High-strength (HS) reinforcing bars (with yield strengths greater than 60 ksi) are currently not permitted by US building codes as primary reinforcement for seismic force resisting systems in high-seismic regions. This is despite the potential benefits of high strength reinforcement to improve the constructability and cost-effectiveness of reinforced concrete structures. The major concern with HS reinforcement is whether it has sufficient strain hardening and ductility to resist fracture under inelastic cyclic loading that may occur in buildings subjected to large earthquakes. This study examines cyclic deformation (strain) demands and acceptance criteria for low-cycle fatigue resistance of steel reinforcement in concrete structures subjected to earthquakes. Using nonlinear analysis, the study integrates demand and performance data from bare reinforcing bar tests, subassembly tests of concrete beams and columns, and overall building system response. The key objectives of this project are to (1) develop a reliability-based methodology for determining the minimum required low-cycle fatigue resistance of steel reinforcement in the seismic design of concrete structures, (2) apply the methodology to assess the cyclic strain/deformation demands in concrete components for a series of archetype concrete shear wall and frame building structures subjected to earthquakes, and (3) develop acceptance criteria for steel reinforcement in concrete structures, which are consistent with the seismic reliability criteria for buildings in ASCE 7 and related building code standards. In the case study of nine archetype 20-story reinforced concrete (RC) moment frames, the increased cyclic strain demand is still durable; however, reduced lateral stiffness and lower T/Y ratio are found to have predominant effects on seismic reliability of HS steel RC frame structures.
- Zhong, K. & Deierlein, G. G. (2018). Assessing Earthquake Loading Demands and Reliablibity of High Strength Reinforcing Steel, 11th U.S. National Conference on Eathquake Engineering, Los Angeles, California, USA.