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Wood Moment Frames

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You appear to have envisioned  two limitations in the prospective wood beam
to steel column connection that would prevent the desired rigidity from
coming true. I wouldn't do it that way either.

>I HAVE A CLIENT WHO WANTS TO USE A WOOD BEAM IN CONJUNCTION WITH STEEL COLUMNS
>TO CREATE A MOMENT FRAME. THIS IS RESIDENTIAL CONSTRUCTION IS SEISMIC ZONE 2.
>
>I AM VERY HESITANT DUE TO:
>1. THE ENORMOUS AMOUNT OF BOLTS REQUIRED AT EACH END
>2. THE IMPRACTICALITY OF EXPECTING RESIDENTIAL CARPENTERS TO GET THE BOLT
>HOLES EXACTLY RIGHT (SINCE THE BOLT HOLE WILL NEED TO BE SNUG WITH THE BOLTS
>IN ORDER TO MAINTAIN A RIGID CONNECTION)
>3. THE POSSIBLE FUTURE ELONGATION OF THE BOLT HOLES DUE TO CONTINUES MOTION
>OVER THE YEARS. 
>

I gather from your description that an array of bolts acting in shear in the
wood and in the steel is the prospective detail. For the reasons you give,
it won't work. And of course you can't tighten the bolts so as to obtain an
enduring frictional grip on the face(s) of the wood beam.

I have designed a connection between the tops of two steel tube columns and
a glue lam beam that spanned across them so as to develop rigid frame action
sufficient for two stories of remodeled woodframe residence above the beams
in zone 4 San Francisco. A series of these beams are about 8 feet apart and
span 20 ft. The seismic burden is from the amount of construction above, in
the same 8ft. wide band. The beams and columns needed to be there anyway to
carry gravity load across the long and newly widened ground floor garage
space; beefing up the column cross section and designing their caps for
moment transfer (and bases for shear) is the enhancement that gained the
moment frame effect. 

The basic principle is like that used with connecting a wooden rake handle
to the business end of the rake, or connecting a wooden fencepost to the
ground: confining the entire flexural depth of the wood member sandwich-like
between opposing faces of the member it connects to, and doing so over a
substantial length of the wood member. Staggered cross-grain bearing on the
wood member's oposite  surfaces, and acting along enough length, gives the
moment couple. Another reason for a liberal length of connection is that the
wood is subject to cross-grain shrinkage after being crunched in restrained
cross-grain expansion, and any residual looseness gives less rotational play
in a longer connection.

In the project mentioned, the tube columns were given long, thick,
flat-topped caps rigidly knee-braced with steel gussets to the column's
sides. The beam rested on the cap top surface. Two widely spaced vertical
threaded rods with nuts at each end pass through the beam to hold it down to
each column cap plate. Large, thick plates as washers spread out the bearing
on the top of the beam, and all parts were alined into parallel bearing and
the rods pulled up tight. 

Calculations were done cautiously and with lots of "what if" inquiry, and
the city plan review commendably gave it due skepticism. The iron work was
shop built, but field assembly was by the framers, as envisioned, since all
the other work at the time was carpentry.

The location in question doesn't have a hot, dry season, and the nuts have
remained acessible to take-up for any beam shrinkage to ambient conditions.
Really dry, fully shrunk beams such as Parallams would be more attractive
for use in dry climates; sealing them against unwanted in-service expansion
would be of interest.    

Perhaps some of these ideas are of use for your application.

Charles O. Greenlaw, SE   Sacramento,  CA