Damage Mechanism of Control Springs in Modular Expansion Joints of Long-Span Bridges

Premature damage in modular expansion joints, especially in control springs, has been observed in several long-span bridges, which calls for an in-depth study on the damage mechanism. In this study, relative movements of lamellae at different locations of the expansion joints were measured in bridge service condition. It is found that the movements of lamellae were nonuniform, and lamellae near the approximately fixed end of the expansion joint showed much larger relative movements than center lamellae. As a result, control springs underneath these lamellae presented more severe damage than the others. To simulate the behavior of the expansion joint, a finite-element (FE) model was developed, through which the vertical load bearing, horizontal slide friction, and self-equivalence of lamella spacing were modeled, and static and dynamic FE analyses were conducted to obtain the responses of control springs at different locations. Finally, four control springs were tested in a laboratory, in which there was no damage under monotonic loading with shear deformation of 80 mm, whereas under high-cycle loading, two damage patterns were observed, i.e., falling off of the metal head and shear cracking in the rubber cylinder. As cyclic displacement amplitudes increased, the lives of control springs decreased significantly.