Special Collection on Recent Advances in Reinforced Concrete Walls Designed to Resist Seismic Loads

The special collection on Recent Advances in Reinforced Concrete Walls Designed to Resist Seismic Loads is available in the ASCE Library (https://ascelibrary.org/page/jsendh/rc_walls_seismic_loads).

For decades, cast-in-place concrete walls have been favorably used in the seismic design of buildings worldwide. This is because of their superior performance over other building systems in terms of limiting lateral drifts and structural damage in past earthquakes that occurred as early as in the 1970s. Over the years, advancements and refinements to wall designs have taken place, and various design codes have been appropriately revised. Contrary to expectations, a number of concrete walls suffered structural damage in the 2010 Chile earthquake and 2011 Christchurch earthquake, raising concerns for their dependable performance in future earthquakes (Sritharan et al. 2014). As witnessed repeatedly, poor seismic performance of concrete members typically originates from inadequate confinement, insufficient shear reinforcement, and/or use of lap splices in the plastic hinge regions. However, the observed wall damage in Chile and Christchurch identified other failure modes. Field observations indicated that these failure modes were caused by out-of-plane wall buckling, premature fracture of longitudinal bars in walls designed with minimum reinforcement, high axial load, and complex configuration of walls with surrounding structures.

This special collection of 10 papers highlights recent advances in seismic design of reinforced concrete walls. Some of the studies originated as a result of the observed damage to structural walls in the Chile and Christchurch earthquakes. The papers by Herrick and Kowalsky (2017) and Dashti et al. (2017) focus on out-of-plane buckling of walls under in-plane loading. The first paper examines the localized lateral instability of walls resulting from plastic tensile strains induced by flexural demands and subsequent load reversals by revisiting previously established buckling models and conducting a parametric study. The second paper uses detailed finite-element models and demonstrates with experimental validation that out-of-plane failure mode can be accurately captured along with other failure modes through numerical simulations involving shell elements embedded with bar elements representing reinforcing steel.

A study by Welt et al. (2017) investigates the confinement behavior of concrete in wall boundary elements using rectangular reinforced concrete prisms to understand the brittle failure of compression regions in concrete walls. The observed results are compared with the expected behavior, and recommendations are made in terms of the influence of loading type, reinforcement details, and the maximum tensile strain developed in the previous cycles.

Lu et al. (2017) present results from cyclic testing of reinforced concrete walls designed with minimum longitudinal reinforcement. When walls are designed with an insufficient amount of minimum reinforcement, they will experience a few flexural cracks and concentration of tensile strains in the longitudinal reinforcing bars, prematurely fracturing them. Using a series of tests, this article establishes recommendations for the minimum amount of flexural reinforcement in walls designed for seismic regions.

Two experimental investigations on T-walls are presented by Fischinger et al. (2017) and Brueggen et al. (2017). Using a one-third-scale model, Fischinger et al. (2017) present a shake table test investigation on a 5-story coupled wall consisting of two T-shaped flanged wall piers connected with thin diagonally reinforced coupling beams. The study used confinement reinforcement as a variable without the use of boundary elements and observed the influence of coupling beam-slab interaction. The experimental work is accompanied by an analytical study based on a three-dimensional multiple-vertical line-element model (MVELM). Two half-scale T-walls are the focus of the study by Brueggen et al. (2017), who subjected the test walls to multidirectional loading. The study examined the effects of distributed longitudinal reinforcement as opposed to concentrating the reinforcement in boundary elements, location of lap splice, shear lag, varying shear reinforcement quantity, and increasing the length of boundary elements beyond the code requirement. Using a 6-story prototype building, the experiment also investigated the minimum number of stories required in the experimental investigation to accurately characterize the seismic behavior of the prototype building.

Kolozvari and Wallace (2016) present an article on practical nonlinear analysis of reinforced concrete walls. Citing the commonly used fiber-based analysis method that neglects the coupling between axial-bending (P-M) behavior and shear (V) force-deformation response, it presents the benefits of using sophisticated models that include coupled P-M-V behavior, which in this case used an MVELM with shear-flexure interaction. A sensitivity analysis reveals the appropriate effective shear stiffness to be used in routine beam-column element models.

Motivated by improving understanding of the behavior of concrete walls with high compression in the boundary elements, Sanada et al. (2018) use experimental and analytical means to study flexure-dominated walls that are designed according to the current Japanese code. The variable investigated in this study includes length of boundary element, quantity, and spacing of transverse reinforcement in the boundary element and loading type.

Finally, Almeida et al. (2017) and Tarquini et al. (2017) present companion papers on how lap splices in the plastic hinge region affect the strength and deformation capacity of reinforced concrete walls. The first paper presents a collection of available data, results from a set of new experiments, and then identifies key parameters for a suitable model development. The analyses of the test results examine the different details of confinement and the corresponding strain capacity of the lap splice. The second paper uses the information presented in the first paper and develops a simple model to estimate deformation capacity of walls with lap splices. By integrating this model in a numerical investigation, the study examines how accurately the strength and deformation capacity of walls with lap splices can be captured.