Have a remodel coming up at my own house and I am looking to open up a
clear span on the back of the house of about 19 ft. The house is a basic 2 story 1980’s New England Cape. I am comfortable with the engineering required to size the steel beam I need to do this.
I looks like the easiest way to do this is to bolt a 12 x 30 Channel onto the rim joist.
The question is about the supporting columns. One end is no problem, there is solid foundation wall directly under the channel.
On the end in the middle of the back wall I am looking at either
10 digging a 6 ft hole down to the bottom of the foundation and pouring a half moon shape concrete tube.
or
How about a column(maybe steel channel thru bolted to the current foundation above grade? The load overall is a little off center but
it seems like it should be fine.
Anyone have any thoughts??
See attached picture.
Replies
not sure what a 12 X 30 channel is, or what that will support, openings are usually supported with doubled up headers and jack studs, or big ones with beams ... they can be sized by a supplier .. not so sure how comfortable you should be with the engineering, no matter how you go, an opening this size requires a permit and drawings by a qualified person ..
30' channel, 19' span?
A 10K1 bar joist (only 10" tall) spans 19' with total load of 221 lbs/lin ft and weighs only 95 lbs. My engineers are always happy with a reinforced concrete column (8") bearing on an adequate footing. Undoubtedly a steel co. could set you up with a steel column.
I didn't look at your drawing 'cause this new computer still isn't configured right.
PAHS Designer/Builder- Bury it!
Tom, I'm interested in the cost of the steel bar joist as compared to wood floor systems. I'm also interested in the span capabilities. Bob's next test date: 12/10/07
Jim, call your steel company? Price varies, sometimes a lot. Wood floor systems I know nothing about. Did have a crane guy about fall over when I told him how little the 40' span 600 lb bar joists he was setting for me cost. He knew from wood trusses, apparently much more expensive.
I pointed out that if I didn't have a 300 ton roof (mostly earth load) to support, I could use a whole lot less steel. Half or less. This is a major part of keeping my costs low.
All bar joists around here are manufactured in one plant in the Shenandoah Valley. They only sell to steel companies. I always call 3 to see who'll go lowest to process some paper and deliver to me, no stocking. No idea what margin they're working on.
Don't make the mistake I did, assuming that because you buy by the pound that the price/lb is constant. Larger bar joists cost less/lb. I was mislead by a company who could only deliver up to 30' bar joists on their straight truck. Had no idea, until the next project, that 40' ones would cost so little more. My span tables go up to 60', with a joist height of 30", total load up to 262 lbs/lin ft.
You'd enjoy a bar joist chart. K Series is common, easy to read, and all that my building dept wants from me. No engineering required anymore. Pick your load (live and total) and span, then go for the smallest bar joist that'll do it, 1/360 or 1/240. The light weight makes handling simple. Powder actuated fasteners are the ticket. And fast.
I've never built with tractor/trailer access, had to rely on straight truck delivery. Can make a large difference. I set the bar joists for my place with a compact tractor and steel cable stretched between trees, comealong doubling sheave riding on the cable. Came off the truck the same way.
I found my bar joist chart on the internet somewhere, but I expect any steel company would be happy to oblige you. Or I could scan the rest, only 4 pages total. Here's the first page, with instructions:
PAHS Designer/Builder- Bury it!
I don't have a steel company...yet. I like the idea of using the steel bar joist and creating a floor out of lightweight concrete. I see this as a niche market here in Austin where a lot of people are interested in healthy alternatives.I'm designing some duplex's and this idea gives me some alternatives for second story stacked units instead of spread out side by side units. My big issue was sound control and this option might solve some of those problems. I googled a bar chart but didn't get any good results. Do you have some key words that will lead me to something I can understand? Bob's next test date: 12/10/07
I scroogled "K Series bar joists", without the quotation marks. First hit was http://www.mc2-ice.com/support/estref/popular_conversion_files/steel/bar_joists.htm which includes a bunch of other bar joists beyond the common K Series, but no complete chart. After that were several pdf files that I've got to reload adobe to open.
As I recall, I did a bunch of looking before finding anybody who bothered to put up that K Series that I downloaded. The first steel company in the phone book is the first one I'd ask to FAX it. Or, if you need engineering anyway (and the engineer is aware of that) they surely have a chart they'd copy for you.
I'm sure you know that you really don't want to get tied into any one steel company. Can't imagine you'd find much difference in service when it's a third party discrete order you're placing. I figure reasonable delivery is at least 2 hrs each way, let them factor that into my cost.
Using steel decking topped with concrete makes perfect sense to me. My slab is nominally 4". B22 is the galvanized decking I use. Don't know the max span, but you'd want to find out to minimize your number of bar joists.
Lightweight concrete's something else I know little about. Weight won't be much of an issue, I'd go for whichever is more soundproof. I did compare bar joists to precast T beams (not that I could get them delivered) and cast-in-place T beams. Major savings with the steel. I was shocked how much. Which is probably why you commonly see bar joists in commercial buildings.
