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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.
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.
Creating a validation example for Computational Fluid Dynamics (CFD) is a critical step in ensuring the accuracy and reliability of simulation results. This process involves comparing the outcomes of CFD simulations with experimental or analytical data from real-world scenarios. The objective is to establish that the CFD model can faithfully replicate the physical phenomena it is intended to simulate. This guide outlines the essential steps in developing a validation example for CFD simulation, from selecting a suitable physical scenario to analyzing and comparing the results. By meticulously following these steps, engineers and researchers can enhance the credibility of their CFD models, paving the way for their effective application in diverse fields such as aerodynamics, aerospace, and environmental studies.
Wind direction plays a crucial role in shaping the outcomes of Computational Fluid Dynamics (CFD) simulations and the structural design of buildings and infrastructures. It is a determining factor in assessing how wind forces interact with structures, influencing the distribution of wind pressures, and consequently, the structural responses. Understanding the impact of wind direction is essential for developing designs that can withstand varying wind forces, ensuring the safety and durability of structures. Simplified, the wind direction helps in fine-tuning CFD simulations and guiding structural design principles for optimal performance and resilience against wind-induced effects.
Compliance with building codes, such as Eurocode, is essential to ensure the safety, structural integrity, and sustainability of buildings and structures. Computational Fluid Dynamics (CFD) plays a vital role in this process by simulating fluid behavior, optimizing designs, and helping architects and engineers meet Eurocode requirements related to wind load analysis, natural ventilation, fire safety, and energy efficiency. By integrating CFD into the design process, professionals can create safer, more efficient, and compliant buildings that meet the highest standards of construction and design in Europe.
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.
The size of the computational domain (wind tunnel size) is an important aspect of wind simulation that has a significant impact on the accuracy as well as the cost of CFD simulations.
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).
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.
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).
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.
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.
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 previous article, titled Lateral-Torsional Buckling in Timber Construction | Examples 1, explains the practical application for determining the critical bending moment Mcrit or the critical bending stress σcrit for a bending beam's lateral buckling using simple examples. In this article, the critical bending moment is determined by considering an elastic foundation resulting from a stiffening bracing.
In this article, representations of a blast scenario of a remote detonation performed in RF-DYNAM Pro - Forced Vibrations are shown, and the effects are compared in the linear time history analysis.
The response spectrum analysis is one of the most frequently used design methods in the case of earthquakes. This method has many advantages. The most important is the simplification: It simplifies the complexity of an earthquake to such an extent that an analysis can be carried out with reasonable effort. The disadvantage of this method is that a lot of information is lost due to this simplification. One way to mitigate this disadvantage is to use the equivalent linear combination when combining the modal responses. This article explains this option by describing an example.
The article titled Lateral-Torsional Buckling in Timber Construction | Theory explains the theoretical background for the analytical determination of the critical bending moment Mcrit or the critical bending stress σcrit for the lateral buckling of a bending beam. This article uses examples to verify the analytical solution with the result from the eigenvalue analysis.
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.
Slender bending beams that have a large h/w ratio and are loaded parallel to the minor axis tend to have stability issues. This is due to the deflection of the compression chord.
In order to consider inaccuracies regarding the position of masses in a response spectrum analysis, standards for seismic design specify rules that have to be applied in both the simplified and multi-modal response spectrum analyses. These rules describe the following general procedure: The story mass must be shifted by a certain eccentricity, which results in a torsional moment.
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").
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.
For crane runways with large spans, the horizontal load from skewing is often relevant for the design. This article describes the origin of these forces and the correct input in CRANEWAY. The practical implementation and the theoretical background are discussed.
In RF-DYNAM Pro - Equivalent Loads, the equivalent seismic loads can be calculated according to different standards. By calculating the equivalent loads for each eigenmode, it is not directly possible to obtain the transversal shear for each story to perform an analysis afterwards. The following example describes the option to calculate the transversal shear quickly and efficiently.
In a multi-modal response spectrum analysis, it is important to determine a sufficient number of eigenvalues of the structure and to consider their dynamic responses. Regulations such as EN 1998‑1 [1] and other international standards require the activation of 90% of the structural mass. This means: to determine so many eigenvalues that the sum of the effective modal mass factors is greater than 0.9.
As an alternative to the equivalent member method, this article describes the possibility to determine the internal forces of a wall at risk of buckling according to the second-order analysis, taking imperfections into account, and to subsequently perform the cross-section design for bending and compression.
The following article describes a design using the equivalent member method according to [1] Section 6.3.2, performed on an example of a cross-laminated timber wall susceptible to buckling described in Part 1 of this article series. The buckling analysis will be performed as a compressive stress analysis with reduced compressive strength. For this, the instability factor kc is determined, which depends primarily on the component slenderness and the support type.
Basically, you can design the structural components made of cross-laminated timber in the RF-LAMINATE add-on module. Since the design is a pure elastic stress analysis, it is necessary to additionally consider the stability issues (flexural buckling and lateral-torsional buckling).
Long-span glued-laminated beams are usually supported by a reinforced concrete column with torsional restraints.
For the ultimate limit state design, EN 1998-1 Section 2.2.2 and 4.4.2.2 [1] requires the 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.