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A new capability within RFEM 6 when designing concrete columns is being able to generate the moment interaction diagram according to the ACI 318-19 [1]. When designing reinforced concrete members, the moment interaction diagram is an essential tool. The moment interaction diagram represents the relationship between the bending moment and axial force at any given point along a reinforced member. Valuable information is shown visually like strength and how the concrete behaves under different loading conditions.
Nodal releases are special objects in RFEM 6 that allow structural decoupling of objects connected to a node. The release is controlled by the release type conditions, which may also have nonlinear properties. This article will show the definition of nodal releases in a practical example.
A standard scenario in timber member construction is the ability to connect smaller members by means of bearing on a larger girder member. Additionally, member end conditions may include a similar situation where the beam is bearing on a support type. In either scenario, the beam must be designed to consider the bearing capacity perpendicular to the grain according to NDS 2018 Sec. 3.10.2 and CSA O86:19 Clauses 6.5.6 and 7.5.9. In general structural design software, it is typically not possible to carry out this full design check, as the bearing area is unknown. However, in the new generation RFEM 6 and Timber Design add-on, the added 'design supports' feature now allows users to comply with the NDS and CSA bearing perpendicular to the grain design checks.
Given that realistic determination of the soil conditions significantly influences the quality of the structural analysis of buildings, the Geotechnical Analysis add-on is offered in RFEM 6 to determine the soil body to be analyzed.
The way to provide data obtained from field tests in the add-on and use the properties from soil samples to determine the soil massifs of interest was discussed in Knowledge Base article “Creation of the Soil Body from Soil Samples in RFEM 6”. This article, on the other hand, will discuss the procedure to calculate settlements and soil pressures for a reinforced concrete building.
The quality of the structural analysis of buildings is significantly improved when the soil conditions are considered as realistically as possible. In RFEM 6, you can realistically determine the soil body to be analyzed with the help of the Geotechnical Analysis add-on. This add-on can be activated in the model’s Base Data as shown in Image 01.
To perform deflection analysis in the right manner, it is important to “inform” the program about the exact support conditions of the element of interest. The definition of design supports in RFEM 6 will be shown for a reinforced concrete member set.
This article describes how a flat slab of a residential building is modeled in RFEM 6 and designed according to Eurocode 2. The plate is 24 cm thick and is supported by 45/45/300 cm columns at distances of 6.75 m in both the X and Y directions (Image 1). The columns are modeled as elastic nodal supports by determining the spring stiffness based on the boundary conditions (Image 2). C35/45 concrete and B 500 S (A) reinforcing steel are selected as the materials for the design.
RFEM 6 includes the Form-Finding add-on to determine the equilibrium shapes of surface models subjected to tension and members subjected to axial forces. Activate this add-on in the model's Base Data and use it to find the geometric position in which the prestress of lightweight structures is in equilibrium with the existing boundary conditions.
In order to create a surface model with failing supports close to reality, an option called "Failure if contact perpendicular to surfaces failed" is available in RFEM 5 for contact solids under "Contact Parallel to Surfaces".
Temporary structures, such as scaffolding or props, are versatile structures that can be adapted very well to different geometric conditions.
A member's boundary conditions decisively influence the elastic critical moment for lateral-torsional buckling Mcr. The program uses a planar model with four degrees of freedom for its determination. The corresponding coefficients kz and kw can be defined individually for standard-compliant cross-sections. This allows you to describe the degrees of freedom available at both member ends due to the support conditions.
In RF-/STEEL EC3, sets of members are calculated according to the General Method (EN 1993-1-1, Cl. 6.3.4) together with the stability analysis. To do this, it is necessary to determine the correct support conditions for the equivalent structure with four degrees of freedom. In most 3D models today, you can quickly lose track of the location of a set of members in the system.
In the case of using slow‑curing concrete (usually for thick components), you can reduce the calculated minimum reinforcement by a factor of 0.85 to apply the load due to restraint, according to EN 1992‑1‑1, Section 7.3.2. However, a precondition for reduction is that the characteristic value of the strength development r = fcm2 / fcm28 does not exceed 0.3. Other key requirements for the application of this reinforcement reduction are specified explicitly in the final planning documents.
For automatic load case combination in RFEM and RSTAB, you have to enter the possible interaction of load cases. In addition to the simultaneous or alternative occurrence of all load cases of an action, an option for different combination conditions is possible.
In the RF-GLASS add-on module, 3D rendering is implemented to facilitate the definition of the support conditions. This interactive graphical visualization facilitates the input and control of line and nodal supports. However, the schematic display can also be selected, if necessary.
When calculating foundations according to EC 7 or EC 2, different foundation types or sizes are usually used in one object. However, boundary conditions like the soil parameters, the materials for foundations, concrete covers, and the load combinations selected for design remain the same for all foundations, as a rule.
You can use the elastic support option to avoid singularities due to a fixed nodal support in RFEM. This can be defined directly in the dialog box of the nodal support as a column in Z. It is necessary to take into account the geometry of the column, the material, and the support conditions. Here, we want to look at the option of modeling the column as a surface foundation.
