×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

One-way or Two-way Concrete Slab?

One-way or Two-way Concrete Slab?

One-way or Two-way Concrete Slab?

(OP)
I have a multi-storey concrete building with an essentially square column grid that has band slabs along the column lines in one direction only (i.e. spanning North-South).

I am wondering how stiff do the band slabs have to be in order to consider this slab as a "one-way" slab?

I know one of the criteria for two-way slabs with beams is a ratio of the stiffness of beams in N-S direction vs the beam stiffness in the E-W direction. In this case I do not have any beams in the E-W direction. Can I assume an equivalent beam width for the slab in the E-W direction in order to compare it to the stiffness of the band slab? If so, what "width" should I use?

For those of you with the Canadian CSA A23.3 Concrete Design Handbook, there is a solved example of this type of slab on page 5-21 in the handbook section but they do not prove that the slab meets the two-way criteria.

Here is some specific design information on the slab:
Grid spacing = 8.0m
Band slab thickness = 450mm
Slab thickness = 200mm
Column size = 500mmx500mm
    

RE: One-way or Two-way Concrete Slab?

Is the slab post-tensioned? If the slab was post-tensioned then I would say that it is definitely one-way spanning.

You could compare the stiffness of the 'column' strips in each direction and find that the stiffness of the banded direction would be 5-10 times stiffer than the unbanded direction. On this theory alone I would say the structure would want to behave in a one-way spanning manner. I read a good saying in a strut-tie article which was:

Quote:

It is useful to remember that the structure tries to carry loads as effectively as possible with the least amount of deformation.
Authors were Nori and Tharval.
I think this is very applicable to your situation. There will be some two-way behaviour of the system and concentration of stresses in the column strip in the unbanded direction but I would say that the one-way action is prominant.  

RE: One-way or Two-way Concrete Slab?

Banded slabs are designed as one-way systems.  There is always some two way action, but that is just a bonus.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources