the reliability of the results in NTHA

[saharnaz]

hi
i'm doing NTHA for a 2D, 6 story RC moment frame . i have a big problem, when i use these analysis options, analysis runs successfully but the results are very different from when i use other analysis options,
test NormDispIncr 1.0e-6 50
algorithm KrylovNewton
integrator Newmark 0.5 0.25
analysis Transient
analyze 2500 0.01
in this case envelope displacement of top story is 57cm, but when i lessen the time step to 0.0025 and use integrator HHT 0.5,the envelope displacement is 8 cm!!!!!
which results are reliable?

[fmk]

HHT should not have an alpha of 0.5 .. look at the notes in the command manual