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RC COLUMN

The function of columns is to act as vertical load carrying members.Loads are primarily compressive although situations do arise wheremoments are also present.Columns are classified as:

SHORT

SLENDER

BRACED

UN-BRACED

Classification of column

The exact type depends upon a variety of factors relating to geometryand factors affecting end restraint.

The provisions for column design o EC! "ppl# o veric"llo"d-$e"ring mem$ers %hose gre"er cross-seciondimension does no e&ceed four imes is sm"ller dimension'Compression mem$ers %ih " l"rger "spec r"io "reconsidered o $e %"lls( "nd slighl# di)eren provisions "ppl#'Columns m"# $e s*u"re( rec"ngul"r( circul"r( ellipic"l(

cruciform or of oher sh"pes'+nii"l dimensions "re norm"ll# deermined $# ",ing ino"ccoun re*uiremens for dur"$ili# "nd re resis"nce. T"$le /'00 1( "nd i is no pr"cic"l o c"s veric"l columnssm"ller h"n !22 mm & !22 mm'

$

h

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PUSAT PENGAJIAN DIPLOMA,UTHM

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Types of column cross-sectionBraced or un-braced columns

Reinforced concree columns "re cl"ssi ed "s eiher $r"cedor un$r"ced' The di)erence rel"es o he m"nner in %hichhe srucure c"rries l"er"l lo"ds( "s sho%n $elo%'

Bracedif shear walls or other bracing used to cope with lateral loadsdue to wind for example.

Shear wall positions in a buildin

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Unbracedif lateral loads are carried by sway action of columns asshown in the !i" below

She"r 3"lls

Columns Un$r"ced in $oh direcions

Columns Br"ced in $oh direcions

Columns Br"ced in # direcion$u Un$r"ced in &

&

#

She"r 3"lls

#lan floor $iew of braced and unbraced column

Onl# $r"ced columns "re considered in his module'

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Short or Slender Columns

Modes of failure

Possible failure mechanisms:

1. Material failure with negligible lateral deflection which usuallyoccurs with short columns but can also occur when there arelarge end moments on a column with an intermediateslenderness ratio.

HJ ROSLAN BIN KOLOP

PUSAT PENGAJIAN DIPLOMA,UTHM

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Table %"&' ( )ffecti$e heiht factors for braced columnsl$% clear height x factor from this table

!iure %"&* ( )nd fi+ity conditions for braced columns

&or a rectangular section the radius of gyration is b,%"* so the limitcan be given as:

Limiting l0/b ratio = (2.0/3.46ABCn = 5.!"ABC /n

4or $r"ced columns conserv"ive v"lues of he p"r"meers"reA 9 2'=( B 9 0'0( C 9 0'=( %hich give