Code of Massachusetts Regulations
780 CMR - STATE BOARD OF BUILDING REGULATIONS AND STANDARDS
Chapter 16 - Structural Design
Section 1607 - LIVE LOADS
Subsection 1607.9 - Reduction in live loads

Universal Citation: 780 CMR MA Code of Regs 1607.9

Current through Register 1531, September 27, 2024

Except for uniform live loads at roofs, all other minimum uniformly distributed live loads, Lo, in Table 1607.1 are permitted to be reduced in accordance with Section 1607.9.1 or 1607.9.2. Roof uniform live loads, other than special purpose roofs of Section 1607.11.2.2, are permitted to be reduced in accordance with Section 1607.11.2. Roof uniform live loads of special purpose roofs are permitted to be reduced in accordance with Section 1607.9.1 or 1607.9.2.

1607.9.1 General. Subject to the limitations of Sections 1607.9.1.1 through 1607.9.1.4, members for which a value of KLLATis 400 square feet (37.16 m2) or more are permitted to be designed for a reduced live load in accordance with the following equation:

Click to view image (Equation 16-22)

where:

L = Reduced design live load per square foot (square meter) of area supported by the member.
Lo = Unreduced design live load per square foot (square meter) of area supported by the member (see Table 1607.1).
KLL = Live load element factor (see Table 1607.9.1).
AT = Tributary area, in square feet (square meters).
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 two or more floors.
TABLE 1607.9.1 LIVE LOAD ELEMENT FACTOR, KLL

ELEMENT KLL
Interior columns
Exterior columns without cantilever slabs		 4 4
Edge columns with cantilever slabs 3
Corner columns with cantilever slabs
Edge beams without cantilever slabs
Interior beams		 2 2 2
All other members not identified above including: 1
Edge beams with cantilever slabs
Cantilever beams
One-way slabs
Two-way slabs
Members without provisions for continuous shear
transfer normal to their span
1607.9.1.1 One-way slabs. The tributary area, AT, for use in Equation 16-22 for one-way slabs shall not exceed an area defined by the slab span times a width normal to the span of 1.5 times the slab span.

1607.9.1.2 Heavy live loads. Live loads that exceed 100 psf (4.79 kN/m2) shall not be reduced.

Exceptions:

1. The live loads for members supporting two or more floors are permitted to be reduced by a maximum of 20 percent, but the live load shall not be less than L as calculated in Section 1607.9.1.

2. For uses other than storage, where approved, additional live load reductions shall be permitted where shown by the registered design professional that a rational approach has been used and that such reductions are warranted.

1607.9.1.3 Passenger vehicle garages. The live loads shall not be reduced in passenger vehicle garages.

Exception: The live loads for members supporting two or more floors are permitted to be reduced by a maximum of 20 percent, but the live load shall not be less than L as calculated in Section 1607.9.1.

1607.9.1.4 Group A occupancies. Live loads of 100 psf (4.79 kN/m2) and at areas where fixed seats are located shall not be reduced in Group A occupancies.

1607.9.1.5 Roof members. Live loads of 100 psf (4.79 kN/m2) or less shall not be reduced for roof members except as specified in Section 1607.11.2.

1607.9.2 Alternate floor live load reduction. As an alternative to Section 1607.9.1, floor live loads are permitted to be reduced in accordance with the following provisions. Such reductions shall apply to slab systems, beams, girders, columns, piers, walls and foundations.

1. A reduction shall not be permitted in Group A occupancies.

2. A reduction shall not be permitted where the live load exceeds 100 psf (4.79 kN/m2) except that the design live load for members supporting two or more floors is permitted to be reduced by 20 percent.

Exception: For uses other than storage, where approved, additional live load reductions shall be permitted where shown by the registered design professional that a rational approach has been used and that such reductions are warranted.

3. A reduction shall not be permitted in passenger vehicle parking garages except that the live loads for members supporting two or more floors are permitted to be reduced by a maximum of 20 percent.

4. For live loads not exceeding 100 psf (4.79 kN/m2), the design live load for any structural member supporting 150 square feet (13.94 m2) or more is permitted to be reduced in accordance with Equation 16-23.

5. For one-way slabs, the area, A, for use in Equation 16-23 shall not exceed the product of the slab span and a width normal to the span of 0.5 times the slab span.

R = 0.08(A - 150) (Equation 16-23)

For SI: R = 0.861(A - 13.94)

Such reduction shall not exceed the smallest of:

1. 40 percent for horizontal members;

2. 60 percent for vertical members; or

3. R as determined by the following equation.

R = 23.1(1 + D/Lo) (Equation 16-24)

where:

A = Area of floor supported by the member, square feet (m2).
D = Dead load per square foot (m2) of area supported.
Lo = Unreduced live load per square foot (m2) of area supported.
R = Reduction in percent.

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