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<p>Design codes commonly adjust the withdrawal capacity of nailed angle brackets with a fixed group-reduction factor, regardless of bracket stiffness or rib geometry. This study proposes a mechanics-based method for predicting the effective number of nails directly from bracket dimensions, yield strength, rib height, and a single-nail withdrawal strength. The closed-form model useful for reliability-based design is obtained assuming a two-hinge kinematic mechanism and requires only one supplemental parameter, the plastic-moment ratio, which is obtained once per bracket series through a simple elastic–plastic finite-element analysis. The formulation is validated against 49 monotonic tests on seven S280GD steel brackets whose leg size, thickness, and rib height were systematically varied. The model reproduces both the observed hinge position along the timber leg and the fraction of nails mobilised at peak load, keeping the prediction error for the effective nail count within ±10 % across all specimens. In comparison, the fixed reduction coefficients overestimate nail utilisation by 25–55% and lead to capacity errors of 60–160%. Since the new expression depends only on mechanical and geometric properties, it provides an elementary but still accurate alternative to fixed group-reduction factors for designing nailed angle-bracket connections governed by withdrawal. The authors have presented illustrative examples of this expression for the reliability-based design of angle brackets for timber structures.</p>

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Effective number of nails in withdrawal for timber angle brackets: a closed-form model for reliability-based design

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年1月23日

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  • Angelo Aloisio,
  • Petr Sejkot,
  • Asif Iqbal,
  • Massimo Fragiacomo

摘要

Design codes commonly adjust the withdrawal capacity of nailed angle brackets with a fixed group-reduction factor, regardless of bracket stiffness or rib geometry. This study proposes a mechanics-based method for predicting the effective number of nails directly from bracket dimensions, yield strength, rib height, and a single-nail withdrawal strength. The closed-form model useful for reliability-based design is obtained assuming a two-hinge kinematic mechanism and requires only one supplemental parameter, the plastic-moment ratio, which is obtained once per bracket series through a simple elastic–plastic finite-element analysis. The formulation is validated against 49 monotonic tests on seven S280GD steel brackets whose leg size, thickness, and rib height were systematically varied. The model reproduces both the observed hinge position along the timber leg and the fraction of nails mobilised at peak load, keeping the prediction error for the effective nail count within ±10 % across all specimens. In comparison, the fixed reduction coefficients overestimate nail utilisation by 25–55% and lead to capacity errors of 60–160%. Since the new expression depends only on mechanical and geometric properties, it provides an elementary but still accurate alternative to fixed group-reduction factors for designing nailed angle-bracket connections governed by withdrawal. The authors have presented illustrative examples of this expression for the reliability-based design of angle brackets for timber structures.