The provisions of this chapter shall govern the materials, quality control, design and construction of concrete used in structures.
Structural concrete shall be designed and constructed in accordance with the requirements of this chapter and ACI 318 as amended in Section 1908 of this code. Except for the provisions of Sections 1904 and 1910, the design and construction of slabs on grade shall not be governed by this chapter unless they transmit vertical loads or lateral forces from other parts of the structure to the soil.
- The specified compressive strength of concrete at the stated ages or stages of construction for which each concrete element is designed.
- The specified strength or grade of reinforcement.
- The size and location of structural elements, reinforcement and anchors.
- Provision for dimensional changes resulting from creep, shrinkage and temperature.
- The magnitude and location of prestressing forces.
- Anchorage length of reinforcement and location and length of lap splices.
- Type and location of mechanical and welded splices of reinforcement.
- Details and location of contraction or isolation joints specified for plain concrete.
- Minimum concrete compressive strength at time of posttensioning.
- Stressing sequence for posttensioning tendons.
- For structures assigned to Seismic Design Category D, E or F, a statement if slab on grade is designed as a structural diaphragm (see Section 22.214.171.124 of ACI 318).
Where maximum water-cementitious materials ratios are specified in ACI 318, they shall be calculated in accordance with ACI 318, Section 4.1.
Concrete shall be assigned to exposure classes in accordance with ACI 318, Section 4.2, based on:
- Exposure to freezing and thawing in a moist condition or deicer chemicals;
- Exposure to sulfates in water or soil;
- Exposure to water where the concrete is intended to have low permeability; and
- Exposure to chlorides from deicing chemicals, salt, saltwater, brackish water, seawater or spray from these sources, where the concrete has steel reinforcement.
Concrete mixtures shall conform to the most restrictive maximum water-cementitious materials ratios and minimum specified concrete compressive strength requirements of ACI 318, Section 4.3, based on the exposure classes assigned in Section 1904.2.
Exception: For occupancies and appurtenances thereto in Group R occupancies that are in buildings less than four stories above grade plane, normal-weight aggregate concrete is permitted to comply with the requirements of Table 1904.3 based on the weathering classification (freezing and thawing) determined from Figure 1904.3 in lieu of the requirements of ACI 318, Table 4.3.1.
MINIMUM SPECIFIED COMPRESSIVE STRENGTH (f' c)
|TYPE OR LOCATION OF CONCRETE CONSTRUCTION||MINIMUM SPECIFIED COMPRESSIVE STRENGTH (f' c at 28 days, psi)|
|Negligible exposure||Moderate exposure||Severe exposure|
|Basement wallsc and foundations not exposed to the weather||2,500||2,500||2,500a|
|Basement slabs and interior slabs on grade, except garage floor |
|Basement wallsc, foundation walls, exterior walls and other |
vertical concrete surfaces exposed to the weather
|Driveways, curbs, walks, patios, porches, carport slabs, steps and |
other flatwork exposed to the weather, and garage floor slabs
|2,500||3,000b, d||3,500b, d|
For SI: 1 pound per square inch = 0.00689 MPa.
- Concrete in these locations that can be subjected to freezing and thawing during construction shall be of air-entrained concrete in accordance with Section 1904.2.1.
- Concrete shall be air entrained in accordance with Section 1904.4.1.
- Structural plain concrete basement walls are exempt from the requirements for exposure conditions of Section 1904.3 (see Section 1909.6.1).
- For garage floor slabs where a steel trowel finish is used, the total air content required by Section 1904.4.1 is permitted to be reduced to not less than 3 percent, provided the minimum specified compressive strength of the concrete is increased to 4,000 psi.
Concrete exposed to freezing and thawing while moist shall be air entrained in accordance with ACI 318, Section 4.4.1.
For concrete exposed to freezing and thawing in the presence of moisture and deicing chemicals, the maximum weight of fly ash, other pozzolans, silica fume or slag that is included in the concrete shall not exceed the percentages of the total weight of cementitious materials permitted by ACI 318, Section 4.4.2.
Concrete shall be proportioned to provide an average compressive strength as prescribed in Section 1905.3 and shall satisfy the durability criteria of Section 1904. Concrete shall be produced to minimize the frequency of strengths below f' c as prescribed in Section 1905.6.3. For concrete designed and constructed in accordance with this chapter, f' c shall not be less than 2,500 psi (17.22 MPa). No maximum specified compressive strength shall apply unless restricted by a specific provision of this code or ACI 318.
