Behaviour of continuous steel-concrete composite beams strengthened with CFRP sheets at hogging-moment region

Although the use of carbon fibre reinforced polymer (CFRP) materials for strengthening reinforced concrete structures and steel structures is well established, relatively few works have been reported for the strengthening of steel-concrete composite structures, especially at their hogging-moment region. In this paper, an experimental program consists of eight beam specimens with different degrees of shear connection, numbers of layers of CFRP sheets and strengthening methods was conducted. The experimental results show that adding CFRP sheets on the top of the concrete slab at hogging-moment region has a great effect on the structural performance in terms of ultimate loading capacity, load-deflection and load-slip responses, crack propagation, ductility, and failure mode, etc. The hybrid bonded FRP (HB-FRP) technique is firstly applied for the strengthening of steel-concrete structures at hogging-moment region in this study, and the advantages of the HB-FRP technique is proved through the comparisons with the externally bonded (EB) method. Based on the experimental observations, an analytical method for estimating the ultimate moment capacity of the strengthened composite beam at hogging- moment region is developed, for which the validity is verified against the experiment results.