Effect of Flange Width on Beam Deflections


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Title: Effect of Flange Width on Beam Deflections

Author(s): H. H. Nassif, M. Sanders, and W. Cao

Publication: Special Publication

Volume: 203


Appears on pages(s): 115-130

Keywords: deflection; effective flange width; finite element analysis; reinforced concrete; stiffness

Date: 8/1/2001

Current concrete design codes use an effective stiffness model to calculate the deflections of T-Beams. Based on the effective flange width, an effective moment of inertia, as well as section properties is computed. This effective flange width is limited by a criterion that is not consistent between various codes and which directly affects the computed deflections, moments, shears, and torques for the beam. In particular,the effect of flange width on serviceability limit states such as deflection, fatigue, cracking, and vibration is evident. There is a need to use more rational as well as realistic effective flange width criteria that would lead to more accurate predictions of beam deflections. An analytical and experimental study has been initiated to assess the contribution of the flange width to the calculation of deflection in concrete T-beams. This paper presents part of the results of an analytical study to model the exact behavior of T-beams with various effective flange widths. The Finite Element Method (FEM) is utilized to model the overall pre-cracking, cracking, and post-cracking, non-linear behavior. Actual data for material properties are used to model concrete and reinforcing steel. The FE Model is validated using available test results from literature and then used to analyze T-beams with various parameters. The beams are incrementally loaded to failure under a two point loading system. The load-deflection relationships are determined. A parametric study is undertaken to determine the effect of overall flange width. and other parameters such as reinforcement ratio, and concrete compressivestrength, on deflections. Results show that deflections for beams subjected to service loads (service load ranging between cracking and 30-40% of ultimate loads) are mainly affected by using the effective flange width rather than full flange width. It is observed that using the actual flange width would provide a better estimate of deflection at service loads.