Crack Width Check Eurocode

[maj.rentung]

Hi Sir,

I have carry out crack width check  for a column using Eurocode and the crack width is 1.05mm much greater as compared to BS 5400 around 0.22mm although with same loadings.

I failed to figure out what I've done wrong.

I did not expect the different is as much as mentioned.

I  attached the ASBD files for your review and kindly advise.

Thank you

Regards,

Lemang Rentung

[dave_geeves · Accepted solution]

Hi,

Thanks for attaching your data file - it helps a great deal.  I have always had difficulty in understanding the crack width calculations for general sections.  The rules in both Eurocodes and BS5400 are fine for standard sections with no biaxial bending, but when you have a non standard shape with multiple layers of reinforcement where biaxial bending provides a neutral axis that is not parallel with the layers of reinforcement or concrete face, the interpretation of the rules is a little vague.  I guess that this is the reason why ASBD provides the capability of calculation the crack width for selected bars and providing an option for using "Extreme faces only" option in the calculations.

If you don't select bars the program looks at all bars in the tension area and has to decide which other bars to use to define the spacing.  By selecting just two bars (potting a window around them in the graphics window) the calculations are done for both bars in turn, using the other bar to determine the spacing, and the worst case is shown.  If you do this for the same bars in each code you will get a better comparison.

I also notice that you are using Eurocodes with no national annex defined.  In this case the cover used in equation 7.11 is always the actual cover to the bar.  For Eurocodes with UK national annex the cover is the lessor of the actual cover and a value of cnom (defined in the NA) and is set in the parameters form for serviceability calculations.  This them makes the calculations as a whole more in line with BS5400.  This seems to be set to 35mm in your file.

When I do this I get a comparison of 0.366mm for Eurocodes and 0.205mm for BS5400  but I notice that the amount of reinforcement is very different between the two files you supplied.

Eurocodes + UKNA

BS5400

I hope this helps and if this has answered your questions than please mark my reply as a solution so that others may benefit.  Thanks

Kind regards

Dave Geeves

[maj.rentung]

Hi Dave,

Thank you for your reply. It helps to clarify matters on the crack width issue. Sorry for wrong the attachments. I manage to check the crack width as per your recommendation with similar reinforcement arrangement & design value for both using BS5400 & EC2 and found the result from EC2 now is acceptable (more logical).

Thank you