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To evaluate whether it is also necessary to consider the second-order analysis in a dynamic calculation, the sensitivity coefficient of interstory drift θ is provided in EN 1998‑1, Sections 2.2.2 and 4.4.2.2. It can be calculated and analyzed using RFEM 6 and RSTAB 9.
For the ultimate limit state design, EN 1998‑1, Sections 2.2.2 and 4.4.2.2 require a calculation considering the second‑order theory (P‑Δ effect). This effect may be neglected only if the interstory drift sensitivity coefficient θ is less than 0.1.
In order to be able to carry out a pushover analysis, it is necessary to transform the determined capacity curve into a simplified form. The N2 method is described in Eurocode EN 1998. This article should help to explain what a bilinearization according to the N2 method involves.
Both the determination of natural vibrations and the response spectrum analysis are always performed on a linear system. If nonlinearities exist in the system, they are linearized and thus not taken into account. They are caused by, for example, tension members, nonlinear supports, or nonlinear hinges. This article shows how you can handle them in a dynamic analysis.
- 001819
- Design
- Aluminum Design for RFEM 6
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- Aluminum Design for RSTAB 9
- Concrete Design for RFEM 6
- Concrete Design for RSTAB 9
- Steel Design for RFEM 6
- Steel Design for RSTAB 9
- Timber Design for RFEM 6
- Timber Design for RSTAB 9
- Concrete Structures
- Steel Structures
- Timber Structures
- Structural Analysis & Design
- Eurocode 0
- Eurocode 2
- Eurocode 3
- Eurocode 5
- Eurocode 9
- ADM
- ANSI/AISC 360
For the serviceability of a structure, the deformations must not exceed certain limit values. This article describes an example that shows how to analyze the deflection of members using Dlubal's design add-ons.
To be able to evaluate the influence of local stability phenomena of slender structural components, RFEM 6 and RSTAB 9 provide you with the option of performing a linear critical load analysis on the cross-section level. The following article explains the basics of the calculation and the result interpretation.
When a concrete slab is set upon the top flange, its effect is like a lateral support (composite construction), preventing problems of torsional buckling stability. If there is a negative distribution of the bending moment, the bottom flange is subjected to compression and the top flange is under tension. If the lateral support given by the stiffness of the web is insufficient, the angle between the bottom flange and the web intersection line is variable in this case so that there is a possibility of distortional buckling for the bottom flange.
Custom sections are often required in cold-formed steel design. In RFEM 6, the custom section can be created using one of the “Thin-Walled” sections available in the library. For other sections that do not meet any of the 14 available cold-formed shapes, the sections can be created and imported from the standalone program, RSECTION. For general information on AISI steel design in RFEM 6, refer to the Knowledge Base article provided at the end of the page.
RFEM 6 offers the Aluminum Design add-on for the design of aluminum members. This article shows how class 4 sections are designed according to Eurocode 9 in the program.
The CSA S16:19 Stability Effects in Elastic Analysis method in Annex O.2 is an alternative option to the Simplified Stability Analysis Method in Clause 8.4.3. This article will describe the requirements of Annex O.2 and application in RFEM 6.
The design of cold-formed steel members according to the AISI S100-16 is now available in RFEM 6. Design can be accessed by selecting “AISC 360” as the standard in the Steel Design add-on. “AISI S100” is then automatically selected for the cold-formed design (Image 01).
The dynamic analysis in RFEM 6 and RSTAB 9 is divided into several add-ons. The Modal Analysis add-on is a prerequisite for all other dynamic add-ons, since it performs the natural vibration analysis for member, surface, and solid models.
Modal analysis is the starting point for the dynamic analysis of structural systems. You can use it to determine natural vibration values such as natural frequencies, mode shapes, modal masses, and effective modal mass factors. This outcome can be used for vibration design, and it can be used for further dynamic analyses (for example, loading by a response spectrum).
You can model and analyze masonry structures in RFEM 6 with the Masonry Design add-on that employs the finite element method for the design. Complex masonry structures can be modeled, and static and dynamic analysis can be performed, given that a nonlinear material model is implemented in the program to display the load-bearing behavior of masonry and the different failure mechanisms. You can enter and model masonry structures directly in RFEM 6 and combine the masonry material model with all common RFEM add-ons. In other words, you can design entire building models in connection with masonry.
RFEM 6 offers the Aluminum Design add-on to design aluminum members for the ultimate and serviceability limit states according to Eurocode 9. In addition to this, you can perform design according to ADM 2020 (US Standard).
