construction joints in composite slabs
construction joints in composite slabs
(OP)
I did some searching in the past Tips on the subject, and still have a couple of questions. This was the best one I found:
www.eng-tips.com/viewthread.cfm?qid=290066
Typical office building floor, steel wide-flange composite beams with composite steel deck and concrete slab system. WWF is provided for shrinkage crack control only, slab spans are designed as simple.
We need to detail where and how to place construction joints for logistical reasons in the field. I understand to place construction joints outside the effective flange width of the composite beams, so I suppose as close to this as possible is ideal. Any other thoughts on where to place them would be great.
Since the slab is in compression, the only issue would be shear that I can think of- but you have WWF and the deck also. Is it standard to provide perpendicular dowels across the joint for shear transfer or are these just for "warm fuzzy" feelings...? #4 @ 18" o.c. x 24"?
Thanks in advance for your input.
www.eng-tips.com/viewthread.cfm?qid=290066
Typical office building floor, steel wide-flange composite beams with composite steel deck and concrete slab system. WWF is provided for shrinkage crack control only, slab spans are designed as simple.
We need to detail where and how to place construction joints for logistical reasons in the field. I understand to place construction joints outside the effective flange width of the composite beams, so I suppose as close to this as possible is ideal. Any other thoughts on where to place them would be great.
Since the slab is in compression, the only issue would be shear that I can think of- but you have WWF and the deck also. Is it standard to provide perpendicular dowels across the joint for shear transfer or are these just for "warm fuzzy" feelings...? #4 @ 18" o.c. x 24"?
Thanks in advance for your input.






RE: construction joints in composite slabs
RE: construction joints in composite slabs
I don't like the practice of designing for simple spans, thus intentionally allowing the slab to crack over the supports.
RE: construction joints in composite slabs
How big is this slab that you cannot pour it in a day?
For anything more than about 50m (160 foot) you should provide a proper expansion/contraction joint unless you can justify it by calculation.
If you do need to push the boundaries then you should consider a pour sequence that skips alternat bands to allow the orifginal bands to shrink prior to pouring the infill. This works better with insitu slabs though it should make a difference on composite.
hokie,
It depends on the fabric and cover used, often the fabric is sufficient to provide for serviceability moments and therefore will be sufficient to limit cracking.
RE: construction joints in composite slabs
however I do have a question for Hokie. would your advice about shear transfer still apply if the building was in a seismic zone thus the slabs could act independently in the along joint direction if the other structural components didn't have enough strength?
How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban
RE: construction joints in composite slabs
RE: construction joints in composite slabs
Not sure I understand your question, but I can't see the slabs on either side of the construction joint acting independently due to seismic load. The deck continues across the joint, the shrinkage reinforcement continues across the joint, and the construction joint is just a joint in concrete, not a slip joint.
RE: construction joints in composite slabs
on seismic projects I have always spent time reinforcing all construction joints in slabs, due to the large potential load that could occur along and across the joint. I guess I just don't like relying on mesh, deck and a little bit of stone friction.
How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban
RE: construction joints in composite slabs