Weina Meng

Experimental and Numerical Studies on Flexural Behavior of Ultrahigh-Performance Concrete Panels Reinforced with Embedded Glass Fiber-Reinforced Polymer Grids

The use of glass fiber-reinforced polymer (GFRP) grids in reinforced concrete construction offers several advantages, such as high tensile strength and excellent corrosion resistance. This paper presents the results of experimental and numerical studies of the flexural performance of ultrahigh-performance concrete (UHPC) panels reinforced with GFRP grids. Such panels can be prefabricated and used as permanent formwork elements for bridge columns or walls. The mechanical properties of GFRP grids and UHPC were experimentally evaluated. The flexural performance of panels containing different reinforcement configurations was evaluated in three-point bending tests. The GFRP grids were found to be able to significantly enhance the flexural performance of the UHPC panels. A three-dimensional nonlinear finite element model was established by using ABAQUS, which incorporated the concrete damage plasticity model and can be used to predict the postfracture behaviors. The numerical model was experimentally validated by using the three-point bending test results and was then used for parametric studies. The studied parameters included the panel thickness and the layer number of the GFRP grids reinforcement. The proposed GFRP–UHPC panel system was shown to be promising for the development of lightweight, high-performance permanent formwork. Such formwork can be used in the accelerated construction of critical infrastructures for the enhancement of crack resistance and extension of the service life.

Flexural Performance of Ultra-High Performance Concrete Ballastless Track Slabs

Ballastless track slab offers excellent stability and durability and has been well accepted in high-speed railways worldwide. Rails are typically laid on precast concrete slabs that are subjected to dynamic load transferred from the rails. Cracks can be induced by shrinkage and mechanical loading in concrete, which accelerates the degradation and affects the performance of the track slab. As tens of thousands of miles of ballastless track are constructed, effective and efficient maintenance for the concrete slabs has become an issue. In this paper, ultra-high performance concrete (UHPC) is proposed to fabricate ballastless track slab. UHPC is a superior fiber-reinforced, cementitioius mortar, which has greatly-improved mechanical strengths and durability. A recently-developed UHPC is evaluated in terms of the flowability, durability, shrinkage, and mechanical properties. A functionally-graded slab design is proposed with the consideration of initial material cost. The slab is cast with two layers: a layer of conventional concrete at the bottom, and a layer of UHPC on the top. A three-dimensional finite element model is developed for ballastless track slab whose flexural performance is investigated and compared with that of slab made with conventional concrete. Concrete damage plasticity model is incorporated to consider the post-cracking behavior. The results indicate that the proposed UHPC is promising for fabricating ballastless track slab with superior performance.Copyright

Kilometer-Long Optical Fiber Sensor for Real-Time Railroad Infrastructure Monitoring to Ensure Safe Train Operation

This study is aimed to develop a real-time safety monitoring of kilometer-long joint rails using a distributed fiber optic sensor. The sensor measures the distribution of Brillouin frequency shift along its length with pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA). The measurement distance and spatial resolution can be up to 25 km and 2 cm, respectively. The fiber optic sensor was first characterized and calibrated for distributed strain and temperature measurement, and then instrumented on a small-scale joint rail-like specimen in laboratory. The specimen was loaded at room temperature, and its strain distribution along the sensor was measured using a Neubrescope with high accuracy and spatial resolution. Given a gage length, the joint open change was determined and visibly identified from the measured strain distribution. Finally, an implementation plan of distributed sensors on a railway is introduced, including sensor deployment, sensor repair when broken, and cost analysis. The gage length at a crack is an important parameter in sensor deployment and investigated using finite element analysis. The results indicate that the distributed sensor can be used successfully to monitor the strain and temperature distributions in joint rails.Copyright