Creep and Shrinkage of a Self-Compacting VHPC in Prebent Composite Beams for Innovative Railway Bridges in France-Part II: Case Study

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Title: Creep and Shrinkage of a Self-Compacting VHPC in Prebent Composite Beams for Innovative Railway Bridges in France-Part II: Case Study

Author(s): S. Staquet, C. Bouley, L. D’Aloia, R. Le Roy, B. Espion, and F. Toutlemonde

Publication: Special Publication

Volume: 246

Issue:

Appears on pages(s): 71-86

Keywords: creep recovery; deflection; very-high-performance concrete

Date: 9/1/2007

Abstract:
An extensive experimental research has been carried out to extend the Belgian technique of steel-concrete prebent beams to Very High Performance Concrete (VHPC: self-compacting C80/95 with silica fume). Besides concerns of mixture proportions optimization with respect to rheological requirements for ensuring a perfect concreting of the thin enough VHPC flange, a major issue of the programme consisted in validating a design method for the prediction of stress redistribution due to concrete creep within the cross-section. Two 13 m-long beams were made and monitored during several months after the VHPC casting. Two months after the VHPC casting, dead loads, representative of upper deck, rails and equipments weight, were applied. The experiments realised on the beams allow drawing the following conclusions: • the evolution of the deflection appears very limited when concrete age is beyond 2 months - corresponding to the period where a significant part of creep and shrinkage has already taken place - what confirms VHPC interest; • the feasability to optimize a prebent beam with a VHPC is demonstrated. Practically, the design is always controlled by the serviceability limit state for this kind of structures, due to the following criteria; • control of the concrete delayed effects by limiting the stress during the prestressing, which implies to have accurate data on creep and mechanical properties of the concrete, particularly at early age; • control of cracking by keeping compression under permanent loads.Detailed results of the global response of one the beams as well as the validation of the computation method for taking creep into account are analyzed in conjunction with deflection and strain measurements.