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Structural
I have never used IBC 1613.5.6.1 provision before and just want to make sure that I am interpreting it correctly so I was hoping that someone would help me out. Our client has a one-story masonry industrial building located in a low seismic area (Category A using IBC Table 1613.5.6(1) and category B using Table 1613.5.6(2)). I am trying to use IBC 2012 provision 1613.3.5.1 and use seismic category A so that I can use empirical approach of masonry code when evaluating how many window openings we can fit in the plain ordinary unreinforced masonry shear walls. The text of 1613.3.5.1 reads as the following.
"1613.3.5.1 Alternative seismic design category determination.
Where S1 is less than 0.75, the seismic design category is permitted to be determined from Table 1613.3.5(1) alone when all of the following apply:
1. In each of the two orthogonal directions, the approximate fundamental period of the structure, Ta, in each of the two orthogonal directions determined in accordance with Section 12.8.2.1 of ASCE 7, is less than 0.8 Ts determined in accordance with Section 11.4.5 of ASCE 7.
2. In each of the two orthogonal directions, the fundamental period of the structure used to calculate the story drift is less than Ts.
3. Equation 12.8-2 of ASCE 7 is used to determine the seismic response coefficient, Cs.
4. The diaphragms are rigid as defined in Section 12.3.1 of ASCE 7 or, for diaphragms that are flexible, the distances between vertical elements of the seismic force-resisting system do not exceed 40 feet (12 192 mm)."
Point #1 and #3 are satisfied in my case. Concerning point #2, according to the following thread I have to do another calculation for base shear using the computed fundamental period of the structure and check story drift limits. As far as #4 is concerned, I believe that by "distances between vertical elements" they mean spacing of my shear walls in one direction should not exceed 40 ft (ie. spacing of shear walls from East to West direction needs to be less than 40 ft when seismic force is acting longitudinally on the East - West walls (along long direction NOT normal to the walls) and when seismic force is acting on the North - South walls, then the longitudinal spacing along North - South shear walls needs to be less than 40 ft). Would that be correct interpretation? Basically, I am trying to make sure that they don't mean spacing of 40 ft between shear walls in BOTH directions simultaneously between all shear walls since my building shell is 60' wide and over 100' long and there are no interior shear walls (see attached rough draft). I believe I'm overthinking it but better safe than sorry so I figured I'd ask.
Thanks in advance for any comments.
"1613.3.5.1 Alternative seismic design category determination.
Where S1 is less than 0.75, the seismic design category is permitted to be determined from Table 1613.3.5(1) alone when all of the following apply:
1. In each of the two orthogonal directions, the approximate fundamental period of the structure, Ta, in each of the two orthogonal directions determined in accordance with Section 12.8.2.1 of ASCE 7, is less than 0.8 Ts determined in accordance with Section 11.4.5 of ASCE 7.
2. In each of the two orthogonal directions, the fundamental period of the structure used to calculate the story drift is less than Ts.
3. Equation 12.8-2 of ASCE 7 is used to determine the seismic response coefficient, Cs.
4. The diaphragms are rigid as defined in Section 12.3.1 of ASCE 7 or, for diaphragms that are flexible, the distances between vertical elements of the seismic force-resisting system do not exceed 40 feet (12 192 mm)."
Point #1 and #3 are satisfied in my case. Concerning point #2, according to the following thread I have to do another calculation for base shear using the computed fundamental period of the structure and check story drift limits. As far as #4 is concerned, I believe that by "distances between vertical elements" they mean spacing of my shear walls in one direction should not exceed 40 ft (ie. spacing of shear walls from East to West direction needs to be less than 40 ft when seismic force is acting longitudinally on the East - West walls (along long direction NOT normal to the walls) and when seismic force is acting on the North - South walls, then the longitudinal spacing along North - South shear walls needs to be less than 40 ft). Would that be correct interpretation? Basically, I am trying to make sure that they don't mean spacing of 40 ft between shear walls in BOTH directions simultaneously between all shear walls since my building shell is 60' wide and over 100' long and there are no interior shear walls (see attached rough draft). I believe I'm overthinking it but better safe than sorry so I figured I'd ask.
Thanks in advance for any comments.
