Design in earthquake zones(acc.to CBC)? 1

[schau]

Hello,
I am a civil eng. in Germany and i am doing for the first time statical calculation according to the american norm and
in particular to California Building Code. That is way i have some questions about calculating steel buildings in earthquake
zones. Based on the code there should be generated two
general load combinations: basic load combination (BLC) and special seismic LC (1,2D+L+Em).
So when i am doing the design checks (ASD) for the BASIC LC i am using the allowable stresses
(nominal Value divided by the safety factor OMEGA) for the comparisson(all./req.). So far so good. Here's the question:
What shall i do by the seismic LC? Can i use the nominal strengths of the members (i mean without dividing by OMEGA,
for Example for Tension would be R=AFy)? If not i am bekomming enormous connections, because the earthquake load is
multiplied by the seismic overstrength factor Omega!!
If i have a comression members (single Angle Bracing), shall i design it for buckling with the special LC or it is enough
to design only the connections with it, and for buckling shall i take the basic LC.

I will be very gratefull if someone can help me with these Problems! A general answer would be ok too, for me
is the basic approach important (how it is proceeded by designing in earthquake zones).

Thanks for the help!

 

[bkgd]

Schau, did you ever get a response if not i may be of some assistance?

 

[schau]

Hi, I have not received any answers yet. If you could write some lines about this topic i would be very gratefull! Thanks

 

[prsconsultant]

Vist the following link. It has design examples of analysis and design. These are based on NEHERP but the concepts are similar in California Building Code.

http://www.bssconline.org/Design Examples/451chapters.htm

 

[whyun]

The current California Building Code is based on the 1997 Uniform Building Code. You may be interested in the three volume Seismic Design Manual based on the 1997 Uniform Building Code, particularly Volume I which covers Chapter 16 of the UBC and Volume III which covers steel and concrete structures with design examples. The design examples indicate which members/connections are to be designed using the Omega factor.

There is a set of Seismic Design Manual based on the IBC. If you need to comply with current California Building Code, be sure to get the 1997 UBC version.

 

[Perennial]

If you like software, I have had great help using LatPro 1.7 which is based on the CBC. It can be found at lateralpro.com and allows the user to enter user defined shear walls, etc so you can try various designs.

 

[LGARG]

Hi schau

If your using ASD and the special load combinations for seismic(omega=2.8) you can increase your allowable stress value by a 1.7 factor. The omega factor is used on connections designs and also in some of the diferent types of discontinuity listed on the Ubc Table 16-M and 16-L. The special Seismic combination is an Strengh design combination so you can use this 1.7 value to change from ASD(Allowable Stress Design) to Strengh design(Limit state design) You should only design the connection w/2.8 Factor, but sometimes for simple moment frames you could calc all the frame with the omega and you don´t have to check the connection and the drift.
I hope that this colud be helpfull for you.



LG