| This study investigated the possibility of delaying shear strength decay while relaxing transverse reinforcement requirements in plastic hinge regions of reinforced concrete (RC) flexural members through the use of fiber reinforced cement composites (FRCCs). Emphasis was placed on the use of high-performance FRCCs, which exhibit a strain-hardening behavior under direct tension. Eight dual-cantilever beam specimens with a shear span-to-effective depth ratio of 3.0 were tested under large displacement reversals. The parameters considered included fiber type and volume fraction, peak shear stress demand, shear strength contribution from transverse reinforcement versus shear demand, and type of fiber cement composite (mortar or concrete). Ultra-high molecular weight polyethylene (Spectra) fibers and steel hooked (Dramix) fibers were used in the FRCC test specimens in volumetric ratios between 1.0% and 2.0%.; Test results showed that strain-hardening FRCC members containing either polyethylene or steel hooked fibers and no transverse reinforcement exhibited a behavior similar to or better than that of a control RC member detailed according to the ACI Building Code, with drift capacities equal to or greater than 4.0% drift. In addition, the strain-hardening FRCC materials were effective in preventing buckling of longitudinal reinforcement up to at least 4.0% plastic hinge rotation. A shear stress limit of 3.5 f'c psi (0.29 f'c MPa) is recommended for estimating the contribution from strain-hardening FRCCs to the shear strength of flexural members, regardless of the member inelastic rotation demand. A critical diagonal crack angle of 60° with respect to the member longitudinal axis is also recommended for determining the number of transverse reinforcement layers effectively providing shear resistance in FRCC beams. A new stiffness damage index, defined as the ratio between the zero force-to-zero displacement secant stiffness and the zero force-to-peak displacement secant stiffness in a given displacement cycle, was proposed as an indicator of the damage in RC and FRCC flexural members. |
