Now that the New York State Code has adopted their own modified version of the 2000 IBC code, non-residential structures must be designed per the seismic portion of the code. The table for selecting the Response Modification Factor (R) only has two options for wood construction and both are light wood framing with shear panels. What have other engineers used as the (R) value and on what basis?

Thank You

I have used the value for shear walls since that is the lateral resisting system I use (Structural Insulated Panels). Are you using the frames to resist the load? If so, that is a whole different ballgame not only for the response factor, but just getting the wood to work in that situation is a real challenge.

T. Ryan

Just a follow-up question.

Is it considered acceptable to assume that a timber framed/SSP wall will act in a shear wall capacity for lateral loads, wind and/or seismic? I've read through some of the work Dick Schmidt has performed and it's clear that the SSPs stiffen a timber framed wall laterally, but I've seen no correlation regarding the response of the timber framed/SSP wall as compared to a conventional shear wall.

Thank You for your responses. The project is a tall open building with frames at 4'-6" o.c. The intent is to design each frame to take out it's own share of the horizontal forces. Being a light single story building with a lot of wind area, I expect that the wind loads will govern.
Regarding SIPS, I have been unable to get any shear values from the manufacturers that apply to spiking or screwing through an entire panel to a timber frame. All of the testing I have seen is based on both skins being nailed to a 2x plate recessed into the bottom of the panel which would require access to both sides of the panel. This is rarely the case when applying panels to a timber frame.
The plot thickens. Chris

From what I can see, the IBC 2000 makes timber framing for other than residential structures very difficult, perhaps impossible if you have no shear walls. 1609.1.5 and 1614.5 requires that the lateral force resisting system shall meet the seismic detailing requirements of the code even when the wind effects are greater than the seismic effects. There are lots of new, complex seismic requirements even in areas that other codes say are not seismically active enough to worry about.

Following is a reply from the New York State Department of State regarding Seismic Parameters for Timber Frame Construction:

Dear Mr. Hoppe:
This is in response to your recent e-mail with questions regarding
timber frame construction.

Q1: What values should be used for braced timber-frame construction?

The Code Sec. 1617.6 states " 1617.6 Seismic-force-resisting systems.
..... For seismic-force-resisting systems not listed in Table 1617.6,
analytical and test data shall be submitted that establish the dynamic
characteristics and demonstrate the lateral-force resistance and energy
dissipation capacity to be equivalent to the structural systems listed
in Table 1617.6 for equivalent response modification coefficient, R,
system overstrength coefficient, W0, and deflection amplification
factor, Cd, values.EXCEPTION: Structures assigned to Seismic Design
Category A."
As stated above the analytical and test data shall be submitted for the
contemplated structural system.

Q2: What values should be used for a structural system using steel and
timber in the same frame?

This question may be interpreted in a number of ways:

1) The structural frame is composed of two materials, steel and timber,
in which case the answer to the previous question would apply -
analytical and test data shall be submitted.

2) The proposed arrangement meets the code definition of dual system
which would be a combination of moment-resisting steel frame and braced
timber frame. The code section quoted below would apply.
"1617.6.1 Dual systems. For a dual system, the moment frame shall be
capable of resisting at least 25 percent of the design forces. The
total seismic force resistance is to be provided by the combination of
the moment frame and the shear walls or braced frames in proportion to
their stiffness."
The design parameters for timber frame would need to be established
based on submitted analytical and test data. The parameters for steel
frame would be from Table 1617.6.

3) Steel frame (other than moment-resisting) and timber frame are used
in combination along the same axis or in two orthogonal directions. The
Code sections "1617.6.2 Combination along the same axis." and
"1617.6.3 Combinations of framing systems." would apply.
Again, design parameters for timber frame would need to be established
based on submitted analytical and test data. The parameters for steel
frame would be from Table 1617.6.

If you have any questions regarding the above please do not hesitate to
contact me at (518) 474-4073.

Sincerely,
Lucjan J. Mitas, P.E.
Sr Bldg Structural Engineer
Division of Code Enforcenment and Administration

Does anyone know of any testing that has been done to establish these parameters?
Thank You,
Chris Hoppe, P.E.

Oooch.

I'm not an expert in this area, but do have a general understanding and interest. As I mentioned above, Dick Schmidt has performed some recent timber frame lateral load response studies. His studies are all static/stiffness related and should translate to dynamic response. I think the rub is the method Dick uses to model the simple structures that he has tested. I believe Dick has shown that analytically predicting frame response is sensitive to joint/peg stiffness representation. I suspect that using Dick's modeling techniques would be difficult and expensive for larger more complicated frames. Dick, are you out there? I also believe there are some papers available through the Timber Frame Business Council regarding timber frame lateral load design.

Providing the information that the above NY building official is requesting might rule out having 'full' code compliant timber frames. I have seen 200-year-old frames that are extremely lightly braced that have withstood the test of time. Many times we have extreme difficulty showing a more heavily braced frame adequate for lateral loads using modern engineering to the latest codes. The above discussion tells me for certain buildings; it may potentially be impossible.

Thank You MTF,
I forgot to mention that the NYS code is essentially the IBC 2000 Code. I recall Ben Brungraber at a TFG conference recalling his experience designing/building a commercial frame in California to meet the seismic code, so it has been done. At the time he said it was his first and last frame designed to meet the California UBC seismic code. (They were required to put screws in to keep the pegs from falling out during a "seismic event").

Chris

Extrapolation of static test results to seismic design has to be performed carefully. The principal response quantities for static loads (for structures, wind load is regarded as static) are strength (measured by total applied load) and stiffness (measured as the ratio between applied load and deflection). Under seismic load, energy dissipation is the key response parameter. At this point, I don't believe that anyone has any energy dissipation data for western style timber frames. Some research has been performed on Chinese and Japanese frame types.

I'm reluctant to predict or recommend an R value for traditional timber frames. It is certainly easier to direct all of the seismic load into shear walls or SIPs, when those load paths are available. Behavior of a stand-alone frame during a seismic event is yet another question.

For SIPs attached to a timber frame, I'm comfortable using load-slip data from our research at UW and designing as if a single skin of OSB (the inner skin attached to the frame) is active in resisting load.

Thank You Dick,
If one were to use an R of 1 it would be as if you were designing the timber frame to respond to an earthquake wholly in the elastic range. It would assume that the frame has no strength beyond what the NDS and your research assumes is safe. The lowest R value published in the Code is 1 1/2 which is for "ordinary plain masonry shear walls." This has a low R value becuse this system has little strength, ductility and ability to absorb energy beyond what is deemed safe for static loads.
This being the case, would you feel comfortable designing a timber frame using an R value of 1 1/2?