This chapter provides design requirements for anchors in concrete used to transmit structural loads by means of tension, shear, or a combination of tension and shear between: (a) connected structural elements; or (b) safety-related attachments and structural elements. Safety levels specified are intended for in-service conditions, rather than for short-term handling and construction conditions.
This chapter applies to cast-in anchors and to post-installed expansion (torque-controlled and displacement-controlled), undercut, and adhesive anchors. Adhesive anchors shall be installed in concrete having a minimum age of 21 days at time of anchor installation. Specialty inserts, through-bolts, multiple anchors connected to a single steel plate at the embedded end of the anchors, grouted anchors, and direct anchors such as powder or pneumatic actuated nails or bolts are not included in the provisions of this chapter. Reinforcement used as part of the embedment shall be designed in accordance with other parts of this Code.
Design provisions are included for the following types of anchors:
(a) Headed studs and headed bolts having a geometry that has been demonstrated to result in a pullout strength in uncracked concrete equal to or exceeding 1.4Np, where Np is given in Eq. (17.4.3.4)
(b) Hooked bolts having a geometry that has been demonstrated to result in a pullout strength without the benefit of friction in uncracked concrete equal to or exceeding 1.4Np, where Np is given in Eq. (17.4.3.5)
(c) Post-installed expansion and undercut anchors that meet the assessment criteria of ACI 355.2
(d) Adhesive anchors that meet the assessment criteria of ACI 355.4
Anchors and anchor groups shall be designed for critical effects of factored loads as determined by elastic analysis. Plastic analysis approaches are permitted where nominal strength is controlled by ductile steel elements, provided that deformational compatibility is taken into account.
Anchor group effects shall be considered wherever two or more anchors have spacing less than the critical spacing as follows:
| Failure mode under investigation | Critical spacing |
|---|---|
| Concrete breakout in tension | 3hef |
| Bond strength in tension | 2cNa |
| Concrete breakout in shear | 3ca1 |
Only those anchors susceptible to the particular failure mode under investigation shall be included in the group.
The design strength of anchors shall equal or exceed the largest required strength calculated from the applicable load combinations in 5.3.
Anchors in structures assigned to Seismic Design Category (SDC) C, D, E, or F shall satisfy the additional requirements of 17.2.3.2 through 17.2.3.7.
Post-installed anchors shall be qualified for earthquake loading in accordance with ACI 355.2 or ACI 355.4. The pullout strength Np and steel strength in shear Vsa of expansion and undercut anchors shall be based on the results of the ACI 355.2 Simulated Seismic Tests. For adhesive anchors, the steel strength in shear, Vsa, and the characteristic bond stresses, τuncr and τcr, shall be based on results of the ACI 355.4 Simulated Seismic Tests.
Where the tensile component of the strength-level earthquake force applied to a single anchor or group of anchors is equal to or less than 20 percent of the total factored anchor tensile force associated with the same load combination, it shall be permitted to design a single anchor or group of anchors to satisfy 17.4 and the tensile strength requirements of 17.3.1.1.
Where the tensile component of the strength-level earthquake force applied to anchors exceeds 20 percent of the total factored anchor tensile force associated with the same load combination, anchors and their attachments shall be designed in accordance with 17.2.3.4.3. The anchor design tensile strength shall be determined in accordance with 17.2.3.4.4.
Exception: 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 shall be deemed to satisfy Section 17.2.3.4.3(d).
Anchors and their attachments shall satisfy one of options (a) through (d):
(a) For single anchors, the concrete-governed strength shall be greater than the steel strength of the anchor. For anchor groups, the ratio of the tensile load on the most highly stressed anchor to the steel strength of that anchor shall be equal to or greater than the ratio of the tensile load on tension loaded anchors to the concrete-governed strength of those anchors. In each case:
(i) The steel strength shall be taken as 1.2 times the nominal steel strength of the anchor.
(ii) The concrete-governed strength shall be taken as the nominal strength considering pullout, side-face blowout, concrete breakout, and bond strength as applicable. For consideration of pullout in groups, the ratio shall be calculated for the most highly stressed anchor.
In addition, the following shall be satisfied:
(iii) Anchors shall transmit tensile loads via a ductile steel element with a stretch length of at least eight anchor diameters unless otherwise determined by analysis.
(v) Where connections are threaded and the ductile steel elements are not threaded over their entire length, the ratio of futa/fya shall not be less than 1.3 unless the threaded portions are upset. The upset portions shall not be included in the stretch length.
(vi) Deformed reinforcing bars used as ductile steel elements to resist earthquake effects shall be limited to ASTM A615 Grades 40 and 60 satisfying the requirements of 20.2.2.5(b) or ASTM A706 Grade 60.
(b) The anchor or group of anchors shall be designed for the maximum tension that can be transmitted to the anchor or group of anchors based on the development of a ductile yield mechanism in the attachment in tension, flexure, shear, or bearing, or a combination of those conditions, and considering both material overstrength and strain hardening effects for the attachment. The anchor design tensile strength shall be calculated from 17.2.3.4.4.
