A lot of heavy steel is going into a new single-family home nearby.
Here is a beam size they are using above the garage doors, picking up second floor loading, with some roof loading coming down from above.
W12x136! What a whopper! That’s 13.41″ deep, 12.4″ wide, flanges 1.25″ thick, and a web thickness of 0.79″. Steel tube columns are picking up its end point reaction loads, and my guess is the total span is about 28 feet. A 29-footer of one of these weighs 3,944 pounds.
Anybody got a beam calc program? The license for mine expired, so I’ve got none right now. If you do, tell us what kind of uniform load that one will handle, while giving 1/4″ maximum deflection, which is somewhat greater than l/1440. Use 50 ksi for the steel’s allowable stress.
I just emailed my steel details to the fabricator, and my entire order, all sixteen members, totals only 400 pounds more than that one beam. My largest are W12x22.
Replies
The last time we used a beam that heavy was to span a high school gymnasium with a science lab on the floor above it...
Sounds to me like some engineer used a hefty safety factor...
I'll do the calcs later on and let you know...Don't have the beam calc here at work...
Are you saying the CLEAR SPAN is 28' ???
If so, I doubt it would carry much of anything. I'd say a deeper and lighter beam would be much better.
Agreed.
Kind of an informal "rule-of-thumb" about structural steel for a single span with end supports: Beam depth in inches should be half the span in feet. So for a 28' span, a beam depth of 14" is a minimum.
Another wild guess is that there was not enough room in the design (or a poor design) to allow for a beam deeper than 12", so the engineer compensated for it by spec'ing a much heavier section.
Of course, there's always the chance it was a mistake, plain and simple; or there's just some info we aren't getting that would have it make sense.
Maybe the builder had it laying around from another job, and he finally found a use for it.
Maybe it's like that space explorer. Some European engineer spec'ed in cm and some American called it inches!
Hope they beefed up the house to carry the beam.
My house has 3 W16x100's that span 27' each, end to end. They support the middle of an elevated slab that itself spans 24' from the beam to the side supports.
This one is in an endwall, and the only floor loading it can be picking up is from one side.
Just for the heck of it, I thought I'd run the thing. But the beam progrogram I have doesn't have a 12X136 in it's database. You never did answer my question as to whether this was clear span or not.
I don't remember being absent minded.
>> But the beam program I have doesn't have a 12X136 in it's database.Can you enter data manually? Machinery's Handbook gives the following data for a W12x136:X-X axis, parallel to the flanges
moment of intertia: 1240 in.^4
section modulus: 186 in.^3
radius of gyration: 5.58 in.Y-Y axis, parallel to the web
moment of intertia: 398 in.^4
section modulus: 64.2 in.^3
radius of gyration: 3.16 in.
The program I have doesn't allow for manual entry of design values. I have a book for hanf calcing steel beams, but I haven't seen it since we moved.
When I was little, my Mom used to make me stand in a closet for five minutes without moving. She said it was elevator practice.
Assuming a 28' clear span, it takes approx. 650 PLF to cause a W12x136 to deflect 1/4".
At 50lb PLF, that's supporting a 13' span, or a 26' deep garage. Seems reasonable, but doesn't match Gene's overkill figures of 120plf and d=720.
Mike
The beams spanning my basement (32') are W10x22. If I had gone to a 16" deep by 50-something weight per foot, I could have clearspanned the entire basement. As it is, they deflect under their own weight and the weight of the floor deck by about 5/8" in the center, unsupported. As it is, there will be two posts at 12' from each end to support the timber frame, so the defelction will be minimal.
Six guys put each beam in by hand. Even seven hundred pounds of steel is a load for six guys without benefit of mechanical devices.
Gut feeling is, somebody really fouled that one up. Probably someone fresh out of college who ran the calcs without really thinking about the end result. If you plug in numbers without understanding the finished product - you can wind up with a very poorly designed end result, or a safety factor of about 10.
Edited 4/25/2005 8:35 pm ET by Jon
I talked to the framer today, and he said the house is loaded with steel, and wood too, because the owners have specified floor loading everywhere at 120 psf with deflection of l/720.
Wow! This, in a private residence for two people!
Some more overkill. They are sheathing all the exterior walls in 5/8 CDX and want all the rough spots sanded down!
Is one of the owners an engineer?
Can't answer that.
Is either of the owners an idiot with way too much money?
It is amusing to see fun poked at engineers and architects from the building trades.Do you ever wonder who they poke fun at?One answer (from my engineering student roommates in college):Just like we poke fun at them, they poke fun at the mathematicians and physcists. There are lots of good engineer and mathematician jokes where the engineer is the practical one and the mathematician the fool.Of course, now I wonder who the mathematicians make fun of?
Those math and physics guys were so far out there, they may as well have been on another planet. I don't think they even realized us engineers were making jokes about them...
I wondered about that. I never did see a group of mathematicians hanging out telling engineer jokes.So you're an engineer from Chatfield then.
Yup, that I am. I went to school first at the junior college in Rochester, then finished up at the U of Minn in 1979.
Edited 5/9/2005 10:21 pm ET by Stuart
> now I wonder who the mathematicians make fun of?
IIRC, they don't make fun of anybody. Just not the sort of thing they think about.
-- J.S. (MA in Math, 1971) ;-)
MA in MAth. Interesting that it's an "arts" degree rather than a science (MS) degree. I use math all the time in my contracting work. I recently picked up "Workshop Math" by Robert Scharff. Good stuff.--B.C. (BS in Forest Ecology) now I'm finding out what happens with the trees after they cut them down.
Hahahahahaha
I hope that framer has a good contract and lots of money up front!
blue
Maybe they have ALOT of sculptures? Or do they just think that over-designing by a factor of three equals better quality?...that's not a mistake, it's rustic
I helped a guy build an addition on his house. He insisted on building forms for the footings instead of just digging trenches (his way was probably better), but he also insisted that where there would be "point loads" like on each side of where there would be a door or window, we had to widen the footings. I tried to explain that it would be easier if he had doubts about the footing width to support the load to just widen all of the footing because it would be acting as a beam anyway. Nope, we made jogs in the formwork. Right after that it rained hard and filled the forms with mud and clay that we had to dig out a second time. But on the roof sheathing, he left it on one side protruding about 2-3 inches past the ridge and got mad at me for wasting time when I cut it off.
Guys,
OK, help me understand how much extra $$$ that will add to the cost of the house? Reason for my ignorance is we don't use any steel beams in Florida in residential units.
I mean if its $1k-2k maybe they have a huge slate pool table or waterbed going in that area and want to assure it will never creak, sag or be an issue?
If only folks here in Florida overbuilt like that, we'd all be happy!
Mike
I had house movers lift my house. They used a pair of W12x75 by 48 feet long, and cribbed near the ends of them, so the span was about 35 feet. There was almost no deflection in the beams, and the mover estimated the weight of the house at 30 tons, so that's 15 tons evenly distributed on each beam.
Oh yeah... and each beam had a weld right in the middle... they'd been made up from 24-foot pieces salvaged from a bridge.
I'm always at how steel can pretty much be cobbled together at will with no loss in strength.Try doing that with doug fir and a scarf joint.
Jon Blakemore
Apparently the weld would not be a failure point the way it was welded.