From the engineering point of view buildings are mechanical structures assembled by plates, shells, beams and rods. As every mechanical structure buildings are vibrating due to the presence of vibration sources. Wind excitation causes a low frequency tilting of the building with high vibration amplitudes (up to 500µm/s) in the horizontal direction. Especially the upper floors are affected by wind excitation. Plants and heavy traffic in the surrounding area result to building vibration of small to mid size amplitudes (typical values are 5 – 100µm/s). The related excitation frequencies are typically in the range of 5 to 100Hz. Seismic excitation causes vibration over the entire building in vertical and horizontal direction, e.g. twisting. The corresponding excitation frequency is very low (0.5 – 10Hz) whereas the amplitudes are varying from small to extreme large values.
Internal machinery, e.g. elevators and air condition systems may generate local vibrations. Local vibrations are limited to a substructure of the building, e.g. a single floor. The related amplitudes are high in the near field of these sources (up to 200µm/s), but they are decreasing rapidly with the distance. The excitation frequencies are very different, depending of the type of internal machinery but as a general rule they are more focused to higher values (10Hz and higher).