Eurocode - Calculation of Crack Width (Urgent)

[xkybb]

I am designing a pumping station (water retaining structure) and I found difficulties in complying with the crack width requirement in eurocode based on the forces I obtained from my structural analysis, and I got a few questions regarding the procedures to calculate the design crack width in accordance with the Eurocode BSEN1992-1-1:2004 & BSEN1992-3 & CIRIAC660.

1. According to BSEN1992-3 Cl.7.3.1, If I am designing for a beam (300mmx400mm) in the substructure (tightness class 1, max water depth 3.9m), is that means the allowable crack width of the beam shall be limited to wk1 = 0.16mm (as hd/h = 3.9m/Min(300mm,400mm)= 13). And same shall apply to the column (400x400mm), ( hd/d = 3.9m/400mm = 9.75)?

2. According to Eq.3.13 in CIRIAC660, I could calculate the crack width due to thermal & shrinkage, but shall I combine it with the flexural crack width calculated from Eqt. 7.9 in BSEN1992-1-1:2004 to check against the allowable crack width limit (0.16mm)? Or the design will be OK if the two resulted crack width satisfy the limit individually.

3. According to 7.3.3(2) in Eurocode BSEN1992-1-1:2004, the crack control shall deem to be OK if either the maximum bar diameter or maximum bar spacing are satisfied, and direct calculate of the crack width is not required. But does it only refer to flexural crack width? Shall I still need to calculate and check the thermal & shrinkage crack width if those crack are expected to occur?

Sorry for my poor English and I have attached my design spreadsheet for your checking.

Many Thanks!!!!!!!!!!!

 

[rapt]

If flexural action and restraint effects to shrinkage and creep are both happening at the same time (which is highly likely), then you need to calculate a crack width under the combined loading.

You do not calculate a crack width for each and add them together.

I have found that the tables of bar spacing/size tend to be conservative compared to crack widths calculated by the Eurocode formula.

 

[IDS]

I have found that the tables of bar spacing/size tend to be conservative compared to crack widths calculated by the Eurocode formula.

The Eurocode tables are based on 25 mm cover. For greater cover they are unconservative, especially for small bar diameters and spacing.

Also the tables only go down to 0.2 mm crack width. For 0.16 mm cover you need to do a calculation.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[xkybb]

Thanks for both of your answer. So, can I conclude that:

1. My interruption on Cl.7.3.1 in BSEN1992-3 about the crack width requirement is correct, and the crack width requirement is as strictly required to 0.16mm in my case.

2. The shrinkage and flexural crack width shall be combined to check against the requriement.

3. Other than having a cover of 25mm and crack width requirement greater than 0.2mm, the tables of bar spacing/size is not applicable and calculation of flexural and shrinkage crack width are necessary.

If the above 3 are correct, eurocode requirement seems too difficult to be met as shown in my spreadsheet that I would either have failed in minimum bar spacing (over reinforced) or failed in the crack width (>0.16mm) for my 300x400mm beam. Same happens even I increase the beam size to 400x600 and assume the same loading. It seems so impossible to control the crack width to be under 0.16mm?

Thanks Again

 

[Klitor]

Not sure about your case (post a sketch maybe?) but Walls/slab of an average pumphouse will fall under 1992-3, but not the roof beam

 

[xkybb]

The configuration of my wet well is just a rectangular RC frame with 4 top beams (300x400), 4 columns (400x400, 3.9m height) at the end of the beams, and 4 sides of wall (200mm thk) all connection to a mat foundation of 600mm.

Since the wet well will contain sewage before discharge, therefore it is expected that the sewage depth will be at max. at 3.9m and reach the top beam if the discharge is disable and the sewage is overflow.

Therefore, my understanding is that I need to design my beam under 1992-3, but is it correct?

If not, then does it mean that usually only wall and slab are requried to design under 1992-3