Steel Base Plate (LRFD, ACI 318-14 / AISC 360-16)

How it calculates

The Steel Base Plate (LRFD) calculator follows AISC Steel Design Guide 1 (2nd Edition, 2006) for plate sizing and plate bending, and ACI 318-14 Chapter 17 for all anchor rod limit states. Factored load combinations are generated per ASCE 7-16.

Load combinations

Dead, live, wind, and seismic loads are entered as unfactored components. The calculator generates all governing ASCE 7-16 LRFD combinations (1.2D + 1.6L etc.) and identifies the critical factored axial load P_u, biaxial moments M_ux and M_uy, and shear demands V_ux and V_uy for each subsequent check.

Concrete bearing capacity (AISC DG1 Cl 3.1)

The factored concrete bearing strength under the plate is:

phi × P_p = phi_c × 0.85 × f'c × A_1 × sqrt(A_2/A_1)

where A_1 is the base plate area and A_2 is the supporting surface area. The geometry factor sqrt(A_2/A_1) is limited to 2.0 per ACI 318-14.

Utilization = P_u / phi × P_p ≤ 1.0

Plate bending - bearing interface (AISC DG1 Cl 3.3 - 3.4)

When the plate is in the small-moment regime (full contact), the plate bending demand at the bearing interface is calculated from the upward bearing pressure over the cantilever projections m and n beyond the column flange and web.

The critical plate moment demand M_u,pl (kip-in/in) is compared to the plate bending capacity:

phi × M_n = phi_p × F_y × t^2 / 4

Utilization = M_u,pl / phi × M_n ≤ 1.0

The minimum required plate thickness t_min is reported from this check.

Plate bending - tension interface (AISC DG1 Cl 3.3 - 3.4)

For large-moment conditions where anchor rods carry tension, the plate is also checked for bending at the tension interface. The anchor rod tensile force creates an upward pull on the plate, and the resulting plate moment is evaluated against phi × M_n.

Anchor rod tensile capacity (ACI 318-14 Cl 17.4)

The calculator checks five tensile limit states for the anchor rod group:

• Steel tensile strength: phi_t × A_se × f_uta
• Concrete breakout (CCD method): based on projected cone area A_Nc relative to basic area A_Nco
• Pullout capacity: phi × 8 × A_brg × f'c per rod
• Side-face blowout: applicable when embedment depth is large relative to edge distance
• Group effects: interaction factors for closely spaced anchors

Utilization = N_u / phi × N_n,g ≤ 1.0

Anchor rod shear capacity (ACI 318-14 Cl 17.5)

Shear demand is checked against:

• Steel shear capacity: phi_v × 0.6 × A_se × f_uta
• Concrete pryout: phi × k_cp × N_cbg (governs for shallow embedments)
• Concrete shear breakout in both X and Y axes using the projected area method

Utilization = V_u / phi × V_n,g ≤ 1.0

Frictional shear capacity (ACI 318-14 Cl 22.9)

The base plate can transfer shear through friction between the plate and the grout or concrete. The friction capacity phi × mu × P_u is added where applicable to supplement anchor shear resistance.

Minimum required plate thickness

The governing minimum plate thickness t_min is reported as the maximum value from the bearing interface check and the tension interface check across both axes.