Earthquake Analysis (Intl Building Code) 3

[PT999]

I am using IBC (New York State edition)
To determine Ss, am I correct as follows:

you first look at Figure 1615 (1) (first Map of US)
For Long Island, the contour value is 30 (or 35). Then because it is states listed as %g, it is actually 0.30

I also saw somewhere that you can get seismic values via zip code location. Is this another code??

Second question:
To determine R for building with metal studs walls, plywood sheathing, and veneer brick fascia, (this is not listed). Do you use same R as timber stud walls. Is there a more complete list of R's somewhere else.

Can you use the simplified method to find V for this case (metal stud walls)

 

[papa2ten]

ICBO provides a cd with user friendly software for determining Ss & S1 using 5 digit code. It will also interpolate the soil factor based on site class.

ICBO also puts out a very helpful booklet entitled "QuickStart Guide to the IBC"

Try

http://www.icbo.org

 

[ERV]

PT9999,
First determine what procedure you are going to use, either the general procedure or the site specific procedure. Then determine the fundamental period of your structure. For your area the general procedure would probably be best.

To apply the general procedure, referrence may be made to the maximum considered earthquake spectral response accelations mapped in the IBC and NEHRP recommended provisions (figure 1615, 2000 IBC). Two sets of maps are provided to designate the two parameters Ss and S1. Ss represents the 5-percent damped, maximum considered earthquake spectral response accelaration for a period of 0.2 second for structures founded on rock (site classification B) and is applicable to short period structures. S1 represents the 5-percent damped, maximum considered earthquakespectral response for a period of 1.0 second for structures founded on rock (site classification B). The two parameters may be used to derive the complete maximum considered response spectrum at a specific location as shown in Figure 1615.1.4 (2000 IBC).

The CD you referred to comes with the 2003 IBC.

and may be available here :

http://geohazards.cr.usgs.gov

For metal stud framing see Section 2211 (2000 IBC).

Brick veneer would not be part of the LFRS, therefore it is not considered.

Metal stud shearwalls CANNOT be designed as wood stud framing. Fasteners and the studs themselves have totally different values.

Another source of information is :

http://www.bssconline.org/pubs/downloads.html

 

[AlohaBob]

To the best of my knowledge, the response coefficient for wood panel shearwalls over wood studs or metal studs is the same.

Just be sure the lateral system is a shearwall system, then the gravity system, whether it's a bearing wall system or not has a minor effect.

The IBC gives some reference flags in table 1617.6 which are helpful to classify varieties of sheathings and their response effects.

 

[JAE]

We do not usually look up the accelleration values in the code but determine them with latitude and longitude off the USGS website here:

http://eqint.cr.usgs.gov/eq/html/lookup.shtml

You can get lat and long from Tiger map:

http://tiger.census.gov/cgi-bin/mapbrowse-tbl

The USGS provides you with a table and you want to use the two values for 1.0 second and 0.2 second for the 2% probabililty in 50 years to match the values from the code.

 

[mjohan]

Any recommendations for which T to use (Ta or T) when applying equation 16-36 (IBC 2000)? The IBC suggests, by my interpretation, to use Ta X Cu to determine T.

Also, for residential buildings with sloped roofs, what do you typically use for the building height... ridge, median roof height, top plate of top floor?

 

[JAE]

mjohan:
We use Ta when calculating it. - If you have a program that directly calculates mode shapes and periods then you can get a T (which is a true T) but the code restricts you to limit your calculated T to Ta x C.

So option 1 is to just calculate Ta and use it.

Option 2 is to calculate Ta x Cu and also calculate T via your model or other rational analysis... then use the lower value in your calcs.

 

[mjohan]

Thanks JAE,

Any recommendations for a program which can calculate an actual T for buildings composed of either wood framed shear walls or steel stud X braced walls? These factors given in the IBC can create enermous seismic forces.

 

[ERV]

mjohan,

I think this may be what you are looking for:

http://www.bssconline.org/pubs/seismic.html

If doing any seismic, this is a must have.

 

[mjohan]

Thanks for the tip ERV.

I hope the cd will shed some light on appropriate T values to use, the intended height of building when calculating T, discussions regarding the appropriate use of site classes, etc.
I have experienced a geotechnical report which actually said, if using Boca 1996, use a site class S1 to define the soil and if using IBC 2000, use site class D. Another experience I have is a geotechnical recommendation to use site class E based on an investigation of the subsoil consisting of borings 50' deep and a low blow count.
The seismic numbers that the IBC assigns to these particular buildings is huge, and in my opinion, incorrect. We have to design for category D, (a california design), in New Jersey.

 

[ERV]

mjohan,

E.V. Leyendecker created the program on the CD, if, after receiving the CD you need further help let me know. I can supply Leyendecker's e-mail address, very helpful man. As I do a lot of research into seismic activity, he has been an invaluable source of information.

ERV