Heads up:
There are no amended sections in this chapter.
This chapter shall apply to the design of anchors in concrete used to transmit 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.
Provisions of this chapter shall apply to the following anchor types (a) through (g):
(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 1.4N_{p}, where N_{p} is given in Eq. (17.6.3.2.2a).
(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 1.4N_{p}, where N_{p} is given in Eq. (17.6.3.2.2b)
(c) Post-installed expansion (torque-controlled and displacement-controlled) anchors that meet the assessment criteria of ACI 355.2.
(d) Post-installed undercut anchors that meet the assessment criteria of ACI 355.2.
(e) Post-installed adhesive anchors that meet the assessment criteria of ACI 355.4.
(f) Post-installed screw anchors that meet the assessment criteria of ACI 355.2.
(g) Attachments with shear lugs.
The removal and resetting of post-installed mechanical anchors is prohibited.
This chapter does not apply for load applications that are predominantly high-cycle fatigue or due to impact.
This chapter does not apply to specialty inserts, through-bolts, multiple anchors connected to a single steel plate at the embedded end of the anchors, grouted anchors, or power driven anchors such as powder or pneumatic actuated fasteners.
Reinforcement used as part of an embedment shall have development length established in accordance with other parts of this Code. If reinforcement is used as anchorage, concrete breakout failure shall be considered. Alternatively, anchor reinforcement in accordance with 17.5.2.1 shall be provided.
Anchors and anchor groups shall be designed for critical effects of factored loads calculated by elastic analysis. If nominal strength is controlled by ductile steel elements, plastic analysis is permitted provided that deformation compatibility is taken into account.
Anchor group effects shall be considered if two or more anchors loaded by a common structural element are spaced closer than the spacing required for unreduced breakout strength. If adjacent anchors are not loaded by a common structural element, group effects shall consider simultaneous maximum loading of adjacent anchors.
Adhesive anchors shall be installed in concrete having a minimum age of 21 days at time of anchor installation.
Adhesive anchors installed horizontally or upwardly inclined shall be qualified in accordance with ACI 355.4 requirements for sensitivity to installation direction.
Modification factor λ_{a} for lightweight concrete shall be in accordance with Table 17.2.4.1. It shall be permitted to use an alternate value of λ_{a} if tests are performed and evaluated in accordance with ACI 355.2 or ACI 355.4.
Table 17.2.4.1—Modification factor λ_{a} for lightweight concrete
Case | λ_{a}^{[1]} |
---|---|
Cast-in and undercut anchor concrete failure | 1.0λ |
Expansion, screw, and adhesive anchor concrete failure | 0.8λ |
Adhesive anchor bond failure per Eq. (17.6.5.2.1) | 0.6λ |
^{[1]}λ shall be in accordance with 19.2.4
The value 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. Post-installed anchors shall not be used in concrete with a strength greater than 8000 psi without testing to verify acceptable performance.
For anchors with diameters d_{a} ≤ 4 in., concrete breakout strength requirements shall be considered satisfied by the design procedures of 17.6.2 and 17.7.2.
For adhesive anchors with embedment depths 4d_{a} ≤ h_{ef} ≤ 20d_{a}, bond strength requirements shall be considered satisfied by the design procedure of 17.6.5.
For screw anchors with embedment depths 5d_{a} ≤ h_{ef} ≤ 10d_{a}, and h_{ef} ≥ 1.5 in., concrete breakout strength requirements shall be considered satisfied by the design procedures of 17.6.2 and 17.7.2.
Anchors shall satisfy the edge distances, spacings, and thicknesses in 17.9 unless supplementary reinforcement is provided to control splitting failure.
Required strength shall be calculated in accordance with the factored load combinations in Chapter 5.
For each applicable factored load combination, design strength of individual anchors and anchor groups shall satisfy ϕS_{n} ≥ U. Interaction between load effects shall be considered in accordance with 17.8.1.
Strength reduction factor, ϕ, shall be determined in accordance with 17.5.3.
Nominal strength for an anchor or anchor groups 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, number of anchors, effects of close spacing of anchors, proximity to edges, depth of the concrete member, eccentric loadings of anchor groups, and influence of cracking shall be taken into account. Limits on edge distance and anchor spacing in the design models shall be consistent with the tests that verified the model. Strength of anchors shall be based on design models that satisfy 17.5.1.2 for the following:
(a) Steel strength of anchor in tension
(b) Concrete breakout strength of anchor in tension
(c) Pullout strength of a single cast-in anchor and single post-installed expansion, screw, and undercut anchor in tension
(d) Concrete side-face blowout strength of headed anchor in tension
(e) Bond strength of adhesive anchor in tension
(f) Steel strength of anchor in shear
(g) Concrete breakout strength of anchor in shear
(h) Concrete pryout strength of anchor in shear
Anchor group effects shall be considered wherever two or more anchors have spacing less than the critical spacing in Table 17.5.1.3.1, where only those anchors susceptible to the particular failure mode under investigation shall be included in the group.
