Time-dependent behaviour of RC beams under eccentric combined loads as a unit of beam-column joint assemblies made from normal strength concrete without/with CFRP wraps

Abstract

The influence of sustained eccentric loads including torsion on the time-dependent behaviour of monolithically framed RC beams into columns is investigated in this paper. The adopted experimental program entails a number of beam-column assemblies tested under sustained concentric and eccentric combined loads (bending, shear, and torsion). The presence of Fibre Reinforced Polymers (FRP) wraps applied to the beam is considered and the time-dependent performance was thoroughly assessed. The outcomes of the experimental program complemented with finite element (F.E.) results illustrated a significant increase in the time-dependent beam’s twisting and deflection levels. The rise in the beam’s time-dependent deflections was quantified in comparison with those predicted according to Eurocode 2. This rise can be explained by the extent of torsional cracks observed, accompanied by high strain levels, resulting from the interaction between combined loads and the time-dependent deformations of concrete. While the FRP wraps considerably improved the time-dependent torsional stiffness compared to the un-strengthened specimens. The numerical models under different loads ratios (torsion to bending-shear ratio) confirmed the role of the level of combined loads and the developed time-dependent cracks of reducing the members’ stiffness and affecting the twisting levels and hence increased the deflection values. A refined approach of the Eurocode 2 modal has been proposed which considers the interaction of combined forces and hence, the developed stresses on the degrees of the loss of tension stiffening.