This chapter shall apply to the design of joints and connections at the intersection of concrete members and for load transfer between concrete surfaces, including (a) through (d):
(a) Connections of precast members
(b) Connections between foundations and either cast-inplace or precast members
(c) Horizontal shear strength of composite concrete flexural members
(d) Brackets and corbels
Transfer of forces by means of grouted joints, shear keys, bearing, anchors, mechanical connectors, steel reinforcement, reinforced topping, or a combination of these, shall be permitted.
Adequacy of connections shall be verified by analysis or test.
Connection details that rely solely on friction caused by gravity loads shall not be permitted.
Connections, and regions of members adjacent to connections, shall be designed to resist forces and accommodate deformations due to all load effects in the precast structural system.
Design of connections shall consider structural effects of restraint of volume change in accordance with 5.3.6.
Design of connections shall consider the effects of tolerances specified for fabrication and erection of precast members.
Design of a connection with multiple components shall consider the differences in stiffness, strength, and ductility of the components.
Required strength of connections and adjacent regions shall be calculated in accordance with the factored load combinations in Chapter 5.
Required strength of connections and adjacent regions shall be calculated in accordance with the analysis procedures in Chapter 6.
For each applicable load combination, design strengths of precast member connections shall satisfy
| ϕSn≥ U | (16.2.3.1) |
At the contact surface between supported and supporting members, or between a supported or supporting member and an intermediate bearing element, nominal bearing strength for concrete surfaces, Bn, shall be calculated in accordance with 22.8. Bn shall be the lesser of the nominal concrete bearing strengths for the supported or supporting member surface, and shall not exceed the strength of intermediate bearing elements, if present.
Except where the provisions of 16.2.5 govern, longitudinal and transverse integrity ties shall connect precast members to a lateral-force-resisting system, and vertical integrity ties shall be provided in accordance with 16.2.4.3 to connect adjacent floor and roof levels.
Where precast members form floor or roof diaphragms, the connections between the diaphragm and those members being laterally supported by the diaphragm shall have a nominal tensile strength of not less than 300 lb per linear ft.
Vertical integrity ties shall be provided at horizontal joints between all vertical precast structural members, except cladding, and shall satisfy (a) or (b):
(a) Connections between precast columns shall have vertical integrity ties, with a nominal tensile strength of at least 200Ag lb, where Ag is the gross area of the column. For columns with a larger cross section than required by consideration of loading, a reduced effective area based on the cross section required shall be permitted. The reduced effective area shall be at least one-half the gross area of the column.
(b) Connections between precast wall panels shall have at least two vertical integrity ties, with a nominal tensile strength of at least 10,000 lb per tie.
Integrity ties in floor and roof systems shall satisfy (a) through (f):
(a) Longitudinal and transverse integrity ties shall be provided in floor and roof systems to provide a nominal tensile strength of at least 1500 lb per foot of width or length.
(b) Longitudinal and transverse integrity ties shall be provided over interior wall supports and between the floor or roof system and exterior walls.
(c) Longitudinal and transverse integrity ties shall be positioned in or within 2 ft of the plane of the floor or roof system.
(d) Longitudinal integrity ties shall be oriented parallel to floor or roof slab spans and shall be spaced not greater than 10 ft on center. Provisions shall be made to transfer forces around openings.
(e) Transverse integrity ties shall be oriented perpendicular to floor or roof slab spans and shall be spaced not greater than the bearing wall spacing.
(f) Integrity ties at the perimeter of each floor and roof, within 4 ft of the edge, shall provide a nominal tensile strength of at least 16,000 lb.
Vertical integrity ties shall satisfy (a) through (c):
(a) Integrity ties shall be provided in all wall panels and shall be continuous over the height of the building.
(b) Integrity ties shall provide a nominal tensile strength of at least 3000 lb per horizontal foot of wall.
(c) At least two integrity ties shall be provided in each wall panel.
Dimensions of bearing connections shall satisfy 16.2.6.2 or 16.2.6.3 unless shown by analysis or test that lesser dimensions will not impair performance.
For precast slabs, beams, or stemmed members, minimum design dimensions from the face of support to end of precast member in the direction of the span, considering specified tolerances, shall be in accordance with Table 16.2.6.2.
Table 16.2.6.2—Minimum design dimensions from face of support to end of precast member
| Member type | Minimum distance, in. | |
|---|---|---|
| Solid or hollow-core slab | Greater of: | ℓn/180 |
| 2 | ||
| Beam or stemmed member | Greater of: | ℓn/180 |
| 3 | ||
Bearing pads adjacent to unarmored faces shall be set back from the face of the support and the end of the supported member a distance not less than 0.5 in. or the chamfer dimension at a chamfered face.
