Are the Walloon viaducts still in good condition and safe? More than 50 years after the construction of many of them, are they still resistant and adapted to a denser road traffic with heavier vehicles and trucks? To answer these questions, the Walloon Public Service (SPW) entrusted a technical mission to a team of researchers and civil engineers from UHasselt, ULB, SECO and ULiège.
Three 30-metre long and 2-metre high beams from the Huccorgne viaduct on the E42 Speedway between Liège and Namur, which is currently being rebuilt, were sent last February to the Application Centre for Concrete and Construction (AC³) at UHasselt, a research and testing centre adapted to analyses of large-scale construction elements.
"We carried out shear force tests on the three concrete bridge girders, applying forces of up to almost 300 tonnes from above using a jack. The beams are equipped with 52 different sensors to obtain information on cracking and residual strength. The pressure tests were carried out at different points each time, at 5.5 metres, 9 metres and 12 metres from the support point," explains Hervé Degée, professor of construction engineering at UHasselt, civil engineer and PhD degree in engineering sciences at ULiège.
On 2 May 2023, strength measurements were carried out on the last of the three beams, closest to the support point, at 5.5 metres. The beam withstood a pressure of 270 tonnes and did not break in two (unlike the test at 12 metres with a pressure of 210 tonnes), despite cracks appearing in many places on the beam.
"These tests show that these beams did not suffer any major degradation more than 50 years after their construction", notes Boyan Mihaylov, professor at the School of Engineering at ULiège (Concrete Structures, UR Urban and Environmental Engineering), who was involved in this test campaign.
Together with his colleagues at ULB, Prof. Mihaylov established virtual models to theoretically map the condition of the Walloon viaduct heritage. "These real-life measurements allow us to verify the relevance of our models, and the results show us that they are very close to the resistance tests on real structures. This is important because it will allow us to tell the Walloon public authorities whether similar beams on existing viaducts still meet the requirements or need to be repaired or replaced.”
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