Measurement and Analysis of Cracking Behaviour of RC Beams Strengthened with NSM CFRP Strips Using Digital Image Correlation

Abstract

AbstractNear-Surface Mounted (NSM) Fibre Reinforced Polymer (FRP) technique has been proved to be an effective method to strengthen Reinforced Concrete (RC) flexural elements. At present there is a lack of provisions for predicting crack width, and the number of experimental data regarding crack width and pattern is still scarce for NSM FRP RC flexural members.This paper presents the preliminary results of an extensive experimental programme aiming at studying the effect of different reinforcement arrangements on crack distribution on NSM Carbon-FRP (CFRP) RC beams. For this purpose, one RC beam and seven RC beams strengthened with different configurations of NSM CFRP strips were tested under a 4-point bending configuration up to failure. A pure bending span of 1100 mm was left in order to obtain a significant number of flexural cracks. Crack patterns were registered with a Digital Image Correlation (DIC) system that allowed obtaining the evolution of all cracks appearing in the pure bending span. Two user subroutines were developed so as to automate the procedure of measuring crack spacing and crack width along the height of the beam and during the test. The effect of dimensions, amount and geometrical distribution of the CFRP reinforcement on crack width and crack spacing were analysed and discussed. In general, it was found that NSM CFRP strengthening provided a reduction of crack width and crack spacing. Moreover, crack width decreased with the increase of the NSM CFRP reinforcement ratio. Finally, no significant effect of the groove distribution was detected.KeywordsCrack widthNSM FRPDICServiceabilityExperimental study