Concrete proportions shall be determined in accordance with the provisions of ACI 318, Section 5.2.
Concrete proportioning determined on the basis of field experience and/or trial mixtures shall be done in accordance with ACI 318, Section 5.3.
Concrete proportioning determined without field experience or trial mixtures shall be done in accordance with ACI 318, Section 5.4.
As data become available during construction, it is permissible to reduce the amount by which the average compressive strength (f' c) is required to exceed the specified value of f' c in accordance with ACI 318, Section 5.5.
Concrete shall be tested in accordance with the requirements in Sections 1905.6.2 through 1905.6.5. Qualified field testing technicians shall perform tests on fresh concrete at the job site, prepare specimens required for curing under field conditions, prepare specimens required for testing in the laboratory and record the temperature of the fresh concrete when preparing specimens for strength tests. Qualified laboratory technicians shall perform all required laboratory tests.
The frequency of conducting strength tests of concrete and the minimum number of tests shall be as specified in ACI 318, Section 5.6.2.
The method and equipment for conveying concrete to the place of deposit shall comply with ACI 318, Section 5.9.
The depositing of concrete shall comply with the provisions of ACI 318, Section 5.10.
The length of time, temperature and moisture conditions for curing of concrete shall be in accordance with ACI 318, Section 5.11.
Concrete to be placed during freezing or near-freezing weather shall comply with the requirements of ACI 318, Section 5.12.
The design, fabrication and erection of forms shall comply with ACI 318, Section 6.1.
The removal of forms and shores, including from slabs and beams (except where cast on the ground), and the installation of reshores shall comply with ACI 318, Section 6.2.
Standard hooks on reinforcing bars used in concrete construction shall comply with ACI 318, Section 7.1.
Minimum reinforcement bend diameters utilized in concrete construction shall comply with ACI 318, Section 7.2.
The bending of reinforcement shall comply with ACI 318, Section 7.3.
The surface conditions of reinforcement shall comply with the provisions of ACI 318, Section 7.4.
The clear distance between reinforcing bars, bundled bars, tendons and ducts shall comply with ACI 318, Section 7.6.
In corrosive environments or other severe exposure conditions, prestressed and nonprestressed reinforcement shall be provided with additional protection in accordance with ACI 318, Section 7.7.6.
Exposed reinforcement, inserts and plates intended for bonding with future extensions shall be protected from corrosion.
Offset bent longitudinal bars in columns and load transfer in structural steel cores of composite compression members shall comply with the provisions of ACI 318, Section 7.8.
Connections between concrete framing members shall comply with the provisions of ACI 318, Section 7.9.
Lateral reinforcement for concrete compression members shall comply with the provisions of ACI 318, Section 7.10.
Lateral reinforcement for compression reinforcement in concrete flexural members shall comply with the provisions of ACI 318, Section 7.11.
Reinforcement for shrinkage and temperature stresses in concrete members shall comply with the provisions of ACI 318, Section 7.12.
Modify existing definitions and add the following definitions to ACI 318, Section 2.2.
DESIGN DISPLACEMENT. Total lateral displacement expected for the design-basis earthquake, as specified by Section 12.8.6 of ASCE 7.
DETAILED PLAIN CONCRETE STRUCTURAL WALL. A wall complying with the requirements of Chapter 22, including 22.6.7.
ORDINARY PRECAST STRUCTURAL WALL. A precast wall complying with the requirements of Chapters 1 through 18.
ORDINARY REINFORCED CONCRETE STRUCTURAL WALL. A cast-in-place wall complying with the requirements of Chapters 1 through 18.
ORDINARY STRUCTURAL PLAIN CONCRETE WALL. A wall complying with the requirements of Chapter 22, excluding 22.6.7.
SPECIAL STRUCTURAL WALL. A cast-in-place or precast wall complying with the requirements of 21.1.3 through 21.1.7, 21.9 and 21.10, as applicable, in addition to the requirements for ordinary reinforced concrete structural walls or ordinary precast structural walls, as applicable. Where ASCE 7 refers to a "special reinforced concrete structural wall," it shall be deemed to mean a "special structural wall."
