Contents lists available at ScienceDirect Composite Structures journal homepage: www.elsevier.com/locate/compstruct Experimental and analytical study on the flexural performance of CFRP- strengthened RC beams at various pre-stressing levels Khuram Rashid a,b , Xiaoda Li a , Jun Deng a, ⁎ , Yan Xie a , Yi Wang a , Sigui Chen a a School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou, Guangdong, PR China b Department of Architectural Engineering and Design, University of Engineering and Technology Lahore, Pakistan ARTICLE INFO Keywords: RC beam Flexural strengthening CFRP plate Pre-stressing level Flexural performance Deflection ABSTRACT This work aimed to evaluate the flexural performanceof RC beams strengthened by carbon fibre-reinforced polymer (CFRP) plates, which were applied at the soffit of beams and pre-stressed at various levels. Six RC beams were prepared that were pre-stressed at 0, 20 and 40% of the ultimate strength of the CFRP plate, and they were subjected to four-point bending tests to evaluate the cracking load, yield load, and ultimate load of the beams. The variation in strain of the CFRP plate and deflection were monitored under applied load. With the pre- stressing level, it was observed that all types of the aforementioned loads were increased, whereas the deflection and ductility were decreased. Cracking moment was evaluated analytically by proposing one modification factor into existing equation that was obtained by regressing the data of 41 analogous RC beams. Modified equation was also verified by the calculated deflection, which have close resemblance with the experimental observations. 1. Introduction Reinforced concrete (RC) structures are widely constructed all over the world, but mechanical deterioration is an important issue for such structures when exposed to harsh environments. Repairing, re- habilitating and strengthening such deteriorated structures are re- quired, and several materials and techniques have been developed for such purposes in recent decades. In materials, fibre-reinforced polymer (FRP) has received increased attention in civil engineering applications due to its advantages, such as its non-corrosive property, light weight, higher ultimate strength, short curing time and easy application [1]. FRPs are widely used, especially carbon fibre-reinforced polymers (CFRPs) as sheets and as strips/plates that have relatively large cross- sectional areas, which can achieve greater strengthening effects if produced by a closely controlled pultrusion process. CFRPs are widely used as a flexural strengthening reinforcement in concrete structures [2,3], but de-bonding is the most common failure mode in such structures. Various types of de-bonding failure modes were observed, such as concrete cover separation, end-peeling or in- termediate crack de-bonding; several models have been proposed to predict de-bonding failure modes [4–12]. FRP U-jackets are commonly used to avoid de-bonding. Recently, it was reported that inclined U- jacketing can effectively mitigate both intermediate crack de-bonding [13] and concrete cover separation [14].Efforts have also been made by researchers to avoid such failure modes by providing an anchorage system that can impede stress concentration. Peeling off can be avoided by providing an adequate anchorage, as the de-bonding occurs due to stress concentration. CFRP is kept aligned and gripped by the anchorage system at both ends and able to enhance flexural performance of strengthened RC beam. However, de-bonding failure was still observed, and the strength of the CFRP was not fully utilized. An alternate way to improve the efficiency of CFRP-strengthened RC structures is by pre-stressing the CFRP. Several ways were adopted for pre-stressing. First, the RC beams were pre-stressed prior to the appli- cation of the CFRP, and then, the pre-stressing force was applied on the bonded CFRP by releasing the pre-stressed force (i.e., by cambering) [15]. Second, the pre-stressing force was applied on the CFRP by an independent frame reaction [16]. In both cases, the flexural perfor- mance was improved, but the mode of failure was still de-bonding. Another way to pre-stress the CFRP is the utilization of an end ancho- rage system, wherein a pre-stressing force is applied on the bonded uncured CFRP sheet/plate on one end, while the other end has already been fixed in a mechanical anchorage system [17,18]. This third way of pre-stressing the CFRP, which is the updated and recent method, may mitigate the issue of de-bonding failure modes. However, the perfor- mance of the strengthened structures depends on the type of anchorage system whose availability varies due to the different boundary condi- tions imposed by the deteriorated structures. The advantages and https://doi.org/10.1016/j.compstruct.2019.111323 Received 31 December 2018; Received in revised form 25 June 2019; Accepted 16 August 2019 ⁎ Corresponding author at: School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou, Guangdong, China. E-mail address: jdeng@gdut.edu.cn (J. Deng). Composite Structures 227 (2019) 111323 Available online 17 August 2019 0263-8223/ © 2019 Elsevier Ltd. All rights reserved. T