In 1967-1985, a research campaign 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 concrete members. The main aim of the research campaign was the determination of the long-term behavior of cracking and deformations subjected to permanent loads considering the influence of the magnitude of the loads and various reinforcement ratios. The objective of this article is twofold: to provide an overview of the measured data of the reinforced beams of the research campaign, which has never been published before, and to propose a simplified calculation method based on available models in literature that can predict the available measurement data. A simplified calculation model is proposed, which accounts for nonlinear creep strains due to high stresses, shrinkage, aging, and cracking in reinforced concrete beams. This numerical method is based on a cross-sectional analysis formulated using the layered Euler-Bernoulli beam theory, allowing fast and accurate predictions of strains, stresses, and deflections as a function of time based on fib Model Code 2010 and EN1992-1-1. The measurements of the beams subjected to high permanent loads during a time period of 4 years are compared to the results evaluated with the proposed simplified calculation model. The results show that the proposed simplified calculation method based on the current models of EN1992-1-1 and fib Model Code 2010 can predict the long-term behavior of reinforced concrete beams subjected to high loads in good agreement with the measurements.
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.
During the period 1967-1985 the Magnel Laboratory for Concrete Research participated in an extensive Belgian research campaign with respect to the influence of creep and shrinkage on the long-term behaviour of reinforced and prestressed concrete beams. This research campaign, jointly conducted at several Belgian research institutes, comprised the investigation of concrete and reinforced concrete beams (phase 1), prestressed concrete beams (phase 2) and partially prestressed concrete beams (phase 3). The main aim of the research campaign was the determination of the long-term behaviour subjected to permanent loads, considering the influence of the magnitude of the loads, different reinforcement ratios and/or prestressing degrees and/or different cross-sectional shapes. These results were obtained by a joint collaboration of 4 Belgian research institutes, each focussing on a different reinforcement ratio and reinforcement arrangement. With respect to the reinforced concrete beams (phase 1), at each institute 12 beams were tested in a 4-point bending configuration, namely 2 static tests at 28 days and 10 long-term tests with a duration of 2 to 4 years, considering different loading levels. In this contribution some results of the reinforced concrete beams (phase 1) will be documented and analysed, comprising the results obtained on 48 reinforced beam specimens with a length of 3.4 m (span of 2.8 m) and cross-section of 0.28 m x 0.15 m. A cross-sectional calculation tool developed at our department -incorporating the current creep and shrinkage models in standards and guidelines -will be employed in order to investigate the accuracy of the available models with respect to their ability to predict the structural behaviour of the documented reinforced concrete beams.
Abstract. The stresses and deformations in concrete change over time as a result of the creep-and shrinkage deformations of concrete. Different material models are available in literature in order to predict this time-dependent behaviour. These material models mostly have been calibrated on large datasets of creep specimens. In order to verify the accuracy of the contemporary material models with respect to the prediction of the creep behaviour of reinforced concrete beams, a cross-sectional calculation tool which employs the age-adjusted effective modulus has been developed and used to analyse an original set of 4 year-long creep data on reinforced beams from the 1960's. Six commonly used material models for the prediction of creep and shrinkage are considered in the current investigation: CEB-FIP Model Code 1990-1999, fib Model Code 2010, the model of EN1992-1-1, model B3, the Gardner Lockmann 2000 model, and ACI 209. The data on reinforced beams relates to an experimental investigation in collaboration with six major research institutes in Belgium. From 1967 until 1972 thirty-two reinforced beams with different reinforcement ratios were subjected, up until 4.5 years, to different stress levels in a four point bending configuration with a span of 2.8 m. In this paper a comparison between the measurements and the calculated deflections and strains is reported. Further, the deflections were also predicted using the contemporary creep models in combination with the nonlinear creep correction factor provided in EN1992-1-1, since the maximum concrete stresses in the beams were outside the service stress range of each of the models. Correcting for the nonlinearity of the creep coefficient significantly improves the calculated deflections. The most accurate predictions of the deflections at early age were obtained by the model of fib Model Code 2010. The Gardner Lockmann 2000 model exhibits the highest accuracy with respect to deflections at the end of loading and with respect to the creep rate.
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