Advanced Materials Research Vols. 255-260

Abstract: The dynamic impact loading has the destructive effect to the surrounding rock mass. Rock specimen such as rock plate was found to become invalid under dynamic impact loading. This paper presents brittle damage evolution law for dynamic impact damage of brittle rock based on low velocity (10m/s~40m/s) impact test, when a source of impact loading is applied to a rock plate specimen, damage cracks are developed from the source to the boundaries. This paper is concerned with the description and explanation of this phenomenon. The test results show that the cracks propagation length and break area are not arbitrary, but are influenced by the angle of dynamic impact loading. According to the test results, the study found that the scope of impact resistance optimization angle is about 30°~45°, and the cuspidal point of impact velocity is about 30m/s~35m/s; The crack length and the break area increase with the increase of the impact loading; When the break area decreases abruptly, the crack length increases suddenly, which shows that there was an obvious incubation period of crack forming, at first some pits appearing on the verge of the rock plate and the propagation rate of crack length and break area decreasing with the impact velocity increasing.

Abstract: Active-type dynamic vibration absorbers (ADVA) is a kind of damping system, installed an actuators in the dynamic vibration absorbers (DVA). According to the actual needs, vibration energy of the structure is transferred to vibration absorbers actively in the process of structural vibration for the effect of external excitation. Therefore, the energy is decayed or transferred quickly and the structural vibration is controlled. If the nature frequency of additional system is the same as external excitation frequency of the original system, actuators doesn’t start and the whole system behaves the property of DVA (passive damping) .Otherwise, actuators starts, which makes the energy of original structure transfer to the vibration absorbers actively, achieving the purpose of energy consumed and vibration reduced. In this paper the concept of ADVA is proposed, and the working principle of ADVA is theoretically analyzed, furthermore the expressions of the system vibration response and active control coefficient are deduced. The curves of active control force and structure amplitude against incentive frequency are plotted respectively by examples.

Abstract: The purpose of this paper, for which a finite element bridge model with 7 degrees of freedom per node and the 1/4 vehicle model with six parameters were established, is to analyze the dynamic response of curved girder bridges under vehicular loads. In the numerical simulation, the vibration characteristics of simply-supported curved girder bridge are analyzed, and the effect to the impact factors were also studied for different radiuses of curvature, eccentricities, ratios between bending and torsion stiffness, and vehicle speeds. The simulated results show that not all the first 5 natural frequencies increase with the variation of radius of curvature. The impact factor variations of vertical deflection and torsion angle are not uniform when parameters changed, and the impact factor of torsion angle would be much larger than that of vertical deflection under the same conditions.

Abstract: The paper concerns on the free vibrations of circular plate with arbitrary number of the mounted masses at arbitrary positions by using the integral equation method. A set of complete systems of orthogonal functions, which is constructed by Bessel functions of the first kind, is used to construct the Green's function of circular plates firstly. Then the eigenvalue problem of free vibration of circular plate carrying oscillators and elastic supports at arbitrary positions is transformed into the problem of integral equation by using the superposition theorem and the physical meaning of the Green’s function. And then the eigenvalue problem of integral equation is transformed into a standard eigenvalue problem of a matrix with infinite order. Numerical examples are presented.

Abstract: Structural signal is taken self-adaptive decomposition by Hilbert-Huang Transform mainly composed of the EMD(empirical mode decomposition) and HT(Hilbert Transform), which is especially suitable for structural projects in the non-linear, non-stationary signal analysis through local characteristic. However, some weak signal may be ignored by EMD resulting in modal missing. Butterworth filter is an electronic filter designed to have flat frequency response. Considering the influence of noise , Hilbert-Huang Transform and Butterworth band pass filter are applied together to process the structural signal in order to obtain the frequency, damping ratio and mode shapes of the structure more precisely in this paper. Numerical Simulation results show that the proposed method in this paper could identify the modal parameters effectively and accurately.

Abstract: In this paper, important buildings of different structure in Xichang are calculated by using the powerful design software PKPM. First, the drawings of the buildings are simplified and the structure forms are input the computer in PMCAD software interface to make model, and the comprehensive seismic capacity index of floors or the story drift angle are calculated. Then, according to the judging principle, the earthquake damage level is gotten.

Abstract: The fire simulation technology is widely used with the rapid development of computer technology. Taking a 12-story building for calculation, numerical simulation method is used to analyze the wind speed distribution characteristics of opening stairwell door and lobby door under different air supply volume. Then the appropriate pressurized air supply mode and back pressure coefficient value under natural smoke venting have been recommended. The researches show that computer simulation can be used in smoke control system design to help determine pressurized air supply mode and design parameters, so as to solve difficult problems in engineering design.

Abstract: The rotational angle of joint is the key factor for segment lining design. Using the nonlinear finite element program of MARC (MSC2003), the 3D numerical analysis on segment joint of prestressed concrete lining has been carried out. During the analysis, Coulomb and Stick-slip friction models were used as the friction type between the concrete and the prestressing steel strands. The selection of friction model used in the numerical analysis is very important. The study showed that the Stick-slip friction model is more suitable than Coulomb friction model for analysis of the P&PCSL joint. The value of friction coefficient should be thought over carefully.

Abstract: The impacting action of flood destroyed dramatically the rural buildings. In this paper, the rural building was analyzed numerically to investigate the destruction of rural building due to the flood impact. The rural building was discretized into 7950 8-node block elements and 4098 Goodman elements to simulate the brick and mortar respectively. The rule impact loading of flood on rural building was calculated using the criterion of gravity similarity according to test results. Finally, the stress, the displacement and the failure process of the rural building are studied. Firstly, the mortar element locates on the wall between the door and the window failure and more and more mortar and brick elements failure with the increasing loading. Finally, the right wall was damaged because the door and the right window decreased its stiffness. Because the failure mortar and brick elements decrease the stiffness of the structure, the displacements of the rural building increased nonlinearly with the increasing loading.

Abstract: For the disadvantage in modeling at complex areas, advancing-frontal triangulation method was firstly applied in building numerical model of FLAC3D software. Suitable date structure and algorithm based on Fish program language was mainly studied. The position criterion of adjacent edges to current edge is brought in to improve the efficiency of algorithm; equilateral triangle or isosceles triangle mesh is generated to improve elements’ quality; element size is controlled by simple mathematics means so smooth graded triangular mesh is constructed. Through the research, the first independent FLAC3D pre-process is developed successfully, without relying on other modeling software. Application example shows the feasibility of the method.