SrVaro
Structural
- Oct 19, 2010
- 53
My company has been trying to get clarification on the Seismic Coeffs for Non-Building Structures Similar to Buildings with no such luck. The question concerns the detailing requirements when R<3 for Ordinary Steel Concenttrically Braced Frames with Permitted Height Increase. This has an R value of 2-1/2.
Per Table 15.4-1, the detailing requirements are AISC 341.
Per AISC 341 page 1-7; "The Seismic Provisions are not intended to apply to structures designed with R equal to 3 or less. These systems are permitted in Seismic Design Categories A, B, and C, but not in Seismic Design Categories D, E, and F."
Thus we are interperting this as for the lower three categories, we do not need to follow AISC 341 and should use AISC 360 for the design and detailing of the structure.
Per AISC 341 section 2.1 page 6.1-15; "These provisions shall apply when the seismic response modification coefficient, R, (as specified in the applicable building code) is taken greater than 3, regardless of the seismic design category. When the seismic response modification coefficient, R, is taken as 3 or less, the structure is not required to satify these provisions, unless specifically required by the applicable building code."
Therefore, we have a continuous loop where the code refers to the provision, but the provision says it is not required unless the stated so within the code.
Has anyone else run into this issue? And if so how have you addressed the issue?
For one project we changed to unlimited hieght, which allows for the use of AISC 360, but at a higher base shear cost. When wind controls, this is not an issue, but when there are heavy wieghts there is an increase in bracings costs, etc. In the future we would like to avoid this if possible. Else we need to detail to the stricter provisions.
Thank you in advance for any guideness or clarifications.
Per Table 15.4-1, the detailing requirements are AISC 341.
Per AISC 341 page 1-7; "The Seismic Provisions are not intended to apply to structures designed with R equal to 3 or less. These systems are permitted in Seismic Design Categories A, B, and C, but not in Seismic Design Categories D, E, and F."
Thus we are interperting this as for the lower three categories, we do not need to follow AISC 341 and should use AISC 360 for the design and detailing of the structure.
Per AISC 341 section 2.1 page 6.1-15; "These provisions shall apply when the seismic response modification coefficient, R, (as specified in the applicable building code) is taken greater than 3, regardless of the seismic design category. When the seismic response modification coefficient, R, is taken as 3 or less, the structure is not required to satify these provisions, unless specifically required by the applicable building code."
Therefore, we have a continuous loop where the code refers to the provision, but the provision says it is not required unless the stated so within the code.
Has anyone else run into this issue? And if so how have you addressed the issue?
For one project we changed to unlimited hieght, which allows for the use of AISC 360, but at a higher base shear cost. When wind controls, this is not an issue, but when there are heavy wieghts there is an increase in bracings costs, etc. In the future we would like to avoid this if possible. Else we need to detail to the stricter provisions.
Thank you in advance for any guideness or clarifications.
