Page 175 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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BUILDING CODES, LOADS, AND FIRE PROTECTION*

BUILDING CODES, LOADS, AND FIRE PROTECTION 4.3

the wind and the geometry of the structure, wind loads may exert either a positive or negative pressure
on a building surface.
All building codes and project specifications require that a building have sufficient strength to
resist imposed loads without exceeding the available strength of any element of the structure. Of
equal importance to design strength is the design requirement that a building be functional as stipu-
lated by serviceability considerations. Serviceability requirements are often given as allowable or
permissible maximum static deflections, either vertical or horizontal, or both. They may also be in
the form of dynamic response characteristics, such as natural frequency or acceleration.

4.4.2 Dead Loads
The dead load of a building includes weights of walls, permanent partitions, floors, roofs, framing,
fixed service equipment, and all other permanent construction (Tables 4.1 and 4.2). The ASCE stan-
dard, “Minimum Design Loads for Buildings and Other Structures” (SEI/ASCE 7-02), gives detailed
information regarding computation of dead loads for both normal and special considerations.

4.4.3 Floor Live Loads
Typical requirements for live loads on floors for different occupancies are summarized in Table 4.3.
These minimum design loads may differ from requirements of local or state building codes or pro-
ject specifications. The engineer of record for the building to be constructed is responsible for deter-
mining the appropriate load requirements.
Temporary or movable partitions should be considered a floor live load. For structures designed
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for live loads exceeding 80 lb/ft , however, the effect of partitions may be ignored, if permitted by
the local building code.
Live Load Reduction. Because of the small probability that a member supporting a large floor area
will be subjected to full live loading over the entire area, building codes permit a reduced live load
based on the areas contributing loads to the member.
The ASCE standard, “Minimum Design Loads for Buildings and Other Structures” (SEI/ASCE
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7-02), permits a reduced live load L (lb/ft ) computed from the following for design of members with
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a value of K LL A T of 400 ft or more:
 15 
L = L 025. +  (4.1)
o
 KA 
LL T
where L o = unreduced design live load (psf) supported by the member
K LL = live load element factor (see Table 4.4)
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A T = tributary area (ft )
The tributary area A T for one-way slabs must not exceed the area defined by the slab span multiplied
by the width normal to the span, nor an area equal to 1.5 times the slab span squared. The reduced
live load should not be less than 0.5L o for members supporting one floor nor 0.4L o for all other load-
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ing situations. If live loads exceed 100 lb/ft , and for garages for passenger cars only, design live
loads may be reduced 20% for members supporting more than one floor. For members supporting
garage floors, roofs, or areas used for public assembly, no reduction is permitted if the design live
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load is 100 lb/ft or less.
4.4.4 Concentrated Loads
Some building codes require that members be designed to support a specified concentrated live load
in addition to the uniform live load. The concentrated live load may be assumed to be uniformly dis-
2
tributed over an area of 2.5 ft and located to produce the maximum load effects in the members.
Table 4.3 lists some typical concentrated loads that may be specified in building codes.

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