# Structural: Seismic Design (Equivalent Lateral Force) Spreadsheet (v1.0)

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### What does the Equivalent Lateral Force Spreadsheet Solve?

This spreadsheet will find your seismic coefficient for structural building (Chapter 12) and non-building (Chapter 15) systems. It only finds your base shear forces, you will still need to plug any seismic shear forces into either your ASD? or LRFD? load combinations to solve for the variety of structural solutions.

This spreadsheet solves for:

• Your Seismic Response Coefficient
• Your Seismic Base Shear Force
 How to Understand this Spreadsheet

### How to use this Spreadsheet:

This spreadsheet works in Microsoft Excel 2003 and later. This spreadsheet will solve for your Seismic Response Coefficient and your Seismic Base Shear.

The portions of the spreadsheet highlighted in yellow are the variables. The portions highlighted in blue are your results:

#### Equations

The top portion of the spreadsheet shows you all of the Seismic Response Coefficient equations. There are multiple equations that determine: the calculated seismic response coefficient, the minimum allowable seismic response coeff, and the maximum allowable seismic response coeff. Fig. 1: Spreadsheet Equations

where:

CS = The Seismic Response Coefficient
SDS = The short period design spectral response acceleration parameter
SD1 = The 1 second design spectral response acceleration parameter
T = The fundamental period of the structure
R = The Response Modification Factor of the structure (this factor is based off of the structural system being used; higher R values react better to earthquakes then lower R values)
I = The Importance Factor of the Structure
TL = The Long-period transition period parameter
S1 = The M.C.E (Maximum Considered Earthquake or Maximum Credible Event) spectral acceleration parameter

#### Site Specific Variables

The next portion of the excel sheet covers all of the site specific variables. These are variables are determined by the location of the building. Fig. 2: Site Specific Equations/Variables

where:

Site Class = Aka Seismic Design Catagory. The Seismic Design Catagory is based off of the occupancy or use of the structure, and the expected soil seismic ground motion. If this variable is unknown it is usually appropriate to use class "D" in seismic zones.
SS = The parameter for the 0.2 second spectral response acceleration
S1 = The MCE (Maximum Considered Earthquake or Maximum Credible Event) spectral acceleration parameter
SMS = The MCE, 5 percent damped, spectral response acceleration at short periods adjusted for site class effects
SM1 = The MCE, 5 percent damped, spectral response acceleration at 1 second adjusted for site class effects
SDS = The design, 5 percent damped, spectral response acceleration at short periods adjusted for site class effects
SD1 = The design, 5 percent damped, spectral response acceleration at 1 second adjusted for site class effects

#### Structure Specific Variables

The next portion of the excel sheet covers all of the structure specific variables. These are variables are determined by the structural system used in the building, the occupancy, and importance. Fig. 3: Structure Specific Equations/Variables

where:

Ct & x = Building period coefficients
hn = the height of the building from the base to level n respectively (conservatively you can use the height of the building)

#### Results

The final section sums everything up. Fig. 4: Spreadsheet Results/Summary

where:

CS How many G's your structure is pulling. So if your answer was 0.3 you could expect an earthquake would produce 0.3*G or 0.3 times the dead load of the structure.
V = The shear force at the base of your structure.

Note: Don't forget that you still need to plug these values into your load combinations to properly analyze the structure.

### Notes:

The following notes must be considered when using this spreadsheet:

1. Designed using the ASCE 7-05 edition.
• See Chapter 12 for Buildings and Chapter 15 for Non-Building structures.
2. If checking Non-Building Structures not similar to buildings (Table 15.4-2), CS-Min will change to not be less that 0.03 or \left(\frac{0.8S_1}{\frac{R}{I}}\right) .

## Addendum

• V1.0: This is the original version of the Equivalent Lateral Force Spreadsheet
Retrieved from http://www.wikiengineer.com/Structural/SeismicBuildingDesignSpreadsheet
Page last modified on February 01, 2012