Instrumentation and Strain Monitoring of BFRP Bars in Pedestrian Bridge Deck Link slab

Abstract

Abstract Eliminating bridge deck expansion joints is considered a feasible alternative for addressing problems associated with deck joints, which results in reduced maintenance and improved bridge-deck design life. Link slabs introduce partially continuity for bridge girders and improve the seismic performance, wind and storm wave loads resistance. It also leads to lower cost, improved riding quality, and improved structural integrity, and may lead to longer spans. The goal of this study is to monitor the performance of a link slab employed in a pedestrian bridge where Basalt Fiber Reinforced Polymer (BFRP) bars were used for its reinforcement. The pedestrian bridge was constructed from simple-span concrete girders that were made continuous by creating the continuity link slab between the girders’ ends. The paper will present the link slab instrumentation, monitoring, and instrumentation system employed in the project. Strain, temperature, and elongation data were collected for the purpose of investigating the performance of link slabs. Two groups of sensors were used in this project, namely surface-mounted and embedded sensors. Monitoring of the link slab occurred during and after concrete casting. Several types of sensors including vibrating wire sensors with integrated thermistors were used in this study. The sensors were installed strategically to detect and capture strains in the BFRP bars, strains in the concrete link slab, and movement of the gap between adjacent girders’ ends. A data acquisition system recorded strains and deformations at regular time intervals. Data was collected during service over two periods of approximately 3 months each. The collected data was in effect a result of temperature and shrinkage of the concrete and did not include any significant live load effect, i.e., the bridge was not load tested with vehicular loads. Sensor measurements were corrected for ambient temperature changes as per the manufacturer’s manual. Based on the monitoring data, it can be concluded that the strains experienced by the sensors in the link slab BFRP were small compared to the BFRP rupture strain. After approximately 90 days since the initial casting date, the average strain recorded in the mid-joint gauges did not significantly change indicating that minimal creep or shrinkage restraint was experienced by the link slab. The maximum daily strain change due to thermal effects was about 500 microstrain. The cyclical nature of thermal effects could contribute to concrete cracking over time in the link slab if tension stresses build up due to global shrinkage and creep restraint of the connected Florida Slab Beams (FSB) spans.