Road planning projects across the straits and important cities have accelerated, and many huge bridges such as cable-stayed bridges and suspension bridges have been constructed. These bridges are supported by cables, and cable tension management is the basis for ensuring the safety and security of the bridges. We use a high-performance laser Doppler vibrometer to manage the cable tension of many cable-stayed and suspended bridges in Japan and

overseas.

Attractiveness of high-performance laser Doppler vibrometer Conventionally, the cable tension is measured by forced vibration of the cable using an

accelerometer. Then, a method of indirectly estimating from the relational expression

between the natural frequency of the cable and the tension is adopted. With this method, it is

necessary to install an accelerometer directly on the cable and forcibly vibrate the cable using

a hammer or the like. If there is a sidewalk, it is easy to approach the cable to be measured.

However, originally, there are many cases where

huge bridges such as cable-stayed bridges and

suspension bridges are crossed by an exclusive

road for automobiles, and it is difficult to measure

easily.We are able to catch multiple high-order

cable vibrations in a completely non-contact manner by using a high-performance laser Doppler

vibrometer and irradiating the target cable with laser light from a position up to 600m away. We do not

need a target for irradiation, so we can measure from anywhere. In addition, since the sampling frequency

is 2.5 MHz, it is possible to perform

measurement by micro vibration due

to wind or constant load, without the

need for forcible cable vibration

work.

Achievements in Japan and Overseas

We are involved in cable tension management for domestic and overseas cable-stayed and suspension bridges. We will introduce the main bridges

that have been measured.

Cable tension management for cable-stayed and suspension bridges

Cable tension management using a

high performance laser Doppler

※上晴の計測技術；実績①-1

Accelerometer

Target cable

ＰＣ

Accelerometer

Data logger

【Conventional method:

Forced vibration method】

Impact by hammer

Laser light irradiation

Measurement by high-performance laser Doppler

vibrometer

Laser Doppler vibrometer

Manhattan Bridge Williamsburg Bridge GeorgeWashing ton Bridge

Wakado-ohashi Bridge Shoyo-ohashi Bridge Kanmon-ohashi Bridge