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Academic year: 2022



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Independent  Advice  to    

NSW  Minister  for  Planning  and  Housing    

19  February  2019



Executive  Summary  ...  1  

TOR  1  –  Causes  of  damage  ...  1  

TOR  2  –  Making  the  Opal  Tower  safe  for  occupancy  ...  1  

TOR  3  –  How  to  avoid  this  type  of  incident  in  the  future  ...  2  

Introduction  ...  3  

Terms  of  Reference  ...  3  

Building  Structure  ...  4  

Investigation  Activities  ...  4  

Observed  Damage  ...  5  

Consequences  of  Damage  ...  6  

Cause(s)  of  Damage  ...  7  

Environment  ...  7  

Materials  ...  7  

Foundations  ...  7  

Construction  ...  8  

Structural  design  ...  9  

Damage  at  Level  4  –  Grid  Line  A  ...  9  

Damage  at  Level  10  –  Grid  Line  C  ...  11  

Investigations  by  Others  ...  12  

Proposed  Rectification  ...  12  

The  Future  ...  13  

Conclusions  ...  16  



Executive  Summary  

At   the   request   of   the   Hon.   Anthony   Roberts,   Minister   for   Planning   and   Housing,   an   investigation  was  carried  out  into  the  cause  or  causes  of  structural  damage  to  the  Opal   Tower   at   Sydney   Olympic   Park,   which   was   first   observed   at   Christmas   2018.     In   addition,  the  investigation  reviewed  possible  remedial  action  to  repair  the  damage  to   the   building.     The   terms   of   reference   also   included   a   request   to   consider   any   recommendations   for   the   future,   with   the   intended   purpose   of   assisting   in   avoiding   problems  with  high-­‐rise  construction  such  as  those  addressed  in  this  report.  

Based   on   all   available   information,   the   following   opinions,   recommendations   and   findings  of  the  investigation  are  presented.    These  are  listed  below  under  each  term  of   reference  (TOR)  provided  by  the  Secretary  of  the  NSW  Department  of  Planning.  

TOR  1  –  Causes  of  damage  

1. The  as-­‐constructed  hob  beam  /  panel  assembly  was  under-­‐designed,  according   to   the   National   Construction   Code   (NCC)   and   the   Australian   Standard   for   Concrete   Structures   (AS36001),   at   a   number   of   locations   in   the   building.     This   left  the  hob  beams  susceptible  to  failure  by  shear  compression  and  bursting.  

2. The   decision,   taken   after   the   initial   design2,   to   grout   only   partially   the   joints   between  the  hob  beams  and  panels,  significantly  raised  the  levels  of  stress  in  the   hob  beams  on  levels  4,  10,  16  and  26.  

3. Construction   and   material   deficiencies   likely   precipitated   the   observed   major   damage  to  hob  beams  on  Level  10-­‐C  (electrical  conduit  and  reinforcing  steel  in   the   cover   region,   and   a   panel   repair)   and   Level   4-­‐A   (lower   strength   concrete   than  used  in  hobs  elsewhere  and  partial  grout  coverage).  

4. The  observed  damage  in  the  concrete  panel  at  Level  10  and  in  the  Level  10  floor   slab   was   likely   a   consequence   of   the   adjacent   hob   beam   failures   and   not   the   original  cause  of  the  damage  observed  at  Level  10.  

TOR  2  –  Making  the  Opal  Tower  safe  for  occupancy  

5. Appropriate   rectification   works   can   address   deficiencies   in   the   original,   as-­‐

constructed,   structural   design  and   ensure   the   building   is   compliant   with   the   NCC.  

6. Significant  rectification  works  are  necessary  to  ensure  that  the  building  and  all   its  structural  components  satisfy  the  NCC  and  specifically  the  current  AS3600-­‐


7. The   damaged   hob   beams   should   be   rectified   to   provide   the   required   load   carrying  capacity.  


1  AS3600  refers  to  the  the  2009  version  of  the  standard  which  was  current  at  time  of  construction,  unless   stated  otherwise  

2  ‘Design’  refers  to  structural  design  in  this  report,  unless  stated  otherwise.  


8. Other   hob   beam   /   panel   elements   of   similar   as-­‐constructed,   structural   design   may   not   comply   with   the   NCC   and   AS3600-­‐2009   and,   if   so,   will   require   rectification   works.   We   also   recommend   checking   of   the   forces   in   other   structural  elements  adjacent  to  the  hob  beams,  such  as  the  columns.  

9. We  agree  in  principle  with  the  rectification  works  planned  to  date,  noting  that   these   have   advanced   considerably   since   our   interim   report   was   released   but   have  yet  to  be  agreed  by  all  parties  and  independently  certified.  

10. We   recommended   that   a   detailed   analysis   be   undertaken   of   the   potential   redistribution  of  loads  from  the  damaged  elements  to  ensure  that  other  newly   loaded   building   elements,   before   and   after   rectification   works,   have   suitable   capacity  and  to  avoid  future  damage.    A  preliminary  analysis  has  been  carried   out  and  indicated  structural  loads  satisfied  the  NCC  in  the  non-­‐damaged  parts  of   the   building   structure.     Nevertheless,   this   finding   should   be   robustly   and   independently  verified.    

11. We   recommend   that   all   designs   and   construction   associated   with   the   rectification   works   be   checked   and   certified   as   safe   for   building   occupancy   by   qualified  independent  structural  engineers.    

12. The  viability  of  residents  re-­‐entering  the  building  extends  beyond  the  structural   issues   considered   here   and   hence   beyond   the   scope   of   this   investigation.    

Nevertheless,  we  would  recommend  that  items  9-­‐11  listed  above  be  completed   prior  to  re-­‐occupation.  

TOR  3  –  How  to  avoid  this  type  of  incident  in  the  future   We  recommend  the  following  should  be  implemented:  

13. The   creation   of   a   government   Registered   Engineers   database   developed   in   partnership  with  an  appropriate  professional  body.  

14. Independent   third   party   checking   and   certification   of   engineering   designs   and   subsequent  changes  to  the  design  of  critical  elements  by  a  Registered  Engineer,   including   confirmation   of   what   are   the   critical   elements   for   all   major   construction  projects.  

15. Critical   stage,   on-­‐site   checking   and   certification   by   a   Registered   Engineer   that   construction  is  as  per  the  design  for  all  major  construction  projects.    All  changes   to   identified   critical   structural   elements   that   are   proposed   and   made   during   construction  should  also  be  certified  by  an  independent  Registered  Engineer.  

