×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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

Jobs

Seismic Analyses Questions

Seismic Analyses Questions

RE: Seismic Analyses Questions

Quote (OP)

1. Why We Make Scale Factor Between Static And Dynamic Seismic Analysis ?
2. After Scale Factor We Design By Load Combinations Included Dynamic Cases Only
Or Static Load Only Or Dynamic And Static ?
3. What is Diaphragm And What is Importance of Diaphragm In Seismic And Wind?
4. When We Define Diaphragm? And We Define As Rigid Or Semi Rigid And What is the Different Between Them?
5. Different Between Displacement And Drift Due to Seismic ?
6. Displacement Due to Seismic Results From Etabs We Multiply it X 0.70 X R ,Why And What About Drift ?
7. We Make 3 Cases For Each Case ( X AND Y ) in Static Analysis What About Dynamic Same Or Not
Static Analysis
Ex
Ex With + Eccentricity
Ex With – Eccentricity
Ey
Ey With + Eccentricity
Ey With – Eccentricity
8. Why We Don't Combine Seismic And Wind in Load Combinations?
9. In Dynamic Analysis , Forces Cause Mode Shapes Or Mode Shapes Cause Forces?
10. Difference Between Response Spectrum ( Dynamic ) And Time History , Which Best?
11. What is the Effect of Seismic in Slabs And Beams?
12. Design Of Slabs And Beams By Load Combination Included Seismic Right Or Wrong?
13. After Finishing 3D Model , What are the Checks For Seismic?
14. Slab On Grade , I Put In Etabs Or Not ?
15. How Building Make Damping For Seismic ,What is Factors Damping Depend on?
16. Different Between Point Drift – Story Drift – Diaphragm Drift ?
17. How Many ETABS Models Should Be Perform For Building to Make Actual Behavior Of Building ? Please Mention Purpose For Each Case ?

These are some pretty general questions. Please consider my answers partial at best.

1) We don't. Static (ELF) and dynamic procedures are two different animals.
2) See #1. Two different paths.
3) Diaphragms distribute seismic loads originating mostly in the floor and roof decks to the vertical lateral force resisting elements (walls, braces, etc.)
4) Generally wood and untopped steel deck diaphragms are flexible while concrete, concrete topped, and discretely braced diaphragms are not. ASCE 7-10 provide guidance.
5) Displacement is usually conceived of as an absolute value; drift is usually evaluated on story by story basis h/xxx.
6) We multiply by R to try to convert an elastic displacement to displacement that includes the effects of post yield displacement.
7) It depends on your local code and the dynamic procedure that you choose. Usually people do employ load cases including eccentricity in dynamic procedures.
8) It is considered improbable that design EQ and design Wind loads will occur simultaneously.
9) Neither. Mode shapes with periods close to the period of the excitation function attract displacements which generate strains and forces.
10) Try this: Link
11) If the members are part of the lateral load resisting system, seismic influences the design significantly. If not, the members need to be able to accommodate the expected seismic drift.
12) See #11.
13) This is too broad a question for me to be able to provide a meaningful answer. Check all members for their capacity to resit load effects including seismic. Follow detailing recommendation in your local code to ensure ductile response where you need it. Check drift limits.
14) Not normally.
15) Damping depends on a number of things, predominately the materials involved in construction. I believe that ELF procedure response spectra are based on 5% critical damping.
16) See #5
17) Generally one. Engineers will often vary parameters in an attempt to bracket behavior.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Seismic Analyses Questions

KootK - There is a requirement in the US codes to limit any dynamic analysis to a percentage of the static analysis base shear.

This appears to be simply a "floor" to the dynamic design to ensure that someone doesn't mis-use or mis-analyze a structure using flawed parameters or assumptions.

See ASCE 7-05 or 7-10 section 12.9.4.

Check out Eng-Tips Forum's Policies here:
FAQ731-376: Eng-Tips.com Forum Policies

RE: Seismic Analyses Questions

I agree JAE. Just wasn't sure that was what was meant by scaling here.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

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!


Resources