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portal frames

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发表于 2009-9-15 13:34:34 | 显示全部楼层 |阅读模式
portal frames
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 !!
check out our whitepaper library.
my recommendation would be to use steel portal frames, so steel columns.  could possibly use a single leg portal, column on one side only.  i think trying to use the concrete panels as portal columns is pushing the system too far.
thanks hokie66
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!!
sorry, i don't think i can help, at least for your case with no shear resisting elements in the ends.  i am in australia also and quite often see things in my travels that don't look right with structures under construction.  tilt wall construction has taken most of the market for light industrial and storage buildings, but i honestly don't know who is designing them or how some things are justified.
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.
thanks barryeng
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?
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.
tilt up panel design is very easy and is very economical to build. you don't need to fix (as in moment connection) the rafters to the panels, just shear connection. you don't want to transfer moments to the panel. the roof bracing (think of it as a horizontal truss) is the key to the design.
i usually create a model in microstran to size up all the   
agree with nicam that you don't want to try to make a moment connection between rafter and panel.  the concentrated moment would cause distress in the panel.  and as he implies, you may be able to provide for overturning by fixing the bases of the panels.  one way of doing this is to cast your footings with slots to receive the panels, and grout them in.  of course this makes the footings large and the panels heavier than usual.
thanks barryeng, nicam and hokie66,
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!

civeng80,
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.
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