16. An   online   database   be   created,   where   all   certifications   may   be   viewed   by   a   broad  range  of  stakeholders  including  owners  and  prospective  owners;  before,   during   and   after   construction.     The   aim   is   to   increase   transparency   of   the   approval  and  certification  process.  

17. A  Building  Structure  Review  Board  be  formed,  with  the  major  purpose  being  to   establish  and  publish  the  facts  relating  to  structural  damage  of  buildings  arising   from   design   and   construction,   investigate   their   causes   and   to   recommend   changes  to  Codes  and  Regulations  where  appropriate.  



The   Opal   Tower   is   a   high-­‐rise   residential   building   located   in   Sydney   Olympic   Park,   NSW.     It   consists   of   36   storeys   above   ground   and   3   basement   levels   below   ground.    

Construction   of   the   building   was   completed   in   2018   and   occupation   of   the   392   residential  apartments  commenced  in  the  second  half  of  2018.  

A  photograph  of  the  Opal  Tower  is  shown  in  Figure  1.    The  building  is  characterised  by   its   overall   triangular   prismatic   shape,   with   a   number   of   insets   in   the   three   external   faces  of  the  building  (see  Figures  1  and  2).    These  architectural  features  are  referred  to   as  “slots”  on  some  design  drawings.  

On  Christmas  Eve  2018,  residents  of  the  Opal  Tower  reported  loud  noises,  including  a   loud   “bang”,   reportedly   of   internal   origin,   and   presumably   associated   with   the   structure   of   the   building.     Early   investigations   of   the   source   of   these   loud   noises   identified  cracks  in  a  load-­‐bearing  panel  on  Level  10  of  the  building,  forming  one  of  the   exterior  walls  at  the  base  of  one  of  the  inset  slots.    Later  investigations  revealed  further   cracking   of   the   hob   beam   supporting   the   cracked   load-­‐bearing   panel.     Subsequent   investigations  also  identified  other  cracked  concrete  structural  members  at  Level  4  of   the  building,  again  at  the  base  of  an  inset  slot  feature.  

Because  of  safety  concerns,  residents  of  the  building  were  evacuated,  first  on  Christmas   Eve  2018.    They  were  subsequently  allowed  to  re-­‐enter  and  then  asked  again  to  depart   the   building   on   27   December   2018,   following   more   detailed   checking   of   structural   elements  and  specifically  the  identification  of  the  additional  structural  damage  on  Level   4  of  the  building.  

On   27   December   2018,   the   NSW   Department   of   Planning   and   Environment   (DPE)   engaged  Professors  John  Carter  and  Mark  Hoffman  to  investigate  a  number  of  matters   related  to  the  cracking  of  the  concrete  structural  members  in  the  building,  including  the   likely   causes   of   the   observed   cracking.     Following   initial   investigations,   Professor   Stephen   Foster   was   also   engaged   to   assist   in   the   investigations,   on   the   recommendation  of  Professors  Carter  and  Hoffman.  

This   report   contains   a   description   of   the   investigations   carried   out   and   presents   the   findings,  recommendations  and  opinions  of  the  investigators.  

Terms  of  Reference  

The  terms  of  reference  of  the  investigation  were  provided  by  the  Secretary  of  the  NSW   Department  of  Planning  as  follows:  

1.  “Determine  the  basis  of  the  failure,  what  happened  and  how?  

2. The  immediate  steps  that  need  to  occur  to  ensure  the  safety  of  the  building  for  its   occupants.  

3. Any  other  recommendations  on  what  needs  to  happen  to  avoid  incidents  like  this   in  the  future.”  

This  final  report  provides  findings  for  all  three  terms  of  reference.    An  earlier,  interim   report,  dated  14  January  2019,  provided  preliminary  findings,  based  upon  information   available  at  that  time,  with  respect  to  the  first  two  terms  of  reference.  


Building  Structure  

The   Opal   Tower   is   a   reinforced   concrete   building   with   post-­‐tensioned   concrete   floor   slabs.    It  has  a  reinforced  concrete  central  core  structure,  which  houses  the  lifts  and  fire   stairs.     The   floors   of   the   building   are   supported   by   the   core   walls   and   reinforced   concrete  columns  and  precast  concrete  elements.    A  particular  feature  of  the  building  is   the  inset  slots  located  on  each  external  face  of  the  building  (see  Figures  1  and  2).    The   walls   of   these   inset   slot   sections   are   constructed   largely   from   precast   reinforced   concrete  panels  (with  some  cast  in  situ  panels).    The  walls  composed  of  these  panels   have  been  designed  to  carry  gravity  loading,  effectively  acting  as  columns,  transmitting   vertical  loads  (from  floors  above  the  inset  slots  and  from  floors  intersecting  them)  to   the  individual  supporting  columns  below  each  inset  slot  feature.    The  columns  of  the   building  are  founded  on  individual  pad  footings  and  the  central  core  is  supported  on   shallow  spread  footings.    All  footings  are  founded  on  shale  bedrock.  

The  major  structural  design  of  the  building  was  carried  out  by  WSP,  an  international   engineering  services  company.    The  design  of  the  post-­‐tensioned  concrete  floors  was   carried  out  by  Australasian  Prestressing  Services  (APS).    The  precast  wall  panels  were   fabricated  by  Evolution  Precast  Systems  (Evolution).    The  building  was  constructed  by   Icon  Co,  an  Australian  building  contractor  and  part  of  the  Kajima  Corporation  of  Japan   (Icon).  

Investigation  Activities  

Our  investigations  included  the  following  activities:  

1. Multiple  visits  to  the  Opal  Tower  site  and  inspection  of  the  damaged  structural   members  in  the  building,  and  members  in  similar  locations;  

2. Review   of   the   design   of   relevant   sections   of   the   building   and   related   documentation;  

3. Review  of  construction  records  and  quality  control  records;  

4. Review  of  defect  notice  No.  84;  

5. Viewing  of  a  security  camera  recording  of  the  garden  area  in  the  slot  on  Level  10   where  damage  to  the  panel  was  first  observed;  

6. Inspection   and   review   of   elements   of   the   structure   repaired   during   initial   construction  (Columns  C1  on  Level  6,  C38  on  Level  7,  and  C21  on  Level  8  as  well   as  the  Level  13  floor  slab);  

7. Discussions   with   representatives   of   the   building’s   structural   designer   (WSP),   floor  slab  designer  (APS)  and  builder  (Icon);  

8. Discussions   with   the   engineering   representative   of   the   Opal   Tower   Strata   Committee  (Cardno);  

9. Discussions  with  the  Executive  of  the  Opal  Tower  Strata  Committee;  

10. Discussions  with  senior  figures  associated  with  the  building  industry  nationally   and  in  NSW;  and  

11. Consideration   of   unsolicited   advice   and   information   provided   by   members   of   the  engineering  profession  and  the  public.  

