Steel Base Plate (LRFD, ACI 318-19 / AISC 360-16)
US structural engineers designing steel column base plates to ACI 318-19 and AISC 360-16 under LRFD - for projects pairing the updated concrete code with the earlier steel specification. Base plate design links directly from the column axial load above - change the column load and the plate dimensions and anchor check update automatically. For new work, use the ACI 318-19 / AISC 360-22 version.
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What it calculates
Base plate design receives column axial load directly - change the column load and the plate thickness and anchor check update automatically. Designs steel column base plates and anchor rods to ACI 318-19 and AISC 360-16 under LRFD, checking bearing, plate bending, and all anchor limit states.
Code standards
- ACI 318-19
- AISC 360-16
How it calculates
The Steel Base Plate (LRFD, ACI 318-19 / AISC 360-16) calculator applies AISC Steel Design Guide 1 (2nd Edition) for plate geometry and bending, with anchor limit states updated to ACI 318-19 Chapter 17. Load combinations follow ASCE 7-16.
Load combinations
Unfactored dead, live, wind, and seismic loads are combined into governing ASCE 7-16 LRFD combinations. The critical combination for each check is identified automatically - compressive axial load governs bearing, while the combination producing maximum moment and minimum axial load governs anchor tension.
Concrete bearing capacity (AISC DG1 Cl 3.1)
The factored concrete bearing strength:
phi × P_p = phi_c × 0.85 × f'c × A_1 × sqrt(A_2/A_1) ≤ 1.7 × phi_c × f'c × A_1
Utilization = P_u / phi × P_p ≤ 1.0
Plate bending (AISC DG1 Cl 3.3 - 3.4)
The plate is checked at the bearing interface and tension interface in both X and Y axes. The critical plate moment demand M_u,pl (kip-in/in of plate width) is the maximum of the cantilever bending from bearing pressure over projections m and n.
Required plate thickness from bending:
t_min = sqrt(4 × M_u,pl / (phi_p × F_y))
Utilization = M_u,pl / phi × M_n ≤ 1.0
Anchor rod tensile limit states (ACI 318-19 Cl 17.6)
Five tensile limit states are checked for the anchor group:
- Steel tensile capacity (Cl 17.6.1): phi_t × N_sa = phi_t × A_se × f_uta per rod
- Concrete breakout in tension (Cl 17.6.2): CCD method with projected area A_Nc, modification factors for edge distance, eccentricity, and cracking
- Pullout (Cl 17.6.3): phi × 8 × A_brg × f'c for headed anchors
- Side-face blowout (Cl 17.6.4): applies when h_ef ≥ 2.5 × c_a1
- Group effects: anchor spacing and edge proximity reduction factors
Utilization = N_u / phi × N_n,g ≤ 1.0
Anchor rod shear limit states (ACI 318-19 Cl 17.7)
Three shear limit states are checked in each principal axis:
- Steel shear capacity (Cl 17.7.1): phi_v × V_sa = phi_v × 0.6 × A_se × f_uta
- Concrete pryout (Cl 17.7.3): governs for short embedment depths
- Concrete shear breakout (Cl 17.7.2): projected area method with edge distance factors
Utilization = V_u / phi × V_n,g ≤ 1.0
Frictional shear capacity (ACI 318-19 Cl 22.9)
Base friction under compressive axial load supplements anchor shear capacity. Friction coefficient mu = 0.55 for steel on grout and 0.70 for steel on concrete.
Seismic provisions
When a seismic design category (C through F) is selected, the calculator applies the additional ACI 318-19 Chapter 17 requirements, including the seismic strength reduction factor and the requirement that anchor steel controls over concrete failure modes where applicable.
Frequently asked questions
What codes and method does this calculator use?
What are the key inputs?
What limit states does it check?
Can it handle combined moment and axial loading?
What concrete strengths and anchor rod specifications are supported?
Can this calculator receive column axial load directly from a column calculator?
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