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Week  4  


Key  Terms   Joist   –   a   length   of   timber,   steel   or   concrete   that   supports   the   structure   of   the  building   Steel   Decking   –   A   metal   sheet   used   to   construct   the   membrane   of   the   roofing   system.   Span   –   The  distance  measured  between   two  structural  supports.   Girder   –   They  are  the  main  beams  of  the   floor  system   Concrete   Plank   –   A   flat   beam   used   for   roofing  and  flooring.   Spacing   –   The   repeating   distance   between   a   series   of   like   or   similar   elements.   Span  and  Spacing   Span-­�   the   distance   measured   between   two   structural   supports.   It   can   be   measured   between   vertical   supports   (for   a   horizontal   member)   or   between   horizontal   supports   (for   vertical   member).   This   is   necessarily   not   the   same  as  the  length  of  a  member.    

Spacing   –   The   repeating   distance   between   a   series   of   like   or   similar   elements.   This   is   associated   with   supporting   elements   (such   as   beams,   columns   etc.)   and   can   be   measured   horizontally   or   vertically.   Spacing   is   measured  centre-­�line  to  centre-­�line.  

Slabs   of   various   types   are   used   to   span   between   structural   supports.   These   can   be   one-­â€?way   or   two-­â€?way   spans   slab   thicker  estimated  to  be  around  the  span   of  the  slab  divided  by  thirty.     đ?‘†đ?‘?đ?‘Žđ?‘›  đ?‘œđ?‘“  đ?‘†đ?‘™đ?‘Žđ?‘? = đ?‘†đ?‘™đ?‘Žđ?‘?  đ?‘‡â„Žđ?‘–đ?‘?đ?‘˜đ?‘›đ?‘’đ?‘ đ?‘    30   To   decide   on   what   span   to   use   (one-­â€?way   or   two-­â€?way)   depends   on   the   cost   efficiency,   workload   and   also   the   function   of   the   building   such   as   the   columns  placements.     Steel  Systems  

Floor  Systems   Floor   systems   consist   of   concrete,   timber  and  steel.  Timber  is  span  joist  to   joist.   Timber   floorboards   need   to   be   thicker.   Open   web   trusses   are   lighter   weight  joist  are  slowly  space.   Concrete  Systems  

Steel   framing   systems   take   various   forms,   with   some   utilizing   heavy   gauge  


structural   steel   members   others   uses   light   gauge   steel   framing.   Many   combinations   of   member   types   (heavy   and   lights)   are   used   depending   on   the   structural  function.     The   open   web   joist   is   a   quite   efficient   used   of   steel   since   it   is   an   expensive   material.   Also   the   services   such   as   water   pipes  can  be  carry  by  the  joist.   Sometimes   steel   framing   systems   combine   with   concrete   slab   systems   to   where   the   particular   benefits   of   steel   framing   and   shallow   depth   floor   slab   systems   and   desired.   The   spanning   capabilities   of   the   particular   materials   help   to   determine   the   spacing   requirements  of  the  supports.   Concrete  is  applied  on  the  steel  decking   to  support  the  tensile  strength.   The   description   of   steel   or   concrete   depends  on  the  factor  of  cost,  fire  rating   of   a   building   (larger   building   such   as   hospitals   tend   to   be   build   in   concrete   which   is   able   to   cope   with   fire   with   a  

longer  period  of  time  then  most  steel  or   timber).   Timber  System   This   is   the   most   common   system   in   Australia.   Traditionally   timber   floor   framing   systems   use   a   combination   of   bearers   (primary   beams)   and   joists   (secondary  beams).   The   span   of   the   bearers   determines   the   spacing   of   the   piers   or   stumps   and   the   spacing  of  the  bearers  equals  the  span  of   the   joist.   Joist   supports   floorboards,   decking   or   ply   panels.   The   joists   are   supported  by  bearers.   Typically  floorboards  span  450-­�600mm.   Bearers   would   be   added   to   reduce   the   span  by  approx.  50%.   Floors   normally   have   a   lot   of   joist.   To   keep  their  cross-­�sectional  area  small,  the   joist   is   tend   not   to   span   from   wall   to   wall,  bearers  are  used  in-­�between  to  cut   down  the  size  o  the  material.     Concrete     Concrete  is  artificial  stone.   Concrete  Components   When   cement   is   mixed   with   water   it   binds   the   sand   gravel   aggregates   together  to  make  the  hard,  solid  material   we  call  concrete.  

