The objective of this study is to investigate the accuracy and computational efficiency of two commonly used formulations for performing the geometrically nonlinear thermal analysis of plane framed structures. The formulations considered are the followings: the Beam-Column formulation and the updated Lagrangian version of the finite element formulation that has been adopted in the commercially well-known software SAP2000. These two formulations are used to generate extensive numerical data for three plane frame configurations, which are then compared to evaluate the performance of the two formulations. The Beam-Column method is based on an Eulerian formulation that incorporates the effects of large joint displacements. In addition, local member force-deformation relationships are based on the Beam-Column approach that includes the axial strain, flexural bowing, and thermal strain. The other formulation, the SAP2000, is based on the updated Lagrangian finite element formulation. The results for nonlinear thermal responses were generated for three plane structures by these formulations. Then, the data were compared for accuracy of deflection responses and for computational efficiency of the Newton-Raphson iteration cycles required for the thermal analysis. The results of this study indicate that the Beam-Column method is quite efficient and powerful for the thermal analysis of plane frames since the method is based on the exact solution of the differential equations. In comparison to the SAP2000 software, the Beam-Column method requires fewer iteration cycles and fewer elements per natural member, even when the structures are subjected to significant curvature effects and to restrained support conditions. The accuracy of the SAP2000 generally depends on the number of steps and/or the number of elements per natural member (especially four or more elements per member may be needed when structure member encounters a significant curvature effect). Succinctly, the Beam-Column formulation requires considerably fewer elements per member, fewer iteration cycles, and less time for thermal analysis than the SAP2000 when the structures are subjected to significant bending effects.

The main objective of this research was to study the buckling and post-buckling response of axially restrained beam-columns under thermal loading. Also the effects of slenderness ratios on pre-buckling and post-buckling behavior which is neglected in AISC specification was examined. The results of this study indicate that: a) Both the deflection and end moment amplification factors are significantly smaller for the restrained beam-columns subjected to temperature increase than the corresponding unrestrained beam-columns subjected to (mechanical) axial loads. b) The deflection amplification factors tend to decrease with decreasing ratio of end moments. However, reverse seems to occur for the moment amplification factors and as the moment amplification factors tend to increase with decreasing moment ratio particularly in the pre-buckling and the initial post-buckling range (0.1 < T/Tcr < 1.5). c) The thermal amplification factors tend to be smaller than the AISC values even in the pre-buckling range with those for the slender beam-columns significantly smaller than those for the shorter beam-columns.

Este trabalho apresenta uma análise numérica e experimental sobre o comportamento estrutural de ligações parafusadas viga-pilar com chapa de topo estendida. Discute-se, em particular, o comportamento da chapa de topo e dos parafusos na determinação da capacidade resistente dessas ligações. A análise de resultados numéricos é utilizada como base para as discussões neste trabalho e a modelagem numérica, realizada em elementos finitos com o software ANSYS&#63720;, incluiu modelos tridimensionais de ligações com chapa de topo estendida e de ligações duplo “T”. Com os resultados numéricos e experimentais, os mecanismos de transferência dos esforços entre viga e pilar e os mecanismos de plastificação da chapa de topo e dos parafusos são observados, avaliando-se as linhas de plastificação na chapa de topo em confronto com a metodologia proposta pelo Eurocode 3 na determinação dos perfis “T” equivalentes. Para esses fatores, observou-se que os modos de falha indicados pelo Eurocode 3 não representam satisfatoriamente o comportamento das ligações analisadas. A modelagem numérica, por sua vez, mostrou-se generalista e representativa como ferramenta para análises paramétricas e como complemento de análises experimentais / This work presents a numerical and experimental analysis on the structural behavior of bolted beam-column extended end plate connections. The behavior of the end plate and bolts used in the calculations of the end plate strength is specially discussed. Numerical results are used as basis to the discussions presented in this work and the modeling methodology, with FE models built with the ANSYS code, included 3D models of extended end plate and T-stub connections. The beam-to-column load transfer mechanisms and the yielding mechanisms at end plates and bolts are observed using numerical and experimental results. The yielding lines at the end plate are evaluated against the methodology proposed by Eurocode 3 for the calculations on the equivalent T-stub. Regarding the aforementioned factors, it is shown that the collapse modes indicated by Eurocode 3 do not represent satisfactorily the behavior of the analyzed connections. The numerical modeling was found to be general in application and reliable as a tool for parametric analyses and as a complement to experiments

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22431号 / 工博第4692号 / 新制||工||1732(附属図書館) / 京都大学大学院工学研究科建築学専攻 / (主査)教授 大崎 純, 教授 西山 峰広, 准教授 聲高 裕治 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

