Product(s):	SACS
Version(s):	23.00
Area:	Dynpac

Problem

I am using SACS Dynpac module. The dyninp*file provides options Consistent Mass and Lumped Mass for Mass calculation. Which approach should I follow?

Solution

In DYNOPT line, SACS allows the user to consider either Lumped mass or Consistent mass. In case of consistent mass, the mass is distributed along the member length. For lumped mass, the mass is present at the member end nodes. For the lumped mass model, total mass and CoG position is same as actual structural mass clubbed with any other imposed mass. Consistent mass approach caters the mass distribution in a better practical way since mass is uniformly distributed along the length of the members. Lumped mass matrix only contains diagonal terms, whereas the consistent mass matrix contains off diagonal terms as well since it is derived from the shape function.