Effect of Cyclic Loading on Bending Stiffness of Glued Laminated Pieces

Glued laminated timber (Glulam) is important structural solution. Knowing its mechanical response under repeated forces, a gap in knowledge area, is fundamental to guarantee structures long-term performance. This study aims evaluating Glulam behavior under fatigue, considering excitation frequency (1 and 2Hz); cycles number (NC – six levels) and their interactions. Marupá and Pequiá, tropical species within density range of Brazilian Code NBR 7190-1, were adopted. Adhesive RS-216-M (CASCO ®, Hexion), usual in industry, was chosen. Modulus of elasticity in bending (E), obtained before cyclic forces application, was taken as reference and determined based usual equation. Results indicated slight stiffness decrease after repeated forces on Glulam pieces. E mean presented significant variation (by ANOVA, 95% significance) when NC ranges from 1,000 to 691,200, both frequencies. NC and frequency explained E variations for Marupá; for Pequiá, only NC. Glue lines were evaluated, in function of NC, without problems identified, enabling both species for Glulam manufacture.