“Investigation of Effective Length Method For Slender Reinforced Concrete Column Having Linearly Varying Cross-Section”
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Date
2013-09
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Addis Ababa University
Abstract
Effective length is the length of the equivalent pin ended column, which has the same
elastic buckling load as the actual column. The effective length method has been used for
many decades as the basis for the design of columns made of reinforced concrete, structural
steel or steel-concrete components. The underlying assumption with this method is the
sweeping generalization that; because the actual column and the equivalent column have the
same elastic buckling load, they also posses the same design resistances in the ultimate limit
state. This assumption has been the subject of many investigations and it was found out that,
although the method gives reliable results that lie on the safe side in many cases, it could
sometimes lie on the unsafe side. The present investigation deals with slender reinforced
concrete columns with linearly varying cross-sections. The effective length method for such
columns poses an additional complication. That is; unlike prismatic columns, the choice of
cross-section for the equivalent column is not straight forward since the cross-section of
actual column is not constant. The results of the present investigation which is limited to pin
ended columns with equal and opposite end moments, have shown that the effective length
method gives reliable results if the cross-section of the equivalent column is chosen as per
certain rules and computations indicated in this document. Extensive tables are compiled for
the determination of equivalent section and effective length for any pin-ended tapered column
which has the same and opposite end moments. Computer programs, which are done using
FORTRAN (FTN95) programming language and MICROSOFT EXCEL spread sheets are
used as a supporting tools for analysis processes committed in this investigation. The result of
this research can be taken as an approach, which replaces the cumbersome and lengthy way of
traditional iterative analysis for tapered columns.
KEY PHRASES AND WORDS:
Effective length, Elastic buckling load, Equivalent section, Failure node, Moment-curvature,
second order analysis, Slender columns, Stabilized length, Tapered column.
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Keywords
Effective length; Elastic buckling load; Equivalent section; Failure node; Moment-curvature; second order analysis; Slender columns; Stabilized length;Tapered colu