effect of cracking in tension region

[oneintheeye]

Hi, how would you approach the analysis of a slab where a crack exists through the centre of the span in one direction. The crack I would say is over 0.3mm although it is hard to say at the moment. How does this effect the analyis? If the depth is not as far as the reinforcement?

 

[cntw1953]

If this is a shallow crack on tension side of slab, it shouldn't affecting the analysis, nor strength. However, find out the cause of cracking, then do proper repair should be in the order.

 

[ishvaaag]

As a last resort, if after your previous investigation you estimate the design can provide a ductile behaviour to the limit state, you can load it to a level equivalent to that of use to ensure by this proof the behaviour will remain sound.

 

[hokie66]

Flexural cracks occur in the bottom at centre span. Analysis allows for flexural cracking. The tension is carried by the concrete. So a flexural crack does not change your analysis. Are you sure it is a flexural crack rather than a direct tension restraint crack which would extend full depth?

 

[apsix]

Hokie meant to say 'The tension is carried by the reinforcement.'

As others have said, the presence of a 0.3mm crack is not normally a cause for concern

What is the reason for the analysis, are there other concerns such as excessive deflection?

 

[rapt]

Actually a .3mm crack would not be a problem as apsix said, but only if the slab is fully loaded.

You said that the crack is only on the tension face so it is probably not restraint. If the load on the slab is significantly under the design laod I would be checking it to make sure there is sufficient reinforcement in the right places. Normally, the reinforcenment required for strength will give a crack width of about .3mm if the cover is not excessive and if there is not a lot of restraint to shortening.

If the slab is not fully loaded, I would start to look at the design in terms of both strength and crack control

 

[hokie66]

Wow, thanks for correcting my post, apsix. I think I meant to say "The tension is NOT carried by the concrete."

 

[oneintheeye]

don't worry I spotted the deliberate error! The floor is going to be loaded more heavily than currently

 

[rowingengineer]

Can we get some more information? Do you know reo size and spacing? How long is the crack? How long has it been visible? Two-way slab or one way? Was it a one-way design for a two-way span? Is it a transfer slab? How do you know the depth of crack? Got a photo?

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[rapt]

herewegothen,

In that case, you need to determine if strength is ok. If there is a load path to get the loads to the supports.

Then you need to check to see if the reinforcement has been placed where the elastic tension stresses occur. If not, it is still possible that you have adequate strength but bot crack control.

Without more information as requested by rowingengineer, we cannot comment further.