sensors

VW No Stress-Strain Meter

Specialized sensor assembly designed to isolate and measure non-load related volume changes in mass concrete.

Model No
G77-V200N
Range
3000 µε
Resolution
1.0 µε

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Overview

Specialized sensor assembly designed to isolate and measure non-load related volume changes in mass concrete.

The Geolook Vibrating Wire No Stress-Strain Meter is an essential instrument for mass concrete monitoring, particularly in large dams. Its primary purpose is to measure volume changes caused by temperature fluctuations, autogenous growth, and moisture changes, while completely isolating the sensor from structural loads. By installing this unit alongside standard strain gauges, engineers can subtract the 'no-stress' data from the 'total strain' data. This calculation isolates the true stress-related strain, which is critical for assessing the actual structural loading and safety factor of the concrete mass.

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Benefits & Features

  • Isolates concrete from external structural stress
  • Measures autogenous growth and thermal expansion
  • Includes a high-precision VW Strain Gauge (G77-V200E)
  • Double-walled stainless steel or plastic container
  • Integral thermistor for precise temperature correlation
  • Frequency signal immune to long cable distances
  • Essential for accurate stress calculation in dams

Detailed Description

The Purpose of 'No-Stress' Measurement

In a massive concrete structure, the strain measured by a standard gauge is the sum of two things: the physical load pressing on the structure, and the natural expansion/contraction of the concrete material itself (due to heat or moisture).

The No Stress-Strain Meter allows engineers to measure the second part—the 'natural' movement—independently. This is the only way to accurately determine how much load a dam is actually carrying.

Independent Container Design

The system consists of a standard G77-V200E strain gauge mounted inside a specially designed double-walled container. This container is filled with the same concrete mix used in the structure.

The outer wall of the container protects the internal concrete from the surrounding structural pressures. This ensures that the concrete inside the 'can' undergoes exactly the same chemical and thermal changes as the rest of the dam, but without being squeezed by the weight of the structure.

Calculating True Stress

To find the 'True Stress-Related Strain,' engineers use a simple subtraction: (Total Strain from standard gauge) - (Strain from No-Stress meter).

This result is then multiplied by the Modulus of Elasticity of the concrete to find the actual Stress. Without the G77-V200N, stress calculations in mass concrete are often inaccurate due to the massive thermal shifts that occur during curing.

Autogenous Growth Monitoring

Over many decades, some concrete mixes exhibit 'autogenous growth'—a slight increase in volume due to chemical reactions within the cement paste. This growth can create internal pressures that threaten structural integrity.

The G77-V200N is the industry-standard tool for tracking this chemical evolution over the 50 to 100-year lifespan of a dam.

Available Models

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Specifications

Model No
G77-V200N
Range
3000 µε
Resolution
1.0 µε
Container Material
Stainless Steel / PVC
Operating Temp
-20°C to +80°C
Sensor Type
Vibrating Wire