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This module designs steel column base plates according to the 13th Edition AISC Steel Construction Manual and the AISC Steel Design Guide 1, Second Edition.

 

This module performs the analysis differently than the similar module in the Version 5 series of the Structural Engineering Library. The prior module used a strain compatibility method which was highly accurate numerically, but was at odds with the building codes that engineers and building departments were most familiar with.

 

There also was published an AISC Base Plate Design Guide 2nd edition which provided expanded coverage of the topic and slightly different methodology. However that guide went out of print quickly, was not republished and is not available to most design offices. For those reasons, its validity as a national design method has not taken hold and is not followed here.

 

This module handles base plate design for the following conditions:

 

This module does not handle conditions where NET UPLIFT is present.  When the summation of factored axial loads in a load combination is negative, then uplift controls and the module will not calculate. Under these conditions, a red error message will be displayed at the bottom of the window to notify you of this condition.

 

 

 

General & Materials Tab

 

 The right side of this tab will look slightly different for LRFD:

 

         

 

For Axial Load Cases Only....

This selection controls the upward pressure used to design the plate. A brief description of each choice is provided below the buttons for each selection.

 

Full Bearing: Bearing is assumed uniform under plate. If plate area is larger than needed, the larger "m" and "n" cantilevered dimensions could result in  a thicker plate than would be required if the pressure was calculated by the other option.

 

Bearing Area = P / Fp: Base plate is considered flexible with bearing concentrated close to column. Maximum Fp is used to calculate ''design'' minimum plate size. Determining the bearing pressure by this method might result in thicker plates if bending stress is high between webs or within pipe or tube walls.

 

AISC 360-05 Method

Select between ASD or LRFD design methods.

 

Steel Base Plate Fy

Specify the yield strength of the base plate material.

 

ASD: ASIF: Allowable Stress Increase Factor

For ASD design this is an allowable stress increase factor that is applied to Fy. Its usage is controlled by the state of the "ASIF" checkbox on the Load Combinations tab.

 

ASD: Omega

Enter the capacity reduction factor, Omega, to be used in ASD per AISC 360-05.

 

LRFD: Phi

Enter the capacity reduction factor, Phi, to be used in LRFD per AISC 360-05.

 

Concrete Support f'c

28-day compressive strength of concrete used to support the base plate.

 

ASD: Allowable Bearing Increase Factor

For ASD design this is an allowable stress increase factor that is applied to f'c for calculation of concrete bearing strength. Its usage is controlled by the state of the "ABIF" checkbox on the Load Combinations tab.

 

Use AISC 360-05 Section J.8 for "Fp" Calculation

Checking this box will tell the module to use AISC 360-05 Section J.8 to calculate the allowable bearing pressure of the support. When unchecked the screen will change slightly as shown below to allow entry of the allowable bearing pressure.

 

 

ASD: Omega per AISC J.8

AISC 360-05 Section J.8 specifies Omega as 2.5. This entry allows the value to be modified.

 

LRFD: Phi per AISC J.8

AISC 360-05 Section J.8 specifies Phi as 0.6. This entry allows the value to be modified.

 

 

Column & Plate Tab

 

 

Steel Section Name & Database Button

Type the AISC section name in the entry and press [Tab]. The module will look up the section in the Steel database and, if found, will retrieve the values. The name must be typed just as it appears in the 13th Edition AISC Steel Construction Manual.

 

Or click the [Section Database] button to display the built-in steel database and select a section.

 

[Edit Values] Button

Clicking this button will allow you to enter the steel properties.

 

Plate Information

Enter the length, width and thickness of the base plate. Use the buttons to quickly change the values...the results are instantly recalculated.

 

Concrete Support

Enter the support dimensions that will be used to calculate the allowable bearing pressure increase, A1 * sqrt(A2/A1).

 

 

Applied Loads Tab

 

 

Py - Axial Load

This column of entries specifies the axial load applied to the base plate. Note that positive values represent downward loads.

 

Vz - Shear

This column of entries specifies the shear applied parallel to the plate and to be resisted by the anchor bolts.

 

Mx - Moment

This column of entries specifies the moment that the column applies to the plate.

 

 

Anchor Bolts Tab

Items on this tab specify the strength and location of the anchor bolts that will resist shear and tension.

 

 

 

Description

Description of the bolt for your reference. Not used by module.

 

Tension Capacity

Net tension capacity of bolt after all capacity factors are applied.

 

Shear Capacity

Net shear capacity of bolt after all capacity factors are applied.

 

Edge Distance

Distance from edge of plate to center of bolt closest to edge.

 

Number of Bolts in a Row

The "Row" referred to is a row of bolts at the plate edge that will take any tension force.

 

Number of Bolt Rows

Number of rows of bolts.

 

Row Spacing

Spacing of rows when more than one row is used.

 

 

Load Combinations Tab

This tab displays the load combinations used for either the ASD or LRFD selections.

 

The screen capture below shows the factors when ASD load combinations are used.

 

 

The screen capture below shows the factors when LRFD load combinations are used.

 

 

Results Tab - Overall

The Results tab contains a list of load combinations on the left and a summary of all the calculated values for each load combination on the right. Click one of the load combinations in the list to view results specifically for that load combination.

 

The very first item in the list will always say Overall Results. The module will examine the results for all of the load combinations and determine which gives the extreme condition of stress and presents it the Overall Results item. This is the governing case for the base plate.

 

 

 

Results Tab - Axial Load Only

When a load combination results in only an axial load being applied, the summary of information below is displayed. See the AISC Design Guide #1 starting on page 4 for a description of the values present here.

 

 

 

Results Tab - Small Eccentricity

When a load combination results in an axial load and very small moment being applied, the summary of information below is displayed. This condition is caused when the moment causes the resultant eccentricity of the axial load to be within the middle 1/3rd of the base plate. See the AISC Design Guide #1 starting on page 19 for a description of the values present here.

 

 

 

Results Tab - Large Eccentricity

When a load combination results in an axial load and large moment being applied, the summary of information below is seen. This condition is caused when the moment causes the resultant eccentricity of the axial load to be outside the middle 1/3rd of the base plate. See the AISC Design Guide #1 starting on page 21 for a description of the values present here.

 

 

 

Sketch Tab