Stress concentration in glass fiber reinforced polymer plates induced by central circular holes and bolted connections

Holes and bolts are frequently incorporated into glass fiber reinforced polymer (GFRP) components in building engineering for wiring and connections, which may lead to stress concentration, reduced strength, and even structural failure. Most existing studies focus on isotropic materials, providing limited insight into orthotropic materials like GFRP. This study systematically investigates the stress concentration behavior of GFRP plates with central holes or bolts under uniaxial tension, considering factors such as fiber orientation, plate thickness, bolt diameter, and bolt modulus. Experimental and finite element (FE) methods were employed, and an orthotropic FE model was developed and validated. The results reveal distinct failure mechanisms: under longitudinal loading, failure primarily occurs as layer peeling, whereas transverse loading causes matrix breakage. The presence of bolts enhances structural integrity and suppresses crack propagation. The ultimate load in the longitudinal direction is approximately 9 times that in the transverse direction. Plate thickness has minimal influence on the stress concentration factor (SCF). Increasing bolt diameter raises the SCF from 3.89 to 5.69 without preload and from 4.04 to 5.07 with preload. The effect of bolt modulus on SCF is preload-dependent, with an optimal preload of 6 kN minimizing SCF, while excessive preload exacerbates stress concentration.