Base Plate Design

Base plates are elements required at the end of columns to distribute the concentrated load of the column over a much larger area of the material that supports it. The design of column base plates involves two main considerations: One, spread the load so as to maintain the bearing pressures under the allowable values, and the second is with the connection, or anchorage, of the base plate and column to the concrete foundation.

The program performs the elastic design of a column steel base plate resting on a concrete pier and subjected to any combination of axial load and bending moment, including uplift loading. The moment is assumed acting about the strong axis of a steel column welded to the plate. In addition, this program computes and checks the maximum bearing stress on the pier, as well as the tension and shear forces per rod.

For axially loaded base plates, such as those in frames assumed to be pinned at the base, the program is based on either the cantilever model or the Thornton method covered in the AISC Manual 13th Edition.

For base plates with moment, two design theories are considered:
a) For plates assumed rigid, the strain compatibility is enforced in accordance with the Blodgett method ("Design of Welded Structures")..
b) For plates assumed flexible, the strain compatibility is ignored in accordance with the DeWolf method ("AISC.Design Guides # 1, Second Edition")

For columns subjected to axial tension or uplift, the Murray method is used. The anchorage is designed per the latest provisions of the ACI-318 Appendix D "Anchoring to Concrete", and includes checks for all failure modes in both tension and shear, interaction effects, and reinforcing design. Shear lugs can be designed as well.

Input Data

The input data required includes the plate, column and pier dimensions, the distance from rods to center of column, the materials properties and the acting service loads.

Example

As an example, consider a W10x100 steel column designed to resist a bending moment of 40 k-ft and an axial load of compression of 60 k and a shear force of 10 k, welded to a 17"x17" plate. Design the base plate thickness and check the bearing stresses on a 25"x25" pier. In addition, design the anchorage using F1554-36 anchor rods.

Output

The plate size is adequate since the maximum bearing stress is 65% of the allowable bearing stress for that pier. The plate thickness required is 1" and the rod embedment length is 12" with additional reinforcement. The combined tension-shear stress for the anchor rods is 97% of the allowable value, therefore the design is correct.

ASDIP generates a graphical view of the designed base plate and the resulting bearing pressures and anchor rod forces, as shown.

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