Advanced Materials Research Vols. 250-253

Abstract: In order to accurately assess the robustness of the complex bridge structure, a method of robustness assessment that takes structure degradation and accidental loads into consideration is proposed. Firstly, the degradation rates of member section properties and the increasing rate of live load are set as variables. The parametrical model of structure is established by the finite element software of ANSYS. Secondly, the structure robustness is based upon analysis from the robustness index, the reserve strength factor and the residual strength factor. The effects of three degradation rates of section properties, the established increasing rate of live loads and accidental loads on the robustness of bridges are considered. Finally, this method is used to analyze the time-variant robustness of Guotai Bridge located on the Haihe River of Tianjin. The results indicate that different degradation rates of member section properties have different effect on the robustness of Guotai Bridge, the effect of accidental loads has a close relationship with its acting position.

Abstract: Based on available research results of precast segmental bridge pier, seismic performance of a continuous girder bridge with precast segmental bridge columns using match-cast dry joints was analyzed with the lumped plastic hinge method verified by experiment, the similarities and differences of seismic performance between the continuous girder bridge with precast segmental bridge columns and that of cast-in-placement reinforced concrete bridge columns were gained. Results show that the maximum displacement response of the continuous girder bridge with precast segmental bridge columns is bigger than that of the continuous girder bridge with cast-in-place reinforced concrete bridge columns. While for the residual displacement, the opposite is true. The reason is that the restoring force exists in the precast segmental bridge pier by the prestress strands. The concentrated plastic hinge method for cast-in-place reinforced concrete bridges could be used to bridges with precast segmental bridge columns.

Abstract: A field test is carried out to study the effect of vibration while treating foundation using vibroflotation method in the deep soil layer in Zhengzhou, China. The vibration attenuation rules and wave propagation rules in different formations caused by different numbers of drills are analyzed. Evaluate the influence on the adjacent buildings. The result shows that the vibration will be generated in foundation obviously in the process of construction using the method. Vibration force, impact frequency and site soil are important influence factors on ground vibration attenuation. The analysis reveals that the maximum vertical acceleration attenuation velocity was much greater in near area than that in the relative far area. The waves caused by vibration propagate in two ways: (1) surface wave is generated on the wall of drill hole and propagated to the ground surface, and attenuated in a certain distance (<8m); (2) shear wave was generated and propagated in the impacting formation and attenuated from the deep formation to the ground surface. Vibration amplitude is mainly distributed in the low frequency range in the areas which far away from vibration source and in the silt layer near the ground surface.

Abstract: With the increasing of the quantity of the tunnel, more and more attentions have been paid to the tunnel destruction induced by earthquake. Based on the software of finite element, the finite element model for deeply buried tunnel have been set up; and the responses about different rigidity of tunnel lining under seismic dynamic load has been analyzed by using elastic finite element theory. The conclusions have been drawn that the change of seismic responses by increasing rigidity of tunnel lining is unobvious, and the method using increasing rigidity of tunnel lining to reduce the seismic responses of tunnel is uneconomical.

Abstract: As a new technique of excavation support structures, outrigger-type diaphragm wall has got an application in deep pit engineering, though the design of its parameters still lacks theoretical guidance. Based on a large-scale deep pit case, a 3-D finite element model is presented to simulate the behavior of outrigger-type diaphragm wall using the software ABAQUS. The soil is assumed to behave as a modified Cam-clay model. The effect of the outrigger length on deformation and internal force of the supporting structure is studied. It is found that the basal heave ,the ground settlement and the horizontal displacements of the retaining wall will increase with the increase of the outrigger length, when the bottom elevation of the supporting structure keeps unchanged. When the outrigger length goes beyond a certain length, the rate of increasing becomes larger. In the outrigger-type diaphragm wall, the vertical stress of inside and outside wall approaches the maximum in the vicinity of the variable cross-section. At the same time, the variable cross-section produces a shear stress mutation because of the abrupt change of stiffness. There exists a reasonable length of the outrigger, which could meet not only the technical requirements of the supporting structure, but also the needs of saving the cost and reducing the difficulty during the construction.

