presented in this thesis was therefore undertaken to investigate the effects of nonuniform moment distribution and load height on the lateral buckling strength of simply supported and cantilever LSBs.
Finite element analyses of LSBs subject to lateral buckling formed the main component of this study. As the first step the original finite element model used to develop the current LSB design rules for uniform moment was improved to eliminate some of the modelling inaccuracies. The modified finite element model was validated using the elastic buckling analysis results from well established finite strip analysis programs. It was used to review the current LSB design curve for uniform moment distribution, based on which appropriate recommendations were made.
The modified finite element model was further modified to simulate various loading and support configurations and used to investigate the effects of many commonly used moment distributions and load height for both simply supported and cantilever LSBs. The results were compared with the predictions based on the current steel code design rules. Based on these comparisons, appropriate recommendations were made on the suitability of the current steel code design methods. New design recommendations were made for LSBs subjected to non-uniform moment distributions and varying load positions. A number of LSB experiments was also undertaken to confirm the results of finite element analysis study.
In summary the research reported in this thesis has developed an improved finite element model that can be used to investigate the buckling behaviour of LSBs for the purpose of developing design rules. It has increased the understanding and knowledge of simply supported and cantilever LSBs subject to non-uniform moment distributions and load height effects. Finally it has proposed suitable design rules for LSBs in the form of equations and factors within the current steel code design provisions. All of these advances have thus further enhanced the economical and safe design of LSBs.
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Kurniawan, Cyrilus Winatama. "Flexural behaviour and design of the new LiteSteel beams." Queensland University of Technology, 2007. http://eprints.qut.edu.au/16674/.
Full textAbstract:
The flexural capacity of the new hollow flange steel section known as LiteSteel beam (LSB) is limited by lateral distortional buckling for intermediate spans, which is characterised by simultaneous lateral deflection, twist and web distortion. Recent research based on finite element analysis and testing has developed design rules for the member capacity of LiteSteel beams subject to this unique lateral distortional buckling. These design rules are limited to a uniform bending moment distribution. However, uniform bending moment conditions rarely exist in practice despite being considered as the worst case due to uniform yielding across the span. Loading position or load height is also known to have significant effects on the lateral buckling strength of beams. Therefore it is important to include the effects of these loading conditions in the assessment of LSB member capacities. Many steel design codes have adopted equivalent uniform moment distribution and load height factors for this purpose. But they were derived mostly based on data for conventional hot-rolled, doubly symmetric I-beams subject to lateral torsional buckling. In contrast LSBs are made of high strength steel and have a unique crosssection with specific residual stresses and geometrical imperfections along with a unique lateral distortional buckling mode. The moment distribution and load height effects for LSBs, and the suitability of the current steel design code methods to accommodate these effects for LSBs are not yet known. The research study presented in this thesis was therefore undertaken to investigate the effects of nonuniform moment distribution and load height on the lateral buckling strength of simply supported and cantilever LSBs. Finite element analyses of LSBs subject to lateral buckling formed the main component of this study. As the first step the original finite element model used to develop the current LSB design rules for uniform moment was improved to eliminate some of the modelling inaccuracies. The modified finite element model was validated using the elastic buckling analysis results from well established finite strip analysis programs. It was used to review the current LSB design curve for uniform moment distribution, based on which appropriate recommendations were made. The modified finite element model was further modified to simulate various loading and support configurations and used to investigate the effects of many commonly used moment distributions and load height for both simply supported and cantilever LSBs. The results were compared with the predictions based on the current steel code design rules. Based on these comparisons, appropriate recommendations were made on the suitability of the current steel code design methods. New design recommendations were made for LSBs subjected to non-uniform moment distributions and varying load positions. A number of LSB experiments was also undertaken to confirm the results of finite element analysis study. In summary the research reported in this thesis has developed an improved finite element model that can be used to investigate the buckling behaviour of LSBs for the purpose of developing design rules. It has increased the understanding and knowledge of simply supported and cantilever LSBs subject to non-uniform moment distributions and load height effects. Finally it has proposed suitable design rules for LSBs in the form of equations and factors within the current steel code design provisions. All of these advances have thus further enhanced the economical and safe design of LSBs.
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Perera, Nilakshi. "Structural behaviour and design of innovative hollow flange steel plate grinders." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/123310/1/Liyanage%20Nilakshi%20Piyahasi_Perera_Thesis.pdf.
Full textAbstract:
This thesis proposes a new Hollow Flange Steel Plate Girder (HFSPG) by welding industrially available cold-formed Rectangular Hollow Sections (RHS) to a web plate for use in long span construction. Design procedures presented in the national and international design guidelines were reviewed and suitable improvements were made to accurately predict the structural behaviour and capacities of HFSPGs by undertaking detailed experimental and numerical studies into their unique structural behaviour. Local buckling/yielding, global buckling and local-global interaction failures were all considered in this thesis.
