Live Load Reduction Based on Alternative Method
Live load reduction is performed according to NYCBC - 2014 Chapter 16 Section 1607.9.2.
Live loads which are classified as “L,L_Heavy or L_Passenger” are permitted to be reduced in the alternative method.
Figure 4
The design live load of any structural member supporting 150 square feet or more is permitted to be reduced.
Reducible live load area is calculated as described below;
→ The tributary area of each column at column design line is determined.
→ The intersection area of the column tributary and the reducible load area is calculated at each floor.
→ Cumulative reducible area is calculated at each floor.
→ Reducible area of the transfer column ( if exists ) is multiplied by the distribution factor and added to cumulative reducible live load area at the transfer floor.
Live load reduction along column design line is calculated as follows;
→ Total reducible area of live load class L (if any) at each column is determined along the column design line as described before.
→ Reduction in percent is calculated based on the following equation;
R= 0.08*(At -150)
→ For one way slabs, tributary area, At, shall not exceed the product of slab span and a width normal to slab span of 0.5 times slab span.
→ Maximum reduction in percent can not be more than %23.1*(1+D/L) where D is dead load per square foot of area supported and L is unreduced live load per square foot of area supported.
L Load Reduction
Live loads not exceeding 100 psf and are other than public assembly or parking vehicle garages are classified as “L” live load.
→ Maximum reduction in percent for columns can not be more than %60.
→ Live load reduction factor is equal to maximum of (0.6, 1- Rmax/100).
L_Heavy Load Reduction
Live loads exceeding 100 psf are considered to be heavy live loads. Live load reduction for L_Heavy is calculated as follows;
→ If column supports 1 floor, live load reduction factor is 1.0
→ If column supports two or more floors, live load reduction factor is the maximum of ( 0.8, 1-Rmax/100 )
L_AssemblyGroupA Load Reduction
Live Loads which are classified as “L_AssemblyGroupA “ are not permitted to be reduced in alternative method. Thus live load reduction factor for L_AssemblyGroupA is always 1.0.
L_ParkingVehicleGarages Load Reduction
Live loads which are classified as “L_ParkingVehicleGarages” are permitted to be reduced as following;
→ If column supports 1 floor, live load reduction factor is 1.0
→ If column supports 2 or more floors, live load reduction factor is the maximum of (0.8, 1-Rmax/100).
Lr Load Reduction
Roof live loads which are classified as ”Lr” is considered to be unreducible live loads.
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