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Understanding Structural Systems and Seismic Impact of Design [Exercise A]
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Can someone explain how to use IBC table 1604.3. The exercise mentions the following: A 20-foot roof beam is constructed from a steel wide flange section and supports a non-plaster ceiling with a point load of 20 psf at midspan.
Per IBC, what is the maximum allowable deflection in inches?
But the IBC table has 3 columns
Thanks!
Great question @Nicolas.Pinzon! The three columns represent different load conditions used to check deflection:
- L or Lr = live load or roof live load
- S or W = snow load or wind load
- D + L = dead load plus live load
You select the column based on the type of load described in the question, then use the deflection limit at the intersection of that column and the applicable member/ceiling condition. So the key is to first identify what load is acting on the member, then select the corresponding column. In this question, the 20 psf load is intended to represent the roof live load (Lr), which is why you use the first “L or Lr” column in Table 1604.3.
Hope this helps!
Kiara Galicinao, AIA, NCARB
Product Coordinator
Black Spectacles