Various problems and deficiencies in the strength and load carrying capacity of the reinforced concrete (RC) walls and columns caused by concealing PVC drain pipes within them have been identified. Alternative methods of positioning the drain pipes outside the columns are proposed. An improved method of the present practice has also been suggested. Finally, the research methodology and investigation of this problem which is presently in progress in the Universiti Teknologi Malaysia, Skudai, has been outline

Bakhteri, Jahangir

Makhtar, Ahmad Mahir

Omar, Wahid

English

Universiti Teknologi Malaysia Institutional Repository

JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15  No. 2, 2002 0128-0147/98 ©Faculty of Civil Engineering,UTM.               A  CRITICAL  REVIEW  OF  THE REINFORCED CONCRETE  COLUMNS  AND  WALLS CONCEALING  RAIN  WATER  PIPE  IN  MULTISTOREY  BUILDINGS  JAHANGIR  BAKHTERI,   Ph.D WAHID  OMAR,   Ph.D AHMAD  MAHIR  MAKHTAR,   Ph.D Department  of  Structures  and  Materials Faculty  of  Civil  Engineering Universiti  Teknologi  Malaysia    ABSTRACT   Various  problems  and  deficiencies  in  the  strength  and  load  carrying  capacity  of  the  reinforced  concrete (RC) walls  and  columns  caused  by  concealing  PVC  drain  pipes  within  them  have  been  identified.  Alternative  methods  of  positioning  the  drain  pipes  outside  the  columns   are  proposed.   An  improved  method  of  the  present  practice  has  also  been  suggested.  Finally,  the  research  methodology  and investigation  of  this  problem  which  is  presently  in progress  in  the  Universiti Teknologi  Malaysia,  Skudai,  has  been  outlined.      INTRODUCTION    Tropical  countries  such  as  Malaysia  are  having  heavy  rainfall  throughout  the year,  which  requires  an  effective  and  proper  drainage  system  in  the  construction  of  any  new  building  project.    The  drainage of  rain  water  from  the  roof  top of  the  buildings  is  always  considered  and  properly  handled  in  the  Malaysian  buildings  construction.  In  many  occasions  rain  water  from  roofs  are  drained  through  PVC  pipes  concealed  in  the  RC  walls  and  columns  and  taken  out i.e. discharged  at the  ground  level.  However, considering the useful  life  of  the  structures,  this  method of  drainage  can  be  hazardous  to  the  safety of  the  buildings.  JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15 No. 2  2002  2   Through  the  intensive  experience  of  the  first  author  in  the  Malaysian  buildings  industry,  it  has  been  observed  sometimes  that  even  in  two  storey  bungalows  which  are  usually  supported  by  125x125mm  or  150x150mm  RC  columns,  the  drain  pipes  are  positioned  inside  the  columns.  Though  in  these  cases  the  loads  might  not  be  very  high,  but  considering  the  size  of  the  columns  it  might  cause  serious  danger  to  the  safety  of  the  structures  in  the  long-term.   PRESENT  PRACTICE  AND  ITS   SHORTCOMING    Concealing  the  PVC  drain  pipes  inside  the  columns  and  walls  in  building  structures  is  a  common  practice  in  Malaysian  buildings. This  condition  has  been  imposed  by  the architects  on  the  basis  that  projecting  them  outside  the  columns  and  walls  will  affect  the  appearance  of  the  buildings.    However,  concealing  the  drain  pipes  inside  the  columns  and  walls  in  buildings  not  only  reduces  the  load  carrying  capacity  of  the  columns  and  walls  but  could  be  very  dangerous  to  the  buildings  safety  as  well.  The  dangers  arising  from  the  concealment  of  the  rain  water  pipes  in  the  building’s  columns  and  walls  are  as  follows :  1.    Positioning  the  drain  pipe  in  the  corner  or  at  the  edge  of  the  column’s  section  will     virtually  reduce  the  effective  cross-sectional  area  of  the  column  as  indicated  in  Fig.1(a), (b), and (c).  The  pipe  may  not  be  held  at  central  position  in  the column/wall, because  during  casting  and  vibrating  of  the  concrete  there  are  chances  that  the  pipe may  get  an  inclined  position  as  shown in  Fig.1(d),  which  will  cause  further  decrease in  load  carrying  capacity  of  the  column / wall.   2.    There  are  chances  of  honeycomb  formation  around  the  drain  pipe  in  the column  as  shown  Fig. 2.  3.    The  pipes  may  have  leakage  at  their  lapping  parts  or  joints  as  indicated  in  Fig. 3, which  in  long-term  can  cause  rusting  of  reinforcement  in  the  structure  hence,  loss  of  bond  and  reduction  in  the  strength  of  the  structural  elements .    JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15 No. 2  2002  3 4.    Due  to  the  presence  of  drain  pipe  in  beam-column  joints,  the  beam’s  reinforcement has  to  be  bent  as  shown  in  Fig. 4,  which  causes irregularity  and  non-uniformity  in  the  beam’s  reinforcement  and  hence  a  reduction  in  strength  and  functioning  of  the beam.  