Numerical simulation of steel-plate strengthened concrete beam

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Strengthening with epoxy bonded steel plate is one of the most widely used techniques for flexural upgrading of reinforced concrete (RC) beams. However, debonding failure at the plate cut-off zone and or in the vicinity of flexure and shear cracks leads to catastrophic failure of the upgraded beams. This particular failure depends on several factors such as the distance of plate curtailment from the support, plate thickness and the provision of end anchors. Since the conventional beam theory cannot predict the debonding failure of such beams, a finite element model capable of predicting the overall behavior of strengthened beams including different failure modes accurately is developed.

This paper presents the formulation of finite elements and material models and simulation results of some RC beams tested for flexural strengthening with epoxy bonded steel plates.

Bonding of a steel plate with epoxy adhesive on the tensile side of a reinforced concrete (RC) beam is one of the most accepted and widely used techniques for flexural strengthening. A number of research works have been conducted on this technique in different parts of the world over the past several decades [1-9]. Despite its long history, a unified and rational design method for strengthening of RC beams with bonded steel plate has not emerged so far. This is partly because most of the studies have been conducted experimentally and partly due to different failure modes that the strengthened beams undergo at ultimate states such as flexural failure, shear failure and debonding failure. Debonding failure due to high stress concentrations at the interface between the steel plate and concrete at plate end and or in the vicinity of shear and flexural cracks is of a catastrophic nature, which is different from the classical flexural and shear failure of plate bonded beams. Debonding failure prevents the strengthened beam from attaining its full flexural capacity.

Thus, the most important point in strengthening techniques is to avoid this type of failure in order to achieve full load-beating capacity maintaining complete integrity of the concrete beam and strengthening steel plate. Debonding is a complex phenomenon that depends on properties of adhesive, adherents, and surface condition of bonding interfaces. In order to establish a rational design method for practical application, detailed study considering wide range of variables is indispensable. Thus, the demand on a generalized tool for analysis of the plate-bonded beam that can predict accurately the overall behavior including different failure modes cannot be overemphasized.

Plate-bonded RC beams are usually analyzed by employing the principles of compatibility of deformations and equilibrium of forces [10]. Such models are normally based on the assumption of perfect bond between the concrete and steel plate and thus cannot model the debonding phenomenon of the plate from concrete beam. Ziraba and Baluch [11] have presented a computational model for analysis by using finite element method (FEM), which consists of a thin layer interface element for epoxy joint between the RC beam and strengthening steel plate. However, their model lacks the effects of end anchors, which are generally used at the plate cut-off zone in practical situations that have significant positive effect against debonding of plate from concrete. Furthermore, the simulations were limited to a few cases and the main parameter dealt was only the plate thickness whereas an important parameter such as plate curtailment distance from the support was not covered.

The purpose of this study is to develop a generalized FEM model for the analysis of RC beams strengthened against flexure by epoxy bonded steel plates at their tensile side. The model takes into account the effect of slip between concrete and the steel plate as well as the effects of end anchors (in the form of anchor bolts) and the non-linear behavior of concrete, reinforcing bars and steel plate.

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Concrete Beam

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