Reinforcement, dowels, or mechanical connectors between a supported member and foundation shall be designed to transfer (a) and (b):
(a) Compressive forces that exceed the lesser of the concrete bearing strengths of either the supported member or the foundation, calculated in accordance with 22.8
(b) Any calculated tensile force across the interface
Upcodes Diagrams
At the base of a composite column with a structural steel core, (a) or (b) shall be satisfied:
(a) Base of structural steel section shall be designed to transfer the total factored forces from the entire composite member to the foundation.
(b) Base of structural steel section shall be designed to transfer the factored forces from the steel core only, and the remainder of the total factored forces shall be transferred to the foundation by compression in the concrete and by reinforcement.
Factored forces and moments transferred to foundations shall be calculated in accordance with the factored load combinations in Chapter 5 and analysis procedures in Chapter 6.
Design strengths of connections between columns, walls, or pedestals and foundations shall satisfy Eq. (16.3.3.1) for each applicable load combination. For connections between precast members and foundations, requirements for vertical integrity ties in 16.2.4.3 or 16.2.5.2 shall be satisfied.
| ϕSn ≥ U | (16.3.3.1) |
where Sn is the nominal flexural, shear, axial, torsional, or bearing strength of the connection.
Combined moment and axial strength of connections shall be calculated in accordance with 22.4.
At the contact surface between a supported member and foundation, or between a supported member or foundation and an intermediate bearing element, nominal bearing strength Bn shall be calculated in accordance with 22.8 for concrete surfaces. Bn shall be the lesser of the nominal concrete bearing strengths for the supported member or foundation surface, and shall not exceed the strength of intermediate bearing elements, if present.
At the contact surface between supported member and foundation, Vn shall be calculated in accordance with the shear-friction provisions in 22.9 or by other appropriate means.
At the base of a precast column, pedestal, or wall, anchor bolts and anchors for mechanical connections shall be designed in accordance with Chapter 17. Forces developed during erection shall be considered.
For connections between a cast-in-place column or pedestal and foundation, As crossing the interface shall be at least 0.005Ag, where Ag is the gross area of the supported member.
For connections between a cast-in-place wall and foundation, area of vertical reinforcement crossing the interface shall satisfy 11.6.1.
Where moments are transferred to the foundation, reinforcement, dowels, or mechanical connectors shall satisfy 10.7.5 for splices.
If a pinned or rocker connection is used at the base of a cast-in-place column or pedestal, the connection to foundation shall satisfy 16.3.3.
At footings, it shall be permitted to lap splice No. 14 and No. 18 longitudinal bars, in compression only, with dowels to satisfy 16.3.3.1. Dowels shall satisfy (a) through (c):
(a) Dowels shall not be larger than No. 11
(b) Dowels shall extend into supported member at least the greater of the development length of the longitudinal bars in compression, ℓdc, and the compression lap splice length of the dowels, ℓsc
(c) Dowels shall extend into the footing at least ℓdc of the dowels
Where tension exists across any contact surface between interconnected concrete elements, horizontal shear transfer by contact shall be permitted only where transverse reinforcement is provided in accordance with 16.4.6 and 16.4.7.
Surface preparation assumed for design shall be specified in the construction documents.
Factored forces transferred along the contact surface in composite concrete flexural members shall be calculated in accordance with the factored load combinations in Chapter 5.
Required strength shall be calculated in accordance with the analysis procedures in Chapter 6.
Design strength for horizontal shear transfer shall satisfy Eq. (16.4.3.1) at all locations along the contact surface in a composite concrete flexural member, unless 16.4.5 is satisfied:
| ϕVnh ≥ Vu | (16.4.3.1) |
where nominal horizontal shear strength Vnh is calculated in accordance with 16.4.4.
If Vu ≤ ϕ(500bvd), Vnh shall be calculated in accordance with Table 16.4.4.2, where Av,min is in accordance with 16.4.6, bv is the width of the contact surface, and d is in accordance with 16.4.4.3.
Table 16.4.4.2—Nominal horizontal shear strength
| Shear transfer reinforcement | Contact surface preparation[1] | Vnh, lb | ||
|---|---|---|---|---|
| Av ≥ Av,min | Concrete placed against hardened concrete intentionally roughened to a full amplitude of approximately 1/4 in. | Lesser of: |  |
(a) |
| 500bvd | (b) | |||
| Concrete placed against hardened concrete not intentionally roughened | 80bvd | (c) | ||
| Other cases | Concrete placed against hardened concrete intentionally roughened | 80bvd | (d) | |
[1]Concrete contact surface shall be clean and free of laitance.
In Table 16.4.4.2, d shall be the distance from extreme compression fiber for the entire composite section to the centroid of prestressed and nonprestressed longitudinal tension reinforcement, if any, but need not be taken less than 0.80h for prestressed concrete members.
