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

 

 

This module handles base plate design for the following conditions:

•where the resultant eccentricity is zero,

•where the resultant eccentricity is within the middle third for full bearing pressure,

•where the resultant eccentricity is outside the middle third resulting in a triangular pressure distribution on part of the base plate, and

•extreme eccentricity conditions where anchor bolts are required.

 

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 in the status bar to notify you of this condition.  Consider using the Steel Base Plate by FEM module for these situations.

 

 

General & Materials

 

 

Steel Design Method

Select between ASD or LRFD design methods.

 

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.

 

Steel Base Plate Fy

Specify the yield strength of the base plate material.

 

ASD: Omega

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

 

LRFD: Phi

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

 

Concrete Support f'c

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

 

ASD: Omega per AISC J.8

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

 

LRFD: Phi per AISC J.8

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

 

 

Column & Plate

 

 

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 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

 

 

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

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

 

 

 

Description

Text 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 on each side.

 

Row Spacing

Spacing of rows when more than one row is used.

 

 

Load Combinations

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

 

The screen capture below shows a sample of the load combinations factors:

 

 

 

 

Calculations - Overall

The Calculations 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.

 

Note that Maximum Bending Stress is calculated using the plastic section modulus, in keeping with AISC Design Guide 1, Second Edition.

 

 

Calculations - Axial Load Only

When the selected 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.

 

 

 

Calculations - Small Eccentricity

When the selected 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.

 

 

 

Calculations - Large Eccentricity

When the selected 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.

 

 

 

2D Sketch

 

 

 

3D Rendering

 

AISC Base Plate Design Example American Code

Below is an example of some American Base Plate Calculations that are commonly used in base plate design. Often when designing base plates, we will consider a few different checks relating to the various components of a base plate, namely:

• The Concrete base – generally checked against bearing and compression forces in reference  to ACI 318
• The Welds – welds need to be checked, to ensure they provide adequate restraint and do not fail under stress to AISC 360
• Anchor Bolts – can fail due to a number of reasons, as shown below in the example anchor bolt design calculations to AISC
• Steel Member (Column) checks – usually based on local steel design standards

Currently, the Steel Base Plate Design module implements the following checks below. The paid version of this software, includes detailed step-by-step calculations, so that engineers can review exactly how these calculations are made!

Try this calculation using SkyCiv Free Base Plate Calculator:

 

Load Combinations:

The Steel Base Plate Design the uses factored load combinations under ASCE 7-10/16 applies as follows:

1. \(1.4D\)
2. \(1.2D + 1.6L + 0.5(L_{r} \text{ or } S \text{ or } R)\)
3. \(1.2D + 1.6(Lr \text{ or } S \text{ or } R) + (L \text{ or } 0.5W)\)
4. \(1.2D + 1.0W + L + 0.5(Lr \text{ or } S \text{ or } R)\)
5. \(1.2D + 1.0E + L + 0.2S\)
6. \(0.9D + 1.0W\)
7. \(0.9D + 1.0E\)

where :

\(D\) = dead load
\(L\) = live load
\(L_{r}\) = roof live load
\(S\) = Snow load
\(R\) = Rain load
\(E\) = Earthquake
\(W\) = Wind load

Try this calculation using SkyCiv Free Base Plate Calculator:

 

ACI Concrete bearing check:

The Steel Base Plate Design checks the Concrete bearing strength (compression) design in according to AISC 360-16 Eq. J8-2.

