Abstract
Studies on U-wraps generally focus on the experimental results and mechanisms of the shear strengthening effect. Only a few studies have focused on the anchoring effect of the longitudinal FRP due to addition of the U-wrap. Lee and Lopez (Constr Build Mater 194:226–237, 2016) have found experimentally from pull-out tests that incremental changes occur in the debonding strain at the concrete-FRP interface depending on the various type of U-wraps. The proposed numerical method using the Frictional Bond-Slip (FBS) model has been validated by comparing the pull-out test results (Lee and Lopez Constr Build Mater 194:226–237, 2016). In the present study, the FBS model was applied to characterize the behavior of a large scale FRP strengthened T-beam with multiple U-wraps. First, the 2-dimensional (2D) model for pull-out test was developed. Debonding load and behavior of the model were compared with both the experimental results (Lee and Lopez Constr Build Mater 194:226–237, 2016) and the simulation results of a 3-dimensional (3D) model from a previous study (Lee and Lopez Constr Build Mater 194:226–237, 2016). Next, the 2D model was applied to model the behavior of a large scale FRP strengthened T-beam with multiple U-wraps. The conducted 2D simulation using the proposed FBS model predicted well the strains at various locations on the FRP sheet, the flexural capacity and complex failure mode of the FRP strengthened beam with several U-wraps. The proposed FBS model was also applied to other comparable studies, and debonding strains were successfully predicted within an margin of error of 7%. Using the validated model, a parametric study of the FRP strengthened T-beam was conducted with various key parameters of the U-wrap, such as the angle of U-wrap and the number of U-wrap.
Highlights
In order to prevent debonding failure of concrete-FRP interfaces, several different types of new anchoring systems for externally bonded FRP applications have been introduced (e.g. Zhang and Smith 2012; Lee et al 2009; Ozbakkaloglu and Saatcioglu 2009; Triantafillou 1998; Grelle and Sneed 2013)
The anchoring effects were verified by Lee and Lopez (2016) through the experimental studies, where most of the U-wrap pull-out specimens showed higher debonding strains than the strains predicted from Chen and Teng’s eqiations (2001)
Since the equations by Chen and Teng (2001) for prediction of debonding strain were developed under the pull-out loading conditions without any U-wraps and widely accepted for the prediction of FRP debonding strain, this result indicated that there was a certain amount of anchoring effect from the U-wraps
Summary
In order to prevent debonding failure of concrete-FRP interfaces, several different types of new anchoring systems for externally bonded FRP applications have been introduced (e.g. Zhang and Smith 2012; Lee et al 2009; Ozbakkaloglu and Saatcioglu 2009; Triantafillou 1998; Grelle and Sneed 2013). Past research (Lee and Lopez, 2016) reported experimentally that frictional behavior between the debonded surfaces of concrete and FRP sheet is a key factor to control the anchoring effect of the FRP U-wrap. The observed friction between a FRP sheet and the surface of the concrete in the U-wrap region has been incorporated into an interfacial model which predicts the debonding strain of the FRP sheet under the U-wrap(s) It is the frictional bond-slip (FBS) model which was used to satisfactorily predict the debonding failure in the U-wrap region and the residual strength of the U-wrap after debonding failure against the pull-out loadings in a threedimensional (3D) space (Lee and Lopez 2019). There was a limited study regarding a FBS model (Lee and Lopez 2019) which has been only applied to the concrete block with an attached FRP sheet under pull-out loading condition. Detailed information on FBS model and calculations for each point that are shown in Fig. 2 can be found in Lee and Lopez (2019)
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