huangyhg

wide flange beam - effect of fastener hole size in flange
i am designing a wide flange beam joined in the middle with flats on either side of the web and one on the top flange. how large can i (or should i) make the fastener for the top joint plate? there will be 1 hole each side of web and each side of joint. i am working with a w6 x 12lb beam, 1/2" bolts, but might consider 3/4" if the holes don't weaken the top tension loaded flange too much.
how do you propose to connect the tension flange together?
the top flange is probably in compression.
if you are asking about weakening of the flange due to the holes, reference section f13 of the aisc specification. but there is still of course a lot more design to address for this situation.
one fastener into the joint plate sounds light ... wouldn't two smaller ones be better than one large one ?
the simple (and perhaps misleading) answer is that you can make the holes as big as the required edge distance from section j3 and the required clearance to the web allow.
however, as haynewp correctly points out, the only way to make the connection work for sure is to look at all the failure modes and see what will work for your specific situation.
i suppose that if this were the only place this occured on the job and throwing an extra 30 bucks of steel at it makes the piece more than adequate by inspection, i might be inclined to do that. however, that method implies experience in connection design.
ok, better explanation of my problem. i have 2 beams, and i want to join the ends together. the resultant beam will be loaded at one end with 1000 lbs. and supported at 6' from the loaded end and at the other end, 16' from the load. the top beam flange will be in tension. i currently have a 1/2" x 4" x 10" flat plate, with 4 holes 9/16" dia. for 1/2" bolts. the flange bolts straddle the break line and web. on the web, i straddle the break line with 2 plates (one each side), 1/4" x 4" x 4", again with 4 holes for 1/2" bolts. at present, i have nothing on the bottom compression flange. i am wondering if i can use 3/4" bolts and not weaken the upper tension loaded flange which is 4" wide.
thanks
am i correct in saying that you are making a moment connection for a propped cantilever at a post with a backspan of 10 ft and a cantilever of 6 ft?
if this is correct, i would shy away from the bolted connection. why not weld the top plate to the top flanges? even if the bolts provide the required moment strength, the holes might allow more slip and subsequent deflection than you want. i would also connect the bottom flanges, even if by (2) plates (1 on each side of the web) on the top of the bottom flange.
is a full pen weld too expensive for this application?
don't forget that on a cantilever it is the top flange that bracing is more critical for, not the compression flange.
in any event, if the holes are not more than 15% of the flange area, you do not need to take a reduction for them.
loading can change, what if the load moves or additional load is placed between the supports? the compression flange switches to the top and the tension flange is not connected. agree with myerges, full penetration weld to connect is safest.

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