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Analysis

Analysis types in FEM-Design

Depending on the current FEM-Design module you can do different calculations: displacement, internal forces, stresses, stability, imperfections, stability analysis, eigenfrequencies and/or seismic analysis. Some extra settings such as cracked-section analysis, non-linear behaviour etc. are also available for certain modules.

 

Overall features Advanced features

 

Finite element mesh in FEM-Design

FEM-Design offers a fully automatic finite element mesh generation by using optimized (factory default) or custom mesh settings.

Automatic finite element mesh generation

The program generates mesh with elements having average element size optimized for the structure and its environment (supports and loads). The process can contain automatic element refinement and peak smoothing algorithm according to the settings. The generated mesh can be modified with special easy-to use edit and modify functions.

Calculation modes of average size of 2D elements

Finite elemnt types:

Depending on the FEM-Design version (FEM-Design Plate / Wall, 3D Structure / Frame), the engine uses the following lfinite elements:

Element type Finite elements
Line elements Beam and truss
2D shell elements 4-, 8-, 9- nodes rectangular elements
3-, 6- nodes triangular elements
3D volume elements 4-, 6-, 8-, 10-, 17-, 27- nodes elements

Line elements mesh   2D mesh in shell structure  2D mesh in shell structure

3D mesh in Soil module
 

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Peak smoothing in FEM-Design

One of the most unique features of FEM-Design is the Peak smoothing that makes it possible to avoid the singularity problems.

Singularity problem

As an effect of the mesh refinement the calculated results are converging to the theoretical solution. The problem is that at certain places we get infinite inner forces according to the theory, so the inner forces increase each time by refining the mesh. These places could be: point supports, end points of edge supports, vertices of surface supports, end points of beams and columns, end points of intersection lines of adjoining surfaces, point loads, end points of line loads, vertices of surface loads etc. In practice, usually, the singularity problem occurs at supports because they heavily influence the inner forces (e.g. negative moments) in ratio.

 

Peak smoothing algorithm (modified inner force diagram)

Peak smoothing region

Program defines peak smoothing regions to solve the possible singularity problems. Basically, these regions are the active zones in the environment of the singularity, where the inner forces change substantially as a result of mesh refinement. Peak smoothing regions can be generated automatically by the mesh generator or calculation processes. Automatic generation always results circular peak smoothing regions with centre points placed in the location of the singularity. The radius of a circular smoothing region depends on the geometry of singularity locations.

Examples for peak smoothing regions by different element-plate connection

 

Internal force “graph” and “section” diagrams after using peak smoothing algorithm

 

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Diaphragm

All of the available calculation in FEM-Design can be performed with diaphragms or without diaphragms if the diaphragms were defined in the model. By the different types of calculation the results will be analogous with the adjusted option.

The behaviour of the diaphragm  The behaviour of the membrane rigid diaphragm

The usage of the diaphragm tool is optimal by storeys of high-rise buildings but the diaphragm modelling tool is also useful by other engineering problems. The diaphragms could be several regions, but they must be horizontal. The shapes of the diaphragms can be arbitrary and they can be separated also on the specific storey levels. There can be more diaphram regions on the same horizontal level and they will work independently from each other. 

There are two different options for the diaphragm calculation:

  • Rigid membrane
  • Fully rigid


Also check:

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We are Scandinavian. We are PRE-CAST!

FEM-Design has all the tools you need to analyze precast concrete structures.

Edge connections with elastic and plastic definition

The key to good analysis results in precast concrete lies in the connections. It is easy to model the connections both elastic and plastic. In FEM-Design all connection components (but also supports) can be set to:

  • “infinite” rigid: blocked motion/rotation
  • “free”: released motion/rotation
  • semi-rigid: given stiffness value (spring) against motion/rotation


Non-linear behavior

Compression and tension behavior of connections (and supports) can be set separately, and by components.

Detach

The nonlinear behavior of supports and connections can be controlled by one signed component. It means, if the force in the connection / support happen to act in this selected direction, all spring constants will be set to 0.

Edge connection definition in FEM-Design   Detach function in FEM-Design

Resultant forces

The program calculates the forces and/or moments in the connection objects by direction component, and their resultants.

Connection forces by connection type   The resultants for edge connection and line-line connection forces

Local stability

Overturning of walls

With the help of resultants of edge connections, wall’s overturning can be examined as below.

Sliding of edge connections

The result is the ratio of the design force and the friction capacity. The friction factor can be set in the edge connection dialog. Edge connection’s sliding is calculated in each edge connection separately by comparing the x’ component of the connection force as design force, and the limit force calculated by the y’ components of the connection forces and the friction coefficient of the edge connection.

Overturning of walls result Sliding of edge connections result

 

Seismic analysis in FEM-Design

FEM-Design offers the seismic analysis in two of its modules: FEM-Design 3D Structure and FEM-Design Frame.

Methods

 

FEM-Design offers the following methods of seismic calculations according to Eurocode 8.

 

  • Modal response spectrum analysis (“Modal analysis”)
  • Linear shape method (Static, linear shape)
  • Mode shape method (Static, mode shape)

Seismic loads

Seismic loads are taken into account according to the Response Spectrum Analysis method of Eurocode 8 or Turkish seismic code.  Only the response spectrum and some additional parameters have to be defined as Seismic load. Required spectrums can be defined with the Seismic load by using standard spectra (automatic) or by manual definition (unique).

Parameters and automatic generation of horizontal spectra

Results

Besides displacements, reactions, connection forces and internal forces, the program calculates the Equivalent loads and the “Base shear force”. Results can be displayed by vibration shape (selected at calculation settings), from torsional effect, from sums by direction and from the total sum (Seismic max). If equivalent loads are displayed, also the “base shear force” appears on screen (in grey color). Torsional moment effect on the whole structure can also be displayed, if torsional effect was taken into consideration during calculation.

Results of Seismic analysis