Diagonals of double angles are used for pipe bridge construction and for truss girders, among other things. They are usually subjected to tension, but it is necessary to transfer them in smaller compression forces with regard to the load application. In the case of slender diagonals in particular, you should also consider the bending due to self‑weight.
In January 2015, DIN Committee NA 005‑08‑23 Steel Bridges applied the introduction of a modification in equation 10.5 of DIN EN 1993‑1‑5. This involves the interaction of longitudinal and transverse pressure in a buckling analysis. Now, the interaction equation provides for auxiliary factor V, which is calculated from the reduction factors of the longitudinal and transverse stresses.
For structural reasons, shear connections usually include fin plates or flange angles. Main and secondary beams arranged on the top edge require notching or long fin plates. Hinged end plate connections are often welded to the web.
Torsional buckling analysis of transverse and longitudinal stiffeners with open cross-sections is described in DIN EN 1993-1-5, Chapter 9. There is a difference between the simplified method and the precise method, which takes into consideration the warping stiffness of the buckling panel. The simplified method applies Equation 9.3 of DIN EN 1993‑1‑5. If warping stiffness is to be taken into account, either Eq. 9.3 or Eq. 9.4 should be followed. Both design methods are implemented in PLATE-BUCKLING.
In addition to the stability designs according to EN 1993‑1‑1, Sections 6.3.1 through 6.3.3, you can apply the General Method according to EN 1993‑1‑1, 6.3.4 in RF‑/STEEL EC3.
In the following example, the stability analysis of a steel frame can be performed according to the General Method in compliance with EN 1993‑1‑1, Sect. 6.3.4 in the RF‑/STEEL EC3 add-on module. The first of my three posts shows the determination of the critical load factor for design loads required by the design concept, which reaches the elastic critical buckling load with deformations from the main framework plane.
In RF-STEEL Surfaces, it is possible to display the stresses relevant for the design of welds, for example, according to EN 1993‑1‑8, Figure 4.5. When evaluating the stress components, the local xyz-axis system of the surfaces must be considered.
The buckling analysis of plates with stiffeners is a special task for engineers. For this, EN 1993-1-5 provides three calculation methods: Effective Cross-Section Method, [1], Sect. 4-7; Reduced Stress Method, [1], Sect. 10; Finite Element Methods of Analysis (FEM), [1], Annex C.
The following article describes the design of a single-span beam subjected to bending and compression, which is performed according to EN 1993‑1‑1 in the RF-/STEEL EC3 add-on module. Since the beam is modeled with a tapered cross-section and thus it is not a uniform structural component, the design must be performed either according to General Method in compliance with Sect. 6.3.4 of EN 1993‑1‑1, or according to the second-order analysis. Both options will be explained and compared, and for the calculation according to the second-order analysis, there is an additional design format using Partial Internal Forces Method (PIFM) available. Therefore, the design is divided into three steps: design according to Sect. 6.3.4 of EN 1993‑1‑1 (General Method), design according to the second‑order analysis, elastic (warping torsion analysis), design according to the second‑order analysis, plastic (warping torsion analysis and Partial Internal Forces Method).
The RF‑STABILITY and RSBUCK add‑on modules for RFEM and RSTAB allow you to perform eigenvalue analysis for frame structures in order to determine critical load factors, including the buckling modes. Several buckling modes can be determined. They provide information about the model areas bearing stability risks.
Critical load factors and the corresponding mode shapes of any structure can be determined efficiently in RFEM and RSTAB, using the RF-STABILITY or RSBUCK add-on module (linear eigenvalue solver or nonlinear analysis).
Buckling analysis according to the effective width method or the reduced stress method is based on the determination of the system critical load, hereinafter called LBA (linear buckling analysis). This article explains the analytical calculation of the critical load factor as well as utilization of the finite element method (FEM).
According to EN 1993-1-1 [1], it is necessary to use the equivalent geometric imperfections with values that reflect the possible effects of all types of imperfections. EN 1993-1-1, Section 5.3, specifies basic imperfections for the global analysis of frames as well as member imperfections.
The product range of Dlubal Software contains various modules for the design of steel and timber connections. The RF-/JOINTS Steel – Column Base add-on module allows you to analyze footings of hinged or restrained steel column bases. The fastener selection, foundation geometry, and material quality are crucial for the cost-effective and safe design of the column base.
A fillet weld is the most common weld type in steel building construction. According to EN 1993-1-8, 4.3.2.1 (1) [1], fillet welds may be used for connecting structural part where the fusion faces form an angle of between 60° and 120°.
