Hygrothermal aging effects on shear behavior of pultruded FRP composite web-flange junctions in bridge application

This paper reports the outcome of the third phase of a multi-phase comprehensive study that aimed at characterizing both short- and long-term behavior of web-flange junctions (WFJs) of pultruded fiber reinforced polymer (PFRP) commonly used in bridge applications. Both monolithic and adhesively-bonded junctions were evaluated. The focus of this paper is on shear characteristics of such junctions before and after exposure to hygrothermal aging. In this study, a total of eighteen shear tests were performed on as-built (unexposed) WFJ specimens, in addition to seventy-six shear tests that were conducted on other specimens that were exposed to both fresh water and artificial seawater environments at temperatures of 40 °C, 60 °C, and 80 °C in order to characterize shear behavior of six types of pultruded web/flange junctions and hygrothermal aging effect of one type of these web-flange junctions. Experimental results showed that increasing the web thickness of the pultruded member has an impact on junction's shear stiffness, however, increasing both flange thickness and junction's fillet radius have less effect on web-flange junctions' shear strength and stiffness. The difference in ultimate shear strength degradation of specimens exposed to freshwater and artificial seawater environments, at temperatures of 40 °C, and 80 °C is relatively small, however, the ultimate shear strength of WFJ specimens exposed to fresh-water environment degraded slightly higher as compared to specimens that were immersed in artificial seawater environment at 60 °C temperature. The difference in mechanical properties degradation at different temperatures was found to be relatively small (from 0.0 h to 672.0 h). However, a relatively higher degradation was observed at higher temperatures during an exposure period from 672.0 h to 4392.0 h. Moreover, the hygrothermal effects on axial, shear and rotation behaviors of web-flange junctions were compared. Based on the results of the three-phases of this multi-phase study, it was shown that the degradation of WFJ's moment capacity is the largest, the reduction in axial capacity is the least and the shear capacity degradation is in the middle when junctions are exposed to both water and artificial seawater aging environments at temperatures of 40 °C, 60 °C and 80 °C.