Study On A New Long-gauge Sensing For Civil Engineering Structures

The civil infrastructures are, generally, large-scaled in volume and dimensions. Especially, for the most applied reinforced concrete structures, there are many tiny damages such as cracks, bubbles inside, so they are easy to crack under pull force. Short-gauge ("point") sensors, such as the conventional strain gauges, are usually affected by these damages so they can not accurately reflect the service conditions of the concrete structures. Long-gauge sensing technology can measure the average strain of the structure even with damages on the surface of the structure, and they can also be applied on whole scale as a distributed sensor network. So long-gauge sensors are more suitable for civil engineering health monitoring.This paper proposed a new long gauge resistance wire (LG-RW) sensor, wherein the constantan resistance wire was used as the sensing element. A series of experiments were carried out to study the sensing performance and applicability of the new sensor.The main content of this paper can be summarized as follow:(1) First, a method was studied to package the constantan resistance wire, and the LG-RW sensors were fabricated with different gauge lengths. These sensors were calibrated with a calibration coefficient of 2. Their resistance increases linearly with the increase in gauge length, but with the similar sensing performance. The LG-RW sensors are characterized by a linearity coefficient of larger than 0.997 and a precision better than 5με under a static calibration.(2) Then, the static monitoring performance of the LG-RW sensors was tested by a RC beam static load test. The displacement and damage status of the RC beam was calculated by the resistance data from the LG-RW sensors. The results show that, the LG-RW sensors could effectively capture the crack. When the strain was at 1000με below, the error is less than 25με, when the strain was above 1000με, as strain increased, the absolute error increased slightly but the relative error was less than 5%.(3) The dynamic monitoring performance of the LG-RW sensor was tested by a damage detection experiment on cantilever beam. The result showed that the LG-RW sensor could accurately obtain the modal participation factor, the recognition result was very close to that of the FBG sensors. The frequency identification error did not exceed 0.2%. The LG-RW sensor could accurately locate the damage and distinguish the rigidity loss of different damage.