Ran into a reinforced concrete engineer at a trade show (apparel and accessories)who was happy to start with a napkin, which turned into major calculations an hour later. We were spouses, time on our hands. Real interesting, for both of us.
Forgot to mention that wiring and HVAC runs are incredible fast with bar joists, which are mostly air.
PAHS Designer/Builder- Bury it!
Edited 3/25/2008 8:05 pm ET by VaTom
Just a note on your use of bar joists, in the same section that the K joist table was found there should be a brace table which tells how many braces MUST be installed to complete the bar joist installation. These are NOT unimportant, these must be installed for a complete job. The brace can run from bar joist to the next bar joist, in an X pattern like wood joist, or from the bar joist to the wall parallel to the joist.
Jim Hannah, steel eng
Thanks, but bracing is always specified/supplied by the steel company, hardware priced with the bar joists. Even comes with bags of the correct bolts when required. Much better than having to decipher another chart. Allows me to deal with loads only. Minimizes my opportunity to err.
KISS, a great concept.PAHS Designer/Builder- Bury it!
Maybe your experience has been better than mine, but I have seen way to many situations where something was left out due the specifier (you in this case unless you hired a licensed engineer to provide a design) not knowing the finer points of required design. The idea that somebody would know that the maximum allowable unbraced length of a bar joist or even a hot rolled section is limited is not a given. So when somebody sings the praise of joists, cold form steel or hot rolled steel and doesn't mention bracing my warning systems start sounding.
Well all is well that ends well or something like that.
Jim Hannah
I get your point, but I would no more specify the bracing than I would the size of the angle iron. Do you engineer the bar joists too?
That's exactly what engineers are for, and why the steel companies employ them. I only provide the load and the span. Reading a bar joist chart is for estimating, and keeping the building inspectors happy.
The steel company is the "specifier". Bracing included.
Both structural engineers I've hired knew less about bar joists than I do. Now, that's scary. They do the same thing I do, rely totally on the steel companies' expertise.
Your market may be different. No other choice here.PAHS Designer/Builder- Bury it!
I think you'll be fine, just need to get enough bolts through the column into the foundation wall. Also might need to weld some ribs at the ends for shear support, so the channel doesn't want to collapse on itself.
Pouring a concrete footing is a safer alternative, though.
Thank Mike,
for your gut feel.
I realize a straight load path to a concrete footing would be ideal but
to get to undisturbed soil I would need to dig down over 6 feet. down
to the edge of the existing wall. Since my little backhoe only digs down 4 ft I would have to excavate a wide section.
Was looking for a simpler to implement alternative.Also interesting that even if I did dig it out the column would be bearing on the edge of the footing not the center.
If you could get a 4' head start with a backhoe, digging another 2' wouldn't be much worse than drilling out the 15 bolt holes you'll need. I'd sleep better knowing I was bearing directly on a footing. Being on the edge of the footing is probably ok.
Of course, it's time to break out the standard disclaimer, internet engineering is not to be followed, get a real engineer to look at it, etc.
My thoughts: aren't you going to do some digging for the foundation for the addition?
Digging a 6' hole doesn't seem like such a daunting task.
Bob's next test date: 12/10/07
You're always safer with direct bearing on a footing. I'd sleep better at night knowing that steel post was sitting on something. What about a tractor powered auger or post hole digger right up against the foundation and cleaning the the corners out by hand? If you could get a utility company truck to come in with one of their augers for power poles, that would do the trick.
If it ain't broke, don't fix it, just open it up to see how it works!
It's very doable. I'm doing something simmilar on a current project actually. A fair amount of engineering went ito it. We are setting the colums on L's with a blade support welded below the column that are through-bolted (with backing plates) to a concrete wall.
I wouldn't worry about it at all if it is engineered and the moment on the foundation, shear on the bolts and pull out strenght of the bolts is accounted for
You have a whole lot of bolts in shear in that design ... plus the disadvantage of a channel is that it is not symmetrical about its axis, therefore it doesn't always react in symmetrical ways. It is 'weak' with respect to any lateral loads from the flange side, for instance.
Instead of that, how about providing temporary support and slipping a flush-framed flitch plate ('Better Header' comes pre-made with flush fasteners) into place? Then the columns sit on the foundation wall.
http://betterheader.com/
Jeff
Edited 3/28/2008 1:34 am ET by Jeff_Clarke
Because his channel will be bolted to the rim joist of the house, it's well braced laterally. Channel has a lot more strength for a given weight than a flitch plate does.
The idea of slipping a beam under the rim joist does make sense to me though.
In place of the rim joist - done all the time.
Jeff
Spanning 19'? C-channel would be a more efficient use of steel. But you can do it your way if you want. ;-)