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ClarkNielsen concrete forces
[Fc(T) and Fc(B)]
The basis of the ClarkNielsen
calculation is ultimate limit state yield criterion.
Accordingly the tensile strength of concrete is ignored
and the calculations primarily relate to reinforcement in
tension. It is assumed that the concrete cracks and the
principal stress in the concrete is zero perpendicular to
those cracks. Stress in the concrete parallel to the cracks
(Fc) may be calculated in order to enable a check against
crushing strength of concrete. It is not normally necessary
to derive the direction of this stress.
In LUSAS
Modeller, top and bottom stresses are calculated [Fc(T) and
Fc(B)] assuming a doubly reinforced slab. The equivalent
sandwich analogy is used to determine Fc(T) and Fc(B)
for a stress field which includes both moments and inplane
forces. However the calculation of Fc(T) and Fc(B) is not
available for angles of reinforcement other than orthogonal.
Where the concrete is uncracked (in compression in the
reinforcement directions), Fc has no literal meaning, being
"the concrete stress parallel to the
cracks". In this instance the second principle
stress (most compressive) is reported. This is as
described in the procedure outlined on the ClarkNielsen
calculation page.
In the notes under the Results Table (pg 402 etc) it is
stated "If a nonzero Kfactor is specified, Fc(T) and Fc(B)
are not available". This should read "nonunity".
In any case the parameter is unavailable for alteration in the
Modeller interface when Fc(T) or Fc(B) are selected.
Other WoodArmer
related topics.