Activities  1  to  6  listed  above  were  focused  on  various  structural  elements  in  sections  of   the  building  located  on  Levels  3,  4,  6,  7,  8,  9,  10,  13,  16  and  26,  as  well  as  the  basement   level  B3.    All  areas  of  known  structural  damage,  both  major  and  minor,  were  inspected.    


structural  panel  walls  and  their  supporting  hob  beams,  and  the  floor  plates  adjacent  to   damaged  hob  beams.  

The   discussions   listed   as   activities   7   to   10   above   aided   our   understanding   of   the   technical  design  and  construction  issues  relating  to  the  Opal  Tower  as  well  as  providing   useful  background  information  pertaining  to  the  building  industry  and  current  building   practices.  

Activity   11   listed   above   was   necessary   to   provide   due   consideration   to   the   concerns   expressed  by  individuals  and  to  reflect  on  the  unsolicited  information  provided.    It  was   not  possible  to  individually  acknowledge  these  contributions  to  our  investigation,  but   we  take  the  opportunity  to  do  so  collectively  now.  

We   were   also   assisted   in   these   various   tasks   by   staff   of   the   NSW   Department   of   Planning  and  Environment.    We  wish  to  thank  the  Department  for  this  assistance.    

We  note  that  the  opinions  and  findings  expressed  here  are  our  own  and  not  necessarily   those  of  any  other  party,  including  the  Department.  

We  wish  to  thank  all  parties  who  provided  information  and  advice  to  this  investigation.    

Their  cooperation  and  assistance  were  invaluable.  

Observed  Damage  

During   the   numerous   visits   to   the   site   of   the   Opal   Tower,   we   inspected   and   re-­‐

inspected  a  number  of  locations  where  significant  damage  had  occurred  to  load  bearing   concrete  members.  

The  areas  of  significant  structural  damage  are  located  on  Levels  4  and  10  of  the  Opal   Tower.    The  approximate  locations  of  these  damaged  regions  are  shown  in  Figures  3   and  4.  

Photographs   of   some   of   the   damaged   concrete   structural   members   are   shown   in   Figures  5  to  12.    Specifically:  

On  Level  10:  

1. A  hob  beam  spanning  between  columns  C21  and  C38  (along  grid  line  C  shown  in   Figure  4)  and  the  Panel  A  resting  on  it  –  see  Figures  5  to  8.    Cracking  was  also   observed  in  the  floor  plate  adjacent  to  column  C21  –  see  Figure  9.    This  was  the   damage  observed  on  Christmas  Eve  and  is  considered  to  be  major  damage.  

On  Level  4:  

2. A  hob  beam  spanning  between  columns  C16  and  C34  (along  grid  line  A  shown  in   Figure  3)  –  see  Figure  10.    This  also  appears  to  be  major  damage.  

3. A  hob  beam  spanning  between  columns  C2  and  C22  (along  grid  line  B  show  in   Figure  3).    These  cracks  could  be  considered  minor  at  this  stage  –  see  Figure  11.  

4. Cracking   was   also   observed   in   the   floor   plate   between   Levels   3   and   4   –   see   Figure  12.    This  was  considered  to  be  major  damage.  

It  is  noted  that  the  vertical  load  lines  along  which  the  observed  major  damage  occurred   are  different  and  hence  these  areas  of  damage  are  likely  to  be  unrelated  to  each  other.  

From  the  security  camera  footage  referred  to  previously,  we  observed  cracking  in  the   bottom   corners   of   the   bottom   panel   (Panel   A)   on   Level   10.     The   time   stamp   on   this  


video  recording  indicated  that  the  cracking  of  the  panel  commenced  at  approximately   2.16  pm  on  Monday  24  December  2018  and  continued  for  approximately  8  seconds.  

Consequences  of  Damage  

As   indicated   already,   all   residents   were   evacuated   from   the   building   by   about   27   December   2018   to   ensure   their   safety   and   to   allow   an   assessment   to   be   made   of   the   extent  and  severity  of  the  damage  to  the  building’s  structure.  

Furthermore,  soon  after  the  structural  damage  to  the  building  was  observed,  WSP  and   Icon   instigated   a   program   of   installing   props   under   the   damaged   areas,   as   a   precautionary  measure,  to  ensure  the  safety  of  these  areas  of  the  building.  

The   greater   proportion   of   the   loading   carried   by   a   reinforced   concrete   building’s   structure  arises  due  to  gravity  and  the  self-­‐weight  of  the  structure  itself  (usually  called   the  “dead  loading”).    

When  structural  damage  occurs  to  an  individual  element(s)  in  a  building,  as  eventuated   in   the   Opal   Tower,   it   is   often   associated   with   overloading   of   one   or   more   of   the   structural   elements   of   the   building   in   combination   with   other   factors.     The   damaged   elements  then  no  longer  have  the  capacity  to  carry  the  loads  that  are  imposed  on  them   in  the  same  manner,  and  at  least  some  of  that  load  will  be  redistributed  to  be  carried  by   other  sections  of  the  structure.  

Given  the  inevitable  redistribution  of  the  loading  as  a  consequence  of  the  damage  to  the   hob   beams   and   neighbouring   elements,   checks   should   be   carried   out   to   assess   the   consequences  of  load  redistribution  and  an  assessment  made  of  the  capacity  of  other   elements   of   the   structure   to   withstand   the   extra   loading   imposed   on   them   as   a   consequence  of  that  redistribution.  

An   analysis   of   this   type   has   been   carried   out   indicating   an   increase   in   some   column   loads   above   the   original   design   load   but   to   levels   that   would   not   exceed   the   requirements  of  the  NCC.    We  advise  that  this  analysis  should  be  verified  by  a  qualified   independent  structural  engineer.  

A  feature  of  the  building’s  design  is  that  most,  if  not  all,  major  columns  in  the  building   had  been  designed  so  that  their  maximum  axial  load  carrying  capacity  far  exceeded  the   design  loading  imposed  on  them,  indicating  a  very  high  factor  of  safety  to  these  critical   elements.     However,   a   preliminary   analysis   of   the   splitting   forces   near   the   interface   with   the   two   hob   beams   reviewed   (Level   4   –   grid   line   A   and   Level   C   -­‐grid   line   C)   indicates  that  this  aspect  of  the  design  should  be  confirmed  by  a  qualified  engineer  for   all  such  features.      

We   have   found   no   evidence   contradicting   our   interim   assertion   that   the   building   is   overall  structurally  sound,  although  there  is  significant  damage  to  some  elements.    It   should   be   noted   that   extreme   environmental   events,   while   rare,   could   precipitate   further  damage  and  consequently  it  would  be  prudent  not  to  delay  rectification  works.  

In   addition,   our   inspection   of   the   columns   that   were   reported   to   us   as   having   been   repaired  during  construction  (Columns  C1  on  Level  6,  C38  on  Level  7,  and  C21  on  Level   8)   revealed   no   evidence   of   structural   distress.     Repairs   of   this   type   are   not   unusual   during  construction.    Details  of  the  repairs  to  these  particular  columns  were  provided   by  Icon.    


Cause(s)  of  Damage  

After  inspecting  the  damaged  areas  of  the  building,  we  initially  hypothesized  a  number   of   factors   that   may   have   been   a   contributing   cause   of   the   observed   cracking   of   the   concrete  hob  beams  on  Levels  4  and  10,  the  damaged  precast  panel  on  Level  10  and  the   damaged   floor   plate   between   Levels   9   and   10   and   Levels   3   and   4.     These   factors   are   categorized  as  follows:  

1. Environmental   factors   such   as   major   storms,   heavy   rainfall,   high   winds   and   extreme  changes  in  temperature  causing  unexpected  and  potentially  damaging   loading  of  the  building;  

2. Poor  quality  construction  materials;  

3. Issues  with  the  foundations,  namely  differential  settlement  of  the  pad  footings   supporting  the  building’s  columns;  

4. Poor  quality  workmanship  or  errors  during  construction;  and   5. Flaws  or  errors  in  the  design  of  the  structural  systems.  

We   considered   and   assessed   each   of   these   factors   in   some   detail   and   ultimately   concluded  that  not  all  of  the  factors  were  relevant  to  the  damage  observed  to  the  Opal   Tower.    Further  details  of  this  assessment  are  provided  as  follows.  


In  particular,  the  environmental  factors  were  considered  to  be  highly  unlikely  to  have   contributed   to   the   damage   because   the   meteorological   records   for   the   few   months   preceding   the   failure,   and   particularly   in   the   period   immediately   prior   to   and   on   24   December   2018,   show   no   extreme   or   adverse   conditions.     The   rainfall   records   show   some   significant   downpours   in   the   months   leading   up   to   Christmas,   but   they   were   considered  not  to  be  unusual.  


In  our  interim  report,  dated  14  January  2018,  we  indicated  that  there  was  no  evidence   in  the  documentation  we  had  reviewed  to  that  date  to  indicate  that  the  materials  used   in  construction  were  inferior  in  quality  or  did  not  meet  the  specifications  required.      

Further  test  records  of  materials  used  in  construction,  received  by  us  after  our  Interim   Report  was  issued,  revealed  at  least  one  case  where  concrete  used  in  a  hob  beam  may   not   have   reached   its   specified   28   day   strength.     This   instance   is   described   in   greater   detail   later   in   this   report,   when   the   possible   causes   of   damage   are   addressed   (see   discussion  under  the  heading  ‘Damage  at  Level  4  –  Grid  Line  A’).    The  reason  for  not   being   definitive   in   the   previous   statement,   is   that   there   was,   and   remains,   some   uncertainty  about  what  strength  concrete  was  actually  specified  for  the  hob  beams,  as   explained  in  more  detail  later.    


In  general,  differential  settlement  of  the  footings  of  a  building  can  occur  for  a  variety  of   reasons.    For  example,  neighbouring  columns  may  experience  large  differences  in  their   compressive  loading  or  the  ground  beneath  neighbouring  footings  may  vary  markedly   in   terms   of   stiffness   and   strength.     Differential   settlement   is   also   likely   if   the   ground   beneath  some  footings,  but  not  others,  softens  over  time,  perhaps  due  to  local  wetting   of  the  ground  beneath  the  footing  causing  softening  of  the  foundation  material.  


The  records  we  inspected  reveal  that  all  column  footings  for  the  Opal  Tower  structure   were   founded   on   shale   of   low   to   medium   strength,   with   the   majority   being   medium   strength.     The   records   we   reviewed   indicate   that   the   spread   footings   supporting   the   tower   core   and   all   but   two   of   the   40   individual   pad   footings   supporting   the   tower   columns  were  inspected  by  a  geotechnical  engineer  prior  to  the  pouring  of  concrete  to   form  the  footings.    All  inspected  footings  were  certified  by  the  geotechnical  engineer  as   suitable  to  carry  a  maximum  allowable  bearing  pressure  of  3.5  MPa.    We  could  not  find   inspection  records  for  columns  designated  as  C8  and  C40  (see  Structural  Drawing  4419   S02.051  A  for  column  designations  and  locations).  

However,  if  differential  footing  settlements  had  been  a  contributing  cause  of  damage  to   the  building,  and  specifically  the  damage  observed  on  Levels  4  and  10,  we  would  have   expected  to  observe  cracking  in  the  floor  slabs  and  at  floor-­‐column  connections  in  the   lower  levels  of  the  building.    Our  inspections  of  these  areas  of  the  building  indicated  no   such  damage.    So  on  the  basis  of  this  observation  and  the  documentary  evidence  of  the   condition  of  the  shale  foundation  at  the  time  the  footings  were  poured,  we  concluded   that  differential  settlement  of  the  column  footings  is  unlikely  to  be  a  contributing  factor   to  the  structural  damage  observed  on  Levels  4  and  10  of  the  Opal  Tower.  


There  are  a  number  of  points  noted  where  construction  differed  from  the  design  and  /   or  Standards:  

(a) Grouting:   design   drawings   indicate   that   full   grout   coverage   was   expected   between   the   panel   and   the   hob   beam.     However,   during   construction   only   the   inner  surfaces  of  approximately  50-­‐70%  of  the  joint  width  appear  to  have  been   grouted,   consistent   with   the   shop   drawings   which   show   the   grout   extending   over  only  the  inner  portion  of  the  hob  beam  to  panel  connection.    Furthermore,   coring   of   the   Level   4   hob   beam   revealed   incomplete   grout   coverage   in   some   places.    This  partial  grout  coverage  led  to  an  eccentric  bearing  load  and  elevated   bearing  and  bursting  stresses  on  the  hob  beams;  

(b) Inadequate  cover  concrete,  specifically  in  the  hob  beam  spanning  columns  C21   and  C38  on  Level  10,  the  location  of  some  reinforcing  steel  in  the  vicinity  of  the   hob   to   column   connection,   the   encroachment   of   discontinued   (anchored)   column   bars   into   the   cover   zone,   and   the   placement   of   an   electrical   conduit   within  the  cover  zone  in  this  area;  

(c) A  dowel  bar  between  the  hob  beam  and  the  panel  on  Level  10  was  observed  to   be  incomplete,  possibly  cut  during  construction;  

(d) The  original  design  drawings  of  the  building  indicate  precast  concrete  panels  of   a  thickness  corresponding  to  the  width  of  the  hob  beam  upon  which  they  rest.  

