A Comprehensive Research of the Air-void Defect of Concrete-filled Steel Tube

Welded spiral steel tubes are adapted for use in a majority of the large-diameter concrete-filled steel tube (CFST) arch bridges due to technical as well as economic reasons. However, the welding temperature and other factors during the process of manufacturing of steel tube, initially result in a reduced spiral-welded seam (SWS) strength. Moreover, with the pumping of concrete into a steel tube, numerous deformities of the likes of laitance coating and air-voids occurred inevitably, particularly with the lack of air-entraining agent in China almost 20 years ago. This work makes use of ultrasonic scanning field experience to investigate the capacity of bearing within a repaired and reconditioned CFST arch bridge rib having defects such as air-void and reduced SWS strength under negligible compression of eccentric axial by carrying out its finite element model analysis of group. The outcome reveals that CFST bearing capacity is only minimally affected by the SWS strength as compared to concrete air-void, which can be ignored. The effect of air-voids and the nonlinear behavior of the constituents on the CFST behavior have also been probed into. The impact of the air-void on the rib capacity of bearing was investigated by conducting parametric studies. To conclude, we proposed a new index defining the ultimate strength of the rib for the defect, and presented a rather simple blueprint to determine the influence of air-void on the final strength of the arch bridge rib of CFST

PZT-Based Ultrasonic Guided Wave Frequency Dispersion Characteristics of Tubular Structures for Different Interfacial Boundaries

For tubular structures, ultrasonic guided waves (UGWs) which are closely related to interfacial boundary conditions such as gas, liquid and solid materials, are usually used in damage detection. Due to the different phase materials inside tubes, the interfacial boundary (connection) conditions are variable, which has a great influence on the dispersion-related UGW propagation characteristics. However, most UGW-based damage detection methods only consider the pipeline structures as hollow tubes, ignoring the interfacial boundary condition influences on the UGW propagation. Based on the UGW theory, this paper aims to propose a novel method for describing the UGW propagation characteristics for different interfaces, and lay a foundation for the UGW-based tubular structure damage detection. Based on the Navier’s equation of motion and combined with interfacial boundary conditions and coordinate conditions, the dispersion equations for a hollow steel tube, a tube filled with liquid, and a concrete filled steel tube (CFST) were established, respectively. Under the given conditions of both materials and geometric parameters, the transcendental dispersion equations were established and solved by using a numerical method. The UGW propagation characteristics in different interfaces were classified and discussed, and the dispersion curves of both group and phase velocities are drawn. To validate the efficiency of theoretical and numerical results, three kinds of model tubular structure experiments filled in air (hollow), water and concrete, respectively, were performed based on lead zirconate titanate (PZT) transducer UGWs. The results showed that the UGWs propagation in different interfaces has the dispersion and multi-modes characters, which are not only related to the product of frequency and thickness, but also to the internal dielectric material parameters and interfacial boundary conditions