τb can be determined iteratively. To do this, the design method must be specified (LRFD or ASD). Then, RFEM calculates the coefficient according to equation (C2-2a) or (C2-2b) in several steps until a convergence occurs.
Member Stiffness According to AISC 360-10 C2.3(2)
With RFEM version 5.06, member stiffnesses can be influenced by methods that are aligned with US steel construction standard ANSI/AISC 360-10. According to this standard, reduction factor τb must be considered for the determination of internal forces in all members of which the flexural resistance contributes to the model's stability. This coefficient depends on the axial force in the member: The larger the axial force, the larger τb is.
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Occasionally, the question arises how to determine the correct load application point of the positive transverse loads in RF-/STEEL EC3 and RF-/STEEL AISC.
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.
The support conditions of a beam subjected to bending are essential for its resistance to lateral-torsional buckling. If, for example, a single-span beam is held laterally in the middle of the span, the deflection of the compressed flange can be prevented, and a two-wave eigenmode can be enforced. The critical lateral-torsional buckling moment is increased significantly by this additional measure. In the add-on modules for member design, different types of lateral supports on a member can be defined using the "Intermediate supports" input window.
When optimizing cross-sections in the add-on modules, you can also select arbitrarily defined cross-section favorites lists - in addition to the cross-sections from the same cross-section series as the original cross-section.
In the "Edit Section" dialog box, you can display the buckling shapes of the Finite Strip Method (FSM) as a 3D graphic.
- Design of five types of seismic force-resisting systems (SFRS) includes Special Moment Frame (SMF), Intermediate Moment Frame (IMF), Ordinary Moment Frame (OMF), Ordinary Concentrically Braced Frame (OCBF), and Special Concentrically Braced Frame (SCBF)
- Ductility check of the width-to thickness ratios for webs and flanges
- Calculation of the required strength and stiffness for stability bracing of beams
- Calculation of the maximum spacing for stability bracing of beams
- Calculation of the required strength at hinge locations for stability bracing of beams
- Calculation of the column required strength with the option to neglect all bending moments, shear, and torsion for overstrength limit state
- Design check of column and brace slenderness ratios
The seismic design result is categorized into two sections: member requirements and connection requirements.
The "Seismic Requirements" include the Required Flexural Strength and the Required Shear Strength of the beam-to-column connection for moment frames. They are listed in the ‘Moment Frame Connection by Member’ tab. For braced frames, the Required Connection Tensile Strength and the Required Connection Compressive Strength of the brace are listed in the ‘Brace Connection by Member’ tab.
The program provides the performed design checks in tables. The design check details clearly display the formulas and references to the standard.
In the Concrete Design provides an option to perform seismic design according to AISC 341-16 for steel members.
Five SFRS types (Seismic Force-Resisting Systems) are available for this.
RF‑STEEL AISC add-module shows non-designable results for general cross-sections because of shear buckling checks according to Chapter G. How do I solve this?
Is it possible to calculate with American steel cross-sections?
Why are my steel members not being designed for stability in RF-STEEL AISC?
Can RF‑STEEL AISC optimize cross-sections for serviceability?
After running the design in RF‑STEEL AISC, I receive error message 1002 - Invalid cross-section of type "Channel" according to F2. What does this error mean?
Does RF‑STEEL AISC perform torsion design per Design Guide No. 9?
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