Have you defined the density property of the material?

This example could be useful to you...

http://www.mece.ualberta.ca/tutorials/ansys/IT/Modal/Modal.html

The modal analysis needs the mass of the structure to be defined. This is gathered from the density of the material used. Check your Engineering Data that the selected material has a density defined. Quick check, use the default material (Structural Steel).

Tq everyone,

Hello sir Bai-qiao chen and Fawzi belblidia,

I have defined solid65 material mass as shown in the picture below, or am i wrong with it? Even there is no mass input required for concrete and linear iso in preprocessors-material props-material models. I have watched some tutorials in youtube about modal analysis. What i have found out that they even don't face with this kind of problem even though i have followed and applied exactly as shown in the tutorials. How I am gonna tackle this problem especially in my current model?

The model analysis does not work if mass matrix is zero. You can avoid the error by either introducing point mass elements or specifying density of the material (see material models).

tq sir stanislav levyakov,

I managed to achieved it last few days. But here I just want to make sure that the density for concrete is 2400kg/m^3 which I used it as the input density(material models).But somehow it will cause the modal analysis process took longer time(up to 5hours) just for a simple model. Is it correct that the unit that was generally set up is kg/m3 or i need to convert it to any other unit?because i could not find out what is the exact unit for density in my Ansys APDL material models. 

in ANSYS there are not appointed units . The key is all the units used are supposed to be in the same system. To avoid mistakes it is better to use SI units. If you use metre and kilogram, the unit for density is kg/m3.

tq sir bai-qiao chen, 

By the way, how can I reset the working unit? I would like to start from the beginning to reduce the errors face in my current model.

in ANSYS there is no way to set the units. You can simply input the values of properties according to SI system.

 I need some help, I have run block lanczos modal analysis. It showed that ' the solution is done ' . However, there is no any result come out in result summary. why?