Figure 5.2: Effect of Integration Time Step on Period Elongation
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For the HHT time integration method, the same guidelines for time step should be applied. Note
that if the same time step and time integration parameters are used, the HHT method will be more
accurate compared to the Newmark method.
An alternative way to select time step size is to use the midstep residual criterion. When this criterion
is used, the response frequency criterion is disabled by default.You have the option to enable the
response frequency criterion along with the midstep residual criterion (see item 6 below).
- Resolve the applied load-versus-time curve(s). The time step should be small enough to "follow" the
loading function. The response tends to lag the applied loads, especially for stepped loads, as shown in
Figure 5.3:Transient Input vs. Transient Response (p. 131). Stepped loads require a small ITS at the time
of the step change so that the step change can be closely followed. ITS values as small as 1/180f may
be needed to follow stepped loads.
Figure 5.3: Transient Input vs. Transient Response
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Transient Dynamic Analysis Options
