CEMP-E
TI 809-02
1 September 1999
CHAPTER 5
SLABS ON GRADE
5-1. INTRODUCTION. This chapter provides design and construction requirements for
industrial type (non-residential) lightly loaded slabs on grade. Industrial type slabs refer to
those slabs that are reinforced to minimize the number of crack control joints (maximize joint
spacing), Guidance for unreinforced residential type concrete slabs, which utilize crack control
joints spaced at frequent intervals to minimize cracking, can be found in the PCA Publication,
"Concrete Floors on Ground." Lightly loaded slabs on grade are those supporting stationary
live loads of not more than 20 kPa (400 pounds per square foot), stationary concentrated line
(wall) loads of not more than 15 kPa (300 pounds per foot), or vehicle axle loads of not more
than 2275 kg (5000 pounds). The guidance is applicable to usual exposure conditions
meaning interior locations other than airplane hangars where slabs are not subject to extreme
climatic changes, and to typical subgrade conditions characterized by sufficient underdrainage
to prevent frost penetration, the absence of a wet environment, i.e., volume change due to
change in moisture content is limited, and the absence of expansive soils. In addition, typical
subgrade conditions are deemed to include only soils classified according to ASTM D 2487,
"Classification of Soils for Engineering Purposes," as either Class ML, any of the S or G
groups, or Class CH, CM, or CL having a modulus of subgrade reaction (k) of 2.75 kg per
cubic centimeter (100 pounds per cubic inch) or greater. Although slabs on grade may be
designed to perform satisfactorily on subgrades of lower strength, design for such conditions is
beyond the scope of this manual. Refer to TI 809-27, "Concrete Floor Slabs on Grade
Subjected to Heavy Loads," for the design of slabs on grade subjected to heavy loads, and to
TI 809-28, "Design and Construction of Reinforced Ribbed Mat Slab" for the design of a
commonly used slab-on-grade system for resisting potential foundation movements at sites
containing expansive soils. Additional information on the design of slabs on grade, primarily
industrial floors, can be found in ACI Committee 360 Report, "Design of Slabs on Grade."
5-2. BASIS FOR DESIGN.
a. General. Slabs-on-grade will be designed for bending stresses due to uniform loads
and concentrated loads and for in-plane stresses due to drying shrinkage and subgrade drag
resistance. When appropriate for the type facility being designed, slabs will be designed for
the effects of warehouse loadings involving aisles, posts and racks, etc. In such instances,
particular attention will be given to the design for negative moment in aisles.
b. Guidance. Proper construction methods, workmanship, and concrete mix
proportioning will follow the guidelines of ACI Committee 302 Report, "Guide to Concrete Floor
and Slab Construction". Slabs are required to have a minimum thickness of 100 mm (4
inches). The following thickness for maximum uniform design live loads will be used provided
the modulus of subgrade reaction (k) is at least 2.75 kg per cubic centimeter (100 pounds per
cubic inch).
5-1
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