Investigation and Repair Schemes of the Cracks in Steel Box Girders of a Cable Stayed Bridge

Abstract

The Hale Boggs Bridge, built in 1978, carries Interstate I-310 over the Mississippi River in Luling, Louisiana. The bridge has an overall width of 82 feet accommodating two 12 ft. lanes with a 4.25 ft. inside shoulder and a 10 ft. outside shoulder in each direction. The main river crossing of the Hale Boggs Bridge is a cable stayed bridge having a total length of 2,732 ft. configured as 260, 508, 1222, 495, and 260 foot spans. The cable stayed bridge consists of two A-shaped towers, fanned cables, and a steel box girder superstructure. The superstructure is composed of two steel tub girders connected with diaphragms and steel orthotropic deck. Recent bridge inspections revealed that cracks occurred in the deck plate and the fillet weld at the connections of the box girder web transverse stiffener to the orthotropic deck. Also, it was found that the cracks only exhibited in the outer web of the box girders under the outside lane of traffic. A three-dimensional structural model was developed for the determination of the likely causes of the cracks. It was found that the cracks are due to the stress concentration in the orthotropic deck due to the presence of the transverse stiffener of the tub girder. In addition, the remaining life of the fatigue detail was evaluated and repair schemes to suppress the cracks were developed and verified with the three-dimensional analysis model.