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Unshored Span of Metal Deck

Unshored Span of Metal Deck

Unshored Span of Metal Deck

(OP)
Does anyone actually use the clear span of the deck for determining beam spacing to ensure unshored construction?  I've only ever used center to center of beams.

RE: Unshored Span of Metal Deck

I think most engineers use center to center spacing. I think clear span is an ace up your sleeve in case you get into trouble during design/construction/renovation etc.

RE: Unshored Span of Metal Deck

For me it kind of comes out in the wash...say 20' columns/girder spacing, design floor load, prelim size of beam, nice even beam spacing...waa laa, clear span of decking--> check for construction.
but, maybe I just have a poor design approach.

RE: Unshored Span of Metal Deck

When shoring - if you get that "close" then you had better re-think your design.  There can be a WIDE variation in loading from actual to theoretical when it comes to shoring...  OSHA recommends a minimum of 2.5:1 factor of safety.  I ususally use around 3:1. So inches of span really should not be a consideration..

RE: Unshored Span of Metal Deck

The published spans can vary from manufacturer, so i tend not to cut it so close that i am counting the width of the beam.

RE: Unshored Span of Metal Deck

Centre to centre spacing. Whenever using a deck product or any product for that matter, I always make sure I am within the recommendations given in the techincal literature provided testing and complience certificates are readily available.

The reality is the product will have additional capacity up its sleeve. We have a product in Australia called Bondek which is a 0.75mm metal sheet (not sure on gage but is approximatley 1/30" thick). Contractors are always saying to me that the deck doesn't deflect when the concrete is placed.

RE: Unshored Span of Metal Deck

I only use center-center spacing. I think it would be mandatory if you are considering 3 or more continuous spans.  I might get tempted to use clear spacing for a single span condition in a pinch.

RE: Unshored Span of Metal Deck

I use centre to centre of the supporting beams, but the actual span will be supported by the outside edges of the steel beams as the deck deflects.  For multi-storey buildings where a beam and concrete slab system was used, I'd modify the -ve moment due to the support width to reduce it a tad...

Dik  

RE: Unshored Span of Metal Deck

(OP)
The usd catalog I have says that center to center of supports must be used for roof deck, but is silent on the composite floor deck. The fact that they mention the center to center for roof deck kind of implies that clear span is ok for floor deck, but I can't find anywhere that explicitly states that. Additionally, there are two conditions to coonsider for floor deck - the weight of the wet concrete as unshored and noncomposite, and the composite state with full load.  In my mind, the wet weight of concrete on unshored deck is identical to the roof deck except the load duration is obviously much shorter.

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