Civil Engineering Reference
In-Depth Information
Chapter 10
Design Considerations for
Fire Resistance
10.1
INTRODUCTION
State and municipal building codes throughout the country regulate the fire resistance of the various elements
and assemblies comprising a building structure. Structural frames (columns and beams), floor and roof
systems, and load bearing walls must be able to withstand the stresses and strains imposed by fully developed
fires and carry their own dead loads and superimposed loads without collapse.
Fire resistance ratings required of the various elements of construction by building codes are a measure of the
endurance needed to safeguard the structural stability of a building during the course of a fire and to prevent
the spread of fire to other parts of the building. The determination of fire rating requirements in building codes
is based on the expected fire severity (fuel loading) associated with the type of occupancy and the building
height and area.
In the design of structures, building code provisions for fire resistance are sometimes overlooked and this may
lead to costly mistakes. It is not uncommon, for instance, to find that a concrete slab in a waffle slab floor
system may only require a 3 to 4-
1
/
2
in. thickness to satisfy ACI 318 strength requirements. However, if the
building code specifies a 2-hour fire resistance rating for that particular floor system, the slab thickness may
need to be increased to 3-
1
/
2
to 5 in., depending on type of aggregate used in the concrete. Indeed, under such
circumstances and from the standpoint of economics, the fire-resistive requirements may indicate another
system of construction to be more appropriate, say, a pan-joist or flat slab/plate floor system. Simply stated,
structural members possessing the fire resistance prescribed in building codes may differ significantly in their
dimensional requirements from those predicated only on ACI 318 strength criteria. Building officials are
required to enforce the stricter provisions.
The purpose of this chapter is to make the reader aware of the importance of determining the fire resistance
requirements of the governing building code before proceeding with the structural design.
The field of fire technology is highly involved and complex and it is not the intent here to deal with the chem-
ical or physical characteristics of fire, nor with the behavior of structures in real fire situations. Rather, the goal
is to present some basic information as an aid to designers in establishing those fire protection features of con-
struction that may impact their structural design work.
The information given in this chapter is fundamental. Modern day designs, however, must deal with many
combinations of materials and it is not possible here to address all the intricacies of construction. Rational
methods of design for dealing with more involved fire resistance problems are available. For more
comprehensive discussions on the subject of the fire resistive qualities of concrete and for calculation methods
used in solving design problems related to fire integrity, the reader may consult Reference 10.1.
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