Mat Chapter 26

of 38

Please download to get full document.

View again

All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
38 pages
0 downs
Mat Chapter 26
  STEEL-CONCRETE COMPOSITE COLUMNS-II   STEEL-CONCRETE COMPOSITE COLUMNS-II 1.0 INTRODUCTION In a previous chapter, the design of a stee-concrete co!posite cou!n under a iaoading #as discussed$ This chapter deas #ith the design of stee-concrete co!positecou!ns su%&ected to %oth a ia oad and %ending$ To   design a co!posite cou!n under co!%ined co!pression and %ending, it is first isoated fro! the fra!e#or', and the end!o!ents #hich resut fro! the ana(sis of the s(ste! as a #hoe are ta'en to act on thecou!n under consideration$ Interna !o!ents and forces #ithin the cou!n ength aredeter!ined fro! the structura consideration of end !o!ents, a ia and transverse oads$)or each a is of s(!!etr(, the %uc'ing resistance to co!pression is first chec'ed #iththe reevant non-di!ensiona senderness of the co!posite cou!n$ Thereafter the!o!ent resistance of the co!posite cross-section is chec'ed in the presence of appied!o!ent a%out each a is, e$g$  x-x  and  y-y  a is, #ith the reevant non-di!ensionasenderness vaues of the co!posite cou!n$ )or sender cou!ns, %oth the effects of ongter! oading and the second order effects are incuded$ 2.0COMBINED COMPRESSION AND UNI-AXIAL BENDING The design !ethod descri%ed here is an e tension of the si!pified design !ethoddiscussed in the previous chapter for the design of stee-concrete co!posite cou!nsunder a ia oad$ 2.1 Interaction Cr!e or Co#$re%%ion an& Uni-a'ia( Ben&in) The resistance of the co!posite cou!n to co!%ined co!pression and %ending isdeter!ined using an interaction curve$ )ig$ 1 represents the non-di!ensiona interactioncurve for co!pression and uni-a ia %ending for a co!posite cross-section$ In a t(pica interaction curve of a cou!n #ith stee section on(, it is o%served that the!o!ent of resistance undergoes a continuous reduction #ith an increase in the a ia oad$*o#ever, a short co!posite cou!n #i often e hi%it increases in the !o!ent resistance %e(ond pastic !o!ent under reative( o# vaues of a ia oad$ This is %ecause under so!e favoura%e conditions, the co!pressive a ia oad #oud prevent concrete crac'ingand !a'e the co!posite cross-section of a short cou!n !ore effective in resisting!o!ents$ The interaction curve for a short co!posite cou!n can %e o%tained %(considering severa positions of the neutra a is of the cross-section, h n , and deter!iningthe interna forces and !o!ents fro! the resuting stress %oc's$+ Cop(right reserved *er%ion II2+-1 2+  STEEL-CONCRETE COMPOSITE COLUMNS-II   It shoud %e noted %( #a( of contrast that  IS: 456-1978  for reinforced concrete cou!nsspecifies a 2 cm  eccentricit( irrespective of cou!n geo!etr($ The !ethod suggestedhere, using EC, ao#s for an eccentricit( of oad appication %( the ter! α    andtherefore no further provision is necessar( for stee cou!ns$ .nother note#orth( featureis the prescription of strain i!itation in  IS: 456-1978 , #hereas EC does not i!pose sucha i!itation$ The reevant provision in the Indian Code i!its the concrete strain to 0.0035 !inus 0.75  ti!es the strain at the east co!pressed e tre!e fi%re/)ig$ 2  sho#s an interaction curve dra#n using si!pified design !ethod suggested in the UK   Nationa .ppication 0ocu!ent for EC   (NAD).  This negects the increase in!o!ent capacit( %e(ond  M   P    discussed a%ove, under reative( o# a ia co!pressiveoads/$ *er%ion II2+-2 Fig. 1 Interaction curve for compression and uni-axial bending   M  P  1 = λ   PP   p  MM   ! 01.01.0   # A D Fig. 2 Interaction curve for compression and uni-axial bending using the simplified method  M   !  P  c  A #   P  M 0 P   ! 0  STEEL-CONCRETE COMPOSITE COLUMNS-II   )ig$ 3 sho#s the stress distri%utions in the cross-section of a concrete fied rectanguar tu%uar section at each point,  A$ # and    of the interaction curve given in )ig$ 2.  It isi!portant to note that2 ã Point  A  !ar's the pastic resistance of the cross-section to co!pression at this pointthe %ending !o!ent is 3ero/$  P   A % P   !   4  A & .'   y  5 γ    a  6 α  c $  A  c.  ('  c   ) cy 5 γ   c  6  A    .'      5 γ    s  7/  M   A  % 0  8/ ã Point  # corresponds to the pastic !o!ent resistance of the cross-section the a iaco!pression is 3ero/$  P   # %0  9/  M   #  % M   !  % !  y  (*   !& -*   !&n  )+    !    (*   ! -*   !n  )+    ! c  (*   !c -*   !cn  )  / #here   *   !  $ *   !& , and  *   !c  are pastic section !odui of the reinforce!ent, stee section, andconcrete a%out their o#n centroids respective($   *   !n  $ *   !&n   and  *   !cn  are pastic section !odui of the reinforce!ent, stee section, andconcrete a%out neutra a is respective($   ã .t point   , the co!pressive and the !o!ent resistances of the cou!n are given asfoo#s:  P     % P  c %    A c  ! c.   ;/  M     % M   !   </ ã The e pressions !a( %e o%tained %( co!%ining the stress distri%utions of the cross-section at points  #  and   : the co!pression area of the concrete at point  #  is e=ua tothe tension area of the concrete at point .  The !o!ent resistance at point    is e=uato that at point  # , since the stress resutants fro! the additiona( co!pressed partsnuif( each other in the centra region of the cross-section$ *o#ever, theseadditiona( co!pressed regions create an interna a ia force, #hich is e=ua to the pastic resistance to co!pression of the concrete  $ P  c   aone$ *er%ion II2+-,  STEEL-CONCRETE COMPOSITE COLUMNS-II   It isi!portant to note that the positions of the neutra a is for points  #  and   , h n , can %edeter!ined fro! the difference in stresses at points  #  and   $ The resuting a ia forces,#hich are dependent on the position of the neutra a is of the cross-section, h n , can easi( %e deter!ined as sho#n in )ig$ 4 $ The su! of these forces is e=ua to  P  c $ This cacuationena%es the e=uation defining h n to %e deter!ined, #hich is different for various t(pes of sections$ (1)  or concrete enca%e& %tee( %ection%*er%ion II2+-/  ! c  2 !  y  P  c 2h n   Fig. 4(a) Variation in the neutral axis positions  y x Fig.  !tress distributions for the points of the interaction curve for concrete filled rectangular tubular sections  y P,n A ! c   !  y  !     P   !  N, m,m/n  x ! c   !  y   !     P,n # M   # %M   !  */, &x& ',c/h n  y x P,n      ! c   !  y  !    2h n    M  %M   !  P     %P  c
Related Search
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks