[Part 2] Step by Step Analysis Procedure of Seismic Loads Based on IBC2012/ASCE7-10

[Part 2] Step by Step Analysis Procedure of Seismic Loads Based on IBC2012/ASCE7-10

After the huge response of the first article of [Part 1] Step by Step Analysis Procedure of Seismic Loads Based on IBC2012/ASCE7-10 , here we go with the second part of the article .

In the first part of the article, we have elaborated the following topics:

1-Determination of maximum considered earthquake and design spectral response accelerations.
2-Determination of seismic design category and Importance factor.
3-Determination of the Seismic Base Shear.
3.1-Equivalent Lateral Force Analysis.

Before continuing this article, it may be useful to have a check on the following posts:

… And here we go:

3.2- Vertical Distribution of Seismic Forces

analyss

where,

Fx = Lateral force at level x
Cvx = Vertical distribution factor
V = total design lateral force or shear at the base of the building
Wx and Wi = the portions of W assigned to levels x and i
hx and hi = heights to levels x and i
k = a distribution exponent related to the building period as follows:
k = 1 for buildings with T less than or equal to 0.5 seconds
k = 2 for buildings with T more than or equal to 2.5 seconds
Interpolate between k = 1 and k = 2 for buildings with T between 0.5 and 2.5

3.3-Horizontal Distribution of Forces and Torsion

Horizontally distribute the shear Vxanalyss2

where,
Fi = portion of the seismic base shear, V , introduced at level i

Accidental Torsion, Mta
Mta = Vx * (0.05B)
Total Torsion, MT , MT= Mt + Mta

3.4- Story Drift

The story drift, Δ , is defined as the difference between the deflection of the center of mass at the top and bottom of the story being considered.

analyss3

Where,
Cd = deflection amplification factor, given in Table 12.2-1
δxe = deflection determined by elastic analysis

table 12.2-1

table 12.2-2

table 12.2-3

table 12.2-4

table 12.2-5

4- Seismic Load Effects and Combinations

4.1 Seismic Load Effect

Use E = ρ QE + 0.2 SDS*D for these combinations

comb1

Use E = ρ QE − 0.2SDS*D for these combinations

comb2

The vertical seismic load effect, SDS , is permitted to be taken as zero when SDS is equal to or less than 0.125.

4.2 Load Effect with Over-strength Factor

comb3

4.3 Redundancy

  • The value of ρ is permitted to equal 1.0 for the following:

1. Structures assigned to Seismic Design Category B or C.
2. Drift calculation and P-delta effects.
3. Design of collector elements.
4. Design of members or connections where the seismic load effects including overstrength factor are required for design.
5. Diaphragm loads.

  • For structures assigned to Seismic Design Category D, E, or F, ρ shall equal 1.3 unless one of the following two conditions is met, whereby ρ is permitted to be taken as 1.0:
    a. Each story resisting more than 35 percent of the base shear in the direction of interest shall comply with Table 12.3-3.
    b. Structures that are regular in plan at all levels provided that the seismic force-resisting systems consist of at least two bays of seismic force-resisting perimeter framing on each side of the structure in each orthogonal direction at each story resisting more than 35 percent of the base shear. The number of bays for a shear wall shall be calculated as the length of shear wall divided by the story height or two times the length of shear wall divided by the story height, hsx , for light-frame construction.

 

Design Example:

For a given building site, the risk-targeted maximum considered earthquake spectral response accelerations Ss, at short periods, and S1, at a 1-second period, are given by the acceleration contour maps in Chapter 22 in Figures 22-1 through 22-6. This example illustrates the general procedure for determining the design spectral response acceleration parameters SDS and SD1 from the mapped values of SS and S1. The parameters SDS and SD1 are used to calculate the design response spectrum in Section 11.4.5 and the design base shear in Section 12.8. The easiest and most accurate way to obtain the spectral values is to use the “U.S. Seismic Design Maps” application from the USGS website (http://geohazards.usgs.gov/designmaps/us/application.php). The USGS application allows for values of SS and S1 to be provided based on the address or the longitude and latitude of the site being entered.

A building site in California is located at 38.123° North (Latitude 38.123°) and 121.123° West (Longitude -121.123°). The soil profile is Site Class D.

We will determine the following:

1. Mapped risk-targeted maximum considered earthquake (MCER) spectral response acceleration parameters Ss and S1.
2. Site coefficients Fa and Fv and MCER spectral response acceleration parameters SMS and SM1 adjusted for Site Class effects.
3. Design spectral response acceleration parameters SDS and SD1.

1. Mapped MCER Spectral Response Acceleration Parameters Ss and S1

For the given site at 38.123° North (Latitude 38.123°) and 121.123° West (Longitude -121.123°), the USGS “U.S. Seismic Design Maps” application provides the values of

SS = 0.634g
S1 = 0.272g.

