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Temporary works monitoring

Some projects require very specific temporary works monitoring due to their complex construction process and its associated risks. This includes the monitoring of jacking and propping operations as well as structural alterations.

James Fisher Strainstall (JF Strainstall) provides construction monitoring systems and services to projects worldwide using automated monitoring technologies supported by manual survey techniques.

We specialise in unusual monitoring applications and provide flexible and innovative systems that are tailored for each specific project. We are happy to discuss and advise on possible options.

We do not provide design or functions, meaning that all our monitoring is unbiased and unfiltered.

Bridge bearing renewal

Whenever bridge bearings are replaced, it is necessary to monitor the structure during the process to ensure:

  • Displacements between deck and substructure do not exceed pre-set limits
  • Strain in deck does not exceed limits
  • Relative positioning between deck and substructure is controlled to avoid misalignment

This is particularly important for situations where the bridge remains open to traffic while being temporarily propped.

Props

The load in props is monitored using strain gauges or load cells, with both hard-wired or wireless options being available. Typically, the purpose is to verify that load readings are as expected, with any changes to normal trends being identified automatically so that alarms are raised.

Structural alterations

During structural refurbishment and alterations, there are often requirements to remove structural elements, either permanently or temporarily.

On both bridges and buildings, tie rods or stay cables occasionally need to be renewed, usually one at a time. Monitoring the strain change in the element being removed and its neighbours enables the load redistribution to be measured, so that the original loads can be restored upon installation of the new element. It can also be necessary to monitor other structural elements to ensure they do not become overstressed during the process.

The formation of openings in slabs or walls – typically for new access ways – also need to be monitored to ensure the load redistribution can be compared with expectations.

The use of in-situ stress measurement techniques can provide valuable information about the pre-alteration loading regime, enabling the informed design of temporary and permanent works.

Monitoring approach

We design complex instrumentation schemes, including bespoke mountings and brackets, and then install them on site. These can comprise of hard-wired or wireless displacement, strain, tilt and temperature sensors, monitoring prisms and automated total stations.

The data can be displayed on our software platform SAMS which provides real-time dashboard visualisation, along with graphing and reporting tools. Going beyond standard sensor readings, the dashboard can also display live derived data to make the process more useful and effective.

A period of pre-works baseline monitoring should be completed before any construction activity starts, so that normal structural responses can be understood.

For more information see our structural monitoring Blackfriars station case study

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