Large scale fibre reinforced concrete beam tests instrumentation project

Morgan Sindall Underground Professional Services Ltd assigned CRD Group to instrument and monitor a series of Fibre Reinforced Concrete Beam Tests. The tests were conducted at the British Research Establishment.

The testing involved four concrete slabs, reinforced with steel fibres, subjected to four point bending.

slab preparation works before bending test

The aim of this research was to reveal the strain distribution at the face of the slab under tension all through the loading history and more specifically at the serviceability limit.

A customized CRD-patch FBG sensor strain sensor was developed for the specific project, that allowed the monitoring of the full displacement field even when the concrete was cracked.

slab #1 top and side view after bending test

slab #1 bending test all FBG sensors' stress-time diagram

slab #2 top and side view after bending test

slab #2 bending test all FBG sensors' stress-time diagram

slab #3 top and side view after bending test

slab #3 bending test all FBG sensors' stress-time diagram

The strain monitoring of the slabs let to the following conclusions:

• the strain of the sensors that happened to bridge a crack becomes exceedingly high
• the sensors next to formed cracks display the characteristic drop of strain as the crack passes nearby them. The closer the sensor to the crack the sharper this drop becomes
• between cracks the strain remains at significant levels

strain - time diagram from a FBG sensor bridging a concrete crack during the slab's bending test

strain - time diagram from a FBG sensor installed between concrete cracks during the slab's bending test

CRD Group is grateful for the cooperation with Prof. M. Sakellariou from NTUA. The instrumentation was jointly designed by CRD and Prof. M. Sakellariou.