The structural analysis software RFEM 6 is the basis of a modular software system. The main program RFEM 6 is used to define structures, materials, and loads of planar and spatial structural systems consisting of plates, walls, shells, and members. The program also allows you to create combined structures as well as to model solid and contact elements.
RSTAB 9 is a powerful analysis and design software for 3D beam, frame, or truss structure calculations, reflecting the current state of the art and helping structural engineers meet requirements in modern civil engineering.
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In order to consider the support of the structure in the soil correctly, it is necessary to excavate the soil accordingly or to provide the solid with a corresponding opening.
The specific soil material models have a variable stiffness that depends, among other things, on the prevailing stress level.
In the analysis of a single load case, this is only impressed on the structure and the soil. No stress level from other loads is taken into account, which might be necessary to obtain and use the correct soil stiffness from the soil material model.
The load case of a live load, for example, will result in different stiffnesses and thus deformations,if it is applied within a load combination on a structure that is already subjected to the soil weight as well as the structural weight and construction load,than it would result if setting it as the "first/single" load, which would be done in the analysis of the load case.
Therefore, it does not make sense to analyze the soil with the specific soil material models subjected to the individual loads / load cases if at least the always prevailing soil self-weight is not taken into account.
Please note that in the first "Main" tab of the Base data, it is necessary to select both the "3D" and "Solids" types of models as the main objects to activate. As soon as you perform these settings, as shown in the image below, you will be able to use the add-on and activate it then.
In the dialog box of structural analysis settings, you can find the "Equilibrium for undeformed structure" checkbox under Options II (Image 01). If this is active, the structure is analyzed with the deformation reset to 0.
In the following, you can see an example of the result of the primary stress state determination; that is, the analysis of a soil massif subjected to its own weight. In Construction Stage 2, the "Equilibrium for undeformed structure" option is activated in the structural analysis settings, compared to Construction Stage 1 with the inactive option.The results are compared in Image 02.
It becomes clear that the stress state in the structures is the same, but when this option is activated, the deformations are reset to 0.
If no angle can be defined in the "Rotation" column, there is an isotropic material model selected for the material, where stiffnesses are identical in all directions and it is not necessary to define an angle.
If you use materials with anisotropic behavior (for example, timber), it is necessary to ensure that the "Orthotropic | Linear Elastic (Surfaces)" material model is selected.
Note: The "Orthotropic | Timber | Linear Elastic (Surfaces)" material model cannot be currently used in combination with the "Layers" thickness type.
As soon as switching to the orthotropic material model, the individual layers can be rotated accordingly.
Masses can be neglected in the modal analysis settings.
It is possible to neglect masses in all fixed nodal supports and line supports, or to create a selection of the individual objects.
To use numerical methods, such as FEM, in geotechnical engineering, it is reasonable to set the cohesion as not equal to zero. Therefore, a small cohesion between 0.5 and 1.0 kN/m² can be applied even for non-cohesive soils.
This is not possible in RFEM 5 or the RF‑STAGES add-on module. However, it is possible in the new program generation. In the Construction Stage Analysis add-on for RFEM 6, you can now modify the properties of structural elements.
The main programs RFEM 6 and RSTAB 9 are distinguished by their clarity. The entire input in the program is set up in such a way that you always obtain a clear result for each calculation task. The design of objects is organized in a similar way. In the input, the program shows the necessary properties for each design object, including the corresponding loads, and outputs a clear result for this object after the analysis.
If you want to determine your own design results for the entire model for different load levels, the "Construction Stages Analysis (CSA)" add-on provides a solution. In addition to the basic simulation of the construction process (the object rise), the program also allows for parallel simulation of models with a constant number of objects. In this special case, the base model is internally juxtaposed several times, and can thus be transferred to the design with different loads.
To do this, proceed as follows:
In the modal analysis settings, you can set the minimum axial strain for cables and membranes in order to apply an initial prestress to the objects and thus improve the convergence of the calculation. The initial prestress is applied to the objects in a simplified approach.
If you compare this setting with a surface load of the Axial Strain load type, you should pay attention to the fact that the two approaches differ. With the surface load, you perform a calculation in such a way that the actual prestress can deviate from the specified prestress. The calculation also takes into account other boundary conditions, such as the Poisson's ratio of the material.
You can easily check this if you vary the Poisson's ratio of the material. A Poisson's ratio other than 0 causes the deformation to interact in the x- and y-directions of the surface, which no longer results in a constant stress/strain over the entire surface.
If the Poisson's ratio is 0, you obtain the same results.