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Say we have a plan of a building as follows and it is required to be designed using DDM (Direct Design Method). since the moment needs to distributed laterally into a column and middle strips and according to ACI 8.4.1.5 "A column strip is a design strip with a width on each side of a column centerline equal to the lesser of 0.25ℓ2 and 0.25ℓ1." but in this case, both L1 and L2 have different spans and i dont know what to choose.

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  • $\begingroup$ To clarify, what do you mean by "both L1 and L2 have different spans"? Is it that, when designing the center-upper horizontal column strip, L1 (the vertical span) can be 7.5 (from the first row of panels) or 5.0 (from the middle row) at the same time? $\endgroup$
    – Wasabi
    Jan 1 '20 at 22:36
  • $\begingroup$ Yes, that is what I meant. usually, when using this method the spans in any direction are equal or close to equal. but here they are different. I found on the internet somewhere that I need to design each span separately so I think I will do that. $\endgroup$
    – user22341
    Jan 2 '20 at 10:36
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The adjacent span ratio disqualify this project for DDM.

The limit is 0.66 or 1.3 ratio. Here we have 7.5/5= 1.5.

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  • $\begingroup$ sorry, that was just an example and i didn't pay attention to the numbers when I but them. $\endgroup$
    – user22341
    Jan 2 '20 at 10:38

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