Title: Seismic Performance of Tall Moment Frames with High- Strength Reinforcement
Author(s): Duy V. To, Drit Sokoli, Wassim M. Ghannoum, and Jack P. Moehle
Publication: Structural Journal
Appears on pages(s): 113-124
Keywords: Grade 100 reinforcement; high-strength reinforcement; low-cycle fatigue; seismic performance; special moment frame
Seismic performance of tall, reinforced concrete special moment resisting frames with high-strength reinforcement is investigated through laboratory tests and nonlinear dynamic analysis. The tests demonstrate that members with higher-grade reinforcement tend to have reduced stiffness because of reduced amounts of reinforcement and increased strain penetration into adjacent connections. In addition, Grade 100 reinforcement may have tensile-to-yield strength ratio that is either lower or higher than typical Grade 60 reinforcement. Changes in tensile-to-yield strength ratio affect strain localization and overall force-deformation hardening response. To study the effects of using different grades of reinforcement, a 20-story reinforced concrete moment frame building was designed in accordance with ASCE 7-16 and an extension of ACI 318-19 at a hypothetical site in San Francisco, CA. Two different designs were done, one with Grade 60 reinforcement and another with Grade 100 reinforcement. The frames had the same gross dimensions and concrete properties, resulting in identical design strength requirements and design lateral drifts. To maintain the same nominal strengths, the frame with Grade 100 reinforcement had a reduced amount of longitudinal reinforcement compared with the frame having Grade 60 reinforcement. Numerical simulations of the nonlinear dynamic response of the frames were carried out to identify effects of the different reinforcement grades on response to strong earthquake ground motion. It was observed that frames with higher-grade reinforcement sustain modestly larger drifts than frames with lower-grade reinforcement. The analysis results also indicated that fracture of longitudinal reinforcement due to low-cycle fatigue in frame models is unlikely under maximum considered earthquake response (MCER)-level earthquakes.