Ji-Hyun Hwang

Tensile Strength of GFRP Reinforcing Bars with Hollow Section

Fiber reinforced polymer (FRP) has been proposed to replace steel as a reinforcing bar (rebar) due to its high tensile strength and noncorrosive material properties. One obstacle in using FRP rebars is high price. Generally FRP is more expensive than conventional steel rebar. There are mainly two ways to reduce the cost. For example, one is making the price of each composition cost of FRP rebar (e.g., fibers, resin, etc.) lower than steel rebar. Another is making an optimized design for cross section and reducing the material cost. The former approach is not easy because the steel price is very low in comparison with component materials of FRP. For the latter approach, the cost could be cut down by reducing the material cost. Therefore, an idea of making hollow section over the cross section of FRP rebar was proposed in this study by optimizing the cross section design with acceptable tensile performance in comparison with steel rebar. In this study, glass reinforced polymer (GFRP) rebars with hollow section and 19 mm of outer diameter were manufactured and tested to evaluate the tensile performance in accordance with the hollowness ratio. From the test results, it was observed that the tensile strength decreased almost linearly with increase of hollowness ratio and the elastic modulus decreased nonlinearly.

Damage detection of a prototype building structure under shaking table testing using outlier analysis

The civil engineering community is becoming increasingly interested in monitoring structural behavior of civil infrastructure and in evaluation of the structural performance. The demand has largely been driven by deficiencies in structural performance due to the aging of the infrastructure, excessive loading, and natural disasters such as an earthquake, a landslide, a typhoon and a tsunami. In this study, a structural health monitoring methodology using acceleration responses is proposed for damage detection of a three-story prototype building structure during shaking table testing. A damage index is developed using the acceleration data and applied to outlier analysis, one of unsupervised learning based pattern recognition methods. A threshold value for the outlier analysis is determined based on confidence level of the probabilistic distribution of the acceleration data. The probabilistic distribution is selected according to the feature of the collected data.

Retrofitting Effects of Seismic Resistance Capacity of Existing RC Wall Type Apartment Slab Structures

A need for seismic design of buildings have been increased dramatically due to the fact that seismic damages have been reported all over the world. In Korea, the seismic design code for buildings was developed in 1988. However, the buildings designed and built before 1988 are expected for serious seismic damages. With this reason, an appropriate seismic retrofitting method is required for such buildings, which needs to be economical and practical. In this study, seismic retrofitting methods by using H-section steel to the slab are developed and introduced applying to the wall-type apartment buildings. As a result, performance of slab test models was improved to satisfy the required retrofitting capacity. Stiffness and energy dissipation capacity of the model were also enhanced.