Shear Strength and Drift Capacity of Reinforced Concrete and High-Performance Fiber Reinforced Concrete Low-Rise Walls Subjected to Displacement Reversals.

Abstract

The use of High-Performance Fiber Reinforced Concrete (HPFRC) in low-rise walls was investigated as a means to simplify reinforcement detailing while enhancing overall seismic performance and damage tolerance. Nine walls with shear span-to-length ratio of either 1.2 or 1.5 and shear stress demands ranging from 4.4√(f_c^' ) to 9.4√(f_c^' ) (psi) were tested under displacement reversals. Four of the walls were constructed with regular concrete (RC) and designed according to the seismic provisions of the 2005 ACI Code. The HPFRC walls were detailed with reduced web reinforcement and little or no confinement in the boundary regions. In addition, the wall-foundation interface in most HPFRC walls was strengthen with dowel bars to prevent early damage localization due to the lack of fibers crossing this section. The HPFRC materials were reinforced with either hooked steel fibers (1.5% or 2% volume fraction) or Spectra fibers (2% volume fraction). The HPFRC specimens exhibited drift capacities equal to or larger than those of the companion RC specimens (1.5%-3.0% in HPFRC walls versus 1.5%-2.1% in RC walls), the larger drift capacities being associated with lower shear stress demands. The RC walls generally exhibited extensive damage in the boundary regions, followed by substantial sliding along the base. Failure in most of the HPFRC walls consisted of the wide opening of and sliding along a flexural crack at the end of the dowel reinforcement. The HPFRC specimens also exhibited superior damage tolerance compared to the RC specimens with a much denser array of narrow cracks and lack of concrete spalling for drifts below 2.0%. No indication of early concrete crushing or buckling of the main vertical reinforcement was observed in the HPFRC specimens. The test results also demonstrated the need for dowel reinforcement to strengthen the cold joint at the HPFRC wall-foundation interface and prevent a premature sliding shear failure. A nearly linear shear strength increase with an increase in the total area of vertical reinforcement was observed for both the RC and HPFRC walls. The contribution of the HPFRC material to wall shear strength was estimated to be in the order of 4.5√(f_c^' ) (psi).