The stability checks for the equivalent member design according to EN 1993-1-1, AISC 360, CSA S16, and other international standards require consideration of the design length (that is, the effective length of the members). In RFEM 6, it is possible to determine the effective length manually by assigning nodal supports and effective length factors or, on the other hand, by importing it from the stability analysis. Both options will be demonstrated in this article by determining the effective length of the framed column in Image 1.
The new RFEM software generation provides the option to perform stability design of tapered timber members in line with the equivalent member method. According to this method, the design can be performed if the guidelines of DIN 1052, Section E8.4.2 for variable cross-sections are met. In various technical literature, this method is also adopted for Eurocode 5. This article demonstrates how to use the equivalent member method for a tapered roof girder.
In the RF-/TIMBER Pro, RF-/TIMBER AWC, and RF-/TIMBER CSA add-on modules, you can consider the resulting deformation of a member or set of members. In addition to the local directions y and z, you have the option "R." This allows you to compare the total deflection of a girder to the limit values given in the standards.
You can make various settings in order to achieve a clearly‑arranged display of the result values. For example, some users may not want the white background in text bubbles. You can adjust the background in "Display Properties" using the Transparent and Background color option.
Besides the standardized gamma method, you can display the semi-rigid composite beams also as a framework model.
Structure stability is not a new phenomenon when referring to steel design. The Canadian steel design standard CSA S16 and the most recent 2019 release are no exception. Detailed stability requirements can be addressed with either the Simplified Stability Analysis Method in Clause 8.4.3 or, new to the 2019 standard, the Stability Effects in Elastic Analysis method provided in Annex O.
- 000945
- Add-on Modules
- RF-FRAME-JOINT Pro 5
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- JOINTS Steel | Column Base 8
- JOINTS Steel | DSTV 8
- JOINTS Steel | Pinned 8
- JOINTS Steel | Rigid 8
- JOINTS Steel | SIKLA 8
- JOINTS Steel | Tower 8
- JOINTS Timber | Steel to Timber 8
- JOINTS Timber | Timber to Timber 8
- RF-JOINTS Steel | SIKLA 5
- RF-JOINTS Steel | Column Base 5
- RF-JOINTS Steel | DSTV 5
- RF-JOINTS Steel | Pinned 5
- RF-JOINTS Steel | Rigid 5
- RF-JOINTS Steel | Tower 5
- RF-JOINTS Timber | Steel to Timber 5
- RF-JOINTS Timber | Timber to Timber 5
- FRAME-JOINT Pro 8
- Steel Structures
- Timber Structures
- Steel Connections
- Eurocode 3
- Eurocode 5
In addition to the result tables, you can create three-dimensional graphics in RF‑/FRAME‑JOINT Pro and RF‑/JOINTS. This is a realistic representation of a connection to scale.
The joint type "Main member only" in RF‑/JOINTS Timber - Steel to Timber can also be applied for more than one connected member.
For a timber connection as shown in Figure 01, you can take into account the torsional spring rigidity (spring stiffness for rotation) of the connections. You can determine it by means of the slip modulus of the fastener and the polar moment of inertia of the connection.
The RF-/LIMITS add-on module allows you to compare the ultimate limit state of members, member ends, nodes, nodal supports, and surfaces (RFEM only) by means of a defined ultimate load capacity. Furthermore, you can check nodal displacements and cross-section dimensions. In this example, the column bases of a carport are to be compared with the maximum allowable forces specified by the manufacturer.
With the RF-/TIMBER Pro add-on module, you can perform the vibration design known from DIN 1052 for the design according to EN 1995-1-1. In this design, the deflection under permanent and quasi-permanent action at the ideal one‑span beam may not exceed the limit value (6 mm according to DIN 1052). If you consider the relation between the natural frequency and the deflection for a hinged single-span beam subjected to a constant distributed load, the 6 mm limit value results in a minimum natural frequency of about 7.2 Hz.
In the default setting, the cross-section class for each member and load case is determined automatically in the design modules. In the input window of the cross sections, however, the user can also specify the cross-section class manually; for example, if local buckling is excluded by the design.
In timber design, beams are often built from several timber elements. The individual elements can be connected with glue, nails, bolts, or dowels. A glued connection is to be assumed as rigid. In the case of dowel‑type fasteners, the joint is compliant (slip joint), and the cross‑section properties of the connected elements cannot be fully applied.
For relatively large or relatively small surfaces, it can happen that the automatically created result values do not fit the model: In the case of large surfaces, there can be too many result values; in the case of small surfaces, too few.
The same structures are often needed in several projects, such as the purlin with columns and braces in this example. The dimensions can be changed directly in RFEM or RSTAB by shifting the nodes.