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.
In CONCRETE and RF‑CONCRETE Members, you can open a dialog box with a 3D rendering of the existing reinforcement in Window 3.1 or 3.2. Now, you can also display different reinforcement views in several dialog boxes at the same time. The "Isometric and 3 Views" option known from RFEM is available here as well.
RWIND 2 is a program for generating wind loads based on CFD (Computational Fluid Dynamics). The wind flow numerical simulation is generated around any building, including irregular or unique geometry types, to determine the wind loads on surfaces and members. RWIND 2 can be integrated with RFEM/RSTAB for the structural analysis and design or as a stand-alone application.
In RF-/STEEL EC3, sets of members are calculated according to the General Method (EN 1993-1-1, Cl. 6.3.4) together with the stability analysis. To do this, it is necessary to determine the correct support conditions for the equivalent structure with four degrees of freedom. In most 3D models today, you can quickly lose track of the location of a set of members in the system.
The new "Result Beam" member type in RFEM 5 allows you to determine the load sums of individual floors easily. To do this, model a member in the relevant floor or in all floors, then specify the relevant walls as inclusive objects in the parameters of the result beam. RFEM then integrates the surface internal forces into member internal forces.
The "Result Beam" member type has been available since the release of RFEM 5. The result beam is a virtual member that does not have any stiffness nor require any support. It can be used in various situations in order to integrate the results from members, surfaces, and solids, and to display them as member internal forces.
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.
In RFEM, you can modify stiffnesses for materials, cross-sections, members, load cases, and load combinations in many places. There are two options in RF‑DYNAM Pro for considering these modifications when determining the natural frequencies.
When modeling frame structures, RFEM and RSTAB provide various options for controlling the transfer of internal forces and moments at the connection points of members. You can use the member types to determine whether only forces act on the connected members, or whether moments act on them as well. In addition, you can use hinges to exclude specific internal forces from the transfer. One special form is scissor hinges, which allow for realistic modeling of roof structures, for example.
To simulate a support clearance in a connection between members, you can use the "Diagram" function for member hinges. To use this function, first define the relevant degree of freedom as release. Then, you can select the "Diagram" function from the drop‑down list.
When using the wind load generator for vertical walls with a roof, it may be necessary to load the edge members on eaves or on a gable only with the wind loads of the roof. For structural reasons, the horizontal wind loads should apply to the vertical walls by the facade. In previous versions, it was necessary to apply the wind loads separately to the walls and the roof with the corresponding generators and exclude the unwanted members.
In RFEM and RSTAB, you can now also display and check the types of members used visually, by means of colors. To do this, an option has been integrated into the Display Navigator.
If the calculation of a member model according to the second-order analysis is terminated with an error message, this instability is often caused by failed tension members: As soon as compressive forces appear in a tension member during a calculation step, this member is no longer considered in the following iterations. Thus, the model can become unstable.
In many frame and truss structures, it is no longer sufficient to use a simple member. You often have to consider cross-section weakenings or openings in solid beams. In such cases, you can use the "Surface Model" member type. It can be integrated into the model like any other member and offers all the options of a surface model. The present technical article shows the application of such a member in an existing structural system and describes the integration of member openings.
The most common causes of unstable models are failing member nonlinearities such as tension members. As the simplest example, there is a frame with supports on the column footing and moment hinges on the column head. This unstable system is stabilized by a cross bracing of tension members. In the case of load combinations with horizontal loads, the system remains stable. However, if it is loaded vertically, both tension members fail and the system becomes unstable, which causes a calculation error. You can avoid such an error by selecting the exceptional handling of failing members under "Calculate" → "Calculation Parameters" → "Global Calculation Parameters".
For recurring elements such as certain structural components or standard parts, you can use the parametrization of a basic model. In the program, the main elements do not represent components but the corresponding node and therefore, they have to be parameterized. For example, a member is not defined by the length, but by the start and end nodes. In this way of modeling, complex formulas may occur especially in the case of three-dimensional structures.
A standard scenario in timber member construction is the ability to connect smaller members by means of bearing on a larger girder member. Additionally, member end conditions may include a similar situation where the beam is bearing on a support type. In either scenario, the beam must be designed to consider the bearing capacity perpendicular to the grain according to NDS 2018 Sec. 3.10.2 and CSA O86:19 Clauses 6.5.6 and 7.5.9. In general structural design software, it is typically not possible to carry out this full design check, as the bearing area is unknown. However, in the new generation RFEM 6 and Timber Design add-on, the added 'design supports' feature now allows users to comply with the NDS and CSA bearing perpendicular to the grain design checks.
Using the RF-TIMBER CSA module, timber column design is possible according to the CSA O86-19 standard. Accurately calculating timber member compressive resistance and adjustment factors is important for safety considerations and design. The following article will verify the factored compressive resistance in the RFEM add-on module RF-TIMBER CSA, using step-by-step analytical equations as per the CSA O86-19 standard including the column modification factors, factored compressive resistance, and final design ratio.
Using the RF-TIMBER AWC module, timber column design is possible according to the 2018 NDS standard ASD method. Accurately calculating timber member compressive capacity and adjustment factors is important for safety considerations and design. The following article will verify the maximum critical buckling in RF-TIMBER AWC using step-by-step analytical equations as per the NDS 2018 standard including the compressive adjustment factors, adjusted compressive design value, and final design ratio.
In this article, the adequacy of a 2x4 dimension lumber subject to combined biaxial bending and axial compression is verified using the RF-/TIMBER AWC add-on module. The beam-column properties and loading are based on example E1.8 of AWC Structural Wood Design Examples 2015/2018.