KelleyA
Structural
- May 1, 2014
- 6
Hello,
I'm currently working on a tier 3 seismic retrofit of an existing 1 story CMU building. When I originally ran through equation (7-21) I used Table 7-3 to obtain a value for my C[sub]1[/sub]C[sub]2[/sub] factor. At the time this got me C[sub]1[/sub]C[sub]2[/sub] = 1.4.
Going through the building though I realize I may have made a bad assumption in my primary components. I assumed that my CMU shear walls would be "Controlled By" shear and used a m-factor of 2.0 for LS and 3.0 for CP. Looking at m values for controlled by flexure though I see my m-factors would be 7.0 for LS and 8.0 for CP, which would raise my C[sub]1[/sub]C[sub]2[/sub] to 1.8. So I have two questions:
1. What defines what the wall is controlled by? Is it a demand-capacity ratio for each type of force at each wall? Or is each wall "controlled by" whichever force you're analyzing at the current time? Ie. when checking flexure you use a m of 7/8 and when checking shear you use a m of 2/3.
2. For equation (7-22) and more specifically (C7-3), can you assume a DCR[sub]max[/sub] of 1.0 if you plan to retrofit everything so that nothing is failing? If everything is adequate there shouldn't be a DCR greater than 1.0. This would set u[sub]strength[/sub] = 1.0 and thus C[sub]1[/sub]C[sub]2[/sub] = 1.0. I feel like this is probably not the case as the DCR probably only refers to the primary components as they exist and not how they will be after being retrofitted.
Thank you for your time.
I'm currently working on a tier 3 seismic retrofit of an existing 1 story CMU building. When I originally ran through equation (7-21) I used Table 7-3 to obtain a value for my C[sub]1[/sub]C[sub]2[/sub] factor. At the time this got me C[sub]1[/sub]C[sub]2[/sub] = 1.4.
Going through the building though I realize I may have made a bad assumption in my primary components. I assumed that my CMU shear walls would be "Controlled By" shear and used a m-factor of 2.0 for LS and 3.0 for CP. Looking at m values for controlled by flexure though I see my m-factors would be 7.0 for LS and 8.0 for CP, which would raise my C[sub]1[/sub]C[sub]2[/sub] to 1.8. So I have two questions:
1. What defines what the wall is controlled by? Is it a demand-capacity ratio for each type of force at each wall? Or is each wall "controlled by" whichever force you're analyzing at the current time? Ie. when checking flexure you use a m of 7/8 and when checking shear you use a m of 2/3.
2. For equation (7-22) and more specifically (C7-3), can you assume a DCR[sub]max[/sub] of 1.0 if you plan to retrofit everything so that nothing is failing? If everything is adequate there shouldn't be a DCR greater than 1.0. This would set u[sub]strength[/sub] = 1.0 and thus C[sub]1[/sub]C[sub]2[/sub] = 1.0. I feel like this is probably not the case as the DCR probably only refers to the primary components as they exist and not how they will be after being retrofitted.
Thank you for your time.
