ACI 209R

Abstract

This report presents a unified approach to predicting the effect of moisture changes, sustained loading, and temperature on reinforced and prestressed concrete structures. Material response, factors affecting the structural response, and the response of structures in which the time change of stress is either negligible or significant are discussed.<br>Simplified methods are used to predict the material response and to analyze the structural response under service conditions. While these methods yield reasonably good results, a close correlation between the predicted deflections, cambers, prestress losses, etc., and the measurements from field structures should not be expected. The degree of correlation can be improved if the prediction of the material response is based on test data for the actual materials used, under environmental and loading conditions similar to those expected in the field structures.<br>These direct solution methods predict the response behavior at an arbitrary time step with a computational effort corresponding to that of an elastic solution. They have been reasonably well substantiated for laboratory conditions and are intended for structures designed using the ACI 318 Code. They are not intended for the analysis of creep recovery due to unloading, and they apply primarily to an isothermal and relatively uniform environment.<br>Special structures, such as nuclear reactor vessels and containments, bridges or shells of record spans, or large ocean structures, may require further considerations which are not within the scope of this report. For structures in which considerable extrapolation of the state-of-the-art in design and construction techniques is achieved, long-term tests on models may be essential to provide a sound basis for analyzing serviceability response. Reference 109 describes models and modeling techniques of concrete structures. For mass-produced concrete members, actual size tests and service inspection data will result in more accurate predictions. In every case, using test data to supplement the procedures in this report will result in an improved prediction of service performance.