When designing bending-resistant connections from I-beams, the connection is dissolved into the individual parts. For these basic components of a joint, there are separate formula calculators for load-bearing capacity and stiffness. In RFEM and RSTAB, frame joints can be designed using the RF-/FRAME-JOINT Pro add-on module.
A single-span beam with lateral and torsional restraint is to be designed according to the recommendations of Eurocode 3 and AISC. If the beam does not reach the required load-bearing capacity, it must be stabilized.
After running an analysis in RF-/STEEL AISC, the mode shapes for sets of members can be viewed graphically in a separate window. Select the relevant set of members in the result window and click the [Mode Shapes] button.
According to EN 1993‑1‑1 [1], it is necessary to use the equivalent geometric imperfections with values that reflect the possible effects of all types of imperfections. EN 1993‑1‑1, Section 5.3, specifies basic imperfections for the global analysis of frames as well as member imperfections.
In this example, the design resistance of an end plate according to EN 1993-1-8 [1] is to be determined; the other components are not described here. To check the results, the dimensions of the connection IH 3.1 B 30 24 of Typified Connections [2] were used. S 235 material and bolts with strength 10.9 are used.
As of the program version X.11, the filter options of small compression forces or moments for stability analysis in RF‑/STEEL EC3 have been revised. The revision of these filter options in the "Stability" tab of the "Details" dialog box allows you to work in the module transparently, since they are now independent of the design.
Shell buckling is considered to be the most recent and least explored stability issue of structural engineering. This is due less to a lack of research activities than to the complexity of the theory. With the introduction and further development of the finite element method in structural engineering practice, some engineers no longer have to deal with the complicated theory of shell buckling. Evidence of the problems and errors to which this gives rise is very well summarized in [1].
This example is described in technical literature [1] as Example 9.5 and in [2] as Example 8.5. A lateral-torsional buckling analysis must be performed for a principal beam. This beam is a uniform structural member. Therefore, the stability analysis can be carried out according to Clause 6.3.3 of DIN EN 1993-1-1. Due to the uniaxial bending, it would also be possible to perform the design using the General Method according to Clause 6.3.4. Additionally, the determination of the moment Mcr is validated with an idealized member model in line with the method mentioned above, using an FEM model.
This example is described in technical literature [1] as Example 9.5 and in [2] as Example 8.5. A lateral-torsional buckling analysis must be performed for a principal beam. This beam is a uniform structural member. Therefore, the stability analysis can be carried out according to Clause 6.3.3 of DIN EN 1993‑1‑1. Due to the uniaxial bending, it would also be possible to perform the design using the General Method according to Clause 6.3.4. Additionally, the determination of the critical load factor is validated with an idealized member model in line with the method mentioned above, using an FEM model.
RFEM offers the following options to design a pinned end plate connection. First, there is the option in RF-JOINTS Steel - Pinned to enter the corresponding parameters quickly and easily to receive a documented analysis, including graphics. It is also possible to model such a connection individually in RFEM and then to evaluate or manually design the results. In the following example, the particularities of this modeling will be explained and the shear forces of the bolts will be compared to the corresponding results from RF-JOINTS Steel - Pinned.
Fin plate connections are a popular form of pinned steel connection and are commonly used for secondary beams in steel structures. They can be used easily in beam structures arranged on the top edge (for example, working platforms). Manufacturing expenditures in the workshop as well as the onsite assembly costs are normally manageable. The design seems to be completed easily and quickly, but it has to be put into perspective to a certain extent in the following text. Moreover, this connection type is basically possible as a pinned beam-to-beam or pinned beam-to-column connection; the former case is the more common one in design practice.
This article deals with the stiffness of standardized joints according to the DSTV (German Steel Construction Association)/DASt (German Committee for Structural Steelwork) standards, often used in steel construction, and its effects on structural analysis and design results according to DIN EN 1993-1-1.
In SHAPE-THIN, the calculation of stiffened buckling panels can be performed according to Section 4.5 of EN 1993-1-5. For stiffened buckling panels, the effective surfaces due to local buckling of the single panels in the plate and in the stiffeners, as well as the effective surfaces from the entire panel buckling of the stiffened entire panel, have to be considered.
The design of a torsional loaded beam according to AISC Design Guide 9 will be shown, based on a verification example. The design will be performed with the RF‑STEEL AISC add-on module and the RF‑STEEL Warping Torsion module extension with 7 degrees of freedom.