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Lateral-Torsional Buckling (LTB) is a phenomenon that occurs when a beam or structural member is subjected to bending and the compression flange is not sufficiently supported laterally. This leads to a combination of lateral displacement and twisting. It is a critical consideration in the design of structural elements, especially in slender beams and girders.
The automatic surface reinforcement design process determines a surface reinforcement that covers the required amount of reinforcement.
- 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.
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).
This article discusses the options available for determining the nominal flexural strength, Mnlb for the limit state of local buckling when designing according to the 2020 Aluminum Design Manual.
The optimal scenario in which punching shear design according to ACI 318-19 [1] or CSA A23.3:19 [2] should be utilized is when a slab is experiencing a high concentration of loading or reaction forces occurring at one single node. In RFEM 6, the node in which punching shear is an issue is referred to as a punching shear node. The causes of these high concentration of forces can be introduced by a column, concentrated force, or nodal support. Connecting walls can also cause these concentrated loads at wall ends, corners, and ends of line loads and supports.
In accordance with Sect. 6.6.3.1.1 and Clause 10.14.1.2 of ACI 318-19 and CSA A23.3-19, respectively, RFEM effectively takes into consideration concrete member and surface stiffness reduction for various element types. Available selection types include cracked and uncracked walls, flat plates and slabs, beams, and columns. The multiplier factors available within the program are taken directly from Table 6.6.3.1.1(a) and Table 10.14.1.2.
Foundations including dimensions can be saved as a template in a user-defined database.
In RFEM 5 as well as RSTAB 8 in RF-/FOUNDATION Pro, you can save the foundation dimensions for all five foundation types as foundation templates in a user-defined database and use them later in other models.
In RF-/FOUNDATION Pro, the foundation design requires the definition of the corresponding loading (load cases, load combinations, or result combinations) for different design situations (STR, GEO, UPL, or EQU).
In RF‑/FOUNDATION Pro, reinforcement drawings are displayed after designing the foundation, where you can record all necessary structures of the reinforcement steel.
In RF‑/FOUNDATION Pro, the available reinforcing steel diameters can be adjusted by the user. The adjustment of the available rebar diameters works similarly to the same function in the RF‑/CONCRETE (Members) and RF‑/CONCRETE Columns add‑on modules.
In RF-/FOUNDATION Pro, the user can freely select the proportion of the relieving soil pressure by means of the factor kred.
In RF‑/FOUNDATION Pro, you now have the option to design a foundation at one or several nodes of the model.
For the design of concrete surfaces, the rib component of the internal forces can be neglected for the ULS calculation and for the analytical method of the SLS calculation, because this component is already considered in the member design. To do this, select the check box in the "Details" dialog box. If no rib was defined, this function is not available.
In RFEM and RSTAB, different graphical representations of the foundation dimensions are available.
For foundation design, it is necessary to define the relevant loads for the respective design situations (STR, GEO, UPL, EQU).
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.
In RF-/FOUNDATION Pro, a graphical display of the result details is available. To see them, go to Window 2.2 Governing Design Criteria after the calculation. In the interactive graphic of this window, individual design-relevant values can be displayed for each design performed.
RF-CONCRETE Members for RFEM or CONCRETE for RSTAB propose an automatically created reinforcement to the user if the "Design the provided reinforcement" option is selected in Window 1.6 "Reinforcement".
The Aluminum Design Manual (ADM) 2020 was released in February 2020. The ADM 2020 gives guidance for both the allowable strength design (ASD) and load and resistance factor design (LRFD) for aluminum members to ensure reliability and safety for all aluminum structures. This latest standard was integrated in the RFEM/RSTAB add-on module RF-/ALUMINUM ADM. The text below will highlight the applicable updates relevant to the Dlubal programs.
In the case of open cross-sections, the torsional load is removed mainly via secondary torsion, since the St. Venant torsional stiffness is low compared to the warping stiffness. Therefore, warping stiffeners in the cross-section are particularly interesting for the lateral-torsional buckling analysis, as they can significantly reduce the rotation. For this, end plates or welded stiffeners and sections are suitable.
In RF-/FOUNDATION Pro, you can also consider the concrete cover for the foundation according to EN 1992-1-1.
Shrinkage and creep are time-dependent deformation properties of concrete that usually have to be considered in the serviceability limit state design.
- 000487
- Modeling | Structure
- RFEM 5
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- 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 RFEM 5 and RSTAB 8, you can design foundations according to EN 1992‑1‑1 and EN 1997‑1 in the RF‑/FOUNDATION Pro add‑on module.
RF‑CONCRETE Surfaces for RFEM 5 allows you to use averaged internal forces for design of concrete surfaces.