To detect deformation in civil engineering structures due to earthquakes,
heavy rainfall and significant age-related degradation, the RTRI developed
U-Doppler, a non-contact-type vibration measuring system applicable to
structures (Fig. 1). This system measures structural vibration caused by
train passage, impact excitation or microtremor by radiating a laser beam
from a point between 1 and 100 m away. It has a function to compensate
for the effects of vibration and inclination of the optical sensor unit
with a built-in vibration sensor to ensure high-precision measurement even
in outdoor environments. Adopting a long-distance remote measurement method
with U-Doppler enables improvement of the efficiency and safety of measurement,
since it is unneccessary to install sensors at locations high above structures
and remove them later.
The U-Doppler is already being used to estimate the natural frequency
of viaducts and bridge piers (Fig.2) and to measure the dynamic deflection
of bridge girders (Fig.3), and further use is planned.