WALL PIER. A wall segment with a horizontal length-to-thickness ratio of at least 2.5, but not exceeding 6, whose clear height is at least two times its horizontal length.
Modify ACI 318 Sections 126.96.36.199 and 188.8.131.52 to read as follows:
184.108.40.206 — Structures assigned to Seismic Design Category A shall satisfy requirements of Chapters 1 to 19 and 22; Chapter 21 does not apply. Structures assigned to Seismic Design Category B, C, D, E or F also shall satisfy 220.127.116.11 through 18.104.22.168, as applicable. Except for structural elements of plain concrete complying with Section 1908.1.8 of the building code, structural elements of plain concrete are prohibited in structures assigned to Seismic Design Category C, D, E or F.
22.214.171.124 — Structural systems designated as part of the seismic-force-resisting system shall be restricted to those permitted by ASCE 7. Except for Seismic Design Category A, for which Chapter 21 does not apply, the following provisions shall be satisfied for each structural system designated as part of the seismic-force-resisting system, regardless of the Seismic Design Category:
- Ordinary moment frames shall satisfy 21.2.
- Ordinary reinforced concrete structural walls and ordinary precast structural walls need not satisfy any provisions in Chapter 21.
- Intermediate moment frames shall satisfy 21.3.
- Intermediate precast structural walls shall satisfy 21.4.
- Special moment frames shall satisfy 21.5 through 21.8.
- Special structural walls shall satisfy 21.9.
- Special structural walls constructed using precast concrete shall satisfy 21.10.
All special moment frames and special structural walls shall also satisfy 21.1.3 through 21.1.7.
Modify ACI 318, Section 21.4, by renumbering Section 21.4.3 to become 21.4.4 and adding new Sections 21.4.3, 21.4.5 and 21.4.6 to read as follows:
21.4.3 — Connections that are designed to yield shall be capable of maintaining 80 percent of their design strength at the deformation induced by the design displacement or shall use Type 2 mechanical splices.
21.4.4 — Elements of the connection that are not designed to yield shall develop at least 1.5 Sy.
21.4.5 — Wall piers not designed as part of a moment frame shall have transverse reinforcement designed to resist the shear forces determined from 21.3.3. Spacing of transverse reinforcement shall not exceed 8 inches (203 mm). Transverse reinforcement shall be extended beyond the pier clear height for at least 12 inches (305 mm).
- Wall piers that satisfy 21.13.
- Wall piers along a wall line within a story where other shear wall segments provide lateral support to the wall piers and such segments have a total stiffness of at least six times the sum of the stiffnesses of all the wall piers.
21.4.6 — Wall segments with a horizontal length-tothickness ratio less than 2.5 shall be designed as columns.
Modify ACI 318, Section 21.9, by adding new Section 21.9.10 to read as follows:
21.9.10 — Wall piers and wall segments.
126.96.36.199 — Wall piers not designed as a part of a special moment frame shall have transverse reinforcement designed to satisfy the requirements in 188.8.131.52.
- Wall piers that satisfy 21.13.
- Wall piers along a wall line within a story where other shear wall segments provide lateral support to the wall piers and such segments have a total stiffness of at least six times the sum of the stiffnesses of all the wall piers.
184.108.40.206 — Transverse reinforcement with seismic hooks at both ends shall be designed to resist the shear forces determined from 220.127.116.11. Spacing of transverse reinforcement shall not exceed 6 inches (152 mm). Transverse reinforcement shall be extended beyond the pier clear height for at least 12 inches (305 mm).
18.104.22.168 — Wall segments with a horizontal length-to-thickness ratio less than 2.5 shall be designed as columns.
Modify ACI 318, Section 21.10.2, to read as follows:
21.10.2 — Special structural walls constructed using precast concrete shall satisfy all the requirements of 21.9 for cast-in-place special structural walls in addition to Sections 21.4.2 through 21.4.4.
Modify ACI 318, Section 22.214.171.124, to read as follows:
126.96.36.199 — Foundations resisting earthquake-induced forces or transferring earthquake-induced forces between a structure and ground shall comply with the requirements of Section 21.12 and other applicable provisions of ACI 318 unless modified by Chapter 18 of the building code.
Modify ACI 318, Section 22.6, by adding new Section 22.6.7 to read as follows:
22.6.7 — Detailed plain concrete structural walls.
