Portal Frames
Portal Frames
(OP)
Does anyone have any knowledge or can they comment on industrial buildings with concrete tilt panels connected to rafters (either UB or open web trusses) with rigid connection to the panel so that the concrete panel (or part of it) acts as a beam column and where shear walls are not possible at the ends of the building (e.g. because of large openings). If so what would be the effective column width of the column/panel?
Can anyone tell me if there is any software/literature available on this subject?
Thanks !!
Can anyone tell me if there is any software/literature available on this subject?
Thanks !!






RE: Portal Frames
RE: Portal Frames
I do agree with what your saying, but I have seen it being used. Im from Australia and the standard codes are AS4100 for steel and AS3600 for concrete. The rafters were open web trusses which were faily light and spanned about 15m to a central wall with another 15m span on the other side. effectively a propped portal.
Its a clean looking building inside of course with no steel columns. I just wonder how it was analysed and designed ??
Thanks!!
RE: Portal Frames
RE: Portal Frames
Have a look at the CIA (Concrete Insitute of Australia, not the US spy agency) manual for tilt up concrete. They have examples showing various configurations of tilt up wall with rafters for the roof & no columns (except for large openings in the shear panel).
When I get back to work, I will find the exact reference & post it here.
RE: Portal Frames
I think I know which reference your refering to. CIA precast concrete handbook right? Example 5.1b. However lateral forces are transfered to shear walls at the end thru roof bracing. One question while Im on this one, what do you think of the connection from rafter to panel, looks a little mickey mouse to me. Is there another more substantial connection available? Also what happens if there are large openings at the ends of the building?
RE: Portal Frames
There is a CIA pub on tilt up conc.
Try also CACA May97 - tilt up const notes - ISBN 1 876278 10 2
& tilt up const bldgs Jun98 Des & co9nst guide (UK) - ISBN 0 7210 15336
These pubs give connection details that may be of use to you.
RE: Portal Frames
I usually create a model in microstran to size up all the members, then use inducta software to do the panels.
if there is a large opening at one end then I normally restrain the end panels at the base to resist over turning.
I hope this helps.
RE: Portal Frames
RE: Portal Frames
I do agree with you nicam and hokie66, portalizing a tilt panel would be pushing the system a bit and I certainly wouldn't do it even for short rafter spans. But the case I've seen its the only way it would have been done, since there is no roof bracing at all and the end walls have very limited panel guts to use as shear walls. Probably a very couragous structural engineer there right hokie66? As I said I wouldn't do it and I'm glad that you guys wouldn't either.
Now Im a civil engineer turned commercial builder I do my own designs (for my own projects) and am very confident in the typical portal frame system. Load bearing tilt panels are ok probably more for the smaller commercial shops, but I would still hesitate to use them in the larger building where forklifts and truck movements occur. I'd like to know what you guys thoughts are on this?
Also for load bearing panels as I mentioned to BarryEng there seems to be a faily flimsey connection with a small angle bracket bolted to the lower flange, why not just have a tee piece connected to the web? (panel can normally be adjusted by props to align the holes. What do you guys think about this?
Anyway thanks a lot guys you have been very helpful, a Merry Christmas to you all and my apology for the long rant.
Thanks!
RE: Portal Frames
What you have seen indicates to me that rather than a courageous structural engineer, there was no structural engineer. Probably more like a builder who thinks no engineer is required, and a private certifier who deals in volume. Glad you are more conscientious.
Personally I prefer framed structures with the precast as cladding, but load-bearing precast is gaining in popularity in Australia, not only for tilt-up industrial buildings, but also for low to medium rise commercial buildings. Done with due care, it is another acceptable and sometimes economic system for consideration. Horses for courses.
I think the main reason for the connection you describe is to prevent prying on the panel, which I suppose supports my aversion to trying to take concentrated moment into the concrete.
Merry Christmas to you and yours.
RE: Portal Frames
Like I said before the roof bracing is the key to the design.
I've design up to 37m clear span and 50m two span tilt up buildings. I used tilt up once for a load bear application, but that was with a combination of steel portal frame, with the columns on the outside of the panels, which were fixed to the columns.
