Seismic Forces 1

[Mike7117]

Regarding ASCE allowable stress design load combinations, and considering seismic force "E", it is shown that the calculated seismic force is an ultimate force. When I compute the base shear value "V" per ASCE equations, is this load also an ultimate force that needs to be reduced to compare to calculated wind forces to find the worst case loading?

 

[JAE]

The calculated V is an ultimate seismic force. If you are "comparing" wind to seismic, then yes, the concept would be to use V/1.4.

However, I think it is incorrect to calculate an overall wind force on the building, and compare it to the overall base shear, and then conclude that one controls over the other for the entire structure.

The design process does not always follow that an overall decision as to ---wind or seismic--- controlling the design occurs at the beginning of the design and then automatically controls for all elements of the structure.

Each element of the structure must be designed for the worst case of its wind or seismic load combination. In some cases, the seismic overload may control a brace connection, while the wind may control another part of the structure - such as the deck diaphragm. You have to check both as you proceed through the entire design.

 

[WillisV]

Unless you are in Florida where earthquakes have been outlawed =).

 

[JAE]

heh