A comparison study between base and forced excitation at the top floor for multi-story structure

Abstract

Multistory buildings may subjected to many types of vibration excitation which affect their structures and properties. The period of vibration or natural frequency is an important parameter in building design as it governs the effect of wind or earthquake. A four story model has been constructed which simulates a multi-story shear structure (like a building). This model is connected to a shaker and a system of accelerometers to measure the dynamic response of that model and to make a comparison for two types of vibration excitations: base excitation and forced excitation at the top floor in order to investigate the dynamic response for the two cases. The results for the base excitation showed that the fundamental natural frequency was less than that for forced excitation at the top floor, and new natural frequencies have appeared in the spectrum. The level of vibration for the natural frequencies is higher compared to forced excitation. The overall level of vibration is higher too, and looks like the system became a self-excitation. The mode shapes for the two cases were determined also, and compared to show that the more critical case is the base excitation.