 Analysis button
Material constitutive law for analysis
Reinforced Steel
CivilFEM allows choosing the analysis type in order to define the material behavior that the program will use during the solving process. There are usually two type of analysis available in order to apply on the model: linear and bilinear. Nevertheless, if the EC2 code has been selected in the "Code&Standards" bar, for the reinforced concrete, the option: bilinear temperature dependent; will be available as well.
Linear
The linear elastic model is the most commonly used model to represent typical engineering materials. This model, that showcases a linear relationship between stresses and strains, is represented by Hooke’s Law. The figure below shows that stresses are proportional to strains in a uniaxial tension test. The ratio of stress to strain is the familiar definition of modulus of elasticity (Young’s modulus) of the material.
E (modulus of elasticity) = (axial stress)/(axial strain)
Linear analysis has the characteristic of not limiting the strain while stresses increase.
We could say that a linear diagram does not follow the real material behavior. However, this diagram is very useful if the user wants to perform an analysis in the linear stages of the material and doesn't need a more detailed but slower non-linear calculation.
If the user does not choose a particular analysis type, CivilFEM will apply a linear analysis by default.
Bilinear
Bilinear analysis is a non-linear analysis type, that behaves according to the following diagram.
A non-linear analysis can be applied in such cases as:
When a geometric non-linearity exists.
When a material non-linearity exists.
When a boundary condition non-linearity takes place, such as in cases having contacts, heat transmission...
The non-linear behavior described in the graphic shows that when a steel material has already reached the strain-stress limit, this value can't be surpassed.
That is, if material passes this strain-stress boundary, a plastic fracture will take place.
On the other hand, if bilinear analysis is active for a steel material, reinforced steel or prestressed steel, the properties bar shows the added "Hardening type" option. This utility will apply a different work hardening rule depending on the established option.
The hardening contains three different options: isotropic, kinematics and combined. Further information is detailed in the "work hardening rules" section.
Bilinear temperature dependent
Bilinear temperature analysis is a non-linear analysis type, that behaves according to the following diagram.
This gives the possibility of being more accurate in case of the existence of a thermal load, due to the fact that CivilFEM would fix the stresses in relation to the applied thermal load. That is, depending on the applied thermal load, CivilFEM would take one or another branch of the analysis diagram, or even will interpolate if the temperature is not one of the specified.
Moreover, the table may be changed by the user depending on their preferences or the model requirements. That is, not only the stresses may be modified, but also the Young modulus changing, as a result of that, the strains and the whole amount of stresses for all the temperatures.
The non-linear behavior described in the graphic shows that when a steel material has already reached the strain-stress limit, this value can't be surpassed.
That is, if material passes this strain-stress boundary, a plastic fracture will take place.
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