Bridges: Lully

Case study: SOFO System

Steel-concrete composite structure
Concrete monitoring during setting
Prestressing monitoring

Project Description

Summary: Concrete monitoring during setting, prestressing monitoring, long-term monitoring

Clients: Fribourg Canton

Place: Fribourg Canton (Switzerland)

Period: 1996 - 1998

Installation: ICOM/IMAC-EPFL

Structure's short description: The Lully highway bridge is an innovative composite bridge. The two independent concrete slabs are supported by a space steel truss. The concrete slab is prestressed in both directions. Setting retardant were added to the concrete mix.

Aim of monitoring: Eleven 1 m long SOFO sensors were installed in the concrete slab to monitor its shrinkage, its interaction with the steel truss and the deformations due to prestressing.

Number of sensor: 11

Main Results: The figure shows the deformations measured by the SOFO sensors during the first 10 days after concreting. In the first phase the concrete shortens due to a temperature sinking during the night after concrete pour. The slab than expands due to the exothermic setting reaction. After reaching a temperature maximum, cooling starts and the slab becomes shorter. Three days after concreting, the slab is prestressed, the resulting slab deformation is clearly measurable and it was possible to verify the amount of prestressing effectively given to the slab. After this operation, the hydraulic shrinkage continues. The concrete pour of the next construction phase does non introduce a significant deformation in the slab.

Deformations measured during the first month after concrete pouring

Bibliography:

Bridge monitoring by interferometric deformation sensors , D. Inaudi, S. Vurpillot, N. Casanova, Conference on Laser Optoelectronics and Microphotonics: Fiber Optic Sensors, Beijing, invited paper, SPIE, Vol 2895, p 34-45, 1996

Fiber optic deformation sensors for bridges monitoring , D. Inaudi, N. Casanova, S. Vurpillot, Int. Conf. on New Technologies in Structural Engineering, Lisboa, Portugal, p 975-982, 1997