Some issues about the behaviour of external pre-stressed steel–concrete composite beams

A numerical experiment is performed to evaluate the behaviour of externally pre-stressed steel–concrete composite beams (EPSCCBs) up to their ultimate stages, considering second-order effects, tendon material and friction at tendon–deviator locations. The tendon force evolution with loading and slip at the steel–concrete interface is explored. A three-dimensional finite-element model is used to include all these aspects. The idea is to deconstruct the project of eight experimental EPSCCBs with different tendon profiles, considering the above-mentioned issues. The main findings indicate that the inclusion of second-order effects is essential for predicting the stress paths near the collapse loads and slip demands at the steel–concrete interface, while external tendons made of carbon fibre-reinforced polymer (CFRP) can be used as a substitute for classical steel ones, as they presented similar behaviours. The largest tendon force increments occurred for the CFRP tendons compared to other tendons made of glass, aramid and basalt fibre-reinforced polymers. Furthermore, it was found that a friction coefficient between 0.2 and 0.4 at the tendon–deviator interface better matches the available experimental tendon force evolution with loading. This finding seems to counteract the common assumption of using a null friction coefficient as suggested in other works.