Compressive ductility of glulam and its influence on component reliability and structural robustness of timber truss systems

The study quantifies the probabilistic consequences of replacing the standard elastic-brittle compression assumption with a calibrated elastic-plastic model for GL24 h glued laminated timber. An elasto-plastic bilinear constitutive law was adopted, and reliability indices are computed by the first order reliability method (FORM) for six timber truss configurations. For each, the structural robustness factor Frob is compared between the brittle and ductile models for four assumed element failure scenarios. The ductile model increased the reliability index of compression elements by 1–14% relative to the brittle model for all configurations. However, this improvement did not propagate to system reliability or Frob for trusses with series load paths (RN1, RN3–RN6), where brittle, irreversible tensile chord failure remains the governing collapse mechanism. The sole exception was truss RN2, whose parallel compression subsystem (X-web) yields ΔFrob =  + 0.23 for compression diagonal failure, without changing the robustness classification. Brittle models were therefore conservative and adequate for robustness assessment of planar, statically loaded timber truss topologies with series load paths, the scope examined here. The material-level ductility benefit was structurally inaccessible in series systems because no load-path alternative exists after tensile chord failure.