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CivilComp Proceedings
ISSN 17593433 CCP: 75
PROCEEDINGS OF THE SIXTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY Edited by: B.H.V. Topping and Z. Bittnar
Paper 13
Investigation of Effective Flange Width Formulas for TBeams M. Utku and A. Aygar
Department of Civil Engineering, Middle East Technical University, Ankara, Turkey M. Utku, A. Aygar, "Investigation of Effective Flange Width Formulas for TBeams", in B.H.V. Topping, Z. Bittnar, (Editors), "Proceedings of the Sixth International Conference on Computational Structures Technology", CivilComp Press, Stirlingshire, UK, Paper 13, 2002. doi:10.4203/ccp.75.13
Keywords: building codes, Tbeams, effective flange width, finite element analysis, regression analysis.
Summary
Most of the reinforced concrete systems are monolithic. During construction,
concrete from the bottom of the deepest beam to the top of slab is placed at once.
Therefore the slab serves as the top flange of the beams. Such a beam is referred to
as Tbeam. In a floor system made of Tbeams, the maximum axial compressive
stress occurs over the web, dropping between the webs. The distribution of
compressive stress on the flange depends on the relative dimensions of the cross
section, span length, support and loading conditions. For simplification the varying
distribution of compressive stress can be replaced by an equivalent uniform
distribution. This gives an effective flange width, which is smaller than the real
flange width (see, for example, [1]). In various codes there are recommendations for
effective flange width formulas. But these code recommendations may be
considered as approximate, since they are expressed only in terms of span length or
flange and web thickness and ignore the other important variables.
The aim of the present study is to investigate the effective flange width formulas for Tbeams. In this study, a threedimensional finite element analysis is carried out on continuous Tbeams. The beam spacing, span, overall depth, web and flange thickness are considered as independent variables in the analysis. The elastic stress distributions on 243 Tbeams are calculated under uniformly distributed load, concentrated load at midspan and concentrated loads at third points. The concrete slab and the beam are modelled by means of solid elements. The element chosen is an eightnode solid element [2]. By using the distribution of the extreme top fiber compressive stresses from the finite element analysis, effective flange widths are calculated for 81 combinations of the independent variables corresponding to each of the three loading conditions. Linear multiple regression analyses are carried out on this available data using the software SPSS [3]. Following multiple regression analysis, three empirical design formulas for effective flange width are derived. These proposed formulas incorporate the beam span, spacing, depth, and flange and web thickness as independent variables. Comparisons are made between the proposed formulas and the ACI Building Code [4], Eurocode [5] and TS500 Turkish Building Code [6] recommendations. The proposed formulas show the effects of loading conditions on effective flange width clearly. The comparison of the results also demonstrates that the building codes considered here give safer values for the effective flange width for the uniformly distributed load case. However, it is found that for the concentrated load cases, the code recommendations seem to be unsafe when the beam spacing is small. References
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