Nonlinear Response Effect For Long-span Structure Under Multi-point Non-stationary Seismic Ground Motion With Spatial Correlation Characteristics

Seismic ground motion is a complicated time-space process,which behaves obviously non-stationary at time domain and the frequency domain.The engineering practice shows that the effect on structures of changes in frequency content of ground motion cannot be ignored.If the non-stationarity of the amplitude is only considered,the structural responses cannot be estimated reasonably.Therefore,while describing the spatial variation of seismic ground motion,it needs to consider the frequency non-stationarity and develop the correspondingground motion synthesis method,which plays an important role in ensuring the safety of long-span spatial structure.By introducing a frequency-dependent amplitude envelope function with statistical significance to simulate the non-stationarity of frequency in earthquake ground motion,a method is developed for the single point non-stationary earthquake ground motion,which takes the response spectrum as the target.Based on this,the coherence function is introduced to develop the method for the spatially correlated multi-point ground motion with frequency non-stationarity.And then,the paper designed some seismic input plans with different frequency spectrum characteristics.By analyzing the seismic response of the regular reinforced concrete frame structures and long-span bridge structure,some conclusions have been obtained,which can provide a usefull theoretical basis for practical engineering applications.The main research contributions of this dissertation are as follows:1.By introducing a frequency-dependent amplitude envelope function with statistical significance,the paper established a method for the seismic ground motion with multiple targets(response spectrum?predominant frequency.PGA).The method can simulate the non-stationarity of frequency in earthquake ground motion,and also agree well with the time-variation of the real ground motion frequency;2.Because the non-stationarity of ground motion frequencies hassome effect on the responses of the structure,there is a risk of underestimating the structural non-linear response with only the non-stationarity of the amplitude.Thus,the non-stationarity of frequency in earthquake ground motion should be considered in the simulation of the artificial ground motion.In this way,the structural nonlinear responses could be estimated reasonably and the safety of the structure design can be guaranteed;3.With the parameters under clear physical meaning,the method for the spatially correlated multi-point ground motion is so clear and easier that it can be easy to master and apply for engineering designers.Meanwhile,the method can both simulate the non-stationarity of frequency and the characteristics of the spatial variation;4.Whether the multi-point input or consistent input of the seismic ground motion,the non-stationarity of frequency can affect the displacement response of the bridge bracings.The analysis show that there exists a risk of underestimating the displacement response of the bridge bracings;5.For the space bridge,the coherent seismic input can underestimate the displacement response of the bridge bracings.Therefore,in the engineering practice,the non-stationarity of frequency and the characteristics of the spatial variation both should be considered reasonably,so that the safety of the structures can be guaranteed.6.Using GUI development environment of Matlab,a visual software for artificial ground motion synthesis has been developed based on the method of single point non-stationary seismic ground motion in the paper.The software is so easy to operate and very suitable for engineering applications.