Testing and Modeling of Reinforced Concrete Coupling Beams
Dissertation – An efficient structural system for tall building construction to resist earthquake loads consists of reinforced concrete shear walls connected by coupling beams. Construction of coupling beams that satisfy the strength and detailing requirements set forth in ACI 318-05 for diagonally reinforced coupling beams is cumbersome and costly; therefore, ACI 318-08 provides a new detailing option which aims to improve the constructability while maintaining adequate strength and ductility. Eight half-scale specimens were tested to compare the performance of beams constructed utilizing new and old detailing options, to compare beams with diagonal reinforcement to beams with straight bars at higher aspect ratios, and to assess the impact of reinforced and post-tensioned slabs. Test results indicate that the new detailing approach provides equal, if not improved behavior as compared to the alternative detailing approach and that including a slab had only a modest impact on strength, stiffness, ductility, and observed damage. Understanding of the load-deformation characteristics is essential to modeling the overall system response to seismic loading. Modeling studies are performed to evaluate the effectiveness of current modeling approaches with respect to key performance parameters, including effective elastic stiffness, ductility, and residual strength. As well, most of the experimental work that has been performed on coupling beams has been on specimens at less than full-scale. The impact of this scaling effect on the full-scale models is presented and shown to be potentially significant on the expected ductility of the member. A brief summary of simplified modeling techniques using commercially available software is presented to provide practical applications for design engineers. Results indicate that these simple modeling approaches reasonably capture measured force versus deformation behavior.