Drift exceeding allowable limits

[hsn199]

That's a thing I shall try. If I may ask another question: the drift in my model accounting for combination "EQUAKEX" is exceeding 0.02, which is not allowed by UBC 97.

The natural period in my building is about 5.89 s which is too much in my belief. I've checked the elasticity of concrete materials, and stiffness modifiers were only applied for slabs (.35 for flexure). Everything seems to be right.

I've provided an attachment of my model (connectivity at bridges ends is Rigid-Hinge). Any help given in relation to this matter is really appreciated. Thx.

PS: When running the analysis without application of stiffness modifiers, the period is somewhere near 4.45 s. Application of stiffness modifiers for SLABS ONLY, made the period 5.89. I believe if something was done wrong, it was done wrong here.

 

[johnbridge231]

If you used rigid connections (no releases) on both edges of the bridge, would you get a better behaviour in terms of developed laterla drifts? I think yes..

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[hsn199]

@ johnbridge231 thanks for the reply, and yes I've tried Rigid connections and it slightly reduced the drift, still exceeding 0.02.

Here's the thread containing the analysis results if any help could be offered:

http://www.eng-tips.com/viewthread.cfm?qid=333719