ACI R: Guide to Design of Slabs-on-Ground. Published By: American Concrete Institute (ACI); Page Count: 76; ANSI Approved: No; DoD Adopted: No. ACI R Guide to Design of Slabs-on-Ground. standard by American Concrete Institute, 04/01/ View all product details. Most Recent. Track It. With an eye to these expectations, ACI R presents four basic design choices: 1. Unreinforced concrete slab. 2. Slabs reinforced to limit crack widths. 3.
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360R-10 Guide to Design of Slabs-on-Ground
The report ad- dresses the planning, design, and detailing of the slabs. Design methods are given for plain concrete, reinforced concrete, shrinkage-compensating concrete, and post- Chapter 3-Soil support systems for slabs on grade, pg. Design examples appear in an appendix. Concrete; curling; design; floors on ground; grade floors; 360t 3.
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In this context, design is defined 7. Information on other aspects, such as 7. In the context of this report, Committee defines Chapter 360f of post-tensioned slabs on grade, pg.
The slab may be plain, reinforced, or pre- 8. The reinforcement or prestressing 8. Chapter 9-Reducing the effects of slab shrinkage and This report covers the design of slabs on grade for curling, pg.
ACI R Design of Slabs on Grade Reported by ACI Committee | Gary Edward Tan –
ACI Committee 9. Although the same gen- 9. The United States Army Corps of Engineers, the National Academy of Develop and report on criteria for design of slabs on Science, and the Department of Housing and Urban De- grade, except highway and airport pavements velopment have developed guidelines for floor slab design and construction. Several industrial associations, 1. It also con- universities and consulting engineers have studied slabs tains information on thickness and finishing requirements on grade and developed recommendations on their de- ack different classes of slabs.
In addition, periodicals such as 1. In developing this report, Committee has committee documents include ACI The magnitude of these stresses depends upon fac- slabs transmit structural loads.
Chapter 13 of ACI R tors such as the degree of continuity, subgrade strength states: In from other parts of the structure to the soil. Slabs on grade are important elements in methods for slabs on grade are based on theories origi- such construction. However, residential slabs generally do nally developed for airport and highway pavements. An not require detailed design unless poor soil conditions early attempt at a rational approach to design was made are encountered.
Although the observations unusual or heavy loads, require more thorough evalua- in the first road test with rigid pavements seemed to be tion of soil properties and their interaction with the slab in reasonable agreement with the predictions of this for- structure. The design pro- tropic, and elastic slab resting on an ideal subgrade that cedures for mat foundations are given in ACI This is known as heavily reinforced than common slabs on grade.
The subgrade is assumed to act as 1. The units are commonly abbrevi- parking lots. While the principles and methods of design ated as pci.
This is the constant now recognized as the in this ACI report are applicable to parking lot coefficient of subgrade reaction, more commonly called pavements, the latter have unique considerations that are the modulus of soil reaction or modulus of subgrade covered in ACI R, which includes design and con- reaction.
Solution of the subgrade. However, although a proper choice of the governing equations by conventional methods is feasible modulus of subgrade reaction was found to be essential only for simplified models, where the slab and the sub- for good agreement with respect to stresses, there grade are assumed to be continuous and homogeneous.
Thus, the use of this ap- mation accumulated to indicate that the behavior of proach is quite limited.
R Guide to Design of Slabs-on-Ground
Various models have been proposed to to evaluate the deformation response of such solids. The sub- finite extent but of finite thickness, Burmister in grade is usually modeled by linear springs the Winkler proposed the layered-solid theory of structural behavior subgrade placed under the nodal joints. While the finite for rigid He suggested that the design should element method offers good potential for complex prob- be based on a criterion of limited deformation under lems, its use in typical designs has been limited.
However, the design procedures for rigid pavements computers may enhance its usage and that of other nu- based on this theory were never developed enough for merical methods in the future. The lack of analogous solu- tions for slabs of finite extent edge and corner cases 1. Other approaches based on Chapter 2 identifies types of slabs on grade and ap- the assumption of a thin elastic slab of infinite extent propriate design methods. Chapter 3 discusses the role of resting on an elastic, isotropic solid have been developed.
Chapter 4 presents a discussion of by assumption, are proportional to applied loads.
Chapters 5 through 9 provide information berg later proposed a strength theory based on the on design methods and the related parameters needed to yield-line concept for ground supported slabs, but the use complete the design.
Design examples in the appendix of strength as a basis for the design of the slab on grade illustrate application of selected design methods. Three different models are used for the slab: This chapter identifies and briefly discusses the Two models used for the subgrade are the elastic-iso- common types of slab-on-grade construction and the de- tropic solid and the so-called Winkler subgrade.