The  problem  will  be  much  critical  in  beams  with  higher  percentage  of reinforcement.   5.    Elbow  part  of  the  pipe,  which  is  used  to  drain  the  rain  water  at  ground  level may  cause  a  huge  reduction  in  the  column’s  strength  at  base  level.  In  the  construction  of  building  projects,  occasionally  it  has  occurred  that  the  drain  pipe has  not  been  taken  out  at  ground  level  i.e. the  positioning  of  the elbow  part  of  the  pipe  has  been  forgotten.  To  rectify  this  mistake,  the  concrete  of  the  column’s section  at  ground  level  has  been  hacked  severely  and  then  the  elbow  part  of  the pipe  has  been  installed  followed  by  grouting  of  fresh  concrete  as  shown  in  Fig.5. However,  the  above  mentioned  method  of  rectification  is very  damaging  to  the robustness  and  safety  of  the  structure.  6.    In the case of  RC  walls, if the drain pipe is positioned  at  either end of the wall’s section as shown in Fig. 6,  it  will be dangerous to the safety of the structure. This is because, the RC walls are mostly  designed  to  resist  lateral  loads  and  are  key elements in the building structures. Therefore, any deficiency at the end of the wall section which is usually a highly stressed zone in the wall, may cause a partial or full collapse to the structure.      PROPOSED  SOLUTIONS      (a) Exterior  Columns:   In  the  case  of  exterior  columns  in  a  building,  the  drain  pipe  can  be  placed  outside  the  column’s  section  and  covered  either  in  a  concrete  box  section  attached  to  the  column  or  in  a  brickwork  box  section  with  concrete  stiffeners  as  shown  in  Fig. 7.  This  method  will  be  very  helpful  in  case  the  drain  pipe  needs  service at  later  stages.    (b) Interior  Columns:    In  the  case  of  interior  columns  in  a  building,  the  drain  pipes  can  be  placed  outside  the  column’s  section  passing  through  the  corner  of  JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15 No. 2  2002  4 the  floor  slab.  Again  they  can  be  covered  either  in  a  concrete  box  or  in  a  brickwork  box  section  as  shown  in  Fig. 8.    (c) Usage  of   steel  pipe   instead  of  PVC   as  an  improvement  of   the  present  practice:   The  usage  of  steel  pipes  instead  of  PVC  pipes is  another  alternative,  provided  that the  steel  pipes  must  have  a  proper  coating  in  order  to  avoid  rusting.  In  this  method the  steel  pipes  can  be  positioned  at  the  center of  the  columns’  section,  which  will act  not  only  as  drain  pipes  but  also  as  a  replacement  for   the  concrete  removed from   the  section.  (d)    In  concrete  walls,  the  pipe  can  be  placed  at  the  middle  third  of  the  wall section  preferably  at  the  centroid  of  the  section  as  shown  in  Fig. 9.  This  is because  of  the  fact  that  mostly  the  extreme  edges  of  the  wall  will have  higher  stresses  than  the  middle  part  of  its  section.   In  case  of  any   deficiency / failure  in  the  wall  around  the  drain  pipe,  the  wall  will  virtually be  converted  to  two  walls  with  smaller  sections  rather  than  partial  or  total collapse  of  the  wall.  However,  in  this  case  as  a  precautionary  measure  additional  reinforcement  around  the  pipe  should  be  provided.                         EXISTING  DESIGN  PRACTICE   The  columns  concealing  drain  pipes  are  usually  designed  by  the  Malaysian  practicing  engineers  on  the  basis  of  their  reduced  cross-sectional  areas  Ar  which  is  calculated  as  follows:       Ar = Ag - Ap      (1)  where,  Ar  is  reduced  area  of  the  section  of  the  column, Ag is gross  area  of  the  column’s  section,  and  Ap  is  cross-sectional  area  of  the  drain  pipe.    In  case  of  the  column  with  higher  flexural  stresses (i.e. moment),  the  assumption  made  in  the  effective  depths  of  the  column  which  contains  drain  pipe  is  usually   inappropriate.  This  is  because,  for  the  design  purposes,  the  practicing  engineers  assume  an  approximate  effective  depth  for  the  column’s  section  and  a  rational  formula  for  the  calculation  of  the  effective  depth  of  such  type  of  columns  is  lacking.    JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15 No. 2  2002  5    ASSESMENT OF LOAD CARRYING CAPACITY OF THE COLUMNS CONCEALING DRAIN PIPES  Assuming the column sections shown in Fig. 1 (a), (b) and (c) are having 350 x 350 mm, 400 x 400 mm and 450 x 600 mm cross-sections respectively and their respective drain pipes to be φ50, φ75 and φ100 (diameters in mm), if 6Y16 bars are used as vertical reinforcement in the column shown in Fig. 1(a), 4Y25 bars in column shown in Fig. 1(b) and 6Y25 bars in column shown in Fig. 1(c), then the probable effective cross-sectional areas of the columns will be:   (a) 350 x (350 – 35 – 25 – 50) =   84000 mm2 (b) 400 x 400 – (35 + 25 + 75)2  =  141775 mm2 (c) 450 x (600 – 35 – 25 – 100)  =  198000 mm2  Using equation (1) the effective areas for the above three columns used by practicing engineers in the industry are 120536 mm2, 155582 mm2 and 262146 mm2 respectively.  