Дисертації з теми "Buckling experiments"
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1
Liu, Bing 1975. "FE analysis of plastic buckling of plates with initial imperfections and simulation of experiments." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100251.
Повний текст джерелаАнотація:
The general problem of plastic buckling of flat metal plates is a fundamental area of investigation in mechanics not only because of its intrinsic importance in the design of engineering structures, but also because it still has not been settled in a satisfying manner. Which theory of plasticity is the correct one to predict the buckling loads in the plastic range is a long-argued problem.This thesis presents finite element analyses of plastic buckling and postbuckling behaviour of columns and plates, taking into account the presence of initial out-of-plane imperfections. The FE programs constructed by the author for this purpose are used to analyze the imperfection growth of such columns and plates under axial loading and simply supported edge conditions. The material behaviour is modeled according to both the incremental and the deformation theories of strain-hardening plasticity. The programs combine both the geometric and material nonlinearities to trace the load-deflection behaviours of these structures in prebuckling (up to the maximum load) as well as postbuckling ranges. The results of the analyses for plates show the extreme sensitivity of the incremental theory, and the relative insensitivity of the deformation theory, to the initial imperfections.
The programs are used to simulate the plastic buckling experiments on Aluminum tubes, taking into account their measured imperfections. The imperfection growth analyses demonstrate that the maximum load predictions of the incremental theory are quite close to those recorded in the experiments.
2
Soroori, Rad Behrooz H. "Experiments on Cold-Formed Steel Beams with Holes." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/42698.
Повний текст джерелаАнотація:
Experimental testing and elastic buckling studies were performed on 68 C-section cold-formed steel joists with unstiffened rectangular web holes. Four Steel Stud Manufacturers Association (SSMA) cross-section types; 800S200-33, 800S200-43, 1000S162-54, and 1200S162-97, were evaluated to explore the influence of holes on local, distortional, and global bucking failure modes. Hole depth was varied in the tests to identify trends in ultimate strength. Ultimate strength was observed to decrease with increasing hole depth for 800S200-33, 1200S162-97 cross-sections. Due to small number of specimen and unidentified behavior of the beams, a more in depth study of the behavior of 800S200-43 and 1000S162-54 beams are necessary. Local buckling of the unstiffened strip above the hole was observed to accompany distortional buckling at the hole for the locally slender 800S200-33 and 1000S162-54 cross-sections. Thin shell finite element eigen-buckling analysis of each joist specimen, including measured cross-section dimensions and tested boundary and loading conditions, were conducted in parallel with the experiments to identify those elastic buckling mode shapes which influence load-deformation response. The distortional and lateral-torsional buckling moments were observed to decrease with increasing hole depth while a contrasting behavior was captured for local buckling modes. A modification to the AISI Direct Strength Method equations for beams with slotted web-holes was compared against the experimental results with predictions lower than tested strength. Initial cross-section imperfections led to inclined webs which decreased the capacity of the beams. The use of a water-jet cutting process was employed successfully to produce accurate holes sizes and locations in each joist specimen and is recommended for researchers and manufacturers as a method for custom fabrication of cold-formed steel members.Master of Science
3
Haidar, Mohamed. "Modelling of failure mechanisms for corrugated board." Thesis, KTH, Hållfasthetslära (Inst.), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-176010.
Повний текст джерелаАнотація:
The present work describes the construction of a semi-analytical model for prediction of buckling loads in simply supported corrugated paperboard panels. The model accounts for transverse shear, due to the weakness of the core in such plates compared to the facings. This was done utilizing energy relations and rst order transverse shear. The panel was homogenised using laminate theory. A detailed model using FEM was derived in order to validate the predictive capabilities of the analytical model. Experimental testing was performed to estimate the accuracy of both theoretical models, and assess the limitation of the analytical model. All modes of analysis showed good agreement for cubic boxes. Further investigation into expanding the scope of the analytical model was carried out and commented on.
4
Barbarella, Elena. "Towards the localization and characterization of defects based on the Modified error in Constitutive Relation : focus on the buckling test and comparison with other type of experiments." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLN066/document.
Повний текст джерелаАнотація:
Des nombreuses industries composites cherchent à étendre le champ d'application des composites structuraux à fibres continues pour d'autre marché que l'aéronautique. Être compétitif sur ces marchés potentiels, tel l'automobile, implique de se conformer à des contraintes différentes; de coût, de temps de mise en œuvre, de trace écologique. Dans ce cadre les résines thermodurcissables sont remplacées par des résines thermoplastiques permettant des temps de cycle cours. Ces temps de cycle cours favorisent l'apparition de défauts potentiellement important et une question récurrente dans ce cadre est: Comment traiter des défauts? Un des aspects de cette question est celui de la détection et de la caractérisation des défauts. L'approche actuelle est celle des techniques non destructives. Celles ci sont longues, coûteuses et complexes et apparaissent donc mal adaptées aux contraintes de coûts et de temps caractéristique de la plupart des produits grands diffusions. Ce problème a motivé ce travail de thèse: est-il possible de détecter et d'estimer l'effet des défauts sans avoir recours à des techniques d'essais non destructifs complexes et coûteuses? Une réponse acceptable pourrait conduire à moins de précision, mais devrait fournir des informations quantitatives suffisantes pour les applications. La voie étudiée dans cette thèse est celle de l'exploitation par approches inverse d'essais mécaniques statiques suivis par mesure de champs par corrélation d'images numériques. Seuls la localisation et la caractérisation de grands défauts est visée. Des essais de flambement ont été choisis en raison de leur sensibilité supposée aux défauts. Parmi les approches inverses, nous nous sommes concentrés sur la méthode de l'erreur en relation de comportement modifiée (MCRE). En effet cette méthode a, par le passé, montrée de très bonnes propriétés de localisation dans le cas d'essais de vibrations couvrant plusieurs fréquences propres. En vue d'obtenir une formulation simple et rapide nous avons privilégié une exploitation approchée des essais par l'intermédiaire d'une approche linéarisée du flambage. Une extension de la MCRE dans ce cadre a été proposée. Cette formulation pose, notamment la difficulté de traiter des résultats expérimentaux qui se présentent non pas sous la forme d'une réponse de flambage pure mais, en raison des défauts géométriques, d'une réponse non-linéaire dés le début des essais. Pour essayer de contourner cette difficulté une exploitation des essais au moyen du diagramme de Southwell a été utilisée. Elle permet, au moins pour des éprouvettes élancées, de déterminer la charge critique théorique d'une éprouvette sans défauts géométriques mais avec défauts matériels. La stéréo corrélation d'images numériques (StereoDIC) est exploitée pour reconstruire la déformée la forme de l'échantillon pendant le test. Les intérêts et les limites de la méthodologie sont discutés sur la base d'essais numériques et l'essai flambage est comparé aux essais de traction, flexion ou de vibration. Il est montré que l'exploitation d'essais de flambage par l'approche proposée est efficace au moins dans le cas d'imperfections géométriques modérées. Finalement la méthode est exploitée dans le cas d'essais expérimentaux à la fois pour un spécimen presque parfait et pour une pièce défectueuse, où une zone d'ondulation de la fibre est introduite. Les résultats obtenus sont encourageantsComposite materials are nowadays extending their operational field to industrial applications other than aeronautics. New potential markets, such as automotive, imply the need to comply with different constraints; reduced cost and production time become more binding, taking the lead over the complete absence of defects. The drawback to fast automatized procedure is the higher defectiveness of the components produced, a deeper control of the part is therefore needed. Non-destructive techniques are expensive both in terms of cost and time and therefore the main question we tried to answer in this thesis is: is it possible to detect and estimate the effect of defects without resorting to the complex and time-consuming NDT techniques? An acceptable answer may potentially lead to a lower precision but should guarantee sufficient quantitative information for these applications. The thesis aims at exploring possibilities to use classical mechanical test combined with Digital Image correlation and inverse procedure to localize and characterized possible (large) defects. Buckling tests have been chosen at first due their supposed sensitivity to defects. Among the possible inverse technique, we have chosen to extend the so-called Modified Error in Constitutive Relation to the case of buckling because, in the case of vibration tests performed with several frequencies, the MCRE proved to have very good localization properties. The dedicated formulation of the MCRE for linearized buckling requires a post-processing of the non-linear experimental results. The Southwell plot is here employed to reconstruct the eigenvalue, the critical load, of the equivalent eigenvalue problem (i.e. the solution of the problem with material defect and no geometrical ones) and the Stereo Digital Image Correlation (StereoDIC) is exploited to reconstruct the deformed shape of the specimen during the test, used as mode. The interests and limits of the methodology are discussed notably through the comparison of numerical results using the MCRE in case of traction, flexion or vibration tests. It is shown that the linearized buckling based MCRE technique proves well for pseudo-experimental measurements at least for moderate geometrical imperfections. In addition first experiments have been performed; the defects are characterized from real experimental specimens, both for a nominally perfect specimen and for a defective one, where a zone of fibre waviness is induced. Stereo Digital Image Correlation (StereoDIC) is exploited to reconstruct the deformed shape of the specimen during the test, this shape being used as an approximation of the buckling mode. While on the first one no defects are detected, on the flawed specimen the localized area is in reasonable agreement with the area affected by fibre undulations
5
Li, Hong. "Experimental micromechanics of composite buckling strength." Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/11719.
Повний текст джерела
6
Schleyer, Graham Klaus. "Buckling of tank roofs : a buckling analysis and experimental investigation of storage tank domed roofs." Thesis, University of Strathclyde, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362804.
Повний текст джерела
7
Eryasar, Mehmet Emrah. "Experimental And Numerical Investigation Of Buckling Restrained Braces." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12610364/index.pdf.
Повний текст джерелаАнотація:
A typical buckling restrained brace (BRB) consists of a core segment and a buckling restraining mechanism. When compared to a conventional brace, BRBs provide nearly equal axial yield force in tension and compression. Buckling restraining mechanism can be grouped into two main categories. Buckling is inhibited either by using a concrete or mortar filled steel tube or by using steel sections only. While a large body of knowledge exists on buckling restrained braces the behavior of steel encased BRBs has not been studied in detail. Another area that needs further investigation is the detailing of the deboding material. For all types of BRBs a debonding material or a gap has to be utilized between the core brace and the restraining mechanism. The main function of the debonding material is to eliminate the transfer of shear force between the core brace and the restraining mechanism by preventing or reducing the friction. A two phase research study has been undertaken to address these research needs. In the first phase an experimental study was carried out to investigate the potential of using steel encased BRBs. In the second phase a numerical study was conducted to study the friction problem in BRBs. The experimental study revealed that steel encased braces provide stable hysteretic behavior and can be an alternative to mortar filled steel tubes. Material and geometric properties of the debonding layer for desired axial load behavior were identified and presented herein.
