Dissertations / Theses on the topic 'Slender beam'

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.

Reinforced concrete deep beams have useful applications in construction. However, their design is not yet covered by the British Standard BS 8110: 1985 which explicitly states that "for the design of deep beams, reference should be made to specialist literature". A selection of literature on deep beams is considered. First, the major works that have led to design recommendations are reviewed. Then, the current major codes and manuals covering deep beams, namely the CIRIA Guide, the European CEB-FIP model code, the American ACI(318-83) (revised 1986) code and the Canadian CAN3-A22.3-MB4 code are outlined; worked examples are given in order to illustrate their practical applications and compare their different approaches to deep beam design. The purpose of this literature review was to define the deep beam problem and identify the major questions still remaining unanswered together with the limitations of the present design documents on the subject. The nature of diagonal cracking in slender deep beams has recently raised a question as to the application of the shear-strength equation in cl.3.4.2 of the CIRIA Deep Beam Guide. The effectiveness of web reinforcement on serviceability and strength of deep beams in general is also an area where strong disagreement exists. A testing programme, consisting of 15 beams of height/thickness ratios ranging from 20 to 50 and grouped in 3 different series, was performed to provide information on these two areas. The main variables were the height/thickness ratio and the quantity and arrangement of web steel. The beams were tested under concentrically applied two point-loads. Based on the test results and observations, modifications are given for the CIRIA equation and other formulae derived from stocky deep beam tests to be used in slender ones for analysis and design purposes. A new formula is also proposed for the prediction of the ultimate shear capacity. The stability of deep beams is another area which has received less attention in the past by researchers and designers who often avoided the problem by opting for stocky sections. To quote from the CIRIA Guide "as a possible criterion of failure, buckling can not be disregarded". However, information on such topic is very scarce in the literature. Currently, the only documents that provide design guidelines for buckling are the CIRIA Guide and the Portland Cement Association Design Aid, both of which are based on theoretical studies and engineering judgement. An experimental testing programme, consisting of 7 large scale beam-panels with height/thickness ratios in the range of 20 to 70 and a constant span/depth ratio of 1.0, provided buckling data against which the reliability of the two design documents was assessed. These tests confirmed that both documents offer a safe buckling design with the CIRIA Guide being too conservative. Although deep beams are frequently continuous over several spans, very little published data exist for such beams. For this purpose, 12 two-span continuous concrete deep beams with span/depth ratios less than 1.0 and having different quantities and arrangements of web reinforcement were tested under two point-loads. The specimens were heavily instrumented to obtain as much information as possible about the behaviour of the beams at each stage of loading. Applied loads and reactions were among the measurements made and enabled the actual bending moment distribution to be determined and compared to that of corresponding continuous shallow beams. Based on the test results and observations and in the light of other published work, recommendations are given for the bearing, shear and flexural design of continuous deep beams.

Crosslinked polymers or elastomers are examples of soft, synthetic material that can bend, crease, snap, wrinkle in response to external stimulus like pH, humidity, electric field or swelling. If a droplet of favorable solvent is placed on top of a thin, elastomer beam, it bends drastically to accommodate the excessive swelling stress. Keeping the solvent and its volume constant if we just increase the thickness of the beam, microscopic surface creases appear on the top surface. In this thesis, we experimentally characterize this transition between global bending to surface creasing. Closing of Venus flytrap leaves is a classic example of well known snap-through instability. A knowledge of the timescale of snapping is crucial in designing advanced functional materials. We perform the simplest experiment of poking an soft, elastomer arch at its apex till it snaps. Combining our experiments with analytical model we are able to predict the purely geometric nature of the snapping timescale. We also develop a simple scaling law that captures the dynamics of jumping toy poppers.
Master of Science

