ANALYTICAL INVESTIGATION OF ENCASED COMPOSITE BEAMS UNDER FLEXURE AND TORSION

Abstract

Research on composite members is popular as they have major role in high rise buildings and bridges with
aesthetically pleasing complex designs. In this study, steel encased composite beams are considered in which structural
steel I section is embedded within the reinforced concrete. A non linear structural analysis of encased composite beams
incorporating the material non linearity and geometric non linearity is conducted to evaluate the flexural behavior and
torsional behavior of composite beams. The primary goal of the research is to conduct an analytical investigation on
fully encased composite beams with various I section of similar cross section area under flexure and torsion. Unlike
other steel encased composite beams, in this study, the longitudinal reinforcement bars are completely excluded.
Therefore, behavior and failure mode of beams are greatly affected by the steel beam core. ie. even in the absence of
longitudinal bars, the steel section can provide the flexural strength for the beam. This research is focused on the
comparison of flexural–torsional behavior of steel-encased composite members with conventional reinforced beams
using five set of I section namely ISHB 150, ISMB 225, ISWB 200, ISLB 250 and ISHB 200. The load-deflection behavior
is plotted. From the above studies, ISHB 200 has shown a better performance under flexure. Moreover, the depth of
section is reduced compared to conventional reinforced beams. In this way the dead load of the structure is been
reduced. But the reduction of depth is limited by incorporating the flexural rigidity of the section. The torsional actions
on beams are studied with ISHB 200 using lateral stirrups of various spacing. Maximum shear strength is attained with
lower spacing of lateral stirrups. Application of frictional surface on the top and bottom flanges of I sections to avoid the
slippage of concrete from steel suface showed a positive effects on the structure.