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  4. Why do Concrete and Diamonds give different results

Why do Concrete and Diamonds give different results

You have made a beam or plate element in Diamonds and ConCrete and you do not get the same results from both programs.


You probably have not made the same assumptions in both programs. To get the same results, you should model the same.

Verify all items in the check list below to obtain the same results. The sequence is important. It has no use comparing reinforcement/ cracked deformation if the elastic results between the software is not the same.

Check list 1: geometry and loads

Geometry Check
Span length
Plate behaviour
A plate in ConCrete is calculate as a beam (= a plate bearing perfectly in one direction).
While in Diamonds multiple plate types are possible. The equivalent icon for a plate bearing in one direction in Diamonds is , or a beam with width 1000m en height equal to the thickness of the plate in Concrete.
Concrete properties
Reinforcement properties
Loads Check
Partial safety factors
Load combinations factors
Chessboard pattern (relevant when beam/ plate has multiple spans).
Diamonds cannot automatically generate a chessboard pattern of the life loads. So If you haven’t entered the chessboard pattern manually in Diamonds, you must turn OFF the chessboard pattern in ConCrete by making the little guys hold hands FOR ALL USED LOADGROUPS.
Eq 6.10 or Eqs 6.10a & 6.10b
Eurocode allows you to generate combinations according to equation 6.10 or 6.10a/b.ConCrete will uses equation 6.10.
In Diamonds you can choose depending on the national annex. So choose equation 6.10 in Diamonds.

>> The internal forces (bending moments, shear force) and elastic deformation are now the same.

Check list 2: elastic analysis & longitudonal reinforcement

Bending moments reduction
Don’t reduce the bending moment near the supports in ConCrete. This feature is not available in Diamonds.
Concrete cover
In Concrete you enter the net cover. Concrete will add 10mm to that to find the gross cover. You enter the gross cover in Diamonds. When you enter 30mm in Concrete, you should enter 40mm in Diamonds.
Design standard
EN 1992-1-1 + NA is used for structures that still need to be build. ENV 1992-1-1 is an old standard. Both give different results.
In Concrete you can change the standard using Preferences > Calculation method.
In Diamonds you can change the standard using Analysis > Concrete standard.
Minimum reinforcement
The minimum longitudonal reinforcement equals As,min,ConCretemin∙b∙d
In Diamonds ρmin is directly linked to a concrete quality with predefined properties. In ConCrete ρmin depends on fck. If you change fck (in this dialog ), you should click on the calculator (in this dialog ) to update ρmin.

>> The longitudinal reinforcement is now the same.

Although small differences are still possible:

  • The stress-strain diagram of concrete is bi-linear in Diamonds, while it is a parabola-rectangle diagram in ConCrete.
  • Diamonds does not redistribute the bending moments (EN 1992-1-1 §5.5) while Concrete does. Therefore peak moments in Diamonds will lead to peak reinforcement, while in Concrete the longitudinal reinforcement is ‘chopped off’.

Check list 3: shear reinforcement

Concrete shear contribution
Set the concrete contribution to shear capacity to 0% in ConCrete. In ENV 1992-1-1 the standard method was used to calculate the stirrups. This method allowed to take the concrete contribution to the shear capacity into account. In EN 1992-1-1 the variable strut inclination method is used where the concrete contribution is neglected. (in concrete parameters window)
Application of the loads
Apply the loads to the lower fibre in ConCrete (in load parameters window).
In Diamonds you can’t choose, it’s always the lower fibre. More info here.

>> The shear reinforcement is now the same.

Check list 4: cracked deformation

Practical reinforcement
Creep coefficient
Make sure the creepfactor for deformation and the creepfactor for stresses are equal.
Load combination for cracking
Diamonds calculates the cracking of the section using the combination SLS RC envelope. Select the same combination in ConCrete (in concrete parameters window).

>> The cracked deformation is now more or less the same. Small differences (<5%) are still possible because the calculation principle in Diamonds is a little different then Diamonds.

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