Chapter 7- Galloping Gertie

Question 1

47. Why was the Tacoma Narrows Bridge nicknamed “Galloping Gertie” from the day it was opened to traffic on 1st July 1940

Answer 1

When the bridge opened in 1940 it was nicknamed galloping gertie because of the undulating motions of the wind. The bridge used to sway due to the wind. The swagging remind people of a galloping horse. The bridge swayed up and down.

Question 2

48. What was the main difference in the structural responses between the wind driven oscillations of Galloping Gertie and those of its sister bridge

Answer 2

1. The bridge was 3 times more flexible than its sister bridges as the stifferns girders were shallow in relations to its span
2. The main difference in the tacoma bridge was that the oscillations did not die out and seemed to last forever. Similar bridge experience oscillations however were damped quickly as they had devices that help do this. Even with the smallest amount of wind the bridge oscillate like a sea.
3. The tamocon bridge had 60 times less damping than the usually bridge.

Question 3

49. Using the observations of the bridge’s movement by Kenneth Arkin on the morning 7 November 1940, when the bridge finally tore itself apart, what stiffness of the deck was too low

Answer 3

1. On the morning that the bridge torn it self apart the wind velocity was 38mph to then 42mph
2. The bridge was bouncing noticeably, and tie down stays were losse.
   At 10am the bridge deck rose and fell at the centre of the bridge 38 times per minute with a 3 ft amplitude.
3. The bridge was observed to move up and down at the centre and consisted by 9 times vertical undulations while also deflecting laterally by 2ft.
4. The bridge also twisted violently as the centre was too stiff and remained motionless

Question 4

50. What physical characteristic of suspension bridges will make them susceptible to collapse in windstorms, and is there a direct link to the answer to question 48

Answer 4

1. The collapsed bridges spans where very narrow in relationship to its length, had a span off 1 to 72. 2. The slenderness makes the bridge very weak to torsion especially with sufficient stiffening in the longitude direction
2. The grinder on the bridge was shallow and not stiff
3. The aerodynamic instability due to the wind and slenderness of the bridge
4. The bronx-Whitestone bridge was similar in design and did not fail was was twice as heavy, twice as wide and comparably. They had more dampers

Question 5

What were the two causes that destroyed Galloping Gertie by aerodynamic wind oscillations

Answer 5

The weakness had two causes which where the shallowness of the stiffness grinders

The narrowness of its road way in relationship to its span length.

Question 6

53. What is the “law of nature’s laziness”

Answer 6

The law of natures laziness is: when given the choice of two or more paths nature always chooses the path with the least resistance. This will be the path with the minimum amount of energy to achieve this goal.