For each applicable factored load combination, design strength of anchors shall satisfy the criteria in Table 17.5.2.
Table 17.5.2—Design strength requirements of anchors
Anchor group^{[1]} | |||
---|---|---|---|
Failure mode | Single anchor | Individual anchor in a group | Anchors as a group |
Steel strength in tension (17.6.1)^{[2]} | ϕN_{sa} ≥ N_{ua} | ϕN_{sa} ≥ N_{ua,i} | |
Concrete breakout strength in tension^{[3]}(17.6.2) | ϕN_{cb} ≥ N_{ua} | ϕN_{cbg} ≥ N_{ua,g} | |
Pullout strength in tension (17.6.3) | ϕN_{pn} ≥ N_{ua} | ϕN_{pn} ≥ N_{ua,i} | |
Concrete side-face blowout strength in tension (17.6.4) | ϕN_{sb} ≥ N_{ua} | ϕN_{sbg} ≥ N_{ua,g} | |
Bond strength of adhesive anchor in tension (17.6.5) | ϕN_{a} ≥ N_{ua} | ϕN_{ag} ≥ N_{ua,g} | |
Steel strength in shear (17.7.1) | ϕV_{sa} ≥ V_{ua} | ϕV_{sa} ≥ V_{ua,i} | |
Concrete breakout strength in shear^{[3]}(17.7.2) | ϕV_{cb} ≥ V_{ua} | ϕV_{cbg} ≥ V_{ua,g} | |
Concrete pryout strength in shear (17.7.3) | ϕV_{cp} ≥ V_{ua} | ϕV_{cpg} ≥ V_{ua,g} |
^{[1]}Design strengths for steel and pullout failure modes shall be calculated for the most highly stressed anchor in the group.
^{[2]}Sections referenced in parentheses are pointers to models that are permitted to be used to evaluate the nominal strengths.
^{[3]}If anchor reinforcement is provided in accordance with 17.5.2.1, the design strength of the anchor reinforcement shall be permitted to be used instead of the concrete breakout strength
The design strength of anchor reinforcement shall be permitted to be used instead of the concrete breakout strength if (a) or (b) is satisfied.
(a) For tension, if anchor reinforcement is developed in accordance with Chapter 25 on both sides of the concrete breakout surface
(b) For shear, if anchor reinforcement is developed in accordance with Chapter 25 on both sides of the concrete breakout surface, or encloses and contacts the anchor and is developed beyond the breakout surface.
Strength reduction factor ϕ for anchor reinforcement shall be in accordance with 17.5.3.
Design of adhesive anchors to resist sustained tension shall satisfy Eq. (17.5.2.2)
0.55ϕN_{ba} ≥ N_{ua,s} | (17.5.2.2) |
where N_{ba} is basic bond strength in tension of a single adhesive anchor and N_{ua,s} is the factored sustained tensile load.
For groups of adhesive anchors subject to sustained tension, Eq. (17.5.2.2) shall be satisfied for the anchor that resists the highest sustained tension.
If both N_{ua} and V_{ua} are present, interaction effects shall be considered using an interaction expression that results in calculated strengths in substantial agreement with results of comprehensive tests. This requirement shall be considered satisfied by 17.8.
Anchors shall satisfy the edge distances, spacings, and thicknesses in 17.9 to preclude splitting failure.
Anchors in structures assigned to Seismic Design Category C, D, E, or F shall satisfy the additional requirements of 17.10.
Attachments with shear lugs used to transfer structural loads shall satisfy the requirements of 17.11.
Strength reduction factor ϕ for anchors in concrete shall be in accordance with Tables 17.5.3(a), 17.5.3(b), and 17.5.3(c). Strength reduction factor ϕ for anchor reinforcement shall be 0.75.
Table 17.5.3(a)—Anchor strength governed by steel
Type of steel element | Strength reduction factor ϕ | |
---|---|---|
Tension (steel) | Shear (steel) | |
Ductile | 0.75 | 0.65 |
Brittle | 0.65 | 0.60 |
Supplementary reinforcement | Type of anchor installation | Anchor Category^{[1]} from ACI 355.2 or ACI 355.4 | Strength reduction factor ϕ | |
---|---|---|---|---|
Tension (concrete breakout, bond, or side-face blowout) | Shear (concrete breakout) | |||
Supplementary reinforcement present | Cast-in anchors | Not applicable | 0.75 | 0.75 |
Post-installed anchors | 1 | 0.75 | ||
2 | 0.65 | |||
3 | 0.55 | |||
Supplementary reinforcement not present | Cast-in Anchors | Not applicable | 0.70 | 0.70 |
Post-installed anchors | 1 | 0.65 | ||
2 | 0.55 | |||
3 | 0.45 |
Nominal concrete breakout strength in tension, N_{cb} of a single anchor or N_{cbg} of an anchor group satisfying 17.5.1.3.1, shall be calculated by (a) or (b), respectively:
(a) For a single anchor
(17.6.2.1a) |
(b) For an anchor group
(17.6.2.1b) |
A_{Nc} is the projected concrete failure area of a single anchor or of an anchor group that is approximated as the base of the rectilinear geometrical shape that results from projecting the failure surface outward 1.5h_{ef} from the centerlines of the anchor, or in the case of an anchor group, from a line through a row of adjacent anchors. A_{Nc} shall not exceed nA_{Nco}, where n is the number of anchors in the group that resist tension.
