Influence of Story Mass Ratio on Seismic Dynamic Response of Embedded Modular Buildings

In the seismic design of embedded modular buildings, the dynamic coupling effect between the main structure and embedded modules is generally simplified or neglected. This study investigates the influence of story mass ratio on the seismic response of a six-story steel frame structure with embedded box modules. A coupled finite element model was established, and the equivalent lateral stiffness simulation method was theoretically verified. Elastic time-history analyses were conducted using three representative ground motions. Eight story mass ratios were considered, and the floor displacement, story shear force, and floor acceleration response spectra were compared between coupled and appended-mass models. The results indicate that the story mass ratio is an important parameter affecting the magnitude of module–main-frame coupling effects within the investigated prototype. For the investigated structural prototype and selected seismic inputs, the differences between the coupled and appended-mass models are relatively small at relatively low mass ratios, while the influence of coupling becomes progressively more significant with increasing μ. With increasing μ, lower-story displacement and story shear increase noticeably (maximum first-floor displacement ratio: 1.157; maximum shear ratio: 1.139), while upper-story responses decrease, with a maximum reduction in top-story shear of 16.9%. In addition, the short-period spectral peak of the floor acceleration response spectra is influenced by the mass ratio. For the investigated cases, noticeable differences in local floor spectral peaks are observed at relatively higher mass ratios, with relative spectral differences exceeding 5% in some floors based on the adopted comparison criterion and significant reductions occurring at larger mass ratios. These results provide preliminary insights into model selection and seismic response evaluation of the investigated embedded modular building prototype.