Influence of long-term creep on prestressed concrete beams in relation to deformations and structural resistance : experiments and modeling

Realistic structural models incorporating the time-dependent effects of concrete are essential in order to make accurate predictions of the time-dependent deflections at any time of the service life. Experimental databases are used to calibrate and validate existing models for creep and shrinkage available in international standards. However, extensive research campaigns on large-scale prestressed beams are scarce. In 1967-1985, a research program comprising a unique set of long-term experimental data on concrete beams was conducted in joint collaboration with four Belgian research institutes to determine the influence of creep and shrinkage on the long-term behavior of reinforced and prestressed concrete members. The main aim of the final part of the research campaign was the determination of the long-term behavior of prestressed and partially prestressed beams subjected to permanent loads, considering the influence of the magnitude of the loads, the degree of prestressing, the shape of the cross-section, the type of prestressing and the stress conditions. This paper reports on the obtained unique set of long-term tests. Additionally, also information related to the creep and shrinkage data of prisms and the results of the static tests in a four-point bending configuration until failure at the age of 28 days and 5 years are presented in this paper. The measurements of the prestressed members are compared with a simplified calculation method based on the direct stiffness method, which accounts for aging, creep, and shrinkage. The proposed simplified calculation model allows fast and accurate predictions of strains, stresses, and deflections as a function of time. The results show that the direct stiffness method in combination with the current models of EN1992-1-1 and fib Model Code 2010 can predict the long-term behavior of concrete beams in good agreement with the available experimental data. The research allows to develop more accurate calculation guidelines with respect to the evolution of deflections, concrete deformations and stresses of prestressed beams as function of the prestress-degree, shape of the cross-section, and the type of prestressing