\( F_{b} = \phi _{bearing} \times 0.85 \times f’_{c} \times \sqrt{ \frac{ A_{2} }{ A_{1} } } \leq F_{b, limit} = 1.70 \times f_{c} \times A_{1} \)

where:
\( f’_{c} \) – concrete compressive strength
\( A_{1} \) – base plate area in contact with concrete surface
\( A_{2} \) – concrete supporting surface
\( \phi_{bearing} \) – resistance factor for concrete ( default value= 0.65 )

Try this calculation using SkyCiv Free Base Plate Calculator:

 

AISC Weld Design Check:

The Steel Base Plate Design checks weld design accordance to AISC 360-16 J2

\( (i) R_{n} = R_{nwl} + R_{nwt} \)

or

\( (ii) R_{n} = 0.85R_{nwl} + 1.5R_{nwt} \)

where:

\(R_{nwl} \) = total nominal strength of longitudinal loaded fillet welds.
\(R_{nwt} \) = total nominal strength of transversely loaded fillet welds.

Try this calculation using SkyCiv Free Base Plate Calculator:

ACI Anchor Design Check:

The Steel Base Plate Design checks Anchor parameters applies using code provisions of ACI 318-19 under Chapter 17.

Anchor rods are designed according to AISC 360-16 – J9 and ACI 318-19 – Chapter 17. The following resistances of anchor bolts are evaluated:

• Steel strength of anchor in tension and shear, \( \phi N_{sa} \) and \( \phi V_{sa} \).
• Concrete breakout strength in tension and shear, \( \phi N_{cbg} \) and \( \phi V_{cbg} \).
• Concrete pullout strength, \( \phi N_{p} \).
• Concrete side-face blowout strength, \( \phi N_{sb} \).
• Concrete pryout strength of anchor in shear, \( \phi V_{cp} \).

Steel strength of anchor in tension and shear

Figure A. (a) unbreakout bolt (b) bolt break-out due to tension failure (c) bolt split-out due to shear failure

Factored steel strength of anchor in tension and shear is determined according to ACI 318-19 – 17.6.1.2 and 17.7.1 as

For Tension

\( \phi _{tension, anc} N_{sa} = \phi _{tension, anc} A_{se,N}f_{uta} \rightarrow \) equation 17.6.1.2

For Shear

\( \phi _{shear, anc} V_{sa} = \phi _{shear, anc} 0.6A_{se,V}f_{uta} \rightarrow \) equation 17.7.1.2b

where:

• \( \phi _{tension, anc} \) – strength reduction factor for anchors in tension ( default value = 0.75 )
• \( \phi _{shear, anc}\) – strength reduction factor for anchors in shear ( default value = 0.65 )
• \( A_{se,N}\) – is the effective cross-sectional area of an anchor in tension.
• \( A_{se,V}\) – is the effective cross-sectional area of an anchor in shear.
• \( f_{uta}\) – specified tensile strength of anchor steel and shall not be greater than \(1.9f_{ya}\) and 125 ksi (861.845 Mpa)

Concrete breakout strength

Figure B. (a) Bolt rest at concrete (b) concrete break-out due to tension force (c) concrete break-out due to shear force

 

Factored concrete breakout strength of anchor in tension and shear is determined according to ACI 318-19 – 17.6.2 and 17.7.1 as

\( \phi N_{cbg} = \phi \frac{ A_{Nc} }{ A_{Nco} } \psi_{ec,N} \psi_{ed,N} \psi_{c,N} \psi_{cp,N} N_{b} \rightarrow \) equation 17.6.2.ab

where:

\( \phi \) – strength reduction factor for anchors in tension ( default value = 0.75 ).
\( A_{Nc} \) – projected concrete failure of a single or group anchors.
\( A_{Nco} \)- project concrete failure area of a single anchor, for calculation of strength in tension if not limited by edge distance or spacing.

\( \psi_{ec,N} \) – Breakout eccentricity factor in tension.

\( \psi _{ec,N} = \frac{1.00}{ 1 + \frac{e^{‘}_{N}}{1.5 h_{ef}} } \leq 1.00 \rightarrow \) equation 17.6.2.3.1

\( \psi_{ed,N} \) – Breakout effect factor in tension.

