Anfangssteifigkeiten S_j,ini berechnen und automatisch in die Gesamtstruktur übertragen

This article describes and explains the influence of bending stiffness of cables on their internal forces. Furthermore, the text provides information on how this influence can be reduced.

The ASCE 7-22 Standard [1], Sect. 12.9.1.6 specifies when P-delta effects should be considered when running a modal response spectrum analysis for seismic design. In the NBC 2020 [2], Sent. 4.1.8.3.8.c gives only a short requirement that sway effects due to the interaction of gravity loads with the deformed structure should be considered. Therefore, there may be situations where second-order effects, also known as P-delta, must be considered when carrying out a seismic analysis.

This article presents the basic concepts in structural dynamics and their role in the seismic design of structures. Great emphasis is given to explaining the technical aspects in an understandable way, so that readers without deep technical knowledge can gain an insight into the subject.

In the Steel Joints add-on, you can classify the joint stiffness.

In addition to the initial stiffness, the table also shows the limit values for hinged and rigid connections for the selected internal forces N, My, and/or Mz. The resulting classification is then displayed in tables as "hinged", "semi-rigid", or "rigid".

Go to Explanatory Video

In the "Steel Joints" add-on, you can consider preloaded bolts in all components during the calculation. You can easily activate the preloading using the check box in the bolt parameters, and it has an impact on the stress-strain analysis as well as the stiffness analysis.

• "Steel Joints" Add-on
• Explanatory Video: Preloaded Bolts for Steel Joints

Preloaded bolts are special bolts used in steel structures to generate a high clamping force between the connected structural components. This clamping force causes friction between the structural components, which allows for the transfer of forces.

Functionality
Preloaded bolts are tightened with a certain torque, causing them to stretch and generate a tensile force. This tensile force is transferred to the connected components and leads to a high clamping force. The clamping force prevents the connection from loosening and ensures safe force transmission.

Advantages

• High load-bearing capacity: Preloaded bolts can transfer large forces.
• Low deformation: They minimize the deformation of the connection.
• Fatigue strength: They are resistant to fatigue.
• Easy assembly: They are relatively easy to assemble and disassemble.

Analysis and Design
The calculation of preloaded bolts is performed in RFEM using the FE analysis model generated by the "Steel Joints" add-on. It takes into account the clamping force, friction between structural components, shear strength of bolts, and load-bearing capacity of the structural components. The design is carried out according to DIN EN 1993‑1‑8 (Eurocode 3) or the US standard ANSI/AISC 360‑16. You can save the created analysis model, including the results, and use it as an independent RFEM model.

The initial stiffness S_j,ini is a decisive parameter for evaluating whether a connection can be characterized as rigid, non-rigid, or hinged.

In the “Steel Joints” add-on, you can calculate the initial stiffnesses S_j,ini according to Eurocode (EN 1993-1-8 Section 5.2.2) and AISC (AISC 360-16 Cl. E3.4) in relation to the internal forces N, M_y, and/or M_z.

The optional automatic transfer of initial stiffnesses allows for a direct transfer as member end hinge stiffnesses in RFEM. Then, the entire structure is recalculated and the resulting internal forces are automatically adopted as loads in the calculation and design of the connection models.

This automated iteration process eliminates the need for manual export and import of data, reducing the amount of work and minimizing potential sources of error.

Explanatory Video: Calculation of Initial Stiffness Sj,ini