Effect of initial panel slenderness on efficiency of Strengthening-By-Stiffening using FRP for shear deficient steel beams

Abstract

The need for strengthening steel structures is as important as it is for concrete structures, or any other aging structure. Strengthening concrete structures by externally bonding thin composite materials in the form of laminates or strips has proven to be an efficient way for enhancing the flexural, shear, and axial strength of deficient elements. Use of external bonding of thin composite material to strengthen steel structures can also be found in literature. This paper presents another effective strengthening technique in which pultruded GFRP sections are bonded to shear deficient regions to enhance the local buckling resistance of thin walled steel structures. Three steel beams with different web thicknesses were tested experimentally with and without GFRP stiffeners to study the efficiency of the new technique; Strengthening-By-Stiffening or SBS. The ultimate shear capacities of the beams were enhanced by a minimum of 30% when one stiffener was used on a beam with a square panel and a maximum of 40% for beams with larger rectangular panel with two stiffeners (one on each side). The initial global stiffness was also enhanced between 5% and 41% for the strengthened beams as a result of the externally bonding the GFRP stiffeners. Unlike the one stiffener configuration which experienced a major load drop at high load levels, the post yielding behavior of the two stiffener configuration exhibited a sustainable load capacity around the peak load without any major load drop. Strain reading from the top and bottom flanges at the loading point revealed that a sway frame mechanism became the main shear resisting mechanism after the critical panel buckled due to shear.