Shear crack kinematics in reinforced engineered cementitious composite (ECC) beams

The fiber's bridging effect across the shear cracks is considered to play an important role of resisting shear in engineered cementitious composite (ECC), and fiber reinforced material in general. To quantify the shear crack kinematics (i.e., shear crack opening and sliding displacements) in reinforced ECC (R/ECC) beams, a crack measuring algorithm based on the full-field displacement spectrum is developed by using the Digital Image Correlation (DIC) technology. In addition, a novel distributed strain-measuring methodology was used to detect the strain distribution along the transverse and longitudinal reinforcement. Reinforced beams made of traditional concrete (R/C) and mortar (R/M) were used as reference. Through aforementioned monitoring schemes, the role of matrix (V_c) and stirrups (V_s) in shear resistance mechanism could be independently understood and evaluated. The R/ECC beams exhibited much higher V_c than the reference reinforced concrete (R/C) beams (by 68%∼104%). Nevertheless, the shear crack measuring results revealed that the higher shear strength in R/ECC did not always result from the fiber's bridging effect across the critical shear crack (CSC) but of high shear-resisting contribution from ECC in shear-compression zone. For a better understanding of the shear failure mechanisms, phenomenological models of shear crack kinematics in R/C and R/ECC beams are proposed.