Investigating a Structural Form System for Concrete Girders Using Commercially Available GFRP Sheet-Pile Sections

This paper presents a new girder consisting of a trapezoidal pultruded glass fiber-reinforced polymer (GFRP) hat-shaped section commercially available as a sheet pile, but used in this study as a structural form for concrete. It can also offer continuity in the transverse direction through a pin-and-eye connection. Five $610\text{mm}\times 325\text{mm}$ and 3,300-mm-long girders were tested in flexure to examine different bond systems, voided and solid concrete cores, and the performance in positive and negative bending. Bond systems were wet adhesive bond to freshly cast concrete, adhesively bonded coarse aggregates, and mechanical shear studs. No slip was observed between concrete and the GFRP section until delamination failure occurred within a thin layer of cement mortar that remained attached to GFRP. The studs failed by pull out from the concrete flange. In general, 47–75% of the full strengths of concrete and GFRP were reached at ultimate bond failure. Wet adhesive bonding was the simplest and quickest to apply, while resulting in a comparable strength to other systems. A “moment-curvature” analytical model, incorporating a robust bond failure criterion, was developed, validated, and used in a parametric study. It showed that varying the concrete compressive strength or thickness of the GFRP section has insignificant effect on the bond failure load. Also, there are critical values for shear span-to-depth ratio, shear strength of cement mortar, concrete strength, and width of the top GFRP flange, beyond which, the desired flexural failure mode would precede bond failure.