Short and long-term deflection behaviour of steel reinforced concrete shallow beams

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University of New Brunswick


Current methods of computing the short and long-term deflection of reinforced concrete members are empirical and have been found to be inaccurate for some cases. The present research will examine the deflection behaviour of reinforced concrete members to explore whether a rational approach for computing short and long-term deflection can be developed. Fourteen steel reinforced shallow beams were cast and used to perform both short and long-term tests. Both traditional and more recent approaches to predict short-term deflection were investigated. Results indicated that selecting an appropriate cracking load has a significant impact on predicting the short-term response. In addition, a rational approach to compute the residual deflection after unloading was developed. Long-term deflection multipliers were computed from the experimental investigation and the results were compared to the CSA A23.3-04 reported values. The long-term deflection multipliers for beams tested at an early age, correspond well with the published values. However, for beams tested at a late age, CSA A23.3-04 long-term deflection multipliers significantly overestimate deflection, as expected. A rational approach to compute long-term deflection has been developed based on theoretical studies of axial members. This approach has been extended to flexural members and the predicted results agree well with the experimentally observed deflections.