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RE: Lateral Analysis Software for Wood Structures?

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I just thought I would (finally) follow-up on this subject.

Based on the feedback I got on this list as well as some cursory
investigation on my own, it seems that Woodworks is probably the best
choice (for me). News Flash! No software will be 100% perfect and solve
all the problems for all of the users! It does seem that Woodworks comes
closest. Short of that, it seems like the best way to go is the old
fashioned way, use the LARUCP approach and overdesign the shear walls
and hold downs by 20%. FWIW, I really enjoyed QLAT in that it seemed to
do everything I wanted it to do (including being able to build custom
shear wall and hold down tables). Alas, it was written as the Dead Sea
Scrolls in that operating system known as D(ead) O(perating) S(ystem)
and printing was a PITA. Unfortunately, it seems that QLAT is not longer
available. Hopefully, Woodworks picks up where QLAT left off.

It's funny (not really) how this request for opinions branched off into
a debate on how a wood structure should be analyzed laterally. After all
this time, there still is no consensus with an associated economical
(from a design point of view) means of solving this problem. I'm also
amazed that more software vendors (i.e., Enercalc and RISA) have not
jumped on this bandwagon.

There's still a misconception that this rigid-flexible diaphragm issue
is a product of the 1997 UBC. This is just flat out not true. There's
been language in the UBC code for along time that the relative rigidity
must be considered and, in 1988 a clear definition was provided in that
if the diaphragm deflection was more than twice the shear wall
deflection, the diaphragm was flexible. Otherwise it was rigid. Of
course, the problem with this solution is that the deflection of wood
elements (diaphragms and shear walls) are more difficult to determine
(blocked or unblocked, etc). So, the "standard practice" was to consider
wood structures flexible up until February 1998 when a seminar sponsored
by SEAOSC purportedly on the seismic provisions of the 1997 UBC.

In addition to discussing the new provisions of the 1997 UBC, the
presenter also spent considerable time (more than half the seminar?) on
how his office designs wood structures by considering the stiffness of
the diaphragms and shear walls. Once this presentation was made public,
Pandora's Box was now open and the "standard practice" could no longer
be a reasonable defense for ignoring the stiffness of wood diaphragms
and shear walls. Since the stiffness of wood elements are not precisely
known nor would we want to under design a line of shear resistance with
small shear walls, the "safe" approach is to do two analyses and
envelope the solution.

Don't get me wrong. I do believe that there are situations where the
stiffness should be considered (interior corridor walls in apartment
bldgs / hotels, etc.), but I think it's a waste of engineering time and
energy to categorically require the designer to envelope the analysis.
For example, I think it would be a far greater benefit to spend that
analysis time ensuring that there is a complete load path from roof to
foundation and then, during construction, to actually observe these
elements installed (what a concept). However, there's too much risk
(business risk that is, assuming a fee to do the design the "old
fashioned way" when the building official is going to require an
envelope solution) not to confer with the building official when
considering a new project.



Bill Allen, S.E. (CA #2607)

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