Steel Base Plate (LRFD)

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Video Overview

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Assumptions and Limitations

• The base plate is assumed to be rigid and resting in the center of the concrete pier.
• Group effects for tensile and shear are limited to the grouped anchors on one side of a plate.
• Cases where net tension is applied to the base plate are not currently supported.

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Inputting Data

1

Key Properties

Begin by defining the geometry and material properties of your column and base plate.

• Column Section Designation: Select your column size from the database (W, S, M, HP, HSS, HSS-R, or PIPE sections).
• Base Plate Dimensions:
  • Thickness ($t_p$): Enter your desired thickness. The calculator will check this against the required minimum thickness ($t_{min}$).
  • Yield Strength ($F_y$): Typically 36 ksi (A36 steel), but can be adjusted.
  • Plate Length ($N$) & Width ($B$): Define the physical dimensions of the plate.

The calculator provides Estimated Minimum Plate Length ($N_{calc}$) and Width ($B_{calc}$) based on the column dimensions and required bearing area to help you size the plate quickly.

2

Anchor Rod Properties

Configure the anchorage for the connection.

• Standard Reference: Choose between ASTM F1554 grades (Grade 36, 55, 105) or Custom anchor rods.
• Rod Diameter ($d_a$): Select a standard diameter (e.g., 3/4”) or enter a custom value.
• Anchor Type: Choose between Straight or Hooked rods.
• Embedment ($h_{ef}$): Define the effective embedment depth.
• Edge Distance ($e_d$): Specify the distance from the center of the anchor to the edge of the plate.

The calculator currently defaults to a 4-bolt configuration.

3

Concrete Properties

Define the supporting concrete pedestal or foundation.

• Concrete Strength ($f'_c$): Compressive strength of the concrete (e.g., 3000 psi).
• Base Dimensions: Enter the length ($L_{conc}$) and width ($W_{conc}$) of the concrete support.
• Grout: You can toggle whether to include a grout pad and specify its strength ($f'_{cg}$).
• Cracked Concrete: Specify if the concrete is assumed to be cracked at service loads (affects anchor breakout capacity).

4

Applied Loads

Input your unfactored loads. The calculator will automatically apply load combinations based on ASCE 7-16 (or your project defaults).

• Axial, Shear, & Moment (X-Axis): Enter loads acting about the X-axis (Strong axis).
• Shear & Moment (Y-Axis): Enter loads acting about the Y-axis (Weak axis).

Axial loads entered in the X-axis table are added to any axial loads in the Y-axis table. Do not duplicate axial loads.

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Understanding the Results

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Summary

• Minimum Required Plate Thickness ($t_{min}$): The governing thickness required to satisfy bending demands from axial and moment loads.
• Concrete Bearing Strength ($\phi P_p$): Checks if the concrete/grout can support the compressive loads.

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Anchor Capacity

• Total Tensile Capacity of Anchors: Checks steel strength, concrete breakout, and side-face blowout.
• Total Shear Strength of Anchors: Checks steel shear strength, concrete breakout, and pryout strength in both X and Y directions.
• Anchor Tensile and Shear Interaction: Checks combined tension and shear interaction (must be $\le 1.2$).

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Detailed Checks

• Plate Bending ($M_{u,pl}$): Verifies the plate’s capacity against the ultimate moment demand at the bearing interface.
• Concrete Breakout ($A_{Nc}, A_{Vc}$): Reviews the projected failure areas and specific modification factors ($\Psi$) used for edge distance, eccentricity, and cracking.
• Frictional Shear ($\phi V_f$): If enabled, calculates the shear capacity provided by friction between the base plate and concrete.