When a structure with an in-plane discontinuous frame is used, a discontinuous load path is formed due to the irregularity. This is continuous load path can lead to the failure of certain elements and the structure as a whole when the structure is exposed to lateral loading. In this study, an in-plane discontinuous frame structure is exposed to gravity as well as lateral loading due to which a discontinuous load path is formed. Due to the discontinuous load path, higher value of axial load is developed on a beam which is generally designed considering it as a flexural member. The main objective of this thesis is to determine if the beam can be designated as the critical member in the in-plane discontinuous frame and the comparison of the critical element with the corresponding element in a frame that has no structural irregularities. The objective is also to design the critical member considering it as a beam-column element considering the combined effect of bending and compression.

This paper is concerned with the behaviour of beam ¿ column connections of steel ¿ concrete composite beams with precast hollow core slabs. Experiments were carried out to investigate the joint rotation characteristics and ultimate moment capacity of these connections. Details of the test specimens, instrumentation, test set-up and test procedures are described. Results obtained for the connection moment capacity, rotation capacity and failure modes are presented. It is found that through proper design and detailing, these simple steel connections display the characteristics of a semi-rigid connection with very little extra cost.

Improvement of Rotation Capacity of Composite Beam-to-HSS Column Connections Using External Horizontal Stiffeners Mahdi Afshar Arjmand This thesis focuses on the analysis of out-of-plane deformation (OOP) in column flange located in the panel zone of composite beam-to-column steel connection, as a critical aspect of steel structural engineering. This type of connection is an integral component of steel structures, and understanding their behavior is essential for ensuring safety and performance. The investigation involves examining the causes, factors influencing, and potential mitigation strategies for out-of-plane deformation of HSS flange column in these connections. Beam-to-column connections play a vital role in transferring loads and maintaining structural stability. Out-of-plane deformation, where the flange displaces from its primary plane, can compromise the connection's performance. This study aims to shed light on the mechanisms causing out-of-plane deformation and explore techniques to minimize its effects. Out-of-plane deformation of column flange connections can result from various factors, including eccentric loading, bending moments, torsion, and material properties. Understanding these causes is crucial for accurate analysis and design. Analytical methods and numerical simulations, such as finite element analysis (FEA), are employed to predict and quantify out-of-plane deformation. Models are created to represent real-world connections, enabling the exploration of their behavior under different loads and conditions. The study investigates strategies to mitigate out-of-plane deformation, such as adding horizontal stiffeners, or vertical stiffeners. These approaches aim to enhance the column flange’s resistance to out-of-plane displacements and improve overall structural performance. Real-world case studies of steel beam to-column connections are analyzed to demonstrate the effects of out-of-plane deformation and the efficacy of mitigation strategies. The results highlight the importance of accurate analysis and design to ensure connection integrity. Based on the findings, the study proposes design guidelines for flange-column connections to minimize out-of-plane deformation. These guidelines provide engineers with insights into optimizing connection design and ensuring stability under varying loads. The unique characteristic of beam-to-HSS column connections is the out-of-plane deformation of the HSS column flange at the beam web-to-column flange interface which can reduce contribution of the connection web to the overall resistance of the connection. To explore effect of the column flange OOP deformation, performance of three connection types, namely composite beam-to-HSS column connection, composite beam-to-HSS column connection with slab-column gap, and bare beam-to-HSS column connections are evaluated using pre-validated 3D finite element (FE) simulations. FE models can simulate low-cycle fatigue and post-rupture behavior of the connection. Comprehensive global and local responses are presented and discussed. It is found that column compactness, i.e., column’s width-to-thickness ratio, has considerable effect on maximum moment capacity, rotation capacity, post rupture residual capacity and energy dissipation capability of the connection. On the other hand, external horizontal stiffeners can significantly increase the rotation capacity of the connection. External horizontal stiffeners in steel beam-to-column connections are crucial for boosting structural efficiency and load-bearing capacity. Carefully designed, accurately placed, and securely attached, they ensure a reliable and safe system capable of withstanding diverse loads and environmental conditions, contributing to the long-term safety and stability of the entire steel structure.

No / The chapter describes the ongoing work on modeling the semi-rigid composite beam-column connections of composite beams with precast hollow core slabs. Using the finite element (FE) software ABAQUS, a three-dimensional (3D) model of a composite joint is set up. The technique of simulating bolt force, endplate, concrete elements, reinforcement, and shear connectors, and the interaction between slabs and steel beams is presented in the chapter. Preliminary results on the steel joint and simplify composite joint are also presented in the chapter. FE model for the bare steel joints and the simplified composite joints are presented, and the result of the simplified composite model showed good agreement with the experimental result but with lower joint stiffness. Further work on the full finite element model of composite joints is still going on.

