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For many mid- and high-rise concrete buildings in seismic regions, earthquake loads are resisted by reinforced concrete walls that respond primarily in flexure (i.e. yielding in flexure without exhibiting significant shear damage or shear failure). Under lateral loading, flexural walls may sustain compressive damage to concrete and reinforcing bars as well as tensile rupture of reinforcement, with the onset of lateral strength loss resulting from one or more of these damage mechanisms. Given the prevalence of concrete walls, there is interest in advancing numerical modeling to enable improved prediction of wall response as well as in advancing wall design and detailing to achieve enhanced performance. The research presented here does both. First, modeling recommendation for nonlinear finite element analyses were developed and validated using data from prior laboratory tests of large-scale structural walls. Second, the validated modeling approach was used to conduct a parametric study to investigate the impact of two critical design parameters, normalized shear stress demand and cross-sectional aspect ratio, on the deformation capacity corresponding to onset of lateral strength loss. Few tests have considered the larger cross-sectional aspect ratios and shear stress demands that are common in design of modern walls. Results of this study show that walls with large cross-sectional aspect ratios and moderate to high shear demands develop high minimum principal stresses within the web region of the wall at the web-boundary element interface; these high stresses can lead to lateral strength loss at relatively low drift levels due to concrete crushing and bar buckling within the web. This failure mode is termed a compression-shear failure. The third phase of the study used the validated modeling approach to conduct a parametric study to develop a mitigation strategy for walls susceptible to compression-shear failure, namely extension of the boundary element confinement into the web of the wall. The results of this study were combined with test data to determine the confined length required to suppress the compression-shear mode. This required confined length is a function of the shear stress demand and is conservatively estimated as c, where c is the depth of the compression region when the wall achieves nominal flexural strength.

This study presents a physics-based rib-scale finite element (FE) model to study bond-zone behavior for spliced longitudinal bars in reinforced concrete beams subjected to monotonically increasing loading. In this model, a high-resolution mesh is used in the vicinity of the bar-concrete interface to capture the geometry of the ribs on the reinforcing steel. At the concrete-bar interface, a contact formulation that properly represents normal and frictional force transfer is used; adhesion between concrete and steel is ignored. The FE model is calibrated using data from beam splice tests performed by Ramirez and Russell [1] . It is observed that concrete tensile strength and tangential friction at the concrete-steel interface determine simulated response; these quantities are calibrated to provide accurate simulation of experimental results. The calibrated model provides results in good agreement with test data. Load-displacement response as well as concrete crack patterns are accurately simulated, and the proposed model can distinguish between the behavior of uncoated and epoxy-coated deformed bars as well as simulate the impact on bond strength of confinement provided by transverse steel.

An advanced modelling technique is developed to model the nonlinear cyclic response of circular RC columns using fibre-based section discretisation method. A comparison between different reinforcing steel models is made. Through a comprehensive parametric study the influence of inelastic buckling of vertical reinforcement on the cyclic response of circular RC columns is investigated. The results have been compared and validated against a set of experimental datasets. The proposed calibrated model accounts for the influence of inelastic buckling of vertical reinforcement and interaction of stiffness of horizontal ties reinforcement with vertical reinforcement. The model also accounts for the fracture of vertical bars due to low-cycle high-amplitude fatigue degradation. Therefore, this model is able to predict the nonlinear cyclic response of circular RC columns up to complete collapse. The results show that the existing uniaxial material models of reinforcing bars that are calibrated using stress–strain behaviour of isolated bars cannot represent the behaviour of reinforcing bars inside RC columns. Moreover, it is found that the buckling length of vertical reinforcement has a significant influence on the pinching response of RC columns and also reduces the low-cycle fatigue life of buckled reinforcement.

The research presented here developed a model for simulating the nonlinear cyclic response of flexure-controlled concrete walls, which meets the dual objectives of accuracy and computational efficiency. The proposed model represents a significant advancement in that it provides accurate simulation of the dominate failure mechanism exhibited by flexural walls in the laboratory and field: compression-controlled failure characterized by simultaneous crushing of concrete and buckling of longitudinal reinforcement. The first steps in the model development effort comprised assembly of an experimental database and review of current modeling approaches for walls (e.g., lumped plasticity, distributed plasticity, and continuum elements). Model evaluation indicated that the most viable option to achieve accuracy and efficiency was the use of beam–column line elements with fiber-type cross-section models at the integration points. Initially, both displacement-based and force-based element formulations were evaluated; however, the displacement-based formulation resulted in an inaccurate representation of the axial force distribution along the length of the element. Therefore, only the force-based formulation was chosen for further study. The basic model included standard 1D constitutive models for confined concrete, plain concrete and reinforcing steel. Comparing simulated and measured response data showed that the concrete and steel material models must be regularized using a mesh-dependent characteristic length and a material-dependent post-yield energy to enable accurate, mesh-objective simulation of strength loss due to compression failure. The post-yield energy values were determined using relevant experimental data, an important but missing component of prior research on material regularization. The results of this study show that use of the regularized constitutive models significantly improved the accuracy of response predictions.