A simple numerical solution strategy for predicting the transient response of slender ductile beams, exhibiting geometric and/or material non-linear behaviour, is presented in this study. In the theoretical development of the problem the governing non-linear equation of motion, in variational form, for the bending and stretching of a Bernoulli-Euler beam is established. The numerical solution procedure is then initiated by employing the assumed displacement version of the Finite Element Method with 1-dimensional 6-DOF beam elements. Elastic-plastic strain-hardening of the beam material is conveniently accounted for by means of the "mechanical sublayer model". Visco-plastic material behaviour is included in the analysis through a simple strain-rate dependent constitutive relationship. The equations of motion for the spatially discretized beam are integrated time-wise by means of the central difference method. A variety of examples are then solved and the results compared with solutions from other sources. In general, the numerical solution strategy yields an efficient and accurate modelling of the non-linear transient response of slender ductile beams.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate

Doutoramento em Engenharia Civil
A presente tese resulta de um trabalho de investigação com o propósito de aumentar o conhecimento do comportamento ao fogo de elementos metálicos com secção transversal de Classe 4, ou seja, suscetíveis à ocorrência de fenómenos de encurvadura local. Os elementos metálicos com secção transversal de Classe 4 são amplamente utilizados na construção metálica por serem soluções bastante atrativas em termos de eficiência e economia de material. No entanto, a verificação da resistência ao fogo destes elementos carece de fórmulas simplificadas que se adequem à mais-valia proporcionada por este tipo de solução. O principal objetivo desta dissertação foca-se no desenvolvimento de metodologias de cálculo para verificação da resistência ao fogo de elementos metálicos com secção transversal de Classe 4 com base em estudos numéricos realizados com elementos finitos de casca recorrendo ao programa SAFIR através de análises material e geometricamente não lineares (GMNIA - geometrically and material non-linear analysis with imperfections). É demonstrado nesta tese que, as fórmulas atualmente propostas no Eurocódigo 3 para verificação da resistência ao fogo de elementos de Classe 4 em situação de incêndio podem ser melhoradas. No que diz respeito à capacidade resistente da secção transversal, a metodologia atual do Eurocódigo 3 subestima a resistência das secções quando constituídas simultaneamente por placas de Classe 4 e de outras classes. Por outro lado, mostra-se que os fenómenos de encurvadura local afetam também as secções de Classe 3 a altas temperaturas. Neste trabalho, ambas as classes foram tratadas como secções transversais esbeltas, tendo sido propostas novas fórmulas para o seu cálculo em situação de incêndio. No caso de vigas com secção transversal esbelta, observa-se que as formulações preconizadas no Eurocódigo 3 são também inadequadas. A proposta para o cálculo da resistência da secção transversal desenvolvida neste trabalho conduz a melhorias na verificação da segurança ao fogo destes elementos mas, não obstante, propõe-se novas expressões que consideram a interação entre a encurvadura local e o fenómeno de encurvadura lateral que ocorre nestas vigas. Assim desenvolveu-se um parâmetro de secção efetiva cuja utilização permite uma verificação ao fogo da encurvadura lateral mais eficiente. Por fim, estudam-se as vigas-coluna com secção transversal esbelta, concluindo-se que as fórmulas de interação do Eurocódigo 3 conduzem simultaneamente a resultados muito conservativos ou fora da segurança. Observou-se que este comportamento se deve essencialmente ao cálculo dos fatores de redução para o comportamento de coluna e viga, mas por outro lado, houve a necessidade de alterar os fatores de interação das curvas para que a verificação da resistência ao fogo destes elementos fosse mais segura.
This thesis is the result of a research work with the purpose of increasing the knowledge on the fire behaviour of steel members with Class 4 cross-section, that is, prone to the occurrence of local buckling phenomena. Steel members with Class 4 cross-section due to their advantages regarding their lightness and efficiency are widely used in steel constructions. However, the verification of the fire resistance of these elements lacks simplified formulas that are in agreement with the added value provided by this type of solutions. The main objective of this thesis aims to develop improved structural fire design rules for the stability check of steel members with Class 4 cross-section based on numerical investigation with shell finite elements carried out with the software SAFIR by performing geometrically and material non-linear analysis with imperfections (GMNIA). It is demonstrated in this work that, the existing design rules preconized proposed in Eurocode 3 for the design of steel members with Class 4 crosssection in case of fire could be improved. In what concerns the cross-sectional capacity, the present methodology of Eurocode 3 underestimates the resistance of the sections when they are built up simultaneous of Class 4 plates and plates of other classes. Moreover, it is demonstrated that local buckling affects also Class 3 cross-sections in case of fire. Thus, in this work, both classes are treated as slender cross-sections and proposals are made for new rules to calculate their capacity in fire situation. For beams with slender cross-sections, it is concluded that the formulae available in Eurocode 3 are also inadequate. The new proposal for the crosssectional resistance calculation leads to improvements in terms of the fire design of these members but, nonetheless, new expressions are proposed that account for the interaction between local buckling and lateral-torsional buckling that occurs in these beams. Accordingly, the effective section factor was developed allowing a better design against lateral-torsional buckling of on beams with slender cross-sections in case of fire. Finally, beam-columns with slender cross-sections are studied, and it is concluded that the present interaction formulae provided by Eurocode 3 leads simultaneous to very conservative or unsafe results. It was observed that this was mainly due to the calculation of the reduction factors for the beam and column behaviour, but besides that, there was the need to change the interaction factors so that the design rules to assess the mechanical resistance of beam-columns in case of fire be safer.