If anchors are located less than 1.5h_{ef} from three or more edges, the value of h_{ef} used to calculate A_{Nc} in accordance with 17.6.2.1.1, as well as for the equations in 17.6.2.1 through 17.6.2.4, shall be the greater of (a) and (b):
(a) c_{a,max}/1.5
(b) s/3, where s is the maximum spacing between anchors within the group.
If 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 1.5h_{ef} 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.
A_{Nco} is the projected concrete failure area of a single anchor with an edge distance of at least 1.5h_{ef} and shall be calculated by Eq. (17.6.2.1.4).
A_{Nco} = 9h_{ef}^{2} | (17.6.2.1.4) |
Basic concrete breakout strength of a single anchor in tension in cracked concrete, N_{b}, shall be calculated by Eq. (17.6.2.2.1), except as permitted in 17.6.2.2.3
(17.6.2.2.1) |
where k_{c} = 24 for cast-in anchors and 17 for post-installed anchors.
k_{c} for post-installed anchors shall be permitted to be increased based on ACI 355.2 or ACI 355.4 product-specific tests, but shall not exceed 24.
For single cast-in headed studs and headed bolts with 11 in. ≤ h_{e}_{f} ≤ 25 in., N_{b} shall be calculated by:
(17.6.2.2.3) |
Modification factor for anchor groups loaded eccentrically in tension, ψ_{ec,N}, shall be calculated by Eq. (17.6.2.3.1).
(17.6.2.3.1) |
If the loading on an anchor group is such that only some of the anchors in the group are in tension, only those anchors that are in tension shall be considered for determining eccentricity e'_{N} in Eq. (17.6.2.3.1) and for the calculation of N_{cbg} according to Eq. (17.6.2.1b).
If the loading is eccentric with respect to two orthogonal axes, ψ_{ec,N} shall be calculated for each axis individually, and the product of these factors shall be used as ψ_{ec,N} in Eq. (17.6.2.1b).
Modification factor for edge effects for single anchors or anchor groups loaded in tension, ψ_{ed,N}, shall be determined by (a) or (b).
(a) If c_{a,min} ≥ 1.5h_{ef}, then ψ_{ed,N} = 1.0 | (17.6.2.4.1a) |
(b) If c_{a,min} < 1.5h_{ef}, then | (17.6.2.4.1b) |
Modification factor for the influence of cracking in anchor regions at service load levels, ψ_{c,N}, shall be determined by (a) or (b):
(a) For anchors located in a region of a concrete member where analysis indicates no cracking at service load levels, ψ_{c,N} shall be permitted to be:
ψ_{c,N} = 1.25 for cast-in anchors
ψ_{c,N} = 1.4 for post-installed anchors, if the value of k_{c} used in Eq. (17.6.2.2.1) is 17. If the value of k_{c} used in Eq. (17.6.2.2.1) is taken from the ACI 355.2 or ACI 355.4 product evaluation report for post-installed anchors:
(i) ψ_{c,N} shall be based on the ACI 355.2 or ACI 355.4 product evaluation report for anchors qualified for use in both cracked and uncracked concrete
(b) For anchors located in a region of a concrete member where analysis indicates cracking at service load levels, ψ_{c,N} shall be taken as 1.0 for both cast-in anchors and post-installed anchors, and 17.6.2.6 shall be satisfied.
Post-installed anchors shall be qualified for use in cracked concrete in accordance with ACI 355.2 or ACI 355.4. 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.
Modification factor for post-installed anchors designed for uncracked concrete in accordance with 17.6.2.5 without supplementary reinforcement to control splitting, ψ_{cp,N}, shall be determined by (a) or (b) using the critical distance c_{ac} as defined in 17.9.5.
(a) If c_{a,min} ≥ c_{ac}, then ψ_{cp,N} = 1.0 | (17.6.2.6.1a) |
(b) If c_{a,min} < c_{ac}, then | (17.6.2.6.1b) |
For all other cases, including cast-in anchors, ψ_{cp,N} shall be taken as 1.0.
Nominal pullout strength of a single cast-in anchor or a single-post-installed expansion, screw, or undercut anchor in tension, N_{pn}, shall be calculated by:
N_{pn} = ψ_{c,P}N_{p} | (17.6.3.1) |
where ψ_{c,P} is given in 17.6.3.3.
