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This paper presents a method to evaluate the seismic performance of RC walls, based on the local (material) response obtained from computational simulation. The latter relies on a recent implementation of the nonlinear truss model, which has been shown capable of capturing all important RC wall failure modes. An enhancement to the method is presented herein, enabling the accurate reproduction of lap-splice failures. The seismic evaluation procedure relies on establishing strain-like acceptance criteria for all significant material damage modes related to Immediate Occupancy, Life Safety and Collapse Prevention performance levels. Truss models are shown to accurately capture the force-displacement response and failure patterns observed in these tests. The threshold limit values for each performance level obtained with the proposed strain-based criteria are consistent with the physical damage and deterioration of the load-carrying capacity of the walls. The study presented in this paper was supported by the National Institute of Standards and Technology (NIST) under award No. 70NANB19H060. Any opinions and findings presented in this paper are those of the authors alone, and do not necessarily reflect the opinions of the sponsor.

This paper presents a simulation-based method to evaluate the seismic performance of RC walls with lap splices. Computational analyses are conducted using a recent implementation of the nonlinear truss model. The uniaxial steel law used in the truss model is modified to account for lap-splice failure of vertical bars using a simple tensile strain criterion. Performance evaluation is conducted using a novel method that employs strain limits associated to damage in concrete and steel. The computational models and strain-based evaluation method are verified with experimental data from tests on wall components with lap splices at their base. Truss models are shown to accurately capture the force-displacement response and failures observed in these tests. The proposed evaluation approach allows for consideration of the post-yield capacity of lap-spliced bars, and the strain-based limits are shown to be consistent with the strength and stiffness deterioration of the walls. The study presented in this paper was supported by the National Institute of Standards and Technology (NIST) under award No. 70NANB19H060. Any opinions and findings presented in this paper are those of the authors alone, and do not necessarily reflect the opinions of the sponsor.

This paper presents an accurate, simple and computationally efficient method called the beam-truss model (BTM), for the computational seismic performance assessment and design of reinforced concrete (RC) structural wall buildings. The BTM has been extensively validated through a number of prior studies, and its capability to enable the accurate simulation of planar and flanged walls, coupled walls and entire building systems, has been demonstrated. A recent implementation of the BTM as a four-node shell macroelement substantially facilitates the definition and post-processing of analysis. The method is currently used for transforming the modeling and seismic performance evaluation of existing RC walls, enabling the formulation and use of performance acceptance criteria based on local material damage states. Furthermore, the BTM enables the fully nonlinear static and dynamic analysis of entire buildings including three-dimensional ground motions improving substantially the predicting capabilities of nonlinear analysis practice for performance-based seismic design (PBSD) and assessment.

Masonry-infilled reinforced concrete (RC) frames constitute a significant part of the building inventory in earthquake-prone regions around the world. The development of accurate analysis tools and of retrofit techniques is important for enhancing the seismic safety of older construction of this type. Most of the existing analytical approaches have either adopted simplified models with limited predictive capabilities or been restricted to the monotonic loading regime. Additionally, many of the retrofit methods used in practice have not been experimentally validated. The present study aimed to establish and use refined computational tools for the reliable and robust analysis of masonry-infilled RC frames with and without retrofit, and to experimentally validate recently developed retrofit schemes. Constitutive models have been developed to allow the analysis of infilled frames. An existing smeared-crack model has been enhanced to accurately describe diffuse cracking and crushing in concrete and masonry under cyclic loading. Furthermore, a novel cohesive interface model has been formulated to describe strongly localized cracks in the concrete columns and the behavior of the mortar joints. The model can account for various aspects of the cyclic behavior, such as the cyclic normal unloading/reloading response, the frictional sliding and geometric dilatation and the irreversible crushing under large compressive stresses. A major challenge was the formulation of a robust stress update algorithm, which is also presented. The models are validated with experimental tests at the material and at the structural level. The analyses demonstrate the capability of the models to accurately capture the response of infilled frames. The results of large-scale, shake-table tests on a masonry-infilled RC frame are also presented. The purpose of the tests was to evaluate two retrofit methods for infills, using overlays of Engineered Cementitious Composite material (ECC) and of Glass Fiber Reinforced Polymer (GFRP). The material properties, specimen configuration, input ground motions and experimental observations are described in detail. Both retrofit techniques improved the performance of the specimen. A series of nonlinear analyses has been conducted to provide further insight on the behavior of the retrofitted specimen. Dynamic analyses have been conducted for infilled RC frames subjected to a collection of eight ground motions, scaled to match a target intensity level. The results of the analyses indicate that the addition of an ECC overlay can significantly improve the performance of an infilled frame

