Impedance Modeling: An Efficient Modeling Method for Prediction of Building Floor Vibrations

Buildings in major cities may be affected by vibrations from many sources such as trains, and subways. These ground-born vibrations are received at the building foundations and propagate up throughout the structures. The prediction of building floor vibrations plays an important role in the design of buildings for human comfort, the operation of sensitive equipment, and in nano-scale manufacturing. The ability to quantify and to predict building floor vibration levels enables engineers to take sufficient preventive measures based on a site condition. The accuracy of Finite Element Analysis (FEA) used for the prediction of building floor vibration depends on the mesh size used for modeling and the frequency range of the excitations. Although fine mesh sizes in FEA leads to greater accuracy, it becomes computationally prohibitive to achieve accurate predictions in higher frequency ranges. An impedance model provides an alternative simplified technique for the prediction of building floor vibration with great accuracy even in higher frequency ranges. This paper successfully illustrates the robustness of impedance modeling as compared to finite element (FE) modeling, in the prediction of building floor vibrations due to measured vibrational excitation at the foundation level. Impedance modeling provides the vibration response with a high degree of accuracy across the full frequency spectrum. Such models show the axial wave propagation along the length of a column when the floors are treated as point impedance discontinuities where they are attached to a column. Compared to FE models, it provides much higher accuracy with a method that is far more computationally efficient. Impedance modeling is a powerful tool for the simplified prediction of train and subway induced vibrations in the design phase of new buildings and may help with mitigating the effects of floor vibrations in existing buildings.