Existing sign methods appropriate for each Table 2. The un- design theories are based on various combinations of derlying theory, critical pressures, and construction these models. The methods presented in this report are features intrinsic to each method are identified. Methods generally graphical, plotted from computer-generated presented are those attributed to the Portland Cement solutions of selected models. As stated in the basic definition of Section 1.
Most currently used theoretical design less than 50 percent of the allowable bearing capacity methods for the rigid pavements use the Winkler model, thereof. There are, of course, exceptions such as where and a number of investigators report good agreement be- the soil is highly compressible and allowable bearing tween observed response of rigid pavements and the pre- pressures are extremely low.
Such situations 30r covered diction based on that model. Xci the same time, the elas- in literature of the Post-Tensioning Institute. Committee believes that slabs, and others.
Although the term also includes park- the best way to obtain 360 flexural strength is to ing lot slabs and paving surfaces, these are not specific- increase the thickness of the slab. This concrete does shrink, but first it expands an amount intended to be slightly greater than a Plain concrete slab its drying shrinkage. Distributed reinforcement for tem- b Slab reinforced for shrinkage and temperature perature and shrinkage 306r to 0. The prestress slab must be isolated from fixed portions of the structure, f Slab reinforced for structural action such as columns and perimeter foundations, with a com- pressible material that allows the slab to expand.
Slab thickness design methods appropriate for each Type C slabs are designed to remain uncracked due type are also shown in Table 2. Slab Types A through to loads applied to the slab surface.
Thickness design is E are designed with the assumption that applied loadings the same as for Type A and B slabs, but joints can be will not crack the slab. For Type F the designer antici- spaced farther apart than in those slabs. Design concepts pates that the applied loadings may crack the slab.
It is designed to remain uncracked ness design procedures like those for Types A, B, and C. The intervals than for Type A, B, and C slabs. The effects of drying shrinkage and uni- dons are required. To reduce Chapter 6is critical to design of Type D slabs. Thickness design cracked slabs, following PTI using active is the same as for plain concrete slabs, and the slab is prestress, which permits the use of thinner slabs.
Shrinkage cracking is controlled by a nominal or inforcement, Type E slabs may incorporate monolithic small amount of distributed reinforcement placed in the beams sometimes called ribs to increase rigiditiy of the upper half of the slab, and therefore joint spacings can section. The Type E slab may be designed to accept structural Joint spacings can be computed using the subgrade loadings, such as edge loadings from a building super- aaci equation Chapter 6 for a pre-selected amount of structure, as well as to resist the forces produced by the steel for shrinkage and temperature control; however, the swelling or shrinking of unstable soils.
Unlike the previously described slab types, the Type F The primary purpose of the reinforcement in axi slab afi designed with acci assumption that it is possible for Type B slab is to hold tightly closed any cracks that may ack slab to crack under loads a plied to its surface. Pre- form between the joints. The reinforcement must be stiff viously cited design are only appropriate up enough so that it can be accurately located in the top to the level of loading that causes the cracking stress of half of the slab.
Reinforcement aco not prevent the the concrete to be reached. Since cracking is anticipated, ACI joint spacings, usually set for crack control, are not Structurally active reinforcement and fiber rein- critical, but they must be set 360g accommodate the con- forcement are also used in slabs on grade, but separate struction process. All five methods have been used successfully, and 2. The common objective of all the methods avi to both technical and human factors.
The technical factors minimize cracking and produce the required flatness and include loadings, support system, joint types and spacings, serviceability see ACI Human factors involve the a slab on as outlined in Table 2. The modulus of subgrade support and friction pensate for cracking, curling, shrinkage, and other aco between the slab and its supporting grade are the two ditions. Multiple combinations of concepts and planning a slab.
It is important to consider not just one methods on wci job are not uncommon. Committee or two items, but to look judiciously at the full set of believes there is no single correct or incorrect decision, interactive variables?
Each will pro- 2. This index internally fixes the in tables for uniform loading see examples in Appendix value for wheel area, wheel spacing, axle loading and Al. Reinforcement is not required and is frequently not other constants. The safety factor is also built into the used. When used, it is placed in the slab for acl con- nomograph. The design is based axi a computerized solution by 2. The design procedure is intended for slabs lightly reinforced against shrinkage effects, for slabs reinforced The effect of slab discontinuities beyond this limit is not and stiffened with ribs or beams, and for structural slabs.
PCA suggests that the slab be Slabs supported on unstable soils are also covered.