Transverse reinforcement in the previously cast concrete that extends into the cast-in-place concrete and is anchored on both sides of the interface shall be permitted to be included as ties for calculation of Vnh.
As an alternative to 16.4.3.1, factored horizontal shear Vuh shall be calculated from the change in flexural compressive or tensile force in any segment of the composite concrete member, and Eq. (16.4.5.1) shall be satisfied at all locations along the contact surface:
| ϕVnh ≥ Vuh | (16.4.5.1) |
Nominal horizontal shear strength Vnh shall be calculated in accordance with 16.4.4.1 or 16.4.4.2, where area of contact surface shall be substituted for bvd and Vuh shall be substituted for Vu. Provisions shall be made to transfer the change in compressive or tensile force as horizontal shear force across the interface.
Where shear transfer reinforcement is designed to resist horizontal shear to satisfy Eq. (16.4.5.1), the tie area to tie spacing ratio along the member shall approximately reflect the distribution of interface shear forces in the composite concrete flexural member.
Transverse reinforcement in a previously cast section that extends into the cast-in-place section and is anchored on both sides of the interface shall be permitted to be included as ties for calculation of Vnh.
Where shear transfer reinforcement is designed to resist horizontal shear, Av,min shall be the greater of (a) and (b):
(a) 
(b) 
Shear transfer reinforcement shall consist of single bars or wire, multiple leg stirrups, or vertical legs of welded wire reinforcement.
Where shear transfer reinforcement is designed to resist horizontal shear, longitudinal spacing of shear transfer reinforcement shall not exceed the lesser of 24 in. and four times the least dimension of the supported element.
Shear transfer reinforcement shall be developed in interconnected elements in accordance with 25.7.1.
Effective depth d for a bracket or corbel shall be calculated at the face of the support.
Overall depth of bracket or corbel at the outside edge of the bearing area shall be at least 0.5d.
No part of the bearing area on a bracket or corbel shall project farther from the face of support than (a) or (b):
(a) End of the straight portion of the primary tension reinforcement
(b) Interior face of the transverse anchor bar, if one is provided
For normalweight concrete, the bracket or corbel dimensions shall be selected such that Vu/ϕ shall not exceed the least of (a) through (c):
(a) 0.2f'cbwd
(b) (480 + 0.08f'c)bwd
(c) 1600bwd
For all-lightweight or sand-lightweight concrete, the bracket or corbel dimensions shall be selected such that Vu/ϕ shall not exceed the lesser of (a) and (b):
(a) 
(b) 
The section at the face of the support shall be designed to resist simultaneously the factored shear Vu, the factored horizontal tensile force Nuc, and the factored moment Mu given by [Vuav + Nuc(h - d)].
Factored tensile force, Nuc, and shear, Vu, shall be the maximum values calculated in accordance with the factored load combinations in Chapter 5.
Required strength shall be calculated in accordance with the analysis procedures in Chapter 6, and the requirements in this section.
Horizontal tensile force acting on a bracket or corbel shall be treated as a live load when calculating Nuc, even if the tension results from restraint of creep, shrinkage, or temperature change.
Unless tensile forces are prevented from being applied to the bracket or corbel, Nuc shall be at least 0.2Vu.
Design strength at all sections shall satisfy ϕSn ≥ U, including (a) through (c). Interaction between load effects shall be considered.
(a) ϕNn ≥ Nuc
(b) ϕVn ≥ Vu
(c) ϕMn ≥ Mu
Nominal tensile strength Nn provided by An shall be calculated by
| Nn = Anfy | (16.5.4.3) |
Nominal shear strength Vn provided by Avf shall be calculated in accordance with provisions for shear-friction in 22.9, where Avf is the area of reinforcement that crosses the assumed shear plane.
Nominal flexural strength Mn provided by Af shall be calculated in accordance with the design assumptions in 22.2.
Area of primary tension reinforcement, Asc, shall be at least the greatest of (a) through (c):
(a) Af + An
(b) (2/3)Avf + An
(c) 0.04(f'c/fy)(bwd)
Total area of closed stirrups or ties parallel to primary tension reinforcement, Ah, shall be at least:
| Ah = 0.5(Asc— An) | (16.5.5.2) |
At the front face of a bracket or corbel, primary tension reinforcement shall be anchored by (a), (b), or (c):
(a) A weld to a transverse bar of at least equal size that is designed to develop fy of primary tension reinforcement
(b) Bending the primary tension reinforcement back to form a horizontal loop
(c) Other means of anchorage that develops fy
Primary tension reinforcement shall be developed at the face of the support.
Development of tension reinforcement shall account for distribution of stress in reinforcement that is not directly proportional to the bending moment.
Closed stirrups or ties shall be spaced such that Ah is uniformly distributed within (2/3)d measured from the primary tension reinforcement.