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Chodraui, Gustavo Monteiro de Barros. "Flambagem por distorção da seção transversal em perfis de aço formados a frio submetidos à compressão centrada e à flexão"." Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-18072003-124917/.
Full textAbstract:
Os perfis de aço formados a frio apresentam, em geral, elevada relação largura/espessura, tornando-os suscetíveis à flambagem local, caracterizada por uma flambagem de chapa, mas que também pode ocasionar um outro modo de flambagem, denominado flambagem por distorção, desconsiderado no dimensionamento de perfis laminados, mas que pode resultar crítico principalmente nos perfis com enrijecedores de borda e constituídos por aço de elevada resistência mecânica. Tal fenômeno é caracterizado pela perda de estabilidade do conjunto formado pelo elemento comprimido e seu enrijecedor de borda, alterando a forma inicial da seção transversal. Portanto, as normas mais atuais têm apresentado procedimentos para avaliar a resistência de barras com base na flambagem por distorção, como o procedimento simplificado da norma australiana AS/NZS 4600:1996, proposto por HANCOCK e que foi também adotado pela recente norma brasileira NBR 14762:2001, o método direto de resistência, recentemente proposto para incorporação à especificação do AISI (American Iron and Steel Institute) e a GBT (Generalized Beam Theory).Nesse trabalho é feita uma abordagem dos procedimentos propostos para a avaliação da flambagem por distorção em barras submetidas à compressão centrada e à flexão, comparando-se os resultados obtidos pelo procedimento da norma brasileira, pela análise elástica via método das faixas finitas - MFF e pela análise via método dos elementos finitos - MEF, admitindo barras sem e com imperfeições iniciais. É feita também uma abordagem com relação aos outros procedimentos internacionais para a avaliação do fenômeno.Cold-formed steel members present, in many cases, an elevated width/thickness ratio (thin-walled members), which probably lead up to the local buckling, which is characterized by a plate buckling, and also may lead up to another buckling mode, called distortional buckling, not considered on the design of hot-rolled members, but which may result critical in cold-formed members, specially in the ones with edge stiffeners and made with high strength steel. Such phenomena is characterized by the instability of the group formed by the compression flange and its stiffener, changing the initial shape of the cross section. Nowadays, codes present procedures to evaluate members resistance also due to distortional buckling, as the simplified method in the Australian code, AS/NZS 4600:1996, proposed by HANCOCK, which was adopted by the new Brazilian code, NBR 14762:2001, the Direct Strenght Method, recently proposed as an AISI (American Iron and Steel Institute) Draft, and the GBT (Generalilzed Beam Theory).This work talks about procedures proposed to evaluate distortional buckling in members under compression and bending, comparing results obtained by the method showed in the brazilian code, by numerical Finite Strip Method elastic analisys - FSM, and by Finite Element Method analisys FEM, on members with and without initial imperfections. It is also done an explanation related to other international procedures to evaluate the phenomena.
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Siahaan, Ropalin. "Structural behaviour and design of rivet fastened rectangular hollow flange channel beams." Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/106913/1/Ropalin_Siahaan_Thesis.pdf.
Full textAbstract:
This thesis presents a study into the structural behaviour and design of the innovative rivet fastened Rectangular Hollow Flange Channel Beams (RHFCB). The RHFCB utilizes the inexpensive self-pierce rivet fastening in its fabrication, providing cost effective structural solutions in floor systems. The first part of the thesis focuses on the section moment capacities of the beams subject to local buckling effects while the second part investigates the member moment capacities of intermediate span beams subject to the unique lateral distortional buckling effects. Each part involves experimental investigations, advanced finite element analyses, parametric studies and design recommendations.
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Jeyaragan, Sivapathasunderam. "Flexural behaviour and design of the new built-up LiteSteel beams." Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/36209/1/Sivapathasunderam_Jeyaragan_Thesis.pdf.
