Numerical study of enhancement of plastic rotation capacity of seismic steel moment connections by fiber reinforced polymer materials

Abstract

Flange and web local buckling in beam plastic hinge regions of welded Steel Moment Frames (SMF) can prevent the beam-column connections to achieve adequate plastic rotations under earthquake induced forces. Reducing the web-flange slenderness ratios is the most effective way in preventing local member buckling as stipulated in the latest earthquake specifications. However, older steel beam-column connections that lack the adequate slenderness ratios stipulated for new SMFs are vulnerable to local plastic buckling. This study investigates postponing the formation of local buckles in beam flanges and webs at the plastic hinge region of modified SMF connections (welded haunch) by the use of externally bonded Glass Fiber Reinforced Polymers (GFRP). The research includes finite element (FE) modeling. The energy dissipation capacity of existing SMF connections is anticipated to increase with GFRP laminates bonded to flanges of beams in plastic hinge locations. Cantilever beams with and without GFRP were analyzed under quasi-static cyclic loading and the effects to the plastic local buckling of the GFRP laminates added to the steel beams were observed.Both geometric and material nonlinearities are considered. The mechanical properties of the GFRP material were obtained through standard ASTM tests and were utilized directly in the FE model. Steel beams with flange slenderness ratios of 8 to 12 and web slenderness ratios of 40-60-80 were analyzed. Results indicate that GFRP strips can effectively delay the formation of local plastic buckling in the plastic hinge region.