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.
A new Chinese suspension bridge, set to open November 25, has won top honors for being such a long three-tower/two span bridge.
When it opens on Nov. 25, Taizhou Bridge will carry six lanes of traffic (plus two maintenance lanes) nearly 3-km across the Yangtze River. Though the total length of 2,940 m is an awfully long way, the bridge has two main spans using three towers rather than the norm of one main span using two support towers.
The two spans are each 1,080 m (3,540 ft) long, which individually is less than the main span of the Golden Gate Bridge at 1,280 m (4,200 ft), and much less than the 1,990-m (12,830 ft) span of the Akashi Kaikyō Bridge, the longest main span of any suspension bridge on Earth. Two end spans of 390 m (1,280 ft) connect Taizhou Bridge with the banks of the river.
But in using two spans the Taizhou Bridge is a major breakthrough in structural engineering. The design requires the perfect balance of flexibility and rigidity in its 192-m (630-ft) steel central tower in order to withstand changing and imbalanced loads to either side. The complementary side towers are 178 m (584 ft) tall, and are made of concrete. The two main cables supporting the bridge are 3,110 m (10,200 ft) long and 72 cm (28 in) in diameter.
Think about it. The central tower is going to be pulled from both directions. Similarly, the outside towers must have incredible strain pulling them towards the center. Balancing it all is an amazing architectural achievement.
Look, why don’t they simply admit it: They really want don’t want any humans to visit these parks, and simply outlaw them all? That way, the job of the National Park Service will be so much easier: They — and their environmentalist buddies — will finally have the park to themselves to play in without being bothered by all those disgusting American citizens.
An evening pause: A different kind of bridge, located in Russia and one that I wouldn’t speed across. Built originally as a railroad bridge to cross the Vitim River, it is 1870 feet long and about 50 feet above the water. Note how many of the cross planks are not attached.