huangyhg

what is the section modulus of 3/8" a36 steel plate
i'm running an analysis of a 11.25" tall (deep) flitch plate - ilevel truss joist beam utilizing a "blt sandwich" of a 1.75" 1.9e lvl microllam, a 3/8" astm a36 steel plate, a 3.5" 1.55e lsl timberstrand, another 3/8" plate, and finally, another 1.75" 1.9e lvl (all being 11.25" and bolted together with 3/4" a325 bolts staggered at 16" o.c. but with 4 stacked bolts at each end). total uniform load is about 15k including 15% for seismic; i.e., max end reaction is about 7.5k and i'm using l/480 (shooting for less than .3" maximum deflection).
will my blt flitch beam work or what is the section modulus of a 3/8" x 11-1/4" astm a36 steel plate?
i must be misunderstanding your question. it sounds like you're saying you can't calculate the section modulus of a rectangle, and surely that is not the case.
hg
the section modulus (elastic) is 7.91 in^3.
most steel plate comes in 1-inch increments, ie 11" wide x 20' long pieces, so i would recommend working with what is readily available to save the contractor. might be better off using a 10" steel beam with packed out webs. have you figured the self weight of this monster?

i should clarify that is per plate.
also, because everything is the exact same depth, the only reason you are bolting them together is for your own peace of mind.
because the load is bearing on all parts of the "beam" and the load is going into the supports through all parts of the "beam" there is no need to transfer load into or out of the wood via the bolts, it will all deflect together naturally and therefore naturally behave the way you would try to get a typical flitch plate beam to behave (by deflecting together, thereby sharing load based on relative stiffnesses). you have it pretty easy, though, as mentioned above. just bolt at some nominal spacing and maybe two bolts at the ends, i wouldn't use four stacked. that is giving a small spacing and cutting into the shear capacity of the wood (which may or may not be a concern, but there is no reason to use four bolts at the end).
thanks for all your input. let me clarify. i did spec a w10x26 w/nailers both sides thru-bolted to pick up joist hangers but the contractor did not want to handle the 416# of the w10x25, so i broke it down as follows:
15'- 3" span, total load is -15k (uniform max ld = 980 plf)
max end vert reaction = -7,500 using l/480 & 40ll + 20dl
max beam depth permitted by existing 12" floor joists is 11.25" +/-
flitch bm solution:
(3)1.75" 1.9 eom microllam lvls + (2) 5/16" a36 plates* bolted at 16" oc w/.625" a307 bolts/nuts/washers; glueing adds 15 psf. total flitch bm wt less bolts is 656# versus w10x26 w/df wood nailers = 575 or diff of 81#
end bearing @ 4.5" using 3.5" x 5.5" x 8' 1.8 eom parallam psl
*may get away with 1/4" plate???

thanks for all your input. let me clarify. i did spec a w10x26 w/nailers both sides thru-bolted to pick up joist hangers but the contractor did not want to handle the 416# of the w10x26, so i broke it down for easier handling, as follows:
15'- 3" span, total load is -15k (uniform max ld = 980 plf)
max end vert reaction = -7,500 using l/480 & 40ll + 20dl
max beam depth permitted by existing 12" floor joists is 11.25" +/-
flitch bm solution:
(3) 1.75" 1.9 eom microllam lvls + (2) 5/16" a36 plates* bolted at 16" oc w/.625" a307 bolts/nuts/washers; glueing adds 15 psf. total flitch bm wt less bolts is 656# versus w10x26 w/df wood nailers = 575 or diff of 81#
end bearing @ 4.5" using 3.5" x 5.5" x 8' 1.8 eom parallam psl
*may get away with 1/4" plate???

you didn't respond to hg's question, and it isn't clear what you want to know. no one here can design it for you and say if you can use something smaller or not.
try reading this article:
the strength of a plate on edge like that will be based on buckling, not just bending stress. refer to the aisc-05.
"flat bar" is available in widths of 10", 12", etc., but not normally 11". "plate" implies a wider width cut to that dimension.

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