188.8.131.52 — Detailed plain concrete structural walls are walls conforming to the requirements of ordinary structural plain concrete walls and 184.108.40.206.
220.127.116.11 — Reinforcement shall be provided as follows:
- 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 18.104.22.168.
- Horizontal reinforcement at least 0.20 square inch (129 mm2) in cross-sectional area shall be provided:
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.
- Continuously at structurally connected roof and floor levels and at the top of walls;
- At the bottom of load-bearing walls or in the top of foundations where doweled to the wall; and
- At a maximum spacing of 120 inches (3048 mm).
Delete ACI 318, Section 22.10, and replace with the following:
22.10 — Plain concrete in structures assigned to Seismic Design Category C, D, E or F.
22.10.1 — Structures assigned to Seismic Design Category C, D, E or F shall not have elements of structural plain concrete, except as follows:
- 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.Exception: Deleted.
- 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.Exceptions:
- 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.
- 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.
Modify ACI 318, Sections D.3.3.4 and D.3.3.5 to read as follows:
D.3.3.4 — Anchors shall be designed to be governed by the steel strength of a ductile steel element as determined in accordance with D.5.1 and D.6.1, unless either D.3.3.5 or D.3.3.6 is satisfied.
- Anchors in concrete designed to support nonstructural components in accordance with ASCE 7 Section 13.4.2 need not satisfy Section D.3.3.4.
- Anchors designed to resist wall out-of-plane forces with design strengths equal to or greater than the force determined in accordance with ASCE 7 Equation 12.11-1 or 12.14-10 need not satisfy Section D.3.3.4.
D.3.3.5 — Instead of D.3.3.4, the attachment that the anchor is connecting to the structure shall be designed so that the attachment will undergo ductile yielding at a force level corresponding to anchor forces no greater than the design strength of anchors specified in D.3.3.3.
- Anchors in concrete designed to support nonstructural components in accordance with ASCE 7 Section 13.4.2 need not satisfy Section D.3.3.5.
- Anchors designed to resist wall out-of-plane forces with design strengths equal to or greater than the force determined in accordance with ASCE 7 Equation 12.11-1 or 12.14-10 need not satisfy Section D.3.3.5.
Delete ACI 318, Section D.4.2.2, and replace with the following:
D.4.2.2 — The concrete breakout strength requirements for anchors in tension shall be considered satisfied by the design procedure of D.5.2 provided Equation D-8 is not used for anchor embedments exceeding 25 inches (635 mm). The concrete breakout strength requirements for anchors in shear with diameters not exceeding 2 inches (51 mm) shall be considered satisfied by the design procedure of D.6.2. For anchors in shear with diameters exceeding 2 inches (51 mm), shear anchor reinforcement shall be provided in accordance with the procedures of D.6.2.9.
Structural plain concrete walls, footings and pedestals shall be designed for adequate strength in accordance with ACI 318, Sections 22.4 through 22.8.
Exception: For Group R-3 occupancies and buildings of other occupancies less than two stories above grade plane of light-frame construction, the required edge thickness of ACI 318 is permitted to be reduced to 6 inches (152 mm), provided that the footing does not extend more than 4 inches (102 mm) on either side of the supported wall.
The design, fabrication, transportation and erection of precast, structural plain concrete elements shall be in accordance with ACI 318, Section 22.9.
Not less than one No. 5 bar shall be provided around window, door and similar sized openings. The bar shall be anchored to develop fy in tension at the corners of openings.
The thickness of concrete floor slabs supported directly on the ground shall not be less than 31/2 inches (89 mm). A 6-mil (0.006 inch; 0.15 mm) polyethylene vapor retarder with joints lapped not less than 6 inches (152 mm) shall be placed between the base course or subgrade and the concrete floor slab, or other approved equivalent methods or materials shall be used to retard vapor transmission through the floor slab.
Exception: A vapor retarder is not required:
- For detached structures accessory to occupancies in Group R-3, such as garages, utility buildings or other unheated facilities.
- For unheated storage rooms having an area of less than 70 square feet (6.5 m2) and carports attached to occupancies in Group R-3.
- For buildings of other occupancies where migration of moisture through the slab from below will not be detrimental to the intended occupancy of the building.
