Advanced Materials Research Vols. 163-167

Abstract: To get massive concrete sidewall hydration heat and the frozen wall’s temperature distribution law, the temperature monitor and analysis were applied in the construction process of deep frozen shaft. Combined with frozen sidewall temperature field numerical calculation finite element method, analyzed the concrete hydration heat on the impact of the artificially frozen wall in the frozen wall’s construction process. Concrete hydration heat release made rapid temperature rise of concrete, the temperature was gradually cooling down effected by the frozen wall’s low temperature and the concrete permanent supporting borders. During large release of concrete hydration heat, the frozen soil curtain was partial heating and melting, the Interface moved quickly and reached the maximum. The results showed that: the change laws of the numerical simulation and the measure point temperature were uniform, and their values were more consistent. This had a certain reference value in improving freezing construction methods and the design of deep frozen wall.

Abstract: Based on the investigation of a constructing dumbbell-shaped concrete-filled steel arch bridge in Nanning, Guangxi, continuous on-site experimental researches on temperature field and its effects were carried out under the influence of hydration heat of concrete in the molding process of concrete-filled dumb-bell steel tubular arch bridge. On the basis of measured data, analysis on time-history law of temperature field and its effect under the impact of hydration heat of concrete of composite structure of concrete-filled steel tubes is made. The results reveal that temperature variation of hydration heat of the concrete within the steel tube is showed as follows: “Temperature up-continuous high temperature-temperature down-balance”. The structural temperature field, generated under the effect of hydration hea in the process of molding arch rib, is nonlinear temperature field. Concrete hydration temperature effect of crown section basically changes with temperature field simultaneously, while the residual strain of arch foot section is relatively large; hydration temperature effect of L/4 Section emerges peak fluctuations in concrete pouring process and finally levels off. Hydration temperature field of concrete has a great effect on crown section, which makes the steel tube continuously withstand the tension and compression alternatively, while the influence on the arch foot steel tube is not obvious. Surface strains of L/8, L/4, 3L/8 sections of steel tube transit from single-wave peak to dual-wave peak and finally turn into a single wave peak.

Abstract: Truss string structure (TSS) is a new type of large-span space structure which is composed of upper spatial truss and bottom high-strength cables with vertical supports. For certain upper truss, the main affect factor of dynamic characteristics of a TSS are prestress of the cables, pole number, rise-span ratio and vertical span ratio. In modal parameters, modal frequencies is the most direct and easily observed parameter, which largely reflects the stiffness of the structure and plays an important role in the dynamic response of the structure. In this paper, the mode testing experiment and finite element analysis is executed, to study the changes of the lower modal frequencies in different prestressed cables and to study the influence of the prestress to the dynamic properties of TSS.

Abstract: Underground arch structure is an important structure form of civil air defense engineering, and its damage detection is an important link in safety evaluation of civil air defense engineering. In this study, a neural networks based damage detection method using the modal properties is presented. Based on the analysis of the dynamic properties of underground arch structure before and after damage, it was proved that the ratio of mode shape was insensitive to finite element model errors. The variation rate of mode shape was taken as the signature for damage detection, and it was proved that the variation of mode shape caused by multiple damage state was transformed into superposition of single damage state. It is not needed to constitute multiple location damage patterns when using the neural networks. A typical underground arch structure is analyzed to demonstrate the effectiveness of the proposed method. When 10%’s modeling errors exists, the damage location and extent can be recognized well.

Abstract: This study was investigated the evolution of fracture damage of reinforced concrete (RC) beams strengthened in flexure with carbon fiber-reinforced polymer (CFRP) sheets or plates using acoustic emission (AE), and developed an AE monitoring strategy that can determine the structural integrity of RC beams strengthened by external bonding of CFRP sheets or plates. In this study, five beams were used, each with a cross sectional area of 200300 mm2 and length of 2,000 mm. Each specimen was simply supported and subjected to three-point loading. The AE signals were monitored during flexural testing of specimen using four sensors located on the side of each beam. The damage behavior and the microscopic fracture process of the RC beams strengthened with CFRP was evaluated using the AE parameters, such as AE duration time, event and amplitude. The two-dimensional AE source location was successful in measuring crack initiation and propagation in the RC beams strengthened with CFRP.

Abstract: According to the vibration characteristics of small sag cable, an equation of non-linear free transverse in-plane vibration of an inclined cable is presented considering the effects of the flexural rigidity. In the equation the influence of the tension variety along the inclined cable was taken into account by using the precise parabola equation of the taut cable. Taking single mode of a cable in consideration, the governing equation was simplified as a traditional Duffing equation with a quadratic term. It was solved by using the method of Fourier series. Combined with engineering practice, an example was provided to study nonlinear natural vibration characteristic of an inclined cable in plane when the length, the inclination angle, the tension were changed separately, whether considering the influence of tension variety along the inclined cable or not.

Abstract: Taking Xinguang Bridge as the engineering background, the way of model establishment for the dynamic characteristics analysis according to the features of Xinguang Bridge is presented. On this basis, the dynamic characteristics testing of Xinguang Bridge is preformed. Finally, the comparison between analysis results and testing results is done.

Abstract: This paper presents a study in the effect of spalling to dynamic parameters such as natural frequencies and mode shapes. Numerical example of a slab is used as an example in this study. The slab will be modelled using ANSYS 11.0 and various types of spalling are imposed. The changes of vibration parameters are monitored and compared. To compare the sensitivity of modal parameters to spalling is determined using the flexibility method. Based on the results it is found that by incorporating mode shapes using flexibility method, damage location and severity can be obtained.

Abstract: A new distributed structural damage detection approach based on a two-stage Kalman estimator approach, which is not available in the previous literature, is proposed for the identification of large size structural parameters under limited input and output measurements. A large size structure is decomposed into small size substructures based on its finite element formulation and each substructure is identified by utilizing the two-stage Kalman estimator approach. It can greatly reduce the time of iteration calculation. Numerical example of identifying the parameters of a large-size plane truss bridge is conducted. Simulation results show that the proposed approach is able to identify structural systems.

Abstract: According to fire station of Tuandao road along to the Yunnan road tunnel of Qingdao Cross-harbor Tunnel Guide Line Project, the blasting vibration test was carried on. This building is three-storied brick-and-concrete building. Then monitoring data of particle vibration velocity was analysised and researched. The results showed that there is magnifying effect of vertical vibration velocity on the roof of the building, but its value is lesser than particle vibration velocity of the first layer. Horizontal tangential vibration velocity was existed on the central of the building. However there was no magnifying effect of horizontal radial vibration velocity. And its value is decreased rapidly from the first layer to the second layer, and then other floors basically keep steady.