FEM-Design is the most powerful FEM software for Concrete Design on the market. Design your beams, columns walls and slabs and even your connections in FEM-Design according to Eurocode with several NA also included (Danish, Swedish, Norwegian, Romanian, UK, Hungarian, Finish, Polish, Estonian and German).
The user can opt for which load combination should be calculated (Calc) and what type of analysis should be performed (non-linear elastic calculation (NLE), plastic analysis (PL), Non-linear soil (NLS), cracked-section analysis (Cr), second order analysis (2nd), imperfection analysis (Im)).
- 1 Buckling improvements
- 2 Concealed bar
- 3 RC Bar Design
- 4 RC Shell Design
- 5 RC Punching Design
- 6 Cracked Section Analysis
1. Buckling improvements
Automatic calculation of beta buckling factors and other improvements in FEM-Design. → Read more...
2. Concealed bar
This feature is typically used for walls. Create bar-reinforcement inside your shell structure, and use the design code for bar design.
A concealed bar allows for designing certain parts of a shell as a bar. For example, a wall region over a door opening can be considered as a concealed beam. → Read more...
3. RC Bar Design
- The RC Design module can do both code check and reinforcement auto design.
- Bars can be designed for both 1st and 2nd order analysis. The nominal stiffness method and Nominal curvature method are both available.
- Utilization for the Section, stirrups, concrete, torsional reinforcement, and crack widths are calculated.
- The sections can be selected from the section database, or it can be customized in the section editor.
- As output, all design formulas are displayed, and design calculations are shown.
4. RC Shell Design
Both Walls and Plates are designed in the RC Module.
Choose between single or double-layer reinforcement. Check the crack widths and the buckling resistance of the shells.
Punching capacity is calculated, and auto design is available for punching reinforcement design.
All equations and calculations used, can be visualized in each node. Again, this is not a black box. → Read more...
5. RC Punching Design
Punching without shear reinforcement
A concrete compression check on u0 is made according to 6.4.5 (6.53).
A concrete shear check on u1 is made for a capacity calculated according to 6.4.4 (6.47).
Punching with shear reinforcement
A concrete compression check on u0 is made according to 6.4.5 (6.53).
Reinforcement is calculated with regard to critical perimeters u1, u2, ... u.nReinf according to 6.4.5 (6.52 ).
(ui are control perimeters above the reinforced region, the distance between them is 'Perimeter distance', defined in the calculation parameter).
A concrete shear check on out is made for a capacity calculated according to 6.4.4 (6.47) (u.out is either the first perimeter that does not need reinforcement or if it is not found, the perimeter that is k deff distance from the outer perimeter of the reinforcement). → Read more...
6. Cracked Section Analysis
Internal forces are calculated according to the occurrence of cracks.
Through iterations, the load is applied, and crack locations are calculated. The stiffnesses in the cracked nodes are decreased for the next calculation.
This method gives internal forces in the range between linear elastic and plastic.
This iteration method can be selected to load combinations, individually.
In FEM-Design a crack analysis technique is applied, where an iteration mechanism is calculating the effect of the cracks.
As the crack analysis is a non-linear calculation the principle of superposition is not true. By this fact, the crack analysis is not applicable for load groups and the calculation has to be executed for every single combination. Generally, the iteration is loading the structure in load steps and modifies the stiffness of it in every step as more and more cracks occur during the loading process. The stiffness of the plate will be decreased only in the direction that is perpendicular to the crack lines, in the direction of the crack lines the stiffness remains the same as for the unracked state. The key to the calculation is the way the crack direction is calculated at a certain point. Dr. Ferenc Németh from the Technical University of Budapest has invented a method for this which is based on experiments. The cracked stiffness calculation is based on a conventional cross-section modulus calculation of the second crack state which is combined with a Eurocode like crack distribution calculation (to consider the effect of uncracked parts of the plate between two cracks). The calculation for one combination is performed in the following steps:
- Loading the structure with loads of the combination and performing a linear calculation of the internal forces.
- Calculating the moment that causes cracks in the structure at every point of the plate. This value is calculated by the tensional strength (limit stress) of the plate’s concrete material, the reinforcements are not taken into account at this point.
- Searching for the place where the ratio of the crack moment and the actual (linear) moment has the smallest value. This value will describe the initial level of the load for the iteration. The size of a load step is calculated by user-defined values.
- In the first step, the initial load acts and is then increased by the calculated load steps.
- In every step is calculated whether the plate is cracked or not at a certain point (comparing the smallest principal moment to the crack moment of the plate). If the plate is cracked the direction of the crack is calculated and the stiffness of the cracked section. The element where the crack occurred then will have reduced stiffness. In the next load step, it will change the behavior of the plate as the crack does in the real structure.
- When the full load is applied to the structure the calculation is continued with full load level to consider cracks occurring in the last load step and to have a stable result. This phase is called the final iteration.
The final iteration is finished when the differences in the sum of the movements are less than a certain error percentage between two steps. The initial error percentage is 1% compared to the previous step, but this value could be adjusted. → Read more...
We are Scandinavian. We are PRE-CAST!
FEM-Design has all the tools you need to analyze precast concrete structures.
Edge connections with an 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
Compression and tension behaviour of connections (and supports) can be set separately, and by components.