However,   the   panels   were   manufactured   to   be   20  mm   thicker   and   erected   so   that  they  overhang  the  inside  face  of  the  hob  beam.    For  example,  on  Level  10   the   panel   was   originally   designed   to   be   manufactured   180  mm   thick   to   correspond  to  the  hob  beam  width,  but  was  constructed  to  be  200  mm  thick  and   overhang  the  inner  face  of  the  hob  beam  by  approximately  20  mm;  

(e) Potentially  inadequate  tensile  capacity  in  the  horizontal  direction  in  the  bottom   region  of  Panel  A  on  that  rests  on  the  hob  beam  spanning  columns  C21  and  C38   on   Level   10.     There   is   compelling   evidence   indicating   that   the   wrong   size   reinforcing  bars  were  placed  in  this  area  during  manufacture  of  this  particular  


panel  –  20  mm  diameter  bars  were  used  instead  of  28  mm  diameter  bars  (see   Figure  8);  and  

(f) We  could  find  no  evidence,  during  our  site  inspections  and  in  the  construction   photos   and   photographs   of   damaged   hobs,   that   reinforcement   cross-­‐ties   were   incorporated  in  those  hobs  to  resist  bursting  forces.  

In   regard   to   the   timing   of   the   observation   of   damage,   it   is   likely   that   the   damage   occurred   after   progressive   build-­‐up   of   load   on   the   structure   as   apartments   became   occupied,   culminating   with   the   observed   damage   at   Level   10   on   24   December.     It   is   unclear  when  the  observed  damage  on  Level  4  occurred.  

The  architectural  design  where  the  major  damage  to  the  hob  beam  has  been  observed   on  Level  4  is  quite  different  to  that  of  the  damaged  hob  beam  on  Level  10.    The  cause  of   the   damage   observed   on   Level   4   and   Level   10   is   considered   in   greater   detail   in   following  sections  of  this  report.  

Structural  design  

Our  investigations  have  identified  at  least  two  areas  of  the  as-­‐built  structure,  which,  in   our  opinion,  do  not  meet  all  requirements  of  the  relevant  Australian  Standard,  AS3600   Concrete   Structures   and   therefore   do   not   meet   the   requirements   of   the   National   Construction  Code  Volume  1  (NCC).    The  specific  areas  of  the  building  coincide  with  the   locations  of  the  most  serious  damage  observed  to  the  concrete  structure.    Our  specific   findings  are:  

(a) At  Level  4  of  the  building  –  inadequate  bursting  (or  splitting)  resistance  of  the   hob  located  immediately  above  column  C34;  and  

(b) At  Level  10  of  the  building  -­‐  inadequate  bursting  (or  splitting)  and  /  or  bearing   resistance  of  the  hob  at  the  locations  of  its  connections  to  columns  C21  and  C38.  

These   findings   are   described   in   greater   detail   below,   together   with   the   reasons   that   support  our  opinions  expressed  here.  

Damage  at  Level  4  –  Grid  Line  A  

The  observed  damage  to  the  hob  beam  spanning  columns  C16  and  C34  at  Level  4  has   been  described  previously.    Our  detailed  investigations  of  this  damage  focussed  on  the   region   of   the   building   structure   in   the   vicinity   of   column   C34,   where   damage   was   observed,  and  included  the  hob  and  the  precast  panel  that  sits  upon  it,  as  well  as  the   connection  between  the  hob  and  the  panel.    These  investigations  included  both  hand   calculations   and   numerical   modelling   using   the   finite   element   method   which   specifically   incorporated   the   (possibly   non-­‐linear)   behaviour   of   reinforced   concrete   (RC)  structures.    The  hand   calculations   were  undertaken  to  assess  the  validity  of  the   finite  element  results  and  the  observed  failure  mechanism.  

The  finite  element  study  investigated  specifically  the  load-­‐deflection  behaviour  (up  to   failure)  of  column  C34  at  the  level  of  the  soffit  of  the  Level  4  floor  slab,  as  well  as  the   stresses  and  strains  induced  in  the  concrete  in  the  column,  floor  slab,  hob  and  precast   panel.    Typical  numerical  predictions  of  the  stresses  in  the  transverse  plane  are  shown   in  Figure  13  and  a  possible  strut-­‐and-­‐tie  model  to  describe  the  load  path  through  the   connection   is   shown   in   Figure   14.     Such   predictions   were   made   to   assess   the   performance   of   these   structural   elements   and   to   observe   the   predicted   mode   of  


deformation.    In  particular,  a  focus  of  these  studies  was  ascertaining  whether  bearing   and  /  or  bursting  of  the  hob  were  possible  causes  of  the  observed  damage.    

The   hand   calculations   considered   the   capability   of   the   hob   in   both   bearing   and   bursting.     The   axial   forces   passing   through   the   pre-­‐cast   wall   panel   to   the   hob   beam   connection,   and   then   into   the   columns,   were   addressed.     Some   of   these   calculations   adopted   the   ‘strut   and   tie   model’   describing   equilibrium   of   forces   in   the   hob   beam   (Figure  14).    This  hand  calculation  method  followed  the  approach  specified  in  AS3600.  

The   finite   element   analysis   (Figure   13),   albeit   preliminary,   indicated   significant   splitting   forces   in   the   column   adjacent   to   the   hob   beam.     It   would   be   prudent   to   undertake   a   more   detailed   analysis   of   this   feature   and   to   confirm   if   appropriate   bursting  reinforcement  is  in  place.    Rectification  works  may  be  necessary  pending  the   outcome  of  the  abovementioned  detailed  analysis.  

The  damage  observed  in  the  hob  beam  above  Column  C34  at  Level  4  is  shown  in  Figure   15.    This  image  indicates  bowing  of  the  reinforcement  steel  outwards  from  the  beam   and  opening  of  the  stirrup.    Also  noticeable  is  a  lack  of  cross-­‐tie  reinforcement  to  guard   against  splitting  failure..  