Full textAbstract:
LiteSteel Beam (LSB) is a new cold-formed steel beam produced by OneSteel Australian Tube Mills. The new beam is effectively a channel section with two rectangular hollow flanges and a slender web, and is manufactured using a combined cold-forming and electric resistance welding process. OneSteel Australian Tube Mills is promoting the use of LSBs as flexural members in a range of applications, such as floor bearers. When LSBs are used as back to back built-up sections, they are likely to improve their moment capacity and thus extend their applications further. However, the structural behaviour of built-up beams is not well understood. Many steel design codes include guidelines for connecting two channels to form a built-up I-section including the required longitudinal spacing of connections. But these rules were found to be inadequate in some applications. Currently the safe spans of builtup beams are determined based on twice the moment capacity of a single section. Research has shown that these guidelines are conservative. Therefore large scale lateral buckling tests and advanced numerical analyses were undertaken to investigate the flexural behaviour of back to back LSBs connected by fasteners (bolts) at various longitudinal spacings under uniform moment conditions. In this research an experimental investigation was first undertaken to study the flexural behaviour of back to back LSBs including its buckling characteristics. This experimental study included tensile coupon tests, initial geometric imperfection measurements and lateral buckling tests. The initial geometric imperfection measurements taken on several back to back LSB specimens showed that the back to back bolting process is not likely to alter the imperfections, and the measured imperfections are well below the fabrication tolerance limits. Twelve large scale lateral buckling tests were conducted to investigate the behaviour of back to back built-up LSBs with various longitudinal fastener spacings under uniform moment conditions. Tests also included two single LSB specimens. Test results showed that the back to back LSBs gave higher moment capacities in comparison with single LSBs, and the fastener spacing influenced the ultimate moment capacities. As the fastener spacing was reduced the ultimate moment capacities of back to back LSBs increased. Finite element models of back to back LSBs with varying fastener spacings were then developed to conduct a detailed parametric study on the flexural behaviour of back to back built-up LSBs. Two finite element models were developed, namely experimental and ideal finite element models. The models included the complex contact behaviour between LSB web elements and intermittently fastened bolted connections along the web elements. They were validated by comparing their results with experimental results and numerical results obtained from an established buckling analysis program called THIN-WALL. These comparisons showed that the developed models could accurately predict both the elastic lateral distortional buckling moments and the non-linear ultimate moment capacities of back to back LSBs. Therefore the ideal finite element models incorporating ideal simply supported boundary conditions and uniform moment conditions were used in a detailed parametric study on the flexural behaviour of back to back LSB members. In the detailed parametric study, both elastic buckling and nonlinear analyses of back to back LSBs were conducted for 13 LSB sections with varying spans and fastener spacings. Finite element analysis results confirmed that the current design rules in AS/NZS 4600 (SA, 2005) are very conservative while the new design rules developed by Anapayan and Mahendran (2009a) for single LSB members were also found to be conservative. Thus new member capacity design rules were developed for back to back LSB members as a function of non-dimensional member slenderness. New empirical equations were also developed to aid in the calculation of elastic lateral distortional buckling moments of intermittently fastened back to back LSBs. Design guidelines were developed for the maximum fastener spacing of back to back LSBs in order to optimise the use of fasteners. A closer fastener spacing of span/6 was recommended for intermediate spans and some long spans where the influence of fastener spacing was found to be high. In the last phase of this research, a detailed investigation was conducted to investigate the potential use of different types of connections and stiffeners in improving the flexural strength of back to back LSB members. It was found that using transverse web stiffeners was the most cost-effective and simple strengthening method. It is recommended that web stiffeners are used at the supports and every third points within the span, and their thickness is in the range of 3 to 5 mm depending on the size of LSB section. The use of web stiffeners eliminated most of the lateral distortional buckling effects and hence improved the ultimate moment capacities. A suitable design equation was developed to calculate the elastic lateral buckling moments of back to back LSBs with the above recommended web stiffener configuration while the same design rules developed for unstiffened back to back LSBs were recommended to calculate the ultimate moment capacities.
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Silva, Julio Cesar Martins da. "Análise teórica-experimental de perfis de aço formados a frio devido à instabilidade por distorção na flexão." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-03062016-135325/.