8
Rastgar, Agah Mobin. "Material Characterization of Aortic Tissue for Traumatic Injury and Buckling." Diss., Temple University Libraries, 2015. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/324268.
Повний текст джерелаАнотація:
Mechanical EngineeringPh.D.
While traumatic aortic injury (TAI) and rupture (TAR) continue to be a major cause of morbidity and mortality in motor vehicle accidents, its underlying mechanisms are still not well understood. Different mechanisms such as increase in intraluminal pressure, relative movement of aorta with respect to mediastinal structures, direct impact to bony structures have been proposed as contributing factors to TAI/TAR. At the tissue level, TAI is assumed to be the result of a complex state of supra-physiological, high rate, and multi-axial loading. A major step to gain insight into the mechanisms of TAI is a characterization of the aortic tissue mechanical and failure properties under loading conditions that resemble traumatic events. While the mechanical behavior of arteries in physiological conditions have been investigated by many researchers, this dissertation was motivated by the scarcity of reported data on supra-physiological and high rate loading conditions of aorta. Material properties of the porcine aortic tissue were characterized and a Fung-type constitutive model was developed based on ex-vivo inflation-extension of aortic segments with intraluminal pressures covering a range from physiological to supra-physiological (70 kPa). The convexity of the material constitutive model was preserved to ensure numerical stability. The increase in ë_è from physiological pressure (13 kPa) to 70 kPa was 13% at the outer wall and 22% at the inner wall while in this pressure range, the longitudinal stretch ratio ë_z increased 20%. A significant nonlinearity in the material behavior was observed as in the same pressure range, the circumferential and longitudinal Cauchy stresses at the inner wall were increased 16 and 18 times respectively. The effect of strain-rate on the mechanical behavior and failure properties of the tissue was characterized using uniaxial extension experiments in circumferential and longitudinal directions at nominal strain rates of 0.3, 3, 30 and 400 s-1. Two distinct states of failure initiation (FI) and ultimate tensile strength (UTS) were identified at both directions. Explicit direct relationships were derived between FI and UTS stresses and strain rate. On the other hand, FI and UTS strains were rate independent and therefore strain was proposed as the main mechanism of failure. On average, engineering strain at FI was 0.85±0.03 for circumferential direction and 0.58±0.02 for longitudinal direction. The engineering strain at UTS was not different between the two directions and reached 0.89±0.03 on average. Tissue pre-failure linear moduli showed an average of 60% increase over the range of strain rates. Using the developed material model, mechanical stability of aorta was studied by varying the loading parameters for two boundary conditions, namely pinned-pinned boundary condition (PPBC) and clamped-clamped boundary condition (CCBC). The critical pressure for CCBC was three times higher than PPBC. It was shown that the relatively free segment of aorta at the isthmus region may become unstable before reaching the peak intraluminal pressures that occur during a trauma. The mechanical instability mechanism was proposed as a contributing factor to TAI, where elevations in tissue stresses and strains due to buckling may increase the risk of injury.
Temple University--Theses
9
Markiz, Nizar. "Experimental Investigation of Lateral Torsional Buckling of Gerber Frames." Thèse, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/20051.
Повний текст джерелаАнотація:
The objective of this thesis is to investigate the elastic lateral buckling resistance of Gerber frames based on full scale tests and finite element analyses. Three experiments were undertaken to obtain elastic buckling loads and the buckling modes were recorded. Shell finite element solutions were conducted to predict the elastic lateral buckling resistance of the frames tested. A comparison between the elastic buckling loads obtained from full scale experiments and those predicted by the FEA models provides an assessment of the ability of the finite element analysis model in predicting elastic lateral resistance and buckled mode shapes of Gerber frames. Conclusions and recommendations for future research are provided.
10
Berrada, Kamal. "An experimental investigation of the plastic buckling of aluminum plates /." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63160.
Повний текст джерела
11
Misseroni, Diego. "Experimental models of Elastic Structures: Tensile Buckling and Eshelby-like Forces." Doctoral thesis, Università degli studi di Trento, 2013. https://hdl.handle.net/11572/367912.
Повний текст джерелаАнотація:
Mechanical models have been invented, designed and realized to experimentally confirm unexpected behaviours theoretically predicted in elasticity:
- instabilities and bifurcations occurring in structures under ‘tensile dead load’ and the influence of the constraint’s curvature;
- the presence of an ‘Eshelby-like’ or ‘configurational’ force in structures with movable constraints.
Furthermore, ‘classical’ features in elasticity have been substantied by testing small-scale models and observing:
- linearity in the mechanical response of a truss-structure, confirming the usual assumption of linear elasticity when small displacements are considered;
- stress singular fields near stiff quadrilateral inclusions embedded in a ‘soft’ elastic plate, validating the model of rigid inclusion.
All the experiments have been performed at the Laboratory for Physical Modeling of Structures and Photoelasticity of the Department of Civil,Environmental and Mechanical Engineering of the University of Trento.
12
Chattopadhyay, Arka Prabha. "Elastic buckling behavior of plate and tubular structures." Thesis, Kansas State University, 2011. http://hdl.handle.net/2097/8702.
Повний текст джерелаАнотація:
Master of ScienceDepartment of Mechanical and Nuclear Engineering
Kevin B. Lease
Xiao J. Xin
The study of buckling behavior of tubular and cellular structures has been an intriguing area of research in the field of solid mechanics. Unlike the global Euler buckling of slender structures under compressive loads, tubular and cellular structures deform with their walls buckling as individual supported plates. The aspect ratio and the dimensional characteristics of the tube define the buckling behavior of any tube structure. In this thesis, a thorough study on the buckling of polygon tubular structures with different cross sections is discussed. In the first study, the theoretical buckling formulation of a square tube using the energy method is reviewed from existing solutions in literature. The elastic critical load of a square tube derived from the theoretical solution is then compared with results of finite element elastic buckling simulations. The formation of lobes along the height of the walls at different aspect ratios of the tube is investigated and compared to theory. Also, the buckling behavior of multi-wall structures is studied and the relationship between these structures and a rectangular simply supported plate is established. A brief study on the buckling behavior of rhombic tubes is also performed. The results of the simulation match closely with the theoretical predictions. The study is then extended to quadrilateral tubes with cross-sections in the shape of square, rectangle, rhombus and parallelogram. The theory of buckling of these tubes is explicitly defined using classical plate mechanics based on the previous works presented in literature. Also, the possibility of global Euler buckling in the tubular structures after a certain critical height is discussed. The prediction from the theory is validated using extensive finite element elastic buckling simulations and experimental tests on square and rhombic tube specimens. The results of the simulations and experiments are observed to be consistent with the theory. Using the formulation of plate buckling under different boundary conditions, the buckling behavior of triangular tubes is also determined. A theoretical formulation for calculating the critical load of triangular tubes is derived. The theoretical critical loads for a range of aspect ratios are compared with corresponding finite element simulation results. The comparisons reveal high degree of similarity of the theoretical predictions with the simulations.
13
Lo, Patrick Kar-Leung. "Comparison of theory and experiment for flexural-torsional buckling of laminated composite columns." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/50051.
Повний текст джерелаАнотація:
Vlasov’s one-dimensional structural theory for thin-walled open section bars was originally developed and used for metallic elements. The theory was recently extended to laminated bars fabricated from advanced composite materials. The purpose of this research is to provide a study and assessment of the extended theory. The focus is on flexural and torsional-flexural buckling of thin-walled, open section, laminated composite columns. Buckling loads are computed from the theory using a linear bifurcation analysis, and are compared to available experimental data. Also, a geometrically nonlinear beam column analysis by the finite element method is developed from the theory. Results from the nonlinear compression response analysis are compared to limited available test data. The merits of the theory and its implementation are discussed.Master of Science
incomplete_metadata
14
Lane, Andrew. "An experimental investigation of buckling mode interaction in PERP wide-flange columns." Thesis, University of Warwick, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269543.
Повний текст джерела
15
Alrsai, Mahmoud S. "Experimental and Numerical Study on Propagation Buckling in Pipe-in-Pipe Systems." Thesis, Griffith University, 2020. http://hdl.handle.net/10072/395531.
Повний текст джерелаАнотація:
Subsea pipe-in-pipe (PIP) systems are being used extensively in the design of high-pressure and high-temperature (HP/HT) flowlines because of their outstanding thermal insulation performance. A typical PIP system consists of concentric inner and outer pipes, bulkheads, and centralizers. The inner pipe (flowline) conveys production fluids, and the outer pipe (carrier pipe) protects the system from high external pressure (water depths up to 3000 m) and mechanical damage. These two pipes are isolated by centralizers at joints and connected through bulkheads at both ends of the pipeline. The annulus (the space between the tubes) is either empty or filled with non-structural insulation material such as foam or water.
The external pressure in the vicinity of local dents or ovality in the outer pipe-wall can cause a local collapse, which may catastrophically propagate along with the PIP system, known as propagation buckling. The lowest pressure required to sustain such a buckle propagation is known as the propagation pressure Pp, which is only 15–30% of the initiation pressure PI of the intact pipe. The propagation buckling (or buckle propagation) has been extensively investigated in single pipelines using analytical, experimental and numerical methods.
Unlike single pipelines, buckle propagation and collapse mechanisms in PIPs have only been marginally addressed. Therefore, this research program aims to investigate propagation buckling of subsea pipe-in-pipe (PIP) systems under hydrostatic pressure; experimentally and numerically. By using experimental results, a finite element (FE) model is validated and is used to conduct a comprehensive parametric study to evaluate the effect of geometric and material parameters affecting the propagation buckling pressure of PIP system. The experimental study performed herein showed that the buckling mechanisms and collapse pressure of the inner pipe of a PIP system are different from those of a single pipeline. Therefore, a chapter of the thesis is dedicated to the investigation of the collapse mechanisms of the inner pipe of a PIP system. Moreover, a parametric study is conducted and the collapse mechanisms of PIPs with various combinations of outer and inner pipes in a broad practical range of diameter-to-thickness ratios (D/t) are evaluated. The thesis is concluded by proposing and investigating the appropriateness of a novel carbon fibre buckle arrestor.