(c) The anchor or group of anchors shall be designed for the maximum tension that can be transmitted to the anchors by a non-yielding attachment. The anchor design tensile strength shall be calculated from 17.2.3.4.4.
(d) The anchor or group of anchors shall be designed for the maximum tension obtained from design load combinations that include E, with E increased by Ω0. The anchor design tensile strength shall be calculated from 17.2.3.4.4.
The anchor design tensile strength for resisting earthquake forces shall be determined from consideration of (a) through (e) for the failure modes given in Table 17.3.1.1 assuming the concrete is cracked unless it can be demonstrated that the concrete remains uncracked:
(a) ϕNsa for a single anchor, or for the most highly stressed individual anchor in a group of anchors
(b) 0.75ϕNcb or 0.75ϕNcbg, except that Ncb or Ncbg need not be calculated where anchor reinforcement satisfying 17.4.2.9 is provided
(c) 0.75ϕNpn for a single anchor, or for the most highly stressed individual anchor in a group of anchors
(d) 0.75ϕNsb or 0.75ϕNsbg
(e) 0.75ϕNa or 0.75ϕNag
where ϕ is in accordance with 17.3.3.
Where anchor reinforcement is provided in accordance with 17.4.2.9, no reduction in design tensile strength beyond that specified in 17.4.2.9 shall be required.
Where the shear component of the strength-level earthquake force applied to the anchor or group of anchors is equal to or less than 20 percent of the total factored anchor shear force associated with the same load combination, it shall be permitted to design the anchor or group of anchors to satisfy 17.5 and the shear strength requirements of 17.3.1.1.
Where the shear component of the strength-level earthquake force applied to anchors exceeds 20 percent of the total factored anchor shear force associated with the same load combination, anchors and their attachments shall be designed in accordance with 17.2.3.5.3. The anchor design shear strength for resisting earthquake forces shall be determined in accordance with 17.5.
Exceptions:
- For the calculation of the in-plane shear strength of anchor bolts attaching wood sill plates of bearing or nonbearing walls of light-frame wood structures to foundations or foundation stem walls, the in-plane shear strength in accordance with 17.5.2 and 17.5.3 need not be computed and 17.2.3.5.3 shall be deemed to be satisfied provided all of the following are met:
- The allowable in-plane shear strength of the anchor is determined in accordance with ANSI/AWC NDS Table 12E for lateral design values parallel to grain.
- The maximum anchor nominal diameter is 5/8 inch (16 mm).
- Anchor bolts are embedded into concrete a minimum of 7 inches (178 mm).
- Anchor bolts are located a minimum of 13/4 inches (45 mm) from the edge of the concrete parallel to the length of the wood sill plate.
- Anchor bolts are located a minimum of 15 anchor diameters from the edge of the concrete perpendicular to the length of the wood sill plate.
- The sill plate is 2-inch (51 mm) or 3-inch (76 mm) nominal thickness.
- For the calculation of the in-plane shear strength of anchor bolts attaching cold-formed steel track of bearing or nonbearing walls of light-frame construction to foundations or foundation stem walls, the in-plane shear strength in accordance with 17.5.2 and 17.5.3 need not be computed and 17.2.3.5.3 shall be deemed to be satisfied provided all of the following are met:
- The maximum anchor nominal diameter is 5/8 inch (16 mm).
- Anchors are embedded into concrete a minimum of 7 inches (178 mm).
- Anchors are located a minimum of 13/4 inches (45 mm) from the edge of the concrete parallel to the length of the track.
- Anchors are located a minimum of 15 anchor diameters from the edge of the concrete perpendicular to the length of the track.
- The track is 33 to 68 mil (0.84 mm to 1.73 mm) designation thickness.
- In light-frame construction bearing or nonbearing walls, shear strength of concrete anchors less than or equal to 1 inch [25 mm] in diameter attaching sill plate or track to foundation or foundation stem wall need not satisfy 17.2.3.5.3(a) through (c) when the design strength of the anchors is determined in accordance with 17.5.2.1(c).
Upcodes Diagrams
Anchors and their attachments shall be designed using one of options (a) through (c):
(a) The anchor or group of anchors shall be designed for the maximum shear that can be transmitted to the anchor or group of anchors based on the development of a ductile yield mechanism in the attachment in flexure, shear, or bearing, or a combination of those conditions, and considering both material overstrength and strain hardening effects in the attachment.
(b) The anchor or group of anchors shall be designed for the maximum shear that can be transmitted to the anchors by a non-yielding attachment.
(c) The anchor or group of anchors shall be designed for the maximum shear obtained from design load combinations that include E, with the horizontal component of E increased by Ωo. The anchor design shear strength shall satisfy the shear strength requirements of 17.3.1.1.
Where anchor reinforcement is provided in accordance with 17.5.2.9, no reduction in design shear strength beyond that specified in 17.5.2.9 shall be required.
Single anchors or groups of anchors that are subjected to both tension and shear forces shall be designed to satisfy the requirements of 17.6, with the anchor design tensile strength calculated from 17.2.3.4.4.