(a) \( \text{if } C_{a,min} \geq 1.5h_{ef} \text{ then } \psi _{ed,N} = 1.00 \) equation 17.6.2.4.1a

and

(b) \( \text{if } C_{a,min} < 1.5h_{ef} \text{ then } \psi _{ed,N} = 0.70 + 0.3\frac{C_{a,min}}{1.5h_{ef}} \) equation 17.6.2.4.1b

\( \psi_{c,N} \) – Breakout cracking factor in tension.

\( \psi _{c,N} = 1.25 \) for cast-in anchors

\( \psi_{cp,N} \) – Breakout splitting factor in tension.

(a) \( \text{if } C_{a,min} \geq C_{ac} \text{ then } \psi _{cp,N} = 1.00 \) equation 17.6.2.4.1a

and

(b) \( \text{if } C_{a,min} < C_{ac} \text{ then } \psi _{cp,N} = \frac{ C_{a,min} }{ C_{ac}} \geq \frac{ 1.5h_{ef} }{ C_{ac} } \) equation 17.6.2.4.1b

\( N_{b} \) – basic concrete breakout strength in tension of a single anchor in cracked concrete.

Concrete pullout strength

Figure C. (a) Bolt rest at concrete (b) bolt pull-off from concrete due to tension force

 

Factored concrete pullout strength of an anchor is defined in ACI 318-19 – 17.6.3 as

ϕNpn = ϕΨc,P Np

where:

\( \phi \) – strength reduction factor for anchors in tension ( default value = 0.70 ).
\( \psi _{c, P} \) – modification factor for concrete condition

For cracked concrete:

\( \psi _{c, P} \) = 1.0

For non-cracked concrete:

\( \psi _{c, P} \) = 1.4

\( N_{p} \) – Anchor pullout strength

For cracked concrete:

\( N_{p} = 8A_{brg}f^{‘}_{c}\) equation 17.6.3.2.2a

For non-cracked concrete:

\( N_{p} = 0.9f^{‘}_{c}e_{h}d_{a} \rightarrow \) equation 17.6.2.2.b

where \( 3d_{a} \leq e_{h} \leq 4.5d_{a} \)

\( f^{‘}_{c} \) – specified compressive strength of concrete.
\( A_{brg} \) – net bearing area of the head of stud, anchor bolt or headed deformed bar.
\( e_{h} \) – distance from the inner surface of the shaft of a J-bolt or L-bolt to the outer tip of the J- or L-bolt.
\( d_{a} \) – outside diameter of anchor or shaft diameter of headed stud, headed bolt, or hooked bolt.

Concrete side-face blowout strength

Figure D. (a) Bolt rest at concrete (b) bolt having concrete failure (Side-blow) near edge to tension force

 

Factored concrete side-face blowout strength of an anchor is defined in ACI 318-19 – 17.6.4 as

\( \phi N_{sb} = 160C_{a1}\sqrt{A_{brg}}\lambda _{a} \sqrt{f^{‘}_{c} } \rightarrow \) equation 17.6.4.1

where:

\( f^{‘}_{c} \) – specified compressive strength of concrete.
\( A_{brg} \) – net bearing area of the head of stud, anchor bolt or headed deformed bar.
\( \lambda_{a} \) – modification factor to reflect the reduced mechanical properties of lightweight concrete in certain concrete anchorage application.

Concrete pryout strength of anchor

\( \text{V}_{ \text{cp} } = \text{k}_{cp} \times \text{N}_{cp} \) 

or 

\( \text{V}_{ \text{cpg} } = \text{k}_{cpg} \times \text{N}_{cpg} \)Concrete Pry-out blowout are evaluated in the equations above and the calculations are based strength between anchor rod and concrete where usual failure installation of post-installation anchor, see Figure E below.

Concrete Pry-out blowout are evaluated in the equations above and the calculations are based strength between anchor rod and concrete where usual failure installation of post-installation anchor, see Figure E below.

Figure E. (a) Bolt rest at concrete (b) bolt having concrete failure (Pry-out) due to shear force. 

 

Try this calculation using SkyCiv Free Base Plate Calculator: