I am fully aware that the consistent mass model in any type of dynamic analysis will lead to more accurate results; in my case, I have a piping system which is subject to a mild seismic incident. the stress results with a lumped mass model are about 65% of code limits but once I switch to consistent mass model and rerun the calculation, I get insanely high stresses about 9000% of code limits.
what baffles me is when I check the "modes unity normalized" in the corresponding mode, the nodes which are tensed the most have been hardly excited!
can anyone tell me what could cause such gigantic difference in the results?