Correlation of Predicted and Observed Suspension Bridge Behavior

Doubts concerning the validity of model tests and analysis as an indication of the behavior to be expected of a suspension bridge in the wind are based on (1) a possible scale effect, and (2) the Difference between the natural wind and the wind used in the model tests. The first doubt may be discounted because scale effects in aerodynamic studies are generally related to streamlined flow rather than to the turbulent flow characteristic of wind about a bridge. Test data are presented to demonstrate that turbulent or dynamic effects dominate the wind action on bridges. As to the second doubt, the best indication of uniformity and other characteristics of natural wind may be obtained by a comparison of the behavior of suspension bridges with their behavior as predicted from model tests. The behavior of the original Tacoma Narrows Bridge provides good correlation with the predictions from model tests and analysis. Even more striking are the results of similar but more extensive studies of the Golden Gate Bridge.