Characterization of the Interfacial Behavior of Hybrid Fiber-Steel Lap Connections Fastened by Steel or FRP Anchors
Fiber reinforced polymers (FRP) are extensively used in several engineering fields due to their superior properties. In structural engineering applications, fiber polymers have been recently used for retrofitting and strengthening of existing structures. A common technique for strengthening steel structures involves bonding FRP composites to targeted steel elements. However, bonding practices and researches revealed undesirable brittle failure of the adhesive at the FRP-steel interface. A recent research program conducted at UAE University validated the effectiveness of using mechanically fastened hybrid FRP (HFRP) laminates in strengthening steel beams. Outcomes of the research program revealed that the fastening technique could provide a good alternative to overcome the unfavorable brittle failure of bonded FRP composites. In addition, the study was enlightening and showed promising results in terms of both yield and ultimate load capacities of the strengthened steel beams. However, a limited range of fastening parameters was examined in the above mentioned research program.
The current research study is motivated by the need to investigate the influence of wider range of fastening parameters and geometrical configurations on the interfacial behavior of fastened HFRP-steel connections. An extensive experimental program was carried out on 62 fastened connections on two phases. In the first phase, the effect of different number of washers-per-bolt, clamping torque, bolt-hole diameter and bolt spacing were investigated on connections formed using steel bolts. While the second phase was conducted using FRP anchors to examine the effect of fastener type and diameter along with the sheared edge distance on the performance of the connections. Test results recommended to snug-tight the steel bolts after placing them in standard hole-diameters with the use of 2 washers-perbolt. Bolt spacing was proven to have insignificant effect on both failure modes and load carrying capacity of the HFRP-steel connections. The study also suggested the use of FRP anchors with 13 mm diameter with a sheared edge distance that is three times the hole-diameter for optimal performance in terms of ductility and load carrying capacity. Recorded experimental measurements were utilized to develop nonlinear load-slip models which were integrated in developing nonlinear 3D finite element (FE) models using ANSYS software. FE models were used to simulate the behavior of the fastened connections and to accurately predict their load carrying capacity. Numerical predictions were in excellent agreement with the experimental findings which verified the accuracy of the proposed nonlinear load-slip models.