Seok Been Im

Summary Review of GPS Technology for Structural Health Monitoring

Over the last two decades, global positioning system (GPS) technology has been developed rapidly and recently applied to civil structures for appropriate monitoring of structural performance. Currently, the GPS technique can only be applied to flexible structures having lower modal frequency ranges, and it still has remaining issues when it comes to obtaining accurate measurements. However, the application of GPS is promising as a monitoring tool because it can measure dynamic characteristics and static displacements in real time, whereas the conventional monitoring system using accelerometers cannot measure static and quasi-static displacements. Furthermore, rapid advancements in GPS devices and algorithms can mitigate erroneous sources of GPS data, and integrated systems using GPS receivers with other supplement sensors are capable of providing accurate measurements. Therefore, GPS technology can provide accurate displacements of structures in real time, and stress and strain conditions of the structures can be computed using finite-element models and numerical analyses. It is also expected that damage localization and severity can be identified using the dynamic characteristics of structures obtained from GPS. This paper summarizes the use of GPS technology for structural health monitoring.

Modeling and Validation of Repair Grout Flow in Voided Ducts

External post-tensioned (PT) tendons in bridges are installed inside box girders with high-density polyethylene ducts. Voids in these ducts can lead to corrosion of the PT strands, which could lead to tendon failure. A grout injection is commonly used to protect exposed tendons. Although experiments using external PT tendons have been performed to investigate effective grouting repair methods and materials, these experiments cannot simulate all parameters of grouting repair encountered in the field. In response, the current study uses a commercial computational fluid dynamics program to investigate grout flows in void-containing ducts. A simplified numerical model then is developed based on previous experimental results. This model can consider all parameters of repair grouting methods not covered by experiments. A validation of the proposed model shows close agreement between numerical and experimental results regarding grout flow and repair performance.

Study of the Structural Displacement Estimation by the Acceleration Measurement with an Effective Noise Filtering Method

In this study, the estimation method for the structural displacements by the acceleration measurement is investigated for effective real-time structural monitoring. Theoretically, the velocity and displacement data during the specific period can be obtained by integration of the measured acceleration. But, the integrated data is highly affected by unexpected error sources such as noise signal. So, the effective and rational method for the noise elimination or minimization should be suggested and used. In this study, an effective noise filtering method for an useful displacement estimation by double integration is suggested based on the characteristics of structural dynamics. For the rational noise filtering technique applied to the measured acceleration data, the multi bandpass filter, which allows the signals nearby the peak frequencies of measured data, is newly suggested. By the suggested filtering and double integration method, the estimation method of structural displacements using an acceleration measurement is suggested in this study. The accuracy and rationality of the suggested method was validated using the numerical example obtained by finite element analysis. In the validation, the displacement data estimated by the suggested method was directly compared with those obtained by highpass filter and bandpass filter, formerly well known methods.