Lumber grading rules, West coast

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Author Message Karen L. Zaterman, CDT Senior Member Username: kittiz Post Number: 20 Registered: 10-2005 Posted on Friday, March 02, 2007 - 08:09 pm:    I'm wondering... if any of you have preferences for using WWPA vs. WCLB Grading Rules and why? Mark Gilligan SE, CSI Senior Member Username: markgilligan Post Number: 135 Registered: 05-2005 Posted on Saturday, March 03, 2007 - 12:17 am:    You do not say whether the lumber is structural or whether you are dealing with non-structural lumber such as boards or siding. My response is in the context of structural lumber. Some species are graded by only one of these agencines. In a few instances you get slightly different allowables when the lumber is graded by one agency as opposed to the other. In fact if you are using Douglas Fir Larch (North) then you will need to specify NLGA. Your Engineer should make the call based on the design values he assumed in sizing members and the Design values in the NDS. Comparing WWPA 1998 with WCLB 1996 it appears that the board grades are totally different. In this case you will probably need to get a copy of the grading rules to figure out what is acceptable. Karen L. Zaterman, CDT Senior Member Username: kittiz Post Number: 21 Registered: 10-2005 Posted on Saturday, March 03, 2007 - 06:40 am:    Thanks, Mark, this helps. I always appreciate your responses. I do have the rules, but that doesn't mean I understand them (and my WWPA is older than yours)! I work in a Civil/Structural Engineering firm so it WILL be going to the SE to verify. This is a Civil/Coastal project and the wood elements are site related: signage, bollards. What actually prompted the question was the formwork section. The Civil PM wanted to use language from "a previous project" [yes... we've been THERE before... I'm working on them]& checking against BSD it looked suspect so I went to the refs. BTW, the WCLB 2000 includes Doug Fir Larch & states it "has similar strength properies and can be manufactured... with identical design values" Mark Gilligan SE, CSI Senior Member Username: markgilligan Post Number: 136 Registered: 05-2005 Posted on Saturday, March 03, 2007 - 04:00 pm:    I believe that it is poor practice to specify the formwork grades or even the grading agency for formwork materials. The responsibility for the structural design of forms and hence the type and quality of formwork materials should be placed on the Contractor. You then do not need to say anything more about the material. If you want a particular finish that requires wood be used you should then focus on the visual characteristics of the material. It might be interesting to look at ACI 301 to see how they address this issue. I believe that they take a similar position. Regretably the norm is that engineers are not familiar with specification writing practices and have not even opened the PRM. They thus copy what they have seen before without thinking. The only solution is 1) education and 2) involving them in the process of writing the technical specification sections. John Bunzick, CCS, CCCA Senior Member Username: bunzick Post Number: 664 Registered: 03-2002 Posted on Monday, March 05, 2007 - 09:02 am:    My understanding is that dimension lumber which meets the requirements of DOC PS 20 is graded under uniform requirements by all of the grading agencies. Of course, different species have different design values. I allow lumber graded by any of the agencies that may be grading materials available in the market of the project's location--this is sometimes all of them. Generally, I prefer to specify dimension lumber by design value so the contractor can obtain the best choice available in the market. However, I agree that formwork grades should be determined by the contractor as part of their design responsibility. Mark Gilligan SE, CSI Senior Member Username: markgilligan Post Number: 139 Registered: 05-2005 Posted on Wednesday, March 07, 2007 - 02:00 am:    Structural design of wood is almost always performed on the basis of a particular species. Because the design values differ so much between species you would be less efficient in use of the material if we designed for the lowest common denominator. Since lumber is sold by grade and because the lumber yards and contractors are not knowedgable about allowables I do not believe it is feasible to specify the design values. Regarding the contractors "design responsibility" for wood construction, in over 30 years of practice in California I am not aware of the contractor being given any design responsibility for wood construction with the exception of purchasing trusses designed by a specialty fabricator. It may have happened but it definately is not common practice. The bottom line is they do not have the expertise. Another difficulty with trying to specify lumber without defining the species is the reality that connection values are dependent on the specific gravity of the wood. Thus if you were to substitue Southern Pine-Fir for Douglas Fir you would have to re-check all the connections that use fasteners. John Bunzick, CCS, CCCA Senior Member Username: bunzick Post Number: 667 Registered: 03-2002 Posted on Wednesday, March 07, 2007 - 09:14 am:    For the projects I have worked on where design values for lumber were specified, the values chosen were not the lowest common denominator, but were based on generally available species and grades. The specified values were determined by the structural engineer. In one case, the contractor proposed a substitution (accepted) of floor framing by decreasing spacing from 16 to 12 inches o.c. Fastening was not affected, as the type and frequency was strictly by the tables in the code, in an low-seismic risk zone. Hem-fir, SPF, Doug. fir and other species designations are variously available, and the market fluctuates.