Adaptive pushover parameters

In Adaptive pushover, loads are applied to the structure in a manner that is largely similar to the case of conventional pushover. For this reason, users who are interested in using adaptive pushover are strongly advised to first consult the Loading Phases section, where the loading application procedure for conventional pushover is described. The latter should be considered as applicable to the adaptive pushover cases, noting however the following differences:

  1. In adaptive pushover, it is required that the inertia mass of the structures is modelled so that eigenvalue analysis, employed in the updating of the loading vector, may be carried out. Further, and for the case of force-based adaptive pushover only, it is necessary for the mass to be adequately distributed throughout the nodes where the incremental loads are to be applied, so that the incremental forces (obtained through the product of mass and acceleration) may be calculated. (for displacement-based pushover this is not necessary, given that the displacement profiles are obtained directly from the eigenvalue analyses)
  2. Although it is permitted to use different nominal values for the loads at different nodes, as in conventional pushover, it is strongly advisable that these incremental loads have equal nominal values (constant load profile) so that the load applied at every node is fully determined by the modal characteristics of the structure and spectral shape used.
  3. The Adaptive Load Control and Adaptive Response Control loading/solution procedures are used in substitution of the load control and response control phases. Their input and functionality are identical, noting however that only one adaptive phase (load or response control) can be applied in adaptive pushover, contrary to conventional pushover analysis where more than one load or response control phases may be simultaneously employed. If users wish to switch from Adaptive Load Control to Adaptive Response Control, or vice-versa, they must first delete whichever of these two phases has already been defined so that the alternative option is made available on the Add New Phase dialog box.

Being an advanced static analysis method, adaptive pushover requires the definition of a number of additional parameters, as included in the Adaptive Parameters module. These parameters are:

Type of Scaling
The normalised modal scaling vector, used to determine the shape of the load vector (or load increment vector) at each step, can be obtained using three distinct types of approaches; Force-based Scaling (scaling vector reflects the modal force distribution at that step), Displacement-based Scaling (scaling vector reflects the modal displacement distribution at that step) and Interstorey Drift-based Scaling (scaling vector reflects the modal interstorey drift distribution at that step). Note that the latter cannot be employed in 3D adaptive pushover analyses, and requires the nominal lateral displacements to be entered in sequence (the 1st floor load being defined first, followed by the displacement nominal load at level 2, and so on).

MPFs degrees-of-freedom
The user has the possibility of specifying the degrees-of-freedom to be considered in the calculation of the participation factors of the modes (which are then employed in the computation of the modal scaling vector). For 3D adaptive pushover analysis, it might be convenient for more than one translation degree-of-freedom to be employed (e.g. X & Y) or, instead, for rotation degrees-of-freedom to be used [e.g. Meireles et al., 2006]. In the more common case of 2D analysis, only one translation degree-of-freedom will be chosen, usually X.

Spectral Amplification
As previously mentioned, the effect that spectral amplification might have on the combination of the different modal load vector solutions, may or may not be taken into account through the choice of one of the three options available within this module:

  1. No Spectral Amplification. The scaling of the load vector distribution profile depends on the modal characteristics of the structure alone, at each particular step.
  2. Given Accelerogram. The user introduces an accelerogram time-history and defines the desired level of viscous damping used by the program to automatically compute an acceleration (when force-based scaling is used) or displacement (when displacement or drift-based scaling is employed) response spectrum (assumed constant throughout the analysis). Note that by default, the resulting response spectrum, as opposed to the accelerogram, is shown to the user. The latter, however, can be visualised through the Accelerogram button.
  3. User Defined Spectrum. The pairs of period and response acceleration/displacement values can be directly introduced, in an input table, by the user. This option is usually employed to introduce code-defined spectra and it is noted that, as in all other SeismoStruct modules, the list of values may be pasted from any other Windows application, as an alternative to direct typing.

Notes

  1. By clicking on the Advanced Settings button, the user can define additional parameters to those presented above.
  2. When running Displacement-based Adaptive Pushover, it is highly recommended, for reasons of accuracy, for Spectral Amplification to be employed. If, for some reason, a user does not have ways to estimate/represent the expected/design input motion at the site in question, then he/she should select Single-Mode analysis in here, so as to run DAP-1st mode (for buildings only).