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SkyCiv Base Plate Design

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Base Plate Connection Overview

In SkyCiv Base Plate and Anchor Rod Degsign Module applies the Triangular Pressure Distribution Method which is permissible and alternatively procedure per AISC – Design Guide 01. This procedure will provide slight thicker base plate and slight smaller anchor rods than the uniform pressure approach.

The Triangular Pressure Distribution Method have two types of behavior:

  1. Small Moment Base, where eekern.
  2. Large Moment Base, where e > ekern .

when ekern  is \( \frac{ \text{ N or B } }{6} \).

The difference behavior of Small Moment Base and Large Moment are is no tension exist between base plate and foundation and the tension anchorage shall be considered in design due to exist tension, respectively.

triangular pressure figure


Figure 1. Bearing behavior between base-plate and concrete produces from small and large eccentricity. Reprinted from the Publication American Institute of Steel Construction – Design Guide 01 (p. 56), by the J.M Fisher and L.A.Kloiber, 2006

Design Procedure reference.

In SkyCiv Baseplate and anchor rod design, the design methodology are been adapted from the following reference.

  • AISC – Design Guide 01 (2nd edition).
  • Haninger, Edward R.; Tong, Bruce M. (2014). “Two-Way Bending of Base Plates under Uniaxial Moment Loading–Alternative Approach,” Engineering Journal, American Institute of Steel Construction, Vol. 51, pp. 229-236.

Base Plate Design Checks

In SkyCiv Baseplate and anchor rod Design Module mainly focuses on Geometry Restriction and Anchor rod Design, which it checks the prescribed loads and geometric inputs are calculated based on the design procedure above and checked against the applicable limit states in the results.

The following checks are included on the report:

I. Geometry Restrictions.

As stated above, the base-plate in triangular distribution are subject in small or large moments, See image below.

II. Anchor rod Design.

The design of anchor rods checks the limit states of tensile steel strength, concrete breakout, pullout, and side-face blowout per ACI 318.

1. Steel strength of anchor.

Tension Shear
\( \text{N}_{ \text{sa} } = \text{A}_{ \text{se}N } \times f_{ \text{uta} } \) \( \text{V}_{ \text{sa} } = \text{A}_{ \text{se}V } \times f_{ \text{uta} } \)

 

Steel strength of anchor for both Tension and Shear are evaluated in the equations above and the calculations are based on the properties of the anchor material and the physical dimensions of the anchor, see Figure A below.

steel strength

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

For more detailed Steel strength of anchor, click here.

2. Concrete breakout.

Type Tension Shear
Single \( \text{N}_{ \text{cb} } = \frac{ \text{A}_{NC} }{ \text{A}_{NCO} } \times \psi _{ ed, N } \times \psi _{ c, N } \times \psi _{ cp, N } \times \text{N}_{b} \) \( \text{V}_{ \text{cb} } = \frac{ \text{A}_{VC} }{ \text{A}_{VCO} } \times \psi _{ ed, V } \times \psi _{ c, V } \times \psi _{ cp, V } \times \text{V}_{b} \)
Group \( \text{N}_{ \text{cbg} } = \frac{ \text{A}_{NC} }{ \text{A}_{NCO} } \times \psi _{ ec, N } \times \psi _{ ed, N } \times \psi _{ c, N } \times \psi _{ cp, N } \times \text{N}_{b} \) \( \text{V}_{ \text{cbg} } = \frac{ \text{A}_{VC} }{ \text{A}_{VCO} } \times \psi _{ ec, V } \times \psi _{ ed, V } \times \psi _{ c, V } \times \psi _{ cp, V } \times \text{V}_{b} \)

 

Concrete breakout for both Tension and Shear are evaluated in the equations above and the calculations are based on the geometric position between Anchor Bolts and edge of Concrete , see Figure B below.

concrete breakout

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

For more detailed Concrete breakout, click here.

3. Concrete Pullout, Npn.

 

\( \text{N}_{ \text{pm} } = \psi _{ \text{c}} \times _{p}\text{N}_{p} \)

Concrete Pullout are evaluated in the equations above and the calculations are based bond strength between anchor rod and concrete, see Figure C below.

 

concrete pullout

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

For more detailed Concrete pullout, click here.

4. Concrete Side-face blowout, Nsb or Nsbg.

\( \text{N}_{ \text{sb} } = 160 \times \text{C}_{al} \times \sqrt{ \text{A}_{brg} } \times \lambda \times \sqrt{ \text{f’}_{c} } \)
 

or
 

\( \text{N}_{ \text{sbg} } = \left( 1 + \frac{ s }{ 6 \times \text{C}_{a1} } \right) \)

Concrete Side-face 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 D below.

concrete sideface

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

For more detailed Side-face blowout, click here.
5. Concrete pryout strength of anchor, Vcp.

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

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 pryout

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

For more detailed pryout strength, click here.

III. Weld Check.

The design of weld checks the limit states of Elastic and Plastic Analysis per AISC Manual and AASHSTO LFRD.

welding sections

Elastic analysis. The stress vectors in three directions are calculated using a conventional approach and then summed geometrically. Elastic analysis can be used for fillet and Partial Joint Penetration (PJP) welds.

 

fillet

Figure . Fillet Welds

 

 

PJP

Figure . Partial Joint Penetration

For a force applied as illustrated in AISC Figure 8-4, the eccentric force, PU is resolved into a force  acting through the center of gravity (CG) of the weld group and a moment, PUe, where e is the eccentricity. Each weld element is then assumed to resist an equal share of the direct shear. PU  and a share of the eccentric moment PU proportional to its distance from the CG. The resultant vectorial sum of these forces rU is the required strength for the weld.

welding eccentritic

The shear per linear inch of weld due to the concentric force, rP. is determined as

\( rP = \frac{PU}{l} \)

where:

l = is the total length of the weld in the weld group. To determine the resultant shear per linear inch of weld, rP must be resolved into horizontal component rPX = rPsinq and vertical componenet rPY = rPcosq The shear per linear inch of weld due to the moment PUe  is rm = PUec/IP

where

c = radial distance from CG to point in weld group most remote from CG. in.

IP = polar moment of inertia of the weld group, in4 per in2 (IP = Ix + Iy)

Horizontal and vertical components of rm are: rmx = PUecy/IP and rmy = PUecx/IP where cx and cy are the horizontal and vertical components of the radial distance c.

The resultant force ru = Ö(rpx+rmx)² + (rpy+rmy)²  should be compared against the available strength found in AISC Specifications Table J2.5.

 

For more detailed Elastic weld strength, click here.

IV. Shear Check.

 

 

Albert Pamonag Structural Engineer, Product Development

Albert Pamonag
Structural Engineer, Product Development

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