Structural health monitoring (SHM, SMS) subsystem

Natural frequency and logarithmic decrement control

Dynamic probing techniques of buildings and structures have been used for stress-strain state control for a long time (and especially during previous 10-15 years). This method is based on measuring bulding’s natural oscillations period and decrement.

Oscillations of buildings and bridges structures may be caused by nearby construction works, traffic and other man-made processes. Thus, for high structures it is necessary to control stress-strain state changes as well as to find particular location of such changes using other methods, which enable measuring process automation.

Exceeding the acceptable level of stress-strain state under certain circumstances may lead to complete or partial destruction of the said structures and other negative consequences. There are a lot of such examples: Egyptian Bridge in St. Petersburg, Tacoma Narrows Bridge in the USA, Volgograd Bridge in Volgograd, etc.

Structural health monitoring subsystem “Natural frequency and logarithmic decrement control” enables automated control of acceptable stress-strain level excession for the purpose of accidents prevention.

Акселерометры ZET 7150

The subsystem “Natural frequency and logarithmic decrement control” is based on ZET 7152-N and ZET 7156 digital sensors and enables automated control of structural elements vibrational acceleration, natural frequencies and corresponding logarithmic decrements.

It is recommended to place the sensors on concrete foundations as close to the supporting pillars / bearing walls of the controlled object (or building) as possible.

General specifications

Controlled parameter Natural frequency Decrement Acceleration Velocity
Module/ digital sensor type ZET 7156 ZET 7152‑N ZET 7156
Measuring unit Hz m/s2 µm/s
Measuring range 0,5…20 0,05…0,9 -140…+140 0,1…250
Minimal registered value 0,02 % 2 % 0,1 0,1
ALARM bottom level 2 % 10 % 3 2

In order to find the optimal areas for digital sensors positioning it is recommended to perform design and survey work using mobile measuring system of natural frequency and logarithmic decrement.

It is also recommended to select the areas having minimal spectral characteristics RMS deviation values within the natural frequencies registered range.

Design and survey work stage also allows to determine basiс values of non-standard buildings and structures natural frequencies.

Chemical and petroleum industry facilities are hazard-prone areas. Hence, it is necessary to prevent technological accidents at explosion-hazard areas, which makes monitoring of such facilities especially important. The products used for the monitoring should meet certain safety requirements. Taking this into consideration, our specialists have developed a compact off-line seismograph with  explosion-proof casing and PB Exd I MB X downhole compliance marking.

Seismic recorder for design and survey works performance

сейсмограф

Seismic recorder for design and survey works performance

at explosion-hazard facilities

Structural health monitoring (SHM) sub-system “Natural frequency and logarithmic decrement control” compares the values registered by digital sensors to the set threshold level parameters for warning and alarm notification. If the threshold values are exceeded, there will be formed corresponding signals: “Warning” or “Alarm“.