DIN EN 1998-1 with the National Annex DIN EN 1998-1/NA specifies how to determine seismic loads. The standard applies to structural engineering in seismic areas.
In accordance with Sec. 6.6.3.1.1 and Sec. 10.14.1.2 of ACI 318-14 and CSA A23.3-14, 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.
Defining the appropriate effective length is crucial in obtaining the correct member design capacity. For X-bracing that is connected at the center, engineers often wonder if the full end-to-end length of the member shall be used, or whether using half of the length to where the members are connected is sufficient. This article outlines the recommendations given by the AISC and provides an example on how to specify the effective length of the X-braces in RFEM.
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.
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.
Utilizing the RF-STEEL AISC add-on module, steel member design is possible according to the AISC 360-16 standard. The following article will compare the results between calculating lateral torsional buckling according to Chapter F and Eigenvalue Analysis.
When introducing and transferring horizontal loads such as wind or seismic loads, increasing difficulties arise in 3D models. To avoid such issues, some standards (for example, ASCE 7, NBC) require the simplification of the model using diaphragms that distribute the horizontal loads to structural components transferring loads, but cannot transfer bending themselves (called "Diaphragm").
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).
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. Straight tension members are very often used in practice. This article will show how you can display them approximately correctly in a dynamic analysis.