It  is  notable  that  the  observed  damage  was  constrained  to  the  inside  facing  of  the  hob   beam;   the   outside   of   the   hob   beam   at   the   critical   section   was   supported   by   a   lateral   garden   bed   wall   (Figure   16)   built   integrally   with   the   slab   and   against   the   hob   beam.    

This  wall  likely  provided  support  to  the  outer  side  of  the  hob  beam  forcing  the  damage   inward  where  such  support  was  lacking.    This  damage  remained  “hidden”  until  exposed   on  27  December  2018  after  removal  of  an  internal  wall  in  the  adjacent  apartment.    It  is   not  known  when  this  damage  occurred.  

The  site  observations  of  the  damaged  beam  are  consistent  with  a  bursting  failure.  

There  are  contradicting  views  and  documentation  as  to  the  design  strength  of  the  hob   beam  concrete  on  Level  4.    Notwithstanding,  65  MPa  concrete  was  understood  to  have   been   poured   during   construction   as   it   was   specified   for   the   puddle   pours   in   the   slab   around  the  columns  and  it  was  considered  expedient  to  use  the  same  batch  of  concrete   when  pouring  the  hob.  

During  our  investigations,  and  subsequent  to  the  issue  of  our  interim  report,  records  of   strength  for  the  concrete  used  to  construct  the  hob  beam  were  provided  to  us.    These   reveal  28  day  strengths  of  these  concrete  samples  as  50  MPa,  where  65  MPa  concrete   was  ordered  for  supply,  indicating  that  the  concrete  in  the  hob  may  also  have  been  of  a   lower   strength.   Our   independent   analysis   of   concrete   core   testing   samples,   extracted   and  tested  in  January  2019  by  Mahaffey  Associates,  did  not  contradict  this  observation.  

Clearly,   this   mis-­‐match   in   design   strengths   points   to   a   possible   and   unfortunate   ambiguity  in  the  interpretation  of  the  design  documentation.  

We   have   drawn   conclusions   from   our   numerical   analyses   of   the   as-­‐built   design,   combined  with  hand  calculations  and  field  observations  of  the  damaged  hob  beam  at   Level  4  –  Grid  Line  A.    In  our  opinion,  these  are  as  follows:  

1. With  the  design  loads  assumed,  the  strength  of  the  Level  4  hob  beam  spanning   columns  C16  and  C34  does  not  meet  the  requirements  of  AS3600–2009  (which   was  the  operative  version  of  the  code  at  the  time  the  structure  was  designed);  


2. The   observed   spalling   of   the   hob   beam   cover   concrete   above   and   adjacent   to   column  C34  implies  that  the  beam  is  in  a  state  of  high  stress;  

3. The  strength  of  the  concrete  in  the  “as  constructed”  hob  beam  was  lower  than   that  assumed  in  the  design;  

4. Splitting   forces   are   significant   and   the   tie-­‐reinforcement   provided   was   inadequate  to  resist  these  forces;  and  

5. The  cause  of  the  damage  to  the  hob  was  by  bursting  (also  known  as  splitting)  of   the  concrete  in  the  hob  beam  section.  

Damage  at  Level  10  –  Grid  Line  C  

The  observed  damage  to  the  hob  beam  spanning  columns  C21  and  C38  at  Level  10  has   been   described   previously.     In   this   case,   our   detailed   investigations   of   the   Level   10   damage  focussed  on  the  region  of  the  building  structure  in  the  vicinity  of  columns  C21   C38,  and  as  for  Level  4  included  the  hob  and  the  precast  panel  that  sits  upon  it,  as  well   as  the  connection  between  the  hob  and  the  panel.  These  investigations  included  both   hand   calculations   and   numerical   modelling   using   the   finite   element   method.     The   numerical  modelling  included  consideration  of  the  conduit  located  in  the  cover  region   and  the  repaired  concrete  patch  in  the  panel.    The  hand  calculations  were  undertaken   to  assess  the  validity  of  the  finite  element  results  and  the  observed  failure  mechanism.      

The   damage   in   the   hob-­‐beam   above   Columns   C21   and   38   at   Level   10   is   shown   in   Figures  17  to  20.    For  the  hob-­‐beam  above  column  C38,  Figure  17  shows  splitting  along   the  lines  of  shear  compression,  indicating  high  levels  of  stress  on  each  of  the  in-­‐plane   and  out-­‐of-­‐plane  surfaces.    While  bursting  appears  to  be  the  dominant  mode  of  failure,   bearing  stresses  appear  to  have  also  been  influential  in  forming  the  failure  surfaces.  

Figure   18   shows   observations   presented   to   us   of   the   hob   beam   above   Column   C38   when  the  walling  was  opened.    These  images  reveal  evidence  of  splitting  along  the  hob   centreline.     A   crack,   running   the   length   of   the   hob   beam   between   the   supporting   columns,  was  also  observed  at  the  soffit  of  the  Level  10  floor  slab  (Figure  19).    Splitting   of  the  hob  and  wall  panel  is  also  evident  in  Figure  20.  

These  observations  are  consistent  with  our  calculations  that  indicate  a  lack  of  capacity   of  the  hob  against  bursting.    As  for  Level  4,  no  cross-­‐tie  reinforcement  is  evident  in  the   hob-­‐beam  at  either  location  where  spalling  or  crushing  occurred.  

We   have   drawn   conclusions   from   our   numerical   analyses   of   the   as-­‐built   design,   combined  with  hand  calculations  and  field  observations  of  the  damaged  hob  beam  at   Level  10  –  Grid  Line  C.    In  our  opinion,  these  are  as  follows:  

1. With   the   design   loads   provided   by   WSP   and   assumed   in   our   calculations,   the   strength  of  the  Level  10  hob  beam  spanning  columns  C21  and  C38  and  the  wall   panel  above  it  do  not  meet  the  requirements  of  AS3600–2009;    

2. The   observed   spalling   of   the   hob   beam   cover   concrete   above   and   adjacent   to   column  C38  implies  that  the  beam  is  in  a  state  of  high  stress;  

3. Splitting   of   the   wall   panel   and   hob   beam   are   evident   and   the   area   of   tie-­‐

reinforcement  provided  was  inadequate  to  control  these  forces;  

4. A   number   of   construction   issues   were   observed   that   may   have   added   to   the   adverse  stress  conditions.    These  include  an  electrical  conduit  passing  through  


the  cover  concrete  in  a  zone  of  high  stress  immediately  above  column  C38  and  a   patch  repair  of  the  wall  panel,  again  in  a  high  stress  region;  and  

5. Construction   issues   observed   in   the   Level   10   C   hob   beam   to   precast   panel   connection  that,  in  our  opinion,  were  not  influential  on  the  failure  include  a  cut   dowel   bar   and   inadequate   anchorage   of   hob   beam   shear   fitments   (90   degree   hooks   located   within   50   mm   of   the   concrete   surface   –   refer   AS3600–2009   Clause  

Investigations  by  Others  

During  the  course  of  our  investigation  other  parties  became  involved,  either  assisting   our  investigations  or  those  conducted  separately  by  Icon  and  WSP,  or  providing  advice   to  the  Owners  Corporation  of  the  Opal  Tower.    Much  of  this  additional  information  has   been  made  available  to  us  with  the  approval  and  cooperation  of  Icon,  WSP  and  others.  

