A Study of Properties and Prediction of Long-term Deformation of Reinforced Concrete Members

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This study develops a new numerical method for prediction of reinforced concrete members subjected to not only constant but also variable sustained bending moments in order to help establish design method of long-term deformation. The calculated results are compared with the results obtained from the experiment in which the effects of both magnitude and hysteresis of sustained loads are mainly investigated.The following conclusions are drawn from these theoretical and experimental studies ;1. The basic differential equations to analyze the time-dependent deformation of reinforced concrete members are formulated in active bond zone taking stress hysteresis in concrete due to creep, drying shrinkage, creep of bond and drop of bond strength near the cracked section into account.2. The present method can predict the time-dependent average curvature, compressive strain in concrete, reinforcement strain of reinforced concrete members subjected to variable sustained loads as well as subjected to constant sustained loads.3. Average curvature observed at 250 days after loading in reinforced concrete member subjected to constant sustained load 30 % larger than that subjected to variable sustained load shows the necessity considering the influence of stress history of concrete in estimating deformation.4. Time-dependent increase of crack width can be explained by small decrease of bond stress, increase of bond slip and that of drying shrinkage.5. The maximum differences between stress calculated by considering the history and that by using effective modulus method are about 10 % in the case subjected to constant sustained load and 20 % in the case subjected to variable sustained load, respectively.