- For driveways, walks, patios and other flatwork which will not be enclosed at a later date.
- Where approved based on local site conditions.
The provisions of this section shall govern the allowable stress design of headed bolts and headed stud anchors cast in normal-weight concrete for purposes of transmitting structural loads from one connected element to the other. These provisions do not apply to anchors installed in hardened concrete or where load combinations include earthquake loads or effects. The bearing area of headed anchors shall be not less than one and one-half times the shank area. Where strength design is used, or where load combinations include earthquake loads or effects, the design strength of anchors shall be determined in accordance with Section 1912. Bolts shall conform to ASTM A 307 or an approved equivalent.
The allowable service load for headed anchors in shear or tension shall be as indicated in Table 1911.2. Where anchors are subject to combined shear and tension, the following relationship shall be satisfied:
|Ps||=||Applied tension service load, pounds (N).|
|Pt||=||Allowable tension service load from Table 1911.2, pounds (N).|
|Vs||=||Applied shear service load, pounds (N).|
|Vt||=||Allowable shear service load from Table 1911.2, pounds (N).|
ALLOWABLE SERVICE LOAD ON EMBEDDED BOLTS (pounds)
|MINIMUM CONCRETE STRENGTH (psi)|
|f' c = 2,500||f' c = 3,000||f' c = 4,000|
For SI: 1 inch = 25.4 mm, 1 pound per square inch = 0.00689MPa, 1 pound = 4.45 N.
The allowable service loads in tension and shear specified in Table 1911.2 are for the edge distance and spacing specified. The edge distance and spacing are permitted to be reduced to 50 percent of the values specified with an equal reduction in allowable service load. Where edge distance and spacing are reduced less than 50 percent, the allowable service load shall be determined by linear interpolation.
The provisions of this section shall govern the strength design of anchors installed in concrete for purposes of transmitting structural loads from one connected element to the other. Headed bolts, headed studs and hooked (J- or L-) bolts cast in concrete and expansion anchors and undercut anchors installed in hardened concrete shall be designed in accordance with Appendix D of ACI 318 as modified by Sections 1908.1.9 and 1908.1.10, provided they are within the scope of Appendix D.
Shotcrete proportions shall be selected that allow suitable placement procedures using the delivery equipment selected and shall result in finished in-place hardened shotcrete meeting the strength requirements of this code.
Coarse aggregate, if used, shall not exceed 3/4 inch (19.1 mm).
The maximum size of reinforcement shall be No. 5 bars unless it is demonstrated by preconstruction tests that adequate encasement of larger bars will be achieved.
When No. 5 or smaller bars are used, there shall be a minimum clearance between parallel reinforcement bars of 21/2 inches (64 mm). When bars larger than No. 5 are permitted, there shall be a minimum clearance between parallel bars equal to six diameters of the bars used. When two curtains of steel are provided, the curtain nearer the nozzle shall have a minimum spacing equal to 12 bar diameters and the remaining curtain shall have a minimum spacing of six bar diameters.
Exception: When specified by the registered design professional, required clearances shall be reduced where it is demonstrated by preconstruction tests that adequate encasement of the bars used in the design will be achieved.
Lap splices of reinforcing bars shall utilize the noncontact lap splice method with a minimum clearance of 2 inches (51 mm) between bars. The use of contact lap splices necessary for support of the reinforcing is permitted when specified by the registered design professional, based on satisfactory preconstruction tests that show that adequate encasement of the bars will be achieved, and provided that the splice is oriented so that a plane through the center of the spliced bars is perpendicular to the surface of the shotcrete.
Shotcrete shall not be applied to spirally tied columns.
When required by the building official, a test panel shall be shot, cured, cored or sawn, examined and tested prior to commencement of the project. The sample panel shall be representative of the project and simulate job conditions as closely as possible. The panel thickness and reinforcing shall reproduce the thickest and most congested area specified in the structural design. It shall be shot at the same angle, using the same nozzleman and with the same concrete mix design that will be used on the project. The equipment used in preconstruction testing shall be the same equipment used in the work requiring such testing, unless substitute equipment is specified by the registered design professional.
Any rebound or accumulated loose aggregate shall be removed from the surfaces to be covered prior to placing the initial or any succeeding layers of shotcrete. Rebound shall not be used as aggregate.
