×
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

How to select the seismic response coefficient (Cs) in ASCE/SEI 7-05

How to select the seismic response coefficient (Cs) in ASCE/SEI 7-05

How to select the seismic response coefficient (Cs) in ASCE/SEI 7-05

(OP)
Hi All

I have been implementing seismic analysis following ASCE7/SEI 7-05 and I meet a big confusion these days when I plan to calculate the equivalent lateral force procedure base shear to scale design values of combined response for modal response spectrum analysis (Section 12.9 of ASCE/SEI 7-05).
According to Section 12.8.1.1 of ASCE/SEI 7-05 (Page 129) we can get this relationship shown in the following:
When T<=TL,S1>=0.6g
 0.5S1/(R/I)<=CS<=SD1/T/(R/I);CS=SDS/(R/I)
Now we have a project:

Ss=1.981;S1=0.926;SDS =1.32;SD1  =0.93:R=1.5;I=1.0;T=2.807s;TL=8s

So  we can get these following results:  
0.5S1/(R/I)=0.5*0.926/(1.5/1)=0.309

SDS/(R/I)=1.32/(1.5/1)=0.88

SD1/T/(R/I)=0.93/2.807/(1.5/1)=0.221

That means Csmax <Csmin,it is very clear that there is a conflict.0.5S1/(R/I)=0.309<CS=0.88>SD1/T/(R/I)=0.221
Then I am confused which number should select for Cs,0.221? or 0.309?

This is an urgent project for me.Could you please help me clarify this confusion? I am very appreciated for your quick reply!


BR


Henry

  

RE: How to select the seismic response coefficient (Cs) in ASCE/SEI 7-05

My interpretation is the following:

Cs is the minimum value of 12.8-2 and 12.8-3(or 12.8-4).  But in addition where S1>0.6, Cs cannot be less than 12.8-6.

So in your case 12.8-6 would govern.

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