For post-installed expansion, screw, and undercut anchors, the values of N_{p} 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 anchors, it shall be permitted to evaluate the pullout strength in tension, N_{p}, for use in Eq. (17.6.3.1) in accordance with (a) or (b). Alternatively, it shall be permitted to use values of N_{p} 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.
(a) For cast-in headed studs and headed bolts, N_{p} shall be calculated by:
N_{p} = 8A_{brg}f_{c}' | (17.6.3.2.2a) |
(b) For J- or L-bolts, Np shall be calculated by:
N_{p} = 0.9f_{c}'e_{h}d_{a} | (17.6.3.2.2b) |
Modification factor to account for the influence of cracking in anchor regions at service load levels, ψ_{c,P}, shall be determined by (a) or (b):
(a) For anchors located in a region of a concrete member where analysis indicates no cracking at service load levels, ψ_{c,P} shall be permitted to be 1.4.
(b) For anchors located in a region of a concrete member where analysis indicates cracking at service load levels, ψ_{c,P}, shall be taken as 1.0.
For a single headed anchor with deep embedment close to an edge (h_{e}_{f} > 2.5c_{a1}), the nominal side-face blowout strength, N_{sb}, shall be calculated by:
(17.6.4.1) |
If c_{a}_{2} for the single headed anchor is less than 3c_{a}_{1}, the value of N_{sb} shall be multiplied by the factor (1 + c_{a}_{2}/c_{a}_{1})/4, where 1.0 ≤ c_{a}_{2}/c_{a}_{1} ≤ 3.0.
For multiple headed anchors with deep embedment close to an edge (h_{ef} > 2.5c_{a}_{1}) and anchor spacing less than 6c_{a}_{1}, the nominal strength of those anchors susceptible to a side-face blowout failure, N_{sbg}, shall be calculated by:
(17.6.4.2) |
where s is the distance between the outer anchors along the edge, and N_{sb} is obtained from Eq. (17.6.4.1) without modification for a perpendicular edge distance.
Nominal bond strength in tension, N_{a} of a single adhesive anchor or N_{ag} of an adhesive anchor group satisfying 17.5.1.3.1, shall be calculated by (a) or (b), respectively.
(a) For a single adhesive anchor:
(17.6.5.1a) |
(b) For an adhesive anchor group:
(17.6.5.1b) |
A_{Na} is the projected influence area of a single adhesive anchor or an adhesive anchor group that is approximated as a rectilinear area that projects outward a distance c_{Na} from the centerline of the adhesive anchor, or in the case of an adhesive anchor group, from a line through a row of adjacent adhesive anchors. A_{Na} shall not exceed nA_{Nao}, where n is the number of adhesive anchors in the group that resist tension.
A_{Nao} is the projected influence area of a single adhesive anchor with an edge distance of at least c_{Na}:
A_{Nao} = (2c_{Na})^{2} | (17.6.5.1.2a) |
where
(17.6.5.1.2b) |
Basic bond strength of a single adhesive anchor in tension in cracked concrete, N_{ba}, shall be calculated by Eq. (17.6.5.2.1)
N_{ba}=λ_{a}τ_{cr}πd_{a}h_{ef} | (17.6.5.2.1) |
Characteristic bond stress, τ_{cr}, shall be taken as the 5 percent fractile of results of tests performed and evaluated in accordance with ACI 355.4.
If 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, τ_{uncr} shall be permitted to be used in place of τ_{cr} in Eq. (17.6.5.2.1) 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 17.6.5.2.5, 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 17.6.5.2.5—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 | τ_{cr}, psi | τ_{uncr}, psi |
---|---|---|---|---|
Outdoor | Dry to fully saturated | 175 | 200 | 650 |
Indoor | Dry | 110 | 300 | 1000 |
^{[1]}If anchor design includes sustained tension, multiply values of τ_{cr} and τ_{uncr} by 0.4.
^{[2]}If anchor design includes earthquake-induced forces for structures assigned to SDC C, D, E, or F, multiply values of τ_{cr} by 0.8 and τ_{uncr} by 0.4.
Modification factor for adhesive anchor groups loaded eccentrically in tension, ψ_{ec,Na}, shall be calculated by Eq (17.6.5.3.1).
(17.6.5.3.1) |
If the loading on an adhesive anchor group is such that only some of the adhesive anchors are in tension, only those adhesive anchors that are in tension shall be considered for determining eccentricity e'_{N} in Eq. (17.6.5.3.1) and for the calculation of N_{ag} according to Eq. (17.6.5.1b).
Modification factor for edge effects for single adhesive anchors or adhesive anchor groups in tension, ψ_{ed,Na}, shall be determined by (a) or (b) using the critical distance c_{Na} as defined in Eq. (17.6.5.1.2b).