Except where permitted herein, unfinished work shall not be allowed to stand for more than 30 minutes unless edges are sloped to a thin edge. For structural elements that will be under compression and for construction joints shown on the approved construction documents, square joints are permitted. Before placing additional material adjacent to previously applied work, sloping and square edges shall be cleaned and wetted.
In-place shotcrete that exhibits sags, sloughs, segregation, honeycombing, sand pockets or other obvious defects shall be removed and replaced. Shotcrete above sags and sloughs shall be removed and replaced while still plastic.
During the curing periods specified herein, shotcrete shall be maintained above 40°F (4°C) and in moist condition.
Shotcrete shall be kept continuously moist for 24 hours after shotcreting is complete or shall be sealed with an approved curing compound.
Strength tests for shotcrete shall be made by an approved agency on specimens that are representative of the work and which have been water soaked for at least 24 hours prior to testing. When the maximum-size aggregate is larger than 3/8 inch (9.5 mm), specimens shall consist of not less than three 3-inch-diameter (76 mm) cores or 3-inch (76 mm) cubes. When the maximum-size aggregate is 3/8 inch (9.5 mm) or smaller, specimens shall consist of not less than 2-inch-diameter (51 mm) cores or 2-inch (51 mm) cubes.
Specimens shall be taken from the in-place work or from test panels, and shall be taken at least once each shift, but not less than one for each 50 cubic yards (38.2 m3) of shotcrete.
When the maximum-size aggregate is larger than 3/8 inch (9.5 mm), the test panels shall have minimum dimensions of 18 inches by 18 inches (457 mm by 457 mm). When the maximum size aggregate is 3/8 inch (9.5 mm) or smaller, the test panels shall have minimum dimensions of 12 inches by 12 inches (305 mm by 305 mm). Panels shall be shot in the same position as the work, during the course of the work and by the nozzlemen doing the work. The conditions under which the panels are cured shall be the same as the work.
The average compressive strength of three cores from the in-place work or a single test panel shall equal or exceed 0.85 f' c with no single core less than 0.75 f' c. The average compressive strength of three cubes taken from the in-place work or a single test panel shall equal or exceed f' c with no individual cube less than 0.88 f' c. To check accuracy, locations represented by erratic core or cube strengths shall be retested.
Reinforced gypsum concrete shall comply with the requirements of ASTM C 317 and ASTM C 956.
The minimum thickness of reinforced gypsum concrete shall be 2 inches (51 mm) except the minimum required thickness shall be reduced to 11/2 inches (38 mm), provided the following conditions are satisfied:
- The overall thickness, including the formboard, is not less than 2 inches (51 mm).
- The clear span of the gypsum concrete between supports does not exceed 33 inches (838 mm).
- Diaphragm action is not required.
- The design live load does not exceed 40 pounds per square foot (psf) (1915 Pa).
The safe supporting capacity of concrete-filled pipe columns shall be computed in accordance with the approved rules or as determined by a test.
Caps, base plates and connections shall be of approved types and shall be positively attached to the shell and anchored to the concrete core. Welding of brackets without mechanical anchorage shall be prohibited. Where the pipe is slotted to accommodate webs of brackets or other connections, the integrity of the shell shall be restored by welding to ensure hooping action of the composite section.
To increase the safe load-supporting capacity of concrete-filled pipe columns, the steel reinforcement shall be in the form of rods, structural shapes or pipe embedded in the concrete core with sufficient clearance to ensure the composite action of the section, but not nearer than 1 inch (25 mm) to the exterior steel shell. Structural shapes used as reinforcement shall be milled to ensure bearing on cap and base plates.
Pipe columns shall be of such size or so protected as to develop the required fire-resistance ratings specified in Table 601. Where an outer steel shell is used to enclose the fire protective covering, the shell shall not be included in the calculations for strength of the column section. The minimum diameter of pipe columns shall be 4 inches (102 mm) except that in structures of Type V construction not exceeding three stories above grade plane or 40 feet (12 192 mm) in building height, pipe columns used in basements and as secondary steel members shall have a minimum diameter of 3 inches (76 mm).
Details of column connections and splices shall be shop fabricated by approved methods and shall be approved only after tests in accordance with the approved rules. Shop-fabricated concrete-filled pipe columns shall be inspected by the building official or by an approved representative of the manufacturer at the plant.