Pushover Analysis | Features

In this article, you will learn how to model and design cable structures in RFEM 6 or RSTAB 9.

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.

• Consideration of nonlinear component behavior using plastic standard hinges for steel (FEMA 356, EN 1998‑3) and nonlinear material behavior (masonry, steel - bilinear, user-defined working curves)
• Direct import of masses from load cases or combinations for the application of constant vertical loads
• User-defined specifications for the consideration of horizontal loads (standardized to a mode shape or uniformly distributed over the height of the masses)
• Determination of a pushover curve with selectable limit criterion of the calculation (a collapse or limit deformation)
• Transformation of the pushover curve into the capacity spectrum (ADRS format, single degree of freedom system)
• Bilinearization of the capacity spectrum according to EN 1998‑1:2010 + A1:2013
• Transformation of the applied response spectrum into the required spectrum (ADRS format)
• Determination of target displacement according to EC 8 (the N2 method according to Fajfar 2000)
• Graphical comparison of the capacity and required spectrum
• Graphical evaluation of the acceptance criteria of predefined plastic hinges
• Result display of the values used in the iterative calculation of the target displacement
• Access to all results of the structural analysis in the individual load levels

During the calculation, the selected horizontal load is increased in load steps. A static nonlinear analysis is carried out for each load step until reaching the specified limit condition.

The results of the pushover analysis are extensive. On one hand, the structure is analyzed for its deformation behavior. This can be represented by a force-deformation line of the system (a capacity curve). On the other hand, the response spectrum effect can be displayed in the ADRS display (Acceleration-Displacement Response Spectrum). The target displacement is automatically determined in the program based on these two results. The process can be evaluated graphically and in tables.

The individual acceptance criteria can then be graphically evaluated and assessed (for the next load step of the target displacement, but also for all other load steps). The results of the static analysis are also available for the individual load steps.

Use the "Independent mesh preferred" option in the FE mesh settings to create an independent FE mesh for the integrated objects. This allows you to generate a significantly more detailed and precise FE mesh for individual objects that are integrated into one another.