Post-installed anchors

Expansion (torque-controlled and displacement-controlled), screw, undercut and adhesive anchors, single or in a rectangular group of up to 4 × 4, in tension and shear, to ACI 318-19 Chapter 17 with ASCE 7-22 strength combinations. You enter the values of the anchor's evaluation report (an ICC-ES ESR or equal, to ACI 355.2 for mechanical anchors and ACI 355.4 for adhesive anchors). ILX Calcs ships no product data. The prefilled values are samples of the kind in ACI SP-17(14) Tables E.1 and E.2, which ACI marks as fictional: replace them. The calculation says so until you name the report. Chapter 17 is strength design, so the calculation always uses the LRFD combinations. For cast-in anchors use Anchors in concrete.

Inputs of the post-installed anchors #

Each hint in the editor says which row of a report the value comes from. You are the engineer of record: a report's value belongs to one anchor, size, embedment and set of conditions, and you choose which conditions apply.

• Anchor: the type, the report's name, diameter da, effective embedment hef (for a screw anchor, less than the nominal embedment), ductile or brittle steel element, the steel strengths Nsa and Vsa, and the anchor category (1, 2 or 3).
• Breakout and pullout values: kc for cracked concrete (17; product tests may raise it to 24, 17.6.2.2.2) and for uncracked concrete with its ψc,N: 1.0 with the report's kc,uncr, or 1.4 with kc = 17 (17.6.2.5.1). Pullout Np for cracked or uncracked concrete from the report, with the f'c it belongs to and the exponent of the report's adjustment; 0 means the report gives no value and pullout is not evaluated (17.6.3.2.1 does not allow it to be calculated). The load-bearing length le (0 = hef; never more than 8 da, 17.7.2.2.1).
• Bond values (adhesive): τcr and τuncr of the report for your temperature range, drilling method and concrete condition, with a factor for the report's modifications (concrete strength, installation); or the minimum values of Table 17.6.5.2.5, indoor or outdoor, under its conditions (17.6.5.2.5). The factors apply to the bond stress in Nba, not to cNa, which uses the characteristic τuncr even in cracked concrete. The anchor category for bond is separate, because reports give it by installation condition (dry, water-saturated, water-filled hole).
• Pattern and edges: anchors along x and y, spacings, the distance from the outermost anchors to the edge on each side (0 = no edge on that side), the member thickness ha.
• Spacing, edge and thickness limits (17.9): smin, cmin and hmin of the report, and cac; 0 uses the code tables. Where a report gives a cmin and smin curve, enter the pair you use. The specified cover and maximum aggregate size also set the minimum edge distance. With supplementary reinforcement to control splitting the limits of 17.9 do not apply and ψcp,N and ψcp,Na are 1.0.
• Concrete: f'c (taken as at most 8,000 psi; above that the anchor needs tests, 17.3.1), λ (λa follows Table 17.2.4.1 for lightweight concrete: 1.0 λ undercut, 0.8 λ expansion, screw and adhesive concrete failure, 0.6 λ bond) or an alternate λa from the report, cracked or uncracked, whether the anchor is qualified for cracked concrete, supplementary reinforcement for tension and for shear (Table 17.5.3(b)), and edge reinforcement for ψc,V.
• Loads: service forces per load type at the group centroid (N, Mx, My, Vx, Vy), where the shear acts, and for each row the part that is sustained, 0 to 1. You decide what is sustained; a dead load row marked as not sustained gets an advisory.
• Seismic: Seismic Design Category C to F; whether the anchor is qualified for earthquake forces (17.10.3); the report's seismic Vsa,eq, Np,eq and factor on τ, used in combinations with E; the tension option of 17.10.5.3 and Ω0.
• Installation and code options: built-up grout pad (0.80 Vsa), concrete at least 21 days old (adhesive, 17.2.2), installation direction, and the temperature range and installation conditions your values assume, which print on the sheet.

Auto-design (editor toolbar) varies the anchor spacing and the embedment of an adhesive anchor within 4 da to 20 da, for the least drilled depth, then the smallest pattern. The diameter and the report's values are kept. The embedment of a mechanical anchor is kept too, because Np and the installation data of a report belong to one embedment: try another line of the report yourself. Every other input is kept; see Auto-design.

Checks performed #

Limitations of the post-installed anchors #

• The values are yours to read correctly: nothing checks them against the report, and no product list ships with the calculation.
• Table 17.9.2(a) has no column for adhesive anchors. The minimum spacing without a report value is 6 da, the value it gives the other post-installed anchors, and the value SP-17(14) uses. Enter smin of the report.
• cNa takes the characteristic τuncr, without the sustained and earthquake notes of Table 17.6.5.2.5 and without your factor on τ. The code does not say this in so many words; it follows R17.6.5.1 and SP-17(14), and is on the safe side near edges and in groups.
• When Seismic is on, the report's seismic values apply in combinations that include E, including where the earthquake share is 20 % or less. 17.10.3 does not tie them to the 20 % rule.
• Not covered: 17.9.3 (a substituted diameter), interpolation of a report's cmin and smin curve, anchor reinforcement (17.5.2.1), shear lugs, fatigue or impact (17.1.4), plastic hinge zones (17.10.2), specialty inserts, through-bolts and grouted anchors (17.1.5), group patterns other than a rectangle, concrete bearing under the attachment (the lever arm is never taken larger than the anchor spacing).
• The sheet draws each anchor as a plain rod to hef; the product's own shape is not part of the calculation.
• For sustained loads longer than the 50 years of ACI 355.4, or at higher temperatures, lower factors should be considered (R17.5.2.2). The 0.55 factor is not changed by the calculation.

Verification examples #

Verification status: 289 values compared in 24 examples (24 published, 0 hand calculations from the cited equations): 270 within tolerance, 19 recorded deviations. Code basis: the provisions it uses were read in the target edition.

ACI SP-17(14), Anchorage Examples, to ACI 318-14 (same equations as ACI 318-19, renumbered); the product data there are ACI's fictional samples. Hilti PROFIS Engineering reports, to ACI 318-19. Values agree within 1 % unless noted.

107 published values in all. One documented difference: Examples 10 and 11 add the interaction ratios with capacities rounded to the nearest 100 lb (printed sums 1.05, 1.08; ILX 1.03, 1.06). In Example 17 the eccentricity differs slightly because ILX takes the resultant of the anchor tensions with the compressed anchor at zero, while the example takes the load's position. Example 17 uses τuncr in a member it treats as cracked: that value is entered as τ to follow its arithmetic.

Not published, hand calculations from the cited equations: ψcp,N and ψcp,Na with cac, λa of Table 17.2.4.1, the f'c cap, the Np adjustment, le = 2 da, the sustained part of a group, the notes of Table 17.6.5.2.5, and every seismic path (no worked seismic post-installed example was on disk). PROFIS distributes forces with concrete bearing under a rigid plate and this calculation does not, so PROFIS's demands under moment are not compared. SP-17 Examples 15 and 19 (shear and moment, column anchors) were not run for the same reason.