Applied Mechanics and Materials Vols. 204-208

Abstract: Two-dimensional finite element model of Longmenshan area was built on the basis of depth study on geological structure conditions and of rock mechanical properties in Longmenshan area, tectonic stress field and variation process of Longmenshan fault belt were inversed after the earthquake. The results show that: (1)After the earthquake, the maximum principal stress appears in fault endpoint, partial inflection point, intersection of Longmenshan fault and Xianshuihe fault and intersection of Minjiang fault, Animaqing-lueyang fault and Longmenshan Fault. The maximum principal stress in area is overall NEE to SEE.(2)After earthquake, shear stress distribution is more uniform, and compared after earthquake to before earthquake, shearing stress of Longmenshan central fault and Qianshan fault reduces obviously, but shear stress of Houshan fault increases.

Abstract: According to the information about underground damage in earthquake all over the world, it is summarized that earthquake damage is caused by mountain slope failure, the collapse of cavern’s export, dislocation damage of cavern’s cross-section, great displacement along the fault intersection, spalling of surrounding rock, disturbance or deformation of the support and lining system, et. The earthquake damage factors of underground cavern were analyzed by using numerical simulation techniques. It is shown that when the earthquake intensity value is high, or the initial stress field is small, or lining stiffness is high, the underground will more easily be destroyed by earthquake. Compared with the square tunnel and horseshoe-shaped tunnel, dynamic stability of circular tunnel is better. The export of cavern is vulnerable to earthquake damage.

Abstract: Nowadays, earthquake prediction is still a worldwide scientific problem, especially the prediction for short-term and imminent earthquake has no substantial breakthroughs. BP neural network technology has a strong non-linear mapping function which could better reflect the strong non-linear relationship between earthquake precursors and the time and the magnitude of a potential earthquake. In this paper, we selected the region of Beijing as the research area and 3 months as the prediction period. Based on BP neural network and integrated with the conventional linear regression method, a regional short-term integrated model was established, which gives the quantitative prediction for the earthquake magnitude. The results show that the earthquake magnitude prediction RMSE (root mean square error) of the integrated model reaches ± 0.28 Ms. Compared with conventional methods, the integrated model improves significantly. The new model has a good prospect to use BP neural network technology for earthquake prediction.

Abstract: This paper presents an experimental study and analysis on three double web plate top and bottom angle steel connections of T-shaped concrete-filled steel column and steel beam under low-cycle repeating horizontal load. The damage form and seismic performance of double web plate top and bottom angle steel connections was studied. The results of analysis indicate that the strength and rigidity of the joint are mainly determined by the strength and rigidity of the thickness of top and bottom angle steel. The thickness of top and bottom angle steel affects the performance of the joint and the joint has good consuming energy capacity and its strength is high. The results provide the theoretical basis to the study and application of double web plate top and bottom angle steel connection joint.

Abstract: Buried culverts are usually considered to be earthquake-resistant underground structures. Therefore, few studies have been conducted to investigate the seismic response of slab culverts under high fill embankment which are usually subjected to extreme dynamic loads. This paper presents a numerical analysis of the seismic response of slab culvert under high fill embankment in a loess region which is also a seismically active area in China. The influence of important factors such as fill height, incident angle of seismic wave and magnitude of earthquake on the response of culvert is carefully examined. And possible failures of culverts are also analyzed according to the numerical results.

Abstract: The source, path and site effects are the main causes for ground motions. Soft alluvial basins especially result in seismic wave amplification as the site effect. Irregular alluvial basins and canyons in this study are semi-cylindrical for simplifying analysis. To deal with the scattering problems in frequency domain, Yeh et al. have gained positive outcomes by using a hybrid method which combined finite elements and the series expansion method to effectively solve the scattering problem in the irregular basins. These displacements derived from the frequency domain are computed with the H/V ratio to estimate the site effect. As the site effect is crucial in earthquake engineering, this study may serve as a quantitative contribution towards the amplified effect in alluvial basins and canyons. It can also simulate the effects of different incident angles on the H/V ratio.

Abstract: With the rapid development of national transportation, many bridges with higher and higher piers crossing sea and clough are constructed. The p-delta effect of tall piers in bridge is so evident that can not be ignored to assure the absolute safety of bridge. Research shows that, in comparison with other ways, energy analysis was simple and versatile for different load combinations in computing upper pier displacement, and neglecting p-delta effect often underestimated the disadvantageous state when the pier is high.

Abstract: Combined with the highway from Lixian to Xiaojin, the in-situ monitoring test for Baozizui rock slope was carried out in Li County earthquake zone of Sichuan province, and three earthquakes whose magnitude exceeds 4.8 times had occurred during the monitoring period. According to monitoring results, the main conclusion was shown that the slope deformation attenuated and tended to be stable after two month of construction. Considered the anti-inclined structural face in the slope, the compacting deformation action, which was beneficial to slope stability. Moreover, seismic load had great influence on horizontal deformation of structural face in surface rock layer. And the reason was that there was regional stress bearing compression and shear in the nappe structures located on the thrust fault upper plate of this slope. The variation of horizontal deformation was frequent in earlier stage located at the road curve, in which there existed the traffic load, seismic excitation effects. And the later observational data indicated that the deformation has been basically stabilized.

Abstract: After the Wenchuan earthquake, Chinese Code for Seismic Design of Buildings (GB50011-2010) adjusts some seismic design parameters. Taking into account the randomness of gravity load and earthquake action and the uncertainty of steel strength and concrete strength, this paper analyzes the reliability of seismic bearing capacity of reinforced concrete frame bottom columns. Based on the structural analysis software PKPM, which is in accordance with code for seismic design of buildings, the reliability index of seismic bearing capacity of reinforced concrete frame bottom columns is calculated by the Monte Carlo method with different parameters, such as different seismic intensity, different building storey number, different seismic adjustment coefficient (increment coefficient of frame columns end moment and increment coefficient of design value of combination moment of underlying frame columns lower end section), different horizontal span number, different column location (side column and interior column) and so on. The results indicate that the reliability index can reach 2.0 or above, and can meet the target requirements for all cases which are designed with the current code for seismic design of buildings (GB50011-2010).

Abstract: A new method is proposed to identify multi-axial seismic loadings from structural dynamic responses on limited degrees of freedom. The seismic loadings acting on structures are modeled by Hartley series approximation, and the sensitivities of structural dynamic response with respect to the unknown approximation coefficients are derived. The identification equation is set up based on best fitting structural measured and calculated responses, and is solved with the damped least-squares method. A five-story three-dimensional steel frame structure excited by El-Centro seismic accelerations is studied for validating the proposed method. Numerical simulations with measurement noise and model errors show that the proposed method can accurately identify all seismic loadings from only several responses of the structure.