Construction Joints in Elevated Concrete and Metal Deck Floor Slab

[olsont]

I'm in the process of designing a elevated composite concrete and metal deck floor slab for a warehouse. This slab will have rolling fork lift loads. The floor has been designed with two mats of steel, 7 1/2" total concrete thickness and 50 ksi steel beams with a single row of shear studs on the beams. The question has come up concrening construction joints in the slab. Should there be any? If they are required where should they be located? Should the shear studs be staggered instead of just a single row?

 

[ash060]

It sounds like this is a reinforced concrete slab. I would not put any joints in it if that is the case. Typically joints only go in unreinforced slabs

 

[delagina]

why not? i see drawings with optional construction joints located at beam/column centerline with one side of slab rebar extending by 1 development length.

 

[sumnerdave]

ACI 318 “Building Code Requirements for Structural Concrete,” ANSI/ASCE 3 “Standard for the Structural Design of Composite Slabs,” and SDI #30 “Design Manual for Composite Decks, Form Decks, and Roof Decks” do not require the use of contraction joints for elevated structural slabs.

However, construction joints happen because you usually can't monolithically pour an entire floor slab at once. As long as the rebar used and the mix of the concrete is correctly designed, the cracking should be minimal. Let it crack and your designed steel will control the crack's width.

 

[delagina]

Can you help me locate exactly where in SDI #30 "Design Manual for Composite Decks, Form Decks, and Roof Decks" it says contraction joint is not needed for suspended slab?

thanks,

 

[delagina]

similar question,

when is it preferable use shear studs as oppose to puddle weld?

thanks,

 

[slickdeals]

Shear studs and puddle welds can never be used interchangeably.

The shear studs are used to transfer force to/from concrete in a composite system. The shear studs are welded to the flange of a beam through the metal deck. In essence, it connects the metal deck also.

Puddle welds are used to transfer shear to/from a bare metal deck to a steel beam/joist.

 

[ash060]

I am sorry I thought he meant control joint. Forget my post above.

 

[delagina]

so if assume metal deck to be non-composite, i cant use shear stud? i must use puddle weld?

if i assume metal deck to be composite, i must use shear stud?

thanks,

 

[slickdeals]

composite concrete slab -> shear studs/ channel connectors etc. (shear studs is the industry norm)

metal deck only --> puddle weld, power actuated pins etc.
You can probably use shear studs on a bare metal deck, but that's just a waste of money.

 

[delagina]

thanks slick deals..

what is your opinion on using

a non-composite metal deck with concrete slab and top and bottom reinforcement and puddle weld.

 

[JAE]

olsant - back to your original posted question - for any cast-in-place concrete construction - construction joints should be placed in the middle third of the slab spans.

Make sure that your natural slab reinforcement is extended through the joints. If you don't have say - top bars at a joint, add some additional bars.

Keep the construction joints away from running parallel to and near to composite beams - place them beyond your effective flange width.

 

[WillisV]

Be careful to differentiate between composite deck and composite beams:

Composite deck has embossments on it that allow the deck itself to resist loads compositely with the concrete for greater load carrying capacity of the deck/slab system. It does not need to be connected with shear studs, but doing so can increase its capacity a little bit due to end restraint.

Composite beams on the other hand must have shear studs so as to act compositely with the floor system.

So, you can use composite deck with noncomposite beams if you wish, though generally since they have to attach the deck down anyway, you might as well use shear studs instead of puddle welds and gain the composite beam action at very little extra labor/cost.

 

[delagina]

@willisV,

when is it preferable using non-composite deck like vulcraft type C?

 

[WillisV]

@delagina - can't think of many reasons to ever use a noncomposite deck if you are going to have concrete fill - budget perhaps if you already have close beam spacing for some reason and do not need the extra load carrying capacity?

 

[delagina]

@willis, am looking at a go-by drawing similar to what i will be doing.

he used composite deck for the roof

and non-composite deck for 2nd floor slab with top and bottom rebars. this is the floor where the equipment is located.

is it preferable to use rebars instead of the metal deck for tension reinforcing, where you have heavy loads?

 

[WillisV]

Yes for equipment loading it makes sense to use a reinforced concrete slab (you are basically just using the deck as the form).