In the analyses of steel framed structures it is customary to assume the beam to column connections as either fully rigid which means that all moments are transferred from beam to column with negligible rotation or ideally pinned that resists negligible moment. This assumption is reasonable for some types of connections. However when considering steel connections such as bolted-bolted double web angle connections it can be seen that the behavior of these connections is in between the two extreme cases. Thus a third connection type, namely semi rigid or partially restrained connection, is introduced. However this type of connection exhibits such a nonlinear behavior that modeling this behavior necessities a substantial effort. Moreover to perform a performance based analyses the true behavior of these connections should be incorporated as part of the modeling effort. Several researches dealing with these two topics have been undertaken in literature. Despite these efforts, modeling of the moment rotation behavior of these connections still requires improvement especially under cyclic loading conditions. In addition to this, performing an analysis with existing elements incorporating semi-rigid connections as a spring attached to beam ends is not practical because of the fact that displacement based formulation increases meshing significantly which requires substantial computational power. In this study a hysteretic (quadra-linear) moment rotation model considering pinching, damage and possibility of residual moment capacity is developed. The behavior is calibrated via experimental data available in the literature. Furthermore a force based macro element considering spread inelastic behavior along the element is presented. With this element several connections located anywhere along the beam could be incorporated in the analysis with less degree of freedom with respect to displacement based elements. Moreover the macro element model can be used in conjunction with corotational formulation for the capture of nonlinear geometric effects.

In the last 35 years, several researchers have proposed, developed and tested different friction devices for seismic control of structures. Their research has demonstrated that such devices are simple, economical, practical, durable and very effective. However, research on passive friction dampers, except for few instances, has not been given appropriate attention lately. This has caused some of the results of old studies to become out-of-date, lose their validity in the context of today's design philosophies or to fall short on the expectations of this century's structural engineering. An analytical study on the behavior of friction devices and the effect they have on the structures into which they are incorporated has been undertaken to address the new design trends, codes, evaluation criteria and needs of today's society. The present study consists of around 7,000 structural analyses that are used to show the excellent seismic performance and economic advantages of Friction Damped Braced Frames. It serves, at the same time, to improve our understanding on their dynamic behavior. Finally, this thesis also sets the basis for future research on the application of this type of seismic energy dissipating systems.

A numerical study has been undertaken to evaluate the response of dual systems which consist of steel plate shear walls and moment resisting frames. The primary objective of the study was to investigate the influence of elastic base shear distribution between the wall and the frame on the global system response. A total of 10 walls and 30 wall-frame systems, ranging from 3 to 15 stories, were selected for numerical assessment. These systems represent cases in which the elastic base shear resisted by the frame has a share of 10%, 25%, or 50% of the total base shear resisted by the dual system. The numerical study consisted of 1600 time history analyses employing three-dimensional finite elements. All 40 structures were separately analyzed for elastic and inelastic response by subjecting to the selected suite of earthquake records. Interstory drifts, top story drift, base shears resisted by the wall and the frame were collected during each analysis. Based on the analysis results, important response quantities such as the response modification, the overstrength, the displacement amplification and ductility reduction factors are evaluated herein. Results are presented in terms of several measures such as the interstory drift ratio and the top story drift ratio. A discussion related to the influence of load share on the response factors is given.

Chevron braced steel frames require large beams to redistribute the unbalanced vertical forces exerted on the beams after brace buckling. A new frame configuration similar to chevron brace was proposed in literature, where zipper columns were attached between mid-spans of the beams from second to top story. During severe ground motion, the unbalanced vertical forces caused by buckling of lower story braces are in this case redistributed to the upper story braces by these zipper columns. Consequently, all story braces buckle successively from first to top story brace instead of concentration of inelastic action in one story. This system has been improved recently by adding an elastic hat truss between the top two stories to prevent formation of a full zipper mechanism and to prevent collapse. Two-phase numerical study is undertaken in this study to evaluate the response of chevron and suspended zipper braced frames, where the objective of the first phase is to observe the change in the performance of the configurations for different sets of initial imperfection and rotational spring stiffness values. Rotational springs are added at the end nodes of the braces to represent the effects of gusset plates and initial imperfection is assigned to the mid-length of the braces to achieve proper buckling behavior. The objective of the second phase is to compare the response of chevron and suspended zipper brace frames. For this purpose, three, nine and twenty-story buildings are designed for both brace configurations. The designed buildings are analyzed under static and dynamic loadings.