Anchor reinforcement used in structures assigned to SDC C, D, E, or F shall be deformed reinforcement and shall be limited to ASTM A615 Grades 40 and 60 satisfying the requirements of 20.2.2.5(b) (i) and (ii) or ASTM A706 Grade 60.
Adhesive anchors installed horizontally or upwardly inclined shall be qualified in accordance with ACI 355.4 requirements for sensitivity to installation direction.
For adhesive anchors subjected to sustained tension loading, 17.3.1.2 shall be satisfied. For groups of adhesive anchors, Eq. (17.3.1.2) shall be satisfied for the anchor that resists the highest sustained tension load. Installer certification and inspection requirements for horizontal and upwardly inclined adhesive anchors subjected to sustained tension loading shall be in accordance with 17.8.2.2 through 17.8.2.4.
Modification factor λa for lightweight concrete shall be taken as:
| Cast-in and undercut anchor concrete failure.......... | 1.0λ |
| Expansion and adhesive anchor concrete failure.... | 0.8λ |
| Adhesive anchor bond failure per Eq. (17.4.5.2)....... | 0.6λ |
where λ is determined in accordance with 19.2.4. It shall be permitted to use an alternative value of λa where tests have been performed and evaluated in accordance with ACI 355.2 or ACI 355.4.
The values of f'c used for calculation purposes in this chapter shall not exceed 10,000 psi for cast-in anchors, and 8000 psi for post-installed anchors. Testing is required for post-installed anchors when used in concrete with f'c greater than 8000 psi.
Strength design of anchors shall be based either on computation using design models that satisfy the requirements of 17.3.2, or on test evaluation using the 5 percent fractile of applicable test results for the following:
(c) Pullout strength cast-in, post-installed expansion, or undercut anchor in tension (17.4.3)
(e) Bond strength of adhesive anchor in tension (17.4.5)
In addition, anchors shall satisfy the required edge distances, spacings, and thicknesses to preclude splitting failure, as required in 17.7.
The design of anchors shall be in accordance with Table 17.3.1.1. In addition, the design of anchors shall satisfy 17.2.3 for earthquake loading and 17.3.1.2 for adhesive anchors subject to sustained tensile loading.
| Failure mode | Single anchor | Anchor group[1] | |
|---|---|---|---|
| Individual anchor in a group | Anchors as a group | ||
| Steel strength in tension (17.4.1) | ϕNsa ≥ Nua | ϕNsa ≥ Nua,i | |
| Concrete breakout strength in tension (17.4.2) | ϕNcb ≥ Nua | ϕNcbg ≥ Nua,g | |
| Pullout strength in tension (17.4.3) | ϕNpn ≥ Nua | ϕNpn ≥ Nua,i | |
| Concrete side-face blowout strength in tension (17.4.4) | ϕNsb ≥ Nua | ϕNsbg ≥ Nua,g | |
| Bond strength of adhesive anchor in tension (17.4.5) | ϕNa ≥ Nua | ϕNag ≥ Nua,g | |
| Steel strength in shear (17.5.1) | ϕVsa ≥ Vua | ϕVsa ≥ Vua,i | |
| Concrete breakout strength in shear (17.5.2) | ϕVcb ≥ Vua | ϕVcbg ≥ Vua,g | |
| Concrete pryout strength in shear (17.5.3) | ϕVcp ≥ Vua | ϕVcpg ≥ Vua,g | |
[1]Required strengths for steel and pullout failure modes shall be calculated for the most highly stressed anchor in the group.
For the design of adhesive anchors to resist sustained tensions loads, in addition to 17.3.1.1, Eq. (17.3.1.2) shall be satisfied.
| 0.55ϕNba ≥ Nua,s | (17.3.1.2) |
where Nba is determined in accordance with 17.4.5.2.
When both Nua and Vua are present, interaction effects shall be considered using an interaction expression that results in computation of strength in substantial agreement with results of comprehensive tests. This requirement shall be considered satisfied by 17.6.
The nominal strength for any anchor or group of anchors shall be based on design models that result in predictions of strength in substantial agreement with results of comprehensive tests. The materials used in the tests shall be compatible with the materials used in the structure. The nominal strength shall be based on the 5 percent fractile of the basic individual anchor strength. For nominal strengths related to concrete strength, modifications for size effects, the number of anchors, the effects of close spacing of anchors, proximity to edges, depth of the concrete member, eccentric loadings of anchor groups, and presence or absence of cracking shall be taken into account. Limits on edge distances and anchor spacing in the design models shall be consistent with the tests that verified the model.
The effect of reinforcement provided to restrain the concrete breakout shall be permitted to be included in the design models used to satisfy 17.3.2. Where anchor reinforcement is provided in accordance with 17.4.2.9 and 17.5.2.9, calculation of the concrete breakout strength in accordance with 17.4.2 and 17.5.2 is not required.
For anchors with diameters not exceeding 4 in., the concrete breakout strength requirements shall be considered satisfied by the design procedure of 17.4.2 and 17.5.2.
