The wind angle is defined as the angle between the normal to the longitudinal direction of the bridge and wind direction, positive if anti-clockwise, measured from the bridge normal to the wind direction. The wind pressure on the superstructure depends on the wind angle and superstructure dimensions. By default, predefined values for wind pressure, in accordance with AASHTO specifications, are used. However, you can overwrite the default wind pressure and input custom values. The superstructure parameters must be defined before Substructure can automatically generate the wind load on structure.

This generation internally accounts for the pier view direction and then generates loads as per the view direction.

The wind load is calculated in two steps:

Calculate the wind load acting on superstructure, and

Calculate the wind load acting on substructure.

To calculate the wind load acting on superstructure, you must first calculate the superstructure area exposed to the wind load. This area is equal to the product of the total superstructure height and the average span length. Next, the wind pressures in the bridge longitudinal and transverse directions are multiplied with area to obtain the total forces, which are decomposed to the global X and Z directions if the bridge has a skew angle. Then, the total forces are averaged over the bearing points. The wind load also produces a moment due to the arm between the total forces and bearing points. This moment is assumed to be balanced by a force couple (in global Y-direction) acting on the external bearing points at left and right end of pier.

To calculate the wind load acting directly on the substructure, the projected area of pier cap and column are calculated first, depending on the wind direction and the bridge skew angle. Taking a column as an example, the calculation of its projected area is illustrated as follows:

where:

The force acting on the cap in Z-direction is represented as a uniformly distributed load over the length of the cap, while the force acting in X-direction is applied as a concentrated load. The length of the column subject to the wind load depends on the elevation above which the wind is applied (value entered by user on the Auto Load Generation: Wind on Structure screen).

For loads generated for 0 degree angle wind, the user can include the load effects due to Art. 3.15.3. If this option is selected, the program computes the total uplift by multiplying the wind pressure and the area of the bridge to the middle of the span on each side. The total force is applied at quarter point on the bridge. This will result in a moment on the bridge, which is equal to force multiplied by a moment arm equal to ¼ bridge width. The outer bearings resist this unbalanced moment and will result in equal force upward on one bearing and downward on the other. If there are two bearing lines present with other bearings having unequal distance, average distance between the extreme bearings will be used to arrive at the bearing force.