How can bridges with stand heavy winds and rain?

Answer 1

Short answer: they are designed to do so. Bridge engineers calculate the forces incurred by the traffic on a bridge and the weight of the bridge itself: these act in the vertical direction, more or less. But we also calculate an assumed load from wind acting horizontally against the sides of a bridge. This is estimated to be so many pounds per square foot of bridge structure and vehicles on the bridge. What is called secondary support members are designed to accept these loads and conduct them to the bridge ends. On some bridges, you can see a series of "X" shaped members under the bridge deck. These are the secondary supports that keep the bridge from moving sideways under wind and traffic loads. Other bridges may not have these members, but the structure is designed to carry the load in another manner.