Effect of Hot-Wet Aging on the Pin-Bearing Strength of a Pultruded Material with Polyester Matrix

This paper presents test results to show the effect of hot-wet conditioning on the pin-bearing strength of a pultruded fiber-reinforced polymer material. Knowledge of this strength property, taking account of any reduction over the service lives of structures, is required to reliably calculate bearing strength when designing bolted connections. Pin-bearing strength is determined using an in-house test method with batches of nominally identical specimens, cut from the web of a 203×203×9.53 mm wide flange shape. This shape is from the 1525 series of Creative Pultrusions and had a polyester-based matrix. Specimens were immersed before strength testing under water for 3,000 h at the constant temperature of 40° C. This paper presents the accelerated aging protocol and its relation to service life, and an explanation is given as to why the material was aged for an unknown number of service years. Variables in the test matrix are the direction of the bearing force (0, 45, and 90° to the direction of pultrusion) and plain pin diameter (four sizes from 9.7–25.4 mm). Comparing aged pin-bearing strengths with equivalent strengths for nonaged material found that the average reduction in characteristic strength (calculated in accordance with Eurocode 0) of the 12 batches is in the range of 18–31%. The extent of strength reduction is found to be independent of pin size, except when the diameter is 25.4 mm. For the 0° situation, a comparison is made between the characteristic strengths for the four pin diameters determined using BS EN 1990:2002 and ASTM D7290 to show that the latter Weibull distribution values are less by 4–18%.