Strength Enhancement of Advanced Grid Stiffened FRP Tube Confined Concrete Cylinders under Fire

Abstract

Recently, a new confining device - a lattice of interlaced fiber-reinforced plastic (FRP) ribs that were wrapped by an FRP skin, has been developed to provide better confinement to a concrete core through interfacial mechanical interlocking [1,2]. A systematic study has validated the enhanced structural capacities over traditional FRP tube encased concrete counterparts. However, like traditional FRPs, advanced grid stiffened FRP tube confined concrete cylinders (AGS-FRPC) are vulnerable to fire hazards. The purpose of this study was to investigate the enhancement of fire tolerance as a result of incorporating organically modified montmorillonite (MMT) and a traditional fire retardant additive (TSWB®) into a vinyl ester (VE) matrix. Two series of samples were prepared. The first series consisted of groups A, B, C, and D, in which A was regular AGS-FRPC, B was enhanced with MMT, C was enhanced with TSWB® fire retardant additive, and D was enhanced with both MMT and TSWB®. The second series of samples was identical to the first series as a control, and it consisted of groups of E, F, G, and H, respectively. The only difference was that the first series was exposed to a jet fire of 982°C for 5 min while the second series was not. It was found that fire exposure had a significant impact on reducing the residual strength of the confined concrete cylinders. The introduction of MMT increased both the fire tolerance and compressive strength of AGS-FRPC. The TSWB additive was effective in minimizing the effect of the fire hazard, but it reduced the compressive strength.