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This chapter shall apply to the design of plain concrete members, including (a) and (b):
(a) Members in building structures
(b) Members in non-building structures such as arches, underground utility structures, gravity walls, and shielding walls
This chapter shall not govern the design of cast-inplace concrete piles and piers embedded in ground.
Plain concrete shall be permitted only in cases (a) through (d):
(a) Members that are continuously supported by soil or supported by other structural members capable of providing continuous vertical support
(b) Members for which arch action provides compression under all conditions of loading
(c) Walls
Structures assigned to Seismic Design Category C, D, E or F shall not have elements of structural plain concrete, except as follows:
  1. Isolated footings of plain concrete supporting pedestals or columns are permitted, provided the projection of the footing beyond the face of the supported member does not exceed the footing thickness.
  2. Plain concrete footings supporting walls are permitted, provided the footings have at least two continuous longitudinal reinforcing bars. Bars shall not be smaller than No. 4 and shall have a total area of not less than 0.002 times the gross cross-sectional area of the footing. For footings that exceed 8 inches (203 mm) in thickness, a minimum of one bar shall be provided at the top and bottom of the footing. Continuity of reinforcement shall be provided at corners and intersections.
    1. For foundation systems consisting of a plain concrete footing and a plain concrete stemwall, a minimum of one bar shall be provided at the top of the stemwall and at the bottom of the footing.
    2. Where a slab on ground is cast monolithically with the footing, one No. 5 bar is permitted to be located at either the top of the slab or bottom of the footing.
Plain concrete shall not be permitted for columns and pile caps.
Design properties for concrete shall be selected to be in accordance with Chapter 19.
Steel reinforcement, if required, 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.
Tension shall not be transmitted through outside edges, construction joints, contraction joints, or isolation joints of an individual plain concrete element.
Walls shall be braced against lateral translation.
Design of precast members shall consider all loading conditions from initial fabrication to completion of the structure, including form removal, storage, transportation, and erection.
Precast members shall be connected to transfer lateral forces into a structural system capable of resisting such forces.
Minimum bearing wall thickness shall be in accordance with Table
Table—Minimum thickness of bearing walls
Wall type Minimum thickness
General Greater of: 5.5 in.
1/24 the lesser of unsupported length and unsupported height
Exterior basement 7.5 in.
Foundation 7.5 in.
Footing thickness shall be at least 8 in.
Base area of footing shall be determined from unfactored forces and moments transmitted by footing to soil and permissible soil pressure selected through principles of soil mechanics.
Ratio of unsupported height to average least lateral dimension shall not exceed 3.
Contraction or isolation joints shall be provided to divide structural plain concrete members into flexurally discontinuous elements. The size of each element shall be selected to limit stress caused by restraint to movements from creep, shrinkage, and temperature effects.
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The number and location of contraction or isolation joints shall be determined considering (a) through (f):
(a) Influence of climatic conditions
(b) Selection and proportioning of materials
(c) Mixing, placing, and curing of concrete
(d) Degree of restraint to movement
(e) Stresses due to loads to which an element is subjected
(f) Construction techniques
Required strength shall be calculated in accordance with the factored load combinations defined in Chapter 5.
Required strength shall be calculated in accordance with the analysis procedures in Chapter 6.
No flexural continuity due to tension shall be assumed between adjacent structural plain concrete elements.
Walls shall be designed for an eccentricity corresponding to the maximum moment that can accompany the axial load but not less than 0.10h, where h is the wall thickness.
For footings supporting circular or regular polygon-shaped concrete columns or pedestals, it shall be permitted to assume a square section of equivalent area for determining critical sections.
The critical section for Mu shall be located in accordance with Table
Table—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
For one-way shear, critical sections shall be located h from (a) and (b), where h is the footing thickness.
(a) Location defined in Table
(b) Face of concentrated loads or reaction areas
Sections between (a) or (b) of and the critical section for shear shall be permitted to be designed for Vu at the critical section for shear.
For two-way shear, critical sections shall be located so that the perimeter bo is a minimum but need not be closer than h/2 to (a) through (c):
(a) Location defined in Table
(b) Face of concentrated loads or reaction areas
(c) Changes in footing thickness
For square or rectangular columns, concentrated loads, or reaction areas, the critical section for two-way shear shall be permitted to be calculated assuming straight sides.
For each applicable factored load combination, design strength at all sections shall satisfy ϕSnU, including (a) through (d). Interaction between load effects shall be considered.
(a) ϕMnMu
(b) ϕPnPu
(c) ϕVnVu
(d) ϕBnBu
ϕ shall be determined in accordance with 21.2.
Tensile strength of concrete shall be permitted to be considered in design.
Flexure and axial strength calculations shall be based on a linear stress-strain relationship in both tension and compression.
λ for lightweight concrete shall be in accordance with 19.2.4.
No strength shall be assigned to steel reinforcement.
When calculating member strength in flexure, combined flexure and axial load, or shear, the entire cross section shall be considered in design, except for concrete cast against soil where overall thickness h shall be taken as 2 in. less than the specified thickness.
Unless demonstrated by analysis, horizontal length of wall to be considered effective for resisting each vertical concentrated load shall not exceed center-to-center distance between loads, or bearing width plus four times the wall thickness.
Mn shall be the lesser of Eq. ( calculated at the tension face and Eq. ( calculated at the compression face:
Mn = 0.85f'cSm (
where Sm is the corresponding elastic section modulus.
Pn shall be calculated by:
Unless permitted by, member dimensions shall be proportioned to be in accordance with Table, where Mn is calculated in accordance with and Pn is calculated in accordance with
Table—Combined flexure and axial compression
Location Interaction equation
Tension face (a)
Compression face (b)
For walls of solid rectangular cross section where MuPu(h/6), Mu need not be considered in design and Pn is calculated by:
Vn shall be calculated in accordance with Table
Table—Nominal shear strength
Shear action Nominal shear strength Vn
One-way (a)
Two-way Lesser of: [1] (b)
[1]β is the ratio of long side to short side of concentrated load or reaction area.
Bn shall be calculated in accordance with Table
Table—Nominal bearing strength
Relative geometric conditions Bn  
Supporting surface is wider on all sides than the loaded area Lesser of: (a)
2(0.85f'cA1) (b)
Other 0.85f'cA1 (c)
At least two No. 5 bars shall be provided around all window and door openings. Such bars shall extend at least 24 in. beyond the corners of openings.
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Reinforcement shall be provided as follows:
  1. Vertical reinforcement of at least 0.20 square inch (129 mm2) in cross-sectional area shall be provided continuously from support to support at each corner, at each side of each opening and at the ends of walls. The continuous vertical bar required beside an opening is permitted to substitute for one of the two No. 5 bars required by 14.6.1.
  2. Horizontal reinforcement at least 0.20 square inch (129 mm2) in cross-sectional area shall be provided:
    1. Continuously at structurally connected roof and floor levels and at the top of walls;
    2. At the bottom of load-bearing walls or in the top of foundations where doweled to the wall; and
    3. At a maximum spacing of 120 inches (3048 mm).
    Reinforcement at the top and bottom of openings, where used in determining the maximum spacing specified in Item 3 above, shall be continuous in the wall.