Applied Mechanics and Materials Vols. 90-93

Abstract: Based on model tests, the wave function expansion method was used to study scattering on the interaction of explosive stress waves and the underground chamber, and analyze the influence of the incident angle, frequency and diameter on blasting vibration velocity of underground chamber. It is obtained that when the cavern was under the plane waves of the vault, the radial vibration velocity of the vault is the largest among the four measured data, and it is the most intense vibrating place. When the incidence direction offsets from the vault to the horizontal direction on the left, the radial velocity facing burst are all larger than the radial velocity back of the burst. When the incident direction is on the dome, the tangential vibration velocity will increase first and then decrease from the vault to the side wall. When the incident direction is at the haunch, the tangential vibration velocity in the corner should be noticed. With increasing of the frequency, the radial vibration velocity and tangential vibration velocity increase accordingly. At the forward part of the burst, the larger the chamber diameter is, the bigger the radial and tangential velocities are. At the back side of the burst, the bigger the chamber diameter is, the smaller the radial and tangential vibration velocities are.

Abstract: Conventional isolation systems may induce an excessive response in near-fault earthquakes. A new short time Fourier transformation (STFT) control algorithm for variable friction dampers (VFD) is developed to improve the performance of base isolation buildings in near-fault earthquakes. The STFT controller varies the clamping force in the VFD damper to achieve the response reduction. In addition, the STFT algorithm is implemented analytically on a multi degree of freedom system (MDOF) with laminated rubber bearings and variable friction dampers in Simulink environment. Three types of earthquakes representing a wide variety of ground motions are considered as the ground excitations in the simulation. The numerical show that, compared with conventional isolation systems, the semi-active isolation system controlled by the STFT algorithm can reduce the excessive response in near-fault earthquakes effectively.

Abstract: The effect of adjacent soil improvement on ground motion is studied using finite element method, when seismic wave is introduced from the single layer on bedrock. The influence of ground motion on soil reinforcement is analyzed; the impacts of the reinforcement zone width, depth, elastic modulus, and the soil improvement interval on response of the ground motion are also investigated. Study shows: for the same site, when the distance between two adjacent foundation consolidation interval is less than 3 to 4 times the width of the reinforcement area, the interaction acceleration response amplitude of various points on the surface of the two adjacent reinforcement area increased significantly than the single block; within the interval , increasing one of the two adjacent foundation’s width, depth, and the other foundation surface, the horizontal acceleration response will Subsequently enlarged; when the interval between the reinforcement area is greater than the range, this effect is negligible.

Abstract: Aiming at failure mechanisms and judgment criterion of progressive collapse for space trusses, the responses and the failure mechanisms of diagonal square pyramid space trusses, leaning laid pyramid space trusses and orthogonal square pyramid space trusses with circumferential simple supports under different seismic waves were analyzed in this paper. The results show that space trusses have a good performance of earthquake resistance, but progressive collapse occurs easily. Based on the failure mechanisms of space truss, a judgment criterion of space truss is proposed under strong earthquakes, according to the characteristics of energy, displacements and plastic levels of members. The judgment criterion is expressed by judgment coefficient J. When J>6, space trusses tend to be ductile failure, however, When J> 6, space trusses tend to be progressive collapse.

Abstract: The U.S. Geological Survey Parkfield Dense Seismograph Array (UPSAR) successfully recorded strong motions during 2003 San Simeon earthquake (M 6.5) and 2004 Parkfield earthquake (M 6.0). Because the array covers a very small area (0.45km²), these data offer some interesting insights into spatial variations of seismic ground motions that suits for engineering scale. In this research, we study the spatial coherency function of seismic ground motion in the horizontal and vertical directions by digital signal processing. The results show that when the circular frequency is smaller than , the degressive trend of the coherency function becomes significant with the separation distance elongation, while the data deviation of the coherency function becomes larger with the frequency rise, which shows no obvious rules. In addition, based on the strong-motion data, a suitable spatial coherency model of ground motion is selected through comparing existing model functions, and the appropriate recommendations for improvement is put forward. Finally, according to different frequency range, the fitting parameters of the spatial coherency function of ground motion are obtained through numerical simulation. The spatial coherency function proposed in this paper is practical in simulation of ground motion field.

Abstract: The combination method implied in the formula used to evaluate the building separation to avoid seismic pounding in current Taiwan Building Code (TBC) is the absolute sum (ABS) method. However, it was demonstrated that the ABS method is not satisfactory. In this study, the seismic pounding risk of buildings is used as an indicator to demonstrate the validity of application of various combination methods to the formula in the pounding related provisions of TBC. The result shows that the building separations based on these combination methods generally provide relatively conservative estimate due to an overestimate property line setback.

Abstract: During the Wenchuan earthquake in 2008, many arch bridges in the seismic zone were damaged. The typical damage included: span collapsed, abutment and arch springing cracked, spandrel arch damaged, damage in the joint member between deck and main arch, damage out of arch plane. Some typical damage examples of the arch bridge are introduced in this paper. The causes and regular pattern features of the earthquake damage are analyzed, and the corresponding countermeasures are proposed.

Abstract: In this paper, the seismic response of underwater shield tunnel to incident P waves is investigated by using the Fourier-Bessel series expansion method. On the basis of the exact analytical solution, it is studied that the seismic response of the system which is made up of tunnel lining structure, underwater soil and water. The influence that water depth and buried depth of shield tunnel put on the seismic response of tunnel lining is given. The analytical result shows that the seismic response of tunnel lining unobvious varies with water depth change when incident P waves have a small incident angle, nevertheless, opposite conclusion appears when oblique incident P waves have a big incident angle. At a certain incident angle, the seismic response of tunnel increases with the increasing of the water depth; and the seismic response decreases with the increasing of the buried depth of underwater tunnel.

Abstract: Earthquake shakes the soil and induces modulus softening and liquefaction of non-cohesive soil, which causes instability of the slope. A practical numerical method is proposed for predicting large deformation and horizontal displacement of submarine gentle slope due to earthquake. The new method take normal wave loads as pseudo-static steady pressure and initial excess pore water pressure. Using 2-D nonlinear effective stress finite element method, dynamic response and liquefaction analysis are conducted with an infinite submarine slope model. Regarding the seismic motion of soil skeleton as process of softening gradually, softened soil modulus is attained during earthquake. Deformation analysis is performed with the modulus of liquefied and softened soil and the process of lateral movement is obtained. Compared with other related researches, the proposed method shows that gives reasonable results for the conditions indicated. The influences of non-liquefied surface layer, liquefied layer thickness and slope angle on horizontal displacement are studied by series of cases.

Abstract: Three specimens with ribbed stainless steel rebar and one specimen with ribbed ordinary steel rebar are tested concerning the strength degradation and energy dissipation of stainless steel reinforced concrete columns. The tests results indicate that the damage of the specimens exhibit ductile failure characteristics, and the reinforced concrete columns with stainless steel rebar damage to a lesser extent, appear good ductility and energy dissipation. The strength degradation of stainless steel reinforced column with high axial compression ratio is quite obvious, and with the increasing of the stirrup ratio of column with stainless steel rebar, the strength of column is enhanced.