Effect of bolt threads on the double lap joint strength of pultruded fibre reinforced polymer composite materials

Abstract

The ability to provide effective and adaptable joints for pultruded fibre reinforced polymer (PFRP) is crucial for its widespread application in civil infrastructure. This experimental based study on 150 double lap joints specimens investigated the effects of threaded bolt and clamping pressure on the joint strength behaviour, failure mechanisms and joint efficiency of bolted joints in PFRP. Double lap joints in both longitudinal and transverse directions of the laminates and with different edge distance-to-bolt diameter (e/db) were prepared and tested in accordance with ASTM D5961 standards. The joint strength in the longitudinal laminates with plain bolt increased for e/db ratio for up to 4 and with no appreciable strength gain after exceeding this ratio. On the other hand, about 30%–40% reduction in joint strength was observed in the longitudinal direction due to the bolt thread tearing through the laminates. This leads to a recommendation of 0.6 reduction factor in preliminary design of PFRP bolted connections with bolt thread present. Meanwhile, only a marginal difference of 7% was observed in transverse direction. Furthermore, the introduction of lateral clamping pressure had increased the joint strength by 60%–90% and this has lessened the thread casualty effect on the pultruded composite joints.