Thepseudoexcitationmethod(PEM)hasbeenimprovedintoamorepracticalform,onwhichtheanalyticformulaeofseismicresponsepowerspectraldensity(PSD)ofsimplifiedlarge-spanstructuralmodelshavebeenderived.TheanalyticformulaeandnumericalcomputingresultsofseismicresponsePSDhavebeenderivedtostudythemechanismofmulti-supportexcitationeffects,suchasthewave-passageeffectandincoherenceeffect,fortheseismicresponseofmultiandlarge-spanstructures.Byusingamulti-spantrussasanexample,theinfluenceofmulti-supportexcitationeffectsontheseismicresponseofsuchstructuresisstudied.