Sunday, December 17, 2017

Bridges of Mexico: Highway 438D Overcrossing near Santiago Atzitzihuacån

September 2017 (18.8268, -98.6038) Highway 438D Overcrossing
Driving west out of Puebla on Highway 438D we came upon an overcrossing in Santiago Atzitz Huacan. It's a 3 span precast girder bridge on very tall single column bents. The bents sit in deep cuts on the highway shoulders. This is because the highway itself is deeply cut into the surrounding hills. The engineers must have carefully calculated the volume of cuts and fills needed to built this road. 

Note the vegetation growing in the expansion joints between the spans. All of the rain and debris caught in the joints must make a fertile environment for any seeds that find a home there.
This seems to me like a very common type of bridge in Mexico, perhaps as a result of having to build highways through the many mountain ranges. I saw much taller bridges during a previous trip through Colima, Mexico. Note that part of the cut around the south bent has sloughed off, probably as a result of the September 19th earthquake. However, no damage or even signs of movement were seen on the columns or on the simply supported spans.

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Sunday, December 10, 2017

Bridges of Mexico: Bike Path on Periférico Ecológico in Puebla City


September 2017 (18.9791, -98.2206) Ciclovía del Periférico Ecológico de Puebla Ciudad
Driving south on Calle Periférico Ecológico in Puebla City I noticed a bright blue bike path in the median. Instead of an elevated bikeway like the one in the median of Hermanosa Serdán Blvd. the Ciclovía del Periférico Ecológico is 'at grade' but with elevated structures about every half mile to get on and off of this limited access expressway (see photo below).
These elevated structures include a narrow 'T' shaped superstructure on single column bents (the overcrossing), a 'C' shaped superstructure on squat four-legged trusses (the main ramp), and on/off ramps that zig-zag along the sides of the expressway.
The median has to be wide enough to accommodate bicyclists continuing their ride on each side of these elevated structures (see above). Since the resulting median could have been used to provide two extra lanes of traffic one might wonder if it's really worthwhile. Perhaps it's because I'm an avid bicyclist that I think the answer is yes!
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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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