(a) If c_{a,min} ≥ c_{Na}, then ψ_{ed,Na} = 1.0 | (17.6.5.4.1a) |
(b) If c_{a,min} < c_{Na}, then | (17.6.5.4.1b) |
Modification factor for adhesive anchors designed for uncracked concrete in accordance with 17.6.5.1 without supplementary reinforcement to control splitting, ψ_{cp,Na}, shall be determined by (a) or (b) where c_{a}_{c} is defined in 17.9.5
(a) If c_{a,min} ≥ c_{ac}, then ψ_{cp,Na} = 1.0 | (17.6.5.5.1a) |
(b) If c_{a,min} < c_{ac}, then | (17.6.5.5.1b) |
For all other cases, ψ_{cp,Na} shall be taken as 1.0.
Nominal steel strength of anchors in shear as governed by the steel, V_{sa}, shall be evaluated based on the properties of the anchor material and the physical dimensions of the anchors. If concrete breakout is a potential failure mode, the required steel shear strength shall be consistent with the assumed breakout surface.
Nominal strength of an anchor in shear, V_{sa}, shall not exceed (a) through (c):
(a) For cast-in headed stud anchor
V_{sa} = A_{se,V} f_{uta} | (17.7.1.2a) |
where A_{se,V} is the effective cross-sectional area of an anchor in shear, in.^{2}, and f_{uta} used for calculations shall not exceed either 1.9f_{ya} or 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
V_{sa} = 0.6A_{se,V}f_{uta} | (17.7.1.2b) |
where A_{se,V} is the effective cross-sectional area of an anchor in shear, in.2, and the value of f_{uta} shall not exceed either 1.9f_{ya} or 125,000 psi.
(c) For post-installed anchors where sleeves extend through the shear plane, V_{sa} shall be based on the 5 percent fractile of results of tests performed and evaluated in accordance with ACI 355.2. Alternatively, Eq. (17.7.1.2b) shall be permitted to be used.
If anchors are used with built-up grout pads, nominal strength V_{sa} calculated in accordance with 17.7.1.2 shall be multiplied by 0.80.
Nominal concrete breakout strength in shear, V_{cb} of a single anchor or V_{cbg} of an anchor group satisfying 17.5.1.3.1, shall be calculated in accordance with (a) through (d):
(a) For shear perpendicular to the edge on a single anchor
(17.7.2.1a) |
(b) For shear perpendicular to the edge on an anchor group
(17.7.2.1b) |
(c) For shear parallel to an edge, V_{cb} or V_{cbg} shall be permitted to be twice the value of the shear calculated by Eq. (17.7.2.1a) or (17.7.2.1b), respectively, with the shear assumed to act perpendicular to the edge and ψ_{ed,V} taken equal to 1.0.
(d) For anchors located at a corner, the limiting nominal concrete breakout strength shall be calculated for each edge, and the lesser value shall be used.
A_{Vc} is the projected area of the failure surface on the side of the concrete member at its edge for a single anchor or an anchor group. It shall be permitted to evaluate A_{Vc} 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 c_{a}_{1} shall be taken as the distance from the edge to this axis. A_{Vc} shall not exceed nA_{Vco}, where n is the number of anchors in the group.
If anchors are located in narrow sections of limited thickness such that both edge distances c_{a}_{2} and thickness h_{a} are less than 1.5c_{a}_{1}, the value of c_{a}_{1} used to calculate A_{Vc} in accordance with 17.7.2.1.1 as well as for the equations in 17.7.2.1 through 17.7.2.6 shall not exceed the greatest of (a) through (c).
(a) c_{a}_{2}/1.5, where c_{a}_{2} is the greatest edge distance
(b) h_{a}/1.5
(c) s/3, where s is the maximum spacing perpendicular to direction of shear, between anchors within a group
A_{Vco} is the projected area for a single anchor in a deep member with a distance from edges of at least 1.5c_{a}_{1} in the direction perpendicular to the shear. It shall be permitted to calculate A_{Vco} by Eq. (17.7.2.1.3), which gives the area of the base of a half-pyramid with a side length parallel to the edge of 3c_{a}_{1} and a depth of 1.5c_{a}_{1}.
A_{Vco} = 4.5(c_{a}_{1})^{2} | (17.7.2.1.3) |
If 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 c_{a}_{1} 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 resisted by this critical anchor row alone.
Basic concrete breakout strength of a single anchor in shear in cracked concrete, V_{b}, shall not exceed the lesser of (a) and (b):
(a) | (17.7.2.2.1a) |
ℓ_{e} = h_{ef} 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;
ℓ_{e} = 2d_{a} for torque-controlled expansion anchors with a distance sleeve separated from expansion sleeve;
ℓ_{e} ≤ 8d_{a} in all cases.
(b) | (17.7.2.2.1b) |
For cast-in headed studs, headed bolts, or hooked bolts that are continuously welded to steel attachments, basic concrete breakout strength of a single anchor in shear in cracked concrete, V_{b}, shall be the lesser of Eq. (17.7.2.2.1b) and Eq. (17.7.2.2.2) provided that (a) through (d) are satisfied.
(17.7.2.2.2) |
where ℓ_{e} is defined in 17.7.2.2.1.
