Sandwich concrete beams with GFRP side faces tested and modeled in flexure

Abstract

The flexural behavior of sandwich concrete beams reinforced with Glass Fiber-Reinforced Polymer (GFRP) side faces is studied. The GFRP faces are commercially available as pultruded sections consisting of flat plates with integrated T-shaped ribs and are used as stay-in-place (SIP) structural forms with the ribs embedded longitudinally into the concrete beam. Nine beams, 170 ×245 mm in cross-section and 1.06 to 1.945 m in length were tested in three-point bending to failure. Five of the beams included GFRP splices at mid-height along the length to simulate sections of continuous wall applications with spliced panels. The main parameters studied were splice method (adhesive and mechanical fasteners at spacing of 3.7%–16.7% the shear span), GFRP reinforcement ratio (7.6 and 10%) which was controlled by rib spacing, and shear span-to-depth (a/d) ratio (1.8–3.7). The test results have shown that the adhesively spliced beams reached 92%–96% the strength of their un-spliced counterparts. As the fasteners spacing reduced from 16.7%–3.7% of shear span, the strength increased from 86 to 92% the strength of the un-spliced counterpart. As a/d ratio reduced from 3.7 to 1.8, the ultimate moment increased by 17%. The beam with 7.6% GFRP reinforcement ratio had the same flexural strength as a conventional reinforced concrete section of the same size with a total steel reinforcement ratio of 3%. A three-dimensional finite element model is also developed and validated using test results and was able to predict all responses and failure modes, within 5%–8% difference in ultimate load. It was then implemented in a parametric study using 10 additional models to investigate the effects of adding a bottom facing and corner connections.