How to determine design story drifts using ASCE 7-10
How to determine design story drifts using ASCE 7-10
(OP)
Hi,
I am having a hard time trying to understand how to determine the design story drifts of a RC building using ASCE 7-10. The building belongs to Seismic Design Category C. Section 12.8.6 (ASCE 7-10) deals with story drift determination and states that:
For me, seismic design forces are those forces computed using 100% of the forces for one direction plus 30% of the forces for the perpendicular direction, according to Section 12.5.3.a (ASCE 7-10). However, I am not quite sure whether I should use the orthogonal combination procedure to determine design story drifts in my building.
Any comments will be greatly appreciated.
Thank you!
I am having a hard time trying to understand how to determine the design story drifts of a RC building using ASCE 7-10. The building belongs to Seismic Design Category C. Section 12.8.6 (ASCE 7-10) deals with story drift determination and states that:
Quote (Section 12.8.6.2 (ASCE 7-10))
For determining compliance with the story drift limits of Section 12.12.1, it is permitted to determine the elastic drifts, (δxe), using seismic design forces based on the computed fundamental period of the structure without the upper limit (CuTa) specified in Section 12.8.2.
For me, seismic design forces are those forces computed using 100% of the forces for one direction plus 30% of the forces for the perpendicular direction, according to Section 12.5.3.a (ASCE 7-10). However, I am not quite sure whether I should use the orthogonal combination procedure to determine design story drifts in my building.
Any comments will be greatly appreciated.
Thank you!






RE: How to determine design story drifts using ASCE 7-10
I take it that a Type 5 horizontal irregularity is driving the need to consider the 100% plus 30% load requirement?
RE: How to determine design story drifts using ASCE 7-10
My building has an "extreme torsional irregularity" (type 1b) and a "reentrant corner irregularity" (type 2). The reentrant corner irregularity is making the building to twist drastically along the CR axis. This is the reason why the building is having an extreme torsional irregularity. So because of that, I think I need to consider torsional and orthogonal effects on my building at the same time. I know that orthogonal effects should only be included when the building has a "nonparallel system irregularity", as prescribed in Section 12.5.3. However, I think orthogonal effects are as equally important as torsional effects in my building. In any case, if my building belonged to Category D, I would have to include orthogonal effects in my building to conform with the minimum requirements of Section 12.5.4, wouldn't I?
Thank you!
RE: How to determine design story drifts using ASCE 7-10
If the code's intent is this hard to understand and the commentary is insufficient, how do you keep from having unintended misinterpretations by regular practising engineers?
Just frustrated about which way things are going in our profession..
RE: How to determine design story drifts using ASCE 7-10
Because the ASCE (and most other major Associations) want you to spend extra money going to their over-priced seminars. Then, and only then, can a normal person ever understand their convoluted codes.
RE: How to determine design story drifts using ASCE 7-10
Given the horizontal structural irregularities you describe, it may very well be prudent for you to exceed the code requirements as far as direction of loading is concerned.
RE: How to determine design story drifts using ASCE 7-10