Advanced Materials Research Vols. 163-167

Abstract: Increasingly large and complex structures make it more complicated in analysis, designing and construction, and through the amplification effect caused by the interaction of various parts of the structure, any tiny error in any link could cause huge damage to the building. However, the relative analysis theory and design method are not consummate enough to assess the influence of all kinds of errors. Under this circumstance, structural health monitoring system is an important guarantee to ensure the safety of the structures in both construction and operation stage, and at the same time contributes to make up for the deficiency of theory [1-2]. The Expo Axis project is the largest single project in Expo Site 2010 Shanghai. The Expo Axis project has adopted a whole new architecture form. The roof design as giant light cable-membrane structure about 1000 meter long and about 80 meter width. The computing displacement of the membrane roof is close to 4m. In order to ensure the safety of this structure, a real-time and long-term computer based health monitoring system is applied in the Axis structures.

Abstract: Based on the pile-soil function and damper boundary condition influence by Finite Element Method, taking Bao-Shu yellow river extra long-span bridge as the project object, the deformation effect of the bridge subjected to flowing and melting ice in spring was analyzed considering dynamical action mode. The results revealed that the deformation from this kind of action is tittly small and the bridge structure is reliable and stable. Then the calculation and analysis have been put into design and construction stage.

Abstract: In this paper, three-Dimensional finite element analysis was used for the research of a base-isolated high-rise building. After studying the effects of different structural systems, action of bidirectional earthquake wave, P-Delta effect and acceleration responses on it, some useful conclusions are given as follows: in the same structural systems, the story shears of the isolated structure are one order of magnitude less than those of the non-isolated structure under the action of the same seismic waves; the story displacements of the isolated high-rise frame-shear structure and those of the isolated high-rise shear wall structure are different under the action of the same seismic waves; under the action of different seismic waves, the earthquake responses of the same structural system are quite different; the effects of bidirectional earthquake waves on some components should be considered; P-Delta effect can be ignored in the base-isolated building; and the acceleration responses of the isolated high-rise building are different from those of the non-isolated counterpart. Results show that the technology of base-isolation can be applied to the high-rise building system.

Abstract: Based on random vibration theory, virtual response is obtained from the measured acceleration signal of Yantan Yellow River Bridge of Lanzhou under ambient excitation, Yantan Yellow River bridge's modal parameters were identified by using the peak picking and stochastic subspace identification, analyzed from theoretical and experimental aspects, compared with the finite element model results and verified the reliability of recognition results. The identified dynamic properties can be served as the basis in the finite element model updating, damage detection, condition assessment and health monitoring of the bridge.

Abstract: Modal curvature difference (MCD) method is an effective damage detection technique for beams but not very feasible for plane member structures, because the MCD of each member is difficult to calculate with the structural modal shapes which are expressed in a global coordinate system. By improving MCD method, this paper develops a general and convenient damage detection method for plane member structures. The new method introduces coordinate transformation technique to settle the calculation difficulty of MCD. To validate the availability of the method, the finite element damage model of a typical structure is built up, and detection effects on the case of single member damage and multiple member damages are studied respectively. The results show that the improved method is especially suitable for the damage detection of plane member structures.

Abstract: In this study a kind of buckling-restrained braces (BRBs) as energy dissipation dampers is attempted for seismic performance of large span double-layer reticulated shell and the effectiveness of BRBs to protect structures against strong earthquakes is numerically studied. The hysteretic curve of such members is obtained through the simulation of the cyclic-loading test, and the equations of motion of the system under earthquake excitations are established. BRBs are then placed at certain locations on the example reticulated shell to replace some normal members, and the damping effect of the two installation schemes of BRBs is investigated by non-linear time-history analyses under various ground motions representing major earthquake events. Compared with the seismic behavior of the original structure without BRBs, satisfactory seismic performance is seen in the upgraded models, which clarifies the BRBs can reduce the vibration response of spatial reticulated structure effectively and the new system has wide space to develop double layer reticulated shell.

Abstract: A method based on Hamiltonian system in complex field is presented in curvilinear coordinates to study elastic waves in pipes of various shapes on two-parameter foundation. The method and its computer program are verified and applied to analyze the axial wave propagation problem of elliptical pipe embedded in foundation. Numerical results show the dispersion changes of varying degree in the presence of foundation and reveal significant influences of the second foundation parameter especially in the low frequency range. The promising and effective way of controlling propagating waves by adjusting the shear ability of foundation is also indicated in the results.

Abstract: In the former research, the Damper control system, TMD control system and the Mixed Control of the active control and passive control were all optimized alone. It is found that less research of the optimization is on the Mixed Control of the Damper system and TMD system. In order to achieve better control effect, we venture to propose a Mixed Control system of third-generation three-dimensional 20-storey Benchmark model under the multi-directional earthquake in this paper. By means of Rayleigh damping and D-value, dynamic equations including the damping matrixes, stiffness matrixes of the structure are obtained. Then in the process of the optimization, the displacement reducing coefficient (DRF) is used as the objective function to optimize the placement of damping devices and control parameters based on Genetic Algorithm (GA). Numerical results in this paper show that the optimal design method proposed in this paper is effective and flexible. It can obviously reduce the seismic responses of building structure.

Abstract: Based on the mechanism of the relative change rate of mode shape (RD), a new damage identification quantity called the vibration mode slope change rate (RD’) is proposed. The new quantity is analyzed with the fundamental principles of function differential method. Dynamic test is carried on 5 RC frame beams, which are subjected to an increasing static load in the middle to introduce cracks. After each load step, unloading, and an experimental dynamic monitoring is performed on the beam, then reloading to the next step. Modal analysis is carried out on frame beams under each load step, and modal displacements are given, the vibration mode slope change rate graphs of the RC beams are calculated, which can be used to detect multiple-damages. By means of SAP2000, the comparison analyses between RD and RD’ indicate that RD’ can effectively avoid the careless judges and misjudge in the damage identification of frame beams.

Abstract: Jiamusi highway prestressed concrete bridge is located in the Jiamusi City within Heilongjiang province in the east north of China. The strengthening and repairing of the bridge structure can be provided an effective and economic solution in appropriate situation. The objective of this study are to monitor the construction process of external prestressing tendons for strengthening of Jiamusi highway prestressed concrete bridge. Monitoring process includes measurement of external prestressing tendons natural frequency, monitoring of tensile forces values of external prestressing tendons, monitoring of development of anchor beams cracks, and monitoring of anchor beam deformation. The results of monitoring process show that the box girder No. 11 has the largest values of proportional coefficient (K) and the maximum value is 327.8. Box girder No. 8 has the largest values of frequency, the maximum value is 3.499. Five levels of tension are used in the application of tensile force in the tension process of external prestressing tendons. These levels are level 1=248.2kN, level 2=496.4kN, level 3=744.6kN, level 4=992.8kN, and level 5=1241kN. The measured tendons elongation values of left box girder No.8 are more than the theoretical values. For left and right box girder No. 9, side external tendons of left box No. 10, and left and right box girder No. 11, the measured values are less than theoretical values of elongation. After tension process, there are no new cracks in the top, web, and bottom of anchor beam and a small number of cracks developed slightly. These cracks are found around ducts of external tendons. The length of cracks rang from 0.03m to 0.5m and width rang from 0.05 mm and 0.25mm. The longitudinal deformation of the interface and top of anchor beam is very small, ranging from 0.001mm to0.115mm, which averaged 0.026mm. The overall state of anchor beams and box girders during strengthening is good.