The thesis makes the following contributions to the knowledge and practice in the area of offshore pipelines. A more accurate simplified analytical expression is proposed to predict the propagation buckling pressure of PIP system. The buckle propagation modes of PIPs are identified and discussed. Subsequently, empirical expressions for each mode are proposed to predict the propagation buckling pressure of PIP systems. Moreover, a parametric study is conducted on the collapse mechanisms of the inner pipe of a PIP system. Comprehensive empirical expressions are proposed for the collapse pressure of the inner pipe, and the upper and lower pressure capacity bounds are quantified. Design charts are proposed to estimate the collapse pressure of the inner pipe and its corresponding collapse modes. In the last part of this research, CFRP buckle arrestors are proposed for subsea pipelines and are shown to achieve higher arresting efficiency compared with the conventional buckle arrestors.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
Full Text
16
Saliés, Jacques Braile. "Experimental study and mathematical modeling of helical buckling of tubulars in inclined wellbores /." Access abstract and link to full text, 1994. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/9522965.
Повний текст джерела
17
Liu, Liu. "Durability of Polymer Composite Materials." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14002.
Повний текст джерелаАнотація:
The purpose of this research is to examine structural durability of advanced composite materials under critical loading conditions, e.g., combined thermal and mechanical loading and shear fatigue loading. A thermal buckling model of a burnt column, either axially restrained or under an axial applied force was developed. It was predicted that for a column exposed to the high heat flux under simultaneous constant compressive load, the response of the column is the same as that of an imperfection column; the instability of the burnt column happens. Based on the simplified theoretical prediction, the post-fire compressive behavior of fiberglass reinforced vinyl-ester composite columns, which have been exposed to high heat flux for a certain time was investigated experimentally, the post-fire compressive strength, modulus and failure mode were determined. The integrity of the same column under constant compressive mechanical loading combined with heat flux exposure was examined using a specially designed mechanical loading fixture that mounted directly below a cone calorimeter. All specimens in the experiments exhibited compressive instability. The experimental results show a thermal bending moment exists and has a significant influence on the structural behavior, which verified the thermal buckling model. The trend of response between the deflection of the column and exposure time is similar to that predicted by the model.
A new apparatus was developed to study the monotonic shear and cyclic-shear behavior of sandwich structures. Proof-of-concept experiments were performed using PVC foam core polymeric sandwich materials. Shear failure occurred by the extension of cracks parallel to the face-sheet/core interface, the shear modulus degraded with the growth of fatigue damage. Finite element analysis was conducted to determine stress distribution in the proposed specimen geometry used in the new technique.
Details for a novel apparatus used for the fatigue testing of thin films and face sheets are also provided.
18
Länsman, S. (Satu). "Evaluation of bioabsorbable poly-L/D-lactide implant for scleral buckling:an experimental study." Doctoral thesis, University of Oulu, 2009. http://urn.fi/urn:isbn:9789514260742.
Повний текст джерелаАнотація:
Abstract
Bioabsorbable materials enable temporary implantation without the need for subsequent implant removal. The aim of the present experimental study was to evaluate the suitability of a fibrous bioabsorbable implant made of poly-L/D-lactide (PLDLA) 96/4 fibres as an episcleral implant.
The general tissue reactions were evaluated in subcutaneous tissues in rats in follow-up periods ranging from 3 days to 48 weeks. The episcleral tissue reactions were studied in rabbits with follow-up periods of one, three, five and 48 weeks. A silicone sponge implant was used as a control material and operations were performed using similar technique with both implants. Tissue reactions were located just around the implant area and consisted of an acute inflammatory reaction in the early follow-up periods, continuing as a foreign body inflammatory reaction. With episcleral implants there were no inflammatory cells seen within the sclera or in the retinal layers, and the structure of the retina and the cornea was also normal. The biocompatibility was good in the 48 week follow-up despite the relatively high surface area of the fibrous implant. The material had not degraded by 48 weeks.
The indentation effect by the PLDLA implant (diameter of 3–3.5mm) was lower than that achieved with the silicone sponge implant (diameter 4mm). The depth of indentation decreased over time in both groups with comparable rates over the follow-up period of 5 months. The duration of the indentation effect was sufficient to be used for scleral buckling in retinal detachment surgery.
In conclusion, the biocompatibility of a fibrous implant made of PLDLA 96/4 placed subcutaneously and episclerally was good in the follow-up lasting 48 weeks despite the relatively high surface area of the implant. The fibrous implant made of PLDLA 96/4 seemed to be well-tolerated by ocular tissues and the indentation effect was sufficiently long.
19
Redmond, Nicholas A. "Experimental and Analytical Investigation of the Shear Strength of Unstiffened Tapered Steel Members." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/36067.
Повний текст джерелаАнотація:
Tapered beams and columns are often used in single story gable framed steel buildings for reasons of economy. By varying the resistance to bending in similar proportion to the bending moments, more economical structures can be obtained. The beam and column connection, or knee area, is generally subject to the greatest bending moments. It is therefore comprised of the deepest sections of the tapered members, which also possess the least resistance to shear buckling. The web elementâ s stress distribution in this region of relatively complicated geometry is unknown. For this reason, web stiffening plates are commonly used to brace the slender web elements against elastic shear buckling. The design and proper installation of these relatively small elements, while proven to be effective, is also costly. Because it is desirable to remove the stiffeners, the shear behavior of unstiffened tapered members near the moment connection was the primary focus of this study. Four knee area specimens were tested to failure under simulated gravity load conditions.
The specimens were analyzed according to the AISC shear provisions for prismatic members. The appropriateness of a modified shear force, which accounts for the influence of inclined flanges, and the role of initial web imperfections were examined as well. Finally an analysis method which most consistently produces conservative results is proposed.
Master of Science
20
Abraham, Jeevan George. "A deflection, buckling and stress investigation into telescopic cantilever beams." Thesis, Brunel University, 2012. http://bura.brunel.ac.uk/handle/2438/7380.
Повний текст джерелаАнотація:
The telescoping cantilever beam structure is applied in many different engineering sectors to achieve weight/space optimisation for structural integrity. There has been limited theory and analysis in the public domain of the stresses and deflections involved when applying a load to such a structure. This thesis proposes (a) The Tip Reaction Model, which adapts classical mechanics to predict deflection of a two and a three section steel telescoping cantilever beam; (b) An equation to determine the Critical buckling loads for a given configuration of the two section steel telescoping cantilever beam assembly derived from first principles, in particular the energy methods; and finally (c) the derivation of a design optimization methodology, to tackle localised buckling induced by shear, torsion and a combination of both, in the individual, constituent, hollow rectangular beam sections of the telescopic assembly. Bending stress and shear stress is numerically calculated for the same structure whilst subjected to inline and offset loading. An FEA model of the structure is solved to verify the previous deflection, stress and buckling predictions made numerically. Finally an experimental setup is conducted where deflections and stresses are measured whilst a two section assembly is subjected to various loading and boundary conditions. The results between the predicted theory, FEA and experimental setup are compared and discussed. The overall conclusion is that there is good correlation between the three sets of data.
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Campos, Eduardo Felipe de. "Análise numérica e experimental de flambagem em cilindros de paredes finas." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/152471.
Повний текст джерелаАнотація:
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Estruturas de paredes finas são muito utilizadas na engenharia moderna devido sua boa relação entre peso e resistência. Sua aplicação vai desde obras civis, como cúpulas em edifícios e pontes, até estruturas aeronáuticas e equipamentos industriais. Uma geometria que é muito comum de ser encontrada nas estruturas de paredes finas são os cilindros, como pode ser observado no corpo dos aviões, tubulações e vasos de pressão. Submetidas a esforços compressivos, essas estruturas ficam suscetíveis ao fenômeno de instabilidade ou flambagem, podendo entrar em colapso repentinamente, mesmo antes de apresentar altas tensões. Assim, compreender o comportamento da instabilidade se torna crucial em um projeto de estruturas de paredes finas. Um dos fatores que influenciam no comportamento da instabilidade é a imperfeição geométrica da estrutura, e qualquer processo de fabricação possui erros associados ao processo. Para iniciar o estudo foi necessário medir os defeitos devido ao processo de fabricação do cilindro. Duas alternativas para realizar as medidas foram propostas, a primeira utilizando LVDTs, que medem a variação do raio do cilindro ao longo de toda sua extensão, e a segunda o fotoprocessamento. Ambos os métodos nos deram uma nuvem de pontos que foram processadas para obter a estrutura 3D CAD, possibilitando sua análise pelo método de elementos finitos e obtenção das respectivas cargas de flambagem numéricas. Além do método numérico foi realizado um ensaio experimental visando validar a análise numérica. O cilindro foi fechado com duas tampas e montado em uma bancada experimental, instrumentado com LVDTs, manômetro e por fim, uma bomba de vácuo foi ligada a uma das tampas. A bomba criou vácuo dentro do cilindro até o mesmo sofrer colapso. As cargas de flambagem numéricas foram superiores a encontrada experimentalmente em 14,48% a geometria foto, 11,72% da geometria LVDT e 39,98% a do cilindro referência. Os resultados mostram que as imperfeições geométricas são de grande relevância na resistência a instabilidade de uma estrutura, e também que grandes imperfeições geométricas tendem a ser o local onde ocorrem as ondas de flambagem. Em relação ao método de medição por fotoprocessamento os resultados mostram que é interessante estudar a técnica para aplicações na área de instabilidade.
Thin-walled structures are widely used in modern engineering because of their good weight-to-strength ratio. Its application ranges from civil works, such as domes in buildings and bridges, to aeronautical structures and industrial equipment. One geometry that is very common to be found in thin-walled structures is the cylinder, as can be seen in the body of airplanes, pipes and pressure vessels. Under compressive stresses, these structures are susceptible to the buckling phenomenon, which can suddenly collapse, even before presenting high stresses. Therefore, understanding the behavior of instability becomes crucial in designing thin-walled structures. One of the factors influencing the behavior of instability is the geometric imperfection of the structure, and any manufacturing process has errors associated with the process. To begin the study it was necessary to measure the defects due to the cylinder manufacturing process. Two alternatives to carry out the measurements were proposed, the first using LVDTs, which measure the variation of the cylinder radius along its length, and the second the photoprocessing. Both methods gave us a point cloud that were processed to obtain the 3D CAD structure, allowing its analysis by the finite element method and obtaining the respective numerical buckling loads. In addition to the numerical method, an experimental test was carried out to validate the numerical analysis. The cylinder was closed with two flat heads and mounted on an experimental bench, instrumented with LVDTs, manometer and finally, a vacuum pump was attached to one of the flat heads. The pump has created a vacuum inside the cylinder until it collapses. Numerical buckling loads were greater than that found experimentally at 14.48 % photo geometry, 11.72 % LVDT geometry and 39.98 % a reference cylinder. The results show that the geometric imperfections are of great relevance in the resistance to buckling of a structure, and also that great geometric imperfections tend to be the place where the buckling waves occur. Regarding the method of measurement by photoprocessing the results show that it is interesting to study the technique for applications in the area of instability.
CAPES: 1544963
22
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.
Повний текст джерелаАнотація:
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.
23
Matsuyama, Yukihiro, Ryu Sasaoka, Hideyuki Azegami, Shunji Murachi, Junzoh Kitoh, Yoshito Ishida, Noriaki Kawakami, and Mitsunori Makino. "Investigation of Buckling Phenomenon Induced by Growth of Vertebral Bodies Using a Mechanical Spine Model." 日本機械学会, 2003. http://hdl.handle.net/2237/7283.
Повний текст джерела
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Lacarbonara, Walter. "A Theoretical and Experimental investigation of Nonlinear Vibrations of Buckled Beams." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36721.
Повний текст джерелаАнотація:
There is a need for reliable methods to determine
approximate solutions of nonlinear continuous
systems. Recently, it has been proved that
finite-degree-of-freedom Galerkin-type
discretization procedures applied to some
distributed-parameter systems may fail to predict
the correct dynamics. By contrast, direct
procedures yield reliable approximate solutions.
Starting from these results and extending some of
these concepts and procedures, we compare the
outcomes of these two approaches (the Galerkin
discretization and the direct application of a
reduction method to the original governing
equations) with experimental results. The nonlinear
planar vibrations of a buckled beam around its first
buckling mode shape are investigated.
Frequency-response curves characterizing
single-mode responses of the beam under a primary
resonance are generated using both approaches and
contrasted with experimentally obtained
frequency-response curves. It is shown that
discretization leads to erroneous quantitative as well
as qualitative results in certain ranges of the buckling
level, whereas the direct approach predicts the
correct dynamics of the system.Master of Science
25
笹岡, 竜., Ryu SASAOKA, 秀幸 畔上, Hideyuki AZEGAMI, 紀明 川上 та Noriaki KAWAKAMI. "脊柱力学模型による特発性側彎症の成因解明". 日本機械学会, 2003. http://hdl.handle.net/2237/12189.
Повний текст джерела
26
Bock, Montero Marina. "Web crippling and local buckling response of stainless steel sections." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/285582.
Повний текст джерелаАнотація:
This thesis examines the response of stainless steel members when subjected to transverse and normal forces triggering the instability phenomena called web crippling and local buckling, respectively. Currently, the part of Eurocode dealing with stainless steel, EN 1993-1-4 (2006) misses design provisions for web crippling and the applicability of some of its aspects is yet to be fully verified especially for application to ferritic stainless steel.
The first part of the thesis laid in the development of design equations for the treatment of web crippling in stainless steel sections which are currently designed following specifications given in EN 1993-1-3 (2006) for cold-formed carbon steel. Two design approaches were derived covering austenitic and ferritic stainless steels: an empiric equation, in line with the current provisions for web crippling design given in EN 1993-1-3 (2006); and an alternative semi-empiric design method based on strength curves which enables a better understanding of the phenomenon and showed to significantly improve web crippling predictions.
For the second part of the thesis, the applicability of the local buckling design provisions given in EN 1993-1-4 (2006) to ferritic stainless steel was examined giving focus to the slenderness limits and the effective width equations. The results showed that EN 1993-1-4 (2006) can safely be applied to ferritic stainless steel, though the code is rather conservative in comparison with other methods. Finally, a modification of the effective width equation incorporating element interaction effects was proposed which allows an improvement of cross-section capacity predictions and enables to amend the effective width method to the same level of alternative design approaches but promoting the use of the concepts currently considered in Eurocode.Esta tesis estudia la respuesta estructural de elementos de acero inoxidable sometidos a fuerzas transversales i normales que desencadenan los fenómenos de inestabilidad llamados web crippling y local buckling, respectivamente. Actualmente, la parte de Eurocódigo que contempla los aceros inoxidables, el EN 1993-1-4 (2006) carece de ecuaciones de diseño para web crippling y la aplicabilidad de algunas de sus especificaciones necesita ser validada especialmente para los aceros inoxidables ferríticos. La primera parte de esta tesis se focaliza en el desarrollo de ecuaciones de diseño para el tratamiento del web crippling en secciones de acero inoxidable que actualmente se diseñan siguiendo las especificaciones dadas en EN 1993-1-3 (2006) para acero al carbono conformado en frío. Dos métodos de diseño para los aceros inoxidables austeníticos y ferríticos: una ecuación empírica en línea con la actual dada en EN 1993-1-3 (2006); y un método de diseño semi-empírico basado en curvas de resistencia que permite entender mejor el fenómeno y muestra una mejora importante de las predicciones a web crippling. Para la segunda parte de la tesis, se ha estudiado la aplicabilidad de las actuales especificaciones para el diseño a local buckling dadas en EN 1993-1-4 (2006) a los aceros inoxidables ferríticos focalizándose en los límites de esbeltez y las ecuaciones de ancho eficaz. Los resultados mostraron que EN 1993-1-4 (2006) puede ser aplicado a los aceros inoxidables ferríticos, aunque el código es bastante conservador en comparación con otros métodos de diseño. Finalmente, se propuso una modificación de la ecuación del ancho eficaz que incorpora la interacción entre los elementos de la misma sección y que permite, además de mejorar las predicciones de la resistencia seccional, llevar el método del ancho eficaz hasta el mismo nivel que otros métodos de diseño pero ensalzando el uso de los conceptos actualmente considerados en Eurocódigo
27
Egorova, Natalia Vadimovna. "Experimental Study of Ring-Shaped Steel Plate Shear Walls." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/52633.
Повний текст джерелаАнотація:
A new type of steel plate shear wall has been devised which resists out-of-plane buckling without requiring stiffeners. The ring-shaped steel plate shear wall (RS-SPSW) includes a web plate that is cut with a pattern of holes leaving ring-shaped portions of steel connected by diagonal links. The ring shape resists out-of-plane buckling through the mechanics of how a circular ring deforms into an ellipse. It has been shown that the ring's compression diagonal will shorten a similar amount as the tension diagonal elongates, essentially eliminating the slack in the direction perpendicular to the tension field. Because of the unique features of the ring's mode of distortion, the load-deformation response of the resulting RS-SPSW system can exhibit full hysteretic behavior and possess greatly improved stiffness relative to thin unstiffened SPSW. The concept has been validated through testing on seven 34 in x 34 in panels. General conclusions about influence of different geometric parameters on plate behavior have been made.Master of Science
28
Rabelo, Marcos Alves. "Estudo experimental do comportamento estrutural de barras curvas." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/3/3152/tde-13102009-151346/.
Повний текст джерелаАнотація:
A presente dissertação trata do estudo experimental do comportamento estrutural de barras helicoidais assentadas sobre superfície cilíndrica e sujeitas a cargas de compressão. Aparato experimental específico foi projetado e construído para este fim. O projeto, bem como a aferição deste aparato, é descrito em detalhes. Este aparato permite ajustar as barras através de um sistema de apoios constituídos por uma série de rolamentos, que podem ser posicionados de forma a conferir liberdade de deslocamento à barra em duas direções distintas: radial (normal à superfície cilíndrica de assentamento) e lateral (tangencial; bi-normal). A aplicação de carga compressiva se faz na direção tangencial à hélice não-deformada. Barras com seção transversal circular e retangular, com diversos comprimentos livres de flambagem e para diferentes ângulos de assentamento, foram ensaiadas. Estudos preliminares, com barras retas, permitiram avaliar as condições efetivas de engastamento proporcionadas pelo aparato. Nestes casos foi possível induzir o fenômeno de flambagem, recuperando-se, consistentemente, os valores de cargas críticas previstas pela teoria de Euler e avaliando-se o grau de engastamento proporcionado pelo aparato experimental. Filmagem com câmera de alta velocidade permitiu observar o fenômeno de instabilidade. O comportamento estrutural das barras curvas, de seção circular e retangular, foi então estudado. Tanto o comprimento livre quanto o ângulo de assentamento foi variado. O estudo permitiu levantar base de dados experimentais do comportamento de barras helicoidais nessas condições de carregamento e de condições de contorno. No entanto, para nenhuma das diversas condições ensaiadas foi possível induzir o fenômeno de instabilidade. Tal fato poderia dar subsídios a inferências acerca do estudo da instabilidade de tubos flexíveis do tipo birdcaging.This dissertation deals with an experimental study on the structural behavior of bars supported on a helical cylindrical surface and subject to compressive loads. A special experimental apparatus was designed and built for this purpose. The design, as well as the adjustment of such an apparatus is described in details. The device allows one adjusting the bars by using a system consisting of a series of bearings that can be positioned to give freedom to the structure in two different directions: radial (normal to the cylindrical surface) and lateral (tangential or bi-normal). The compressive load is applied in the tangential direction of the helix. Bars with circular and rectangular cross sections, with various buckling lengths and different helix angles, were tested. Preliminary studies with straight bars, have allowed to evaluate the boundary conditions offered by the apparatus. In these cases, it was possible to induce the phenomenon of buckling, obtaining, consistently, the values of critical loads provided by the theory of Euler and to evaluate the boundary conditions provided by the apparatus. The use of a high-speed camera allowed to observe the phenomenon of instability. The structural behavior of curved bars of circular and rectangular sections was also studied. Both, the test free length as the helix angle were varied. The study enabled us to get a huge amount of experimental data about the behavior of helical bars, subjected such loading and boundary conditions. However, the phenomenon of instability could not be induced, for any condition tested. This fact could collaborate for further inferences about the study of the birdcaging instability at flexible pipes.