A finite element (FE) model is used to simulate bond-zone behavior in a pullout test of a single bar embedded in concrete. The proposed FE model treats both the concrete and reinforcing bar in the bond-zone with refined solid elements to explicitly represent the deformations of rebar and the surrounding concrete and employs the surface-to-surface contact model on the concrete-rebar interface to simulate proper load transfer. In modeling of pullout tests, the significance of using a concrete model that can accurately simulate nonlinear response under high confining pressures is emphasized. Two concrete models are discussed and compared from a constitutive modeling perspective: (1) concrete damaged-plasticity (CDP) model and (2) concrete damage plasticity model 2 (CDPM2). Three pullout tests are simulated via the proposed modeling approach each with two concrete models. It is shown that the FE model with CDPM2 produced bond stress and slip responses comparable to test data, while the FE model with CDP model overpredicted bond stress due to concrete response overestimated under high confining stress states. The FE models with CDPM2 can capture different failure modes for different types of specimens: splitting failure for the specimen without confinement and pullout failure for the specimen with confinement.

An optical surface measurement technique was used to characterise three-dimensional corrosion pattern of reinforcing bars subjected to accelerated corrosion. After the optical measurement process was performed, the corroded bar specimens were tested under monotonic and cyclic axial loading. The optical measurement data were used to develop a 3D micro-fibre finite element model developed for simulation of the physical testing and parametric study of the influence of corrosion pattern on stress–strain response of corroded bars. It was observed that the irregular cross sectional shape of pitted sections has a significant influence on the inelastic buckling and nonlinear cyclic response.

Experimental and numerical studies have shown self-centering steel plate shear walls (SC-SPSWs) to exhibit enhanced performance including recentering during extreme loading, making them a viable lateral load resisting system for high seismic regions capable of reducing structural repair costs and loss of building functionality after an earthquake. SC-SPSWs utilize thin steel web plates to provide lateral load resistance and energy dissipation, while rocking post-tensioned (PT) beam-to-column connections recenter the building and, if properly designed, eliminate costly damage to the boundary frame. A series of quasi-static cyclic tests have been conducted on SC-SPSW subassemblages. The purpose of these tests is to better understand SC-SPSW and component behavior and the impact of certain web plate and PT connection parameters on performance. This paper presents the results from the test program and also compares the experimental results to those of simple numerical models.

Reinforced concrete structural walls are used commonly as the primary lateral-load resisting system in buildings. The research presented here represents the results of the first phase of a multi-year research effort aimed at developing tools to enable performance-based earthquake engineering (PBEE) of structural walls. The first phase of the research effort focused on the seismic behavior and analysis of slender planar walls and included laboratory testing of four planar wall sub-assemblages. The walls simulated the bottom three stories of a 10-story prototype building; loading apparatus available at the University of Illinois, Network for Earthquake Engineering Simulation laboratory were used to simulate the load demands, permitting maximum test-specimen scale and realistic demand patterns. The walls were detailed to modern code requirements and standard practice and included heavily reinforced boundary elements. The test matrix studied the effects of reinforcement layout, shear demand, and lap splices at the base of the wall. All of the walls exhibited damage in the compression region, even at relatively low drifts. The splice affected the location of the damage. Walls without splices sustained damage at the base of the wall; walls with splices sustained damage at both the top of the splice and the base of the wall, with the critical region depending on the shear demand. Shear demand also affected response; a moderate increase in shear demand resulted in the failure mechanism changing from bar fracture to flexure–compression failure of the boundary elements.

A model is developed to simulate the nonlinear response of planar reinforced-concrete frames including all sources of flexibility. Conventional modeling approaches consider only beam and column flexibility using concentrated plasticity or springs to model this response. Although the joint may contribute the majority of the deformation, its deformability is typically not included in practice. In part, this is because few reliable, practical approaches for modeling all sources of frame nonlinearity are available. The research presented herein was undertaken to develop a practical, accurate nonlinear model for reinforced concrete frames. The model is appropriate for predicting the earthquake response of planar frames for which the nonlinearity is controlled by yielding of beams and/or non-ductile response of joints and is compatible with the ASCE/SEI Standard 41-06 nonlinear static procedure. The model was developed to facilitate implementation in commercial software packages commonly used for this type of nonlinear analysis. The nonlinearity is simulated by introducing a dual-hinge lumped-plasticity beam element to model the beams framing into the joint. The dual-hinge comprises two rotational springs in series; one spring simulates beam flexural response and one spring simulates joint response. Hinge parameters were determined using data from 45 planar frame sub-assemblage tests. Application of the model to simulate the response of these sub-assemblages shows that the model provides accurate simulation of stiffness, strength, drift capacity and response mechanism for frames with a wide range of design parameters.

The results of previous experimental tests indicate that reinforced concrete interior beam column joints may exhibit significant strength and stiffness loss under earthquake loading, and the results of post-earthquake reconnaissance indicate that joint failure may result in structural collapse. Thus seismic evaluation and design of reinforced concrete frames requires accurate prediction of the potential for joint failure. This paper presents a binomial logit model, developed using data from 110 experimental tests, which define the probability that a reinforced concrete interior beam–column building connection, with a specific set of design parameters, will exhibit either a non-ductile joint shear failure prior to beam yielding or a ductile failure that initiates with beam yielding. The calibrated model identifies the relative importance of various design parameters in determining the connection’s response mechanism. The model can be used by an engineer designing a new connection, constructed of normal or high-strength materials, to estimate the likelihood of joint failure initiation. The model can also be used by an engineer evaluating an existing structure to estimate the likelihood of joint failure, determine the factors that most significantly affect this likelihood, and, thereby, develop a suitable and efficient retrofit strategy.