Human-induced Vibration Comfort And TMD Vibration Control Of Long-span Cantilevered Floor Structure By Liu Kaifang

Large-span cantilevered structures,as more typical structural forms in spatial structures,have been more widely used in public buildings such as stadiums,exhibition halls and office buildings.Compared with the ordinary floor,the cantilever structure has a lower damping and lower natural frequency due to its unique shape and special boundary conditions.When people move,the dynamic response of the structure is more obvious and it is easy to cause resonance.Although this phenomenon does not pose a certain safety threat to the structure,excessive vibration will make the site personnel feel uncomfortable and easily cause panic and other comfort degree problems that seriously affect people's normal activities,Therefore,for this type of cantilever structure,its comfort under human-induced vibration is more worthy of study.The research on the comfort of the floor can usually be divided into two aspects.The first aspect is to make a preliminary prediction based on the modal frequency of the structure,and the second aspect is to study the vibration response of the floor under the action of the crowd.The main highlight of this article is to quickly predict the vibration response of the building under pedestrian excitation by referring to the frequency response function analysis method for cantilever structures proposed in the second edition of the American Code.And a comprehensive set of two methods of numerical analysis and experimental testing are comprehensively evaluated for the comfort of the floor.Researched the subject from the following aspects:(1)Taking the cantilevered floor of the Gansu Gymnasium as the engineering background,first,a 15mx62.4m large-span cantilevered floor model established by the finite element analysis software ANSYS was used to obtain the modal characteristics of the structure through modal analysis.Secondly,after the completion of the construction,an on-site experimental modal test was carried out,and the dynamic response of the floor under the environmental excitation was tested using the 941 B low-frequency sensor and the INV3060 V acquisition instrument.According to the results of experimental modal analysis,the finite element model is modified,including optimization of boundary conditions and curtain wall parameters,and equivalent simulation.An equivalent simulation method to realize the contribution of the curtain wall to the constraint stiffness of the cantilevered floor by supporting systems with relatively high strength such as hanging columns is emphasized.The rationality of this method is verified by experimental modal results.(2)Based on the modified finite element mode,The frequency response function analysis method proposed in accordance with the AISC and the harmonic response analysis module in ANSYS are used to quickly predict the acceleration peak of the floor under the action of the crowd.A preliminary assessment of the comfort of the floor is also carried out.(3)Subsequently,the finite element software ANSYS was used to simulate the vibration response of the floor under the excitation of pedestrian loads.For the pedestrian load model,the contribution of the sub-harmonic component to the Fourier series model and the biomechanical model is further considered,taking into account the main harmonic component.Secondly,the on-site human-induced vibration test was carried out,and the vibration response of the floor under the excitation of free and rhythmic sports including: stepping,walking and jumping and running under the most unfavorable working conditions were tested respectively.The vibration response of the floor to different areas,different routes,different numbers of people and different loading methods are discussed.Based on the test results,verify and discuss the results of the specifications and numerical simulation analysis.The peak acceleration was used as an indicator to evaluate the comfort of the floor using three methods: comprehensive norms,a simulated crowd load model,and field tests.(4)Finally,two methods are used to study the damping effect of the floor under the tuned mass damper.Design of TMD parameters according to the test modal characteristics of the floor,among them,the numerical simulation analysis and experimental test of the floor acceleration of the 40 people fully meet the comfort limit,and the vibration reduction rates are 63% and 48%,respectively.The unfavorable conditions of the field test,that is,the vibration reduction effect under running and jumping excitation are also obvious.