Hot-spot stress determination of tubular arch bridge joints using strain gauges

The Woluwe Lane tubular arch bridge is highly appreciated because of its aesthetic value, but the design required particular care due to the use of welded joints. The fatigue strength of this structure is important because high stresses, so-called hot-spot stresses, are reached near the weld toe of the joints. These are due to geometric discontinuities and to the welding process, making this type of bridge prone to fatigue damage caused by varying train loads. In the particular case being considered, the hot-spot stresses of the joints are too high. Hence, diaphragms were placed inside the arch tube to reinforce the joints at the weld toe. To investigate the behaviour of this bridge and the influence of the diaphragms, a finite element (FE) model has been created. Using this model, the hot-spot stresses of the joints can be determined. These stresses can be used to predict the fatigue life of the bridge. In order to validate this FE model, strain measurements have been carried out on this tubular arch bridge. 454 strain gauges have been installed on the arches and struts. Two load tests have been executed to measure the strains in the structure. A good agreement between the measured and computed strain values is demonstrated. Also, the behaviour of the bridge could be demonstrated thanks to the strain measurements. The measured hot-spot strains are low enough to assure a longer fatigue life.