Slender structures are elegant aesthetically. The insufficiency
in knowledge of the real resistance to buckling of very slender
reinforced concrete columns leads to an exaggeration of the sizes of the
columns.
_The
examples of concrete compression members cited and constructed
in Industry on a global basis suggest that very slender columns have
inherent safety both from the point of view of the ultimate strength
and stability. The strengths of columns given. by the British codes
would seem to be exceeded by many of the long slender reinforced
concrete columns and struts which have been used Internationally.
Both the theoretical and the experimental short term investigations
have been carried out to establish the behaviour of hinged, very slender
reinforced concrete columns at various stages'of axial loading. Forty
three very slender reinforced concrete columns of two different square
cross sections with two sizes of longitudinal reinforcements with lateral
ties were cast. Slenderness rates,
L A, were varied from 30 to 79.
Special factors were obtained to relate the actual modulus of
elasticity of concrete in columns at buckling failure to a knowledge
of the initial modulus of elasticity of concrete in control cylinder
specimens. Both theoretical and experimental graphs of load against moment, made dimensionless for critical sections of columns have been obtained. Dimensionless load-moment interaction diagrams using material failure as the criterion have been superimposed on these graphs to show
considerable inherent material strength of the tested columns near
buckling collapse failures.
A theory using the fundamental approach has, been developed to predict the deflected shape and moments along the, heights of the columns at various stages of loading. The proposed theory predicts with good
correlations the experimental deflections and moments of any loading
stages of the columns. The theory has been used to obtain the required
variables, to arrive at the initial predicted design loads of the
investigated columns. Good correlations of the moments derived from
observed strains have also been obtained.
The developed theory predicts satisfactorily the buckling collapse
loads of the columns. Although the theory has been derived for axially I loaded very slender reinforced concrete-columns, it seems to accept
satisfactorily eccentricities of up to about 10 mm. This was confirmed
after extensive comparisons of the theoretical buckling collapse loads
with the applicable tests of other authors.
Creep In the columns investigated was discovered to be one of the
major factors for serious consideration. This was conclusively revealed
from the observations on the last two very long term creep tests on
columns. The actual safe sustained loads for these very slender columns
of slenderness ratios,
L/H, between 40 and 79 seem to be between 33% and 19% of the short term buckling collapse loads. The reduced modulus
approach to predict the safe long term sustained loads seems to give
reasonable values for L/H
ratios of 40 and 50.
The recommendations given for the proposed design of very slender
reinforced concrete columns seem to be adequate and simple to use in
practice. They are further simplified by the derivation of two equations
for the reduction factors, R, for the slenderness ratios between 36 and
40 and between 40 and 79 respectively.
The investigation has proved that very slender reinforced concrete
columns are very dangerous structural members, as they tend to have violent
buckling failures. Nevertheless, It must be prudent not to design against
disaster at any cost. This Investigation seemed to have enhanced considerably
knowledge of the design of very slender reinforced concrete columns. / Scientific Research Council
| Identifer | oai:union.ndltd.org:BRADFORD/oai:bradscholars.brad.ac.uk:10454/3871 |
| Date | January 1977 |
| Creators | Pancholi, Vijayshanker Ravishanker |
| Contributors | Wilby, C.B. |
| Publisher | University of Bradford, Postgraduate School of Studies in Civil and Structural Engineering |
| Source Sets | Bradford Scholars |
| Language | English |
| Detected Language | English |
| Type | Thesis, doctoral, PhD |
| Rights | <a rel="license" href="http://creativecommons.org/licenses/by-nc-nd/3.0/"><img alt="Creative Commons License" style="border-width:0" src="http://i.creativecommons.org/l/by-nc-nd/3.0/88x31.png" /></a><br />The University of Bradford theses are licenced under a <a rel="license" href="http://creativecommons.org/licenses/by-nc-nd/3.0/">Creative Commons Licence</a>. |
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