Bridges of Mexico: Metro Viaduct in Mexico City

September 2017 (19.3017, -99.0520) Metro Viaduct

About 10 km to the northeast of the Tlapan Viaduct is another viaduct that carries light rail trains. The Metro Viaduct is about 20 km long, it was recently built, and it had some surprising damage during the 9/19/2017 earthquake.

The Metro Viaduct has a two steel girder superstructure (and three girders at the elevated stations) supported on single column bents. At the first site we saw evidence that a column foundation had rocked during the earthquake (above photo). Looking up at the superstructure we could see damage resulting from this movement (photo below). Steel keeper plates had busted out of the bent cap during the earthquake (although still restrained by the reinforcement). Also note the vertical slot in the column, meant to hold a drainage pipe. Like the previously studied Tlapan Viaduct, the drainage for these viaducts was never built.

Walking west along Avenue Tlahuac we continued to see signs of banging between the simply supported steel girder spans and the reinforced concrete bent caps (see figure below). However a few hundred meters to the west we saw some surprisingly serious damage.

At this location the column didn't rock because the column base was weaker and broke instead. After the earthquake the superstructure was supported on steel shoring while engineers made plans to repair the column.

In the photo below we can see that not only had the column's cover concrete spalled off but the cracks extended into the core concrete. Looking at the damage, we noted the lack of transverse reinforcement in the column. Also, the main column reinforcement had bundled bars with splices, which shouldn't be located in the plastic hinge zone.  Fortunately the viaduct didn't collapse at this location. However, there was only moderate shaking in Mexico City from the 9/19/2017 earthquake. Imagine the damage that could occur if strong shaking were to occur. Even with only moderate shaking, about 40 buildings collapsed.

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Bridges of Mexico: Tlapan Viaduct in Mexico City

September 2017 (19.2389, -99.1468) Tlapan Viaducto

After leaving Coajomulco, we continued north on Highway 95D to the newly constructed Viaducto Tlapan in southern Mexico City. The government really must like these elevated expressways (maybe because of the tolls they collect) and almost every highway in Mexico City now has a viaduct in the median. I wrote about the construction of these viaducts and the documentary film they inspired in a previous blog.

When we stopped at the viaduct to take photos, the highway police came over to talk to us. They were very nice (as were all the police and soldiers that we met) and they allowed us to continue shooting.

 We asked the police if this long viaduct had been damaged during the recent earthquake. They said they did a complete inspection following the earthquake and didn't see any damage. The one thing they did notice was that water began leaking out of the expansion joints at the ends of the spans after the earthquake. I think the reason for this is that they never completed the drainage system on the viaducts for some reason. Water that had accumulated inside the box girder supertructure was finally able to escape due to shaking during the earthquake.

The viaduct is composed of spans that cantilever over single column bents with a seat for the next span at the end of the cantilever. In this way a 20 km long viaduct is created (see photo above). This simple pattern is modified as required due to a variety of structures crossing the highway (see photo below).

I also wanted to mention the beautiful views on the east side of the highway at this location. Mexico City is at an elevation of 7000 ft with volcanoes encircling the city such as Volcan Guadalupe shown in the photo below.

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Bridges of Mexico: Highway 95D Overcrossing in Coajomulco

September 2017 (19.0323, -99.2057) Overcrossing in Coajomulco

Heading back to Mexico City we stopped to photograph an overcrossing on Highway 95D. Although there's nothing special about this bridge it has a handcrafted look that's different from the cookie cutter appearance of most expressway bridges in the United States.

This bridge is composed of precast slab elements for the superstructure and wall elements for the substructure. The walls at the abutments have stone masonry wingwalls and the pier wall has pegs at the top to act as catchers. The bridge is painted white to complete its handmade appearance.

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