Rheological modeling and finite element simulation of epoxy adhesive creep in FRP-strengthened RC beams

Abstract

We have shown that a significant creep occurs at the concrete–fiber reinforced polymer (FRP) interface based on double shear long-term test. The primary test parameters were the shear stress to ultimate shear strength ratio, the epoxy curing time before loading as well as the epoxy thickness. The test results showed that when the epoxy curing time before loading was earlier than seven days the shear stress level significantly affected the long-term behavior of epoxy at the interfaces, and in particular the combined effect of high shear stress and thick epoxy adhesive can result in interfacial failure if subjected to high-sustained stresses. In this paper, based on the previous experimental observations, an improved rheological model was developed to simulate the long-term behavior of epoxy adhesive at the concrete–FRP interfaces. Furthermore, the newly developed rheological creep model was incorporated in finite element (FE) modeling of a reinforced concrete (RC) beam strengthened with FRP sheets. The use of rheological model in FE setting provides the opportunity to conduct a parametric investigation on the behavior of RC beams strengthened with FRP. It is demonstrated that creep of epoxy at the concrete–FRP interfaces increases the beam deflection. It is also shown that consideration of creep of epoxy is essential if part or the entire load supported by FRP is to be sustained.

Keywords:

• creep
• epoxy
• finite element analysis
• FRP
• rheological modeling

Acknowledgment

This work has been financially supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0020944).

Notes

aF and B indicate front and back faces of double shear test specimens (refer to Figure 1).

bShear stress applied to test specimens.

cUltimate shear strength of test specimens (0.56 MPa).

dEpoxy thickness.

aCoefficient of Hookean spring in branch I in MM model.

bCoefficient of Hookean spring in branch II in MM model.

cViscosity of the dashpot fluid in branch I.