Seismic Design 4

[jmp02t]

All,

I am having trouble here understanding seismic design. I'm a young engineer and haven't had much experience with this.

I have a two story steel framed building. The floor level is a rigid diaphragm (concrete on metal deck) ~15' AFF. The roof level is a flexible diaphragm (metal deck) that is another 15'. I have calculated the base shear for the structure, but am confused as to where to go from there. (I've done seismic design for a one story, and know the basic half the load to the top, half to the foundation.. that's a given) I am not sure now how to determine the load that is distributed to the floor, roof and foundation based on the types of diaphragms.

Any help would be great. I've been searching for example problems online and haven't found anything useful. If you have anything, I would appreciate it a lot.

Thanks!

 

[jtx]

ASCE 7 section 12.8.3 has an equation that you can use to determine the vertical distribution of the base shear to the upper floors.

 

[IceNine]

Check out the following website for FEMA 451 - Design Examples. This document is free, and covers steel,concrete,masonry,wood...

http://www.nibs.org/index.php/bssc/publications/2003/fema451designexamples/

 

[2Hats]

Wow! That nibs link a fantastic resource -- not only that particular page, but the ones around it too. Thanks for sharing!

 

[ToadJones]

There is also a "Code Master" 10 page or so pamphlet out there that outlines a design procedure.

 

[steellion]

ASCE gives clear guidance on how to determine the load at each floor level. From there, the roof diaphragm would distribute the loads to your lateral load-resisting elements based on their tributary width because it is a flexible diaphragm. The 2nd floor rigid diaphragm will distribute loads to the lateral FRS elements is proportion to their relative stiffness.

 

[msquared48]

Just remember that, in gerneral, the percent of the base shear that is assigned to each floor is based on the deadload of that story times its height above the base level over the sum of all the floor dead loads times their heights above the base level.

Until you get to higher buildings, that will work for you.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[jmp02t]

Thank you all so much! I appreciate the help