CYCLIC RESPONSE OF CONCRETE BEAMS REINFORCED WITH ULTRAHIGH STRENGTH STEEL
Open Access
- Author:
- Tavallali, Hooman
- Graduate Program:
- Architectural Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 08, 2011
- Committee Members:
- Dr Andres Lepage, Dissertation Advisor/Co-Advisor
Andres Lepage, Committee Chair/Co-Chair
Ali M Memari, Committee Member
M Kevin Parfitt, Committee Member
Maria Lopez De Murphy, Committee Member - Keywords:
- Concrete
Structures
Ultrahigh Strength Steel
Cyclic Response
Fiber Reinforced Concrete
Deformation Capacity - Abstract:
- Seismic applications of concrete members flexurally reinforced with ultrahigh strength steel bars (yield strength greater than 80 ksi) have been limited by U.S. building codes since 1963. The limitation has been primarily due to paucity of experimental data. This investigation aimed at providing benchmark data for studying the cyclic response of concrete beams reinforced with steel bars having nominal yield strengths of 97 ksi. Seven beams were subjected to large transverse displacement reversals: three beams were reinforced longitudinally with conventional steel bars (Grade 60) and four with ultrahigh strength steel bars (Grade 97). All transverse reinforcement was Grade 60. Other experimental variables were spacing of transverse reinforcement (d/4 or d/2), volume fraction of steel-hooked fibers (0 or 1.5%), and ratio of compression-to-tension longitudinal reinforcement (ρ’/ρ = 0.5 or 1.0). The beams reinforced with ultrahigh strength steel bars had drift ratio capacities in excess of 10%, comparable to the deformation capacities of similar beams reinforced with conventional steel bars. Numerical models were developed for the calculation of the moment-curvature relationship and the load-displacement response of the tested beams. The calculated values show good correlation with the measured data. For beams with nearly identical strength, the measured yield displacement of beams reinforced with Grade 97 bars was about 25% greater than in beams reinforced with Grade 60 bars, which led to a reduction of the area inside the load-deformation hysteresis loops. However, nonlinear seismic analyses of single-degree-of-freedom systems indicate that the displacement calculated for systems representing the beams with Grade 97 bars are, on average, less than 10% larger than the displacement calculated for systems representing the beams with Grade 60 bars. The evidence presented suggests that ultrahigh strength steel bars (Grade 97) are a viable option for the longitudinal reinforcement of beams in earthquake-resistant structures.