Is there an option in Staad to not lump the mass on nodes for Modal analysis and instead distribute the mass (like uniformly distributed load) along the length?
This could be important as it may affect member design for response spectrum analysis. For example, minor axis bending of beam due uniformly distributed mass along a beam will not be captured in the design.
STAAD.Pro follows a lumped mass concept in modal analysis. If you have a non-uniform loading in a member, the mass distribution is being done considering the non-uniformity of the loading. For RSA, the responses are being properly captured in the nodes.
Is there option to lump mass not at end nodes of the member but along the length of the member?
To explain you further -
If I use Equivalent Lateral Force Method and apply uniformly distributed load (weight) of a member as a lateral uniformly distributed load, lets say along the direction of minor axis of a wide flange beam then my beam will show minor axis bending force. In case I use RSA where the mass is transferred to nodes the minor axis bending of beam is not captured.
No, masses are lumped at the nodes only.