Seismic Design, R Coeff. Question 1

[gjb2]

I'm designing a 15 ft high single story addition in SDC D, SUG-II, with log columns, glulam beams, and log "K-braces" for lateral force resistance. The roof will be 3x6 T&G. In ASCE 7-02, Table 9.5.2.2 I'm trying to determine what R coefficient to use and I don't see any that look applicable. They all seem to apply to steel, concrete, masonry, or wood shear panels. Does anyone have any experience with this?

 

[samdamon]

gib-

You are talking about a timber frame, in essence. Agree that the chart isn't much use for that particular lateral force resisting system. There doesn't seem to be a lot out there about timber FRAME design.

However fyi some research results on timber frame lateral design at the following link:
scholar.lib.vt.edu/theses/available/etd-08142002-232925/

Good resource for timber connection designs is timber framers guild,

http://www.tfguild.org.

They have several useful publications about joint design. (Joint design will probably be critical for your building).

Please post if you find any opinions about what R values are recommended. Good luck.

 

[fndn]

UBC 1997 or CBC 2001, volume 2 has those R values based on your structural building components. Seismic design book by Lindeburg and Baradar-8th edition describe the procedures. You may view this book at

http://www.ppi2pass.com

 

[gjb2]

fndn,

Thanks. It was there in the 1997 UBC, in Table 16N. R=5.6 for Building Frame System - Heavy Timber.

 

[archeng59]

is that R value ok to use if it isn't listed in the IBC? just wondering if we can use R values that are not listed in the IBC, but are valid in other codes?

 

[gjb2]

I don't see why not. There isn't much of anything on log construction in the IBC, so you have to find resources elsewhere. I have used the '97 UBC before when I ran into something that wasn't covered in the IBC. As long as the item isn't prohibited by the IBC, I would prefer to find another reference than try to make an educated guess.

 

[fndn]

gib2;
I should have added chapter 16 on my previous post. I am glad you found it.

 

[archeng59]

thanks, gjb. when the code isn't explicit on something, I use other references or codes for guidance. just wondered what others thought about that.

 

[VTPE]

According to IBC Section 1614.1, exception #3, wood framed buildings constructed in accordance with section 2308, Conventional Light Framed Structures, do not have to be analyzed in accordance with section 1616.1, Structural Design Criteria.

If your building can be considered conventionally light framed, and you abide by the detailing required in chapter 2308, you will not have to perform a seismic analysis.