Advanced Materials Research Vols. 255-260

Abstract: In order to study the dynamic responses of stiffened plate under underwater contact explosions, the FEM code LS-DYNA is used to discuss the problem, six different stiffened plates are included. The stiffened plate’s distortion, the size of crevasses in the numerical simulation are analyzed. The position where the maximum plastic strain appears, the effective stress and acceleration are also described. It is revealed that the deformation of stiffened plate is different with the position of the stiffener, but the stiffener can harmonize and reduce the deformation of plate, and the whole structure will be more safety when it is subjected to explosions. So the research of this paper can be help to the design of steel structure explode resistance.

Abstract: A new spectral representation method of earthquake recordings using an improved Hilbert-Huang transform (HHT) is proposed in the paper. Firstly, the problem that the intrinsic mode functions (IMFs) decomposed by the empirical mode decomposition (EMD) in HHT is not exactly orthogonal is pointed out and improved through the Gram-Schmidt orthogonalization method which is referred as the orthogonal empirical mode decomposition (OEMD). Combined the OEMD and the Hilbert transform (HT) which is referred as the improved Hilbert-Huang transform (IHHT), the orthogonal intrinsic mode functions (OIMFs) and the orthogonal Hilbert spectrum (OHS) and the orthogonal Hilbert marginal spectrum (OHMS) are obtained. Then, the IHHT has been applied for the analysis of the El Centro earthquake recording. The obtained spectral representation result shows that the OHS gives more detailed and accurate information in a time–frequency–energy presentation than the Hilbert spectrum (HS) and the OHMS gives more faithful low-frequency energy presentation than the Fourier spectrum (FS) and the Hilbert marginal spectrum (HMS).

Abstract: A non-linear dynamical system identification method using Hilbert transform (HT) and empirical mode decomposition (EMD) is proposed. For a single-degree-of-freedom (SDOF) nonlinear system, the Hilbert transform identification method is good at identifying the instantaneous modal parameters (natural frequencies, damping characteristics and their dependencies on a vibration amplitude and frequency). For the multi-degree-of-freedom (MDOF) non-linear uncoupled dynamical systems, the EMD method is attempting for the decomposition of response signals into a collection of mono-components signals, termed intrinsic mode functions (IMFs). Considering the IMFs admit a well-behaved Hilbert transform, the HT identification method has been applied for the identification of nonlinear properties. The numerical simulation of a 2-dof shear-beam building model with nonlinear stiffness illustrated the proposed technique.

Abstract: Analytic solution for the dynamic response of underground structure is generally based on the theory of cylindrical shell. The underground structure constructed to resist internal blast is not suitable to be treated as cylindrical shell structure and is difficult to get analytic solution. In this paper, finite element code LS-DYNA is employed to calculate the dynamic response of underground blast-resistant structures exposed to internal blast. Two structures with different thickness buried in four types of surrounding rocks are calculated, and the influence of the surrounding rocks to the dynamic response of underground blast-resistant structures is analyzed.

Abstract: The AASHTO Correction model is proposed to better adapt the model to the special conditions occurring in Fujian inland waterways. These conditions include ship Type, visibility, and up-down water, navigation systems. The proposed model is related to the probability of ship collision with bridge multi-factor, and further example analysis of this model is also introduced in this paper.

Abstract: The objective of the paper is to determine the structural dynamic characteristics from the low level structural seismic response data in small earthquakes. The off-line time-domain system identification method ARX (AutoRegressive with eXternal input) model is adopted to identify the time-invariant transfer functions, and then the structural parameters such as modal frequencies and damping ratios are determined. A 7-story reinforced concrete structure on which the strong motion monitoring system was installed and recorded seismic response in 3 small earthquakes was used for the analysis. It is found that the structural dynamic characteristics can be determined from low level acceleration response records in small earthquakes in which the structure can be assumed as a linear and time-invariant system. The results can be referenced by structure health monitoring, structural control and related works.

Abstract: As a new type structure, the dynamic behavior of the irregular concrete filled steel tube arch bridge under moving vehicles was rarely studied. In this paper, taking the bridge crossing Yitong river in Changchun of China as an example, the dynamic response of the bridge is investigated by the self-compiling vehicle-bridge coupled vibration analysis program. The surface roughness and vehicle speed are considered in the analysis. The results show that impact factors of the bridge increase as surface roughness deteriorated; the impact factor varies obviously for the different component; the tension impact factor of the short suspender is larger than that of long ones; damping ratio of structure has little effect on the impact factors. The research conclusions can be referred in the design and assessment for the similar bridges.

Abstract: On the basis of the potential fluid theory, the effect of hydrodynamic force on the dynamic response of a typical rectangular solid pier as prototype was analyzed at different water depths under two types of seismic waves. At the same time, the distribution of the hydrodynamic pressure, the action spot of the hydrodynamic force and the effect of fluid on the seismic response of the piers were analyzed in seismic waves. The results include the vibration period, the peak of displacement, shear and moment of pier are increased as the rise of water depth. The effect of fluid on the dynamic response of pier should not be ignored. The influence of different seismic loads on the distribution of hydrodynamic pressure is not identity.

Abstract: Comparative analyzing pre-cutting seam in size between 0.5 m and 0.8 m in the top of bridge arch, and vice-arch column blasting range between 1.6 m and 0.8 m , numerical simulations on typical highway double curved arch bridge structure blasting demolition process are carried out adopting common node separate reinforced concrete model. Simulation result indicates that, common node separate model can reflect mechanical properties difference of concrete and reinforcement through analysis on their loading process. Adopting 0.5 m in size of pre-cutting seam is sufficient to ensure the superposition and complete collapse of the bridge. The vice-arch blasting range by 1.6 m can make the bridge more complete disintegration, and it can also decrease the whole collapse time and the height of muck pile.

Abstract: The influence of column stiffness on the modal contribution in the transverse direction of singe-column bent viaducts in the nonlinear range is investigated in this paper. The modal contribution ratio is introduced as a measure of the importance of a mode after a bridge yields. Three typical mathematical models of irregular singe-column bent viaducts are selected for analytical seismic response. The comparative evaluation of modal contribution ratios are carried out when columns with different stiffness yielded individually. Results show that yielding of a stiffer column affects the contribution of the fundamental mode as well as that of the higher modes significantly while the yielding of a more flexible column affects the modal contribution of the fundamental mode only.