(a) Steel attachment thickness is the greater of 0.5d_{a} and 3/8 in.
(b) Anchor spacing s is at least 2.5 in.
(c) Reinforcement is provided at the corners if c_{a}_{2} ≤ 1.5h_{ef}
(d) For anchor groups, the strength is calculated based on the strength of the row of anchors farthest from the edge.
Modification factor for anchor groups loaded eccentrically in shear, ψ_{ec,V}, shall be calculated by Eq. (17.7.2.3.1).
(17.7.2.3.1) |
If the loading on an anchor group is such that only some of the anchors in the group are in shear, only those anchors that are in shear in the same direction shall be considered for determining the eccentricity e'_{V} in Eq. (17.7.2.3.1) and for the calculation of V_{cbg} according to Eq. (17.7.2.1b).
Modification factor for edge effects for single anchors or anchor groups loaded in shear, ψ_{ed,V}, shall be determined by (a) or (b) using the lesser value of c_{a}_{2}.
(a) If c_{a}_{2} ≥ 1.5c_{a}_{1}, then ψ_{ed,V} = 1.0 | (17.7.2.4.1a) |
(b) If c_{a}_{2} < 1.5c_{a}_{1}, then | (17.7.2.4.1b) |
Modification factor for the influence of cracking in anchor regions at service load levels and presence or absence of supplementary reinforcement, ψ_{c,V}, shall be determined as follows:
(a) For anchors located in a region of a concrete member where analysis indicates no cracking at service load levels, ψ_{c,V} shall be permitted to be 1.4.
(b) For anchors located in a region of a concrete member where analysis indicates cracking at service load levels, ψ_{c,V} shall be in accordance with Table 17.7.2.5.1.
Table 17.7.2.5.1—Modification factor where analysis indicates cracking at service load levels, ψ_{c,V}
Condition | ψ_{c,V} |
---|---|
Anchors without supplementary reinforcement or with edge reinforcement smaller than a No. 4 bar | 1.0 |
Anchors with reinforcement of at least a No. 4 bar or greater between the anchor and the edge | 1.2 |
Anchors with reinforcement of at least 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. | 1.4 |
Nominal pryout strength, V_{cp} of a single anchor or V_{cpg} of an anchor group satisfying 17.5.1.3.1, shall not exceed (a) or (b), respectively.
(a) For a single anchor
V_{cp} = k_{cp}N_{cp} | (17.7.3.1a) |
(b) For an anchor group
V_{cpg} = k_{cp}N_{cpg} | (17.7.3.1b) |
where
k_{cp} = 1.0 for h_{ef} < 2.5 in.
k_{cp} = 2.0 for h_{ef} ≥ 2.5 in.
For cast-in anchors and post-installed expansion, screw, and undercut anchors, N_{cp} shall be taken as N_{cb} calculated by Eq. (17.6.2.1a), and for adhesive anchors, N_{cp} shall be the lesser of N_{a} calculated by Eq. (17.6.5.1a) and N_{cb} calculated by Eq. (17.6.2.1a).
For cast-in anchors and post-installed expansion, screw, and undercut anchors, N_{cpg} shall be taken as N_{cbg} calculated by Eq. (17.6.2.1b), and for adhesive anchors, N_{cpg} shall be the lesser of N_{ag} calculated by Eq. (17.6.5.1b) and N_{cbg} calculated by Eq. (17.6.2.1b).
It shall be permitted to neglect the interaction between tension and shear if (a) or (b) is satisfied.
(a) N_{ua}/(ϕN_{n}) ≤ 0.2 | (17.8.2a) |
(b) V_{ua}/(ϕV_{n}) ≤ 0.2 | (17.8.2b) |
If N_{u}_{a} /(ϕN_{n}) > 0.2 for the governing strength in tension and V_{u}_{a}/(ϕV_{n}) > 0.2 for the governing strength in shear, then Eq. (17.8.3) shall be satisfied.
(17.8.3) |
Minimum spacings and edge distances for anchors and minimum thicknesses of members shall conform to this section, 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 17.9.3, minimum spacing parameters shall conform to Table 17.9.2(a).
Table 17.9.2(a)—Minimum spacing and edge distance requirements
Spacing parameter | Anchor type | |||
---|---|---|---|---|
Cast-in anchors | Post-installed | |||
Not torqued | Torqued | Adhesive, expansion and undercut anchors |
Screw anchors | |
Minimum anchor spacing | 4d_{a} | 6d_{a} | 6d_{a} | Greater of 0.6h_{ef} and 6d_{a} |
Minimum edge distance | Specified cover requirements for reinforcement according to 20.5.1.3 | 6d_{a} | Greatest of (a), (b), and (c): (a) Specified cover requirements for reinforcement according to 20.5.1.3 (b) Twice the maximum aggregate size (c) Minimum edge distance requirements according to ACI 355.2 or 355.4, or Table 17.9.2(b) when product information is absent |
Table 17.9.2(b)—Minimum edge distance in absence of product-specific ACI 355.2 or ACI 355.4 test information
Post-installed anchor type | Minimum edge distance |
---|---|
Torque-controlled | 8d_{a} |
Displacement-controlled | 10d_{a} |
Screw | 6d_{a} |
Undercut | 6d_{a} |
Adhesive | 6d_{a} |
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 given in 17.9.2, calculations shall be performed by substituting for d_{a} a lesser value d_{a}' that meets the requirements of 17.9.2. Calculated forces applied to the anchor shall be limited to the values corresponding to an anchor having a diameter of d_{a}'.
