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This chapter shall apply to the design of nonprestressed and prestressed foundations, including shallow foundations (a) through (e) and, where applicable, deep foundations (f) through (i):
(a) Strip footings
(b) Isolated footings
(c) Combined footings
(d) Mat foundations
(e) Grade beams
(f) Pile caps
(g) Piles
(h) Drilled piers
(i) Caissons
Design properties for concrete shall be selected to be in accordance with Chapter 19.
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Design properties for steel reinforcement shall be selected to be in accordance with Chapter 20.
Materials, design, and detailing requirements for embedments in concrete shall be in accordance with 20.7.
Structural members extending below the base of the structure that are required to transmit forces resulting from earthquake effects to the foundation shall be designed in accordance with 18.2.2.3.
For structures assigned to Seismic Design Category (SDC) D, E, or F, shallow and deep foundations resisting earthquake-induced forces or transferring earthquake-induced forces between structure and ground shall be designed in accordance with 18.13.
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Slabs-on-ground that transmit vertical loads or lateral forces from other parts of the structure to the ground shall be designed and detailed in accordance with applicable provisions of this Code.
Slabs-on-ground that transmit lateral forces as part of the seismic-force-resisting system shall be designed in accordance with 18.13.
Plain concrete foundations shall be designed in accordance with Chapter 14.
Foundations shall be proportioned to resist factored loads and induced reactions.
Foundation systems shall be permitted to be designed by any procedure satisfying equilibrium and geometric compatibility.
Foundation design in accordance with strut-and-tie modeling, Chapter 23, shall be permitted.
External moment on any section of a strip footing, isolated footing, or pile cap shall be calculated by passing a vertical plane through the member and calculating the moment of the forces acting over the entire area of member on one side of that vertical plane.
Mu at the supported member shall be permitted to be calculated at the critical section defined in accordance with Table 13.2.7.1.
Table 13.2.7.1—Location of critical section for Mu
| Supported member | Location of critical section |
|---|---|
| Column or pedestal | Face of column or pedestal |
| Column with steel base plate | Halfway between face of column and edge of steel base plate |
| Concrete wall | Face of wall |
| Masonry wall | Halfway between center and face of masonry wall |
Circular or regular polygon-shaped concrete columns or pedestals shall be permitted to be treated as square members of equivalent area when locating critical sections for moment, shear, and development of reinforcement.
Development of reinforcement shall be in accordance with Chapter 25.
Calculated tensile or compressive force in reinforcement at each section shall be developed on each side of that section.
Critical sections for development of reinforcement shall be assumed at the same locations as given in 13.2.7.1 for maximum factored moment and at all other vertical planes where changes of section or reinforcement occur.
Adequate anchorage shall be provided for tension reinforcement where reinforcement stress is not directly proportional to moment, such as in sloped, stepped, or tapered foundations; or where tension reinforcement is not parallel to the compression face.
Minimum base area of foundation shall be calculated from unfactored forces and moments transmitted by foundation to soil or rock and permissible bearing pressure selected through principles of soil or rock mechanics.
Overall depth of foundation shall be selected such that the effective depth of bottom reinforcement is at least 6 in.
In sloped, stepped, or tapered foundations, depth and location of steps or angle of slope shall be such that design requirements are satisfied at every section.
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Reinforcement shall be distributed uniformly across entire width of one-way footings.
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In square two-way footings, reinforcement shall be distributed uniformly across entire width of footing in both directions.
In rectangular footings, reinforcement shall be distributed in accordance with (a) and (b):
(a) Reinforcement in the long direction shall be distributed uniformly across entire width of footing.
(b) For reinforcement in the short direction, a portion of the total reinforcement, γsAs, shall be distributed uniformly over a band width equal to the length of short side of footing, centered on centerline of column or pedestal. Remainder of reinforcement required in the short direction, (1 — γs)As, shall be distributed uniformly outside the center band width of footing, where γs is calculated by:
 | (13.3.3.3) |
where β is the ratio of long to short side of footing.
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The design and detailing of combined footings and mat foundations shall be in accordance with this section and the applicable provisions of Chapter 8.
The direct design method of 8.10 shall not be used to design combined footings and mat foundations.
Distribution of bearing pressure under combined footings and mat foundations shall be consistent with properties of the soil or rock and the structure, and with established principles of soil or rock mechanics.
Minimum reinforcement in nonprestressed mat foundations shall be in accordance with 8.6.1.1.
Number and arrangement of piles, drilled piers, and caissons shall be determined from unfactored forces and moments transmitted to these members and permissible member capacity selected through principles of soil or rock mechanics.
Overall depth of pile cap shall be selected such that the effective depth of bottom reinforcement is at least 12 in.
Factored moments and shears shall be permitted to be calculated with the reaction from any pile assumed to be concentrated at the centroid of the pile section.
Except for pile caps designed in accordance with 13.2.6.3, the pile cap shall be designed such that (a) is satisfied for one-way foundations and (a) and (b) are satisfied for two-way foundations.
Calculation of factored shear on any section through a pile cap shall be in accordance with (a) through (c):
(a) Entire reaction from any pile with its center located dpile/2 or more outside the section shall be considered as producing shear on that section.
(b) Reaction from any pile with its center located dpile/2 or more inside the section shall be considered as producing no shear on that section.
(c) For intermediate positions of pile center, the portion of the pile reaction to be considered as producing shear on the section shall be based on a linear interpolation between full value at dpile/2 outside the section and zero value at dpile/2 inside the section.
Portions of deep foundation members in air, water, or soils not capable of providing adequate restraint throughout the member length to prevent lateral buckling shall be designed as columns in accordance with the applicable provisions of Chapter 10.