A computational study was conducted to evaluate the extent to which the column panel zone in a gable frame knee joint can develop tension field action when subjected to positive bending (top flange of the rafter is in tension). Past testing was reviewed and used to validate finite element models. The validated finite element modeling approach that utilized shell elements, was then used in a parametric study to evaluate the post-buckling strength of the panel zone beyond the shear buckling strength. In addition, a plastic mechanism model was used to derive an equation for the post-buckling shear strength of the panel zone and the derived equation was validated against the results of the parametric study. The result was a proposed equation for tension field action strength of the panel zone when subjected to positive bending that had an average error of 1% compared to the model results. Metal Building Manufacturers Association American Iron and Steel Institute

© 2014 John Wiley & Sons, Ltd.This paper uses nonlinear truss models for the analysis of shear-dominated reinforced concrete (RC) columns subjected to cyclic loading. A previously established method, aimed to the analysis of RC walls, is enhanced to allow simulations of column members. The concrete constitutive equations are modified to account for the contribution of the aggregate interlock to the shear resistance. Additionally, an equation is proposed to determine the inclination angle of the diagonal members in the truss models. The modeling approach is validated using the results of quasi-static and dynamic tests on shear-dominated RC columns. The combination of predictive capabilities and conceptual simplicity establishes truss-based models as an attractive approach for the systematic analysis of shear-dominated RC frame construction.

Masonry-infilled reinforced concrete (RC) frames constitute a significant portion of the building inventory in many earthquake-prone areas around the world. Although infill walls are commonly treated as nonstructural components, they can interact with the surrounding frame under lateral loads, significantly enhancing the strength and stiffness of the system. However, sometimes, the increase in lateral resistance due to infill walls may not be sufficient to ensure a satisfactory performance for old, nonductile, infilled RC frames. The interaction of infill walls with RC frames may result in undesired failure mechanisms. For this reason, the retrofit of such structures is often deemed necessary. This study analytically investigates the behavior of unretrofitted and retrofitted infilled RC frames subjected to in-plane seismic loads. The retrofit method examined here is based on the addition of overlays of engineered cementitious composite (ECC) material on masonry infill walls. The analyses have been conducted using refined finite element models which can capture the cyclic behavior of the RC members, infill walls and ECC overlays. A simplified method has been formulated and employed to account for the effect of the construction sequence and the creep of the concrete and masonry on the gravity load distribution between the RC frame columns and infill walls. The analysis scheme has been validated using data from shake-table tests on a retrofitted infilled frame specimen. Dynamic analyses have been conducted for infilled RC frames subjected to a collection of eight ground motions which had been scaled to match the design-level and MCE-level intensities for downtown Los Angeles. The analyses have shown that the addition of a relatively thin ECC overlay can significantly enhance the seismic performance by limiting the extent of cracking in the infill walls and in the RC frame. Results of additional static analyses have demonstrated that the performance of a retrofitted structure can be greatly improved by preventing the failure of shear dowels which connect the retrofit overlays to the frame. This allows to fully exploit the ductile inelastic behavior of the ECC material. A simplified analytical method to assess the shear capacity of an ECC overlay and to determine the number and size of shear dowels required to prevent dowel failure has been proposed.

This paper presents a study that investigated the effectiveness of retrofitting unreinforced masonry infill walls with composite materials to enhance the seismic performance of infilled nonductile RC frames. The primary retrofit scheme considered was the use of engineered cementitious composite overlays. Shake-table tests were conducted on a 2/3-scale, 3-story, 2-bay, masonry infilled RC frame that had one bottom-story wall retrofitted with engineered cementitious composites. The influence of this retrofit on the performance of the structure was investigated using the experimental observations and results of nonlinear finite element analyses. Furthermore, after walls in the second story of the structure were damaged, they were repaired by injecting epoxy into cracked mortar joints, and strengthened with a glass-fiber reinforced polymer overlay. It has been shown that both retrofit schemes are effective in enhancing the seismic performance of the structure and preventing diagonal shear failures of the RC columns.