For adhesive anchors with embedment depths 4da ≤ hef ≤ 20da, the bond strength requirements shall be considered satisfied by the design procedure of 17.4.5.
Strength reduction factor ϕ for anchors in concrete shall be as follows when the load combinations of 5.3 are used:
| (a) Anchor governed by strength of a ductile steel element | |
| (i) Tension loads.................................................. | 0.75 |
| (ii) Shear loads..................................................... | 0.65 |
| (b) Anchor governed by strength of a brittle steel element | |
| (i) Tension loads.................................................. | 0.65 |
| (ii) Shear loads..................................................... | 0.60 |
| (c) Anchor governed by concrete breakout, side-face blowout, bond, pullout, or pryout strength | |
|
Condition A
|
Condition B
|
|
| (i) Shear loads................................... |
..........0.75.........
|
...................0.70 |
| (ii) Tension loads | ||
| Cast-in headed studs, headed bolts, or hooked bolts..................................................... |
..........0.75.........
|
...................0.70 |
| Post-installed anchors with category as determined from ACI 355.2 or ACI 355.4 | ||
| Category 1.......................................... |
..........0.75.........
|
...................0.65 |
| (Low sensitivity to installation and high reliability) | ||
| Category 2........................................... |
..........0.65.........
|
...................0.55 |
| (Medium sensitivity to installation and medium reliability) | ||
| Category 3......................................... |
..........0.55.........
|
...................0.45 |
| (High sensitivity to installation and lower reliability) | ||
Condition A applies where supplementary reinforcement is present except for pullout and pryout strengths.
Condition B applies where supplementary reinforcement is not present, and for pullout or pryout strength.
The nominal strength of an anchor in tension as governed by the steel, Nsa, shall be evaluated by calculations based on the properties of the anchor material and the physical dimensions of the anchor.
The nominal strength of an anchor in tension, Nsa, shall not exceed
| Nsa = Ase,N futa | (17.4.1.2) |
where Ase,N is the effective cross-sectional area of an anchor in tension, in.2, and futa shall not be taken greater than the smaller of 1.9fya and 125,000 psi.
The nominal concrete breakout strength in tension, Ncb of a single anchor or Ncbg of a group of anchors, shall not exceed:
(a) For a single anchor
 | (17.4.2.1a) |
(b) For a group of anchors
 | (17.4.2.1b) |
Factors ψec,N, ψed,N, ψc,N, and ψcp,N are defined in 17.4.2.4, 17.4.2.5, 17.4.2.6, and 17.4.2.7, respectively. ANc is the projected concrete failure area of a single anchor or group of anchors that shall be approximated as the base of the rectilinear geometrical figure that results from projecting the failure surface outward 1.5hef from the centerlines of the anchor, or in the case of a group of anchors, from a line through a row of adjacent anchors. ANc shall not exceed nANco, where n is the number of anchors in the group that resist tension. ANco is the projected concrete failure area of a single anchor with an edge distance equal to or greater than 1.5hef
| ANco = 9hef 2 | (17.4.2.1c) |
The basic concrete breakout strength of a single anchor in tension in cracked concrete, Nb, shall not exceed
 | (17.4.2.2a) |
where kc = 24 for cast-in anchors and 17 for post-installed anchors.
The value of kc for post-installed anchors shall be permitted to be increased above 17 based on ACI 355.2 or ACI 355.4 product-specific tests, but shall not exceed 24.
Alternatively, for cast-in headed studs and headed bolts with 11 in. ≤ hef ≤ 25 in., Nb shall not exceed
 | (17.4.2.2b) |
Where anchors are located less than 1.5hef from three or more edges, the value of hef used for the calculation of ANc in accordance with 17.4.2.1, as well as for the equations in 17.4.2.1 through 17.4.2.5, shall be the larger of (ca,max)/1.5 and s/3, where s is the maximum spacing between anchors within the group.
The modification factor for anchor groups loaded eccentrically in tension, ψec,N, shall be calculated as
 | (17.4.2.4) |
but ψec,N shall not be taken greater than 1.0. If the loading on an anchor group is such that only some anchors are in tension, only those anchors that are in tension shall be considered when determining the eccentricity e'N for use in Eq. (17.4.2.4) and for the calculation of Ncbg according to Eq. (17.4.2.1b).
In the case where eccentric loading exists about two axes, the modification factor ψec,N shall be calculated for each axis individually and the product of these factors used as ψec,N in Eq. (17.4.2.1b).
The modification factor for edge effects for single anchors or anchor groups loaded in tension, ψed,N, shall be calculated as
| If Ca,min ≥ 1.5hef, then ψed,N = 1.0 | (17.4.2.5a) |
If Ca,min < 1.5hef, then  | (17.4.2.5b) |
For anchors located in a region of a concrete member where analysis indicates no cracking at service load levels, the following modification factor shall be permitted:
(a) ψc,N = 1.25 for cast-in anchors
(b) ψc,N = 1.4 for post-installed anchors, where the value of kc used in Eq. (17.4.2.2a) is 17
Where the value of kc used in Eq. (17.4.2.2a) is taken from the ACI 355.2 or ACI 355.4 product evaluation report for post-installed anchors qualified for use in both cracked and uncracked concrete, the values of kc and ψc,N shall be based on the ACI 355.2 or ACI 355.4 product evaluation report.
