Concrete Deck Design Concerns 1

[RM87]

Hello folks,

I am in the process of designing a concrete deck above an operable garage. The client decided to go with concrete after the original wood framing supporting the deck was deteriorated by dryrot.

The current garage is retaining soil from both neighboring sides and from the rear - and the same conditions will remain. The three retaining walls form the perimeter of a C-shaped elevated deck (not an exact C shape, but a close enough example). At the foundation level, I will be designing a mat slab to accommodate all three retaining walls. I was hoping that the five of the six surfaces from within the garage would be composed of concrete, but the wall facing the street, where I would be replacing the garage door would be wood framed. I don't particularly see any issue with this as long as the concrete isn't bearing on the wood, but I just wanted to check that with all of you. Also, would you calculate this as a one-way slab or a two-way?

I was also thinking about forming the concrete with elevated plywood and pouring the concrete as designed. I see all around that people are using metal decks. Is there a requirement for the use of metal decks or is it a matter of preference? I don't expect fire rating to be an issue, but for arguments sake, I want a 1-hr rating to future proof it.

Any tips? Suggestions? Cautionary tales to be aware of?

Thank you, sincerely,
Rod

 

[Ron]

Don't see an issue as long as properly designed for deflection/serviceability in conjunction with structural. Front opening might need intermediate columns and soffit beam, depending on spans.

Metal decking can be part of structural design, for forming convenience or both. Nothing wrong with plywood forms, provided the form supports are properly designed.

 

[RM87]

I was thinking of designing the slab as one-way and spanning it 16' (worst-case scenario) between the two retaining walls.

 

[RM87]

Bump - Still could use some additional advice.

 

[CELinOttawa]

Bump after an hour and a half? You're going to need to be more patient to get the best advice... Some of our members who are the most knowledgeable are asleep while the rest of us work, if you get my drift.

A bit of help:

- One way spanning is always easiest to design, and simplest to construct. I like to design as one way continuous when possible.
- Metal deck pan is popular because your form becomes part of the permanent structure. It is efficient. In the case of exposure conditions which include salt or other deliterious materials (proximity to sea or ocean, salting of roads, fertilizer factories, etc) you should *not* count on the metal deck pan, but rather just use it as formwork. Effectively building from plain reinforced concrete appears cheapest until you factor in the labour and materials for the forms.

 

[hokie66]

You can certainly use plywood forms. As to the structural system, a one way slab could be used, but as Ron suggested, stiffening the front edge with a deepened band would be my preference.

 

[RM87]

@Cel - Thank you for the advice. Didn't realize I was that neurotic
@hokie - Will do. Thank you.