Papers by Author: Yong Xia

Abstract: In the mesoscale modeling, concrete is assumed consisting of three components, i.e., coarse aggregates, mortar matrix, and the interfacial transition zone (ITZ), each with different material behavior. The shape and the percentage of the coarse aggregate are the key factors in the mesoscale numerical simulation. The present paper investigates the effect of the coarse aggregate shape on the concrete behavior under high strain rate compression. Simplified methods are adopted to construct the aggregate distribution. Three different aggregate shapes, i.e., circular, oval and polygons, are generated to model the gravel and crushed stone aggregates, respectively. Using these different aggregate shapes, concrete specimens under high strain rate compression are modeled. Numerical results show that the aggregate shapes have a significant effect on the crack path, whereas little effect on the overall responses of the concrete specimen.

Abstract: Concrete might be subjected to impact or blast loading. To analyze the concrete behaviors under such loading cases, it is of interest to study the dynamic damage and failure behavior of concrete under high strain rate. In the present paper, a mesoscale model is developed to numerically analyze the dynamic damage process of concrete samples under high strain rate tension. In the mesoscale model, the concrete is regarded as a three-phase composite consisting of coarse aggregate, mortar matrix, and interfacial transition zone (ITZ) between the aggregate and the mortar matrix. Different coarse aggregate shapes, such as circular, oval, and polygon, are calculated and compared. It is found that the shapes of the coarse aggregates do affect the tensile strength and failure pattern.

Abstract: A long-term structural health monitoring (SHM) system consisting of more than 600 sensors has been designed and is being implemented by The Hong Kong Polytechnic University to the Guangzhou New TV Tower (GNTVT) of 610 m high. This monitoring system is one of few SHM practices that integrate in-construction monitoring and in-service monitoring. It is also designed to perform a special function of verifying the effectiveness of vibration control devices to be installed on the tower. The sensory system for in-construction monitoring includes a weather station, a total station, anemometers, zenithal telescopes, level sensors, theodolites, global positioning systems, vibrating wire gauges, thermometers, digital video cameras, and accelerometers (for ambient vibration monitoring at several construction stages), and the sensory system for in-service monitoring includes a weather station, anemometers, wind pressure sensors, vibrating wire gauges, thermometers, global positioning systems, digital video cameras, accelerometers, a seismograph, corrosion sensors, tiltmeters, and fiber optic sensors (for dynamic strain and temperature monitoring). The strain and temperature at the inner structure during construction are continuously monitored by a wireless data acquisition system. This paper outlines the design and implementation of this SHM system.

Abstract: Under the auspices of the Asian-Pacific Network of Centers for Research in Smart Structures Technology (ANCRiSST) and the International Society for Structural Health Monitoring of Intelligent Infrastructure (ISHMII), a structural health monitoring benchmark problem for highrise slender structures is being developed by taking the instrumented Guangzhou New Television Tower as a test bed. The benchmark problem consists of the following four tasks: (i) output-only modal identification and finite element model updating, (ii) damage detection using simulated data, (iii) optimal sensor placement for structural health monitoring, and (iv) damage detection using field measurement data. This paper will address some key issues related to the development of this first benchmark problem for high-rise structures. More details of the study can be found in the website: http://www.cse.polyu.edu.hk/benchmark/index.htm