Experimental and analytical research on the flexural behaviour of steel–ECC composite beams under negative bending moments

Abstract

Due to the strain-hardening and multi-cracking properties, engineered cementitious composite (ECC) is a new solution to the cracking issue in the negative bending moment region of steel–concrete composite beams. This paper presents an experimental and analytical study on the flexural performance of composite steel–ECC beams subjected to negative bending moments as well as the tension stiffening behaviour of reinforced ECC (R/ECC) flange slabs. Three beams with different slab materials and reinforcement ratios were tested under a hogging moment. Experimental results demonstrated significant enhancement in stiffness and crack resistance for the steel–ECC composite beams. A practical four-parameter fibre-bridging model was established to describe the strain-hardening behaviour of different ECC materials. Then, a modified analytical tension-stiffening model for R/ECC was formulated considering the strain-hardening behaviour of ECC and rebar–ECC bond–slip interaction based on the conventional tension-stiffening model for reinforced concrete. This modified model was verified by several direct tensile tests of R/ECC members. In addition, by applying the model to the traditional fibre beam–column element model, the mechanical performance and crack opening of general R/ECC structures were derived. The simulation results of the steel–ECC composite beams demonstrated satisfactory accuracy compared with the test results. Finally, a parametric study based on the new model was conducted to identify the influence of several important material and structural parameters on the flexural performance of steel–ECC composite beams under negative moments.