In EN 1993-1-1, the General Method was introduced as a design format for stability analyses that can be applied to planar systems with arbitrary boundary conditions and variable structural height. The design checks can be performed for loading in the main load-bearing plane and simultaneous compression. The stability cases of lateral-torsional buckling and flexural buckling are analyzed from the main supporting plane; that is, about the weak component axis. Therefore, the issue often arises as to how to design, in this context, flexural buckling in the main load-bearing plane.
When using the RF‑GLASS add‑on module, you can define just the geometry in the main program, as well as the load situation of the structural component to be designed. The respective support conditions and all further design-relevant definitions (for example, the layer structure and support conditions), can be further specified in RF‑GLASS.
- 000487
- Modeling | Structure
- RFEM 5
-
- RF-STEEL 5
- RF-STEEL AISC 5
- RF-STEEL AS 5
- RF-STEEL BS 5
- RF-STEEL CSA 5
- RF-STEEL EC3 5
- RF-STEEL GB 5
- RF-STEEL HK 5
- RF-STEEL IS 5
- RF-STEEL NBR 5
- RF-STEEL NTC-DF 5
- RF-STEEL SANS 5
- RF-STEEL SIA 5
- RF-STEEL SP 5
- RF-ALUMINUM 5
- RF-ALUMINUM ADM 5
- RSTAB 8
- STEEL 8
- STEEL AISC 8
- STEEL AS 8
- STEEL BS 8
- STEEL CSA 8
- STEEL EC3 8
- STEEL GB 8
- STEEL HK 8
- STEEL IS 8
- STEEL NBR 8
- STEEL NTC-DF 8
- STEEL SANS 8
- STEEL SIA 8
- STEEL SP 8
- ALUMINUM 8
- ALUMINUM ADM 8
- Steel Structures
- Process Manufacturing Plants
- Stairway Structures
- Structural Analysis & Design
- Eurocode 3
- ANSI/AISC 360
- SIA 263
- IS 800
- BS 5950-1
- GB 50017
- CSA S16
- AS 4100
- SP 16.13330
- SANS 10162-1
- ABNT NBR 800
- ADM
The support conditions of a beam subjected to bending are essential for its resistance to lateral-torsional buckling. If, for example, a single-span beam is held laterally in the middle of the span, the deflection of the compressed flange can be prevented, and a two-wave eigenmode can be enforced. The critical lateral-torsional buckling moment is increased significantly by this additional measure. In the add-on modules for member design, different types of lateral supports on a member can be defined using the "Intermediate supports" input window.
In addition to the basic combination rules of EN 1990, there are other combination conditions for actions on road bridges specified in EN 1991‑2 that must be taken into account. RFEM and RSTAB provide automatic combinatorics that can be activated in the General Data when selecting the standard EN 1990 + EN 1991‑2. The partial safety factors and combination coefficients depending on the action category are preset when selecting the respective National Annex.
This article describes how to determine the contact force between two objects behaving like walls that are diagonally inclined at a certain angle on top of each other. Define a nodal release to determine this contact force. Since a nodal release requires certain conditions, this article shows two examples.
When designing steel columns or steel beams, it is usually necessary to carry out cross-section design and stability analysis. While the cross-section design can usually be performed without giving further details, the stability analysis requires further user-defined entries. To a certain extent, the member is cut out of the structure; therefore, the support conditions have to be specified. This is particularly important when determining the ideal elastic critical moment Mcr. Furthermore, it is necessary to define the correct effective lengths Lcr. These are required for the internal calculation of slenderness ratios.
The RF-/FOUNDATION Pro add‑on module designs single foundations (foundation plates, bucket and block foundations) for all support forces arising in the RFEM/RSTAB model. The geotechnical designs are performed according to EN 1997-1.
In practice, an engineer often faces the task of representing the support conditions as close to the reality as possible in order to be able to analyze the deformations and internal forces of the structure subjected to their influence and to enable construction that is as cost efficient as possible. RFEM and RSTAB provide numerous options for defining nonlinear nodal supports. This second part describes the options for creating a nonlinear support for a restraint and provides a simple example. For a better understanding, the result is always compared to a linearly defined support.
For suspension cranes, the bottom chord of the runway girder is subjected to local flange bending due to the wheel loads in addition to the main load-bearing capacity. The bottom chord behaves like a slab due to these local bending stresses, and has a biaxial stress condition [1].
Singularities occur in a limited area due to the concentration of the stress-dependent result values. They are conditioned by the FEA methodology. In theory, the stiffness and/or the stress in an infinite size concentrate on an infinitesimally small area.
Cable and tensile membrane structures are regarded as very slender and aesthetic building structures. The partly very complex double-curved shapes can be found using suitable form-finding algorithms. One possible solution is to search for the form via the equilibrium between the surface stress (provided prestress and an additional load such as self-weight, pressure, and so on) and the given boundary conditions.
In practice, an engineer often faces the task of representing the support conditions as close to the reality as possible in order to be able to analyze the deformations and internal forces of the structure subjected to their influence, and to enable construction that is as cost-effective as possible. RFEM and RSTAB provide numerous options for defining nonlinear nodal supports. The first section of my article describes the options for creating a nonlinear free support and provides a simple example. For a better understanding, the result is always compared to a linearly defined support.
In the case of plate structures, it is always necessary to consider realistic definition support conditions. Depending on the way of defining the flexibility of the supports, clear differences may occur in the results.