No
In this work, experimental and numerical investigations were performed on the behaviours of circular concrete filled double steel tubular (CFDST) slender columns and beams, in which the external tube employed stainless steel tube. Eighteen specimens, 12 slender columns and 6 beams, were tested to obtain the failure patterns, load versus deflection relationships and strain developments of stainless steel tube. A finite element (FE) model was developed and verified by experimental results. The validated FE model was then employed to investigate the effects of key parameters, including hollow ratio, eccentric ratio and material strength, on the load-carrying capacity. The load distribution among the components and contact stress between steel tube and sandwiched concrete were also analyzed. Finally, the design methods for CFDST, hollow CFST and solid CFST members with carbon steel external tube respectively suggested by Han et al. (2018), Chinese GB 50936-2014 (2014) and AISC 360-16 (2016) were employed to evaluate their applicability for the circular CFDST slender columns and beams with stainless steel outer tube.
The authors gratefully acknowledge the Shanxi Province Outstanding Youth Fund (No. 201701D211006) and the National Natural Science Foundation (No. 51838008).
The full-text of this article will be released for public view at the end of the publisher embargo on 9th Nov 2021.

Mestrado em Engenharia Civil
A presente dissertação tem como propósito aumentar o conhecimento do comportamento ao fogo de vigas-coluna metálicas de secção transversal esbelta, isto é, suscetíveis à ocorrência de fenómenos de instabilidade, tais como a encurvadura local, lateral e por flexão. Sabe-se que os elementos metálicos com secção transversal esbelta possuem vantagens em termos de eficiência e economia de material. Esta atratividade faz com que sejam amplamente utilizados na construção. Contudo, a verificação da resistência ao fogo destes elementos carece de fórmulas simplificadas que se adequem a esta solução. O principal objetivo desta dissertação direciona-se na elaboração de um estudo numérico do comportamento ao fogo de vigas-coluna em aço com secção transversal esbelta. Seguidamente, efetuar-se-á uma comparação entre os resultados obtidos numericamente através do método de elementos finitos e as metodologias presentes no Eurocódigo 3, no que se refere especificamente às fórmulas a frio, contidas nas Parte 1-1 e às fórmulas para situação de incêndio na Parte 1-2. No que diz respeito ao estudo numérico, este foi efetuado com elementos finitos de casca recorrendo ao programa SAFIR. É demonstrado que a metodologia presente no Eurocódigo 3 para a verificação da resistência em situação de incêndio pode ser melhorada. Sendo assim, são propostas alterações a nível do cálculo dos fatores de interação. Finalmente, concluiu-se que as fórmulas de interação do Eurocódigo 3 conduzem a resultados fora da segurança ou muito conservativos e que necessitam de ser melhoradas para que seja possível calcular estruturas mais seguras e económicas.
The present thesis aims to increase the knowledge of the fire behaviour of steel beam-columns with slender cross-section, that is, susceptible to the occurrence of instability phenomena, such as local, lateral-torsional and bending buckling. It is known that steel members with slender cross-section have advantages in terms of efficiency and economic material. This attraction makes them widely used in construction. However, the verification of the fire resistance of these members need simplified formulas that are appropriate to this solution. The main objective of this thesis consist in the elaboration of a numerical study of the fire behaviour of steel beam-columns with slender cross-section. Posteriorly, shall be make a comparison between the results obtained numerically with the finite element method and the methodologies in Eurocode 3, which specifically refers to cold formulas, contained in Part 1-1, and fire situation formulas, contained in Part 1-2. Regarding the numerical study, this was made with finite shell elements using the program SAFIR. It is shown that the present methodology in Eurocode 3 for the verification of the resistance in fire situation can be improved. Therefore, some changes are proposed in the calculation of the interaction factors. Finally, it was concluded that the interaction formulas of Eurocode 3 lead to results that may be outside the safety or be very conservative and need to be improved so that becomes possible to calculate safer and more economical structures.

