Linear and Geometric Nonlinear Effect of Axial Load on Flexural Deformation of Reinforced Concrete Members
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Date
2018-04
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Addis Ababa University
Abstract
The problem of a concrete cross section under flexural and axial loading is indeterminate
due to the existence of more unknowns than equations. Therefore proper analysis of
reinforced concrete member is important for understanding the actual behavior and
economical use of sections. The main objective of this Thesis is to investigate geometric
nonlinear effect of axial load on flexural deformation of reinforced concrete members.
Flexural members, which are subjected to gravity central point load, external
compressive axial load and combination of those load with different support conditions,
cross section and span length are analysed using linear and geometric nonlinear method
of analysis to investigate the effect of axial load on flexural deformation of flexural
members. The percentage variation of flexural deformation under linear and geometric
nonlinear analysis for various conditions of members is calculated to achieve the
objective. Finally four story reinforced concrete residential building frame is analysed
using linear and geometric nonlinear analysis. Both linear and geometric nonlinear
analysis is done by using STAAD Pro and linear analysis using FEM based code using
Scilab and ETABS. After the analysis of flexural members it is found that: The
percentage variation of linear and geometrical nonlinear deflection is very high for beam
with lesser depth. It was found that the support conditions also affect variation of
deflection for the linear and nonlinear cases. The variation between linear and
geometrical nonlinear deflection of beam is negligible when the ends are fixed. But for
the same beam with simply supported end conditions the defections were found having
variation up to 17.571 percentages. Geometrical nonlinearity is more when the load is
very high and lesser depth. At the initial stages of loading behavior of beam is linear only
and it behaves nonlinear when we go for higher loads. As the deforming of middle plane
(Neutral axis) starts, the stiffness of structure increases (axial stiffness is added with
bending stiffness).Thus the beam becomes stiffer progressively. It is a positive aspect of
geometric nonlinearity.
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Keywords
Nonlinear Analysis, Finite Element Method, Flexural Deformation, Reinforced Concrete Beam, STAAD.Pro, Scilab.code