Applies To
	Product(s):	STAAD.Pro
	Version(s):	All
	Environment:	N/A
	Area:	Analysis Solutions
	Subarea:	Time History Analysis
	Original Author:	Bentley Technical Support Group

Why am I getting a warning saying the "number of time steps for time history results for solids is too large"?

**WARNING: NUMBER OF TIME STEPS FOR TIME HISTORY RESULTS FOR SOLIDS IS TOO LARGE.
ONLY EVERY 2TH STEP OF FIRST 5580 STEPS WILL BE CALCULATED.

This time history warning is reported when the amount of data generated by the dynamic analysis becomes too great for the program to handle.  This typically occurs in big models containing many elements when the time step (DT) is small and the number of cycles is large.  As such, there are two ways to resolve this problem:

1.  Reduce the number of cycles.

2.  Increase the integration time step value. 

The number of cycles determines the length or duration of the time history load, so it is best to first review how many cycles are specified in the time history definition to see if makes sense.  For example, suppose you have a time history definition in which the frequency is defined as 60 Hz and the number of cycles is specified as 100, as shown below:

In such a scenario, the total duration of loading is 100 cycles / 60 Hz = 1.667 seconds, which is relatively short.  However, if the number of cycles was instead specified as, say, 10000 cycles, the total duration would be 166.67 seconds (or 2 minutes 47 seconds) which is far too long.  While the ideal time history load duration will vary depending on a number of variables (dynamic characteristics, mass, type of structures, damping, number of load points, phase angles, etc.), the general rule of thumb is that it should be long enough for the system to move past the initial transient phase and achieve a steady state, but not so long as to generate excessive data, long analysis times, etc.  Typically 5 - 15 seconds is enough.  

If you reduce the number of cycles to achieve a reasonable load duration and still get the warning, the next thing to try is increasing the integration time step value in the time history definition.  The default is 0.0013888 s.  It is important to note that if the value is increased too much there will be a reduction in accuracy, so it's best to make a small increase at first (say, to 0.005) then test to see if the warning is eliminated.

   

 You may have to keep incrementally increasing the integration time step several times before landing on one that works.