can we camber and shore girder at the same time
can we camber and shore girder at the same time
(OP)
Just wondering for composite girders, I called cambers based on composite section, say 1" camber. But during concrete pour, the dead load on steel girder would be 2", should I call shore during concrete pour?
Thanks
Thanks






RE: can we camber and shore girder at the same time
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: can we camber and shore girder at the same time
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: can we camber and shore girder at the same time
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: can we camber and shore girder at the same time
I see no reason you couldn't do both BUT WHY NOT JUST INCREASE YOUR CAMBER?
RE: can we camber and shore girder at the same time
Then when I check, I need to make sure steel can take the dead load and without too much deflection. It looks like load capacity is ok, but deflection is big.
So basically all your cambers should design on non-composite steel beam properties, and we'll get larger cambers. Just wondering this should be the way for cambering.
Thanks KootK and jike!
RE: can we camber and shore girder at the same time
RE: can we camber and shore girder at the same time
Keep in mind that if you do specify shoring, you should carefully review how the contractor proposes to shore the beams AND consider how the shoring will behave based upon what it bears on.
It's very simple to specify that shoring is required. It's not always a simple matter to determine if the shoring will actually prevent the deflection that you are concerned about. Further, the results will also depend on how the contractor will screed the concrete during its placement. If you expect the some camber to remain after concrete placement is complete, then the concrete screeding must be based on thickness of slab and NOT on elevation (usually not considered by some contractors).
From a constructability perspective, I believe it is wiser to camber for dead load deflection so that the slab can be placed to the specified elevation (i.e. level).
Ralph
Structures Consulting
Northeast USA
RE: can we camber and shore girder at the same time
RE: can we camber and shore girder at the same time
not really, shoring only removed after concrete being cured, the composite section will work so section properties is greatly increased, and wont deflect much after shoring being removed.
RE: can we camber and shore girder at the same time
I have to admit I have never been the EOR on this type of project though. I'm just basing this on the number of composite beam models I see (I work for a structural software firm). And, very, very few of them specify shoring. I don't even remember the last time I saw a model come in with shoring specified.... it's been awhile!
RE: can we camber and shore girder at the same time
RE: can we camber and shore girder at the same time
JoshPlum - I'm not so sure that it's expensive but rather can it been executed reliably? For a single level structure with good ground conditions the shoring will do what's expected. When shoring is used on a multi level structure its reliability depends on how the shoring is supported by the level below. Multiple levels of shoring (to insure a deflection-free support) then starts to get expensive. It also can begin to affect the trades that follow.
Ralph
Structures Consulting
Northeast USA
RE: can we camber and shore girder at the same time
RE: can we camber and shore girder at the same time
non-composite steel will deflect under 60psf dead load and 20 psf construction load, that's almost the full load. then what's the purpose of composite?
RE: can we camber and shore girder at the same time
If you have access to the contractor for your project, I'd be sure to check with them about the "goodness" of shoring. You'll be tempting the cruel wrath of the rework gods otherwise.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: can we camber and shore girder at the same time
The primary reason for using composite beams and girders is strength and the ability to shallow-up beams and girders relative to non-composite framing. For the same size beam or same beam depth, you can typically space composite beams farther apart than non-composite beams, thus reducing the steel tonnage (though the savings is partially offset by the cost of the shear studs).
RE: can we camber and shore girder at the same time
I realize the post-composite moment of inertia is larger. The Steel Construction Manual table 3-120 has lower bound moment of inertia for composite beams. For instance, a W25x55 has a precomposite moment of inertia of 1350 and a post composite moment of inertia between 1970 and 4210. The original post mentions 2" deflection from concrete weight. If the deck is shored and the composite moment of inertia is 4x the bare beam, the floor surface may deflect the 1/2" from the weight of concrete when the shoring is removed. (This example is only meant to give a point of reference because there are other factors that affect composite beam deflection) In most cases, the floor flatness is much more important than the deflected shape of the beam below the concrete. Typically, I will look at the precomposite beam deflection to make sure the excess concrete I assumed is acceptable and the deflection is not ridiculously large.
RE: can we camber and shore girder at the same time
But I still feel shoring is a good way for composite beams. I will only need one mid point shoring for all steel beams, and the slab will be perfectly flat or slope.
The most important thing is that no matter how many times the new section I is bigger, if we put all dead load and construction load on bare steel, we don't utilize much of the composite advantages, and our beam sizes and depths will be no much difference.
RE: can we camber and shore girder at the same time
The benefits of composite construction are not negated when shores are omitted. Beam sizes are reduced. You will find, as evidenced by this thread, that unshored construction is overwhelmingly the choice of contractors and your colleagues in the structural engineering community.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.