Energy Calculation Of Structural Response And Its Preliminary Application Under Seismic Excitation

With the development of studies on seismic response of structures, a common view has been developed for expressing the structural seismic damage via two parameters, which correlates well with both the actual damage and the experimental results. The failure criteria based on two parameters are based on the first time of exceeding maximum displacement and the accumulated energy for plastic damage.Further researches suggest that adopting energy dissipation to represent accumulated energy for structural plastic damage for structrual energy response not only has simple form, but also better represents the effects of earthquake intensity, characteristics of frequency spectrum and especially the duration effect of intensive earthquake ground motions on structural failure.Based on the seismic energy formula of single degree of freedom(SDOF) system total input seismic energy,hysteretic dissipated energy and damping energy can be obtained.In this paper, the concepts for both self-dissipation energy and self-dissipation coefficient are proposed. Based on the analysis of a SDOF system subjected to the earthquake excitation, the relations of earthquake total input energy, self-dissipation energy, earthquake input energy, self-dissipation coefficient , natural frequency and damping ratio are calculated. The results indicate that when natural frequency equals to or is close to earthquake dominant frequency, self-dissipation coefficient is smaller, earthquake input energy is larger, the capability of self-dissipation of the structure is weaker and damping ratio has a bigger impact on the peak value of earthquake input energy. When natural frequency is far away from earthquake dominant frequency, self-dissipation coefficient increases, earthquake input energy decreases, the capability of self-dissipation becomes stronger, natural frequency of the structure has a bigger impact on earthquake input energy, and the damping ratio is unrelated with earthquake input energy.A new method of subsoil damping ratio identification based on law of conservation of energy is proposed in this paper. This method considers the whole time histories of vibration, which differs from the traditional damping ratio identification method in the time domain which uses merely the amplitude to calculate damping ratio, and overcomes the defect of the traditional logarithmic decrement method for high accuracy requirement of amplitude. The subsoil damping ratio of a massive concrete foundation is tested and calculated. The tested result shows that this method is of higher precision, has stronger anti-noise ability and better stability compared with the traditional logarithmic decrement method. Even if the data acquisition is disturbed seriously by noise, the method proposed in the paper is still effective and reliable.