Common  concrete  mix  is     1: 2: 4: 0.4 − 0.5   đ??śđ?‘’đ?‘šđ?‘’đ?‘›đ?‘Ą: đ??šđ?‘–đ?‘›đ?‘’  đ??´đ?‘”đ?‘”đ?‘&#x;đ?‘’đ?‘”đ?‘Žđ?‘Ąđ?‘’: đ??śđ?‘œđ?‘Žđ?‘&#x;đ?‘ đ?‘’  đ??´đ?‘”đ?‘”đ?‘&#x;đ?‘’đ?‘Žđ?‘”đ?‘Žđ?‘Ąđ?‘’: đ?‘¤đ?‘Žđ?‘Ąđ?‘’đ?‘&#x;     Cement     Fine   Coarse   Aggregates   Aggregate   Portland   Sand   Crushed  rocks   Lime      

Provenance   When   the   cement   powder   and   water   are   mixed,   a   chemical   reaction   takes   place   and   heat   is   released.   This   process   is   called   hydration.   During   this   process   crystals   are   formed   that   interlock   and   bind   the   sand,   crusted   rock   and   cement/water  paste  together.   If   too   much   water   is   added   to   the   concrete   mix,   the   final   concrete   will   not   be  strong  enough  (weak).   If   too   little   water   is   added,   the   concrete   mixture   will   be   too   stiff   and   it   will   be   difficult  to  work  with  (unworkable).   Process   An   advantage   of   concrete   is   that   it   is   plastic   before   it   set.   One   of   the   great   advantages   of   concrete   is   that   it   is   fluid  


and   shapeless   before   it   hardens.   It   can   be  formed  in  to  any  shape  we  desire.   Formwork   is   the   term   used   for   the   temporary   support   or   moulds   used   to   hold   the   liquid   concrete   in   place   until   it   becomes   hard.   Formwork   can   be   built   at   the  building  site  (IN  SITU)  or  in  a  factory   (Pre   Cast)   out   of   a   range   of   different  

materials:  timber,  plastic,  formply  etc.         During   the   curing   process   the   framework   needs   to   be   supported,   as   the   weight   of   the   wet   concrete   is   very   heavy.  As  the  concrete  sets,  it  carries  its   own   weight   transferring   the   load   through  the  support,  which  could  be  the   floor,   column   or   walls.   This   is   achieved  

by   using   props   and   bracings   of   various   types.   Concrete   generally   reaches   75%   of   its   compressive   strength   in   approx..   7   days   with   testing   for   the   required   strength   occurring   at   28   days.   Once   the   concrete   is   hardened   and   strong   enough,   the   formwork   is   carefully   removed.   Formwork  is  often  removed,  stored  and   reused   or   it   may   stay   in   place   forever   (sacrificial  formwork).   Finishes   There   are   many   finishes   of   concrete   such  as:   • Sand  –blasted   • Exposed  aggregate   • Raked  finish   • Bush  hammered     • Board  –  marked   • Board  &  batten.   Reinforcement     Concrete   is   also   known   as   ‘artificial   stone’.  This  suggests  that  the  properties   of  concrete  and  stone  are  similar.   Concrete   is   very   strong   in   compression   but   is   weak   in   tension.   To   improve   its   structural   performance,   a   steel   (very   strong   in   tension)   reinforcement   in   the   form  of  mesh  or  bars  is  added.    

