21.05: Strength evaluation of steel beams prestressed with CFRP plates

Abstract

The use of CFRP (carbon fibre reinforced polymer) material for repair and strengthening of steel members has numerous benefits over the traditional methods of bolting or welding of steel plates. However, research on the application of CFRP composites to steel structures has still been limited. The RUT's research work was conducted to evaluate the strength of steel I-beams prestressed with CFRP plates and to study the effect of strengthening. The evaluation of flexural behaviour of passively and actively CFRP strengthened beams was the main goal of this research. The strengthening material included CFRP plates with high strength and intermediate modulus of elasticity. The active plates were prestressed with three different levels including 40%, 50% and 60% of the ultimate tensile strength of the CFRP. An innovative anchorage system was applied to posttension CFRP plates against the beam itself. Flexural tests were carried out under 4-point bending on several medium scale steel beams. The beams were loaded in a force-control mode to track their full load response and to reach the ultimate load carrying capacity. A set of performance indicators was evaluated to analyse the behaviour and verify the strength of the tested beams. The performance indicators that have been established are all related to the response of the beams in terms of displacement and these are: ultimate-to-yield load ratio, displacement ductility ratio, effective elastic stiffness, strengthening effect on moment at yield as well as strengthening effect on ultimate moment. On the basis of the test results, the following conclusions are drawn: CFRP prestressed system was effective enough, strengthening steel beam with CFRP plates does not increase the stiffness while enhance the ductility of beam in the plastic range, level of prestressing has no considerable influence on beam performance and failure of prestressed beam is sudden attributable to either anchorage slippage or CFRP rapture. Finally, the effectiveness of strengthening and the influence of various parameters on this effectiveness was established.

Feasibility of Reusing Damaged Steel Beams in Temporary Structures

“…They stated that even though the bearing capacity of the beams was increased, the ductility decreased as the notch size increased and the premature debonding mode of failure took place. Siwowski and Siwowska [8] and Siwowska and Siwowski [9] experimentally compared the flexural behavior of steel beams strengthened with CFRP plates. Four different configurations of strengthened steel plates with a center notch under fatigue load (adhesive-bonded non-prestressed plates and adhesive-bonded prestressed plates) were considered.…”