Mat Chapter 25

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Mat Chapter 25
  Fig. 1 : Typical cross - sections of fully and partially concrete encased columns c  y c  y  x yh     h   c b c bc  x c  x (a) b c b    h  =    h   c  x y ( c )(b)    h  =    h   c  xb = b c  y   Fig. 2 : Typical cross-sections of concrete filled tubular sections d  y xd  y xb   h y x STEEL-CONCRETE COMPOSITE COLUMN-I STEEL-CONCRETE COMPOSITE COLUMNS-I 1.0 INTRODUCTION A steel-concrete composite column is a compression member, comprising eiter aconcrete encase! ot-rolle! steel section or a concrete ille! tubular section o ot-rolle!steel an! is generall# use! as a loa!-bearing member in a composite rame! structure$T#pical cross-sections o composite columns %it ull# an! partiall# concrete encase!steel sections are illustrate! in &ig$ 1 $ &ig$ 2  so%s tree t#pical cross-sections o concrete ille! tubular sections$ Note tat tere is no re'uirement to pro(i!e a!!itional rein orcingsteel or composite concrete ille! tubular sections, e)cept or re'uirements o ireresistance %ere appropriate$* Cop#rigt reser(e! Version II25-1 25  STEEL-CONCRETE COMPOSITE COLUMN-I In a composite column bot te steel an! concrete %oul! resist te e)ternal loa!ing b#interacting togeter b# bon! an! riction$ Supplementar# rein orcement in te concreteencasement pre(ents e)cessi(e spalling o concrete bot un!er normal loa! an! irecon!itions$In composite construction, te bare steel sections support te initial construction loa!s,inclu!ing te %eigt o structure !uring construction$ Concrete is later cast aroun! testeel section, or ille! insi!e te tubular sections$ Te concrete an! steel are combine! insuc a asion tat te a!(antages o bot te materials are utilise! e ecti(el# incomposite column$ Te ligter %eigt an! iger strengt o steel permit te use o  smaller an! ligter oun!ations$ Te subse'uent concrete a!!ition enables te buil!ing rame to easil# limit te s%a# an! lateral !e lections$+it te use o composite columns along %it composite !ecing an! composite beamsit is possible to erect ig rise structures in an e)tremel# e icient manner$ Tere is 'uite a(ertical sprea! o construction acti(it# carrie! out simultaneousl# at an# one time, %itnumerous tra!es %oring simultaneousl#$ &or e)ample ã One group o %orers %ill be erecting te steel beams an! columns or one or t%ostore#s at te top o rame$ ã T%o or tree store#s belo%, anoter group o %orers %ill be i)ing te metal !ecing or te loors$ ã A e% store#s belo%, anoter group %ill be concreting te loors$ ã As %e go !o%n te buil!ing, anoter group %ill be t#ing te column rein orcing barsin cages$ ã et anoter group belo% tem %ill be i)ing te orm%or, placing te concrete intote column moul!s etc$Te advantages  o composite columns are. ã increase! strengt or a gi(en cross sectional !imension$ ã increase! sti ness, lea!ing to re!uce! slen!erness an! increase! bucling resistance$ ã goo! ire resistance in te case o concrete encase! columns$ ã corrosion protection in encase! columns$ Version II25-2  STEEL-CONCRETE COMPOSITE COLUMN-I ã signi icant economic a!(antages o(er eiter pure structural steel or rein orce!concrete alternati(es$ ã i!entical cross sections %it !i erent loa! an! moment resistances can be pro!uce! b# (ar#ing steel ticness, te concrete strengt an! rein orcement$ Tis allo%s teouter !imensions o a column to be el! constant o(er a number o loors in a buil!ing, tus simpli #ing te construction an! arcitectural !etailing$ ã erection o ig rise buil!ing in an e)tremel# e icient manner$ ã orm%or is not re'uire! or concrete ille! tubular sections$ 2.0 MATERIALS2.1 Strutur! Stee All structural steels use! sall, be ore abrication con orm to  IS: 1977-1975, IS: 2062-1992 , an!  IS: 8500-1977   as appropriate$ Some o te structural steel gra!e commonl#use! in construction as per  IS: 961-1975  an!  IS: 1977-1975  are gi(en in Table 1 $ Table1(a) : Yield strength f   y of steel sections  Nominal steel gra!eNominal ticness/!iameter 0 mm 1iel! stress  , f   y  0  MPa 1&e 234-5T t < 67246 ≤  t    ≤ 8972489 <   t ≤  :27:4&e 2:4+-5T t < 67246 ≤   t ≤ ;6724;6 <   t ≤ 787:4&e :;4-O0not sub<ecte! to !#namic loa!ing oter tan %in!1  t < 68246 ≤   t ≤ 8482484 <   t ≤ :48:4  Table1(b) : Yield strength f   y of steel sections as per I 2! 2#1$$2  Nominal steel Nominal ticness/!iameter 0 mm 1iel! stress  , f   y  0  MPa 1&e :;4+ A= 8482484 - :48:4> :4874&e :;4+ ?= 84824 Version II25-#  STEEL-CONCRETE COMPOSITE COLUMN-I 84 - :48:4> :4874&e :;4+ C= 8482484 - :48:4> :4874 2.2Conrete Concrete strengts are speci ie! in terms o te caracteristic cube strengts, 0  f  ck   ) cu  , measure! at 28  !a#s$ Table 2  gi(es te properties o !i erent gra!es o concreteaccor!ing to  IS: 456-2000 an! te correspon!ing  !4  (alues$ Table 2# %roperties of concrete @ra!e esignation  M  82  M  74  M  72  M  :4 f  ck   ) cu #$mm 2  ) 827472:4 f  ck   ) cy #$mm 2  ) 84828978  f  ctm #$mm 2  ) 8$88$68$97$7    cm =5700 √  fck) cu #$mm 2  ) 892447;8847738476424%ere, f  ck   ) cu  caracteristic compressi(e 0cube1 strengt o concrete f  ck   ) cy caracteristic compressi(e 0c#lin!er1 strengt o concrete, gi(en b# 4$9 times 89 !a#s cube strengt o concrete accor!ing to EC:  f  ctm mean tensile strengt o concrete&or ligt%eigt concrete, te    cm  (alues are obtaine! b# multipl#ing te (alues romTable 2  b#  ρ    / 2400 ,%ere  ρ   is te unit mass 0 k%$m &  ) 2.# Rein$orin% Stee Steel gra!es commonl# use! in construction are gi(en in Table &'  It soul! be note! tataltoug te !uctilit# o rein orcing bars as a signi icant e ect on te bea(iour o  continuous composite beams, tis propert# as little e ect on te !esign o compositecolumns$ Concrete ille! tubular sections ma# be use! %itout an# rein orcement e)cept or reasons o ire resistance, %ere appropriate$   Table &# 'haracteristic strengths of reinforcing steel  T#pe o steelIn!ian Stan!ar!Nominal siBe 0 mm 1iel! Stress  , f   (k  0  #$mm 2 1Mil! steel @ra!e I 0plain bars1  IS:4&2 Pat1)-1982d  ≤ 8482484 *d  ≤ 248:4Mil! steel @ra!e II 0plain bars1  IS:4&2 Pat1)-1982d  ≤ 8488284 *d  ≤ 248;2Me!ium tensile steel0plain bars1  IS:4&2 Pat1)-1982d  ≤ ;62:4;6 *d  ≤ 782:4 Version II25-&
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