29
Pokharel, Narayan. "Behaviour and design of sandwich panels subject to local buckling and flexural wrinkling effects." Thesis, Queensland University of Technology, 2003. https://eprints.qut.edu.au/15890/1/Narayan_Pokharel_Thesis.pdf.
Повний текст джерелаАнотація:
Sandwich panels comprise a thick, light-weight plastic foam such as polyurethane, polystyrene or mineral wool sandwiched between two relatively thin steel faces. One or both steel faces may be flat, lightly profiled or fully profiled. Until recently sandwich panel construction in Australia has been limited to cold-storage buildings due to the lack of design methods and data. However, in recent times, its use has increased significantly due to their widespread structural applications in building systems. Structural sandwich panels generally used in Australia comprise of polystyrene foam core and thinner (0.42 mm) and high strength (minimum yield stress of 550 MPa and reduced ductility) steel faces bonded together using separate adhesives. Sandwich panels exhibit various types of buckling behaviour depending on the types of faces used. Three types of buckling modes can be observed which are local buckling of plate elements of fully profiled faces, flexural wrinkling of flat and lightly profiled faces and mixed mode buckling of lightly profiled faces due to the interaction of local buckling and flexural wrinkling. To study the structural performance and develop appropriate design rules for sandwich panels, all these buckling failure modes have to be investigated thoroughly. A well established analytical solution exists for the design of flat faced sandwich panels, however, the design solutions for local buckling of fully profiled sandwich panels and mixed mode buckling of lightly profiled sandwich panels are not adequate. Therefore an extensive research program was undertaken to investigate the local buckling behaviour of fully profiled sandwich panels and the mixed mode buckling behaviour of lightly profiled sandwich panels. The first phase of this research was based on a series of laboratory experiments and numerical analyses of 50 foam-supported steel plate elements to study the local buckling behaviour of fully profiled sandwich panels made of thin steel faces and polystyrene foam core covering a wide range of b/t ratios. The current European design standard recommends the use of a modified effective width approach to include the local buckling effects in design. However, the experimental and numerical results revealed that this design method can predict reasonable strength for sandwich panels with low b/t ratios (< 100), but it predicts unconservative strengths for panels with slender plates (high b/t ratios). The use of sandwich panels with high b/t ratios is very common in practical design due to the increasing use of thinner and high strength steel plates. Therefore an improved design rule was developed based on the numerical results that can be used for fully profiled sandwich panels with any practical b/t ratio up to 600. The new improved design rule was validated using six full-scale experiments of profiled sandwich panels and hence can be used to develop safe and economical design solutions. The second phase of this research was based on a series of laboratory experiments and numerical analyses on lightly profiled sandwich panels to study the mixed mode buckling behaviour due to the interaction of local buckling and flexural wrinkling. The current wrinkling formula, which is a simple modification of the methods utilized for flat panels, does not consider the possible interaction between these two buckling modes. As the rib depth and width of flat plates between the ribs increase, flat plate buckling can occur leading to the failure of the entire panel due to the interaction between local buckling and wrinkling modes. Experimental and numerical results from this research confirmed that the current wrinkling formula for lightly profiled sandwich panels based on the elastic half-space method is inadequate in its present form. Hence an improved equation was developed based on validated finite element analysis results to take into account the interaction of the two buckling modes. This new interactive buckling formula can be used to determine the true value of interactive buckling stress for safe and economical design of lightly profiled sandwich panels. This thesis presents the details of experimental investigations and finite element analyses conducted to study the local buckling behaviour of fully profiled sandwich panels and the mixed mode buckling behaviour of lightly profiled sandwich panels. It includes development and validation of suitable numerical and experimental models, and the results. Current design rules are reviewed and new improved design rules are developed based on the results from this research.
30
Pokharel, Narayan. "Behaviour and Design of Sandwich Panels Subject to Local Buckling and Flexural Wrinkling Effects." Queensland University of Technology, 2003. http://eprints.qut.edu.au/15890/.
Повний текст джерелаАнотація:
Sandwich panels comprise a thick, light-weight plastic foam such as polyurethane, polystyrene or mineral wool sandwiched between two relatively thin steel faces. One or both steel faces may be flat, lightly profiled or fully profiled. Until recently sandwich panel construction in Australia has been limited to cold-storage buildings due to the lack of design methods and data. However, in recent times, its use has increased significantly due to their widespread structural applications in building systems. Structural sandwich panels generally used in Australia comprise of polystyrene foam core and thinner (0.42 mm) and high strength (minimum yield stress of 550 MPa and reduced ductility) steel faces bonded together using separate adhesives. Sandwich panels exhibit various types of buckling behaviour depending on the types of faces used. Three types of buckling modes can be observed which are local buckling of plate elements of fully profiled faces, flexural wrinkling of flat and lightly profiled faces and mixed mode buckling of lightly profiled faces due to the interaction of local buckling and flexural wrinkling. To study the structural performance and develop appropriate design rules for sandwich panels, all these buckling failure modes have to be investigated thoroughly. A well established analytical solution exists for the design of flat faced sandwich panels, however, the design solutions for local buckling of fully profiled sandwich panels and mixed mode buckling of lightly profiled sandwich panels are not adequate. Therefore an extensive research program was undertaken to investigate the local buckling behaviour of fully profiled sandwich panels and the mixed mode buckling behaviour of lightly profiled sandwich panels. The first phase of this research was based on a series of laboratory experiments and numerical analyses of 50 foam-supported steel plate elements to study the local buckling behaviour of fully profiled sandwich panels made of thin steel faces and polystyrene foam core covering a wide range of b/t ratios. The current European design standard recommends the use of a modified effective width approach to include the local buckling effects in design. However, the experimental and numerical results revealed that this design method can predict reasonable strength for sandwich panels with low b/t ratios (< 100), but it predicts unconservative strengths for panels with slender plates (high b/t ratios). The use of sandwich panels with high b/t ratios is very common in practical design due to the increasing use of thinner and high strength steel plates. Therefore an improved design rule was developed based on the numerical results that can be used for fully profiled sandwich panels with any practical b/t ratio up to 600. The new improved design rule was validated using six full-scale experiments of profiled sandwich panels and hence can be used to develop safe and economical design solutions. The second phase of this research was based on a series of laboratory experiments and numerical analyses on lightly profiled sandwich panels to study the mixed mode buckling behaviour due to the interaction of local buckling and flexural wrinkling. The current wrinkling formula, which is a simple modification of the methods utilized for flat panels, does not consider the possible interaction between these two buckling modes. As the rib depth and width of flat plates between the ribs increase, flat plate buckling can occur leading to the failure of the entire panel due to the interaction between local buckling and wrinkling modes. Experimental and numerical results from this research confirmed that the current wrinkling formula for lightly profiled sandwich panels based on the elastic half-space method is inadequate in its present form. Hence an improved equation was developed based on validated finite element analysis results to take into account the interaction of the two buckling modes. This new interactive buckling formula can be used to determine the true value of interactive buckling stress for safe and economical design of lightly profiled sandwich panels. This thesis presents the details of experimental investigations and finite element analyses conducted to study the local buckling behaviour of fully profiled sandwich panels and the mixed mode buckling behaviour of lightly profiled sandwich panels. It includes development and validation of suitable numerical and experimental models, and the results. Current design rules are reviewed and new improved design rules are developed based on the results from this research.
31
Perea, Tiziano. "Analytical and experimental study on slender concrete-filled steel tube columns and beam-columns." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37303.
Повний текст джерелаАнотація:
The use of composite steel-concrete columns and beam-columns in many structural systems is increasing globally due to the intrinsic synergy when these materials are designed and detailed together properly. However, limited test data are available to justify the structural system response factors and comprehensive design equations in current design specifications. This research, through the testing of 18 full-scale, slender concrete-filled steel tube (CFT) beam-columns, attempts to address the latter need. The circular and rectangular CFT specimens tested for this research are by far the longest and the most slender full-scale CFT members tested worldwide. These CFT specimens were subjected to a complex load protocol that includes pure compression, uniaxial and biaxial bending combined with compression, pure torsion, and torsion combined with compression. In addition, data from the hydrostatic pressure on the steel tubes due to the fresh concrete at casting was evaluated. The single most important contribution of this research is the clarification of the interaction between strength and stability in slender composite concrete-filled columns and beam-columns. Parallel to the experimental study, advanced computational analyses were carried out to calibrate material and element models that characterize the salient features of the observed CFT response, such as steel local buckling and residual stresses, concrete confinement, stability effects, strength, and stiffness degradation, among others. Based on the observed behavior, simplified guidelines for the computation of the strength and stiffness parameters for CFT columns and beam-columns are proposed for design purposes.
32
PURGATO, RAFAEL T. "Medida do buckling e da probabilidade de fuga de nêutrons do núcleo do reator IPEN/MB-01." reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/23276.
Повний текст джерелаАнотація:
Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-01-19T10:26:11Z
No. of bitstreams: 0Made available in DSpace on 2015-01-19T10:26:11Z (GMT). No. of bitstreams: 0
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Stephens, Max Taylor. "Numerical and Experimental Analysis of Composite Sandwich Links for the LCF System." PDXScholar, 2011. https://pdxscholar.library.pdx.edu/open_access_etds/579.
Повний текст джерелаАнотація:
Shear links are used as fuse elements in lateral load resisting systems to provide ductility and dissipate seismic energy. These links have traditionally been employed in eccentrically braced frames, but have more recently been suggested for use in the innovative linked column frame system (LCF). Current design specifications for shear links require intermediate web stiffeners to provide out-of-plane web stability so ductility requirements can be achieved. This research focused on moving from discrete transverse web stiffening to continuously stiffened webs in built up shear links. Built up links were designed to yield in shear when subjected to severe cyclic loading, however the webs of the links were designed using two metal sheets joined by an elastic core. These composite "sandwich" webs allowed for an increase in web thickness (and inherent flexural rigidity) without increasing the shear strength of the links. Numerical and experimental investigations were conducted to assess the performance of composite sandwich links subjected to severe loading. Numerical results showed improved web behavior in sandwich links in which the core material was assigned an elastic modulus greater than 5000psi. Due to fabrication limitations, experimental specimens were fabricated with a core material elastic modulus of 1000psi. These specimens did not perform as well as unstiffened base case links in terms global hysteretic behavior or ductility.
