Determining the Dynamic Increase Factor for Glued-Laminated Timber Beams

Abstract

This paper presents the results from an experimental program that investigated the flexural behavior of glulam beams subjected to dynamic loading. A total of thirty-eight beams consisting of three different cross-sections were tested destructively under both static and dynamic loads. The analysis resulted in a dynamic increase factor (DIF) of 1.14 for strain-rates ranging between .14 and .51 s−1, however, the increase was only observed when the outer tension laminate did not include continuous finger-joints (single laminate width) or closely aligned finger-joints (multiple laminates width) in the high moment region causing a straight fracture across the width. No increase due to high strain-rate effects was found when a continuous failure across the width due to finger-joints (FJs) were present in the outer tension laminate, and thus if continuous laminates, uninterrupted by FJs cannot be guaranteed, a dynamic increase factor of unity is suggested for design. Since the beams exhibited little to no ductility, it is recommended that a linear-elastic resistance curve be used to generate the dynamic resistance curve. An equivalent single-degree-of-freedom (SDOF) model accounting for high strain-rate effects using the derived DIF, where appropriate, captured the displacement at failure, time to failure, and displaced shape with reasonable accuracy.