Keywords: steel beam, glass fibre, retrofit, adhesive, flexural, bridge.

Steel members in bridges are subject to corrosion and environmental conditions as well as fatigue. In other cases, the demands of increased service load makes rehabilitation indispensable. Normally, a cost effective solution for such problems puts bridge replacement at the bottom of the list, unless it is inevitable. Accordingly, a cost-effective rehabilitation technique with minimal disruption is required. Strengthening steel bridges using either fibre reinforced polymers (FRP) or glass fibre reinforced plastics (GFRP) represents a very attractive solution. The FRP material possesses several advantages such as high strength to weight ratio, durability, ease of handling and installation, etc. Very few studies were performed on the rehabilitation of steel structures using FRP. When bonded to steel flexural bridge members, FRP plates can increase ultimate capacity and reduce stress at service, thus increasing the service life span of the bridge. A recent study [3] showed that the CFRP sheets could significantly restore and increase the ultimate load carrying capacity of the girders and also increase the stiffness of damaged composite girders. Adhesive (peel and shear) was the predominant mode of failure in all cases.

The enhancement in the flexural capacity of steel beams due to the addition of glass fibre reinforced plastic (GFRP) layers also has been assessed experimentally and studied by [1], where a composite steel bridge was designed to satisfy the serviceability and strength limit state design conditions using the loads described by the Canadian highway bridge design code, CHBDC [2]. The dimensions of the bridge were carefully selected such that no reserve in strength exists under the specified loads. Accordingly, the bridge would become unsafe in case of increase in the specified live load values.

This paper presents an innovative technique to enhance the flexural capacity of composite steel bridges using glass fiber reinforced plastic plates (GFRP). The concept involves bonding GFRP plates to the bottom flanges of the steel girders using a heavy duty adhesive system. A detailed non-linear finite element modeling, that incorporates adhesive properties based on previously conducted test results, is conducted in this study. Moving load analysis is conducted first to determine the critical load configuration corresponding to the absolute maximum of various parameters that might govern the failure of the retrofitted girders.

The analyses revealed that the same load configuration leading to absolute bending moment values is critical for concrete, GFRP and adhesive peel stresses. The absolute maximum adhesive shear stress value is governed by another load configuration corresponding to maximum shear force at the section located at the edge of the GFRP sheet. The study proceeded by conducting non-linear analyses using three different values for the length of the GFRP sheets under the critical load configuration established from the moving load analysis. A 25% increase in the truck load carrying capacity of the girders can be achieved using this retrofitting scheme without suffering from premature failure in either, the concrete, GFRP or adhesive. No benefit is achieved by increasing the length of the GFRP sheet beyond this value.

1

Abushagur, M., Enhancement of flexural capacity of steel beams using GFRP, Ph.D. Thesis, Dept. of civil Eng., University of Western Ontario, 2004.

2

CAN/CSA-A6-00, Canadian highway bridge design code (CHBDC), Canadian Standards Association, Rexdale, Ontario, 2000.

3

Tavakkolizadeh M. and Saadatmanesh H., "Strengthening of steel-concrete composite girders using CFRP sheets", Journal of Structural Engineering, pp. 30-40, 2003. doi:10.1061/(ASCE)0733-9445(2003)129:1(30)

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