Finite Element Simulation of the Crack Development in the Gröndal Bridge

Abstract

Two cantilever prestressed bridges (Gröndal and Alvik Bridges in Stockholm) were closed to traffic a few months after their opening when an inspection revealed cracks in the webs. The present work is a study by means of Fracture Mechanics (FM) and Finite Element Methods (FEM) of the causes and loads that generated crack initiation as well as further widening and propagation. Some critical stages were considered: cantilever construction phase, closure, transfer of prestress and addition of finishing loads. Non-linear and time dependent characteristics of the materials were also included. The results obtained from the computer simulations were studied and compared to the expected crack openings and spacing calculated by EC2 and to the crack pattern in the Gröndal Bridge, showing satisfactory agreement. Comments are given upon the feasibility to perform non-linear finite element analyses with the aid of fracture mechanics, as well as the combined utilization of CAD and FEM software for a better design. The analysis showed that the largest contribution to the crack development of the Gröndal Bridge, was provided by the temperature gradient intended to simulate the sun radiation on the southwest web of the box girder. It also showed that the cracks appeared right after construction and they widen due to time-dependent effects. In this thesis it was shown that the crack widths can be calculated with good accuracy from the linear FE-analysis, where the cross-section is built up by shell elements. Consequently, this has shown to be a possible tool that can be used to design the web reinforcement with respect to the requirement in SLS.