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Time-related deflections of cantilever bridges

Abstract:

Many prestressed concrete bridges with spans between 100 and 160 m have been built in the Netherlands. The method of construction is the so-called in situ free cantilever construction. The first bridge executed according to this method was built in 1966. Starting from that date deflections were measured yearly by the Ministry of Transport, Public Works and Water Management. The observation of the actual performance of bridges revealed that in general the deflections were much larger than expected. Furthermore, no limit value of the actual deflection was reached even after 25 years. The deflections were mainly caused by shrinkage and creep of the concrete. A second reason for the deflections is the construction method: cantilever bridges, which are isostatic during the construction period are made continuous by keying the different beams. Starting from the end of the 70's a computer program was used to pbkp_redict the deflections. The time-related losses were based on the CEB-FIP Model Code 1978. The computer pbkp_redictions were compared with the field measurements. It appeared that these pbkp_redictions underestimated the actual deflections by at least 20 percent. A further study on the effect of the time-related losses, if the CEB-FIP Model Code 1990 is used, is in progress. Although, this investigation is still in an early stage, some conclusions are discussed.