0 8 / 0 7 / 0 8 R e v 1 Technical Data Application Strain Measurement Temperature monitoring Datalogging Static load testing Long term monitoring Advantages • Accurate strain measurement • Accurate temperature measurement • Automated sensor interrogation • Remote data collection Various types of pile instrumentation can be used to measure changes in physical properties of the concr ete and steel mass of a pile during static load testing or during long term monitoring. Cementation Skanska has extensive experience in the use of vibrating wire strain gauges, rod extensometers and temperature measuremen t and can provide a full in- house service from installation to reporting. Cementation has installed embedment and sister bar strain gauges to measure the transfer of load along the length of the pile during the short term or long term loading of the structure. Both types of sensor work on the principle that a tensioned wire housed within the sensor when electronically plucked will change the frequency of its response with a change in length. The output frequency of the sensor is recorded by a dedicated datalogger. The embedment or dumbbell gauge (pictured overleaf) is designed to measure strain in concrete, this vibrating wire strain gauge is typically tied to a Pile Instrumentation reinforcing cage. It is usual to install them in arrays of three or four gauges at several depths horizons within the structure. The sister bar strain gauge comprises of two lengths of ribbed rebar welded to a central gauge section. The central gauge section has a miniature stainless steel, vibrating wire strain gauge element, fitted along the longitudinal axis of the gauge. Incorporated within the gauge section are two coils for excitation and output of the vibrating wire strain g auge element. This type of gauge is particularly rugged and reliable. They are particularly applicable for strain measurements in mass concrete pours where placing of concrete is remote and uncontrolled such as typically occurs in diaphragm walls or deep piles, since the instruments are capable of withstanding impact from tremie pipes and large concrete flows. For installation, the sister bars are simply tied by soft iron tie wire to an adjacent reinforcing bar. As the sister bars are of long length, they are readily able to maintain their orientation to the reinforcing cage Single and multi-point rod extensometers have been used to as an alternative measurement of strain or in conjunction with