OneSteel Australian Tube Mills has recently developed a new hollow flange channel cold-formed section, known as the LiteSteel Beam (LSB). The innovative LSB sections have the beneficial characteristics of torsionally rigid closed rectangular flanges combined with economical fabrication processes from a single strip of high strength steel. They combine the stability of hot-rolled steel sections with the high strength to weight ratio of conventional cold-formed steel sections. The LSB sections are commonly used as flexural members in residential, industrial and commercial buildings. In order to ensure safe and efficient designs of LSBs, many research studies have been undertaken on the flexural behaviour of LSBs. However, no research has been undertaken on the shear behaviour of LSBs. Therefore this thesis investigated the ultimate shear strength behaviour of LSBs with and without web openings including their elastic buckling and post-buckling characteristics using both experimental and finite element analyses, and developed accurate shear design rules. Currently the elastic shear buckling coefficients of web panels are determined by assuming conservatively that the web panels are simply supported at the junction between the web and flange elements. Therefore finite element analyses were conducted first to investigate the elastic shear buckling behaviour of LSBs to determine the true support condition at the junction between their web and flange elements. An equation for the higher elastic shear buckling coefficient of LSBs was developed and included in the shear capacity equations in the cold-formed steel structures code, AS/NZS 4600. Predicted shear capacities from the modified equations and the available experimental results demonstrated the improvements to the shear capacities of LSBs due to the presence of higher level of fixity at the LSB flange to web juncture. A detailed study into the shear flow distribution of LSB was also undertaken prior to the elastic buckling analysis study. The experimental study of ten LSB sections included 42 shear tests of LSBs with aspect ratios of 1.0 and 1.5 that were loaded at midspan until failure. Both single and back to back LSB arrangements were used. Test specimens were chosen such that all three types of shear failure (shear yielding, inelastic and elastic shear buckling) occurred in the tests. Experimental results showed that the current cold-formed steel design rules are very conservative for the shear design of LSBs. Significant improvements to web shear buckling occurred due to the presence of rectangular hollow flanges while considerable post-buckling strength was also observed. Experimental results were presented and compared with corresponding predictions from the current design rules. Appropriate improvements have been proposed for the shear strength of LSBs based on AISI (2007) design equations and test results. Suitable design rules were also developed under the direct strength method (DSM) format. This thesis also includes the shear test results of cold-formed lipped channel beams from LaBoube and Yu (1978a), and the new design rules developed based on them using the same approach used with LSBs. Finite element models of LSBs in shear were also developed to investigate the ultimate shear strength behaviour of LSBs including their elastic and post-buckling characteristics. They were validated by comparing their results with experimental test results. Details of the finite element models of LSBs, the nonlinear analysis results and their comparisons with experimental results are presented in this thesis. Finite element analysis results showed that the current cold-formed steel design rules are very conservative for the shear design of LSBs. They also confirmed other experimental findings relating to elastic and post-buckling shear strength of LSBs. A detailed parametric study based on validated experimental finite element model was undertaken to develop an extensive shear strength data base and was then used to confirm the accuracy of the new shear strength equations proposed in this thesis. Experimental and numerical studies were also undertaken to investigate the shear behaviour of LSBs with web openings. Twenty six shear tests were first undertaken using a three point loading arrangement. It was found that AS/NZS 4600 and Shan et al.'s (1997) design equations are conservative for the shear design of LSBs with web openings while McMahon et al.'s (2008) design equation are unconservative. Experimental finite element models of LSBs with web openings were then developed and validated by comparing their results with experimental test results. The developed nonlinear finite element model was found to predict the shear capacity of LSBs with web opening with very good accuracy. Improved design equations have been proposed for the shear capacity of LSBs with web openings based on both experimental and FEA parametric study results. This thesis presents the details of experimental and numerical studies of the shear behaviour and strength of LSBs with and without web openings and the results including the developed accurate design rules.

