Strength model for end cover separation failure in RC beams strengthened with near-surface mounted (NSM) FRP strips

Abstract

Abstract:As an alternative to externally bonded FRP reinforcement, near-surface mounted (NSM) FRP reinforcement can be used to effectively improve the flexural performance of RC beams. In such FRP-strengthened RC beams, end cover separation failure is one of the common failure modes. This failure mode involves the detachment of the NSM FRP reinforcement together with the concrete cover along the level of the steel tension reinforcement. This paper presents a new analytical strength model for end cover separation failure in RC beams strengthened in flexure with NSM FRP strips (i.e. rectangular FRP bars with a sectional height-to-thickness ratio not less than 5), which was formulated on the basis of extensive numerical results from a parametric study undertaken using an efficient finite element approach. The proposed strength model consists of an approximate analytical equation for the debonding strain of the FRP reinforcement at the critical cracked section and a conventional section analysis to relate this debonding strain to the moment acting on the same section (i.e. the debonding strain). Once the debonding strain is known, the load level at end cover separation of an FRP-strengthened RC beam can be easily determined for a given load distribution. Predictions from the proposed strength model are compared with those of two existing strength models of the same type and available test results, which shows that the proposed strength model is in close agreement with test results and is far more accurate than the existing strength models.

Reinforced concrete beams strengthened in flexure with near-surface mounted (NSM) CFRP strips: Current status and research needs

“…debonding is also an important debonding failure mode, especially for NSM FRP-strengthened RC beams with a relatively large beam width [28]. The present paper aims to clarify the failure mechanism of the above debonding failure modes, to summarize the established strength models and to identify the gaps of knowledge for future research.…”

“…These two models can be also applied to NSM FRP strip-strengthened RC beams with proper modifications. More recently, Teng et al [28] developed a strength model for end cover separation in NSM FRP strip-strengthened RC beams, also based on the "concrete tooth" concept. These three strength models are described here followed by a discussion of their performance.…”

“…[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], theoretical [e.g. 14,15,19,[21][22][23][24][25][26][27][28][29] and numerical [e.g. 9, 15, 30-32] studies into the behaviour of concrete structural members strengthened with various NSM FRPs.…”

Simulating concrete cover separation in RC beams strengthened with near-surface mounted reinforcements

“…Al-Mahmoud et al [12] also applied a method with a similar concept to the concrete tooth model in conjunction with finite element modelling. The most recent method is the model by Teng et al [13], which is a model formulated from finite element analysis. All of the methods mentioned above can be used to predict concrete cover separation, although the accuracy varies from one model to the other.…”

Experimental Study on Fracture Behaviors of Concrete Beams Strengthened with FRP Sheet of Different Width

“…For the failure mode of the FRP reinforced concrete beams, the interfacial bond failure, occurs before the full strength capacity of the laminate can be developed [10]. Teng studied the end cover separation failure in RC beams strengthened with near-surface mounted FRP strip [11]. A review on the bond behavior of FRP NSM systems in concrete was investigated in [12].…”