Concrete Anchor Design: undercut
Concrete anchor design data per ACI 318-19 Chapter 17. Covers cast-in and post-installed anchor types: cast-in headed bolt (F1554 Gr.36/55/105), cast-in J-bolt, cast-in headed stud (AWS/A108), expansion wedge anchor, expansion sleeve anchor, undercut anchor, adhesive threaded rod (AC308), adhesive rebar, and concrete screw anchor. Fields include nominal diameter, effective embedment hef, effective stress area Ase, bearing area Abrg, steel tensile strength Nsa, shear strength Vsa, concrete breakout Nb at f'c=4000 psi (kc=24 cast-in, kc=17 post-installed), pullout Np, critical edge distance cac, critical spacing, minimum member thickness, installation torque, phi factors for tension and shear, and seismic qualification. Sources: ACI 318-19 Ch.17, ACI 355.2/355.4, ASTM F1554, ASME B1.1, ICC-ES AC193/AC308.
| anchor type | record id | Fu ksi (ksi) | Fy ksi (ksi) | anchor area Ase in2 (in2) | bearing area Abrg in2 (in2) | concrete breakout Nb lb (lb) | critical edge distance cac in (in) | critical spacing in (in) | effective embedment hef in (in) | min member thickness in (in) | nominal diameter in (in) | nominal diameter mm (mm) | notes | phi shear | phi tension | pullout Np lb (lb) | seismic qualification | steel grade | steel shear strength lb (lb) | steel tensile strength lb (lb) | torque installation ft lb (ft-lb) | typical applications |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| undercut | UC_1000_01 | 90 | 72 | 0.6057 | 2.832 | 22,084 | 11.25 | 15 | 7.5 | 15 | 1 | 25.4 | Nb=17*sqrt(4000)*7.5^1.5=22084 lb; large undercut head Abrg=2.832 in2; Np=8*2.832*4000=90624 lb | 0.7 | 0.75 | 90,624 | Yes | High-str | 32,698 | 54,513 | 150 | critical overhead, seismic moment connections, bridge bearings |
| undercut | UC_500_01 | 90 | 72 | 0.1419 | 0.69 | 8,601 | 6 | 8 | 4 | 8 | 0.5 | 12.7 | Undercut anchor: mechanical interlock gives phi=0.75 (ductile); Nb=17*sqrt(4000)*4.0^1.5=8601 lb (kc=17 post-installed); Np=8*Abrg*fc=8*0.690*4000=22080 lb; higher phi vs expansion due to ductile failure mode per ACI 17.5.3.1.1 | 0.7 | 0.75 | 22,080 | Yes | High-str | 7,662 | 12,771 | 20 | high-load seismic, overhead applications, SDC D+ |
| undercut | UC_750_01 | 90 | 72 | 0.3345 | 1.58 | 13,868 | 8.25 | 11 | 5.5 | 11 | 0.75 | 19.1 | Undercut 3/4in; futa=90ksi; Nb=17*sqrt(4000)*5.5^1.5=13868 lb; Np=8*1.58*4000=50560 lb; phi=0.75 ductile | 0.7 | 0.75 | 50,560 | Yes | High-str | 18,059 | 30,105 | 75 | heavy overhead, seismic structural connection, safety-critical |
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