Question

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.

The maximum and minimum extreme values (the envelope) are displayed in result tables and graphics. It is possible to add them to the global RSTAB printout report.

You can also design the internal forces of super combinations in many RSTAB add-on modules.

For superpositioning, it is necessary to select one of the integrated standards. The partial safety factors are preset by default. It is also possible to create a new standard and to save it with the user-defined safety factors.

The combination criterion defines which load cases, load combinations, or result combinations are to be considered by which model. The actions can be scaled by factors and classified as 'permanent' or 'potentially'. Alternative examinations in the form of a 'or' superposition are also possible. Graphic representations facilitate the allocation of the relevant models.

When determining extreme values, SUPER-RC imports the results of structures and superimposes them according to the combination criterion. The results are compared using the member and node numbers.

A basic model is created and saved under different names depending on the construction progress. These structural models are then used for the supercombination. The superpositioning can be performed in the same way as for an RSTAB result combination.

By modeling various construction or operational conditions, different geometric boundary conditions can be represented: It is possible to add or remove supports, members, or elastic foundation of the model, for example.