The Background

Tretten Bridge collapsed in 2022 after just 10 years since its construction. According to the investigations of NSIA (Havarikommisjon), the collapse was a consequence of a brittle failure in one of the dowel-connections in the timber diagonals of the truss.  

The failure was caused by the block-shear phenomenon which involves both the shear and the tensile capacity of timber. NSIA (Havarikommisjon) concluded that this failure mechanism likely occurred due to fatigue, where the capacity of the connection decreases over time because of sustained traffic load. 

Despite the growing interest in timber as a sustainable construction material, and despite the numerous timber bridges existing nowadays, research on fatigue in timber connections is extremely limited. Currently, the basis for the evaluation of fatigue of dowel-connections in typical timber truss bridges comes from an experimental study conducted at NTNU in connection with the construction of the Evenstad timber bridge in 1996. However, its scope was limited to a specific configuration and thus does not have general validity.  
 

The objectives

The objective of the project is two-fold. First, to evaluate the fatigue capacity under cyclic tensile load and under cyclic shear load of dowel-connections for timber bridges and provide improved fatigue data and design rules. Second, to explore if and how reinforcements to the dowel connections can enhance their fatigue capacity. Addressing these gaps will provide critical insights into the long-term performance of timber bridges and help optimize connection design for improved durability. 

The project is a cooperation between the Department of Structural Engineering of NTNU and Statens Vegvesen.