Value of h_{ef} for a post-installed expansion, screw, or undercut post-installed anchor shall not exceed the greater of 2/3 of the member thickness, h_{a}, and the member thickness minus 4 in., unless determined from tests in accordance with ACI 355.2.
Critical edge distance c_{ac} shall be in accordance with Table 17.9.5 unless determined from tension tests in accordance with ACI 355.2 or ACI 355.4.
Table 17.9.5—Critical edge distance
Post-installed anchor type | Critical edge distance c_{ac} |
---|---|
Torque-controlled | 4h_{ef} |
Displacement-controlled | 4h_{ef} |
Screw | 4h_{ef} |
Undercut | 2.5h_{ef} |
Adhesive | 2h_{ef} |
Anchors in structures assigned to Seismic Design Category (SDC) C, D, E, or F shall satisfy the additional requirements of this section.
Post-installed anchors shall be qualified for earthquake-induced forces in accordance with ACI 355.2 or ACI 355.4. The pullout strength, N_{p}, and steel strength in shear, V_{sa}, of post-installed expansion, screw, 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, V_{sa}, and the characteristic bond stresses, τ_{uncr} and τ_{cr}, shall be based on results of the ACI 355.4 Simulated Seismic Tests.
Anchor reinforcement used in structures assigned to SDC C, D, E, or F shall be deformed reinforcement and shall be in accordance with the anchor reinforcement requirements of 20.2.2.
If the tensile component of the strength-level earthquake-induced force applied to a single anchor or anchor group does not exceed 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 anchor group in accordance with 17.6 and the tensile strength requirements of Table 17.5.2.
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 17.10.5.3. The anchor design tensile strength shall be determined in accordance with 17.10.5.4.
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 17.10.5.3(d).
Anchors and their attachments shall satisfy (a), (b), (c), or (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 anchors loaded in tension 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 8d_{a} unless otherwise determined by analysis.
(v) If connections are threaded and the ductile steel elements are not threaded over their entire length, the ratio of f_{uta}/f_{ya} shall be at least 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-induced forces shall be in accordance with the anchor reinforcement requirements of 20.2.2.
(b) Anchor or anchor groups 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, considering both material overstrength and strain-hardening effects for the attachment. The anchor design tensile strength shall be calculated in accordance with 17.10.5.4.
(c) Anchor or anchor groups 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 in accordance with 17.10.5.4.
The anchor design tensile strength shall be calculated from (a) through (e) for the failure modes given in Table 17.5.2 assuming the concrete is cracked unless it can be demonstrated that the concrete remains uncracked.
(a) ϕN_{sa} for a single anchor, or for the most highly stressed individual anchor in an anchor group
(b) 0.75ϕN_{cb} or 0.75ϕN_{cbg}, except that N_{cb} or N_{cbg} need not be calculated if anchor reinforcement satisfying 17.5.2.1(a) is provided
(c) 0.75ϕN_{pn} for a single anchor or for the most highly stressed individual anchor in an anchor group
(d) 0.75ϕN_{sb} or 0.75ϕN_{sbg}
(e) 0.75ϕN_{a} or 0.75ϕN_{ag}
where ϕ is in accordance with 17.5.3.
If anchor reinforcement is provided in accordance with 17.5.2.1(a), no reduction in design tensile strength beyond that given in 17.5.2.1 shall be required.
If the shear component of the strength-level earthquake-induced force applied to a single anchor or anchor group does not exceed 20 percent of the total factored anchor shear associated with the same load combination, it shall be permitted to design a single anchor or anchor group in accordance with 17.7 and the shear strength requirements of 17.5.2.
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 17.10.6.3. The anchor design shear strength for resisting earthquake forces shall be determined in accordance with 17.7.
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 17.7.2 and 17.7.3 need not be computed and 17.10.6.3 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 1^{3}/_{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 17.7.2 and 17.7.3 need not be computed and 17.10.6.3 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 1^{3}/_{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 17.10.6.3(a) through (c) when the design strength of the anchors is determined in accordance with 17.7.2.1(c).
Anchors and their attachments shall satisfy (a), (b) or (c).
(a) Anchor or anchor groups shall be designed for the maximum shear that can be transmitted to the anchor or anchor groups 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 in the attachment.
(b) Anchor or anchor groups shall be designed for the maximum shear that can be transmitted to the anchors by a non-yielding attachment.
