Enhancement of moment resistance of steel beams with initial imperfections and residual stresses by using stiffeners and GFRP plates

Abstract

The present study proposes three strengthening solutions for wide flange steel beams having residual stresses and initial imperfections. In Solution 1, a midspan web stiffener is applied to such beams, aiming at reducing local web buckling. In Solution 2, two GFRP plates are bonded to the beam flanges in order to reduce local flange buckling. Solution 3 is a combination of the Solutions 1 and 2. Moment resistances of the strengthening systems are numerically evaluated and compared against those of the corresponding bare beam. Key observations obtained include (i) All Solutions 1, 2 and 3 are effective in increasing the moment resistance of the beam structure, (ii) When initial imperfection and residual stresses are excluded, the failure mode of the bare beams is mostly governed by local flange buckling. The moment resistances of the steel beam in Solution 1 are approximately equal to a fully plastic section moment. Meanwhile, the moment resistances of Solutions 2 and 3 are based on GFRP rupture failure mode. The strengthening solutions by using GFRP plates are the most effective while the addition of a web stiffener only plays a minor role, (iii) When initial imperfection and residual stresses are included, the failure mode of the steel beams is governed by local web buckling. The web stiffener in Solutions 1 and 3 plays an important role to increase the beam moment resistances. And (iv) For long spans, the moment resistances of Solutions 2 and 3 are significantly higher than those of Solution 1.