34
Javaroni, Carlos Eduardo. "Perfis de aço conformados a frio submetidos à flexão: análise teórico-experimental." Universidade de São Paulo, 1999. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-11122017-112750/.
Повний текст джерелаАнотація:
Atualmente, os perfis de chapa dobrada têm encontrado intensa aplicação como elementos estruturais nas construções em aço e como consequência, estão sujeitos aos mais diversos tipos de carregamentos. Este trabalho apresenta os aspectos gerais do dimensionamento de perfis de chapa dobrada submetidos à flexão enquanto utilizados como vigas propriamente dito e, também, enquanto utilizados como terças. Analisam-se seções tipo U, tipo U enrijecido e tipo Z enrijecido. Os ensaios em perfis fletidos foram realizados sobre 3 diferentes condições de carregamento, com dois vãos distintos, em um total de sessenta e quatro perfis ensaiados. Para os perfis conectados às telhas de aço, os ensaios foram realizados em uma \"caixa de sucção\" desenvolvida especificamente para este projeto. Os perfis foram conectados às telhas pela mesa por meio de parafusos auto-brocantes, sendo realizados quinze ensaios. Os resultados dos ensaios são comparados com os resultados teóricos, resultados normatizados e resultados de alguns procedimentos aproximados.Nowadays, the cold-formed steel members have intense application as structural elements in constructions and, in consequence, they are subjected to several types of loads. This work presents the general aspects of the study of cold-formed steel members subjected to flexion used as beams and, also, as purlins. Sections of type U, type C and type Z are analysed. The tests in beams were carried out under three different conditions of loads, with two distinct spans, in total of sixty four tests. For the purlins connected to roof system, the tests were in a \"suction box\", developed especially for this project. The purlins were connected to the roof system by the flange by using self-drilling screws, being carried out fifteen tests. The results of those tests are compared with the theoretical results, design specification provisions and results of some approximated procedures.
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Pešek, Ondřej. "Stabilitní problémy prutů z vrstveného konstrukčního skla." Doctoral thesis, Vysoké učení technické v Brně. Fakulta stavební, 2018. http://www.nusl.cz/ntk/nusl-390277.
Повний текст джерелаАнотація:
Transparent and subtle structures are features of modern architecture. Structural glass is constructional material that provides to realize architect's visions and ideas. Glass as a constructional material is more often used as a material for primary load-bearing structures. Realization of safe, reliable and economic glass structure is real challenge for structural engineers because of absence of standards for designing of glass members and elements. Compressed members (columns), bended members (beams) and members loaded by compression and bending (beam-columns) were analysed in the frame of the doctoral thesis whereby the emphasis is being placed on the lack of stability – flexural buckling, lateral-torsional buckling and flexural-lateral-torsional buckling. Measuring of shape and amplitude of initial geometrical imperfections is a part of doctoral thesis. The theoretical analysis describes the behaviour of the member by means of solving the differential equations. The solution according to the second order theory developed for metal members is applied on structural laminated glass members with use of effective cross-sectional characteristics. Numerical analysis is focused on the use of commonly available software based on finite element method in order to predict the load-bearing resistance of laminated glass members. Actual behaviour of laminated and monolithic structural glass members was found within experimental program. The correctness of FEM model and analytical solutions were evaluated by comparing with test results. The goal of the doctoral thesis was determine of buckling curves for calculation of flexural buckling and lateral-torsional buckling resistances by the same calculation procedure as for metal members. Because of small number of experimentally tested specimens the Monte Carlo simulation was performed.
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Koen, Damien Joseph. "Structural Capacity of Light Gauge Steel Storage Rack Uprights." Thesis, The University of Sydney, 2008. http://hdl.handle.net/2123/3880.
Повний текст джерелаАнотація:
This report investigates the down-aisle buckling load capacity of steel storage rack uprights. The effects of discrete torsional restraints provided by the frame bracing in the cross-aisle direction is considered in this report. Since current theoretical methods used to predict the buckling capacity of rack uprights appear to be over-conservative and complex, this research may provide engineers an alternative method of design using detailed finite element analysis. In this study, the results from experimental testing of upright frames with K-bracing are compared to finite element predictions of displacements and maximum axial loads. The finite element analysis is then used to determine the buckling loads on braced and un-braced uprights of various lengths. The upright capacities can then be compared with standard design methods which generally do not accurately take into account the torsional resistance that the cross-aisle frame bracing provides to the upright. The information contained in this report would be beneficial to engineers or manufacturers who are involved in the design of rack uprights or other discretely braced complex light gauge steel members subject to axial loads.
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Koen, Damien Joseph. "Structural Capacity of Light Gauge Steel Storage Rack Uprights." University of Sydney, 2008. http://hdl.handle.net/2123/3880.
Повний текст джерелаАнотація:
Master of Engineering (Research)This report investigates the down-aisle buckling load capacity of steel storage rack uprights. The effects of discrete torsional restraints provided by the frame bracing in the cross-aisle direction is considered in this report. Since current theoretical methods used to predict the buckling capacity of rack uprights appear to be over-conservative and complex, this research may provide engineers an alternative method of design using detailed finite element analysis. In this study, the results from experimental testing of upright frames with K-bracing are compared to finite element predictions of displacements and maximum axial loads. The finite element analysis is then used to determine the buckling loads on braced and un-braced uprights of various lengths. The upright capacities can then be compared with standard design methods which generally do not accurately take into account the torsional resistance that the cross-aisle frame bracing provides to the upright. The information contained in this report would be beneficial to engineers or manufacturers who are involved in the design of rack uprights or other discretely braced complex light gauge steel members subject to axial loads.
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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.
Повний текст джерелаАнотація:
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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Blum, Hannah Beth. "Long-Span Cold-Formed Steel Double Channel Portal Frames." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/16290.
Повний текст джерелаАнотація:
A comprehensive study on long-span cold-formed steel portal frames composed of back-to-back channel sections is presented. The aim of the study is to determine appropriate design guidelines in order for engineers to safely and efficiently build larger frames. The system analyzed herein is a haunched portal frame with a knee brace connected between the column and rafter. The objectives of the research were achieved through an extensive experimental study as well as numerical investigations. A comprehensive experimental program was completed to determine the strength and behavior of the frames. A total of nine full scale portal frame systems were tested, eight of which had unbraced columns. Variations to the frame layout, including modifications to the knee connection and the addition of sleeve stiffeners, were tested for both vertical and combined wind and vertical loading conditions. Column base rotational stiffness was quantified in the full scale experiments and in separate component tests. An advanced shell finite element model was created and calibrated with measured material and sections properties and column base stiffness, and was validated with the experimental results. A parametric study was completed to determine the effects of various configurations of the knee brace connection, as well as column base stiffness, on frame ultimate load. A larger span model was created to determine the suitability of the frame design for larger spans. A design procedure was developed to determine frame design loads. An energy method approach was employed to calculate the elastic buckling capacity of the column, which considers the elastic torsional restraint provided by the knee connection. A calibrated beam element model was used to determine the internal actions of the frame. A reliability check was completed and it was determined that the developed design method is suitable to design cold-formed steel portal frames.
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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/.
Повний текст джерелаАнотація:
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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Mentes, Yavuz. "Analytical and experimental assessment of steel truss bridge gusset plate connections." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42767.
Повний текст джерелаАнотація:
The I-35W Bridge over the Mississippi River in Minneapolis, MN had a catastrophic failure in the main span of the deck truss in 2007. This collapse has brought significant attention on the gusset plate connections in steel truss bridges throughout the U.S. Steel truss bridge gusset plate design has not received much focus in the past 40 years, and there is a lack of consensus within the design profession on the procedures to evaluate, design, and rate these critical elements. In the short term, based on the best available information on the gusset plate design, the Federal Highway Administration (FHWA) has issued preliminary guidance. Although some experimental research has been conducted on the ultimate strength of gusset plates, much of this work has been directed toward the performance of tension members and their connections. There has been limited experimental work on the compression capacity and stability of gusset plates, but most of this work is relevant primarily to bracing connections common in building structures. This research focuses on comprehensive experimental and analytical studies on steel truss bridge gusset plate behavior. The studies include comparisons of advanced analytical models with the responses from large-scale experimental tests using discrete and innovative full-field measurements. The calibrated finite element analysis models are then utilized to study a variety of gusset plate configurations. Improved mechanistic idealizations that better capture the observed behavior in the experiments and analytical studies are proposed as the result of this work. The design checks recommended in this thesis present a comprehensive methodology for determining the ultimate gusset plate resistance. This research provides a large database of original results that will be useful for future similar studies. In addition, this research provides modeling procedures that permit the study of steel truss bridge connections and their adjacent framing members using truss bridge sub-assemblies. Based on the comprehensive analytical studies, simple and accurate design calculation procedures to assess the nominal ultimate strength of steel truss gusset plate connections are recommended for steel truss bridge gusset plate connections.
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ALMEIDA, Ariovaldo Fernandes de. "Análise experimental de vigas constituídas de perfis formados a frio com emendas soldadas submetidas à flexão simples." Universidade Federal de Goiás, 2009. http://repositorio.bc.ufg.br/tede/handle/tde/649.
Повний текст джерелаАнотація:
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Previous issue date: 2009-09-23The cold-formed steel sheets have been sufficiently used when it is thought of manufacturing a metallic structure with reduced weight. Its use until some time ago in construction was limited to the secondary structures, but, with considerable growth in research involving this type of material together with development of technical standards, made its use a good solution for certain types of light structures. The present work presents considerations on cold-formed steel sheets, the patened steel, processes of welding and the result of experimental tests with beams with composed section of two profiles U constituted with cold-formed steel sheets, manufactured with two types of patened steel produced in Brazil. In some of these beams, welded sections with coated electrode had been used and were made the comparison with the reference beam, where it was possible to study the influence of the process of welding in the ultimate resistance and the ductility of the beam.
