Props provide monitoring as well as support

Edited by the Engineeringtalk editorial team Jan 17, 2008

AVT engineers have strain gauged 48 props which are being used during major refurbishment work being carried out at junction 13 on the M4 in Berkshire

On-site strain gauging carried out by AV Technology (AVT) is playing a vital role in two quite different applications at opposite ends of the UK.

The gauges have been applied to Megashore structural support props to monitor the axial compressive loads during complex jacking procedures being carried out by Bill Boley.

AVT engineers have strain gauged 48 props which are being used during major refurbishment work being carried out at junction 13 on the M4 in Berkshire, adjacent to Chieveley Services.

A crucial part of the project has involved replacing all the support piers and during this work the motorway deck has been supported by twenty four 300 tonne jacks mounted in pairs on top of the strain gauged supports in close proximity to the piers being demolished.

During the demolition and rebuild process it is important for engineers to be aware of any movement in the foundations, which could have an impact of the integrity of the overall bridge structure.

Untoward changes in axial loads in the props are indicative of movement and the system is configured so that data can be remotely accessed on a regular basis.

In the second application, eight similarly strain gauged Megashore props are recording data during construction of the Chips building on the New Islington Millennium Village site in East Manchester.

When completed, this somewhat bizarre building, designed by Will Alsop, will comprise 145 one, two and three-bedroom apartments.

At nine storeys high, it gets its name from the way it zigzags along the edge of the Ashton Canal as a group of three-storey elements or 'Chips' stacked on top of each other.

At one end of the building the middle three-storey element is cantilevered out by 13m and the props are part of the complex support structure being deployed during construction.

Bill Boley has installed eight 100 tonne jacks, in two sets of four on top of the strain gauged props and is using the load data from the strain gauges to monitor the loading as the building work progresses.

On completion, when the jacks are lowered, the whole cantilevered section has been calculated to drop by 30mm.

In both applications, the props have been strain gauged on site using encapsulated gauges in full bridge configurations, with wiring back to the Bill Boley instrumentation.

Reliability is of paramount importance and such installations must be capable of withstanding the harsh environments experienced on construction sites together with external weather conditions.

The strain gauged support structures act like giant load cells and provide axial load information via Campbell Scientific data loggers with built-in modems.

This remote monitoring capability allows long-term load trends for both projects to be monitored remotely by AVT and Bill Boley .

In addition the 'text message' alarm feature automatically warns designated recipients of any out-of tolerance load excursions.