Abstract:
To accommodate over growing population, scarcity of land and amplified price of
property in Bangladesh, vertical extension of buildings has now become essential and
many high-rise buildings are now being constructed in major cities. In addition, the use
of high strength materials with innovative design approach with the help of design
software, it is now possible to design smaller cross section of structural members than
those designed in earlier time. This reduction incross-section is very important for
column design as slenderness might influence the adequacy of the column. The design
load of a slender column might approach buckling load and sway of the frame might be
large enough to increase the moments obtained from first order analysis. Consideration
of these effects is essential as column is the most important member in a structure. An
inadequately designed column without any attention to slenderness might result in
catastrophic failure of the whole structure ..
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,- To build awareness about slender column, this study has been carried ouLfor beamcolumn
and flat-plate concrete structures; where corner, edge and inner columns have
been considered, The methods described in ACI Code-318 (1999) for designing slender
column have been reviewed. Slender column design procedures of ETABS and
PCACOL software have been validated against manual calculation as per the -
provisions of ACI Code. A limited parametric study has also been performed to identify
the influencing factors of slenderness that should be considered before any design
process started.
The findings of the study are noticeable. Considering slenderness in column design is
extremely important. Designer should check the slenderness effect in column before
starting column design. The ACI Code limits for neglecting sway effect has been
checked and found acceptable. P-Delta analysis should be run for every high-rise
concrete structure to incorporated possible sway effect. Flat-plate frame structure has
more sway effect than beam-column frame structure. Corner and edge columns need
more attention due to susceptibility to slenderness. Column with height greater than 15'
is substantially vulnerable to sway effect. The steel ratio might increase abruptly when
slenderness exceeds a certain limit.
Hopefully this study will increase some awareness to structural designers regarding
slender column design. The designers should be able to decide when slenderness effect
need to be taken care of and he could properly take the advantage of automatic design
feature of software and the design will be more effective and correct.
