Effects of off‐axis load direction on tensile properties of pultruded fiber‐reinforced polymer bolted joints with multi‐directional fiber lay‐ups

Abstract

The limited joint performance of unidirectional (UD) pultruded fiber‐reinforced polymer (FRP) composites poses a critical issue that constrains their application in structural engineering. Moreover, UD pultruded FRP joints display a notable reduction in strength and stiffness as the load angle diverges from the fiber pultrusion direction. This paper presents a numerical study of bolted pultruded FRP joints with different off‐axis loading directions. Two types of fiber lay‐ups, including UD and multi‐directional (MD), were investigated. Static tensile tests were conducted with the loading direction parallel to the pultrusion. A finite element model was validated by the test results. Studied geometric parameters includes the end‐to‐diameter (e/d) ratio, width‐to‐diameter (w/d) ratio, and bolt arrangement. Compared to UD joints, MD joints exhibited significant advantages in strength and stiffness under off‐axis loading with an increasing of 78.3% at a loading angle of 90°. Compared to the end distance, plate width has a more significant impact on the off‐axis behaviors of MD joints, especially between 30° and 75°. Multi‐bolted joints were more susceptible to net‐tension failure than single‐bolted joints. Furthermore, classical laminate theory and Hashin failure criterion were employed to predict the resistance of single‐bolted FRP joints with different loading angles, achieving high accuracy.Highlights Under increased off‐axis loading angles, compared with unidirectional (UD) joints, multi‐directional (MD) joints display a less reduction in both strength and stiffness. At a 90° angle UD joints displayed only 21.7% of the joint resistance of MD joints. Compared to the end distance, plate width has a more significant impact on the off‐axis behaviors of MD joints, especially between 30° and 75°. Classical Laminate Theory, Hashin failure criterion were effectively utilized to predict the ultimate strength of pultruded joints under various tensile loading angles, yielding high accuracy. The error between theoretical and simulated values is within 20%.