I did example 4, portal 2DElasticElement frame uniform dynamic analysis. The output does not make sense to me. The base shear forces are saved to RBase.out.
why is the shear force at column 1 positive while the one at column 2 is negative? Since it is uniform earthquake ground motion, the shear force should always be at one direction at a time.
Thanks.
Question Solved.
In the static analysis, the shear force at each column foundation are of the same value with opposite direction.
The value and direction changes with time when the dynamic analysis is running. The following figure well illustrates the process.
Last edited by yuejun on Tue Sep 23, 2008 5:26 am, edited 3 times in total.
you are looking at the results at the start of the analysis when the only load acting is basically the gravity load, suggest you look further into the motion & subtract off the initial values or remove gravity load to satisy yourself.