February 27, 2024

circular-base-plate-example

The design of circular base plates may present a challenge when considering axial load and bending moments that produce large eccentricities. This document shows a step-by-step circular base plate example using ASDIP STEEL software.

Circular Base Plate Example

As an example, consider the circular base plate subject to the dead and wind loads shown below. The outside diameter of the steel column pipe is 16 inches. Design and optimize the base plate and the anchor rods per the AISC 360 and ACI 318 provisions.

circular-base-plate-example

Circular Base Plate Example Input

Enter the information given in the statement of the example. Go to the Geometry tab and select Circular Base Plate type. Click on the Steel Database tab and select the column size from the steel sections database. Enter the plate diameter as 22 inches, assuming a rod edge distance of 1.5 inches. For now, let's assume that the concrete support is 2 inches larger than the plate all around, therefore the support diameter is 26 inches.

Go to the Materials tab and enter f'c and rebars fy as 4 and 60 ksi respectively. Specify the plate fy as 50 ksi, end mark the check box to force plate to remain elastic. This will ensure the strain compatibility during the analysis, and the plane sections will remain plane after bending. Finally, specify 12 anchor rods 1" diameter, F1554-36. 

Use the Loads tab to enter the unfactored loads given in the statement of the problem. The design method is LRFD. Finally, go to the Anchorage tab and specify 1 #5 anchor reinforcement to avoid a breakout failure.

circular-base-plate-1

Circular Base Plate Example Output

The At-a-Glance tab shows a summary of the design for a quick overview of your work as you go. The green check marks indicate that the checks passed. The Condensed tab shows a condensed set of calculations with the most important information grouped by topic for a more in-depth check. The Detailed tab shows a step-by step detailed set of calculations with exposed formulas and references to the design code.

In this example, the maximum bearing stress is 2.5 ksi and the maximum anchor tension is 8,1 kips. Since the controlling limit state was Side Face Blowout, increasing the support diameter to 28 inches also increased the tension capacity. The required plate thickness is 1.77 inches, so either 1.75 or 2.0 inches will work.

The anchor tension design ratio is 0.83, and the shear ratio is 0.33, giving a combined stress ratio of 0.94, therefore the design is acceptable. It can be shown that the anchor reinforcement cannot be removed, otherwise the breakout failure will control the design. Please note that further optimization can be done, either reducing the rod diameter, or increasing the support size. Here the designer plays an important role in deciding if the design can be optimized further, as shown below.

circular-base-plate-2

Takeaway

ASDIP STEEL includes the design of Circular Base Plates, with multiple options to model and optimize the design easily. This circular base plate example shows that the design can be completed and optimized using ASDIP STEEL in minutes.

For our collection of blog posts about structural steel design please visit Steel Design. For our collection of blog posts about anchor rods design please visit Anchor Rods Design.

Detailed information is available about this structural engineering software by visiting ASDIP STEEL. You are invited to download the Free 15-day Software Trial, or go ahead and Place your Order.

Best regards,

Javier Encinas, PE

ASDIP Structural Software

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