IELTS Reading Table Completion Example 1

Tacoma Narrows Bridge – Disaster Strikes

A. When the Tacoma Narrows Bridge opened for traffic on 1 July 1940, it was celebrated as a major engineering achievement. Even before construction was completed, however, flaws in the design were apparent; workers sucked on lemon slices to avoid motion sickness as the structure swayed in the relatively mild winds. Engineers tried three different revisions during construction to address the vibration problem. Shortly after opening, the bridge quickly acquired the fond nickname of “Galloping Gertie” because of the way it would roll in either side-to-side or lengthways movements – known in physics terms as the longitudinal and transverse modes of vibration respectively. These movements did not compromise the core integrity of the structure but did make the crossing of a somewhat white-knuckle affair.

B. Four months later, however, a never-before-seen type of vibration began afflicting the bridge in what were still fairly gentle winds (about 40kmph). Rather than the simple “wave” motion that characterizes longitudinal and transverse vibration, the left side of the bridge would rise while the right side fell, but the centre line of the road would remain completely level. This was proved when two men walked along the centre of the bridge completely unaffected by the rocking motions around them. Visually, the bridge’s movements seemed to be more like a butterfly flapping its wings than a simple rolling motion. Engineers now understand this to be the torsional mode of vibration, and it is extremely hard to detect.

1. Longitudinal
2. Transverse
3. Butterfly