A Research Based On Time-domain Constitutive Seismic Response Method

Seismic damages indicate that different site conditions lead to diverse ground motion, accordingly have different impact on structures. How to describe the site response effectively and reasonably, which provides scientific and reasonable design earthquake ground motion parameters for seismic design, has become one of the most important tasks in seismic resistance. However, research findings and engineering practices show that equivalent linear method still has limitations to simulate nonlinearity and other aspects. As a nonlinear mothod, time domain integral method is a more accurate way of estimating seismic response of nonlinear soil layers, and the soil dynamic constitutive model is the key factor for the accuracy of estimating. The Unsymmetrical Exponential(UE) dynamic constitutive model has advantages of low memorization, explicit physical meanings of parameters, simple expressions and describing asymmetric cyclic loading. However, the model is asymmetric and is unable to fit the distribution of soil damping ratio variate with changing strain appropriately, when it is used to describe the soil hysteresis loop under constant amplitude cyclic loading. Based on existing research, this paper proposed a modified UE model which is used to fit damping ratio. The new model was verified by strong ground motion records of Xiangtang three dimension array in Tangshan and arrays in Japan. The main research achievements in this paper are discribed as follows:1. The research status of soil dynamic 1D nonlinear constitutive models were summarized.In this paper, the proposing process and the basic principle of equivalent linear method and time-domain integral method were summarized briefly. In addition, the current domestic and international soil dynamic constitutive models were expounded. Then, the models’ proposing process, basic principle and application areas were clarified.2. A modified UE soil dynamic constitutive model was proposed.The original UE model’s structure principle, derivation process and defects that unable to fit damping ratio effectively and asymmetric hysteresis loops were introduced briefly. Then, a modified UE model based on Luan Maotian Semi-analytical and Semi-discrete method proposed to modify these defects. In order to verify the model’s effects on damping ratio fitting and symmetrical characteristic of hysteresis loop, a series of tests were conducted by a project site data in Harbin. Then, use the soil dynamic test data which obtained by Yuan Xiaoming and other researchers to summarize the change trend of the parameters in the modified model.3. The NDsoil-1D program was tested by strong ground motion records of Xiangtang array in Tangshan.This paper selected three strong bedrock motion records of Xiangtang borehole array(3#) site as the input ground motion, then used equivalent linear method and time-domain integral methods embedded with the modified UE model, the original UE model and the “dynamic skeleton curve” model respectively to calculate site seismic response analysis. Finally, the advantages and disadvantages of each method were summarized by comparing computing results with the actual records.4. The NDsoil-1D program was tested by strong ground motion records of Japanese array.The modified UE model was tested by ground motion from a wide range of input intensity, which selected from two Japanese array sites. And the computing output acceleration time history, Fourier spectrum and response spectrum were compared with the actual records to validate the modified UE model again. Finally, the causes of calculation errors were analysed.