CONSTRUCTION


Historic Bridge Continues to Take the Strain


Strain measuring technology is playing a crucial role in the reconstruction of a 90-year-old suspension bridge in Brazil.


90-year-old structure will provide safe passage for numerous pedestrians and vehicles crossing each day.


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A CENTURY OF CHANGE The Hercílio Luz bridge was originally opened in 1926 to link the Island of Santa Catarina to mainland Brazil and has since maintained its original structure despite sea corrosion and ever-increasing vehicle weight. The loads that the bridge has to bear now are much higher than they were originally and the characteristics of the loads have changed as both the volume and type of traffic that use it have developed over nearly a century of use. In 1991, the bridge was closed due to safety fears but was declared a historical landmark with plans to restore the bridge to its original glory with an ability to cope with modern weights and vibration.


REHABILITATION Teixeira Duarte was hired for the complete rehabilitation of the Bridge, including replacement of bearing supports in the main towers, reinforcement and recovery of foundations, plus the application of new decks for vehicles and pedestrians. The most critical part of the project involved the


transfer of load from the central span of the bridge to auxiliary structures. To overcome this challenging step, Teixeira Duarte chose HBM’s technology, including sensors and optical interrogators with Fiber Bragg Grating (FBG) technology. This technology was used to monitor strain at critical points in the structure alongside electrical sensors for reading various signals including inclination, temperature, wind and sea current. According to Ricardo Martins, Teixeira Duarte’


Project Engineer, the more technically complex activity is the load transfer procedure which consists of the tension relief on the eye-bars allowing their sequential replacement. The execution of this procedure required the assessment of several points of the original and provisional metallic structure


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❱ ❱ Measuring strain during load transfer in the Hercílio Luz bridge reconstruction project is critical to prevent structural failure


using strain sensors and the application of other electric sensors as inclinometers as well as climatic sensors making a total of 312 sensors. “HBM supplied and installed the required equipment to achieve this through the optimised use of combined technologies. This included optical technology for strain measurements and data transmission to the control centre and electrical for other measurements. All this installation had to be coordinated with the physical schedule of the work,” explains Martins.


CRITICAL LOAD TRANSFER According to HBM, the load transfer operations are critical because this is when the hydraulic jacks are actuated to raise the deck of the bridge in order to transfer the load supported by the eye-bars to the lower temporary structure, which consists of four support towers. In a structure of this size, and with the severe damage exhibited on such an old bridge, a load transfer of this type can cause a structural failure in the bridge or temporary structure, and it is at this point that the instrumentation becomes fundamental. To ensure that the entire process was carried out with maximum safety, the multiple strain signals in the temporary structure were measured to assess whether the load was being homogeneously transferred by the structure of the bridge to evaluate if the load relief was occurring as expected. The load transfer process was carried out in stages,


and after each step the results were compared with numerical simulations by the engineers responsible for the project, in order to confirm that the behaviour of the structure was within the expected range. With restoration well under way and a completion


date expected in the first quarter of 2020, the Hercílio Luz bridge could soon be carrying traffic once more and coping with the loads and vibrations of the 21st century.


s part of a major project to restore Brazil’s longest suspension bridge, construction company Teixeira Duarte has been using optical and strain gauge technology from HBM to ensure the


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