Composite Slabs - Construction Joints

[kvillebasser]

When using composite slabs (3 1/4" concrete over 2" metal deck for total slab thickness of 5 1/4") where do you guys allow a construction joint to be, if the GC decides he needs one?

Could this joint be at the midspan of the typical floor beams? This would seem to make since to me as the shear is zero in a uniformly loaded beam, thus having the minimum requirement for shear studs at this location....but what bothers me about placing a construction joint at midspan is the fact that the maximum moment is in that location as well.

Additionally, if you provide the construction joint parallel to beams and perpindicular to girders, that seems to have a negative effect on the ability of the floor deck system to span between beams.

I realize we've got to be out out of the region of the effective flange width of the composite members when running a joint parallel to the member, but my concern is really where the joint should be when oriented perpindicular to a member.

Thanks for ya'lls input.

 

[JAE]

Midspan midspan midspan.

You don't want to have a vertical joint in the slab near places where the slab has high shear. This is true even though the primary failure mechanism in composite slabs is horizontal shear-bond failure between deck and concrete.

Also, by running the joint at midspan, you are midway between composite beams, staying out of the effective width, which is desired, but not essential.

As the joint crosses the supporting girder, it being perpendicular to the girder, the composite action and compressive forces in the slab will not be disturbed by the joint...the joint will be squeezed together even more.