The design of cold-formed steel members according to the AISI S100-16 / CSA S136-16 is available in RFEM 6. Design can be accessed by selecting “AISC 360” or “CSA S16” as the standard in the Steel Design Add-on. “AISI S100” or “CSA S136” is then automatically selected for the cold-formed design.
RFEM applies the Direct Strength Method (DSM) to calculate the elastic buckling load of the member. The Direct Strength Method offers two types of solutions, numerical (Finite Strip Method) and analytical (Specification). The FSM signature curve and buckling shapes can be viewed under Sections.
Various design parameters of the cross-sections can be adjusted in the serviceability limit state configuration. The applied cross-section condition for the deformation and crack width analysis can be controlled there.
For this, the following settings can be activated:
Crack state calculated from associated load
Crack state determined as an envelope from all SLS design situations
Cracked state of cross-section - independent of load
Consideration of 7 local deformation directions (ux, uy, uz, φx, φy, φz, ω) or 8 internal forces (N, Vu, Vv, Mt,pri, Mt,sec, Mu, Mv, Mω) when calculating member elements
Usable in combination with a structural analysis according to linear static, second-order, and large deformation analysis (imperfections can also be taken into account)
In combination with the Stability Analysis add-on, allows you to determine critical load factors and mode shapes of stability problems such as torsional buckling and lateral-torsional buckling
Consideration of end plates and transverse stiffeners as warping springs when calculating I-sections with automatic determination and graphical display of the warping spring stiffness
Graphical display of the cross-section warping of members in the deformation
You can perform the calculation of the warping torsion on the entire system. Thus, you consider the additional 7th degree of freedom in the member calculation. The stiffnesses of the connected structural elements are automatically taken into account. It means, you don't need to define equivalent spring stiffnesses or support conditions for a detached system.
You can then use the internal forces from the calculation with warping torsion in the add-ons for the design. Consider the warping bimoment and the secondary torsional moment, depending on the material and the selected standard. A typical application is the stability analysis according to the second-order theory with imperfections in steel structures.
Did you know that The application is not limited to thin-walled steel cross-sections. Thus, it is possible for you, for example, to perform the calculation of the ideal overturning moment of beams with solid timber cross-sections.
Due to the integrated RF-/STEEL Warping Torsion module extension, it is possible to perform the design according to Design Guide 9 in RF-/STEEL AISC.
The calculation is performed with 7 degrees of freedom according to the warping torsion theory and enables a realistic stability design, including consideration of torsion.
The determination of the critical buckling moment is carried out in RF-/STEEL AISC by using the eigenvalue solver which allows an exact determination of the critical buckling load.
The eigenvalue solver shows a display window of the eigenvalue graphics, which enables checking of the boundary conditions.
In STEEL AISC, it is possible to consider lateral intermediate supports at any location. For example, it is possible to stabilize only the upper flange.
Furthermore, user-defined lateral intermediate supports can be assigned; for example, single rotational springs and translational springs at any location at the cross-section.
Since RF-/STEEL Warping Torsion is fully integrated in RF-/STEEL AISC and RF‑/STEEL EC3, the data are entered in the same way as for the usual design in these modules. It is only necessary to select the option "Perform warping analysis" in the Details dialog box, tab Warping Torsion (see the figure on the right). You can also define the maximum number of iterations in this dialog box.
The warping torsion analysis is performed for sets of members in RF-/STEEL AISC and RF‑/STEEL EC3. You can define boundary conditions such as nodal supports or member end releases for them. It is also possible to specify imperfections for the nonlinear calculation.
The nonlinear calculation is activated by selecting the design method of the serviceability limit state. You can individually select the analyses to be performed as well as the stress-strain diagrams for concrete and reinforcing steel. The iteration process can be influenced by these control parameters: convergence accuracy, maximum number of iterations, arrangement of layers over cross-section depth, and damping factor.
You can set the limit values in the serviceability limit state individually for each surface or surface group. Allowable limit values are defined by the maximum deformation, the maximum stresses, or the maximum crack widths. The definition of the maximum deformation requires additional specification as to whether the non-deformed or the deformed system should be used for the design.
