huangyhg

microlam question - connections & torque issues - historical
hi. i am a civil/env enr by day, but evenings & weekends am renovating 140-yr old house (my home). a structural pe that i hire as my struct sub at work, designed following solution for me to open up one side of stairway.
house is balloon-frame. studs on west side of stairway carry stairways of 1st to 2nd flr and 2nd to 3d flr. also these studs form a second floor wall. these studs bypass just inside of a full(!) 3"x8" 2nd flr joist (13.5 ft. span) and found on 1st flr directly over a similar 1st flr joist. i added jack columns in the basement at third points under the first floor joist to take out some sag.
my struct enrs solution was to add three (3) microlams (1 5/8"x 7 5/16") parallel to the 3x8 and bolt each stud (w/ two 1/2" dia carriage bolts) through the assembly. he instructs to glue each lam together and to the joist. end support will be stud column at one wall end; the other end is to be "t"ed into an existing orthogonal nominal 5"x12" microlam i installed to replace an old 2"x8" beam (13-ft. span) which was deflecting 1 3/4" when i aquired the house. engineer says way over-designed, so it can support the new point load. the "t" is to be supported with 90deg vert angles of 1/4" steel w/ 2" legs. all connections to be 1/2" dia. carriage bolts. my enr says the made-up thick beam (3 microlams) is to resist the torque of being side loaded with the studs which he says are actually rather a light load.
also, i plan on leaving two studs in to the first floor at locs 8'8" and 10'4" from the wall end. these form a wire chase to the 2nd flr. and can provide additional support to the new beam.
i bought the material to do the job, but when my buddy (who used to restore old houses for a profession) came to look at it and help me - he voiced concerns over the carriage bolts pulling through the 3x8 or the torque cracking the drywall wall on the 2nd flr. (i replaced the plaster walls). he also says you are not supposed to drill holes in microlaminate beams. he wants to build fallswork to support the second floor wall, cut the studs off and install 2 of the microlams under the studs. the non-wall end of the beam, as he would have it, would fall on one of the studs to remain. that span would be about 9 ft.)
i am confused. my questions are:
is it true you are not allowed to drill microlams?
are broadly compact beams ok to side load?
can anyone out there give a thumbnail critique or opinion?
thank you very much.
scott (sgwpe1)
(remember i'm a civil and environmental engineer - gimme questions on roads, hydraulics or hazardous waste - but i do need help with structural issues)
scott,
i see nothing wrong with your structural engineer's approach. he is trying to protect not only the eccentric load on the 3x8, but limit further creep deflection as well.
yes, you can drill laminates. preferable to drill perpendicular to glue plane, but can be done otherwise as well, assuming stresses are low and edge distances sufficient.
its redundant to ron's answer but just to second his comments - microlams are bolted many times. used in trusses, etc. as well. you can confirm this by calling your lumber supplier who can put you in touch with the microlam manufacturer.
any beam loaded eccentrically will twist, to differing amounts depending on the size (cross-sectional area) and modulus of the material. wood isn't all that rigid so you should always take care in situations like yours. while the beam may not fail, you would still get, perhaps, too much deformation that would not be acceptable.
if its a great house...do it right.

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