The   resulting   material   is   known   as   reinforced   concrete,   which   is   strong   in   both  compression  and  tension.   Reinforcement   is   often   used   to   form   a   fixed   or   rigid   joint   between   a   slab   or   wall.   Reinforcement   bars   extend   out   of   the  concrete  so  another  concrete  can  be   placed   onto   it.   The   amount   of   reinforcement   is   adjusted   by   different   level  of  loading.   Properties   The  properties  in  the  ‘fresh  wet;  -­‐  plastic   state  and  hardened  state  depend  on  the   physical   characteristics,   chemical   composition   and   the   proportions   of   the   components.   The   list   below   addresses   the  hardened  state.   Hardness  –  High.  Can  be  scratches  with   a  metallic  object   Fragility  –  low.  Can  be  chipped  with  a   hammer     Ductility  –  very  low  ductility   Flexibility/  Plasticity    -­‐  low  flexibility   and  plasticity   Porosity/  Permeability  –  medium-­‐low.   Depending  on  proportions  and   components     Density  –  Medium-­‐high.  Approx.  2.5x   dense  than  water.  


Conductivity  –  poor  conductor  of  heat   and  electricity   Durability/Life  Span  –  typically  very   durable   Reusability/Recyclability  –  medium-­‐ low.  Can  be  partially  re-­‐used  when   crushed  to  be  used  as  aggregate  for  new   concrete  elements.   Sustainability  and  Carbon  Footprint  –   High  embodied  energy.  Non  renewable,   long  lasting.   Cost  –  Generally  cost  effective.  Labour   dependent  for  formwork  and  pouring.   Considerations   Concrete  is  permeable  (not  completely   waterproof).  This  is  one  of  the  main   sources  of  problems  in  concrete.  If  the   steel  bars  are  too  close  to  the  surface   they  will  not  be  protected  from  moisture   and  oxidation.  This  will  cause  both   aesthetic  and  structural  degradation  of   the  concrete.   Another  common  cause  of  problems  is   poor  vibration  of  the  concrete  during   the  pouring  process.  Concrete  is   vibrated  to  get  rid  of  the  air  bubbles  that   get  caught  during  the  pouring  process.   These  bubbles  can  lead  to  the  element   failing.  

In  situ  Concrete   In   situ   concrete   are   added   on   the   construction   site.   Trucks   deliver   this   liquid  to  the  site.   This   is   any   concrete   element   that   has   been   poured   into   formwork   and   cured   on   the   building   site.   This   process   includes  the  fabrication  and  assembly  of   the   formwork,   placing   any   required   reinforcement,   the   pouring,   vibration   and  the  curing  of  the  concrete.   Once   the   concrete   has   been   poured,   there   is   a   limited   time   before   the   concrete   starts   to   harden   and   become   unworkable   to   ensure   that   the   concrete   is   placed   in   the   proper   position,   the   air   bubbles   removed   (vibrated)   and   the   desired  finish  applied.   This   is   labour   intensive   process,   resulting   in   congestion   of   the   construction   site.   Uses   floats   to   make   a   flat   finish.   This   is   done   by   hand.   Note   that  it  is  difficult  to  control  strength  and   quality  of  the  In  Situ  concrete.     Uses    When  to  use  In  Situ?  In  Situ  concrete  in   a   great   many   applications.   It   is   generally   used  for  structural  purposes  (either  self   supporting  or  as  primary  structure)  

Widely   used   in   footings,   retaining   walls   and   all   bespoke   (non   standard)   structural  elements.   Sometimes   concrete   is   sprayed   into   place   using   a   pressure   hose   (shotcrete).   This   is   useful   for   landscapes,   swimming   pools,   and   basements   walls   between   piers  or  overhead  surfaces.   Joints   There   are   wo   types   of   joints   in   In   Situ   concrete:   construction   and   control   joints.   1. Construction   joints   –   used   to   divide   the   construction   into   smaller   and   more   manageable   sections  of  work.  We  can’t  lay  all   the  concrete  on  the  site  at  once.   2. Control   Joints   –   Required   to   absorb   the   expansions   and   contractions   that   thermal   variations   cause   and   the   long   term   tendency   variations   cause   and   the   long   term   tendency   of   concrete  to  shrink  over  time.  The   elongation/shrinkage   is   proportional   to   the   temperature   differential,   the   material   coefficient  and  the  dimensions  of   the  piece.  


