Comparison between simplified and refined models for deflection in continuous reinforced concrete T-beams

Verification of the Serviceability Limit State for allowable displacements is a mandatory step in the design of a reinforced concrete (RC) beam. In order to proceed this verification, simplified methods recommended by Design Codes or analytical models can be employed. In these models, the variation in flexural stiffness due to the concrete cracking is the primary factor to be considered. A “T” cross-section beam present greater stiffness compared to a rectangular section of equal height and area. The concentration of more area at one end of the section raises questions about whether this type of section exhibits the same behavioral response as the rectangular section when applying the models for predicting deflection as indicated by Codes. In this work, a comparative study of different simplified methods and finite element (FE) models used for calculating deflections in reinforced concrete T-beams is performed. Simplified methods employed are the one recommended by Brazilian Code ABNT NBR 6118, and the Bilinear method recommended by the fib Model Code. Two FE models are adopted, in which the material nonlinearities are considered by means of moment-curvature diagrams, these based on the simplified methods. The deflections obtained by the different models are compared for several examples of continuous RC T-beams at service, by varying the beam geometry and the reinforcing ratio. The results are analyzed for short-term deflections and long-term deflections. In the end of this work, differences between the models are pointed and recommendations regarding the use of then are drawn for this specific section type.