Sunday, December 3, 2017

Bridges of Mexico: Xonacatepec OC across 150D in Puebla

September 2017 (19.0674, -98.1181) Xonacatepec Road OC
Driving west on 150D we approached a very strange looking overcrossing carrying Xonacatepec Road across the expressway. Note the diagonal tower with cables on the east side of the bridge supporting the two northern spans. You can't see from the photo (shot while hanging out of the passenger window) but there is an identical tower on the west side supporting the two southern spans. The diagonal towers positioned asymmetrically from each other must provide torsional and bending moments. Perhaps the asymmetrically positioned cable towers are to compensate for the torsion due to the highly skewed bridge?
A year ago there were no service roads and the overcrossing had fewer spans (see above). Looking at a later photo shows the new overcrossing being built (shown below). Note the tower that will support the cables sitting on the north shoulder (in the photo below). There's another tower sitting on the south shoulder on the west side of the bridge.
Looking at a photo of the bridge deck (below), we can see that this wide bridge was able to handle traffic during construction by working on half the bridge while allowing traffic to ride on the other half. Once that half was rebuilt, traffic was moved onto it while the other half was rebuilt.
One last photo (below) of the overcrossing through the (dirty) rear window. You can clearly see the diagonal towers on opposite ends and opposite sides of the bridge. What I find particularly interesting is that the engineer was allowed to design such an unusual structure on an interstate highway. I think California's bridge engineers may be too cautious and conservative to design something so unusual.
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