Dans la nature les plantes sont sans cesse soumises à des sollicitations mécaniques qui affectent et modifient leur croissance. Un aspect remarquable de cette réponse est qu’elle n’est pas seulement locale mais non-locale : la flexion d’une tige ou d’une branche inhibe rapidement la croissance loin de la zone sollicitée. Cette observation suggère l'existence d'un signal pouvant se propager à travers toute la plante. Parmi les différentes hypothèses, il a été suggéré que ce signal pouvait être purement mécanique, et provenir d’un couplage hydro/mécanique entre la déformation du tissu et la pression de l’eau contenue dans le système vasculaire de la plante. L’objectif de cette thèse est de comprendre l’origine physique de ce couplage par une approche biomimétique. Pour cela, nous avons développé des branches artificielles micro-fluidiques possédant des caractéristiques mécaniques et hydrauliques similaires à celles d'une branche d'arbre. Nous avons montré que la flexion de ces branches génère une surpression globale non-nulle dans le système, qui varie comme le carré de la déformation longitudinale. Un modèle simple basé sur un mécanisme analogue à l’ovalisation des tubes permet de prédire cette réponse poroélastique non-linéaire et d’identifier le paramètre physique clé pilotant cette réponse en pression : le module de compressibilité de la branche. A la lumière de ces résultats, des expériences sur des branches d'arbre ont ensuite été conduites et des signaux similaires sont obtenus et comparés au modèle théorique. La similitude suggère le caractère générique du mécanisme physique identifié pour la génération de signaux hydraulique dans les plantes
Plants are constantly subjected to external mechanical loads such as wind or touch and respond to these stimuli by modifying their growth and development. A fascinating feature of this mechanical-induced-growth response is that it is not only local, but also non-local: bending locally a stem or a branch can induce a very rapid modification of the growth far away from the stimulated area, suggesting the existence of a signal that propagates across the whole plant. The nature and origin of this signal is still not understood, but it has been suggested recently that it could be purely mechanical and originate from the coupling between the local deformation of the tissues and the water pressure in the vascular system. The objective of this work is to understand the origin of this hydro/mechanical coupling using a biomimetic approach. Artificial microfluidic branches have been developed, that incorporate the mechanical and hydraulic key features of natural ones. We show that the bending of these branches generates a steady overpressure in the whole system, which varies quadratically with the bending deformation. A simple model based on a mechanism analogue to tube ovalization enables us to predict this non-linear poroelastic response, and identify the key physical parameter at play, namely the elastic bulk modulus of the branch. Further experiments conducted on natural tree branches reveal the same phenomenology. Once rescaled by the model prediction, both the biomimetic and natural branches falls on the same master curve, showing the universality of the identified mechanism for the generation of hydraulic signals in plants

