Research On Human-Induced Vertical Vibration Serviceability Of Large-Span Suspended Floor

Large-span suspended floors have emerged in the field of building structure because of their unique architectural design,excellent structural performance and strong functionalities.Because this type of structure usually uses hanging pillars to suspend the substructure system on the top main bearing components,the vertical support stiffness is smaller than that of ordinary floors,and the vertical vibration serviceability under human-induced load is more prominent.As an important indicator of human vibration perception,vibration serviceability has gradually attracted the attention in engineering and academia,and has developed into the main control factor of flexible structure design.How to accurately and quickly evaluate the human-induced vertical vibration serviceability of long-span suspended floors has important practical application value and practical guiding significance.Relying on the project of National Natural Science Foundation of China“The theory and technology of three-element passive mitigation of structural vibration and its performance improvement for vibration control of stay cables”(51878274),the suspended corridor floor between the super high-rise towers of Nanjing Global Trade Plaza is taken as the engineering background.According to the modal results of field test,the validity analysis of finite element modeling of suspended floor is carried out.The overall and local equivalent finite element modeling methods for accurate evaluation of vibration serviceability are proposed.Based on the bending vibration theory of rectangular thin plate and energy principle,a simplified calculation formula of fundamental frequency of the suspended floor is derived.The multi-factor influence analysis of fundamental frequency and peak acceleration is carried out,and a rapid evaluation process of vertical vibration acceleration under human-induced load is proposed.The main conclusions are as follows:(1)In the analysis of dynamic characteristics of suspended floor,the effectiveness of the overall finite element modeling can be improved by considering the influence of the decorative surface layer,structural additional mass and boundary conditions on the natural frequency of the suspended floor.A local equivalent finite element model is established by simplifying the hanging pillars as an equivalent mass distributed vertically along its position,and simulating the elastic support with adjustable vertical stiffness at the suspension point.The dynamic characteristics are consistent with the overall finite element model and the measured results.Based on the bending vibration theory of floor and energy principle,the simplified fundamental frequency formula of suspended floor is derived,and the theoretical calculation value is in good agreement with the finite element value.The fundamental frequency of the suspended floor is affected by factors such as rib beam spacing,rib beam stiffness,hanging pillars stiffness,layout of hanging pillars and floor loads.Effective structural measures can be taken in the design to avoid floor resonance caused by human-induced excitation frequency on the basis that the natural frequency of the floor meets the requirements of the vibration serviceability specification.(2)In the dynamic response analysis of the suspended floor under human-induced load,the vertical acceleration time history response and 20 s root mean square acceleration response of the suspended floor predicted by the local equivalent finite element model are always consistent with the overall finite element model,and the numerical results of the vibration response under the condition of single person walking in situ are in good agreement with the measured results.The theoretical simplified formulas of peak acceleration and root mean square acceleration in the code can be used for rapid evaluation of vertical vibration serviceability of the suspended floor under walking loads.The peak acceleration of the suspended floor is affected by factors such as rib beam spacing,rib beam stiffness,hanging pillars stiffness,layout of hanging pillars and floor load.Effective structural measures can be taken to improve the vibration comfort of suspended floors during engineering design,providing reference design suggestions for structural serviceability analysis and structural design.(3)In the study of vibration control of suspended floor by tuned mass damper(TMD),the RMS acceleration of finite element for the single person walking in situ(WP-1)condition is decreased from 0.0107m/s~2 to 0.0060m/s~2,with a vibration reduction rate of 43.93%,and the RMS acceleration measured in the field is decreased from 0.0095m/s~2 to 0.0061m/s~2,with a vibration reduction rate of 35.8%.The single-layer local equivalent finite element model proposed in this paper can replace the overall finite element model to predict actual vibration responses of the suspended floor with TMDs.After installing TMDs,the vibration response of the floor under various working conditions fully meets the comfort limit,and the maximum vibration reduction rate can reach 69%when four peoples run synchronously(RP-4).