Dead Load vs Live Load

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Introduction

Generally, structural loads including forces, deformations or accelerations applied to a structure can be divided into two main category: 1- Dead load, and 2- Live load

Concepts and Formulas

Dead loads

Dead loads are static forces that are relatively constant for an extended time; usually the weight of materials plus immovable fixtures such as carpet, roof and etc. Minimum design dead load can be found in ASCE 7 Table C3-1.

Building materials are not dead loads until constructed in permanent position.

Live loads

Live loads are usually unstable or moving loads (temporary loads) and based on the functionality of the structure. These dynamic loads may involve considerations such as impact, momentum, vibration, and etc.

Roof and floor live loads are produced during maintenance by workers, equipment and materials, and during the life of the structure by movable objects, such as planters and people.

Minimum design live load can be found in ASCE 7 Table 4-1 or IBC Table 1607.1.

Examples:Office building:

Lobbies and first-floor corridors: 100 psf (uniform) 2000 lbs (concentrated)
Offices: 50 psf (uniform), 2000 lbs (concentrated)
Corridors above first floor: 80 psf (uniform), 2000 lbs (concentrated)

Partition load: 15 psf

Live load reduction:

Floor live load reduction: (ASCE 7-05/10, IBC 2006/2009/2012)

For live load not exceeding 100 psf, not in passenger garages, not in assembly uses, with K_LL x A_T more than 400 square ft², Live load can be reduced by the following equation

$L=L_0(0.25+frac{15}{sqrt{K_{LL}A_T}})$

where L₀ is unreduced live load; A_T is tributary area; and K_LL is the live load reduction element factor:

K_LL	Use
4	interior column and exterior columns without cantilever slabs.
3	edge column with cantilever slabs.
2	corner column with cantilever slabs, edge beams without cantilver slabs, and interior bams.
1	all other conditions

Alternate floor live load reduction: (IBC)

For live load not exceeding 100 psf, not in passenger garages, not in group A occupancies of IBC, supporting more than 150 square ft², Live load can be reduced by the following percent.

R = 0.08*(A-150)

A is tributary area

R is percent of reduction shall not be more than 40 percent for horzontal member, and 60 percent for vertical member, and not exeeding

R = 23.1 (1+D/L_o)

where D is floor dead load:

Roof live load reduction:

Roof live load may be reduced by the following equation:

L_r = L_o R₁ R₂

Where L_r shall not be less than 12 psf and not more than 20 psf

R₁ =1 for A_t less than or equal to 200 psf,
R₁ = 1.2 - 0.001 A_t for between 200 psf and 600 psf
R₁ =0.6 for A_t greater than or equal to 600 psf,
R₂=1 for F less than or equal to 4
R₂ = 1.2 - 0.01 F for between 200
R₂ =0.6 for F greater than or equal to 600 psf,

where F is number of inches of rise per foot.

Handrails, Guardrail systems, and grab bar:

Handrail: 200 lbs concentrated load in any direction, any point.

Guardrail: 50 lb/ft uniform load and 200 lbs concentrated load at top. 50 lbs in 1 ft square area for intermediated rails, panel filters, etc.

Grab bar: 250 lbs concentrated load in any direction, any point.

Vehicle Barrier System:

6000 lbs concentrated load in 1 square foot area at 1 ft 6 inches above floor or ramp surface.

Fixed ladder: 300 lbs concentrated load in any direction.

Crane wheel loads:

Maximum Crane wheel load shall be the sum of weight of bridge, crane load capacity, and weight of trolley with trolley in a position that produces maximum load

Design load increase for crane wheel load:

Vertical impact force:

Monorail cranes (powered) : 25%
Cab-operated or remotely operated bridge cranes (powered): 25%
Pendant-operated bridge crane (powered): 10%
Hand-geared bridge, trolley, and hoist: 0%

Lateral force: 20%

Longitudinal force: 10%

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