Flexural capacity design model of reinforced concrete beams strengthened with hybrid bonded CFRP

Abstract

In order to improve the calculation methodology for the flexural capacity of RC (Reinforced Concrete) beams strengthened with HB-CFRP (Hybrid Bonded-Carbon Fiber Reinforced Polymer), three-point bending tests were conducted in this study. The experimental setup involved 9 HB-CFRP strengthened T-shaped beams and 1 unstrengthened beam for comparison. The effects of anchor spacing, anchor pressure, CFRP thickness, and anchor distribution pattern on the flexural performance of strengthened beams were investigated. Additionally, the development of the full range load-deflection curves of the HB-CFRP strengthened specimens was analyzed. Two bond strength models (the Wu model and Liu model) were modified. Six parameters were considered in the modified model, namely, the CFRP elastic modulus, CFRP thickness, number of mechanical fasteners in the shear span, CFRP-concrete width ratio, concrete cylinder compressive strength and normal pressure applied to the mechanical fasteners. The accuracy of the modified models was compared on the basis of three specifications. Results indicated a notable enhancement in the flexural capacity of the strengthened beams, ranging from 61.1 % to 158.1 % compared to the unstrengthened beam. Taking the ACI specification as an example, the mean value and coefficient of variation (COV) of the flexural capacity obtained by directly using the Wu model were 1.187 and 0.169, respectively; the results obtained by using the modified Wu model based on the measured FRP strain were 1.038 and 0.125, respectively; and the results obtained by using the modified Wu model based on the ACI reversed-calculated strain were 1.012 and 0.106, respectively. After the strengthened beam reached the peak load, the load then decreased abruptly to the vicinity of the moment mid-span deflection curve of the reference beam. As the loading continued, the resistance improved by 27.4 %∼79.3 % due to the increase in interface friction in the mechanical fasteners and concrete.