Loading phases

In pushover analysis, the applied loading usually consists of permanent gravity loads in the vertical (z) direction and incremental loads in one or both transversal (x & y) directions. As discussed in here, the magnitude of increment loads Pi at any given analysis step i is given by the product of its nominal value P0, defined by the user in the Applied Loading module, and the load factor at that step:

The manner in which the load factor is incremented throughout the analysis or, in other words, the loading strategy adopted in the pushover analysis, is fully defined in the Loading Phases module, where an unlimited number of loading/solution stages can be defined by applying different combinations of the three distinct pushover control types available in SeismoStruct, indicated below.

It is noteworthy that the incremental loading P may consist of forces or displacements, thus enabling for both force- and displacement-based pushover to be carried out. Clearly, for most cases, application of forces will be preferred to the employment of displacement incremental loads, since constraining the deformation of a structure to a predefined shape may conceal its true response characteristics (e.g. soft-storey), unless the more advanced adaptive pushover analysis type is employed. For this reason, the most common loading strategy in non-adaptive pushover analysis is force-based pushover with response control, described below:

• Load control phase
• Response control phase
• Automatic response control phase

Notes

1. Users may take advantage of the Add Scheme button to apply typical loading phases schemes that will work for the majority of cases. Note, however, that no loading phases should be already defined in order for this facility to be available.
2. It is highlighted again that an unlimited number of loading/solution strategies can be defined, by applying different combination of the three distinct load phase types available. For instance, the user may wish to:
   a) apply the pushover loads in two or more load control phases, using a different incremental step for each of those (e.g. larger step in the pre-yield stage, smaller step in the inelastic range)
   b) employ several phases to push a 3D model, first in one direction, then in the other, then back in the first one, and so on
   c) carry out cyclic pushover analysis, pushing and pulling the structure in successive cycles (the Static time-history analysis modality is however better tailored for such cases)
3. Even in those cases where no permanent loading is present, it might result handy to apply a nil load vector somewhere in the structure, so that the initial permanent loads step is carried out and hence the pushover curve is "forced" to start from the origin, which renders it slightly "more elegant".