Os perfis metálicos formados a frio tem sido bastante usados quando se pensa em fabricar uma estrutura metálica com peso próprio reduzido. O seu uso até a algum tempo atrás na construção civil estava limitado apenas a estruturas secundárias, mas, com o crescimento considerável de pesquisas envolvendo este tipo de material associadas ao desenvolvimento de normas técnicas, fez com que o seu uso apresentasse uma boa solução para determinados tipos de estruturas leves. O presente trabalho apresenta considerações sobre perfis formados a frio, aços patináveis, processos de soldagem e o resultado de ensaios experimentais de vigas bi-apoiadas constituídas de perfis formados a frio compostas pela junção de dois perfis U enrijecidos, fabricadas com dois tipos de aço patináveis produzidos no Brasil, comparando-se os resultados. Em algumas destas vigas foram feitas emendas soldadas com eletrodo revestido e foi feita a comparação com vigas de referência, sem emenda soldada, possibilitando o estudo da influência do processo de soldagem na resistência à flexão e na ductilidade das vigas.
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Balázs, Ivan. "Klopení tenkostěnných ocelových nosníků s vazbami vybočení z roviny ohybu." Doctoral thesis, Vysoké učení technické v Brně. Fakulta stavební, 2017. http://www.nusl.cz/ntk/nusl-371784.
Повний текст джерелаАнотація:
The doctoral thesis focuses on problem of stability of steel thin-walled beams with lateral and torsional restraints along the spans. Theoretical background of lateral-torsional buckling of an ideal beam with and without restraints preventing out-of-plane buckling is briefly described. In the following chapters the problem of stabilization of steel thin-walled beams by planar members is dealt with. The state of the art in this field is summarized and some open questions are identified. The research in this field could bring new findings about actual behavior of these structural systems. The rate of stabilization can be quantified using values of shear and rotational stiffness provided to a thin-walled member by a planar member. In the frame of the thesis the problem of torsional restraint given to steel cold-formed members by sandwich panels under load is discussed. In case of the uplift load applied on the sandwich panels the torsional restraint should be verified by experimental analysis. To contribute to this field, experimental verification of rotational stiffness provided to steel cold-formed beams by sandwich panels was proposed and performed. Torsional restraint under no external load as well as under uplift load applied on the panels was investigated. The purpose was to obtain the values of the rotational stiffness provided by planar members. The performed tests indicate significant and practically applicable rate of the torsional restraint even in case of the uplift load on the surfaces of the panels. Utilization of the values of the rotational stiffness might result in more economical, effective and reliable structural design. Selected problems were investigated using numerical modeling in a finite element method based software.
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Vild, Martin. "Zesilování ocelových prutů namáhaných osovou silou pod zatížením." Doctoral thesis, Vysoké učení technické v Brně. Fakulta stavební, 2018. http://www.nusl.cz/ntk/nusl-390269.
Повний текст джерелаАнотація:
Dissertation focuses on strengthening of axially loaded steel members strengthened under load. Strengthening under load using welding is time and financially efficient. Plastic design can be used for members without stability problems. However, the design of members susceptible to buckling is difficult and opinions of researchers differ on this matter and there are only several experiments. The dissertation is focused on strengthening under load of members with selected cross-sections susceptible to flexural buckling. It is necessary to check the resistance of the base member weakened by the elevated temperatures caused by welding. The preload and welding – residual stress and deformations – must be taken into account for the determination of the buckling resistance of the member strengthened under load. The aim of this dissertation is to provide the load resistance of selected compressed members strengthened under load. Author performed experiments on members with the H and L shaped cross-sections and seamless tubes. Other experiments were performed on members with H shaped cross-section and rectangular hollow sections to determine the resistance of base member during welding. These served to validate numerical models which helped to increase the number of specimens for statistical evaluation. Analytical models to determine the load resistances of the base member during welding and the strengthened member were developed using experiments from literature and author’s experiments and numerical models. The simplified model is conservative and suitable for practical design. The complex model is suitable for scientific purpose and it provides both deformation and load resistance using modified imperfection factor. It provides a good agreement with the experiments. Doctoral thesis also includes practical recommendations for design and execution of strengthening under load using welding.
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Sauvageon, Alexis. "Instabilités locales de structures en composite acier-béton aux températures élevées." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLN003/document.
Повний текст джерелаАнотація:
Les éléments de construction en béton renforcé par plaque constituent une technologie de construction émergente dont l’utilisation commence à se développer. Ces éléments sont constitués de deux plaques en acier en parement d’un béton de remplissage. Les plaques, connectées entre elles par des tiges métalliques, travaillent de façon composite pour octroyer à la structure ses propriétés de résistance mécanique. En cas de voilement local, les transferts d’action acier-béton ne sont plus développés entraînant une perte de résistance globale de la structure. Le présent document est consacré au risque voilement local induit par une élévation de la température. Deux aspects seront particulier étudiés : définir un domaine de flambement tenant compte de la plasticité local et obtenir une estimation de la déformée à une température donnée. Les résultats seront confrontés aux solutions issues de la simulation numérique et de l'expérimentationSteel concrete structures are a new building technology and its use starts to spread in civil engineering. these structures are made of two steel plates connected by tiebars and a concrete core. In order to provide resistance, steel and concrete must develop composite actions. In case of buckling of the steel plate, the transfer of the actions between steel and concrete is lost. This paper focus on preventing buckling failure’s mode of the structure in case of thermal loading. Two main issues are studied : defining an analytic operating for steel concrete structures regarding thermal buckling aspect including yielding coupling and getting an analytic estimation of the deflection. The results are finally confronted with numerical simulation and experimentation
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Piloto, P. A. G. "Análise experimental e numérica do comportamento de estruturas metálicas sujeitas à acção do fogo." Doctoral thesis, Universidade do Porto, Faculdade de Engenharia, 2001. http://hdl.handle.net/10198/2093.
Повний текст джерелаАнотація:
Neste trabalho é apresentado um estudo sobre o efeito da acção do fogo em estruturas
metálicas, tendo sido elaborado um estudo numérico e experimental de um fenómeno de instabilidade
estrutural relativo à encurvadura lateral torsional de vigas a elevadas temperaturas. Foram efectuados
ensaios destrutivos em vários perfis com vista à determinação da carga limite resistente ou de colapso.
O efeito do fogo, como elemento activo e prejudicial à resistência do elemento estrutural, foi
determinado tendo-se verificado uma substancial diminuição das capacidades resistentes, devendo por
isso as acções serem convenientemente determinadas e analisadas.
No âmbito deste trabalho foram ainda estudadas as acções em estruturas sujeitas à acção do
fogo, a variação das propriedades mecânicas e térmicas do aço com a temperatura e o comportamento
não linear geométrico e material da estrutura.
Tendo como objectivo o desenvolvimento de ensaios experimentais em vigas de perfil
comercial, foi elaborada a candidatura de um projecto de Investigação e Desenvolvimento, intitulado
“Lateral Buckling of Steel Beams Under Fire Conditions”, financiado pelo Ministério da Ciência e da
Tecnologia, o que tornou possível a constituição de todo o equipamento que serviu de base a este
trabalho. Neste caso construiu-se um “setup” com as vertentes térmica e estrutural necessárias para
ensaiar estruturas em situação acidental de incêndio.
Paralelamente foram desenvolvidos vários ensaios numéricos do fenómeno de encurvadura
lateral a elevadas temperaturas com um programa de análise não linear geométrica e material, como são
exemplo os programas SAFIR, ANSYS e Cosmos/M, os quais permitiram validar os restantes
resultados e justificar a necessidade da revisão de algumas formulas simplificadas que o Eurocódigo 3
apresenta, nomeadamente as que dizem respeito à determinação da resistência de vigas à encurvadura
lateral, em situação de incêndio.
No final é apresentada a validação de uma proposta de cálculo simples para verificação de elementos estruturais à encurvadura, que se propõe em alternativa à proposta apresentada pelo Eurocódigo 3. In this thesis a numerical and experimental validation of the lateral torsional buckling
phenomenon of steel I beams under fire conditions is presented. A set of experimental destructive tests
were made in several I beams profiles for the buckling moment resistance determination.
The fire effect as an active element may produce a severe reduction in structural strength. The
numerical simulation of this phenomenon was done by means of a finite element code with non linear
material and geometrical behaviour, based on elevated and constant temperatures.
The structural actions under fire conditions, the material behaviour regarding its mechanical
and thermal properties variation with temperature and the non linear behaviour of structures were also
studied..
Having in mind the development of experimental tests in the commercial profiles IPE100, a
research project “ Lateral Buckling of Steel I Beams Under Fire Condition” has been financed by the
Science and Technology Portuguese Ministry, helping us to build a thermal and structural set up for this
propose.
In parallel, several numerical simulations had been done by means of the material and
geometrical non linear finite element code SAFIR, as well as, with other commercial codes, ANSYS
and CosmosM. This lead us to the justification and the needed of reviewing some simple formulas in
Eurocode regarding the lateral buckling behaviour of structures under fire conditions.
Finally a validation of a new proposal for a simple model in lateral torsional buckling under fire conditions is presented, different from that used in Eurocode, that seams to give unsafe results.
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Horáček, Martin. "Klopení tenkostěnných ocelových nosníků s otvory ve stěně." Doctoral thesis, Vysoké učení technické v Brně. Fakulta stavební, 2016. http://www.nusl.cz/ntk/nusl-355631.