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Apresenta-se neste trabalho um estudo teórico-experimental sobre a instabilidade de perfis formados a frio submetidos à flexão. A instabilidade distorcional se faz comum na presença de tensões de compressão atuando sobre perfis enrijecidos e fabricados com aços de elevada resistência mecânica. A parte teórica abrange os métodos de cálculo analíticos e numéricos para a análise de instabilidade distorcional de perfis de seção aberta formados a frio. Na parte experimental inclui-se o estudo de perfis formados a frio com seções do tipo U enrijecidos submetidos aos ensaios à flexão. Nestes ensaios variou-se a altura de alma e espessura de chapa procurando-se abranger maior número de condições geométricas para análise da estabilidade distorcional. Inclui-se também a análise de instabilidade numérica dos perfis do programa experimental através do método de resistência direta via método das faixas finitas. Com base nos resultados experimentais, numéricos e na análise teórica do problema, verificou-se o procedimento adotado pela NBR14762/2001 e efetuou-se comparação entre curvas de resistência propostas para o dimensionamento de perfis formados a frio à flexão. Foi verificado que o fenômeno de instabilidade distorcional pode ser o estado limite último crítico para o dimensionamento dos perfis formados a frio.This work present a study theoretical-experimental about the distortional buckling of cold-formed steel members under bending. The distortional buckling is common for members with edge-stiffened sections and manufactured with steel of high strength. The theorical part present the analitic and numerical methods for stability analysis by distortional buckling. The experimental part included the study of cold-formed with sections channel altering flange width and thickness by proof in flexural members. Included too the numerical analysis by Direct Strength Method in Finite Strip Method on members with the same configurations of experimental investigation. Based on the experimental measurements, numerical analysis and in the theorical analysis of work, verified the procedures adopted in brazilian code NBR14762/2001 and compared with others distortional curve proposed for to design of cold-formed members under bending. Verified that the distortional buckling may control the design being the critical mode for the ultimate limit state.
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Anapayan, Tharmarajah. "Flexural behaviour and design of hollow flange steel beams." Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/36210/1/Tharmarajah_Anapayan_Thesis.pdf.
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The LiteSteel Beam (LSB) is a new hollow flange channel section developed by OneSteel Australian Tube Mills using a patented Dual Electric Resistance Welding technique. The LSB has a unique geometry consisting of torsionally rigid rectangular hollow flanges and a relatively slender web. It is commonly used as rafters, floor joists and bearers and roof beams in residential, industrial and commercial buildings. It is on average 40% lighter than traditional hot-rolled steel beams of equivalent performance. The LSB flexural members are subjected to a relatively new Lateral Distortional Buckling mode, which reduces the member moment capacity. Unlike the commonly observed lateral torsional buckling of steel beams, lateral distortional buckling of LSBs is characterised by simultaneous lateral deflection, twist and web distortion. Current member moment capacity design rules for lateral distortional buckling in AS/NZS 4600 (SA, 2005) do not include the effect of section geometry of hollow flange beams although its effect is considered to be important. Therefore detailed experimental and finite element analyses (FEA) were carried out to investigate the lateral distortional buckling behaviour of LSBs including the effect of section geometry. The results showed that the current design rules in AS/NZS 4600 (SA, 2005) are over-conservative in the inelastic lateral buckling region. New improved design rules were therefore developed for LSBs based on both FEA and experimental results. A geometrical parameter (K) defined as the ratio of the flange torsional rigidity to the major axis flexural rigidity of the web (GJf/EIxweb) was identified as the critical parameter affecting the lateral distortional buckling of hollow flange beams. The effect of section geometry was then included in the new design rules using the new parameter (K). The new design rule developed by including this parameter was found to be accurate in calculating the member moment capacities of not only LSBs, but also other types of hollow flange steel beams such as Hollow Flange Beams (HFBs), Monosymmetric Hollow Flange Beams (MHFBs) and Rectangular Hollow Flange Beams (RHFBs). The inelastic reserve bending capacity of LSBs has not been investigated yet although the section moment capacity tests of LSBs in the past revealed that inelastic reserve bending capacity is present in LSBs. However, the Australian and American cold-formed steel design codes limit them to the first yield moment. Therefore both experimental and FEA were carried out to investigate the section moment capacity behaviour of LSBs. A comparison of the section moment capacity results from FEA, experiments and current cold-formed steel design codes showed that compact and non-compact LSB sections classified based on AS 4100 (SA, 1998) have some inelastic reserve capacity while slender LSBs do not have any inelastic reserve capacity beyond their first yield moment. It was found that Shifferaw and Schafer’s (2008) proposed equations and Eurocode 3 Part 1.3 (ECS, 2006) design equations can be used to include the inelastic bending capacities of compact and non-compact LSBs in design. As a simple design approach, the section moment capacity of compact LSB sections can be taken as 1.10 times their first yield moment while it is the first yield moment for non-compact sections. For slender LSB sections, current cold-formed steel codes can be used to predict their section moment capacities. It was believed that the use of transverse web stiffeners could improve the lateral distortional buckling moment capacities of LSBs. However, currently there are no design equations to predict the elastic lateral distortional buckling and member moment capacities of LSBs with web stiffeners under uniform moment conditions. Therefore, a detailed study was conducted using FEA to simulate both experimental and ideal conditions of LSB flexural members. It was shown that the use of 3 to 5 mm steel plate stiffeners welded or screwed to the inner faces of the top and bottom flanges of LSBs at third span points and supports provided an optimum web stiffener arrangement. Suitable design rules were developed to calculate the improved elastic buckling and ultimate moment capacities of LSBs with these optimum web stiffeners. A design rule using the geometrical parameter K was also developed to improve the accuracy of ultimate moment capacity predictions. This thesis presents the details and results of the experimental and numerical studies of the section and member moment capacities of LSBs conducted in this research. It includes the recommendations made regarding the accuracy of current design rules as well as the new design rules for lateral distortional buckling. The new design rules include the effects of section geometry of hollow flange steel beams. This thesis also developed a method of using web stiffeners to reduce the lateral distortional buckling effects, and associated design rules to calculate the improved moment capacities.
