here is my question:www.linkedin.com/.../2259298-6002067863056179201the modal analysis results of sap2000 &rm bridge are the same(almost) .. but not the RSA result..
i add additional mass on the third girder,
the third pier should have larger moment than the fourth one during a longitudinal earthquake .
sap2000 get the intuitive result but not rmbridge..
In systems where there are same frequencies at different positions it can happen that the CQC superposition method doesn't lead to the expected results. In your system we would suggest changing to the CQCX method and increasing the number of "eigen frequencies".