Orthotropic Box Girder Research Articles

Safety of Cable-Supported Bridges during Fire Hazards

AbstractUnderstanding of the performance of critical bridges, such as cable-supported bridges, during accidental fire is necessary for developing mitigation strategies against potential fire damage. In this research, the structure–fire interaction of long-span cable-supported bridges, in particular, anchored suspension bridges, self-anchored suspension bridges, and cable-stayed bridges, was investigated through nonlinear finite-element analysis. To investigate the stability of these bridges during fire, a typical steel orthotropic box girder was exposed to different fire scenarios representing fires during ship and truck accidents. The stability of the three bridges during two fire scenarios was investigated in terms of fire intensity and duration and axial compressive force in the deck. Simulation results indicate that the existing axial force in the deck negatively affected the structural performance by causing buckling failure under fire loads. Generally, anchored suspension bridges had the largest saf...

Optimization Study on Open Shaped Ribs Arrangement and Diaphragm Cutout for Steel Orthotropic Box Girder

The ramp B of one overpass was designed as curved steel orthotropic box girder, whose deck was welded with open shaped bulb ribs in the range of driveways. Then, one detailed finite element model was built to simulate the structure. For the two arrangements of bulb towards and back to web in the cantilever, the tangential stresses of diaphragm cutout were compared under the action of vehicle load. In accordance with above research, it can be concluded that the stress will be more reasonable with the bulb back to web. After altering the transverse position of the vehicle load and calculating the tangential stress along the edge of diaphragm cutout, based on further analysis, it’s generally believed that the following two reasons made the arrangement of bulb back to web more appropriate at least. First of all, the diaphragm connected with the rib adjacent to the web could share part of vertical load. What's more, it could increase the distance from the edge of the cutout to the web center. What come next was to change the diaphragm cutout size, and that parameter optimization was carried out. The results show that a radius of 40-50mm is more applicable for the arc on the bottom of the diaphragm cutout.

Launching of the San Cristobal Bridge

The San Cristobal Bridge in Chiapas, Mexico, is a three-span (71.5, 180, and 71.5 m) curved steel composite and orthotropic box girder erected by incremental launching. Lessons learned from the collapse during launching of the San Cristobal Bridge as well as the redesign and relaunching of the new bridge are discussed. After the collapse of the San Cristobal Bridge, T. Y. Lin International was hired by the new contractor, Ingenieros Civiles Asociados, to investigate the cause of the collapse of the original bridge, check the redesign of the bridge, and perform the erection engineering of the bridge. From the site investigation, it was concluded that the collapse of the structure was caused primarily by the failure of the shear studs and the consequent loss of composite action of the girder cross section over Pier 2. To ensure the safe erection of the structure, the redesign of the new bridge included the following changes: addition of shear studs, increase of deck posttensioning during launching, increase of the concrete slab strength, and addition of stiffeners to the bottom flange and webs. To match the predicted and measured deflections during launching, a calibration of the effective deck inertias (consistent with a 12 × tslab and contrary to the AASHTO specifications) was necessary to account for the effects of shear lag and the actual effective slab width.

New Carquinez Strait Suspension Bridge, San Francisco, California

The new Carquinez Strait bridge in California with a total length of 1060m and a major span of 728m is the first major suspension bridge to be built in North America in over thirty years. It incorporates the latest in seismic analysis, foundation design and a state-of-the-art steel orthotropic box girder superstructure. The 1927 bridge was replaced mainly because of modern seismic resistance requirements. The bridge is situated in one of the most active seismic regions in the world. In an extreme event, the bridge should suffer only repairable damage. The superstructure is welded continuously from one end to the other, and is isolated from the towers using only rocker links for supports. These rocker links allow the box girder to swing freely between the tower legs, reducing interaction between the towers and the orthotropic box girder. Because of variable geology including soft clays, claystones, shale and fractured claystones and sandstones, the tower foundations were constructed of groups of twelve piles, each consisting of 3-m diameter reinforced concrete piles cast in driven steel shells. Details of the bridge deck are given.