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Nagy, T. "Investigation of thermal techniques to mitigate buckling distortion in welding panels." Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/7798.
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This thesis describes the advancements of the application of thermal tensioning techniques to different weld geometries in order to eliminate buckling distortion. The main goal of this work is to better understand these techniques through experimental and numerical investigation and increase their technological maturity to aid industrial implementation. The thermal tensioning techniques investigated in this work are Thermal Tensioning by Cooling and Thermal Tensioning by Heating. The investigation for both techniques encompasses thermal source characterisation, application to different weld geometries and residual stress measurements and analysis of both butt and fillet welded samples. A detailed technology transfer study of Thermal Tensioning by Cooling was carried out in which different aspects of the application of TTC to arc welding (Gas Metal Arc Welding and Gas Tungsten Arc Welding) was examined. This study focused on the influence of both the liquid CO2 delivery system installation and welding tooling and jigging on the effectiveness of Thermal Tensioning by Cooling in reducing buckling distortion. Experimental and numerical cooling source characterisation was also carried out in the Thermal Tensioning by Cooling work to investigate the characteristics of the cooling source under different cooling conditions. The Thermal Tensioning by Cooling work was then concluded with welding trials and residual stress measurement and analysis. The results of the Thermal Tensioning by Cooling study show that the installation of the liquid CO2 delivery system as well as the welding tooling and jigging has a major influence on the effectiveness of Thermal Tensioning by Cooling in reducing buckling distortion. The cooling source characterisation work reveals that the most important parameter of the cryogenic nozzle delivery system used in this work is the Air Entrainment Gap. A description of a control system of Thermal Tensioning by Cooling is suggested based on controlling the Air Entrainment Gap. The residual stress analysis shows a reduction in the Applied Weld Load and minor changes in the tensile peak of the residual stress distribution of both butt and fillet welded panels. The Thermal Tensioning by Heating investigation includes heat source characterisation, application of Thermal Tensioning by Heating on butt and fillet welds, utilisation of alternative heat sources and residual stress analysis. The results of these investigation show that Thermal Tensioning by Heating is also highly effective in eliminating buckling distortion in butt, fillet and overlapped panels. The applied heating temperature in this work is typically in the range of 160-250 °C but not greater than 330 °C. The residual stress measurements reveal that the additional heating of Thermal Tensioning by Heating generates a positive stress gradient at the location of heating.
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Regensburger, Jochen. "Nichtlineares Deformationsverhalten von Karosserie-Außenhautbauteilen aus Aluminium im Lacktrocknungsprozess." Universitätsverlag der Technischen Universität Chemnitz, 2017. https://monarch.qucosa.de/id/qucosa%3A21182.
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In dieser Arbeit wird die Berechenbarkeit des Deformationsverhaltens von Aluminiumaußenhautbauteilen in einem für die Automobilindustrie typischen Lacktrocknungsprozess um den irreversiblen Kriecheffekt erweitert. Untersucht wird dabei die in Europa oft für Außenhautbauteile eingesetzte Legierung AA6016 mit Hilfe von Zug- und Biegetests, aus denen ein geeignetes Werkstoffmodell für die numerische Simulation abgeleitet wird. Dabei wird auch der Einfluss des Umformgrades im Blechbauteil aus dem Herstellprozess untersucht und bewertet. Die seriennahe Validierung des Werkstoffmodells findet anhand einer eigens ausgelegten Baugruppe statt, die nach dem Wärmeprozess optisch sichtbare Formabweichungen aufweist. Mittels optischer Messungen wird die Baugruppe dabei vor, im und nach dem Wärmeprozess analysiert und die berechneten Formänderungen validiert. Im Ergebnis kann mit dem Werkstoffmodell die Auswirkung thermisch induzierter Spannungen unterhalb der klassischen Streckgrenze auf die Formänderung von Aluminiumblech in der frühen Produktentwicklungsphase prognostiziert werden.In this work, the computability of the deformation behaviour of aluminium car body panels in a typical automotive paint drying process is enhanced by the irreversible creep effect. The alloy AA6016, which is often used in Europe for aluminium car body panels, is examined with the aid of tensile and bending tests from which a suitable material model for numerical simulation is derived. The influence of the plastic deformation in the sheet metal component due to the manufacturing process is also examined and evaluated. The near-series validation of the material model takes place on the basis of a specially designed assembly which shows optically visible shape deviations after the heating process. Using optical measurements, the assembly is analyzed before, during and after the heating process and the calculated shape changes are validated. As a result, the material model can be used to predict the effect of thermally induced stresses below the classic yield strength on the deformation of aluminium sheet in the early product development phase.