Using innovative materials or devices in techniques for strengthening or repair of RC concrete members may provide interesting alternatives for structural engineers. Laboratory tests were conducted on full scale reinforced concrete columns and a masonry wall that suffered severe damage. Carbon Fiber Reinforced Polymer - CFRP sheets and anchors were used to improve shear capacity or ductility elements. CFRP jacket were installed on column hinge regions while diagonal ties (tension braces) were used on the masonry wall. Mechanical splices were used in columns where concrete crushed and bars buckled by replacing the buckled bars and providing continuity to the longitudinal reinforcement. It was found that performance of the retrofitted members was comparable to that using conventional techniques and the performance was generally better than certain “fast” retrofit procedures reported in the literature. The choice of technique depends on the degree of damage, the cost of replacement, and performance required. Having the results of cyclic load tests of rehabilitated concrete members, envelope or backbone curves were obtained following the ASCE41-07 and proposed ASCE41-13 procedures. The backbone curves were used to develop behavioral models that can be used in the analysis and design of those types of concrete members and retrofit procedures. The inclusion of the behavioral models into current Performance Based Seismic Design procedures for strengthening of existing or repaired damaged buildings is proposed. / text

A procedure for improved nonlinear analysis of reinforced concrete (RC) slab and shell structures is presented. The finite element program developed employs a layered thick-shell formulation which considers out-of-plane (through-thickness) shear forces, a feature which makes it notably different from most shell analysis programs. Previous versions were of limited use due to their inabilities to accurately capture out-of-plane shear failures, and because analyses were restricted to force-controlled monotonic loading conditions. The research comprising this thesis focuses on addressing these limitations, and implementing new analysis features extending the range of structures and loading conditions that can be considered. Contributions toward the redevelopment of the program include: i) a new solution algorithm for out-of-plane shear, ii) modelling of cracked RC in accordance with the Disturbed Stress Field Model, iii) the addition of fibre-reinforced concrete (FRC) modelling capabilities, and iv) the addition of cyclic and dynamic analysis capabilities. The accuracy of the program was verified using test specimens presented in the literature spanning various member types and loading conditions. The new program features are shown to enhance modelling capabilities and provide accurate assessments of shear-critical structures. An experimental program consisting of RC and FRC slab specimens under dynamic loading conditions was performed. Eight intermediate-scale slabs were constructed and tested to failure under sequential high-mass low-velocity impact. The data from the testing program were used to verify the dynamic and FRC modelling procedures developed, and to contribute to a research area which is currently limited in the database of literature: the global response of RC and FRC elements under impact. Test results showed that the FRC was effective in increasing capacity, reducing crack widths and spacings, and mitigating local damage under impact. Analyses of the slabs showed that high accuracy estimates can be obtained for RC and FRC elements under impact using basic modelling techniques and simple finite element meshes.

