×
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

Abrupt change in stiffness

Abrupt change in stiffness

Abrupt change in stiffness

(OP)
Hello,
Working on a new two-storey steel frame college building where the architect allows no vertical braces. I tried moment frames as a lateral resisting system, but story drifts exceeded the allowed limits, then I used some of the CMU infill walls as shear wall in combination with some moment connections in the framing of the roof where needed, which made drifts acceptable. The problem is that some of the walls I used in level 2 are not continued down to level 1 and level 1 is stiffer that level 2. Should I be worried about this abrupt change in stiffness?
Thanks for the inputs.

RE: Abrupt change in stiffness

In a high seismic zone that would possibly create a vertical irregularity that should be considered in the design.  What code are you designing with?

 

RE: Abrupt change in stiffness

(OP)
JAE,
It is the National Building Code of Canada. The area is not a high seismic zone. The seismic hazad index, Ie.Fa.Sa(0.2), is 0.52.

RE: Abrupt change in stiffness

I could be wrong on this, if so, please correct me.

Because the infill-shear walls, shouldn't be the 2nd floor stiffer than the first foor, eventhough the steel elements are smaller? Since it is in low seismic zone, as long as all members in a joint can adequatelly carry their's share of loads, the walls are properly anchored to the beams, and all deflections are within allowable limits, I don't see much of problems. Do you have specific concern in mind?

RE: Abrupt change in stiffness

(OP)
My concern is that the code allows using static analysis for a building like this one with stiffness irregularity if its period is smaller than 0.5 sec. But, really, how you calculate the period correctly?   

RE: Abrupt change in stiffness

I evision a steel moment frame (1st story) supporting a rigid body (2nd story) above. Maybe you can find the period by computer modeling.  

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