Effect of Connection Techniques on the Static and Fatigue Performance of Pultruded Basalt FRP Multibolted Joints

Abstract

The loading capacity of pultruded fiber-reinforced polymer (FRP) multibolted joints typically controls the structural design of composite structures. This study focuses on enhancing the low loading capacity of conventional unidirectional pultruded FRP-bolted joints by investigating the efficiency of three types of connection techniques: bonded and bolted joints, resin-injected bolted joints, and bolted joints with additional bidirectional FRP layers. Sixty-eight specimens of double-lap multibolted basalt FRP (BFRP) joints, constructed with stainless steel (SS), BFRP, or hybrid steel-FRP bolts (HSFRP), were tested under static, fatigue, and postfatigue static loadings. The results indicated that an increase of up to 60% in the loading capacity of the conventional bolted connection could be achieved by adopting the aforementioned three techniques. Furthermore, at a targeted fatigue life of two million cycles, the resin-injected bolted joints and bolted joints with additional bidirectional BFRP layers improved the load efficiency of the conventional joints by 24%. Additionally, the proposed BFRP and HSFRP bolts proved their reliability in replacing conventional SS bolts without affecting the loading capacity of the composite joints, regardless of the connection technique used.