Analysis of the effect of shoring on the behaviour of reinforced concrete slabs

The purpose of this work is to study the influence that the construction stage has on the distribution of stresses and strains in solid slabs. To that purpose, a numerical simulation framework for thermomechanical analysis has been implemented and deployed, with due account to the evolution of concrete properties at early ages. This framework was then used to simulate the behaviour of several alternative procedures to define the shoring system and scheduling that can be adopted in the construction phase, with the aim of identifying the best practices to control and reduce the residual stresses attained during the construction stage, which may in turn be responsible for less-than-optimum cracking behaviour in service. The results obtained confirmed that, for the particular case under study, delaying the shoring removal until concrete has reached its 28-day characteristic strength corresponds in fact to the best practice as it reduces the stresses and prevents cracking of the slab in the first 28 days. However, it was also seen that other more ambitious practices, leading to an early withdrawal of the shoring (before 28 days), are also perfectly acceptable in terms of stresses and deformations in the slab under study. Only in premature withdrawal schemes (before 7 days) the likelihood of early cracking is more significant, and so these situations can in fact demand a sophisticated study of stress history to adequately take into account the influence of the initial stresses on the service life behaviour of the slab.The authors gratefully acknowledge the support of the CERISICIST Research Institute, IST, University of Lisbon and the FCT (Foundation for Science and Technology). Funding provided by the Portuguese Foundation for Science and Technology (FCT) and COMPETE2020 to the Research Project PTDC/ECM-EST/1056/2014 (POCI-01-0145-FEDER-016841), as well to the Research Unit ISISE (POCI-01-0145-FEDER-007633) are gratefully acknowledged.