TR.37.6.1 Purpose

This analysis type is used to model steady, harmonically varying load on a structure to solve for the steady harmonic response after the initial transient response has damped out to zero. STAAD.Pro Steady State analysis options include results for one forcing frequency or for a set of frequencies. You may specify ground motion or a distributed joint loading in one load case. Damping is required either in this input or from the Modal Damp input or from the Composite Damping input.

This command is used to specify the analysis request, specify that the load case with the MODAL CALCULATION command (which must be prior to this analysis command) be used as the definition of the mass distribution, and to begin a block of data input describing the steady state forcing functions, the output frequencies, and the printing of the joint responses.

All of the input and output frequencies are in Hertz (Hz or CPS).

Related topics can be found in the following sections:

Note: The Modal Calculation command is required in the weight/mass definition load case.

General Format

PERFORM  STEADY  STATE  ANALYSIS

This command directs the program to perform the analysis that includes:

Checking whether all information is provided for the analysis;
Forming the joint stiffness matrix;
Solving simultaneous equations;
Solving for modes and frequencies;
Computing for the steady state joint displacements, velocities & accelerations and phase angles;
Computing the above quantities versus frequency and displaying the results graphically.
Member & element forces & stresses and support reactions are not currently computed.

The first input after the Perform Steady State Analysis command is:

BEGIN ( { STEADY | HARMONIC } ) ( { FORCE | GROUND } )

Steady or Harmonic

Steady = the analysis is at one forcing frequency

Harmonic = the analysis is at several frequencies

Force or Ground

Choose whether the loading is a distributed joint force load or a ground motion.

This command selects which of the 4 load/analysis types, that are available, will be used in this analysis. These four are described in sections TR.37.6.4 Steady Ground Motion Loading through TR.37.6.7 Harmonic Force Loading.

This block of data should be terminated with the END STEADY command as mentioned in TR.37.6.9 Last Line of this Steady State/Harmonic Analysis.

The steady state/harmonic analysis will calculate the maximum displacement and the associated phase angle for each of 6 joint directions, relative to the ground motion, for each frequency defined in TR.37.6.2 Define Harmonic Output Frequencies.

In PRINT JOINT DISP and in Post processor displayed results, the load case displacement for a given joint and direction will be the maximum value over all of the frequencies (without the phase angles) for a Steady State load case.

In post-processing for harmonic analysis, Log-Log graphs of any joint’s relative translational displacement or velocity or acceleration versus frequency may be selected.

See TR.37.6.8 Print Steady State/Harmonic Results for printing displacements with phase angles by frequency.