JPH04216425A - Installing method of optical fiber sensor - Google Patents

Abstract

PURPOSE:To easily install an optical fiber sensor to a concrete object without damaging the sensor when the temperature distribution of the concrete object is to be continuously measured with the use of a DTS measuring system by mounting a temporary fixing ring to the object and passing the optical fiber sensor through the ring, with using a pulley at a turning point of the sensor. CONSTITUTION:A temporary fixing ring is mounted to a reinforcing bar. An optical fiber sensor is extended through the temporary fixing ring. A pulley is provided at a turning point. The extending direction of the sensor is reversed by the pulley. After the optical fiber sensor is installed at a predetermined position, the ring is fixed and the pulley at the turning point is exchanged with a fixing member having the curvature not smaller than the permissible bending radius of the sensor. The optical fiber sensor is fixed along the fixing member.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of installing an optical fiber sensor on an object when continuously measuring the temperature distribution of a concrete structure using the optical fiber itself as a sensor.

0002

2. Description of the Related Art Thermocouples are widely used as sensors for measuring temperature. This utilizes thermoelectromotive force generated by the Seebeck effect when heating or cooling the junction of two types of metal wires. There are also thermistors and the like as temperature sensors whose electrical resistance changes with temperature, but all of these measure temperature at a point and cannot measure continuous temperature distribution.

On the other hand, DTS (Detributed Temperature Transmission) is one of the technologies that can continuously measure physical quantities along the sensor using an optical fiber itself as a sensor.
A temperature measurement system called a temperature sensor has been developed. This consists of a sensor section made of an optical fiber installed on the object to be measured, a laser light source connected to one end of the optical fiber, a measurement section made up of a light receiving circuit, etc., and a processing section using a computer. Then, by inputting a light pulse from a laser light source into an optical fiber and measuring the delay time of the backscattered light, the generation position of the backscattered light is determined, and then the intensity of the Raman scattered light included in the backscattered light is detected. By doing this, the temperature at each position is determined. Therefore, by using DTS, it becomes possible to measure continuous temperature data in the length direction of the optical fiber.

0004

SUMMARY OF THE INVENTION In order to measure temperature distribution using the conventional point sensors such as thermocouples described above, an extremely large number of sensors are required and the cost becomes high. Furthermore, since the installation of sensor cables becomes complicated, there is a problem that the number of sensors is naturally limited.

[0005] On the other hand, the above problem can be solved by applying a DTS that can continuously measure the temperature in the longitudinal direction by installing a single optical fiber. However,
When pouring concrete, pressure from the poured concrete and vibrations from the vibrator act on the optical fiber, so when applying DTS, the challenge is to protect the optical fiber from these external forces and to be able to easily install the optical fiber. there were.

[0006]

[Means for Solving the Problems] The present invention solves the above-mentioned problems, allows easy installation of optical fibers, protects the optical fibers from external forces acting on the optical fibers, and enables temperature distribution measurement by DTS. The present invention provides a method for installing an optical fiber sensor, which is characterized by attaching temporary fixing rings to the constructed reinforcing bars at appropriate intervals, and arranging a pulley at the turning point, so that the optical fiber sensor can be installed at the temporary fixing point. The wire is extended through the ring, and at the turning point, it is reversed through the pulley, and after the optical fiber sensor is laid in a predetermined position, the ring is fixed, and at the turning point, the optical fiber sensor is used in place of the pulley. A fixing member having a curvature greater than the bending radius is installed and fixed along the fixing member.

[0007]

[Operation] When installing optical fiber sensors along the reinforcing bars inside a concrete structure, there are problems such as the optical fiber sensor becoming entangled with other adjacent reinforcing bars during the wire extension, or friction with the reinforcing bars at the folded part. This may cause the optical fiber to break or be damaged. In the installation method of the present invention, temporary fixing rings are attached at appropriate intervals to the reinforcing bars to be installed using insulation locks, etc., and the wire is extended through the optical fiber sensor, thereby preventing entanglement with other reinforcing bars. Further, at the folded portion of the optical fiber sensor, a pulley such as a metal wheel is provided, and the optical fiber sensor is reversed via this, so that friction that may cause wire breakage or damage does not occur.

