Fiber-reinforced polymer is gaining attention in the construction industry for its lightweight, high strength, and corrosive resistance. FRP is a composite material made of a polymer matrix reinforced with fibers. Its durability and resistance to corrosion make it ideal for use in harsh environments (sea salt and deicing chemicals) and caustic industrial conditions (chlorine manufacturing). Finding the right solution for connecting FRP plates will be an important consideration to maximize the benefits of this material. While steel bolted connections have been the preferred method, engineers have realized that the strength of the connections in pultruded FRP composites often controls the design of pultruded FRP frames.


Researchers conducted a critical review of studies on bolted connections in pultruded FRP. The research began with a review of 350 experiments of steel bolted connections using FRP framing from 10 experimental research programs. In “Assessment of Resistance Factors for LRFD of Steel Bolted Connections in Pultruded FRP Frames,” the authors performed a statistical analysis of the strength ratio to assess the resistance factors. They then compared the resistance factors to the factors prescribed by ASCE/SEI 74-23. Learn more about their research to better quantify the strength of steel bolted connections in pultruded FRP in the Journal of Composites for Construction, at The abstract is below.



Resistance factors (ϕ-factors) are reliability-based factors of safety used in load and resistance factor design (LRFD) of structural systems. The ϕ-factors specified in the consensus standard for the structural design of pultruded fiber-reinforced polymer (FRP) structural members and connections are generally lower than the ϕ-factors used for more conventional materials (e.g., structural steel, reinforced concrete, and wood) for comparable limit states, consequently potentially limiting the application of pultruded FRP as a structural material. This work describes a review of 350 published experimental tests of bolted connections in pultruded FRP and compares these test results with the nominal strengths from equations in the consensus standard. Subsequently, a first-order reliability method analysis—following the methodology proposed by Ellingwood for pultruded FRP composites—was performed to re-examine ϕ-factors for the most common limit states of bolted connections in pultruded FRP. All relevant limit states for bearing-type connections as defined by the consensus standard were considered in the study and the derived ϕ-factors were compared with the ϕ-factors prescribed in the consensus standard with the goal of highlighting the need for additional research.

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