This project explores a novel technique for the vibration control of slender beam-like flexible structures. For this purpose, a new method is developed based on minor structural modifications. Three applications are chosen to demonstrate the new method. The first is the sensing wire oscillations of a hot-wire probe. The second application is the problem of tool chatter due to milling tool vibration, while the third application is the bending of an arrow as it is released from a bow. Although these applications sound quite different, they are in fact similar problems dynamically. They are related to the forced transverse structural vibrations of slender beams. For all applications, the external force input is of a broadband nature in frequency, similar to a white noise excitation. This force excites the slender beams into large amplitude resonance which in the case of a hot-wire probe, causes measurement inaccuracies, for milling, causes rough surface finish and slower machining times, whereas for archery causes reduced accuracy. The choice of the particular problems to demonstrate the effectiveness of the technique is due to the current research interests and available expertise in this area in the School of the Built Environment at Victoria University. However, the methods developed through the course of this research are general methods applicable to all other slender beam-like structures with step changes in cross sectional geometry, such as flexible robotic arms or power transmission cables.

This project explores a novel technique for the vibration control of slender beam-like flexible structures. For this purpose, a new method is developed based on minor structural modifications. Three applications are chosen to demonstrate the new method. The first is the sensing wire oscillations of a hot-wire probe. The second application is the problem of tool chatter due to milling tool vibration, while the third application is the bending of an arrow as it is released from a bow. Although these applications sound quite different, they are in fact similar problems dynamically. They are related to the forced transverse structural vibrations of slender beams. For all applications, the external force input is of a broadband nature in frequency, similar to a white noise excitation. This force excites the slender beams into large amplitude resonance which in the case of a hot-wire probe, causes measurement inaccuracies, for milling, causes rough surface finish and slower machining times, whereas for archery causes reduced accuracy. The choice of the particular problems to demonstrate the effectiveness of the technique is due to the current research interests and available expertise in this area in the School of the Built Environment at Victoria University. However, the methods developed through the course of this research are general methods applicable to all other slender beam-like structures with step changes in cross sectional geometry, such as flexible robotic arms or power transmission cables.

High strength thin-walled concrete-filled steel tubular (CFST) slender beam-columns may undergo local and global buckling when subjected to biaxial loads, preloads or cyclic loading. The local buckling effects of steel tube walls under stress gradients have not been considered in existing numerical models for CFST slender beam-columns. This thesis presents a systematic development of new numerical models for the nonlinear inelastic analysis of thin-walled rectangular and circular CFST slender beam-columns incorporating the effects of local buckling, concrete confinement, geometric imperfections, preloads, high strength materials, second order and cyclic behavior. In the proposed numerical models, the inelastic behavior of column cross-sections is simulated using the accurate fiber element method. Accurate constitutive laws for confined concrete are implemented in the models. The effects of progressive local buckling are taken into account in the models by using effective width formulas. Axial load-moment-curvature relationships computed from the fiber analysis of sections are used in the column stability analysis to determine equilibrium states. Deflections caused by preloads on the steel tubes arising from the construction of upper floors are included in the analysis of CFST slender columns. Efficient computational algorithms based on the Müller’s method are developed to obtain nonlinear solutions. Analysis procedures are proposed for predicting load-deflection and axial load-moment interaction curves for CFST slender columns under axial load and uniaxial bending, biaxial loads, preloads or axial load and cyclic lateral loading. The numerical models developed are verified by comparisons of computer solutions with existing experimental results and then utilized to undertake extensive parametric studies on the fundamental behavior of CFST slender columns covering a wide range of parameters. The numerical models are shown to be efficient computer simulation tools for designing safe and economical thin-walled CFST slender beam-columns with any steel and concrete strength grades. The thesis presents benchmark numerical results on the behavior of high strength thin-walled CFST slender beam-columns accounting for progressive local buckling effects. These results provide a better understanding of the fundamental behavior of CFST columns and are valuable to structural designers and composite code writers.

