seismic design base shear 1

[F1955]

Where you are required to show the seismic design base shear on the drawings, should you show the total value or the diaphragm value? Thank you much.

 

[JAE]

The total value should be shown, not the diaphragm value.

The diaphragm value is a special shear at ONE level only, that is predicated by a min. and max. limit as well as offset vertical brace lines, etc.

 

[TFL]

I HAVE BEEN WONDERING ABOUT THIS........
WHY IS THIS REQ'D ON DRAWINGS BY IBC?

 

[JAE]

I believe that the base shear gives a solid basis for everyting else related to seismic. It indicates the total design demand on the structural system and allows plan checkers to verify (to a degree) whether the seismic loading has been properly applied from the code.

It also provides future engineers with some quantative data for future analysis should the owner decide to alter the building somehow.

 

[TFL]

SO DO YOU HAVE TO DO IT IN BOTH DIRECTIONS?

OK USING THE SAME LOGIC IF IT IS SO IMPORTANT THEN WHY DON'T I PROVIDE IT FOR WIND DESIGN AS WELL.

 

[JAE]

Base shear is the same value in any direction.

For wind design, I believe the code requires the design wind speed and exposure to be stated (we do on every project)

IBC 2000 -section 1603.1.4 calls for the following info to be placed on the drawings:

1. Basic wind speed
2. Wind importance factor
3. Wind exposure
4. Internal wind coefficient
5. Component and cladding pressure for elements not designed by the engineer.

 

[Taro]

Be careful. Base shear is not necessarily the same in each direction. Sometimes different lateral systems are provided in each direction. In this case, the design information should be listed for each direction.

 

[JAE]

Taro - right - forgot about the possibility of different systems.