MODIFIED WEB SLENDERNESS CLASSIFICATION FOR COMPOSITE GIRDERS IN CODE PROVISIONS

Abstract

Composite girder is one of the main structural systems used in bridges and buildings. The same
slenderness limits requirements for steel sections are used also for the composite sections in most specifications
without considering the effect of concrete slabs. In fact, for composite sections under positive moments, the
compression concrete slab restrains the buckling of the top flange and the compressed part of the web, in
addition the steel plates behave plastically up to failure. By accounting concrete slabs attached to the steel
compression elements, the section may be placed in more favorable class. The main objective of this study is
to verify a reasonable relaxed slenderness limits for steel compact composite sections compared to compact
steel section only and investigate the influences of the span length of girder and the concrete strength of slab,
on the slenderness limits. An extensive parametric study using ANSYS, a commercial finite element (FE)
software, was held using different web slenderness, various concrete strengths and girder lengths. The section
classifications were evaluated, and the results were compared to the Egyptian code, Eurocode and AASHTO.
A new relaxed equation and new classification limits have been developed considering the effect of the concrete
slab strength.