Both   construction   and   control   joints   are   potential   weak   points   and   must   ensure   that   be   detailed   appropriately,   especially   in   terms   of   water  and  moisture  control.   Pre-­‐cast  Concrete   Pre-­‐cast   concrete   is   any   concrete   element   that   has   been   fabricated   in   a   controlled   environment   and   then   transported  to  site  for  installation.   This   process   ensures   a   much   more   standardized  outcome  that  avoids  many   of   the   quality   control   issues   associated   with   In   Situ   concrete.   Pre-­‐cast   concrete   elements   also   allow   work   on   site   to   progress  at  a  much  faster  rate.  

Uses  

Pre-­‐cast  concrete  is  widely  used  in  many   different   applications.   It   is   often   associated   with   the   structure   of   a   building,   bridge   or   civil   works,   forming   part   of   the   primary   structure   or   self-­‐ support  panel  type  elements.   Although   rarely   used   in   footings,   it   is   common   in   retaining   walls,   walls   and   columns.   Joints   There   are   two   joints:   construction   and   structural  joints.   1. Construction   joints   –   the   panel/elemental   nature   of   pre-­‐ cast   concrete   mean   that   joints   natural   occur   when   one   precast   element  meets  another.   2. Structural   Joints   –   the   type   and   performance   of   the   structural   connections   joining   the   precast   elements   to   each   other   and   to   other   parts   of   the   structure   are   critical   for   the   overall   performance  of  the  building.   Construction   and   structural   joints   will   greatly   depend   on   the   desired   aesthetic   outcome.   If   joints   are   visible,   it   needs   to   be   looked   after   carefully.  

Finishes   They   need   to   be   taken   care   of   when   transferring  it  to  the  site.   Considerations   Pre-­‐cast   concrete   elements   can   be   limited  in  size  due  to  the  transport  in  the   city.     On   site   changed   are   very   difficult   to   incorporate.   Also   the   cost   benefits   in   repetition   where   it   can   be   re-­‐used   with   multiple  panels.   Beams  and  Cantilevers   Beams   A  beam  is  a  (mostly)  horizontal  element.     The   function   of   the   beam   is   to   carry   loads   along   the   length   of   the   beam   and   transfer   these   loads   to   the   vertical   supports.   • A  beam  can  be  supported  at  both   ends  of  the  beams   • Supported   at   numerous   points   along  the  length  of  beam   • Supported   at   points   away   from   the   ends   of   the   beam   (creating   overhangs/cantilevers   beyond   the  supports)  


on of a BEAM is to carry loads along the length of the beam and transfer these loads to the vertical supports. A BEAM can be: CANTILEVER OF -  supported at both ends of the beam PORTION THE COLUMN! -  supported at numerous points along the FLOOR! length of beam -  supported at points away from the ends of the beam COLUMN!

A CANTILEVER is created when a structural element is supported at only one end (or the overhanging portions of a member are significant). The function of a CANTILEVER is to carry loads along the length of the member and transfer these loads to the support.

(creating overhangs / cantilevers beyond the supports)

Supported  at  only  one  end  of  the   -  •supported at only one end of the beam (these beams are called cantilevers) beam   (these   beams   are   called   FLOOR! cantilevers)  

BEAM!

A CANTILEVER can be: - horizontal -  vertical -  angled

FLOOR LOAD! CANTILEVER!

CANTILEVER!

LOAD!

CANTILEVER! FLOOR!

SUPPORT!

ionblog/wp-content/uploads/2011/06/ -stair-front-view-detail.jpg

BEAM!

BEAM!

SUPPORT!

SUPPORT!

Illustration from CHING ‘ Building Construction Illustrated”, 4.02 (2008) Illustration from CHING ‘ Building Construction Illustrated”, 5.36 (2008)

  Cantilevers   A   cantilever   is   created   when   a   structural   element  is  supported  at  only  one  end  (or   the   overhanging   portions   of   a   member   are  significant).   The   function   of   a   cantilever   is   to   carry   loads   along   the   length   of   the   member   and  transfer  these  loads  to  the  support.   A  cantilever  can  be:   • Horizontal   • Vertical     • Angled          

SUPPORT! Illustration from CHING ‘ Building Construction Illustrated”, 4.11 (2008)

FIXED SUPPORT!

http://studio-tm.com/constructionblog/wp-content/uploads/2011/06/ exterior-concrete-cantilevered-stair-front-view-detail.jpg


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Week 4 compressed