Time Integration Parameters Form

Choose the analysis method to be used and use the available edit boxes to enter the necessary values.

As shown, a variety of common methods are available for performing direct-integration time-history analysis. Because they are well documented elsewhere, we will not describe them further here, except to suggest that you use the default "Hilber-Hughes-Taylor alpha" (HHT) method, unless you have a specific preference for a different method.

The HHT method uses a single parameter called alpha. This parameter may take values between 0 and -1/3.

For alpha = 0, the method is equivalent to the Newmark method with gamma = 0.5 and beta = 0.25, which is the same as the average acceleration method (also called the trapezoidal rule). Using alpha = 0 offers the highest accuracy of the available methods, but may permit excessive vibrations in the higher frequency modes, i.e., those modes with periods of the same order as or less than the time-step size.

For more negative values of alpha, the higher frequency modes are more severely damped. This is not physical damping, since it decreases as smaller time-steps are used. However, it is often necessary to use a negative value of alpha to encourage a nonlinear solution to converge.

For best results, use the smallest time step practical, and select alpha as close to zero as possible. Try different values of alpha and time-step size to be sure that the solution is not too dependent upon these parameters.