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Bolted connections between fibre-reinforced polymer (FRP) components are typically designed considering the mechanical properties in the longitudinal (θ = 0°) and transverse (θ = 90°) directions, w.r.t. the main fibre orientation. However, in composite structures, loads at connections are not always applied in those directions (e.g., frames with moment-resisting beam-to-column connections or bracing members, trusses with diagonal members). Available studies on bolted connections subjected to “off-axis” loading are scarce. Consequently, design provisions addressing the effect of the load angle concerning the main fibre direction (θ) are limited. For instance, the European Technical Specification CEN/TS 19101:2022 (“Design of Fibre-Polymer Composite Structures”) considers the mechanical properties in the longitudinal or transverse directions for load angles in the ranges of 0° ≤ θ ≤ ± 5° or ±5° < θ ≤ ±90°, respectively, with no additional provisions for intermediate angles. This may lead to significant underestimations of the actual strength of connections subjected to off-axis loading and, therefore, to non-economic designs. To address this research gap, an experimental campaign was conducted involving single-bolt glass fibre-reinforced polymer (GFRP) double-lap connections between composite laminates subjected to loading at different angles (0°, 5°, 10°, 15°, 30°, 45°, 60°, 75°, and 90°), to investigate the influence of load direction on the bearing, shear-out, and net-tension resistances. Pultruded laminates made of E-glass fibres impregnated with vinylester resin, with a thickness of 6 mm, were used to produce the lap specimens, which were monotonically loaded to failure. The results show that, for the pultruded material tested, the load direction has a limited effect on the connection shear-out resistance; however, it significantly influences the resistance under both bearing and net-tension failure. Based on the results obtained, it can be concluded that the formulae of CEN/TS 19101:2022 are overly conservative for off-axis loading.

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Single-Bolt Double-Lap Connections Between GFRP Laminates Subjected to Off-Axis Loading: Experimental Study and Assessment of Resistance Formulae

  • 会议论文

  • 发表日期：

    2026年

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  • Carlos A. Seruti,
  • Tiago R. da Silva,
  • André D. Martins,
  • José Gonilha,
  • João Ramôa Correia,
  • Nuno Silvestre

摘要

Bolted connections between fibre-reinforced polymer (FRP) components are typically designed considering the mechanical properties in the longitudinal (θ = 0°) and transverse (θ = 90°) directions, w.r.t. the main fibre orientation. However, in composite structures, loads at connections are not always applied in those directions (e.g., frames with moment-resisting beam-to-column connections or bracing members, trusses with diagonal members). Available studies on bolted connections subjected to “off-axis” loading are scarce. Consequently, design provisions addressing the effect of the load angle concerning the main fibre direction (θ) are limited. For instance, the European Technical Specification CEN/TS 19101:2022 (“Design of Fibre-Polymer Composite Structures”) considers the mechanical properties in the longitudinal or transverse directions for load angles in the ranges of 0° ≤ θ ≤ ± 5° or ±5° < θ ≤ ±90°, respectively, with no additional provisions for intermediate angles. This may lead to significant underestimations of the actual strength of connections subjected to off-axis loading and, therefore, to non-economic designs. To address this research gap, an experimental campaign was conducted involving single-bolt glass fibre-reinforced polymer (GFRP) double-lap connections between composite laminates subjected to loading at different angles (0°, 5°, 10°, 15°, 30°, 45°, 60°, 75°, and 90°), to investigate the influence of load direction on the bearing, shear-out, and net-tension resistances. Pultruded laminates made of E-glass fibres impregnated with vinylester resin, with a thickness of 6 mm, were used to produce the lap specimens, which were monotonically loaded to failure. The results show that, for the pultruded material tested, the load direction has a limited effect on the connection shear-out resistance; however, it significantly influences the resistance under both bearing and net-tension failure. Based on the results obtained, it can be concluded that the formulae of CEN/TS 19101:2022 are overly conservative for off-axis loading.