Experimental study and analysis model of flexural synergistic effect of reinforced concrete beams strengthened with ECC

• The flexural synergistic effect of RC beams strengthened with ECC is synthetically investigated. • A synergy analysis model is proposed to determine critical ECC strengthening layer thickness and predict crack propagation pattern. • A critical ECC strengthening layer thickness is determined to obtain the optimal crack resistance. This work aims to synthetically investigate the flexural synergistic effect of reinforced concrete (RC) beams strengthened with engineered cementitious composite (ECC) through both experimental study and analysis model. Eight beam specimens are prepared to investigate the effects of five important parameters on the flexural synergistic effect, including the ECC compressive strength, interface roughness, fiber type, ECC mixture consolidation level, and ECC casting method. The experimental results are analyzed to characterize the failure mode, crack propagation pattern, crack load, crack width, ultimate load, load–displacement curve, and strain distribution at mid-span cross section. Besides, a bond-slip model of ECC and concrete interface is adopted in finite element analysis to simulate and validate failure mode, load–deflection response, and strain distribution at mid-span cross section. More importantly, a synergy analysis model is proposed to determine critical ECC strengthening layer thickness and predict crack propagation pattern. The prediction results of proposed model are in consistent with the experimental results from not only this study but also other research, indicating that the proposed model can effectively predict the crack propagation pattern of RC beams strengthened with ECC. This study is expected to promote a comprehensive understanding for application of ECC for strengthening or retrofits of existing RC structures.