Structural Engineering Research Projects:

FE Models of GFRP and CFRP Strengthening of Reinforced Concrete Beams

In the last decade, fiber reinforced polymer (FRP) composites have been used for strengthening structural members of reinforced concrete bridges which are structurally deficient or functionally obsolete due to changes in their use or consideration of increased loadings (Kachlakev 1998). Many researchers have found that FRP composites applied to such members provide reliable and cost effective rehabilitation (Kachlakev 1998 and Tedesco et al. 1996).

In some cases the currently available design and simplified analysis tools cannot provide complete and accurate predictions of the structural behavior for reinforced concrete members strengthened with FRP composites, partly due to the fact that these methods were developed originally for behavior of steel reinforced concrete structures. To overcome these difficulties, the finite element method (FEM) is employed in this study to analyze the behavior of FRP-strengthened reinforced concrete beams.

Over the past few years, a number of researchers have studied the behavior and modeling of reinforced concrete members strengthened with FRP composites. In these studies, the FE method was used with eight-node isoparametric elements and a smeared cracking approach for modeling the concrete; and two dimensional plate elements (Malek et al. 1998) or truss elements (Ross et al. 1999) for the FRP composites.

Load-Compressive Strain Plots for Concrete: (a) Unstrengthened Beam; (b) Flexural-Strengthened Beam; (c) Shear-Strengthened Beam; (d) Flexural plus Shear-Strengthened Beam (Experimental beam did not fail)

In the experiment conducted at Oregon State University, four beams (McCurry 2000) were tested.The analysis results were compared with data obtained from full-scale beam tests through the linear and nonlinear ranges up to failure.

Experimental Beams at Failure: (a) Unstrengthened Beam; (b) Flexural-Strengthened Beam; (c) Shear-Strengthened Beam

The general behaviors of the FE models show very good agreement with observations and data from the full-scale beam tests. The load-strain plots showing local behavior at selected locations from the FEA in general show good agreement to the experimental data. Load-deflection plots at midspan from the FE models have similar trends with those from the experimental beams, but the FE models are slightly stiffer than the experimental beams both in the linear and nonlinear ranges. The effects of bond slip (between the concrete and steel reinforcing) and microcracks occurring in the actual beams were excluded in the FE models and resulted in the higher stiffnesses. Crack patterns at the final loads from the FE models correspond well with the failure modes of the experimental beams. Final loads from the FEA are lower than the experimental ultimate loads by 6%-18%. The three-dimensional cracking FE models presented in this study demonstrate the behaviors of the full-scale beams and provide additional large-scale test results and a better understanding of FRP-strengthened concrete beams.

Knowledge gained from this study can be used to conservatively estimate load-carrying capacity of FRP-reinforced concrete beams using FE models. The FEM models can be used in further studies to develop design rules for strengthening reinforced concrete members using FRP. It should be pointed out that one of the limitations of these FE results is that they predict failures that are not failures of, or in, the FRP or epoxy bond. A multitude of other failure modes may exist and need to be investigated in future research.

 

Back to Structural Engineering Research Page.