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Saadé, Katy. "Finite element modeling of shear in thin walled beams with a single warping function." Doctoral thesis, Universite Libre de Bruxelles, 2005. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211043.
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The considerable progress in the research and development of thin-walled beam structures responds to their growing use in engineering construction and to their increased need for efficiency in strength and cost. The result is a structure that exhibits large shear strains and important non uniform warping under different loadings, such as non uniform torsion, shear bending and distortion.A unified approach is formulated in this thesis for 3D thin walled beam structures with arbitrary profile geometries, loading cases and boundary conditions. A single warping function, defined by a linear combination of longitudinal displacements at cross sectional nodes (derived from Prokic work), is enhanced and adapted in order to qualitatively and quantitatively reflect and capture the nature of a widest possible range of behaviors. Constraints are prescribed at the kinematics level in order to enable the study of arbitrary cross sections for general loading. This approach, differing from most published theories, has the advantage of enabling the study of arbitrary cross sections (closed/opened or mixed) without any restrictions or distinctions related to the geometry of the profile. It generates automatic data and characteristic computations from a kinematical discretization prescribed by the profile geometry. The amount of shear bending, torsional and distortional warping and the magnitude of the shear correction factor is computed for arbitrary profile geometries with this single formulation.
The proposed formulation is compared to existing theories with respect to the main assumptions and restrictions. The variation of the location of the torsional center, distortional centers and distortional rotational ratio of a profile is discussed in terms of their dependency on the loading cases and on the boundary conditions.
A 3D beam finite element model is developed and validated with several numerical applications. The displacements, rotations, amount of warping, normal and shear stresses are compared with reference solutions for general loading cases involving stretching, bending, torsion and/or distortion. Some examples concern the case of beam assemblies with different shaped profiles where the connection type determines the nature of the warping transmission. Other analyses –for which the straightness assumption of Timoshenko theory is relaxed– investigate shear deformation effects on the deflection of short and thin beams by varying the aspect ratio of the beam. Further applications identify the cross sectional distortion and highlight the importance of the distortion on the stresses when compared to bending and torsion even in simple loading cases.
Finally, a non linear finite element based on the updated lagrangian formulation is developed by including torsional warping degrees of freedom. An incremental iterative method using the arc length and the Newton-Raphson methods is used to solve the non linear problem. Examples are given to study the flexural, torsional, flexural torsional and lateral torsional buckling problems for which a coupling between the variables describing the flexural and the torsional degrees of freedom occurs. The finite element results are compared to analytical solutions based on different warping functions and commonly used in linear stability for elastic structures having insufficient lateral or torsional stiffnesses that cause an out of plane buckling.
Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished
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Charnvarnichborikarn, Pimarn. "Distortional buckling of cold-formed steel Z-sections." 1992. http://hdl.handle.net/1993/18002.
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Aihua, Liang. "Finite element analysis of distortional buckling of cold-formed stainless steel columns." Thesis, 2012. http://hdl.handle.net/10210/4302.
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M.Ing.Because cold-formed stainless steel is a new type of light steel material and dose not have a long history of utilisation in structures, there are many issues that need to be researched and discussed. Making a more thorough investigation and study of cold-formed stainless steels is essential. As a numerical analysis tool, the finite element method proves to be useful in structural analysis. The buckling modes of cold-formed stainless steel members, such as local, flexural, torsional and torsional-flexural buckling, are well known and well documented in design specifications. Distortional buckling is a special kind of buckling mode, which is less well known. Researchers have recently paid more attention to this problem. For stainless steel structures, it is necessary to investigate their behaviour when distortional buckling occurs. In this project, the distortional buckling of cold-formed stainless steel columns under axial compression is investigated. The finite element method is used to analyse and calculate different buckling modes, especially distortional buckling. This is compared to experimental results and other theoretical predictions. The ABAQUS finite element code is used throughout. Finite element modelling is very important prior to processing and analysis. ABAQUS models are created to study distortional buckling. The initial imperfection of structural members is taken into account with these models, using specific sine wave descriptions with respect to different structural parameters. A dynamic processing approach is chosen in the finite element analysis. The effectiveness and accuracy of these models have been verified by both experimental tests and theoretical calculations. Buckling mode and behaviour are predicted and analysed in terms of the finite element models and processes. Suggestions are made for buckling analysis and design based on the research results.
