Impact of High Strength Rebars on Seismic Behavior of Lightly Reinforced Boundary Elements

Considering economic reasons and attempting to reduce the carbon footprint of concrete structures, there is an increasing tendency toward the use of high strength reinforcement in seismically active regions. ACI 318-19, Iranian steel rebars standard INSO 3132 and next edition of Iranian national building allow the use of high strength rebars in elements of ductile force-resisting systems. Therefore it is important to verify that if S520 rebars are capable of providing adequate, a) strain capacity, b) out of plane buckling deformation capacity, which are the two common sources of failures observed in recent earthquakes in boundary elements of lightly reinforced shear walls. An experimental program is designed to compare strain capacity of boundary elements reinforced with S400 and S520 rebars, which include monotonic and cyclic loading considering probable loading on lightly reinforced boundary elements. Considering test results for specimens under monotonic and cyclic loading it is shown that, a) gauge length suggested by INSO for rebar test could be misleading in the evaluation of rebar axial strain capacity, b) S520 rebars have limited ductility compared to S400, but considering strain demand, this limited strain capacity is adequate to avoid rebar fracture, c) local strain (crack width) has a better correlation with out of plane buckling compared to average strain as suggested by some researchers, d) it seems that out of plane buckling for S520 rebars occurs at smaller deformation, which means there is the need for larger minimum dimension for sections reinforced with S520 compared to S400.