This page contains frequently asked questions related to time history analysis.
On this page:What value of scale factor should be used for the definition of the time history load case?
The are the following two possibilities:
- When the load type is set to Load pattern, the time history function values multiplied by the scale factor are unitless and should describe the variation of loads applied in the load pattern in time.
- When the load type is set to Accel, the time history function values multiplied by the scale factor should be entered such that they are equal to the desired acceleration in current units. If the time history function values are in the same units as the current units, then scale factor of 1 would be used. Otherwise the scale factor should reflect the conversion from time history function units to the current units.
As an example, if the time history data are in cm/sec/sec units and the current units are ft/sec/sec, then a scale factor of 0.0328 should be entered, because 1(ft) / 30.48(cm) = 0.0328.
What forces are included in reactions for time history analysis?
Question: What forces are included in the reactions that are reported for direct integration time history analysis, are they:
- structural forces corresponding to K*u
- damping forces corresponding to C*du/dt
- inertia forces corresponding to M*d^2u/dt^2
- or a combination of the above?
Response: The reactions include the effects of only elastic (or inelastic) forces unless links are connected at the joints in which case the damping forces from links are also included in computing the joint reactions.
What value should I set for output time-step size for time history analysis?
The output time-step size should be small enough to provide sufficient resolution for the analysis. The required resolution depends on the characteristic of applied loading and also on the characteristics (such as natural periods) of the structure itself. You can determine whether the resolution is sufficient by decreasing the time-step size until the step size is small enough that results are not longer affected by it.
What time-step size should be set for input acceleration record? And what time-step size should be set for input displacement record?
Extended Question: Say that the analysis resolution requires 0.005 sec output time-step size. What time-step size should be used for input acceleration record and what time-step size should be used for input displacement record?
Answer: → Open Question