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Breda, Ricardo André Simões. "Optimização de estruturas modulares em aço enformado a frio." Master's thesis, 2013. http://hdl.handle.net/10316/38480.
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Dissertação de Mestrado Integrado em Engenharia Civil apresentada à Faculdade de Ciências e Tecnologia da Universidade de CoimbraNa indústria da construção, a sustentabilidade adquiriu um papel fundamental. O tema da dissertação surge no seguimento do projeto I&DT Cool Haven, que visa desenvolver um conceito inovador de construção, que consiste em conferir aos espaços uma sustentabilidade assente na eficiência estrutural e adaptabilidade das estruturas às várias exigências funcionais durante a vida útil da construção. Associado a este conceito surge a construção modular e a construção metálica de aço enformado a frio. A construção modular exibe francas vantagens pelo facto dos trabalhos de execução serem maioritariamente desenvolvidos em fábrica, reduzindo assim o tempo de execução em obra e, simultaneamente a probabilidade de existirem erros e consequentes defeitos na estrutura. A construção metálica, por sua vez, exibe vantagens óbvias pelo facto do aço ser um material totalmente reciclável e de grande eficiência estrutural. A presente dissertação está relacionada com a necessidade de transformar este conceito de construção inovador, competitivo e atrativo a nível económico. O objetivo desta dissertação foi desenvolver uma ferramenta de suporte essencial na otimização de estruturas modulares de aço enformado a frio em termos de eficiência estrutural. Como tal, foi desenvolvida a ferramenta de cálculo computacional Cold-Formed Design, por forma a facilitar o dimensionamento e otimização de elementos de aço enformado a frio, a qual foi posteriormente utilizada na otimização das estruturas modulares de aço enformado a frio. O documento começa por referir as principais características associadas aos elementos de aço enformado a frio, bem como as vantagens e desvantagens resultantes da sua utilização na construção. Posteriormente é apresentada, pormenorizadamente, o Cold-Formed Design. Numa fase final do documento são apresentadas a análise e otimização das estruturas modulares planas, sendo apresentadas as características das estruturas modulares otimizadas e a redução das quantidades de aço resultante da otimização estrutural
In the construction industry the sustainability has acquired a key role. The dissertation topic is developed within the framework of the project I&DT Cool Haven, which aims to develop an innovative concept of construction, giving a sustainability based on structural efficiency and adaptability of the structures to the various functional requirements during the life of the building. Associated with this concept is the modular construction and metal construction of cold-formed steel. The modular construction displays serious advantages by the fact that the construction process are mostly developed in the factory, reducing the workload in site, the probability of issues and consequent problems with the structure. The metallic construction exhibits obvious advantages by the fact that steel is a totally recyclable material and because of the high structural efficiency. This thesis is associated with the need to transform this concept of innovative, competitive and attractive building, economically. The main purpose of this dissertation is to develop a supporting tool for the optimizing of modular structures of cold-formed steel in terms of structural efficiency. Such as, a computational tool Cold-Formed Design was developed, in order to simplify the design and optimization of elements of cold-formed steel. The developed tool was then applied in the optimization of modular plane structures. In the first part of document the main characteristics of the elements of cold-formed steel, as well as the advantages and disadvantages of their use in construction are described. Then, the Cold-Formed Design is explained in detail. At the end of this document, the analysis and the optimization of plane modular structures are introduced and the characteristics of modular structures optimized and reduced amounts of steel that results from the structural optimization are presented.
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Pereira, Flávio José Rosa. "Encurvadura e vibração de perfis de aço enformados a frio : modelação de secções com dobras." Master's thesis, 2016. http://hdl.handle.net/10400.26/15418.