As far as the the connection detail, I too asked this question when I first designed tilt up, but this has been the norm for connection panel to rafter (angled bracket) I've used this method of connection all the time without any problems. Also no moment tranfer.
RE: Portal Frames
So 37m clear span with no columns? Also do you use microstran then just to design the simply supported rafters? What about end walls do you use the same rafter section at the end walls or a ledger angle supported continously ?
RE: Portal Frames
with the 37m span you would use either WB for rafters or truss, I normally would use trussess, but on that ocation I used a 900WB.
End wall don't need rafters used raking angles as you mentioned.
I only us MS for larger buildings but for small rectanglar build I just use hand calc's
RE: Portal Frames
RE: Portal Frames
900WB for a 37m span sounds about right I presume it had a ridge at the centre with a roof pitch of about 5 degrees? Was the connection to the concrete panel still an angle seat about 150 x 150 x 16thick, was there any web connector as well to prevent rotation? I think for that sought of span I would tend to think more about portal frames rather than load bearing tilt up panels. For one reason you just mentioned and the other one is that better sight control is required for tilt up panels especially for the larger building (although this is not the designers problem).
Ive been looking at castellated beams lately rather than open web trusses what do you think of those for the large span buildings?
Cheers !
RE: Portal Frames
The use of castellated beams would depend on fabrication costs. The only times I have used them is for gymnasium roofs when the architect wanted that look.
RE: Portal Frames
Cheers !
RE: Portal Frames
The vertical shear connection to the wall can take various forms, as long as the connectors into the wall are more or less in a horizontal line to prevent prying. The connection doesn't have to be right at the bottom of the beam. One common connection consists of an angle each side of the beam or slotted through, in turn seated on angles each side which are bolted to the wall.
RE: Portal Frames
Vertical shear connection. Do you mean 2 horizontal angles(or slightly graded to suit rafter slope) welded (say) on both sides of the web and supported on a prepared welded angle bracket with the bottom leg graded to suit the rafter slope and slotted for the web and a row of horizontal bolts connected to the wall?
Maybe use this method to connect to the top flange and restrain the bottom flange using the walers?
One further question. For a rafter supported at the bottom with an angle bracket can proper restraint be achieved from the purlins and/or flybraces?
Cheers!
RE: Portal Frames
Cheers!
RE: Portal Frames
2. The angle on the rafter would typically be one piece, with the inside of the vertical leg welded to the end of the rafter web, and the horizontal leg slotted through the web and welded both sides.
3. Connection doesn't have to be at bottom, could be near the top. Just watch things like edge distance to top of wall. Waler needs to be in bracing plane.
4. Restraint of top flange in completed structure will be primarily by purlins, but I think some restraint is required for erection of deep sections. The method of providing this restraint also may depend on other details of your building like box gutters, downpipes, etc.
I am not saying this is the only way of detailing this connection. Just trying to point out one way and some of the problems which can be encountered if the details are not thought through well.
RE: Portal Frames
Cheers and thanks for your interest ! I may never use this connection but still very interested in the detail. If you dont mind I may detail it up and post it to make sure its what your describing.
RE: Portal Frames
Thanks !
RE: Portal Frames
Glad you found my advice interesting. Would have been better if I could have sent you a sketch instead of describing it in words, but never mind, we worked it out. Good luck on your projects and a Happy New Year.
RE: Portal Frames
Its fortunate that we engineers use drawings to convey much of our information as words can sometimes be so confusing and misleading. Thanks again !
Likewise a Happy and successful new year to you and yours!
RE: Portal Frames
Is it possible that the portal frame is designed as a T-shaped rigid frame with rigid connections to the central column and only pinned connections to the external panels.
I did renovation work on a bunnings warehouse that was designed exactly that way. The panels then act like mullions at each end resisting the compression/tension from the beam reaction. The central column needs to be twice as stiff though.
RE: Portal Frames
Ok but it required a steel column in the centre with moment connections, what sort of spans were involved here?
RE: Portal Frames