The nonlinear behaviour of supports and connections can be controlled by one signed component. It means, if the force in the connection/support happens to act in this selected direction, all spring constants will be set to 0.
The program calculates the forces and/or moments in the connection objects by direction component and their resultants.
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 dialogue. 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.
Based on a model in FEM-Design, our new software PREFAB Print automatically generates a report of the vertical and horizontal load takedown and stability check for an entire building consisting of concrete elements.
The report is made as an interactive PDF file with clickable objects containing information regarding wall geometry and wall material as well as load distribution and EuroCode verification checks.
To ensure a smooth transition between FEM-Design and PREFAB Print please make sure to follow our modelling guidelines in the video below/above. → Read more...
1. Coordinate system in edge connections
PREFAB-Print imports the results of each edge connection in FEM-Design and alters the results in both the x- and y-direction. See fig.
The x-direction is positioned along the direction of the edge connection and the y-direction is perpendicular to the edge connection in the plane of the element. Forces in the z-direction, which is perpendicular to the plane of the element, are not shown in PREFAB-Print.
2. Force distribution
2.1. Default force distribution PREFAB-Print uses the average result for each finite element in FEM-Design which is the value shown by the default force distribution, “Constant by element”. See fig. 2.
2.2. Force distribution in the y-direction
Finite elements with an average force less than 10 % of the average force in the finite element with the highest value are neglected. See fig. 3.
If the neglected area is between two separated areas, the neglected area is considered as a simply supported beam where the reactions are found by static equilibrium. If the neglected area is positioned at the end of an edge connection, it is considered as a cantilever beam and therefore a force and a moment is added to the separated area next to it. The remaining areas are now separated and considered as individual areas. This redistribution of forces in each edge connection is done to prevent forces in openings and tiny areas and does not alter the state of equilibrium of the elements since the size and position of the resultant force is unchanged. For each separated area, the eccentricity is determined by the formula e = M/N, and the size of the eccentricity determines the appearance of the force distribution.
The force distribution can be chosen as elastic or plastic in the “Calculation settings” in PREFAB-Print.
For the elastic distribution, a positive value of the eccentricity results in a peak value to the right, whereas a negative value results in a peak value to the left. See fig. 5.
Regarding the plastic distribution, a positive value “pushes” the distribution to the right, and a negative value pushes it to the left. See fig. 6.
Force distribution in the x-direction
Forces in the x-direction, regarding sliding and shear joints, are distributed in one of the following ways:
1. If the detach y’ tension property has been selected in the edge connection properties menu, see fig. 7, forces are distributed only in compression zones, and with a value relative to the resultant compression force. See fig. 8.
2. If, however the detach property has not been selected, forces are distributed evenly across the entire edge connection. See fig. 8.
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The Dynamics module include Footfall analysis, Seismic analysis and Stability analysis.
1. Footfall analysis
This calculation method allows for checking the structure's response for an exciting vibration. The calculation can be started in Analysis/Calculations/Footfall analysis. The settings for the calculation can be found under the Setup.... Here one can select one of the three available methods:
- Self excitation
- Full excitation
- Rhythmic crowd load (Load case shall be selected with this method)
Watch Webinar about Footfall Analysis in FEM-Design.
2. Seismic analysis
FEM-Design offers the seismic analysis in two of its modules: FEM-Design 3D Structure and FEM-Design Frame.
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 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).
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 the torsional effect was taken into consideration during the calculation.
Watch Webinar about Seismic analysis in FEM-Design.
3. Stability analysis
At the description of the second-order theory, it was pointed out that the resultant stiffness of the system depends on the normal force distribution. In case of linear elastic structures the geometrical stiffness matrix is a linear function of normal forces and consequently of loads:
KG (λN) = λ KG
The structure loses its loadbearing capability if the normal forces decrease the stiffness to zero, i.e. the resultant stiffness matrix becomes singular:
det [K + λ KG (N)] = 0
It is an eigenvalue calculation problem, and the smallest λ eigenvalue is the critical load parameter.
The calculation has to be performed in two steps. First, the normal forces of the elements have to be calculated by using the K matrix. In the second step KG and the λ parameter can be determined. The critical load is the product of the load and the λ parameter. The above-mentioned eigenvalue problem is solved by the so-called Lanczos method in FEM-Design. The results of the calculations are as many buckling shapes as the user required and the matching λ critical load parameters.
In the example below, the eH value of the first shape is 89%, which means it is probably a global buckling shape with horizontal displacement. Displaying the result (see the leftmost inset above) and examining the buckling shape shows that this is indeed a case of global buckling with the horizontal displacement of the frame’s top. The same structure’s second shape possesses a very high rZ value (99%), meaning this almost certainly is a global torsional buckling shape (shown in the middle inset). The fourth shape’s eH, eV and rZ values are significantly lower, which implies it is a local buckling shape. As the rightmost inset shows, the assumption was correct (local buckling of both columns).
Watch a basic course on Stability Analysis in FEM-Design
Documentation in FEM-Design
This chapter summarizes the documentation possibilities of FEM-Design projects, models and results. It introduces the printing and listing (summary tables) functions and the automatic documentation based on templates (Documentation module). → Read more...