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Dissertação de mestrado em Engenharia Civil - Área de especialização: EstruturasA presente dissertação reporta um trabalho académico no âmbito do qual se desenvolveu uma aplicação informática, intitulada “Rounded Corners 1.0”, que facilita a modelação geométrica de secções transversais que contenham dobras circulares – o que constitui uma situação comum no caso dos perfis enformados a frio, por exemplo. A aplicação foi desenvolvida na linguagem Visual Basic 6, usando o ambiente de desenvolvimento Visual Studio 2013, e contém um interface gráfico user-friendly que permite uma fácil e intuitiva introdução dos parâmetros, permitindo a modelação automática de secções em forma de “L”, “C”, “Z” ou “RHS”. Os inputs são os parâmetros geométricos (i) da secção transversal e (ii) das dobras (o raio de curvatura 𝑅 e o número de segmentos da aproximação 𝑁), sendo o output um ficheiro de dados (coordenadas de nós, etc.) formatado de acordo com as especificações do programa GBTUL – exportando-se assim os dados para este último, pode prosseguir-se para a análise estrutural propriamente dita (de encurvadura ou de vibração). Deduziram-se, e implementaram-se na aplicação, fórmulas matemáticas gerais que permitem determinar as coordenadas dos nós dos segmentos de aproximação de dobras, com várias possíveis orientações. Após o desenvolvimento, a aplicação foi testada com sucesso. Por fim, utilizou-se a mesma em algumas pequenas análises de encurvadura e vibração de perfis de aço enformados a frio, tendo os resultados obtidos sido comparados com valores fornecidos por (i) fórmulas analíticas, (ii) artigos científicos e (iii) o programa CUFSM 4.05. O programa, cujo interface foi escrito convenientemente com instruções em Inglês, será disponibilizado gratuitamente no site http://www.civil.ist.utl.pt/gbt/. Ficará assim à disposição da comunidade técnica e científica e espera-se que seja útil para a investigação nesta área.
This dissertation reports an academic work under which it was developed a computer application entitled "Rounded Corners 1.0", which facilitates the geometric modeling of cross-sections containing circular folds – a fairly common situation in the case of cold formed members. The application was written in Visual Basic 6 language, using Visual Studio 2013 development platform, and contains a user-friendly graphical interface which allows easy and intuitive introduction of input parameters, allowing the automatic modeling of "L", "C", "Z" or "RHS" sections. The inputs are the geometrical parameters defining (i) cross-section geometry and (ii) its folds (the curvature radius 𝑅 and the number of segments 𝑁 of the approximation), while the output is a data file (coordinates of nodes, etc.) formatted according to the specifications of GBTUL program – the structural analysis itself (buckling or vibration) is performed by the latter, after importing the data from that file. General mathematical formulae, for determining the coordinates of the approximation segment nodes of quadrants with possible orientations, are derived and implemented on the code. After development, the application has been successfully tested. Finally, the application was used in a few buckling and vibration analyses of cold-formed steel columns and the results obtained were compared with values provided by (i) analytical formulae, (ii) results in scientific literature, and (iii) (buckling) estimates provided by the CUFSM 4.05 program. The program, its interface having conveniently been written in English, will be made available as freeware on the website http://www.civil.ist.utl.pt/gbt/. It will thus be available to the scientific and technical community and is expected to be useful for research in this area.
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Chang, Wen-Hsuan, and 張文瑄. "Modeling and analysis of welding-induced distortion and residual stress in pressure vessel and Its effect on buckling strength." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/5vuuwh.
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碩士國立臺灣海洋大學
系統工程暨造船學系
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The welding technique, such as gas metal arc welding (GMAW) and shield metal arc welding (SMAW), are commonly used to connect the components of ship in shipyard. During the welding process, the large input of heat causes the distortion and the generation of residual stress of the weldment. Also, it affects the geometry and strength of the component after welding. In this thesis, we simulate the process of plate welding by commercial finite element software, ABAQUS, and we analyze the post-weld residual stress distribution and distortion. We further study the buckling strength of the cylindrical shell after welding. We first perform the welding analysis of flat plate and compare the numerical results with experimental results to verify our simulation process. Then, we performed the analysis of buckling strength of cylindrical shell from the previous experience. There are two steps in the cylindrical shell welding analysis: First, we use coupled temperature-displacement elements to simulate the heating process. The change of the material properties at different temperature, such as Young’s modulus, yield strength, Poisson’s ratio, etc., are considered. And we study the distortion of cylindrical shell after welding, and find out the distribution pattern of distortion and residual stress near the weld bead. Second, we apply the welding-induced distortion and residual stress on the cylindrical shell to perform the buckling analysis, and discuss the influence of the welding-induced distortion and residual stress on the buckling strength of the cylindrical shell. According to the buckling strength analysis of cylindrical shell by solid-element model and plate element model, we know that the plate-element model tends to overestimate the post-welding buckling strength of cylindrical shell. The results of welding simulation in different temperature show that magnitude of deformation and the distribution range of residual stress of the weldment increase as the welding temperature increase. And the buckling strength of cylindrical shell decreases when the welding temperature is increased. By analyzing the different kinds of simplified model of cylindrical shell, we found that the buckling strength of the cylindrical shell which only considers post-welding deformation is underestimated when the buckling wavenumber is low, and the buckling strength is overestimated when the buckling wavenumber is high.