RF-CONCRETE Members
The nonlinear calculation can be applied to the ultimate and the serviceability limit state designs. In addition, you can specify the concrete tensile strength or the tension stiffening between the cracks. The iteration process can be influenced by these control parameters: convergence accuracy, maximum number of iterations, and damping factor.
The results of warping torsion analysis are displayed in RF-/STEEL AISC and RF-/STEEL EC3 in the usual way. Among other results, the corresponding result windows include the critical warping and torsional values, internal forces, and design summary.
The graphical display of mode shapes (incl. warping) enables a realistic assessment of buckling behavior.
The nonlinear deformation analysis is performed by an iterative process considering the stiffness in cracked and non-cracked sections. The nonlinear reinforced concrete modeling requires definition of material properties varying across the surface thickness. Therefore, a finite element is divided into a certain number of steel and concrete layers in order to determine the cross-section depth.
The mean steel strengths used in the calculation are based on the 'Probabilistic Model Code' published by the JCSS technical committee. It is up to the user whether the steel strength is applied up to the ultimate tensile strength (increasing branch in the plastic area). Regarding material properties, it is possible to control the stress-strain diagram of the compressive and tensile strength. For the concrete compressive strength, you can select a parabolic or a parabolic-rectangular stress-strain diagram. On the tension side of the concrete, it is possible to deactivate the tensile strength as well as to apply a linear-elastic diagram, a diagram according to the CEB-FIB model code 90:1993, and concrete residual tensile strength considering the tension stiffening between the cracks.
Furthermore, you can specify which result values should be displayed after the nonlinear calculation at the serviceability limit state:
Deformations (global, local based on non-/deformed system)
Crack widths, depths, and spacing of the top and bottom sides in principal directions I and II
Stresses of the concrete (stress and strain in principal direction I and II) and of the reinforcement (strain, area, profile, cover, and direction in each reinforcement direction)
RF-CONCRETE Members:
The nonlinear deformation analysis of beam structures is performed by an iterative process considering the stiffness in cracked and non-cracked sections. The material properties of concrete and reinforcing steel used in the nonlinear calculation are selected according to a limit state. The contribution of the concrete tensile strength between the cracks (tension stiffening) can be applied either by means of a modified stress-strain diagram of the reinforcing steel, or by applying a residual concrete tensile strength.
Iterative nonlinear calculation of deformations for beam and plate structures consisting of reinforced concrete by determining the respective element stiffness subjected to the defined loads
Deformation analyses of cracked reinforced concrete surfaces (state II)
General nonlinear stability analysis of compression members made of reinforced concrete; for example, according to EN 1992-1-1, 5.8.6
Tension stiffening of concrete applied between cracks
Numerous National Annexes available for the design according to Eurocode 2 (EN 1992-1-1:2004 + A1:2014, see EC2 for RFEM)
Optional consideration of long-term influences such as creep or shrinkage
Nonlinear calculation of stresses in reinforcing steel and concrete
Nonlinear calculation of crack widths
Flexibility due to detailed setting options for basis and extent of calculations
Graphical representation of results integrated in RFEM; for example, deformation or sag of a flat slab made of reinforced concrete
Numerical results clearly arranged in tables and graphical display of the results in the model
Complete integration of results in the RFEM printout report
After the calculation, the module shows clearly arranged tables listing the results of the nonlinear calculation. All intermediate values are included in a comprehensible manner. Graphical representation of design ratios, deformations, concrete and reinforcing steel stresses, crack widths, crack depths, and crack spacing in RFEM facilitates a quick overview of critical or cracked areas.
Error messages or remarks concerning the calculation help you find design problems. Since the design results are displayed by surface or by point including all intermediate results, you can retrace all details of the calculation.
Due to the optional export of input or result tables to MS Excel, the data remain available for further use in other programs. The complete integration of results in the RFEM printout report guarantees verifiable structural design.