Time-dependent behavior of pin-bearing bolted connections in pultruded fiber reinforced polymer composites under normal and elevated temperatures

Abstract

Fiber-reinforced polymer (FRP) members can offer significant advantages such as high strength-to-weight and stiffness-to-weight ratios, resistance to corrosion, non-conductivity, design flexibility, and ease of installation. The successful assembly of structural systems made of FRP materials requires connections between elements; these connections must be considered when assessing the overall behavior of the structure. A large number of previous studies have focused on the influence of various connection parameters on the short-term response of bolted connections in pultruded FRP composites; however, few have examined their long-term behavior. This research study examines the short- and long-term response of an E-glass/polyester pultruded FRP material subjected to single pin-bearing loads. The investigation involves experiments on single-bolt tension connections under a double-lap shear configuration at normal and elevated service temperatures. Elevated temperature tests are conducted at 43.3, and 60°C (110, and 140°F). The effect of specific connection parameters including diameter-to-thickness ratios, bolt-hole clearances, and bolt tightening torques on the short-term bearing strength of a connection is evaluated. Based on the short-term test results, time-dependent pin-bearing tests are conducted at various load levels and temperature exposures. Sustained load tests are carried out on material coupons for time durations of up to 1,000 hours. Based on the experimental results, and similar to design procedures developed for wood and for pultruded FRP structures, a semi-empirical predictive model is proposed for the time-dependent behavior of the pultruded FRP materials subjected to single pin-bearing loads. Finally, an equation is proposed to estimate the time-dependent pin-bearing strength of a connection that considers the effect of temperature and connection conditions.