Instrumentation of the T3 and G9 motorway bridges of Egnatia Odos S.A.

T3 motorway bridge

The T3 motorway bridge, located in Derveni, has three 28m long openings, each with seven prefabricated, prestressed beams. The T3 bridge is a typical bridge of the Egnatia motorway. The instrumentation of the bridge created a lot of interest and was considered to be an important development in the monitoring of highway structures.

8 Fibre Bragg Grating optical sensors were installed on the beams bearing the largest load due to heavy vehicle traffic.

view of T3 bridge

T3 bridge model simulation

T3 bridge FBG sensors' positions

G9 motorway bridge

The G9 bridge was constructed with the balanced cantilever method. It has two 85m long post-tentioned concrete openings. The G9 bridge is also a typical bridge of the Egnatia motorway, and is ideal for monitoring.

8 Fibre Bragg Grating optical sensors were installed on the elements most affected by creep after the cantilever's final placement.

view of G9 bridge

G9 bridge model simulation

G9 bridge FBG sensors' positions

instrumentation and measurements

The sensors (Smart Patch®) were incorporated in FRP casing and were attached on the concrete’s surface with epoxy resin. Thermal FBG sensors were also installed on both bridges, to ensure the measurements’ independence from the sensors’ temperature dependences.

Smart Patch® FBG sensor

FBG sensor's installation on T3 bridge

During the bridges' construction measurements were taken for the most representative and the maximum loads of the bridge. Afterwards, these measurements were compared to the model behaviour of the bridge.

T3 bridge sensor No7 strain - time measurements during the crossing of 5 heavy loaded trucks. The middle peak corresponds to the 60tn graduated vehicle crossing.

strain – time chart of top and bottom surfaces of a T3 bridge’s beam during the 60tn graduated vehicle crossing

strain – time chart of top and bottom surfaces of G9 bridge’s box cross section during the 60tn graduated vehicle crossing

An agreement of the measured strain curves to the theoretical influence lines, in terms of the position of the extreme strain value and of their shape, can be observed. The extreme experimental strain values are well enveloped by the extreme theoretical static values.

extreme experimental strain values - extreme theoretical static values of a T3 bridge beam's tension area

extreme experimental strain values - extreme theoretical static values of G9 bridge's tension area

The ratio of the theoretical to the experimental strain was used for the determination of the live load carrying capacity of the two instrumented bridges, which is required for the evaluation of their structural and functional sufficiency.

Furthermore, the bridges instrumentation’s results verify a stiffer behavior, already observed by experimental non destructive tests conducted on these bridge types. Through more persistent research, the real load carrying capacity of the bridges could be evaluated.