Intermediate Crack-induced Debonding Failure Research Articles

Modeling NSM FRP strengthened RC beams under fatigue due to IC-debonding

This paper presents an analytical model proposed to predict the flexural fatigue behavior and fatigue life of reinforced concrete (RC) beams strengthened with near-surface mounted (NSM) fiber reinforced polymer (FRP) reinforcements subject to intermediate crack-induced debonding failure. In deriving this model, a trilinear behavior is assumed for the bond-slip relationship of FRP-concrete interface. Based on a model previously developed for strengthened beams under monotonic loading, the proposed fatigue model considers the fatigue bond heterogeneity by imposing a degradation law for the peak interfacial shear stress. Theoretical solutions to the flexural behavior throughout the fatigue life are obtained by imposing appropriate boundary conditions. The predicted fatigue life under debonding failure mode and flexural behavior (e.g., tensile strain of the NSM reinforcement) are further verified by comparisons with existing experimental data, where good agreement is reached. The subsequent parametric study shows that higher concrete compressive strength and bond strength of NSM improves the flexural behavior under fatigue and elongates the fatigue life. The diameter and Young’s modulus of the NSM reinforcement have insignificant effect on the fatigue flexural behavior.

Behavior of reinforced concrete beams strengthened with CFRP rod panels CRP 195

This paper investigates the behavior of reinforced concrete beams strengthened in flexure using externally bonded carbon fiber reinforced polymer (CFRP) rod panels (CRPs) fabricated using 4 mm rods spaced at 9.5 mm. The experimental program consisted of a control beam and three beams strengthened with either a continuous CRP, a spliced CRP with two half-length CRPs spliced through a 150 mm finger joint, or a spliced and end-anchored CRP. Spliced panel performed similar to the continuous one, with no debonding observed at finger joint. They resulted in a comparable strength increase relative to the non-strengthened control beam of 95 and 104%, respectively, and failed by concrete cover separation (CCS) at CRP end. When the spliced CRP was end-anchored, the increase in strength was 195% relative to the control beam, with the finger-joint still intact, and the failure mode changed to intermediate crack-induced debonding (ICID). The analytical model, developed from sectional analysis and strength models for debonding failures, is capable of predicting the load-deflection response and ultimate loads, including the two observed debonding failures. For CCS failure, two models are presented, one is based on the concrete tooth model, and the other on the shear capacity model. The ICID failure was based on limiting the CFRP strain in accordance with ACI 440.2R-17 design guide. Results showed a good correlation between analytical predictions and test data.

Reliability analysis of intermediate crack-induced debonding failure in FRP-strengthened concrete members

This paper presents a study on the reliability analysis of intermediate crack-induced (IC) debonding failure, which is a dominant failure mode in concrete members strengthened with externally bonded fibre-reinforced polymer composites. First, the probabilistic characteristics of the model uncertainties for several typical IC debonding models are evaluated and presented, based on a comprehensive test database that contained 217 specimens that experienced IC debonding failure. Second, a Monte Carlo simulation analysis is performed to examine the variability in the IC debonding resistance considering the scatterness of different design variables. Subsequently, the reliability index is estimated by utilising the reliability analysis method, first-order reliability method, for each design case. The effect of each design variable on the average reliability index is examined. Finally, reduction factors for the investigated IC debonding models are calibrated based on the reliability analysis with the aim of meeting a target reliability index of 3.5.

Assesment of Main Models for Predicting Debonding Load-Bearing Capacity against Intermediate Crack-Induced Debonding Failure in FRP-Strengthened RC Beams

intermediate crack-induced debondingis one of the most dominant failure modes in FRP-strengthened RC beams. Different code models and provisions have been proposed to mitigateintermediate crack-induced debondingfailure.However, these models and provisions can not mitigate this failure mode effectively. Recnetly, new models have been proposed to solve this problem. Out of all the existing models, four typical ones are investigated in the current study. A comprehensivecomparison among these models is carried out in order to evaluate their performance and accuracy. Test results offlexural specimens with intermediate crack-induced debonding failurecollected from the existing literature are used in the current comparison. The effectivenessand accuracy of each model have been evaluated based on these experimental results. It is shown that the current modals are all conservative and inadequite to effectively mitigate intermediate crack-induced debonding in flexurally strengthened members.

Evaluation of Main Code Models for Predicting Flexural Load-Bearing Capacity against Intermediate Crack-Induced Debonding in FRP-Strengthened RC Beams

Intermediate crack-induced debonding is one of the most dominant failure modes in FRP-strengthened RC beams. Different code models and provisions have been proposed to predict intermediate crack-induced debonding failure. Out of all the existing code provisions and models, four typical ones are investigated in the current study. A comprehensive comparison among these code provisions and models is carried out in order to evaluate their performance and accuracy. Test results of flexural specimens with intermediate crack-induced debonding failure collected from the existing literature are used in the current comparison. The effectiveness and accuracy of each model have been evaluated based on these experimental results. It is shown that the current recommendations are inadequite to effectively mitigate intermediate crack-induced debonding in flexurally strengthened members.

Evaluation of Allowable FRP Tensile Strain in Main Codes for Mitigation of Debonding Failure in FRP-Strengthened RC Beams

Intermediate crack-induced debonding is one of the most dominant failure modes in FRP-strengthened RC beams. Different code models and provisions have been proposed to mitigate intermediate crack-induced debonding failure. Out of all the existing code provisions and models, six typical ones are investigated in the current study. These available guidance for mitigating debonding failure of externally bonded fiber reinforced polymer composites applied to concrete is evaluated based on data obtained from experimental programs. It is shown that the current recommendations are inadequate to effectively mitigate intermediate crack-induced debonding in flexural members.

Investigation on Intermediate Crack Induced Debonding Failure of FRP Laminates in Flexurally FRP-Strengthened RC Beams

Debonding failure is commonly observed in FRP-strengthened RC beams. It can be classified into two types: plate end debonding and intermediate crack induced debonding. Intermediate crack induced debonding is the main failure mode in FRP-strengthened RC beams.There is no specialized experiment study on this failure mode. To investigate intermediate crack induced debonding failure of FRP-strengthened reinforced concrete beams, 9 CFRP-strengthened reinforced concrete beams were tested. Based on the investigation of the strain in the FRP laminates, the width of the main crack and tributary crack, as well as the phenomena of the test beams, the whole debonding process can be separated into three stages: initial debonding stage, stable debonding stage, and the final debonding failure. The fundamental reason of intermediate crack indued debonding are the opening-up of intermediate crack and the flexural deformation induced high interfacial shear stress and peeling stress. When the principal tension stress acting on the concrete substrate exceeded the tension stress of concrete, the CFRP laminate would debond from the concrete substrate.