Where the value of kc used in Eq. (17.4.2.2a) is taken from the ACI 355.2 or ACI 355.4 product evaluation report for post-installed anchors qualified for use in uncracked concrete, ψc,N shall be taken as 1.0.
When analysis indicates cracking at service load levels, ψc,N, shall be taken as 1.0 for both cast-in anchors and post-installed anchors. Post-installed anchors shall be qualified for use in cracked concrete in accordance with ACI 355.2 or ACI 355.4. The cracking in the concrete shall be controlled by flexural reinforcement distributed in accordance with 24.3.2, or equivalent crack control shall be provided by confining reinforcement.
The modification factor for post-installed anchors designed for uncracked concrete in accordance with 17.4.2.6 without supplementary reinforcement to control splitting, ψcp,N, shall be calculated as follows using the critical distance cac as defined in 17.7.6
| If Ca,min ≥ Cac, then ψcp,N = 1.0 | (17.4.2.7a) |
If Ca,min < Cac, then  | (17.4.2.7b) |
but ψcp,N determined from Eq. (17.4.2.7b) shall not be taken less than 1.5hef/cac, where the critical distance cac is defined in 17.7.6.
For all other cases, including cast-in anchors, ψcp,N shall be taken as 1.0.
Where an additional plate or washer is added at the head of the anchor, it shall be permitted to calculate the projected area of the failure surface by projecting the failure surface outward 1.5hef from the effective perimeter of the plate or washer. The effective perimeter shall not exceed the value at a section projected outward more than the thickness of the washer or plate from the outer edge of the head of the anchor.
Where anchor reinforcement is developed in accordance with Chapter 25 on both sides of the breakout surface, the design strength of the anchor reinforcement shall be permitted to be used instead of the concrete breakout strength in determining ϕNn. A strength reduction factor of 0.75 shall be used in the design of the anchor reinforcement.
The nominal pullout strength of a single cast-in, post-installed expansion, and post-installed undercut anchor in tension, Npn, shall not exceed
| Npn = ψc,PNp | (17.4.3.1) |
where ψc,P is defined in 17.4.3.6.
For post-installed expansion and undercut anchors, the values of Np shall be based on the 5 percent fractile of results of tests performed and evaluated according to ACI 355.2. It is not permissible to calculate the pullout strength in tension for such anchors.
For single cast-in headed studs and headed bolts, it shall be permitted to evaluate the pullout strength in tension using 17.4.3.4. For single J- or L-bolts, it shall be permitted to evaluate the pullout strength in tension using 17.4.3.5. Alternatively, it shall be permitted to use values of Np based on the 5 percent fractile of tests performed and evaluated in the same manner as the ACI 355.2 procedures but without the benefit of friction.
The pullout strength in tension of a single headed stud or headed bolt, Np, for use in Eq. (17.4.3.1), shall not exceed
| Np = 8Abrg f'c | (17.4.3.4) |
The pullout strength in tension of a single hooked bolt, Np, for use in Eq. (17.4.3.1) shall not exceed
| Np = 0.9f'cehda | (17.4.3.5) |
For an anchor located in a region of a concrete member where analysis indicates no cracking at service load levels, the following modification factor shall be permitted
ψc,P = 1.4
Where analysis indicates cracking at service load levels, ψc,P shall be taken as 1.0.
For a single headed anchor with deep embedment close to an edge (hef > 2.5ca1), the nominal side-face blowout strength, Nsb, shall not exceed
 | (17.4.4.1) |
If ca2 for the single headed anchor is less than 3ca1, the value of Nsb shall be multiplied by the factor (1 + ca2/ca1)/4, where 1.0 ≤ ca2/ca1 ≤ 3.0.
For multiple headed anchors with deep embedment close to an edge (hef > 2.5ca1) and anchor spacing less than 6ca1, the nominal strength of those anchors susceptible to a side-face blowout failure Nsbg shall not exceed
 | (17.4.4.2) |
where s is the distance between the outer anchors along the edge, and Nsb is obtained from Eq. (17.4.4.1) without modification for a perpendicular edge distance.