2. Site Coefficients Fa and Fv and MCER Spectral Response Acceleration Parameters SMS and SM1 Adjusted for Site Class Effects ( §11.4.3 )

For the given Site Class D and the values of SS and S1 determined above, the site coefficients are

Fa = 1.293                                                                                    T11.4-1
Fv = 1.856.                                                                                   T11.4-2

The MCER spectral response acceleration parameters adjusted for Site Class effects are

SMS = Fa* SS = 1.292(0.634g) = 0.819g                              Eq 11.4-1
SM1 = Fv* S1 = 1.857(0.272g) = 0.505g                               Eq 11.4-2

3. Design Spectral Response Acceleration Parameters SDS and SD1 ( §11.4.4 )

SDS = (2/3) SMS = (2/3)(0.819g) = 0.546g                        Eq 11.4-3
SD1 = (2/3) SM1 = (2/3)(0.505g) = 0.337g                         Eq 11.4-4

The USGS application “U.S. Seismic Design Maps” requires the risk category to be specified, even though that category is not necessary for determining SDS and SD1.

Check also [part 1] – Step by Step Analysis Procedure of Seismic Loads Based on IBC2012/ASCE7-10

Post Author: Zahi Baroudi

32 thoughts on “[Part 2] Step by Step Analysis Procedure of Seismic Loads Based on IBC2012/ASCE7-10

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  • Anthony Ede

    (September 15, 2016 - 11:26 AM)

    Very good work. keep it up. Please can I get the the PDF of the 2 parts. Thanks.

  • Satish yumnam

    (September 11, 2016 - 2:06 PM)

    Could I get pdf for both parts please and thank you.

  • Satish yumnam

    (September 11, 2016 - 2:05 PM)

    Could I get pdf for both parts pleas and thank you.

  • Mukhallad Murad

    (September 11, 2016 - 1:19 AM)

    Great Information. Can I get the two part as pdf.
    eng.mukhallad.civilian@gmail.com

  • mohamed mubarak

    (September 9, 2016 - 4:23 AM)

    great article. indeed it will help me on a current project that i am attached to. can you pls send me the pdf file? wish to thank you in advance

    • Zahi Baroudi

      (September 9, 2016 - 8:49 AM)

      Hello Mohamaed,
      Send me your email please.

  • Lu

    (September 8, 2016 - 2:57 PM)

    This is really helpful. Could you send me the PDF of both two parts please? lsun85@gmail.com

  • JonCivil2009

    (September 7, 2016 - 11:25 PM)

    Thank you so much. My email address is jon.jenkins02@gmail.com. Greatly appreciate the information.

  • Javier Sánchez

    (September 7, 2016 - 8:48 PM)

    Great! Thanks for posting these articles. May I get a copy of these articles in PDF please? My email: Javiersanchez.11.04@gmail.com

  • Matt Groves

    (September 7, 2016 - 4:49 PM)

    Wonderful information and reference guide from a young Engineer In Training. I would also like to have these (part 1 and 2) in pdf format if you wouldn’t mind sending them to me. Thanks for the great analysis procedures. My email follows:

    matthew.groves553@topper.wku.edu

    • Zahi Baroudi

      (September 7, 2016 - 5:01 PM)

      Glad to hear that you found these articles useful. I’ll send you both parts in PDF format.

  • JonCivil2009

    (September 7, 2016 - 8:57 AM)

    May I get a copy of Part 1 and 2 in PDF form please?

  • Mehrdad Pairawan

    (September 6, 2016 - 7:10 PM)

    Very useful and well presented article. How can I get pdf of Part 1 and Part2? How long will this article and other related ones stay online? Thans!

    • Zahi Baroudi

      (September 6, 2016 - 9:24 PM)

      Hello Mehrdad,
      Thank you for your good feedback. You may leave your email to get the both parts as PDF and those articles will not be removed.

  • Sharath

    (September 5, 2016 - 11:18 PM)

    This is brilliant.can I have the etabs model for the same

  • Ghossun

    (September 5, 2016 - 5:20 PM)

    Could I get pdf for both parts pleas and thank you

  • Kishor Kabnurkar

    (September 4, 2016 - 4:59 PM)

    I would like to know how to input parameters in StaadPro and ETABS. I would appreciate if somebody will provide *.std file or *.EDB file as an example.

    • Zahi Baroudi

      (September 4, 2016 - 9:20 PM)

      Hello Kishor,
      You may stay tuned to the blog as we are going to start a series to master ETABS.
      And in case you want a sample model, you may give us your email and we’ll send you one.

      • david

        (September 5, 2016 - 3:31 PM)

        this is really helpful. i would like to have that sample model,if its alright

  • MSA Mihraj

    (September 3, 2016 - 3:52 AM)

    Excellent

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