Papers by Author: Gao Lin

Abstract: The dynamic response of reservoir-gravity dam-foundation interaction is calculated using the scaled boundary finite element method (SBFEM) in frequency domain. The transmitting boundary for the structure-unbounded foundation interaction analysis in frequency domain is used. The lingering effect of the unbounded foundation on the earthquake response of the dam is analyzed. Characteristics of several approximate models developed in the literature are investigated and compared. The results show that the dynamic stress modeled by mass-less foundation overestimate the earthquake response of the dam and the maximum stress considering the effect of the lingering effect is more than that of no lingering effect.

Abstract: Numerical analysis methods in time-domain and frequency-domain are commonly considers as two important ways for seismic evaluation of structure responses. FFT plays a unique role in building the equivalent expression between the structural dynamic signals in time domain and frequency domain, such as computing frequency spectrum values at discrete frequency points for time history data. On the basis of radix-4 and radix-2 FFT techniques, an improved district fast Fourier transfer FFT is presented in this paper to improve the transform efficiency, in which radix-4 transform is applied in most iterative steps, besides radix-2 transform used in the last one iterative step. As compared to the traditional radix-2 FFT, the new mixed-radix FFT leads to distinct reducing in computing amount, while the equivalent precision and the same discrete frequency points remain. Also by taking the trigonometric coefficient method as theoretical results, it’s numerically validated through some examples that the new improved FFT transform technique suits the engineering application of the fast numerical transform in the time and frequency domain for structural frequency spectral analysis.

Abstract: An experimental study of the damage behavior of two kinds of concrete with different strength grades has been performed using 100mm cubes subjected to increasing hydrostatic loading history, namely, the isotropic compression at high pressure. The compressive strength and ultrasonic velocity are measured before and after loading history, respectively. The damage degree of these cubes is defined as the reduction of compressive strength based on the continuum damage mechanics theory. Linear and exponential curve fit of experimental data is performed respectively to describe the evolution of damage as well as the descent of ultrasonic velocity with respect to the loading history. It can be seen that, the influence of hydrostatic loading history upon strength and ultrasonic velocity could really reflect that upon the degree of damage development. In general, ultrasonic inspection is convenient and applicable to estimation of damage of concrete due to loading history in engineering practice.

Abstract: An elastoplastic-anisotropic damage constitutive model for the description of nonlinear behavior of concrete is presented. The yield surface is developed in effective stress spaces, which takes into account the hardening effect and better match the experimental data. The stiffness degradation and softening effect are considered in the framework of continuum damage mechanics formulation. The second-order damage tensor is used to characterize the anisotropy induced by the orientation of microcracks. In order to simulate the unilateral effect, the elastic Helmholtz free energy is decomposed into a volumetric part and a deviatoric part. The different behavior under tensile and compressive loadings is modeled by using different variables in effective stress and damage tensor. Numerical results of the model accord well with experimental results at the material and structural levels.

Abstract: When pseudostatic method is employed to analyze slope seismic stability of high earth- rock dams, earthquake load is computed according to dynamic seismic coefficient figure in the present Specifications for Seismic Design of Hydraulic Structures (DL5073-1997). The figure is only suitable for earth-rock dams lower than 150m. While at the present time, many earth-rock dams to be constructed are higher than 150m. Compared with low dams, high order self-vibrating period of high dams is easy to coincide with seismic predominant period, and high order vibrations are constantly to be activated and amplified, which result in seismic acceleration distribution is different from low dams. With analytical and finite element method respectively, seismic acceleration distribution of high earth-rock dams is analyzed. Suggested dynamic seismic coefficient figure of earth-rock dams 300m-level in height is put forward, which offer a supplement for the present Code for Seismic Design of Hydraulic Structure.

Abstract: Before concrete structures are subjected to dynamic loadings such as earthquake, usually they have already withstood static loads. Accordingly, the study on the strain-rate sensitivity of concrete should also be closely related to the initial static loads that concrete structures experience. But majority of the available documents concerning the dynamic properties of concrete do not take initial static load into consideration. In this study, experiments were carried out to investigate the effect of initial static load on the dynamic strength and deformation characteristics of concrete in compression. A load was initially applied on the specimen at a very low speed to a specified value and then the dynamic load was applied at a high strain rate up to the failure of the specimen. From the test results it was revealed that the initial static load had significant influence on the dynamic strength. The dynamic strength tended to decrease as initial static load increased. An exponential function was proposed to formulate the relationship between the initial static load and the dynamic strength.

Abstract: Understanding the behavior of concrete under dynamic loading conditions is an issue of great significance in earthquake engineering. Moisture content has an important influence on the strain-rate effect of concrete. In this study, both tensile and compressive experiments were carried out to investigate the rate-dependent behavior of concrete. Tensile experiments of dumbbell-shaped specimens were conducted on a MTS810 testing machine and compressive tests of cubic specimens were performed on a servo-hydraulic testing machine designed and manufactured at Dalian University of Technology, China. The strain rate varied in a wide range. The analytical formulations between the dynamic strength and strain rate were proposed for both compressive tests and tensile tests. It was concluded from the results that with the increasing strain rate, strengths of specimens with both moisture contents tended to increase and the increase seemed to be more remarkable for the saturated specimens; based on the experimental observation, a better explanation for the dynamic behavior is presented.

Abstract: Understanding the dynamic behavior of concrete in rapid loading is an issue of great importance in civil engineering. In this study, an experimental program was performed to investigate the dynamic behavior of concrete subjected to different strain-rate loadings. From the test results the rate-dependent effect on the ultimate strength of concrete was confirmed, i.e., the strength increases with the increasing strain rate. The dynamic failure process of concrete in tension and physical mechanism were discussed based on the experimental observations.

Abstract: The phenomenon creep fracture is well-known for concrete. In the present paper, the Material Failure Process Analysis (MFPA2D) model for concrete in the failure process is coupled in series with the time-dependence of the concrete damage and deformation. Further, the progressive creep failure of concrete specimens under constant tensile loading was numerically simulated and the typical time-dependent deformations: the transient creep, the steady-state creep and the accelerating creep were also represented. The numerical simulations indicate that the macroscopic creep failure is induced by clusters of micro-fractures on a mesocopic scale. The above numerical results offer us some theoretical indications and instructions to further investigate the instability failure mechanisms of engineering concrete structures in civil and hydraulic engineering.