Boundary element detailing in special concrete structural walls

Reinforced concrete structural walls are expected to provide significant strength and ductility under cyclic earthquake loading due to the enhanced compressive deformability provided well-detailed boundary elements. However, compression failures observed following recent earthquakes and in laboratory testing suggest that the compressive behavior of such boundary elements may not meet the design intent. An experimental research program was undertaken to investigate the response of structural wall boundary elements based on a number of design parameters including: vertical spacing of transverse reinforcement, pattern of longitudinal bar restraint, and the use of crossties in place of hoops. Results, combined with a number of existing data sets, indicate that sections with minimum ACI 318 detailing requirements exhibit little improvement in strength or deformability over unconfined concrete, and that crossties are ineffective unless fully developed into the confined core. A widely accepted model for confined concrete was examined for its accuracy in predicting the results of the experimental database. The results suggest that the accuracy of this commonly used model is limited. Modifications are proposed to account for a number of shortcomings in the existing model's ability to predict the response of boundary elements of modern design.