Research And Improvement On Traditional Response Spectrum CQC Method

The most important task of anti-seismic design of structures is to determine the earthquake action and its effect which act as an important basis of design and verification. At the present time, the response spectrum CQC method is the most recommended method by code for anti-seismic design of structures in China and most other countries. As the ground action is in fact a random process which depending on quake scale, quake mechanism, propagation path and site condition, etc. it is reasonable to perform the anti-seismic design with random vibration analysis method in theory. The complex calculation and expensive cost of random vibration analysis method make it be the bottleneck of its wide application. In order to bypass the application difficulties of random vibration analysis method, engineers have no choice but to explore other methods which can improve calculation efficiency significantly and can ensure enough accuracy, hence the response spectrum CQC method is introduced. It is regarded by engineering world that the earthquake and its effect obtained with traditional response spectrum CQC method can ensure enough accuracy as well as less calculation cost. But when be putting into practice, the results obtained with traditional response spectrum CQC method may be much less than the real ones, and some time they can't explain the damage causes by earthquake, and some time they don't agree with the results of model test. In this paper, all works are centered about the object to improve the accuracy of traditional response spectrum CQC method, and intensive researches are performed according to random vibration theory and response spectrum theory. The following are some primary achievements:1. The improved response spectrum CQC method which features good accuracy is introduced, while the improved method doesn't increase calculation difficulties and complexities. By means of calculating with well-known commercial program MSC.Nastran and comparing results of traditional response spectrum method and improved response spectrum method with results of random vibration analysis method and time history analysis method respectively, it comes to conclude that the improved response spectrum method is more reasonable while the traditional response spectrum method is not satisfactory.2. The acceleration response spectrum defined in state design code is transformed to consistent power spectrum density. Using the white noise assumption of ground action and the consistent power spectrum density respectively, modal correlation coefficient is calculated, and then using results from modal analysis with MSC.Nastran, calculation is performed with traditional response spectrum CQC method and improved response spectrum CQC method and self-coded program. It's proved that the white noise assumption of ground action is fully reasonable after comparing above results each other, so it is possible for the improved response spectrum CQC method to be widely applied in engineering.3. Results obtained with random vibration analysis method show that when calculating earthquake action and its effect of structure components of complicated buildings with response spectrum CQC method, the influence of truncated high frequency mode can not be neglected, especially at location near bottom. Therefore, in order to get more accurate results, it is suggested that the calculation be performed with improved response spectrum CQC method and the influence of truncated high frequency mode also be included.4. The accuracy degree of results obtained with response spectrum CQC method also depends on number of combined modes to a great extent. At present time, the widely applied method to determine reasonable number of combined modes is mass participation ratio method. In this paper, deficiencies of mass participation ratio method are analyzed and efficient frequency control method which can act as a good supplement is introduced at the same time. Compared with mass participation ratio method, the frequency control method can efficiently increase accuracy of results obtained with response spectrum CQC method.