The seismic response of diagonally reinforced slender coupling beams is investigated. Primarily, a typical coupling beam found in high-rise buildings in the Vancouver area is studied. Compared to past experiments, this study takes into account a new variable, the axial restraint given by the concrete slab surrounding the coupling beam. Desirable and ductile properties of the beam are studied throughout this work, such as ductility capacity, stiffness degradation, overstrength and energy dissipation capability. A finite element analysis was performed to study the axial restraint parameter mentioned above and assess the degree of restraint given by the slab to the coupling beam. Parameters such as the slab dimensions, slab pre-cracking, slab thickness, mesh size of the model and tension stiffening model are considered. This analysis indicated that the tension stiffening model used for the concrete is the most important parameter. A full-scale coupling beam specimen was tested to develop an analytical model and compare the results with well-known formulas recommended by various Codes. The specimen represented a typical coupling beam found in high-rise buildings in the Vancouver area. The specimen was subjected to cyclic loading and Dywidag bars were provided to model the slab axial restraint. The results showed higher overstrength and stiffness degradation factors than the ones expected from well-known formulas. As expected for diagonally reinforced coupling beams, the specimen showed good ductility and energy dissipation properties. An analytical model based on a truss structure was developed to better understand the behaviour of diagonally reinforced coupling beams. The model gave insight to main factors of the problem, such as diagonal reinforcement, geometry, concrete considered and slab restraint. The monotonic prediction of the model was reasonably similar to the envelope given by the experimental results. Expressions were developed from this model to predict the cracked stiffness and overstrength factor.

This research study examined the effect of corrosion of web reinforcement (stirrups) on the shear behaviour of slender reinforced concrete (RC) beams. The experimental program consisted of seventeen slender shear-critical RC beams: five uncorroded and twelve corroded beams. The test variables included: 1) corrosion level (0%, 7.5% and 15%); 2) type of stirrups (smooth and deformed); 3) stirrup diameter (D6, D12 and 10M); 4) stirrups spacing (100mm and 200mm); and 5) the presence of CFRP repair. The corroded beams had their stirrups subjected to corrosion using an accelerated corrosion technique and the mass loss in the stirrups was estimated based on Faraday’s law. All of the beams were monotonically tested to failure in three point bending. The corrosion cracks formed were parallel to the locations of stirrups as evidence of the corrosion damage in the corroded beams. The maximum decrease in the ultimate shear strength ranged from 11% to 14.4% for beams with high corrosion level of 15.6% mass loss. At a low corrosion level (4.39% mass loss), the shear strength of beams with smooth stirrups increased up to 35% due to the enhancement of shear friction at the concrete-corroded stirrups interface. The stiffness of the corroded beams was enhanced in comparison to the control beams. The ultimate deflection of the corroded beams was decreased up to 25% in comparison to the control beams. The CFRP repair increased the shear strength by 36% and improved the overall stiffness by 39% in comparison to the corroded unrepaired beams. All of the unrepaired beams failed in diagonal tension splitting, while the CFRP repaired corroded beams failed in diagonal tension splitting in addition to debonding of the FRP or concrete cover delamination. The actual corrosion mass loss results were in good correlation with Faraday’s law for the D12 and 10M stirrups. Poor correlation between actual and estimated mass loss was obtained for D6 smooth stirrups, possibly due to errors in the impressed corrosion. iv The analytical model used the modified compression field theory (MCFT) to predict the shear strength of uncorroded and corroded slender RC beams. In the corroded beams, two reduction factors were added to the MCFT model including the mass loss factor and the effective web width. Predictions based on the model revealed that the control beams gave a very good correlation with the ratio of experimental to predicted values that ranged from 0.94 to 1.02. On other hand, the ratio of experimental to predicted strength in the corroded beams ranged between1.06 to 1.4. The poor correlations were obtained for the beams with the D6 smooth stirrups. This study demonstrates that corrosion of web reinforcement can have a detrimental effect on the shear strength and ductility of slender shear-critical RC beams. The experimental results and analytical approach will be very useful for practicing engineers and researchers dealing with corrosion damage in slender RC members.