[0008] When placing concrete, a method is widely used in which the fresh concrete is vibrated with a vibrator to accelerate the flow in order to spread the fresh concrete to every corner of the reinforcing bars, but the laying method of the present invention In this case, the pressure caused by the flow of fresh concrete and the vibration caused by the vibrator are received by the reinforcing bars and the fixing member disposed at the folded portion, thereby effectively acting on protecting the optical fiber sensor.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram of a wire extension in the method of laying an optical fiber sensor according to the present invention. In the drawing, 1 is an optical fiber sensor, 2 is a constructed reinforcing bar, 3 is a temporary ring attached to the reinforcing bar 2 at appropriate intervals, and 4 is a pulley such as a metal wheel arranged at a turning point. The optical fiber sensor 1 is extended through the temporary fixing ring 3 in the direction of arrow a in the figure. Then, the direction of the wire is reversed via a pulley 4 provided at the turning point, and the wire is extended in the direction of arrow b through a temporary fixing ring 3 attached to the reinforcing bar 2 above.

FIG. 2 is a diagram showing the state in which the optical fiber sensor is fixed to the reinforcing steel after the wire has been laid. After installing the optical fiber sensor 1 at a predetermined position, the ring is fixed 3'. Also, the pulley 4 is removed, and instead of the pulley 4, a fixing member 5 having a curvature larger than the allowable bending radius of the optical fiber sensor is installed at the turning point, and the optical fiber sensor 1 is fixed along the fixing member 5. , the installation of the optical fiber sensor 1 is completed.

FIG. 3 is a diagram showing the installation state of an optical fiber sensor in an experiment to confirm the installation method of the present invention. Optical fiber sensors 1 with a length of 120 m were folded in seven stages at a pitch of about 250 mm and laid on reinforcing bars 2 inside a concrete frame 6 measuring 1,700 mm in height x 1,400 mm in width x 20,000 mm in length using the laying method of the present invention. In this experiment, it was confirmed that the installation work was easy, the loss increase in the optical fiber sensor after concrete placement was less than 1 dB, and there was no problem at all with temperature distribution measurement by DTS.

[0012] Furthermore, by the installation method of the present invention, the bottom plate of the expressway tunnel section (height 1700 mm x width 16000 mm x
DT is applied to the mass concrete with a length of 20,000 mm.
A temperature distribution measurement system using S was applied. Optical fiber sensors were laid in seven stages at a pitch of 100 to 300 mm in the depth direction, and three rows of this arrangement were provided in the length direction (total length of the optical fiber sensors was about 300 m). Temperature data every 5m along the length of the optical fiber sensor is made to correspond to each position of the concrete structure, and software processing displays temperature distribution by color on the cross section of the structure.
It is now possible to extract depth direction temperature graphs and time-series temperature change graphs at any location. As a result, it has become possible to understand the continuous and three-dimensional temperature distribution inside mass concrete.

[0013]

Effects of the Invention As explained above, according to the method for laying an optical fiber sensor of the present invention, the optical fiber sensor can be easily extended without getting entangled with other reinforcing bars when it is being extended, and it can be easily installed in concrete. Even at times, the optical fiber sensor can be protected from external forces.

[0014] Therefore, by applying the DTS temperature measurement system, it is possible to grasp the continuous and three-dimensional temperature distribution inside mass concrete, and in the future, it will be possible to grasp temperature cracks, which is one of the problems with mass concrete in the civil engineering field. It is extremely effective when used in temperature stress analysis for control, design consideration, and construction management, and can be expected to be used for information management construction.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of wire extension in the optical fiber sensor installation method of the present invention.

FIG. 2 is a diagram showing the state in which the optical fiber sensor is fixed to the reinforcing steel after the wire has been extended.

FIG. 3 is a diagram showing the installation state of an optical fiber sensor in an experiment to confirm the installation method of the present invention.

[Explanation of symbols] 1 Optical fiber sensor 2 Reinforcing bars 3 Temporary fixing ring 4 Pulley 5 Fixed member 6 Concrete ▲Structure▼Body

Claims (1)

[Claims] Claim 1: A method for installing an optical fiber sensor for measuring the temperature of a concrete structure using the optical fiber itself as a sensor, which comprises attaching temporary fixing rings to the constructed reinforcing bars at appropriate intervals, and installing a pulley at the turning point. arranged,
The optical fiber sensor is extended through the temporary fixing ring, and at the turning point, it is reversed via the pulley, and after the optical fiber sensor is installed at a predetermined position, the ring is fixed, and at the turning point, the wire is fixed to the pulley. A method for installing an optical fiber sensor, characterized in that a fixing member having a curvature greater than the allowable bending radius of the optical fiber sensor is installed instead and fixed along the fixing member.