Calculation of Initial Stiffness Sj,ini

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 have this option to consider the preloaded bolts in the calculation of all components.

You can easily activate the prestress using the check box in the bolt parameters, and it has an impact on the stress-strain analysis as well as the stiffness analysis.

Go to Explanatory Video

In the Steel Joints add-on, you can determine the initial stiffness Sj,ini according to Eurocode and AISC. This can be done for selected members with reference to the internal forces N, My, and Mz.

In the Members tab of the input dialog box of the Steel Joints add-on, you can select the desired internal forces via a checkbox. Multiple selection is possible. For these internal forces, the stiffness analysis is carried out with a positive and a negative sign.

Go to Explanatory Video