This study investigates the tensile behavior of pultruded composite square tubes with single- and double-bolt joints to evaluate their ultimate load-bearing capacity and failure modes. A series of experiments was carried out to examine the effects of hole size, edge distance, and the presence of a reinforcing gasket on joint performance. The results indicate that incorporating a multiaxial fiber-reinforced resin matrix composite gasket significantly enhances joint strength, achieving up to a 295% increase in bearing capacity. In single-bolt configurations, reducing the edge distance improved the effectiveness of the gasket, leading to higher ultimate strength, as it enhances the lateral confinement of the gasket. For double-bolt joints, a shorter spacing between holes further amplified the reinforcing effect of the gasket under constant hole size and edge distance. A theoretical model was developed to estimate the ultimate load, and the calculated results showed strong agreement with experimental observations. Numerical predictions showed a strong correlation with experimental findings, confirming the model’s reliability and accuracy.

Pultruded glass fibre-reinforced polymer (GFRP) profiles are promising structural cores for lightweight sandwich panels, but their strong longitudinal response is accompanied by weak transverse resistance and local web instability. A matched experimental programme examined rectangular hollow pultruded GFRP profiles and vacuum-infused sandwich panels under four-point bending, short-span three-point bending and flatwise compression in H and V orientations. Changing from H to V increased the peak loads of individual profiles by 9.35% in four-point bending and by 26.06% in short-span loading but reduced the flatwise compressive peak load by 30.12%. For integrated panels, the same reorientation increased the four-point bending peak load by 22.74%, caused only a marginal change in short-span capacity and reduced the flatwise compressive peak load by 28.24%. Failure involved local web buckling, web shear damage, longitudinal splitting, laminate delamination and interfacial debonding. Continuous face sheets and wrapping laminates restrained local deformation and contributed to substantial post-damage resistance, consistent with load redistribution within the integrated section. Relative to a baseline comprising three individual profiles and the corresponding hollow FRP reference panel, integrated-panel capacities increased by 15.76%, 37.71% and 78.44% under four-point bending, short-span loading and flatwise compression, respectively. These results identify profile orientation and transverse web stability as key design parameters for pultruded-profile-core sandwich panels.