About the skulls

Afther the reinforcement calculation , you get the following message:

[NL]: De doorsnede van sommige elementen is ontoereikend.

[FR]: La section de quelques éléments est insuffisante.

[ES]: La sección de algunos elementos es insufieciente.

How to handle the skulls

What causes the skulls?

• This message is given when the theoretical reinforcement calculated by Diamonds, is more than the maximum allowed reinforcement percentage¹ (usually 4% of the concrete section) imposed by the selected concrete standard.
• Click ‘OK’ to close the error.
• A skull will be shown in (the centre of gravity of) each element with a problem.
  

  Example: skull in a line element	Example: skull in a surface element

  The position of the skull is thus not representative for the position of the problem. Although in a surface element, you can see were the reinforcement could not be calculated by the whites zones. More on that later in this article.
  

• While looking at a reinforcement result, double click an element to see the cause of the problem.
  Possible causes are:
  • ULS (Ultimate Limit State)
    Too much reinforcement required to take axial force N and/or bending moment M in ULS.
  • SLS (Service Limit State)
    Too much reinforcement required to limit the concrete and steel stresses based on the internal forces in SLS.
  • Shear and/or torsion
    Too much reinforcement required to take the shear V and/or torsional force Mx in ULS.
  • Buckling
    Too much reinforcement required to meet the requirements for buckling according to EN 1992-1-1 §5.8.8

Solution

	skull in a line element	skull in a surface element
ULS or SLS	Increase section, choose better concrete quality.	Determine if the skull is a peak-related problem or a field related problem (see below).
Shear and/or torsion	Check if the correct internal boundary conditions between beams and plates are defined. If so, and the element is not sufficiant: increase section, choose better concrete quality	Diamonds doesn’t verify shear/ torsion in surface elements
Buckling	When a beam and plate are poured together, the beam is often placed eccentric. The eccentricity will cause axial forces (compression) in the beam. Since Diamonds doesn’t know they will be poured together, and that the beam can’t buckle, he’ll perform a buckling check on it, causing high reinforcement. To turn off the buckling check for this type of beam, select the beam, click on in the geometry configuration . Unselect the boxes before the buckling lengths. If a column is not sufficiant: check if buckling length is well defined. If so: increase section, choose better concrete quality	Diamonds doesn’t verify buckling in surface elements

Note: sometimes it is interesting to know the results behind the skull (to see how much exceedance there is) or to even hide the skull (if the skulls result from peaks). Read here how to do so.

Peak-related versus a field related problem

In order to judge how to deal with skulls in surface elements, you need to know what the cause of the skull is. Or by extension: where are the white zones located? In a peak-sensitive area or in the middle of the plate?

Peak related	Field related
If the skull is peak related, the white zone has a radius of one mesh triangle. There are a few typical places where peak results intend to occur: Above point supports Where a line support suddenly ends Inner corners	If the skull is field related, the white zone has a radius of more than one mesh triangle.
This article gives more information on what peaks are, how they arise and how to handle them.	When a surface-elements contains a fiels-related skull, the only solution is to increase the cross-section or material.

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