(c) Anchor or anchor groups shall be designed for the maximum shear obtained from factored load combinations that include E, with E_{h} increased by Ω_{o}.
If anchor reinforcement is provided in accordance with 17.5.2.1(b), no reduction in design shear strength beyond that given in 17.5.2.1 shall be required.
Single anchors or anchor groups that resist both tensile and shear forces shall be designed in accordance with 17.8, and the anchor design tensile strength calculated in accordance with 17.10.5.4.
It is permitted to design attachments with shear lugs in accordance with 17.11.1.1.1 through 17.11.1.1.9. Alternatively, it is permitted to design using alternative methods if adequate strength and load transfer can be demonstrated by analysis or tests.
Shear lugs shall be constructed of rectangular plates, or steel shapes composed of plate-like elements, welded to an attachment base plate.
A minimum of four anchors shall be provided that satisfy the requirements of Chapter 17 with the exception of the requirements of 17.5.1.2(f), (g), and (h) and the corresponding requirements of Table 17.5.2 for steel strength of anchors in shear, concrete breakout strength of anchors in shear, and concrete pryout strength of anchors in shear.
For anchors welded to the attachment base plate, tension and shear interaction requirements of 17.8 shall include a portion of the total shear on the anchor.
Bearing strength in shear shall satisfy ϕV_{brg,sl} ≥ V_{u} with ϕ = 0.65.
Nominal bearing strength in shear, V_{brg,sl}, shall be determined by 17.11.2.
Concrete breakout strength of the shear lug shall satisfy ϕV_{cb,sl} ≥ V_{u} with ϕ = 0.65.
Nominal concrete breakout strength, V_{cb,sl}, shall be determined by 17.11.3.
For attachments with anchors in tension, both (a) and (b) shall be satisfied:
(a) h_{ef}/h_{sl} ≥ 2.5
(b) h_{ef}/c_{sl} ≥ 2.5
Horizontally installed steel base plates with shear lugs shall have a minimum 1 in. diameter hole along each of the long sides of the shear lug.
The effective bearing area, A_{ef,sl}, shall be below the surface of the concrete, perpendicular to the applied shear, and composed of areas according to (a) through (d):
(a) Bearing area of shear lugs located within 2t_{sl} of the bottom surface of the base plate if the top or bottom surface of the base plate is flush with the surface of the concrete
(b) Bearing area of shear lugs located within 2t_{sl} of the surface of the concrete if the base plate is above the surface of the concrete
(c) Bearing area of shear lugs located within 2t_{sl} of the interface with stiffeners
(d) Bearing area on the leading edge of stiffeners below the surface of the concrete
Modification factor, ψ_{brg,sl}, for the effects of axial load, P_{u}, on bearing strength in shear, shall be determined by (a), (b), or (c):
(a) For applied axial tension:
(17.11.2.2.1a) |
where P_{u} is negative for tension and n is the number of anchors in tension.
(b) For no applied axial load:
ψ_{brg,sl}= 1 | (17.11.2.2.1b) |
(c) For applied axial compression:
(17.11.2.2.1c) |
where P_{u} is positive for compression.
For attachments with multiple shear lugs arranged perpendicular to the direction of applied shear, the bearing strength of the individual shear lugs may be considered to be additive provided the shear stress on a shear plane in the concrete at the bottom of the shear lugs, and extending between the shear lugs, does not exceed 0.2f_{c}'. The nominal bearing strength of each individual lug shall be determined by Eq. (17.11.2.1) using the effective area of the lug.
Nominal concrete breakout strength of a shear lug for shear perpendicular to the edge, V_{cb,sl}, shall be determined from 17.7.2 using Eq. (17.7.2.1a), where V_{b} is calculated using Eq. (17.7.2.2.1b) with c_{a}_{1} taken as the distance from the bearing surface of the shear lug to the free edge and where A_{vc} is the projected area of the failure surface on the side of the concrete member.
A_{vc} is the projected concrete failure area on the side face of the concrete that is approximated as the rectangular shape resulting from projecting horizontally 1.5c_{a}_{1} from the edge of the shear lug and projecting vertically 1.5c_{a}_{1} from the edge of the effective depth of the shear lug, h_{ef,sl}. The effective area of the shear lug, A_{ef,sl}, shall not be included. The effective embedment depth of the shear lug, h_{ef,sl}, shall be taken as the distance from the concrete surface to the bottom of the effective bearing area, A_{ef,sl}.
Nominal concrete breakout strength of a shear lug for shear parallel to the edge shall be permitted to be determined in accordance with 17.7.2.1(c) using Eq. (17.7.2.1(a)) with c_{a}_{1} taken as the distance from the edge to the center of the shear lug and with ψ_{ec,V} taken as 1.0.
For shear lugs located at a corner, the limiting concrete breakout strength shall be determined for each edge, and the minimum value shall be used.
For cases with multiple shear lugs, the concrete breakout strength shall be determined for each potential breakout surface.