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Optimum multi-layered feed-forward neural network (NN) models using a resilient back-propagation algorithm and early stopping technique are built to predict the shear capacity of reinforced concrete deep and slender beams. The input layer neurons represent geometrical and material properties of reinforced concrete beams and the output layer produces the beam shear capacity. Training, validation and testing of the developed neural network have been achieved using 50%, 25%, and 25%, respectively, of a comprehensive database compiled from 631 deep and 549 slender beam specimens. The predictions obtained from the developed neural network models are in much better agreement with test results than those determined from shear provisions of different codes, such as KBCS, ACI 318-05, and EC2. The mean and standard deviation of the ratio between predicted using the neural network models and measured shear capacities are 1.02 and 0.18, respectively, for deep beams, and 1.04 and 0.17, respectively, for slender beams. In addition, the influence of different parameters on the shear capacity of reinforced concrete beams predicted by the developed neural network shows consistent agreement with those experimentally observed.

This thesis investigates the application of ultra-high modulus carbon fiber reinforced polymer (CFRP) plates to strengthen damaged reinforced concrete beams and slender columns. In the first phase, two different pre-repair loading histories were simulated in seven 3000x300x150 mm reinforced concrete beams, namely cracking within the elastic range, and overloading in the plastic range. After unloading, the beams were repaired with either high- or ultra-high modulus (210 or 400 GPa) CFRP plates, or a hybrid system, and then reloaded to failure. It was shown that the level of pre-existing damage has an insignificant effect on the strengthening effectiveness and the failure mode at ultimate. The 210 and 400 GPa CFRP of reinforcement ratio ρf = 0.17% increased the ultimate strength by up to 29 and 51%, respectively, despite the 40% lower tensile strength of the 400 GPa CFRP, due to the change in failure mode from debonding to rupture. Doubling ρf of the 400 GPa CFRP to 0.34% resulted in a 63% overall gain in flexural strength, only 8% increase in ultimate strength over ρf = 0.17%, due to change in failure mode from rupture to concrete cover delamination. The beam retrofitted by hybrid CFRP showed remarkable pseudo ductility and warning signs before failure. However, a parametric study revealed a critical balance in proportioning the areas of hybrid CFRP to achieve reliable pseudo ductility. In the beam with ρf =0.34%, this was achieved using a maximum of 30% ρf of the 400 GPa CFRP. The second phase of this thesis presents an analytical model developed by modifying the provisions of the ACI 318-08 code and employing the computer software Response 2000, to predict the performance of CFRP strengthened slender reinforced concrete columns. Response 2000 is used to establish the interaction curve while the modified ACI 318-08 code is used to acquire the slender column loading path to failure including the second order effects. The model predicts that the effectiveness of the FRP strengthening system increases as the slenderness ratio and FRP reinforcement ratio increase.
Thesis (Master, Civil Engineering) -- Queen's University, 2013-09-24 12:36:48.352

Conventional three dimensional structural analysis methods prove to be expensive for the preliminary design of wind turbine blades. However, wind turbine blades are large slender members with complex cross sections. They can be accurately modeled using beam models. The accuracy in the predictions of the structural behavior using beam models depends on the accuracy in the prediction of their effective section properties. Several techniques were proposed in the literature for predicting the effective section properties. Most of these existing techniques have limitations because of the assumptions made in their approaches. Two generalized beam theories, Generalized Timoshenko and Generalized Euler-Bernoulli, for the static analysis based on the principles of the simple 1D-theories are developed here. Homogenization based on the strain energy equivalence principle is employed to predict the effective properties for these generalized beam theories. Two efficient methods, Quasi-3D and Unit Cell, are developed which can accurately predict the 3D deformations in beams under the six fundamental deformation modes: extension, two shears, torsion and two flexures. These methods help in predicting the effective properties using the homogenization technique. Also they can recover the detailed 3D deformations from the predictions of 1D beam analysis. The developed tools can analyze two types of slender members 1) slender members with invariant geometric features along the length and 2) slender members with periodically varying geometric features along the length. Several configurations were analyzed for the effective section properties and the predictions were validated using the expensive 3D analysis, strength of materials and Variational Asymptotic Beam Section Analysis (VABS). The predictions from the new tools showed excellent agreement with full 3D analysis. The predictions from the strength of materials showed disagreement in shear and torsional properties. Explanations for the same are provided recalling the assumptions made in the strength of materials approach.