Time-dependent behaviour of precast concrete sandwich panels

Abstract

The time-dependent behaviour of precast concrete sandwich panels (PCSPs) is investigated in this thesis, with particular focus on panels made with diagonal-bar FRP connectors that are anchored to the steel reinforcement and with two concrete layers of the same thickness. The instantaneous structural response of PCSPs is studied first, which provides a basis for the long-term analysis. Within this, a finite element (FE) model was developed and an experimental program that included testing of ten full-scale panels to failure was conducted. The panels under 4-point bending exhibited partial composite action and suffered typical flexural failure via yielding of steel reinforcement. The panels under eccentric axial compression showed nonlinear behaviour and failed by a limit-point type of buckling failure. Good correlation between the FE results and the experimental ones was observed. An experimental study was then conducted to investigate the effect of shrinkage on the early-age behaviour of PCSPs. Five full-scale panels were tested and a FE model was developed, which correlated well with the experimental results. The results showed that a bilinear shrinkage profile through the thickness of each concrete layer can be used. It was found that cracking due to early-age shrinkage can happen if curing is not properly implemented or if relatively high quantity of reinforcement is used. The numerical investigation of the time-dependent response of PCSPs is conducted by developing a nonlinear long-term model in the user subroutine UMAT of ABAQUS. The experimental study that consisted of testing four PCSPs under sustained loads provided a validation of the FE model. Two panels were loaded under 4-point bending and the other two were subjected to eccentric axial compression. The results showed that creep of concrete can improve the composite action in panels that were under bending but it can also cause creep buckling in axially loaded panels. Based on the results presented in this thesis, it can be concluded that the time-dependent response of PCSPs is a complex phenomenon that needs to be considered in their design. The FE models developed here provide an effective tool to analyse their behaviour and to give predictions of their structural capacities.