Designing Suspention Bridge: The Tacoma Narrows Collapse

When bridges are poorly constructed, they may fail due to load they carry, collision by derailed trains or even by vehicles that lose control leading to catastrophic incidences. However, if bridges are well-constructed, the chances or injury are greatly minimized in the event of an accident. Discussed in the subsections are the requirements of AS 5100 standards in relation to cable-stayed bridges and include design requirements for bridges, bridge aesthetics, bridge functional requirements, bridge component design requirements and bridge construction

The tension in the suspenders transfers to the cables which run horizontally between the two far-flung anchorages, through which the tensional forces pass in to the ground and are dissipated. (Bagga 2014).

Initially, suspension bridges before 1940 were made of piers, towers, wires, anchorages, and roadways. Piers were the main foundation for the suspension bridges. There usually were two of them, which were made out of cement and were entrenched in ground underneath the body of water that the bridge was spanned across. Towers were built on top of the piers to provide a means of connection for the roadways and wires. Wires were connected to the towers, roadways, and anchorages to provide tension support for the weight of the bridge. The anchorages were large cement platforms that were planted into the ground on either side of the land so that the wires could be connected to it. Lastly, the roadways were the main point of the suspension bridge. They usually were wide enough to provide four lanes of traffic and stretched from one side of the bridge to the other. This was the basic design of the suspension bridges

When the bridge was tested, at 26 pounds of pressure, it began to buckle. The top support near the middle of the bridge on one side caved in, and as the weight increased, more of the top supports collapsed. At 47.3 pounds of pressure, the bridge snapped in half. By the end of the testing, the bridge had lost all of it’s top supports, two sections of diagonal supports on either side, and a small portion of the roadway.

The second bridge I will be talking about is the Batman Bridge. The Batman Bridge is a cable-stay bridge

The buckling resistance of slender webs can be increased by the provision of web stiffeners. In general the webs of plate girders used in buildings are either unstiffened or have transverse stiffeners

It is shaped in a way to transfer weight to the towers and anchors with its tension (O'Connor, 1971, p. 372). Cables are made of high strength wires spirally bound to form a rope (O'Connor, 1971, p. 372). Vertical cable suspenders that are fastened to the main cables hang the actual roadway. Stiffening girders and trusses are along the side of the bridge to distribute concentrated loads and help to keep the motion of the bridge at a minimum (Troitsky, 1994, p115).

The bridge has a strong tower keeping the bridge away from collapsing, while the web trusses were used to hold up the deck and the road from breaking and snapping but also a resistant to shear forces and torsion. In today’s bridge structures, they often fail under strong winds, therefore there is a supporting system beneath the bridge called a deck truss. This reinforces the bridge’s deck and it decreases the tendency of the roadway to wave and move. However, the dead loads are the external forces that are acting on the bridge are the gravity and the materials that were used to build, it also refers to the weight of the bridge itself as a dead load. The live loads are the carts, cars, trains and even humans are the external forces that the

Biaxial tensile testing were conducted by means of EnduraTec ELF 3200 (Bose, Minnesota, USA). This mechanical tester has two vertical axes each of which has a 1 kg load-cell (Model 31, Sensotec Honeywell) and a displacement transducer. The apparatus is equipped with a black-and-white CCD-camera video-extensometer (Watec America LCL 902C camera with Computar TEC55 Lens), allowing the automatic tracking of gauge marks, four dots forming a square plotted on the surface of the specimens.

Three kinds of forces operate on any bridge: the dead load, the live load, and the dynamic load. Dead load refers to the weight of the bridge itself. Like any other structure, a bridge has a tendency to collapse simply because of the gravitational forces acting on the materials of which the bridge is made. Live load refers to traffic that moves across the bridge as well as normal environmental factors such as changes in temperature, precipitation, and winds. Dynamic load refers to environmental factors that go beyond normal

As a replacement for the ferry system in place to venture across the Tacoma Narrows, the 2,800 feet long bridge was created. However, in an attempt to make the bridge more cost-effective, it was built with an unusual design for a suspension bridge- an extremely thin frame of only thirty-nine feet. This created sufficient space for only two lanes on the roadway. Originally, the bridge was supposed to be made more sturdy through the addition of trusses, yet there were inadequate funds. As a result, a cheaper alternative- 8-foot girders- were added on. They were included on the entire expanse of the bridge. However, there was not a sufficient stiffening effect created on the bridge by these girders. There was not enough research in existence on aerodynamic stability for suspension bridges, and wind tunneling/aerodynamic lift was thus not properly accounted

There are three sorts of statically determinate trusses, which are immediate, compound, and complex. (Stray pieces, n.d.)

The Tacoma Narrows Bridge was designed for a wind speed of 100 miles per hour and a static wind pressure of 30 pounds-force per square foot but unfortunately the bridge failed at a wind speed of less than half and a static wind pressure of one-sixth (Delatte, 2009). This phenomenon raises a big question mark on how this is possible. At first, resonance was suspected to be the main cause of the bridge failure (The New York Times, 1940). After some proper research and thorough investigations by engineers, they came up with several theories on how did the bridge collapse. The primary cause of the collapse lies in the general proportions of the bridge and the type of stiffening girders and floor. The ratio of the width of the bridge to the length of the main span was so much smaller and the vertical stiffness was so much less than those of previously constructed bridges that

It is a very unique bridge. A suspension bridge is a bridge with the weight of the deck supported by cables suspended from larger cables that run between the towers. The main parts of a suspension bridge are the towers, anchors, main cables, suspension cables, and the road way. It is one of the most expensive bridges to build in the world. Suspension bridges are mainly made out of steel these days. But some of them are made out of different things. A suspension bridge is very different from arch bridges, even though there can be arch in a suspension bridge.

Suspension bridges need to be flexible enough to move with the wind, but not until conditions become severe and then breaks. Since movement needs to be applied to the bridge, the cable system will move in windy conditions, since movement needs to be applied to the bridge. It may require closure during strong earthquakes or in any extremely turbulent conditions.