Strengthening of short splices in RC beams using Post-Tensioned Metal Straps

This paper investigates the effectiveness of a novel and cost-effective strengthening technique using Post-Tensioned Metal Straps (PTMS) at enhancing the bond behaviour of short lap spliced steel bars in reinforced concrete (RC) beams. Twelve RC beams with a short lap splice length of 10d b (d b = bar diameter) at the midspan zone were tested in flexure to examine the bond splitting failure. The effect of confinement (no confinement, internal steel stirrups or external PTMS), bar diameter and concrete cover were examined. The results show that, whilst unconfined control beams failed prematurely due to cover splitting, the use of PTMS confinement enhanced the bond strength of the spliced bars by up to 58 % and resulted in a less brittle behaviour. Based on the test results, a new analytical model is proposed to predict the additional bond strength provided by PTMS confinement. The model should prove useful in the strengthening design of substandard lap spliced RC elements

Bond strength of short lap splices in RC beams confined with steel stirrups or external CFRP

This paper investigates the bond behaviour of lapped steel bars using fifteen RC beams tested in flexure. Twelve of the beams were designed to fail by bond splitting at midspan, where the main flexural reinforcement was lapped 10 bar diameters. The parameters studied include the amount and type of confinement at midspan (no confinement, internal steel stirrups or externally bonded carbon FRP), concrete cover and bar size. The results show that the CFRP confinement enhanced the bond strength of the lapped bars by up to 49 % with reference to unconfined beams, and improved significantly the overall behaviour of the specimens. The experimental results are compared with existing models to predict the bond strength enhancement provided by CFRP confinement. It is shown that existing models overestimate considerably the CFRP strains and show a large scatter when predicting experimental results. Based on the test results, a new approach to predict the bond strength enhancement due to CFRP confinement is proposed. This can be used during the assessment and strengthening of substandard RC constructions. © 2013 RILEM