Yes / A novel prestressed precast reinforced concrete (RC) beam-column joint, composed of prestressed tendons, stiffened steel sleeves, and high-strength bolts, having improved self-centring ability and assembly efficiency is proposed in this paper. Four prestressed precast RC joints assembled by steel sleeves and one cast-in-place RC joint were tested under cyclic loading to investigate the seismic response of the proposed joint. The main parameters studied are the axial compression ratio of columns, stirrup ratio in the core area of the proposed joint and effective prestress of tendons. The energy dissipation capacity, bearing capacity, and self-centring ability of the prestressed precast RC beam-column joints assembled by steel sleeves are higher than those measured for the cast-in-place RC joint. For the prestressed precast RC joints assembled by steel sleeves, both yield and ultimate displacements increase with the increase of the axial compression ratio, stirrup ratio and effective prestress, but the ductility decreases with the increase of the axial compression ratio and effective prestress. The increasing of axial compression ratio can lead to an increase in the energy dissipation capacity, shear capacity and residual displacement. Finally, formulae to predict the shear capacity of prestressed precast RC joint assembled by steel sleeves are proposed, being in good agreement with the experimental results. / The authors would like to thank the financial support provided by the Natural Science Foundation of Jiangsu Province, China (BK20201436), the Open Foundation of Jiangsu Province Engineering Research Center of Prefabricated Building and Intelligent Construction (2021), the Blue Project Youth Academic Leader of Colleges and Universities in Jiangsu Province (2020) and the Postgraduate Research & Practice Innovation Program of Jiangsu Province, China (KYCX21_3225).

This dissertation addresses the ultimate strength analysis of nonlinear beam-columns under axial compression, the sensitivity of the ultimate strength, structural optimization and reliability analysis using ultimate strength analysis, and Reliability-Based Design Optimization (RBDO) of the nonlinear beam-columns. The ultimate strength analysis is based on nonlinear beam theory with material and geometric nonlinearities. Nonlinear constitutive law is developed for elastic-perfectly-plastic beam cross-section consisting of base plate and T-bar stiffener. The analysis method is validated using commercial nonlinear finite element analysis. A new direct solving method is developed, which combines the original governing equations with their derivatives with respect to deformation matric and solves for the ultimate strength directly. Structural optimization and reliability analysis use a gradient-based algorithm and need accurate sensitivities of the ultimate strength to design variables. Semi-analytic sensitivity of the ultimate strength is calculated from a linear set of analytical sensitivity equations which use the Jacobian matrix of the direct solving method. The derivatives of the structural residual equations in the sensitivity equation set are calculated using complex step method. The semi-analytic sensitivity is more robust and efficient as compared to finite difference sensitivity. The design variables are the cross-sectional geometric parameters. Random variables include material properties, geometric parameters, initial deflection and nondeterministic load. Failure probabilities calculated by ultimate strength reliability analysis are validated by Monte Carlo Simulation. Double-loop RBDO minimizes structural weight with reliability index constraint. The sensitivity of reliability index with respect to design variables is calculated from the gradient of limit state function at the solution of reliability analysis. By using the ultimate strength direct solving method, semi-analytic sensitivity and gradient-based optimization algorithm, the RBDO method is found to be robust and efficient for nonlinear beam-columns. The ultimate strength direct solving method, semi-analytic sensitivity, structural optimization, reliability analysis, and RBDO method can be applied to more complicated engineering structures including stiffened panels and aerospace/ocean structures. / Ph. D. / This dissertation presents a Reliability-Based Design Optimization (RBDO) procedure for nonlinear beam-columns. The beam-column cross-section has asymmetric I shape and the nonlinear material model allows plastic deformation. Structural optimization minimizes the structural weight while maintaining an ultimate strength level, i.e. the maximum load it can carry. In reality, the geometric parameters and material properties of the beam-column vary from the design value. These uncertain variations will affect the strength of the structure. Structural reliability analysis accounts for the uncertainties in structural design. Reliability index is a measurement of the structure’s probability of failure by considering these uncertainties. RBDO minimizes the structural weight while maintaining the reliability level of the beam-column. A novel numerical method is presented which solves an explicit set of equations to obtain the maximum strength of the beam-column directly. By using this method, the RBDO procedure is found to be efficient and robust.