Abstract: Take the Liujiaxia bridge as engineering background. Based on classical flutter theory, It focus on research critical factors which affect the critical velocity about the ultra-narrow steel truss stiffening girder suspension bridge in order to provide theoretical basis to the problem of low flutter stability of Liujiaxia bridge. The results show that critical velocity will decrease with increase about the vertical bending frequency and will increase with the torsion frequency and torsion-bend-frequency ratio. But the critical velocity will keep stabilize when torsion-bend-frequency ratio exceeds than 1.2. Though Changing sag-span ratio, width and height of beam can improve the critical velocity, it maybe increase cost of bridge remarkably when width and height of beam reach to some level. It is uneconomic if only adopting structural measures by means of optimization of design parameters, as a result, aerodynamic measures is more important.

Abstract: Najin Bridge, located in Lasa of China, is an extradosed bridge with three towers and with the (70+117+117+70)m spans. The turning radius of all saddle in the main tower of this bridge is 2.5 m. Now minimum radius of the saddle at extradosed bridges in China is 2.8m. For the security and reliability of the bridge, we researched and analyzed the stress of saddle segment by the ANSYS software accurately, and carried on the full-scale model test. Some suggestions are proposed for this bridge.

Abstract: Erosive Karst Tiankeng has been a new type of Tiankeng Since the Collapsed Karst Tiankeng was found and primarily research by Zhu Xuewen, a famous geologist. But, how the Erosive Karst Tiankeng evolved and developed How can we find the proofs on formation and evolutional processes of Erosive Karst Tiankeng Few scholar focused on this new field. According to the first-hand datum by geological Expedition and study in Xingwen World Geopark, the results and datum show that apart from Dayanwan and Xiaoyanwan collapsed karst Tiankeng, there are other karst landforms in Bowang Mount scenic spot of Xingwen World Geopark such us Feiwu Cave, Dao Cave, Cangshuiyan Gorge, Nanxing TanKeng and so on. These typical karst landforms could be regarded as different vestiges of erosive karst Tiankeng of Xingwen World Geopark, which stand for the evolutional processes of erosive karst Tiankeng separately. Moreover, the evolutional processes of erosive karst Tiankeng could be divided into the following continuous processes: an erosive karst Tiankeng develops from the processes of eroding and dissolving & extending of silo Sinkhole, and subsequently degrades to a large gorge or doline. It is worth pointing out that except for erosion of flowing water, at the same time, collapse’s effect has been playing extremely important role in the forming processes of these special erosive landforms.

Abstract: Kelly and Xiyuan Zhou research on upper single-degree-of–freedom model of regular isolated building, and give necessary computing formulas. For various middle or low isolated building, the result is satisfied by using the model. Recently isolation technique was applied to high-rise buildings. For isolated building systems with large aspect ratio, high-order mode parts of upper structure can not be ignored. It brings large errors to use single-degree-of–freedom model. In the paper, according to the equivalent rules of equal structure period and total base shear, the computing formula of structure parameters is deduced. After numerical analysis for some regular buildings, a simplified method for equivalent model is given. By analyzing the earthquake responses of equivalent model and original structure, it is proved that the equivalent method is simple and feasible.

Abstract: In order to accurately evaluate the reliability of the existing cable-stayed bridge, a method based on inspection information is proposed to update the system reliability. Using Bayesian method and inspection information, the modified model of cable-stayed bridge random variables is established, and then the failure probability of cable-stayed bridge components is updated. The β-T curves of changing rules of inspection information on system reliability index and service life are obtained. The method has been applied to a cable-stayed bridge, the results show that the proposed method is effective to update the system reliability and can predict the residual life of the existing cable-stayed bridges.