Live Load Reduction

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.

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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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