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The coming dark age: The Miami pedestrian bridge that collapsed yesterday only five days after installation did not have its required tower and suspension cables in place.
Engineering experts say investigators looking into the collapsed ‘instant’ bridge in Miami will want to know why a central tower which is usually built to support a suspension bridge was not in place when it collapsed onto Tamiami Trail on Thursday afternoon.
Last week, Florida International University’s official Twitter account posted a rendering of the bridge in its completed form as envisioned by the planners before its opening to foot traffic in early 2019. The rendering shows a tall central column with cables connecting it to the main span. Engineers say the design is known as a ‘cable-stayed bridge,’ which is a kind of suspension bridge, according to USA Today.
The bridge did not have the central tower in place, even though experts say it is usually placed at the early stages of construction. In the absence of a tower, there is usually a temporary support, though in this case it is unclear what the builders were using in the absence of a central structure.
I have never heard of any kind of suspension bridge ever being built in this sequence. Such bridges always install the towers and the cables, then the roadbed. Here, it increasingly looks like they put up the road bed before the tower and cables, an approach that practically guarantees the bridge will fail.
The images at the link show the presence of temporary support structures under the bridge, so it could be that the builders were using these to support the bridge until the central tower and cables could be installed. However, the bridge was made of concrete, which is far heavier and does not have the same structural strength as steel. It could be they overestimated the ability of this concrete structure to stand, without the cables.