Dead Load according to the 2009 IBC
Dead load is due to the weight of the structure itself, plus permanently attached components. Calculation of dead loads is not discussed further at this point. It is discussed in specific examples, as are IBC loading combinations including dead load.
Floor Live Load according to the 2009 IBC
Live load is prescribed by the 2009 IBC. The loading provisions of the 2009 IBC are discussed here using the section numbers taken from that document. The 2009 IBC itself uses loads that are almost identical to those prescribed by ASCE 7-05 (Supplement). In the future, the IBC will tend more and more to reference ASCE 7 loads directly. Minimum live loads (L) for floors (from Table 1607.1 of the 2009 IBC) are given in Table 3.1.
By Sec. 1607.9.1 of the 2009 IBC, live loads are permitted to be reduced based on the tributary area over which those live loads act. Live loads in public assembly areas (balconies, corridors, and stairs) are not permitted to be reduced. The live-load reduction factor, shown below, applies to elements for which the product KLL AT equals or exceeds 400 ft2 as shown here
L shall not be less than 0.50 Lo for members supporting one floor and L shall not be less than 0.40 Lo for members supporting more floors. Live-load reduction factors are given in Table 1607.9.1 of the 2009 IBC, reproduced in this chapter as Table 3.2.
Example of Floor Live-Load Reduction according to the 2009 IBC
Consider an interior beam of an office floor with a tributary area of 400 ft2 (KLL = 2).
Roof Live Load according to the 2009 IBC
In accordance with Sec. 1607.11.2 of the 2009 IBC, the minimum roof live load for most roofs is 20 psf. Roof live loads are permitted to be reduced in accordance with the following:
Lr = Lo R1R2
where Lr = reduced roof live load per square foot
Lo = unreduced roof live load per square foot
R1 = see Fig. 3.2
R2 = 1.0 for flat roofs
The minimum reduced roof live load is 12 psf. The reduction is shown graphically in Fig. 3.2.