huangyhg

doubling smaller i-beams in a bearing wall removal project
i am replacing a bearing wall and have calculated that i need either a w8x14 or w6x20 i-beam but i am losing precious inches of headroom. is possible to double 4x9.50s i-beams side by side and get the same support?
minheadroom,
i'm not a structural engineer but what calcs did you use to arrive at a w6 x 20 or a w8 x 14. i can only find a w8 x 13 or w8 x 15. the properties of these sections are close but (2) s4 x 9.5 figures for moment of inertia and section modulus are are fraction of the other two.
no - an s4x9.5 only has a moment of inertia, ix = 6.76in^4.
a w8x15 (there is no 14) has a moment of inertia, ix = 48 in^4
a w6x20 has a moment of inertia, ix = 41.5 in^4.
so two s4's do not come close.
for general stiffness, your beam should be at least (span in feet)/2 in inches of depth (a 12' span should require a 6" beam)
you would be better served to try to raise the beam up within the floor/roof structure to avoid head clearance problems.
minheadroom,
i suspect this is in a basement as it has been done many times before. for many reasons, it is desirable to have a nice open basement whether it be for a games room or whatever.
what is the beam span and how many posts could you tolerate as intermediate supports. in your enthusiasm, don't overlook how you will get the beam into the desired location.
assuming the dbl, 4x9.5 beams there are a couple of other "potential" solutions.
bury a deeper beam within the floor, or wall above. it's more work, but work eventually ends, and you will forget all about it after a while enjoying the room with all that open space.
also, how are your connections? did you design it as a moment frame? this might increase the carring capacity of the beam enough. don't neglect the design of the connection, & columns.
thanks to haggis,jae and sro. though your news was disappointing, all your tips were great. i was a step away from a serious mistake. back to the drawing board. thanks again, minheadroom
i don't know what you are basing your decision on, deflection or stress, but (2)-hss 4.5x4.5x1/2's would give more section than either the w8x15 or the w6x20 but not as much inertia (be aware the steel strength difference between hss and w shapes). i think it is hard to say what is best without knowing more about your situation.

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