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Internal strain prediction of full scale and small scale concrete members due to creep and shrinkage effects

The stress and strain in a reinforced or prestressed concrete structure are subject to change during a long period of time due to the effects of creep and shrinkage of concrete and relaxation of prestressed steel. These time-dependent effects can cause undesired cracking and large deflections. A cross-sectional based calculation tool was developed based on international standards and recently published literature to determine the effect of cracking and internal stresses and strains of a concrete beam as function of time based on the step-by-step method. The accuracy of the structural analysis can be further improved using adjusted creep and shrinkage models for steel fibre reinforced concrete.
Large scale tests are required to validate the proposed models. At BOKU Vienna (Institut für Konstruktiven Ingenieurbau) four prestressed TT-elements subjected to environmental influences with a span of 33m and small scale beams with a span of 5m kept in lab conditions were subjected to proof loading. These concrete members were continuously monitored using internal stain gauges fixed to the reinforcement bars. A sensitivity and uncertainty analysis is performed to estimate confidence intervals of the analysis results due to the large error (30%) of creep and shrinkage models. Considering this extensive test series, the performance of the developed cross-sectional calculation tool and the associated creep and shrinkage models are investigated by comparing the analysis results with measurement data obtained from practical case studies.

Author(s):

Nicky Reybrouck    
Ghent University
Belgium

Bernhard Krug    
University of Natural Resources and Life Sciences
Austria

Alfred Strauss    
University of Natural Resources and Life Sciences
Austria

Robby Caspeele    
Ghent University
Belgium

Luc Taerwe    
Ghent University
Belgium