Experimental and numerical investigation into flexural bond strength of RC beams exposed to elevated temperature

Abstract

The flexural bond strength of reinforced concrete beams exposed to elevated temperature has been investigated experimentally as well as numerically. The variables such as diameter of bar, lap or development length (Ld), concrete strength and thermal loading has been considered. The normal and high strength (NSC and HSC) RC beams of size 80 × 120 × 900 mm with different Ld provided at mid-span were cast and cured for 28 days. RC beams were then tested in flexure for bond strength after the single heating-cooling cycle of elevated temperature ranging from 200 °C to 800 °C at an interval of 200 °C corresponding to a heating rate of 5 °C/min. for 3 hrs heating duration. The cracks observed in most of the beams were propagating horizontally and were confined along the lap length due to lateral extension of bars causing bond loss when subjected to elevated temperatures. The NSC beams persisted up to 600 °C while HSC beams survived the thermal exposure up to 800 °C with some residual strength. It has been observed that the strength and stiffness of beams decrease with increase in temperature and decrease in lap length. It has also been observed that with decrease in the diameter of rebar result in increased bond strength, while the stiffness of the beam increased the ductility reduced as the diameter of the tension splice increased. Good agreement has been observed between the measured bond stresses and predicted bond stresses using the equations proposed by researchers and design codes. The numerical analysis of RC beams with different splicing length (Ld) has been successfully carried out using the finite element modelling. The numerical results showed an adequate estimate of the experimental results. Further, the numerical studies based on the finite element based model are extended for the parametric studies considering the lap length and the diameter of rebar as variable parameters.