Appropriate transverse confinement can significantly improve strength, ductility and energy dissipation capacity of reinforced concrete columns, therefore enhancing their seismic resistance. This study is conducted to evaluate the seismic behaviour of concrete columns transversely confined by steel spirals, ties or fiber reinforced polymer (FRP) wrapping. In the experimental program of this study, fifteen circular concrete columns of 356 mm (14 in.) diameter and 1473 mm (58 in.) length were tested under lateral cyclic displacement excursions while simultaneously subjected to constant axial load thus simulating earthquake loads. Eight columns were solely confined by various amounts of steel spirals, while seven other columns containing only minimal steel spirals were retrofitted by external FRP wrapping. Test results revealed that the increased transverse confinement can improve the energy dissipation capacity, ductility, deformability and flexural strength of concrete columns. The required transverse confinement should also be enhanced with the increase of axial load level to satisfy certain seismic design criterion. A computation program was developed to conduct monotonic pushover analysis for confined concrete columns, which can predict the envelope curves of moment vs. curvature and shear vs. deflection hysteresis loops with reasonable accuracy for columns subjected to simulated seismic loading. Based on extensive numerical analysis, expressions were developed for the relationships between the amount of transverse confinement and different ductility parameters, as well as the strength enhancement of confined columns. Finally, design procedures to determine the amount of transverse confinement were developed for concrete columns to achieve a certain ductility target. The enhancement of flexural strength of columns due to transverse confinement was also evaluated.

A procedure for improved nonlinear analysis of reinforced concrete (RC) slab and shell structures is presented. The finite element program developed employs a layered thick-shell formulation which considers out-of-plane (through-thickness) shear forces, a feature which makes it notably different from most shell analysis programs. Previous versions were of limited use due to their inabilities to accurately capture out-of-plane shear failures, and because analyses were restricted to force-controlled monotonic loading conditions. The research comprising this thesis focuses on addressing these limitations, and implementing new analysis features extending the range of structures and loading conditions that can be considered. Contributions toward the redevelopment of the program include: i) a new solution algorithm for out-of-plane shear, ii) modelling of cracked RC in accordance with the Disturbed Stress Field Model, iii) the addition of fibre-reinforced concrete (FRC) modelling capabilities, and iv) the addition of cyclic and dynamic analysis capabilities. The accuracy of the program was verified using test specimens presented in the literature spanning various member types and loading conditions. The new program features are shown to enhance modelling capabilities and provide accurate assessments of shear-critical structures. An experimental program consisting of RC and FRC slab specimens under dynamic loading conditions was performed. Eight intermediate-scale slabs were constructed and tested to failure under sequential high-mass low-velocity impact. The data from the testing program were used to verify the dynamic and FRC modelling procedures developed, and to contribute to a research area which is currently limited in the database of literature: the global response of RC and FRC elements under impact. Test results showed that the FRC was effective in increasing capacity, reducing crack widths and spacings, and mitigating local damage under impact. Analyses of the slabs showed that high accuracy estimates can be obtained for RC and FRC elements under impact using basic modelling techniques and simple finite element meshes.

Appropriate transverse confinement can significantly improve strength, ductility and energy dissipation capacity of reinforced concrete columns, therefore enhancing their seismic resistance. This study is conducted to evaluate the seismic behaviour of concrete columns transversely confined by steel spirals, ties or fiber reinforced polymer (FRP) wrapping. In the experimental program of this study, fifteen circular concrete columns of 356 mm (14 in.) diameter and 1473 mm (58 in.) length were tested under lateral cyclic displacement excursions while simultaneously subjected to constant axial load thus simulating earthquake loads. Eight columns were solely confined by various amounts of steel spirals, while seven other columns containing only minimal steel spirals were retrofitted by external FRP wrapping. Test results revealed that the increased transverse confinement can improve the energy dissipation capacity, ductility, deformability and flexural strength of concrete columns. The required transverse confinement should also be enhanced with the increase of axial load level to satisfy certain seismic design criterion. A computation program was developed to conduct monotonic pushover analysis for confined concrete columns, which can predict the envelope curves of moment vs. curvature and shear vs. deflection hysteresis loops with reasonable accuracy for columns subjected to simulated seismic loading. Based on extensive numerical analysis, expressions were developed for the relationships between the amount of transverse confinement and different ductility parameters, as well as the strength enhancement of confined columns. Finally, design procedures to determine the amount of transverse confinement were developed for concrete columns to achieve a certain ductility target. The enhancement of flexural strength of columns due to transverse confinement was also evaluated.

- / -