The  additional  parties  include  the  following:  

1. Cardno,  an  engineering  services  company  with  structural  engineering  expertise,   engaged   by   the   Owners   Corporation   of   the   Opal   Tower.     We   understand   that   Cardno  has  been  involved  in  reviewing  the  proposed  rectification  measures  for   the  Opal  Tower;  

2. Rincovitch,  a  company  with  structural  engineering  expertise,  engaged  by  Icon  to   independently  review  the  design  of  the  building  and  the  proposed  rectification   works;  

3. Slab   Scan   Pty   Ltd,   a   company   that   specialises   in   structural   investigative   reporting   and   the   application   of   ground   penetrating   radar   to   locate   post-­‐

tensioning,  reinforcing,  and  electrical  and  other  services  in  concrete.    In  this  case   Slab  Scan  was  commissioned  to  carry  out  investigations  of  the  precast  concrete   panels   and   the   associated   supporting   hobs   throughout   the   Opal   Tower   and   specifically  those  on  Levels  3,  4,  9,  10,15,  16,  25  and  26.    The  objective  of  their   investigation  was  to  confirm  the  as-­‐built  reinforcement  details.    All  hob  beams   on  Levels  4,  10,  16  and  26  were  accessible  at  the  time  of  the  investigation  and   their  reinforcement  was  assessed;  and  

4. Mahaffey  Associates,  specialist  consultants  in  concrete  technology  and  structure   condition  assessment,  who  were  engaged  by  Icon  to  undertake  strength  testing   of  precast  wall  panels  and  hob  concrete  at  the  Opal  Tower.  

The   reported   findings   of   Slab   Scan   are   most   pertinent   and   provide   a   measure   of   confidence   that   the   investigated   structural   elements   were   generally   constructed   according   to   the   original   shop   drawings,   with   a   few   exceptions.     The   exceptions   generally  relate  to  the  hob  beams  and  were  described  as  “shear  tie  spacing  was  slightly   sporadic”.  

Proposed  Rectification  

As   previously   mentioned,   soon   after   the   structural   damage   to   the   building   was   observed,  WSP  instigated  a  program  of  installing  props  under  the  damaged  areas,  as  a   temporary  measure,  to  ensure  the  safety  of  these  areas  of  the  building.  


Icon   and   WSP   have   briefed   us   on   the   structural   principles   behind   their   proposal   for   permanent  repair  of  the  damage  observed  on  Levels  4  and  10  and  strengthening  of  the   associated  structural  members,  viz.,  the  hob  beam  and  lowest  panel  at  these  locations.    

We   also   understand   that,   as   advised   for   consideration   in   our   interim   report,   rectification  works  to  bolster  other  hob  beam  /  panel  elements  on  Levels  4,  10  and  16   are  being  undertaken,  and  considered  for  Level  26.    We  understand  that  this  bolstering   will  include  a  combination  of  grouting  of  the  hob  to  panel  joints,  the  provision  of  cast   in  situ  sandwich  panels  enclosing  the  hob  and  the  panel  that  sits  immediately  upon  it,   and   the   addition   of   exterior   columns   adjacent   to   some   pre-­‐cast   panel   walls.     We   understand   that   the   joint   between   all   hob   beam   /   panel   elements   has   now   been   retrospectively  fully  grouted  and  we  support  this  as  a  preliminary  measure.  

It  is  our  opinion  that  the  structural  principles  behind  the  proposal  for  rectification  are   sound,  as  stated  in  our  interim  report,  and  considerable  progress  has  been  made  in  this   regard.    

However,   we   have   not   received   complete   details   of   a   structural   analysis   of   the   proposed   rectifications.     We   recommend   that   detailed   plans   for   the   proposed   rectification   works   should   be   checked   by   an   independent   qualified   structural   engineering  organisation.  

As   mentioned   previously,   the   observed   damage   on   Levels   4   and   10   will   have   caused   load,  designed  to  be  taken  by  the  damaged  elements,  to  be  redistributed  to  other  parts   of  the  structure.    A  preliminary  analysis  has  been  carried  out  indicating  an  increase  in   some  column  loads  above  the  original  design  load  but  to  levels  that  would  not  exceed   the   requirements   of   the   NCC.     We   advise   that   this   analysis   should   be   verified   by   a   qualified  independent  structural  engineer.  

In  addition  to  restoration  works  for  the  hob  beam  and  wall  panels  on  Levels  4,  10,  16   and   possibly   26,   it   is   recommended   that   the   following   additional   structural   elements   should   be   checked   for   adequacy   with   respect   to   their   load   carrying   capacity   and   rectification  work  be  undertaken,  if  needed:  

1. All  hob  beams  and  connecting  wall  panels  in  the  building  of  similar  design;  

2. Other   components   that   may   be   subjected   to   splitting   forces,   such   as   columns   supporting  hob  beams;  and  

3. The   longitudinal   tension   force   that   may   derive   in   the   hob   beam   connecting   columns  C16  and  C34  at  Level  4  resulting  from  discontinuation  of  the  panels  at   the  expansion  joint.  

We   remain   available   to   provide   further   advice   to   government   once   the   full   details   of   the  proposed  rectification  scheme  have  been  determined.  

It  is  also  our  opinion  that  appropriate  rectification  works  can  address  any  deficiencies   in  the  original,  as-­‐constructed,  design  and  should  ensure  the  building  is  compliant  with   the  NCC.  

The  Future  

Our   third   term   of   reference   asked   us   to   make   any   other   recommendations   on   what   needs  to  happen  to  avoid  future  incidents  such  as  the  one  discussed  in  this  report.    Our   investigations  of  this  rare  but  concerning  case  of  structural  damage  in  a  relatively  new  


high-­‐rise   apartment   block,   have   provided   us   with   relevant,   important   and   unique   insights.  

