Hello,
I came across above warning, inspite of providing density in material.
input file for the same is:
STAAD SPACESTART JOB INFORMATIONENGINEER DATE 19-Jan-18END JOB INFORMATIONINPUT WIDTH 79UNIT MMS KGJOINT COORDINATES1 0 0 0; 2 1000 0 0;MEMBER INCIDENCES1 1 2;DEFINE MATERIAL STARTISOTROPIC ENE 21406.7POISSON 0.3DENSITY 7.85e-006ALPHA 1.2e-005DAMP 0.03TYPE STEELSTRENGTH FY 23.955 FU 36.7 RY 1.5 RT 1.2G 8256.88END DEFINE MATERIALCONSTANTSMATERIAL EN ALLMEMBER PROPERTY INDIAN1 TABLE ST ISMB150SUPPORTS1 2 PINNEDLOAD 1 LOADTYPE None TITLE FREQUENCY CALCULATIONSELFWEIGHT X 1 SELFWEIGHT Y 1 SELFWEIGHT Z 1 MEMBER LOAD1 CON GY 2000 5001 CON GX 2000 5001 CON GZ 2000 500MODAL CALCULATION REQUESTEDPERFORM ANALYSISFINISH
Check this Wiki post for an answer (3rd item in your case): https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/29002/no-unsupported-masses-entered-error
Answer Verified By: Vishal Girase
Hello Modestas,
Could you please tell me, why it is dependent on presence of free node?
Also what was surprising for me, that with increasing no of nodes the eigen solution chages (frequency decreases).
Why it is so?
Vishal : In order to get a frequency analysis or get the mode shapes, there has to be masses that can vibrate. Masses are lumped at the nodes. So if you have a single beam with a concentrated load in the middle and if you pin both ends of the beam, the masses which are lumped at the two ends of the beam, are prevented from vibrating by the pinned supports .That is why you are getting the error. As Modestas suggested you need to split the beam into segments.
Having additional nodes mean that the distribution of the mass also changes as masses are lumped at the nodes and it would affect the modes and the frequency calculation. For your model you need to split the beam so that you have a node at the middle and then you need to change the member load to nodal load. I have attached two versions of your model
Model 1 : split into 4 segments
Model 2: split into 8 segments
The frequencies are practically the same for both models.
3108.Model1.STD
Model2.STD
Hello Sye,
Thanks for the explanation.
I have one more doubt, in case of UDL or selfweight (which act as udl), there will be only member load.
Then in that case only providing free node will be sufficient?
I think its location will also matter?
Providing a center node will be conservative.
Just need confirmation for :the load defined shall be in newton (force), irrespective of units selected.
Vishal : Just as a concentrated load, selfweight and udl would also be lumped at the end nodes. So if your end nodes have supports defined, you would need to add intermediate nodes to the beam. If you are going to add one node, adding it at the center would be good. If there is a significant concentrated load at some other location whose vibration with respect to the ends is important to consider, then having additional node at that location may be considered. Load can be defined in any units of force and the software would internally convert those into mass.