Повний текст джерелаАнотація:
The current trend in the design of steel structures leads, due to the saving of the material, to the frequent use of thin-walled cold formed steel sections. Thin cold-formed steel profiles are often manufactured with web holes. A specific example of thin-walled steel profiles are Sigma beams used in additionally installed built-in floors systems in warehouses. The aim of doctoral thesis is the analysis, assessment and experimental verification of the technical solution of thin-walled steel beams with web openings loaded in bending with respect to lateral torsional buckling. The objective is to develop knowledge about the real properties of steel members of considered structural arrangement in order to specify the methods of analysis and design in industrial practice. The theoretical analysis describes the behavior of the beams by means of solving the differential equations of the equilibrium on deformed element of thin walled member under bending. In case of beams with web holes is used the solution in the form of introduction of substitute cross-section properties, which are defined as the weighted average of the properties of full and weakened section. The numerical analysis is focused on the use of commonly available software in order to predict the bending resistance of beams with web opening with respect to lateral torsional buckling. Since the software used in practice solves only the prismatic beams without option to model the web openings, it is in frame of numerical analysis verified the model of beam with reduced thickness of web constantly over the whole beam length in the zone of perforation. The experimental analysis is firstly focusing on the verification of real bending and torsion stiffness of the beams, based on which are being derived the values of basic cross-sectional properties. Subsequently the experimental verification of real bending resistance with respect to the lateral torsional buckling is being performed.
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Perret, Adrien. "Étude du comportement en post-flambement d’un panneau de fuselage composite infusé avec structures intégrées." Thesis, Toulouse, INPT, 2011. http://www.theses.fr/2011INPT0035/document.
Повний текст джерелаАнотація:
Ces travaux concernent l’étude numérique et expérimentale d’un panneau composite autoraidi fabriqué par le procédé d’infusion de résine (Liquid Resin Infusion LRI). Le procédé LRI permet d’intégrer des structures sur les peaux d’un panneau représentatif d’un fuselage composite. Dans l’étude numérique, des modèles éléments finis sont réalisés, pour étudier le comportement global du panneau en post-flambement. Cela permet de mettre au point un dispositif d’essai. L’approche expérimentale consiste en l’application de différentes méthodes pour contrôler la pièce et réaliser l’essai. Des essais de caractérisation sont aussi réalisés pour obtenir les propriétés mécaniques nécessaires à l’élaboration de modèles numériques locaux, permettant de décrire la décohésion des structures intégréesThese works are related to the numerical and experimental study of a composite stiffened panel, which is manufactured by a resin infusion process (Liquid Resin Infusion LRI). This manufacturing process allows structures to be integrated onto the skins of a panel being representative of a composite fuselage. Finite element models are built along with the numerical study, in order to deal with the post-buckling global behaviour of this panel. This leads to perfect a test set-up addressed during the experimental investigation. Several experimental methods are used to check the test panel and achieve the test. Material properties are also determined through material testing intended for the development of local numerical models, describing the integrated structures decohesion
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Baleshan, Balachandren. "Numerical and experimental studies of cold-formed steel floor systems under standard fire conditions." Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/53096/1/Balachandren_Baleshan_Thesis.pdf.
Повний текст джерелаАнотація:
Light gauge cold-formed steel frame (LSF) structures are increasingly used in industrial, commercial and residential buildings because of their non-combustibility, dimensional stability, and ease of installation. A floor-ceiling system is an example of its applications. LSF floor-ceiling systems must be designed to serve as fire compartment boundaries and provide adequate fire resistance. Fire rated floor-ceiling assemblies formed with new materials and construction methodologies have been increasingly used in buildings. However, limited research has been undertaken in the past and hence a thorough understanding of their fire resistance behaviour is not available. Recently a new composite panel in which an external insulation layer is used between two plasterboards has been developed at QUT to provide a higher fire rating to LSF floors under standard fire conditions. But its increased fire rating could not be determined using the currently available design methods. Research on LSF floor systems under fire conditions is relatively recent and the behaviour of floor joists and other components in the systems is not fully understood. The present design methods thus require the use of expensive fire protection materials to protect them from excessive heat increase during a fire. This leads to uneconomical and conservative designs. Fire rating of these floor systems is provided simply by adding more plasterboard sheets to the steel joists and such an approach is totally inefficient. Hence a detailed fire research study was undertaken into the structural and thermal performance of LSF floor systems including those protected by the new composite panel system using full scale fire tests and extensive numerical studies.
Experimental study included both the conventional and the new steel floor-ceiling systems under structural and fire loads using a gas furnace designed to deliver heat in accordance with the standard time- temperature curve in AS 1530.4 (SA, 2005). Fire tests included the behavioural and deflection characteristics of LSF floor joists until failure as well as related time-temperature measurements across the section and along the length of all the specimens. Full scale fire tests have shown that the structural and thermal performance of externally insulated LSF floor system was superior than traditional LSF floors with or without cavity insulation. Therefore this research recommends the use of the new composite panel system for cold-formed LSF floor-ceiling systems.
The numerical analyses of LSF floor joists were undertaken using the finite element program ABAQUS based on the measured time-temperature profiles obtained from fire tests under both steady state and transient state conditions. Mechanical properties at elevated temperatures were considered based on the equations proposed by Dolamune Kankanamge and Mahendran (2011). Finite element models were calibrated using the full scale test results and used to further provide a detailed understanding of the structural fire behaviour of the LSF floor-ceiling systems. The models also confirmed the superior performance of the new composite panel system. The validated model was then used in a detailed parametric study.
Fire tests and the numerical studies showed that plasterboards provided sufficient lateral restraint to LSF floor joists until their failure. Hence only the section moment capacity of LSF floor joists subjected to local buckling effects was considered in this research. To predict the section moment capacity at elevated temperatures, the effective section modulus of joists at ambient temperature is generally considered adequate. However, this research has shown that it leads to considerable over- estimation of the local buckling capacity of joist subject to non-uniform temperature distributions under fire conditions. Therefore new simplified fire design rules were proposed for LSF floor joist to determine the section moment capacity at elevated temperature based on AS/NZS 4600 (SA, 2005), NAS (AISI, 2007) and Eurocode 3 Part 1.3 (ECS, 2006). The accuracy of the proposed fire design rules was verified with finite element analysis results. A spread sheet based design tool was also developed based on these design rules to predict the failure load ratio versus time, moment capacity versus time and temperature for various LSF floor configurations.
Idealised time-temperature profiles of LSF floor joists were developed based on fire test measurements. They were used in the detailed parametric study to fully understand the structural and fire behaviour of LSF floor panels. Simple design rules were also proposed to predict both critical average joist temperatures and failure times (fire rating) of LSF floor systems with various floor configurations and structural parameters under any given load ratio.
Findings from this research have led to a comprehensive understanding of the structural and fire behaviour of LSF floor systems including those protected by the new composite panel, and simple design methods. These design rules were proposed within the guidelines of the Australian/New Zealand, American and European cold- formed steel structures standard codes of practice. These may also lead to further improvements to fire resistance through suitable modifications to the current composite panel system.
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Chodraui, Gustavo Monteiro de Barros. "Análise teórica e experimental de perfis de aço formados a frio submetidos à compressão." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-31082006-152727/.
Повний текст джерелаАнотація:
Os perfis de aço formados a frio apresentam, em geral, maior esbeltez local (relação largura-espessura dos elementos) em relação aos clássicos perfis laminados, acentuando a instabilidade local. Além disso, em se tratando de seções abertas com paredes muito delgadas, a rigidez à torção resulta muito pequena, o que torna os modos globais de torção e flexo-torção muitas vezes dominantes em relação aos modos de flexão. Outro modo de instabilidade que pode se manifestar é o modo distorcional, característico nos perfis com enrijecedores de borda. Com relação à análise do modo global, as normas para cálculo de perfis formados a frio têm adotado as mesmas curvas de resistência à compressão desenvolvidas para os perfis laminados e soldados, como a curva do SSRC (Structural Stability Research Council), adotada pela NAS (North American Specification), e as curvas européias, adotadas pela norma brasileira. Embora alguns estudos indiquem que as citadas curvas sejam aceitáveis para os perfis formados a frio, há também referências explícitas quanto à necessidade de um maior aprofundamento na investigação sobre o comportamento estrutural destes perfis, uma vez que apresentam particularidades quanto às tensões residuais, imperfeições geométricas e interação entre modos de instabilidade. Nesse trabalho é apresentada uma análise experimental em perfis usualmente empregados no Brasil (perfis U, U enrijecidos e cantoneiras simples e duplas), e uma estratégia de análise numérica não-linear, considerando os efeitos das imperfeições geométricas globais e localizadas (de chapa e distorcional), bem como das tensões residuais, de modo a se obter teoricamente um valor confiável da força normal de compressão resistente da barra. Os resultados permitiram constatar a viabilidade do emprego das atuais curvas de resistência à compressão para os perfis formados a frio. Complementando, foi analisada a aplicação do método da resistência direta (MRD) a todos os perfis estudados, confirmando bons resultados. Especial atenção foi dada ao estudo da estabilidade elástica de cantoneiras, com foco principal na coincidência entre o modo local-chapa e o modo global-torsional, o que tem gerado controvérsias na aplicação dos métodos de cálculo. Além disso, como as cantoneiras não são pré-qualificadas para aplicação do MRD, foram analisadas várias opções para emprego do método, onde pode-se concluir que desconsiderar a torção na análise do modo global conduz a resultados contra a segurançaCold-formed steel members present, in general, higher local slenderness than classical hot- rolled ones, which make them more prone to local buckling. Besides, thin-walled open sections have small torsional stiffness, and hence global torsional and flexural-torsional instability modes are many times more critical than global flexural ones. Also, distortional mode can happen in sections with lips (edge stiffener). Concerning on global buckling for members under compression, curves used in cold-formed steel design are based on hot-rolled and welded members. For example, the SSRC (Structural Stability Research Council) buckling curve, adopted by NAS (North American Specification), and Eurocode buckling curves, adopted by brazilian codes. Although some papers indicate these curves are acceptable for cold-formed steel members, others claim for a deeper analysis on their unique structural behavior, specially on residual stress, geometric imperfections and coupled buckling modes. It is presented in this thesis an experimental analysis of sections usually used in Brazil (simple and lipped channels, and also single and built-up angles). Moreover, it is developed a strategy for numerical non-linear analysis, considering the effects of global and local (also distortional) geometric imperfections and residual stress as well, in order to obtain a trustable theoretical value for the axial member stength. Results show the viability of the current buckling curves for cold-formed steel members. Finally, direct strength method (DSM) was analysed for all studied members, showing good results. Special attention to angles elastic stability, focusing on the coincidence between local-plate and global-torsional mode, which still causes confusion in design methods. Also, due to the fact angles are not pre- qualified sections for using DSM, many options on its application were studied, where it was concluded that negleting torsion in global analysis leeds to unconservative results