Boundary element detailing in special concrete structural walls

Reinforced concrete structural walls are one of the most commonly used lateral force-resisting systems for buildings located in regions of high seismicity. Structural walls are expected to provide significant strength and ductility under cyclic earthquake loading. However, compression failures observed following recent earthquakes and in laboratory testing have resulted in concern by the structural engineering community that wall boundary elements may not be able to sustain significant cyclic demands without significant damage. An experimental research program was undertaken to investigate the response of structural wall boundary elements, with a specific focus on boundary element detailing. The test program was developed as multiple series of tests of rectangular prisms that were intended to simulate the effects of geometry, confining reinforcement, and axial loading on the compressive strength and deformability of boundary elements. Each test series studied key confinement detailing parameters, such as vertical spacing of transverse steel, pattern of bar restraint, and the use of crossties in place of continuous hoops. In addition, impact of loading protocol was also studied. These test results were combined with data from existing test programs to form an extensive database, which was used to evaluate impact of such parameters on the distribution of plasticity and strength loss with respect to various ACI 318-14 detailing requirements. Results indicate that boundary elements tested in axial compression just meeting the minimum ACI 318 requirements exhibit strength and strain capacities that are, on average, 20% and 10% larger than unconfined concrete, respectively. The database was also used to develop new detailing recommendations for the spacing and pattern of confinement needed to achieve larger levels of confined response and deformability.