Bridge pier is the key components for transferring loads between the bridge and foundation. Its status significantly impacts on the safety of the entire bridge. While the sudden external force (e.g. vehicle collision, explosion, earthquake etc.) could cause catastrophic properties loss and casualties. Therefore, many anti-collision implementations are used in the bridge pier. The rigid protections and soft buffer structures, which are the conventional anti-collision methods. The former cannot lower the damage to vehicle and passengers, and the latter is capable of withstanding the minor or moderate vehicle collision only. In order to overcome the shortcomings of the conventional anti-collision method, tensegrity as a prestressed tensioned structure is proposed to be integrated with the bridge pier as a shielding component. The integrated tensegrity can absorb impact energy of the vehicle-pier-collision through large deformation or localized damage to protect the core pier. Therefore, this paper proposed a detailed anti-collision design with integration of tensegrity for the bridge pier. Additionally, the assessments of its statics and dynamics are given. Furthermore, the anti-collision effect has been illustrated, numerically. The process of the vehicle-pier-collision in three different velocities were simulated by ANSYS/LS-DYNA; the energy absorption is analyzed. The relationship between deformation state and absorbed energy was also obtained. Therefore, the feasibility of the proposed design has been fully explained. It provides an option for the anti-collision design in the bridge pier.
Half grouted sleeve connection has been widely used in the rebars connection of prefabricated concrete (PC) structure. Mostly, the implementation of grouted should be finished on site. Meanwhile, the internal defects are inevitable due to the concrete nature. Currently, there is few methods available, which can effectively and rapidly evaluate the quality of the connection. Therefore, in this paper, we propose a combination of low-frequency linear ultrasound (LUT) and nonlinear ultrasound (NLUT) to quantitatively characterize defect. The internal artificial defects are concentrated defects, and the defect content is 10%, 20%, 30% and 40% respectively. Through transmission mode was adapted for both LUT and NLUT. The UT wave propagation was distorted by different defects, which was the results of LUT. For NLUT with higher resolution, the complex distribution and different level of defect together will introduce nonlinearity. The experimental results show that the grouted defects reduce the ultrasonic energy of LUT, and increase the nonlinearity from NLUT with the increase of the defect size and randomness. The defect has a significant impact on the ultrasonic features. Therefore, Low-frequency LUT and NLUT methods are potential to realize the visualization the defects of half grouted sleeve connection.
Currently, ultrasonic testing (UT) is widely used in concrete for identifying the sub-surface or surface flaws. However, most the UT can only provide the qualitive evaluation of the flaws. Tomography technology is capable to visualize the damage and provide its positioning information in concrete by reconstructing the ultrasound. For example, the slurry leakage state in the grouting sleeve, and the location of the inclusion in the concrete pile foundation can be displayed by ultrasonic tomography. However, concrete material is highly heterogenous due to its complex components (aggregate, mortar, internal void). All those complexities can cause significant impact on the tomographic results. Especially for the aggregate, sometimes its dimension is very closed to the testing objects. It greatly affects the recognition and location of defects by ultrasonic testing. Therefore, this research proposed to reveal the influence of aggregate, defect size and the effect of type, tomographic pixels on tomographic images in concrete. An optimum transducer arrangement and tomography algorithms in terms of ray-trace method was proposed to achieve the high accurate and resolution of tomography. Finally, the comparison of tomographic images between the imaged location and the embedded location is evaluated and then tomographic states is assessed accordingly.
Currently, the glass curtain wall has become very popular in contemporary architectural wall decoration method because of its aesthetics, lightweight, energy saving, and thermal insulation. However, the damage of the glass curtain wall is inevitable due to its material nature. Currently, the detection method of glass curtain wall is to use regular manual detection, It highly depend on the experiences of the inspector and are not real-time monitoring method. Therefore, it is necessary to develop a monitoring method for the evaluation of status of glass curtain wall, which can realize the real-time monitoring and high reliability. This paper proposed a combined acoustic emission and vibrational modal analysis method to achieve multi-scale damage detection for glass curtain wall: Modal analysis is used to detect structural silicone sealant failure, bolt loosening and corrosion of glass curtain wall, which refers to the first-step inspection to approximately determine the damage status. And Acoustic emission (AE) is further used to continuously monitor the glass curtain wall to provide more detailed damage evaluation. The proposed scheme is verified by COMSOL Multiphysics 5.5. The relationship between the damage degree of structural silicone sealant, bolt failure and the modal frequency of the glass panel was also obtained. And also, AE has been proved to be able to realize real-time monitoring and early warning of objects. Therefore, the feasibility of the proposed design has been fully explained. It provides an option for glass curtain wall inspection.
Concrete is the most widely used material in civil engineering, which has many advantages in terms of strength, accessibility, and durability. Currently, the high-strength concrete has been used in some projects. However, its failure mode is more complex than the regular concrete. Especially for the loading rate, it may significantly affect the failure mode. Therefore, it is essential to quantify the process of the failure for better application of high-strength concrete with consideration loading rate. Due to many merits of acoustic emission (AE), it has been successfully used for evaluating the progress of concrete damage. Therefore, in this study, the experiments were proposed to correlate the AE with failure mode in the high-strength concrete. As progress of the damage, the AE activities show highly related to the mechanical response. Additionally, the loading rate directly related to the failure mode is also considered. Compared with the regular concrete, the failure of the high-strength concrete shows more brittle behavior. And the phase of AE signals has been changed from obvious three stages to two stages with increase of loading rate, which can be used for further identification of failure mode.
In high-rise building structures, only using structural stiffness to resist the seismic energy is not economic and effective. Therefore, various energy dissipation devices are deployed to the structure, such as friction type energy dissipation device, Buckling Restrained Bracing (BRB) and viscous damper. Many researchers have been working on improving the performance of the dissipation devices. Though the plastic or residual deformation after earthquakes can consume the energy, the irreversible damage was introduced. In addition, its capability highly depends on the materials. Therefore, we proposes to take advantage of the mechanical bistablity to design a novel energy dissipation device, Mechanical bistability is defined as availability of two stable equilibrium configurations in the structure in response to the same loading conditions. The bistablity was realize by constructing a mechanical metamaterial: the snapping and buckling behavior were used to control the multistable response. The load-displacement curve was obtained by the analytical model. The results show that bistable stage was achieved. With bistablity and hysteretic characteristics, the proposed design can dissipate considerable energy. It provides a new strategy to develop the energy dissipation device.
The understandings of seismic mechanisms of tensegrity are highly demanded for perfecting the design principle. Due to the characteristics of periodicity, the effect of pre-stress on the frequencies of unit cell is investigated. And the stiffness of the basic tensegrity units was derived analytically. Then the vibration analysis of the entire assembly tensegrity structure is conducted numerically. Through parametric study, the influence of the pre-stress level on strength capacity of tensegrity is investigated. The cables yielding and bars buckle are considered. The influential factors on stiffness were evaluated, which can provide a guidance to the seismic mitigation optimization.
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