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Technical Data

ApplicationStrain Measurement

Temperature monitoringDatalogging

Static load testingLong term monitoring

Advantages• Accurate strain measurement

• Accurate temperaturemeasurement

• Automated sensor interrogation

• Remote data collection

 

Various types of pile instrumentation can be used to measure changes in physical

 properties of the concrete and steel massof a pile during static load testing orduring long term monitoring. CementationSkanska has extensive experience in theuse of vibrating wire strain gauges, rodextensometers and temperature

measurement and can provide a full in-house service from installation toreporting.

Cementation has installed embedment

and sister bar strain gauges to measure thetransfer of load along the length of the pile during the short term or long term

loading of the structure. Both types ofsensor work on the principle that atensioned wire housed within the sensorwhen electronically plucked will changethe frequency of its response with achange in length. The output frequency of

the sensor is recorded by a dedicateddatalogger.

The embedment or dumbbell gauge(pictured overleaf) is designed to measure

strain in concrete, this vibrating wirestrain gauge is typically tied to a

PileInstrumentation

 

reinforcing cage. It is usual to install them inarrays of three or four gauges at several depthshorizons within the structure.

The sister bar strain gauge comprises oftwo lengths of ribbed rebar welded to a centralgauge section. The central gauge section has a

miniature stainless steel, vibrating wire straingauge element, fitted along the longitudinalaxis of the gauge. Incorporated within thegauge section are two coils for excitation andoutput of the vibrating wire strain gaugeelement. This type of gauge is particularly

rugged and reliable. They are particularlyapplicable for strain measurements in massconcrete pours where placing of concrete isremote and uncontrolled such as typicallyoccurs in diaphragm walls or deep piles, sincethe instruments are capable of withstanding

impact from tremie pipes and large concreteflows. For installation, the sister bars aresimply tied by soft iron tie wire to an adjacentreinforcing bar. As the sister bars are of longlength, they are readily able to maintain theirorientation to the reinforcing cage

Single and multi-point rod extensometershave been used to as an alternativemeasurement of strain or in conjunction with

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 Further information

Cementation SkanskaMaple Cross House

Denham WayMaple Cross

RickmansworthHertfordshire

WD3 9SWUnited Kingdom

Tel: +44 (0)1923 423100Fax: +44 (0)1923 423681

cementation@skanska.co.uk

www.skanska.co.uk

OfficesHead Office +44 (0)1923 423100

North +44 (0)1302 821100

South West, Midlands & Wales+44 (0)1454 453200

Scotland +44 (0)1698 735899

Northern Ireland +44 (0)28 9024 2746

Republic of Ireland +353 (0)1296 0790

strain gauges. Extensometers are steeltubes attached to the reinforcement cage

and cast into the pile. Rods are theninserted into the steel tubes, these rodswill behave independently of the steeltubes as the pile is loaded. The rod

appears to protrude from the top of thesteel tube as load is increased and thismovement can be accurately measuredusing displacement transducers. Multiplerod extensometers can measure strain atdifferent levels. Temperature monitoring

using thermocouples has been used todetermine the temperature profile during

curing of the concrete mass.

We also has extensive experience inthe interrogation on large numbers ofsensors by dedicated datalogging systems.

For example 260 strain gauges have beeninstalled in 8 piles at the Bankside 123

 project, London. These sensors areinterrogated every hour by threenetworked dataloggers with remote accessusing GSM technology to allow data

collection from the Maple Cross office.

PileInstrumentation