The nominal bond strength in tension, Na of a single adhesive anchor or Nag of a group of adhesive anchors, shall not exceed
(a) For a single adhesive anchor:
 | (17.4.5.1a) |
(b) For a group of adhesive anchors:
 | (17.4.5.1b) |
Factors ψec,Na, ψed,Na, and ψcp,Na are defined in 17.4.5.3, 17.4.5.4, and 17.4.5.5, respectively. ANa is the projected influence area of a single adhesive anchor or group of adhesive anchors that shall be approximated as a rectilinear area that projects outward a distance cNa from the centerline of the adhesive anchor, or in the case of a group of adhesive anchors, from a line through a row of adjacent adhesive anchors. ANa shall not exceed nANao, where n is the number of adhesive anchors in the group that resist tension loads. ANao is the projected influence area of a single adhesive anchor with an edge distance equal to or greater than cNa:
| ANao = (2cNa)2 | (17.4.5.1c) |
where
 | (17.4.5.1d) |
and constant 1100 carries the unit of lb/in.2
The basic bond strength of a single adhesive anchor in tension in cracked concrete, Nba, shall not exceed
 | (17.4.5.2) |
The characteristic bond stress τcr shall be taken as the 5 percent fractile of results of tests performed and evaluated according to ACI 355.4.
Where analysis indicates cracking at service load levels, adhesive anchors shall be qualified for use in cracked concrete in accordance with ACI 355.4.
For adhesive anchors located in a region of a concrete member where analysis indicates no cracking at service load levels, τuncr shall be permitted to be used in place of τcr in Eq. (17.4.5.2) and shall be taken as the 5 percent fractile of results of tests performed and evaluated according to ACI 355.4.
It shall be permitted to use the minimum characteristic bond stress values in Table 17.4.5.2, provided (a) through (e) are satisfied:
(a) Anchors shall meet the requirements of ACI 355.4
(b) Anchors shall be installed in holes drilled with a rotary impact drill or rock drill
Table 17.4.5.2—Minimum characteristic bond stresses[1][2]
| Installation and service environment | Moisture content of concrete at time of anchor installation | Peak in-service temperature of concrete, °F | τcr, psi | τuncr, psi |
|---|---|---|---|---|
| Outdoor | Dry to fully saturated | 175 | 200 | 650 |
| Indoor | Dry | 110 | 300 | 1000 |
[1]Where anchor design includes sustained tension loading, multiply values of τcr and τuncr by 0.4.
The modification factor for adhesive anchor groups loaded eccentrically in tension, ψec,Na, shall be calculated as:
 | (17.4.5.3) |
but ψec,Na shall not be taken greater than 1.0.
If the loading on an adhesive anchor group is such that only some adhesive anchors are in tension, only those adhesive anchors that are in tension shall be considered when determining the eccentricity e'N for use in Eq. (17.4.5.3) and for the calculation of Nag according to Eq. (17.4.5.1b).
In the case where eccentric loading exists about two orthogonal axes, the modification factor ψec,Na shall be calculated for each axis individually and the product of these factors used as ψec,Na in Eq. (17.4.5.1b).
The modification factor for edge effects for single adhesive anchors or adhesive anchor groups loaded in tension, ψed,Na, shall be calculated as
| If Ca,min ≥ CNa, then ψed,Na = 1.0 | (17.4.5.4a) |
If Ca,min < CNa, then  | (17.4.5.4b) |
The modification factor for adhesive anchors designed for uncracked concrete in accordance with 17.4.5.2 without supplementary reinforcement to control splitting, ψcp,Na, shall be calculated as:
| If Ca,min ≥ Cac, then ψcp,Na = 1.0 | (17.4.5.5a) |
If Ca,min < Cac, then  | (17.4.5.5b) |
but ψcp,Na determined from Eq. (17.4.5.5b) shall not be taken less than cNa/cac, where the critical edge distance cac is defined in 17.7.6. For all other cases, ψcp,Na shall be taken as 1.0.
The nominal strength of an anchor in shear as governed by steel, Vsa, shall be evaluated by calculations based on the properties of the anchor material and the physical dimensions of the anchor. Where concrete breakout is a potential failure mode, the required steel shear strength shall be consistent with the assumed breakout surface.
The nominal strength of an anchor in shear, Vsa, shall not exceed (a) through (c):
(a) For cast-in headed stud anchor
| Vsa = Ase,V futa | (17.5.1.2a) |
where Ase,V is the effective cross-sectional area of an anchor in shear, in.2, and futa shall not be taken greater than the smaller of 1.9fya and 125,000 psi.
(b) For cast-in headed bolt and hooked bolt anchors and for post-installed anchors where sleeves do not extend through the shear plane
| Vsa = 0.6Ase,V futa | (17.5.1.2b) |
where Ase,V is the effective cross-sectional area of an anchor in shear, in.2, and futa shall not be taken greater than the smaller of 1.9fya and 125,000 psi.
(c) For post-installed anchors where sleeves extend through the shear plane, Vsa shall be based on the results of tests performed and evaluated according to ACI 355.2. Alternatively, Eq. (17.5.1.2b) shall be permitted to be used.
Where anchors are used with built-up grout pads, the nominal strengths of 17.5.1.2 shall be multiplied by a factor 0.80.
The nominal concrete breakout strength in shear, Vcb of a single anchor or Vcbg of a group of anchors, shall not exceed:
(a) For shear force perpendicular to the edge on a single anchor
 | (17.5.2.1a) |
(b) For shear force perpendicular to the edge on a group of anchors
 | (17.5.2.1b) |
(c) For shear force parallel to an edge, Vcb or Vcbg shall be permitted to be twice the value of the shear force determined from Eq. (17.5.2.1a) or (17.5.2.1b), respectively, with the shear force assumed to act perpendicular to the edge and with ψed,V taken equal to 1.0.