Australia  enjoys  a  strong  regulatory  environment  in  construction,  especially  in  regards   to   building   structural   safety,   through   the   National   Construction   Code   and   associated   mechanisms,   including   in   New   South   Wales.     This   has   provided   Australia   with   an   excellent   record   in   terms   of   building   structural   safety   with   few   if   any   of   the   catastrophic   incidents   recorded   in   many   other   international   jurisdictions.     Standards   and   Codes   are   generally   built   into   our   regulatory   systems   to   specify   minimum   safety   criteria,  which  must  be  attained.  

Australia   is   also   home   to   some   of   the   world’s   best   architects,   design   engineers   and   construction   companies   who   enjoy   high   international   reputations   for   their   work   globally,   including   the   firms   associated   with   the   design   and   construction   of   the   Opal   Tower.  

However,   community   and   consumer   expectations   rise   far   higher   than   just   overall   building   structural   safety,   with   a   reasonable   belief   that   all   components   of   a   building   should  be  structurally  sound  and  stable.    In  the  case  of  the  Opal  Tower,  this  expectation   was  clearly  not  satisfied.  

Structural  design  and  construction  codes  in  Australia  are  based  upon  the  principle  of   performance   pathways,   which   focus   on   overall   building   performance   requirements   rather  than  specifying  how  it  is  to  be  constructed.    This  approach  enables  innovation   and   evolution   in   terms   of   architectural   appearance   and   construction   techniques,   and   has  become  a  celebrated  feature  of  the  Australian  built  environment.    This  includes  not   only   Performance   Solutions   under   the   NCC   but   also   performance-­‐based   design   and   construction  in  accordance  with  Australian  Standards.    Performance-­‐based  design  and   construction  enables  the  creation  of  attractive  novel  architectural  and  structural  design   solutions   with   increasing   efficiencies,   countering   the   architectural   ‘sameness’   and   higher   construction   costs   that   can   arise   from   highly   prescriptive   construction   procedures.  

While  it  was  not  within  the  scope  of  our  review  to  look  closely  at  the  certifications  that   took   place   on   the   Opal   Tower,   we   found   no   evidence   that   the   building   certifiers   had   been  deficient  in  regards  to  statutory  expectations.    Nevertheless,  there  was  a  range  of   construction  issues  that  occurred  which  were  not  compliant  with  Australian  standards,   and   aspects   of   the   design   which   led   to   structurally   inadequate   sections   of   the   Opal   Tower.    While  no  evidence  has  been  found  that  those  responsible  for  certifying  work   did   not   conform   with   requirements,   it   is   evident   that   a   number   of   checks   for   compliance  were  not  undertaken  or  undertaken  with  insufficient  rigour.  

Through  the  course  of  the  investigation  of  the  Opal  Tower,  it  has  become  evident  that   tensions   between   the   application   of   performance-­‐based   design   and   construction   and   the  regulatory  environment  and  processes  have  led  to  deficiencies  where  community   expectations   of   building   quality   have   not   been   met.     We   believe   that   these   can   be   resolved   with   improvements   to   the   regulatory   environment   without   altering   the   benefits   of   the   current   overarching   approaches   to   design   and   construction   in   New   South  Wales  and  Australia.  

From  the  outcomes  of  our  investigation  we  make  the  following  recommendations.    The   first   three   recommendations,   if   they   had   been   in   place,   would   have   significantly   reduced   the   likelihood   of,   or   avoided,   the   Opal   Tower   damage.     The   last   two   are   put  


forward   as   mechanisms   to   raise   the   overall   standards   of   building   design   and   construction  and  community  confidence.  

1. Creation  of  a  Registry  of  Engineers.    Registered  engineers  should  have  a  high   level   of   competency   including   recognised   qualifications   benchmarked   to   international  education  standards,  minimum  level  of  professional  practice  and   currency   of   continuing   technical   professional   development   (particularly   important   in   an   evolving   field   such   as   building   design   and   construction).     The   Registry  should  be  managed  by  government  in  partnership  with  an  appropriate   professional  body.  

Certifications   and   approvals   associated   with   the   design   and   construction   of   a   building   should   then   only   be   undertaken   by   Registered   Engineers   in   their   specialised  area  of  expertise.  

2. Independent   third   party   certification   of   engineering   designs.   All   engineering  designs  for  major  projects  should  require  checking  and  certification   by   a   Registered   Engineer.     For   identified   critical   elements   of   a   design,   certification  should  be  by  a  third  party  Registered  Engineer,  fully  independent   from  the  original  designer.  

This   requirement   should   also   extend   to   all   changes   to   critical   elements   that   occur   up   until   the   completion   of   construction,   and   essentially   to   any   alternations   that   may   subsequently   occur   during   the   operational   life   of   a   structure.  

Major  projects  are  those  that  are  clearly  significant;  a  detailed  definition  should   be  developed  with  all  stakeholders.  

3. Regime  of  critical  stage,  on-­‐site  inspections  by  an  independent  Registered   Engineer.    A   mandated   regime   for   inspections   on   major   projects   should   be   developed  for  critical  stages  of  construction  and  for  identified  critical  elements   to  ensure  that  construction  is  according  to  certified  designs.    Furthermore,  these   inspections  should  be  undertaken  by  an  engineer  who  is  registered  and  present   on-­‐site.     Recommendations   for   what   constitute   the   ‘critical   stages   of   construction’   should   be   made   by   the   structural   designer,   and   independently   verified  as  a  part  of  the  design  certification  process.  

It  would  also  be  preferable  to  have  a  Registered  Engineer  on  site  who  certifies   that  all  elements  of  a  building  are  as  per  the  approved  design.  

4. Raise   transparency   through   the   creation   of   an   open   repository   for   all   certifications.     This   repository   may   be   accessed   by   a   broad   range   of   stakeholders  including  owners  and  prospective  owners;  before,  during  and  after   construction.     This   is   intended   to   raise   the   accountability   of   certification   processes   and   simultaneously   provide   confidence   to   the   community   that   appropriate   certifications   are   being   undertaken,   confirming   the   integrity   of   all   aspects  of  design  and  construction.  

For   the   current   investigation,   we   have   been   provided   with   all   available   information   requested.     As   independent   expert   reviewers,   however,   we   have   noted   that   the   time   taken   to   obtain   documentation   and   its   curation   and   completeness  was  at  times  challenging.    We  do  not  believe  that  this  is  an  ideal   situation  and  that  the  community  would  benefit  from  increased  transparency.  


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