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Anchor Bolt Design Seismic Provisions - ACI 318-19





Step 1: Check Seismic design category SDC >= C         Back to Top

Seismic Design Category SDC
ACI 318-19  17.10.1

Anchors in structures assigned to Seismic Design Category (SDC) C, D, E, or F shall satisfy the additional requirements of this section.


ACI 318-19 17.10.1

 

How to find out your structure's  Seismic Design Category SDC


1) Refer to ASCE 7-16 page 2 Table 1.3-1 to find out the Risk Category of your structure based on your structure's type and usage.

2) Refer to ASCE 7-16 page 84 Section 11.4.5 to find out the design spectral response acceleration parameters SDS and SD1 based on your structure's location

3) Refer to ASCE 7-16 page 85 Section 11.6 Table 11.6-1 and 11.6-2 to find out the SDC for your structure.


 ASCE 7-16 page 85 Section 11.6

 



Step 2: When SDC >= C, Check If Anchor Bolt Load E <= 0.2U - Tensile         Back to Top

ACI 318-19  17.10.5.1

This input is required when seismic SDC>=C. User can ignore this input when seismic SDC=A or B

Select Yes when E <= 0.2U
Select No   when E > 0.2U

E - Seismic component in the total factored tensile load Nu user input above
U - Total factored tensile load Nu user input above

Below are load combinations from ACI 318-19  5.3.1 by which user uses to get the total factored tensile load Nu for anchor bolt design.

 ACI 318-19   5.3.1 ACI 318-19  17.10.5.1

 


Step 3: When E > 0.2U , Select Anchor Bolt Seismic Design Option - Tensile         Back to Top

Tensile - Options to Satisfy Additional Seismic Requirements
ACI 318-19  17.10.5.3 (a) ~ (d)

This input is required        when     Seismic SDC >= C (17.10.1)     AND
                                                   Tensile E > 0.2U    (17.10.5.2)


User can ignore this input when     Seismic SDC < C   (17.10.1)      OR  
                                                   Tensile E <= 0.2U (17.10.5.1)


If user selects Option D below, check this help file  for more details on Ωo factor


If user selects Option D above, check this help file  for more details on Ωo factor



Step 4: When SDC >= C, Check If Anchor Bolt Load E <= 0.2U - Shear         Back to Top

Anchor Bolt Shear Load Seismic Component E<=0.2U
ACI 318-19  17.10.6.1

This input is required when seismic SDC>=C
User can ignore this input when seismic SDC=A or B

Select Yes when E <= 0.2U
Select No   when E > 0.2U

E - Seismic component in the total factored shear load Vu user input above
U - Total factored shear load Vu user input above

Below are load combinations from ACI 318-19  5.3.1 by which user uses to get the total factored shear load Vu for anchor bolt design.
 
 ACI 318-19   5.3.1 ACI 318-19  17.10.6.1


 


Step 5: When E > 0.2U , Select Anchor Bolt Seismic Design Option - Shear         Back to Top

Shear - Options to Satisfy Additional Seismic Requirements
ACI 318-19  17.10.6.3 (a) ~ (c)

This input is required          when   Seismic SDC >= C (17.10.1)       AND
                                                   Shear E > 0.2U      (17.10.6.2)


User can ignore this input  when   Seismic SDC < C     (17.10.1)       OR
                                                  Shear E <= 0.2U     (17.10.6.1)


If user selects Option C below, check this help file  for more details on Ωo factor


If user selects Option C above, check this help file  for more details on Ωo factor



Anchor Bolt Seismic Design Provision - Seismic Overstrength Factor Ωo         Back to Top

For anchor bolt design when SDC>=C and E>0.2U, anchor bolt design shall satisfy
For tension , one of the 4 options in ACI 318-19 17.10.5.3 (a)~(d)  or
For shear ,   one of the 3 options in ACI 318-19 17.10.6.3 (a)~(c)

For steel structure, the practical options engineers normally choose are

For tension , ACI 318-19 17.10.5.3 (a)~(d) , use option (a) or (d) , select option (a) by adopting anchor chair and
using anchor tensile load with Ωo=1.0 is the most practical and preferable option

For shear ,   ACI 318-19 17.10.6.3 (a)~(c) , use option  (c)

If for tension 17.10.5.3 (d) is chosen or for shear shear 17.10.6.3 (c) is chosen, user need to increase the seismic
load E by multiplying overstrength factor Ωo

ACI 318-19 17.10.5.3 Option (d) ACI 318-19 17.10.6.3 Option (c)

Refer to section right below on how to get the Ωo values based on the type of your steel frame.


Where Can I Find This Seismic Design Overstrength Factor Ωo for My Anchor Bolt Design         Back to Top

When the steel frame engineer proceeds with the steel frame seismic design, the enginner first needs to figure out
what seismic design parameters shall be used.

Below are some parameters which are related to seismic anchorage design
SDC   Seismic Design Category
R       Response Modification Coefficient
Ω0     Overstrength Factor

It depends on what category user's steel frame can be classified into, user needs to select one from multiple tables in
ASCE 7-16 to get the correct R and Ω0 factor for seismic anchorage design.

ASCE 7-16 Table 12.2-1 for residential/commercial building structures, such as highrise office and condo buildings
ASCE 7-16 Table 15.4-1 for industrial structures - nonbuilding structures similar to buildings, such as mill buildings
ASCE 7-16 Table 15.4-2 for industrial structures - nonbuilding structures not similar to buildings, such as anchorage for tank, vessel, silo etc
ASCE 7-16 Table 13.6-1 for Mechanical and Electrical components


Table 12.2-1 for residential/commercial building structures, such as highrise office and condo buildings

Refer to ASCE 7-16 Table 12.2-1, in summary, the Ωo values for steel frames are



ASCE 7-16 Table 12.2-1




Table 15.4-1 for industrial structures - nonbuilding structures similar to buildings, such as mill buildings

The author is on industrial design background. Most industrial steel structures, such as mill buildings and piperack structures, are in this category.

ASCE 7-16 Table 15.4-1



From above Table 15.4-1
Ωo =2.0 for both OCBF/OMF/IMF highlighted as yellow
Ωo =1.0 for all NL=No Limit height option highlighted as green


Table 15.4-2 for industrial structures - nonbuilding structures not similar to buildings, such as anchorage for tank, vessel, silo etc

The author is on industrial design background. Most industrial equipment supports, such as vessel and tank support, are in this category.

ASCE 7-16 Table 15.4-2





Table 13.6-1 Seismic Coefficients for Mechanical and Electrical Components

This table is for Mechanical or Architectural components attached to building

ASCE 7-16 Table 13.5-1 & 13.6-1







How Can I Incorporate This Seismic Design Overstrength Factor Ωo for My Anchor Bolt Designgn         Back to Top

1. Once you get the overstrength Factor Ωo , you can incorporate this Ωo factor into the seismic component in the load combinations as shown
    below in red.

2. In Civilbay anchorage program load input fields, input the tensile Nu and shear Vu loads getting from load combinations where the E component
    was increased by multiplying overstrength factor Ωo.

ACI 318-19  5.3.1

3. Select Tensile = Option D and Shear = Option C as shown below in Civilbay anchorage design program.