Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Special seismic load combinations

Special seismic load combinations

Special seismic load combinations

In IBC 2003, the maximum seismic load effect Em (1617.1.1.2) is used with load combinations in sec 1605.4. That section further says, this Em is required for the design of vulnerable elements critical to the stability of the structure. But, It didn’t spell out specific elements crictical to stability?
Then, in sec 1620.2.9, the code says, This Em is required for elements supporting discontinuous walls and frames. ( according to IBC commentary) That means, if we have a discontinuous shaer wall or bracing, we have to design the columns above which we have the discontinuous shear wall or bracing.
But, some of my collegues use this Em for all the bracing elemnts and the columns.
Could you please spend some times and clarify this Sections?
Also, Please try to explain the use of this special seismic load combinations.
Thanks in advanc

RE: Special seismic load combinations

I would agree that the code is not particularly clear on when you use these provisions, other than the example you cited.  There are also some Em requirements in regard to collector elements.  
For steel design, the higher level seismic requirements get defined by the AISC Seismic Provisions (2002 edition for IBC 03).  There are specific requirements in that book in regard to the use of Em type seismic combinations.  For concentrically braced frames, Section 14.2 specifically states that the Em type combinations be used for design of both members and connections.
This will be changing with IBC 06, ASCE7-05, and AISC Seismic 05 to the more normal E for members, Em for connections, but they have drastically reduced the R factor as part of the change.

RE: Special seismic load combinations

Yes,from 2002 AISC Seismic Provisions to that of 2005, They changed the requirement of Em for members. Originally, FEMA 302 does not require Em for all members. According to FEMA 302, the special seismic combinations are for special situations, example collector/chord, column in discontinuous braces and connections.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close