(d) For anchors located at a corner, the limiting nominal concrete breakout strength shall be determined for each edge, and the minimum value shall be used.
Factors ψec,V, ψed,V, ψc,V, and ψh,V are defined in 17.5.2.5, 17.5.2.6, 17.5.2.7, and 17.5.2.8, respectively. Vb is the basic concrete breakout strength value for a single anchor. AVc is the projected area of the failure surface on the side of the concrete member at its edge for a single anchor or a group of anchors. It shall be permitted to evaluate AVc as the base of a truncated half-pyramid projected on the side face of the member where the top of the half-pyramid is given by the axis of the anchor row selected as critical. The value of ca1 shall be taken as the distance from the edge to this axis. AVc shall not exceed nAVco, where n is the number of anchors in the group.
AVco is the projected area for a single anchor in a deep member with a distance from edges equal or greater than 1.5ca1 in the direction perpendicular to the shear force. It shall be permitted to evaluate AVco as the base of a half-pyramid with a side length parallel to the edge of 3ca1 and a depth of 1.5ca1
| AVco = 4.5(ca1)2 | (17.5.2.1c) |
Where anchors are located at varying distances from the edge and the anchors are welded to the attachment so as to distribute the force to all anchors, it shall be permitted to evaluate the strength based on the distance to the farthest row of anchors from the edge. In this case, it shall be permitted to base the value of ca1 on the distance from the edge to the axis of the farthest anchor row that is selected as critical, and all of the shear shall be assumed to be carried by this critical anchor row alone.
The basic concrete breakout strength in shear of a single anchor in cracked concrete, Vb, shall be the smaller of (a) and (b):
(a)  | (17.5.2.2a) |
ℓe = hef for anchors with a constant stiffness over the full length of embedded section, such as headed studs and post-installed anchors with one tubular shell over full length of the embedment depth;
ℓe = 2da for torque-controlled expansion anchors with a distance sleeve separated from expansion sleeve, and ℓe ≤ 8da in all cases.
(b)  | (17.5.2.2b) |
For cast-in headed studs, headed bolts, or hooked bolts that are continuously welded to steel attachments having a minimum thickness equal to the greater of 3/8 in. and half of the anchor diameter, the basic concrete breakout strength in shear of a single anchor in cracked concrete, Vb, shall be the smaller of Eq. (17.5.2.2b) and Eq. (17.5.2.3)
 |
(17.5.2.3) |
where ℓe is defined in 17.5.2.2 provided that:
(a) For groups of anchors, the strength is determined based on the strength of the row of anchors farthest from the edge
(c) Reinforcement is provided at the corners if ca2 ≤ 1.5hef
Where anchors are located in narrow sections of limited thickness such that both edge distances ca2 and thickness ha are less than 1.5ca1, the value of ca1 used for the calculation of AVc in accordance with 17.5.2.1 as well as for the equations in 17.5.2.1 through 17.5.2.8 shall not exceed the largest of:
(a) ca2 /1.5, where ca2 is the largest edge distance
(b) ha /1.5
The modification factor for anchor groups loaded eccentrically in shear, ψec,V, shall be calculated as
 | (17.5.2.5) |
but ψec,V shall not be taken greater than 1.0.
If the loading on an anchor group is such that only some anchors are loaded in shear in the same direction, only those anchors that are loaded in shear in the same direction shall be considered when determining the eccentricity of e'V for use in Eq. (17.5.2.5) and for the calculation of Vcbg according to Eq. (17.5.2.1b).
For anchors located in a region of a concrete member where analysis indicates no cracking at service loads, the following modification factor shall be permitted
ψc,V = 1.4
For anchors located in a region of a concrete member where analysis indicates cracking at service load levels, the following modification factors shall be permitted:
ψc,V = 1.0 for anchors in cracked concrete without supplementary reinforcement or with edge reinforcement smaller than a No. 4 bar
ψc,V = 1.2 for anchors in cracked concrete with reinforcement of a No. 4 bar or greater between the anchor and the edge
ψc,V = 1.4 for anchors in cracked concrete with reinforcement of a No. 4 bar or greater between the anchor and the edge, and with the reinforcement enclosed within stirrups spaced at not more than 4 in.
Where anchor reinforcement is either developed in accordance with Chapter 25 on both sides of the breakout surface, or encloses the anchor and is developed beyond the breakout surface, the design strength of the anchor reinforcement shall be permitted to be used instead of the concrete breakout strength in determining ϕVn. A strength reduction factor of 0.75 shall be used in the design of the anchor reinforcement.
The nominal pryout strength, Vcp for a single anchor or Vcpg for a group of anchors, shall not exceed:
(a) For a single anchor
| Vcp = kcp Ncp | (17.5.3.1a) |
For cast-in, expansion, and undercut anchors, Ncp shall be taken as Ncb determined from Eq. (17.4.2.1a), and for adhesive anchors, Ncp shall be the lesser of Na determined from Eq. (17.4.5.1a) and Ncb determined from Eq. (17.4.2.1a).
