×
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

Concrete Slabs - Center line Cracking

Concrete Slabs - Center line Cracking

Concrete Slabs - Center line Cracking

(OP)
I have been experiencing the same crack pattern in most of my garage slabs. A centre line crack from front to back of garage floor. This is fine, and to be expected. But in some cases, the crack has opened wider than I would like to see (~3mm). This results in return trips a year later to epoxy or caulk the line in for rebar protection.

Beam Analysis

Ive begun to analyze the slab treating like a beam. Is this a correct assumption of what is going on? If so, the extreme cases to me seem a rebar problem. Perhaps my finishers are leaving the rebar low, or there is insufficient area of steel in the slab to begin with.

Can anyone carry out the area of steel calculation necessary for this design moment? The slab here is 20' wide, 22' long, 4" thick. I appreciate any help, thanks for weighing in.

Chad

RE: Concrete Slabs - Center line Cracking

(OP)
And yes, a centre line expansion joint is a solution I have worked with. But I would like to ease the stress on that centre crack.

RE: Concrete Slabs - Center line Cracking

No, it is not "like a beam". In a slab on ground, the force is applied as direct tension to the slab as the concrete shrinks, and the subgrade restrains this shrinkage. There are two ways of dealing with this type of cracking: 1) Use a lot of reinforcement, say 0.5%AG, which doesn't prevent the cracking, but controls the width of cracks; or 2) Provide control joints, which are also cracks, but nice and straight. The second solution is usually used in things like garages.

RE: Concrete Slabs - Center line Cracking

Cracking of concrete for some reason scares people. How about cross ways half way into the garage? I usually call for joints there, because shrinkage is expected. Fill the cracks and they look even more obvious.

What do you spec for slump Sacks per yard? High slump and low cement content both contribute to increased shrinkage per unit length.

RE: Concrete Slabs - Center line Cracking

You have a 20'x22' slab, 4" thick. Rule of thumb says you should have joints spaced at between 8 and 12 feet. If your crack occurred at the middle of the 20' width....it's right on target!

As OG says, put joints in cross pattern and you won't have issue again.

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