Hygro-thermal–mechanical coupling analysis for early shrinkage of cast in situ concrete slabs of composite beams: Theory and experiment

Abstract

The steel girder of the steel–concrete composite bridge restricts the deformation induced by variations in the temperature and relative humidity of the concrete. Thus, concrete component is prone to early cracking, which significantly impacts its durability. This study investigated the hygro-thermal–mechanical behaviors and early cracking mechanism of the concrete slab in composite beams using field measurements of composite beams and coupled finite element simulation. The findings demonstrate that temperature significantly impacts relative humidity development and that temperature and relative humidity are the primary determinants of early stress development of concrete. Then, a parameter study was conducted with four working conditions, including adiabatic boundary, heat open boundary, moisture-heat open boundary for the upper surface, respectively, as well as the test condition, to investigate the impact of temperature and humidity convection on the cracking of the concrete during the curing period. The results indicate that, whereas ambient humidity mainly influences the incidence of shallow cracks, ambient temperature significantly impacts early cracking that can fully propagate inside the concrete deck with thickness less than 25 cm. The existence of steel girder alters the original temperature boundary of the concrete surface at the steel–concrete bonding interface, which then directly or indirectly influences temperature and relative humidity distribution and stress of the concrete slab in the nearby 5–10 cm range and even causes the concrete enormous cracking risk. For the composite beams cast in volatile environments, consideration should be given to the excellent thermal conductivity of the steel girders. Heat preservation and moisture retention needs of the cast-in-place steel–concrete composite beam should be appropriately enhanced to prevent early cracking of the concrete deck.