(b) For a group of anchors
| Vcpg = kcp Ncpg | (17.5.3.1b) |
For cast-in, expansion, and undercut anchors, Ncpg shall be taken as Ncbg determined from Eq. (17.4.2.1b), and for adhesive anchors, Ncpg shall be the lesser of Nag determined from Eq. (17.4.5.1b) and Ncbg determined from Eq. (17.4.2.1b).
In Eq. (17.5.3.1a) and (17.5.3.1b), kcp = 1.0 for hef < 2.5 in.; and kcp = 2.0 for hef ≥ 2.5 in.
If Vua/(ϕVn) ≤ 0.2 for the governing strength in shear, then full strength in tension shall be permitted: ϕNn ≥ Nua.
If Nua/(ϕNn) ≤ 0.2 for the governing strength in tension, then full strength in shear shall be permitted: ϕVn ≥ Vua.
If Vua/(ϕVn) > 0.2 for the governing strength in shear and Nua/(ϕNn) > 0.2 for the governing strength in tension, then
 | (17.6.3) |
Minimum spacings and edge distances for anchors and minimum thicknesses of members shall conform to 17.7.1 through 17.7.6, unless supplementary reinforcement is provided to control splitting. Lesser values from product-specific tests performed in accordance with ACI 355.2 or ACI 355.4 shall be permitted.
Unless determined in accordance with 17.7.4, minimum edge distances for cast-in anchors that will not be torqued shall be based on specified cover requirements for reinforcement in 20.6.1. For cast-in anchors that will be torqued, the minimum edge distances shall be 6da.
Unless determined in accordance with 17.7.4, minimum edge distances for post-installed anchors shall be based on the greater of specified cover requirements for reinforcement in 20.6.1, or minimum edge distance requirements for the products as determined by tests in accordance with ACI 355.2 or ACI 355.4, and shall not be less than twice the maximum aggregate size. In the absence of product-specific ACI 355.2 or ACI 355.4 test information, the minimum edge distance shall not be less than:
| Adhesive anchors...................................................................... | 6da |
| Undercut anchorss .................................................................. | 6da |
| Torque-controlled anchors...................................................... | 8da |
| Displacement-controlled anchors........................................... | 10da |
For anchors where installation does not produce a splitting force and that will not be torqued, if the edge distance or spacing is less than those specified in 17.7.1 to 17.7.3, calculations shall be performed by substituting for da a smaller value d'a that meets the requirements of 17.7.1 to 17.7.3. Calculated forces applied to the anchor shall be limited to the values corresponding to an anchor having a diameter of d'a.
Unless determined from tests in accordance with ACI 355.2, the value of hef for an expansion or undercut post-installed anchor shall not exceed the greater of 2/3 of the member thickness, ha, and the member thickness minus 4 in.
Unless determined from tension tests in accordance with ACI 355.2 or ACI 355.4, the critical edge distance cac shall not be taken less than:
| Adhesive anchors.................................................................. | 2hef |
| Undercut anchors................................................................. | 2.5hef |
| Torque-controlled expansion anchors............................... | 4hef |
| Displacement-controlled expansion anchors................... | 4hef |
Construction documents shall specify use of anchors with a minimum edge distance as assumed in design.
Anchors shall be installed by qualified personnel in accordance with the construction documents and, where applicable, manufacturer's instructions. The construction documents shall require installation of post-installed adhesive anchors in accordance with the Manufacturer's Printed Installation Instructions (MPII). Installation of adhesive anchors shall be performed by personnel trained to install adhesive anchors.
Installation of anchors shall be inspected in accordance with 1.9 and the general building code. Adhesive anchors shall be also subject to 17.8.2.1 through 17.8.2.4.
For adhesive anchors, the construction documents shall specify proof loading where required in accordance with ACI 355.4. The construction documents shall also specify all parameters associated with the characteristic bond stress used for the design according to 17.4.5, including minimum age of concrete; concrete temperature range; moisture condition of concrete at time of installation; type of lightweight concrete, if applicable; and requirements for hole drilling and preparation.
Installation of adhesive anchors horizontally or upwardly inclined to support sustained tension loads shall be performed by personnel certified by an applicable certification program. Certification shall include written and performance tests in accordance with the ACI/CRSI Adhesive Anchor Installer Certification program, or equivalent.
The acceptability of certification other than the ACI/CRSI Adhesive Anchor Installer Certification shall be the responsibility of the licensed design professional.
Adhesive anchors installed in horizontal or upwardly inclined orientations to resist sustained tension loads shall be continuously inspected during installation by an inspector specially approved for that purpose by the building official. The special inspector shall furnish a report to the licensed design professional and building official that the work covered by the report has been performed and that the materials used and the installation procedures used conform with the approved construction documents and the Manufacturer's Printed Installation Instructions (MPII).