Assuming these columns as short braced columns with minimum moment, the maximum axial load capacity of each column can be calculated using equation 39 of the BS 8110: Part 1 (clause 3.8.4.4) reproduced below as equation (2).    N =  0.35fcuAc + 0.67Ascfy     (2)  Where, Ac is the net concrete area, Asc is steel area, fcu and fy are characteristic strengths of concrete and steel respectively.  In the present study the strengths are  assumed as fcu = 35 N/mm2 and fy = 460 N/mm2 and 25 mm nominal concrete cover to the links of all columns which are assumed to be 10mm bars.  The maximum load carrying capacity of the above mentioned columns considering the two different effective cross-sectional areas are calculated and presented in Table 1.  The values in the table are obtained by using Equation (2) and their differences in percentage have also been indicated.  Table 1 Maximum Axial Load Capacity of Columns Using Equation (2)  Column shown in Fig. Columns’s exterior dimension (mm) (A) Column’s axial load capacity on the basis of Industry’s effective area (kN) (B) Column’s axial load capacity using effective area by present study (kN) Differences in percentage between the two axial load capacities (A) & (B) JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15 No. 2  2002  6 1 (a) 350 x 350 1850 1441 28.38% 1 (b) 400 x 400 2514 2345 7.21 % 1 (c) 450 x 600 4124 3338 23.55 %  Table 1 indicates that the industry engineers assume the axial load capacity of columns as high as 28% in comparison to the present case which can be a threat to the safety of the structure.    RESEARCH  METHODOLOGY                  (a) Investigation  is  undertaken  to  estimate  the  reduction  in  load  carrying  capacity  of  column  containing  drain  pipe  including  elbow  part .   (b) Research  is  going  on  to  study  the  effects  of  drain  pipes  on  the  slenderness of  the  columns.  (c) The  investigation  will  also  determine  the  effects  of  drain  pipes  on  the  buckling  mode  of  columns.    (d) Methods  of  Research :  (i) Experimental  method :  Testing  of  various  scaled  models  with  different sizes  of  drain  pipes  including  elbow  part.  (ii)  Numerical  method :  Finite  Element  Modeling  and  Analysis  of  the  tested models  to  validate   the  experimental  results.   CONCLUDING  REMARKS  In  this  paper  a  critical  review  of  the  ongoing  practice  of  concealing  drain  pipes  inside  the  RC  column  and  wall  sections  in  the  Malaysian  buildings’  industry  has  been  provided.  Since  a  rational  and  reliable  design  formula  for  the  calculation of load  carrying  capacity  of  the  affected  columns  is  not  available, it  is  therefore  recommended  that  the  proposed  alternative  solutions  may  be  adopted.    The probable effective areas such as those shown in Fig. 1(a), (b) and (c) can also be adopted for design purposes as a second alternative tentatively.  This will reduce the threat to the safety of structure.  JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15 No. 2  2002  7 The  research  initiated  at  UTM  will  assess  the  actual  load  carrying  capacities  of  columns  concealing  drain  pipes including their elbow parts.  On  the  basis  of  outcome  of  this  research  it  will  be  possible  to  provide  an  approximate  but  realistic  formula  for  the  design   of  such  columns.    REFERENCES  BS  8110 : Structural use  of  concrete,  Part 1 :  Code  Of  Practice  For  Design  And  Construction, Part 2 :  Code Of Practice For Special  Circumstances, British  Standards  Institution, London, 1997.   Reynolds, C.E. and  Steedman,  J.C.  Reinforced  concrete designer’s  handbook, London,  E. & F.N.  SPON,  1988.                                   JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15 No. 2  2002  8           JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15 No. 2  2002  9                      Fig. 1 Inappropriate Positioning of Rain Water Pipe In Column’s Section JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15 No. 2  2002  10                                                 Fig. 2 Formation of Honeycombs Around The Drain Pipe JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15 No. 2  2002  11                                                 Fig. 3 Leakage In The Lapping parts of The PVC Drain Pipes JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15 No. 2  2002  12                                                 Fig. 4 Congestion and Nonuniformity In Beams Reinforcements At Column’s Section Caused By The Presence of Drain Pipe JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15 No. 2  2002  13                                                 Fig. 5 Elbow Part of The Drain Pipe At The Ground Level JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15 No. 2  2002  14                                                 Fig. 6 Drain Pipe Positioned At The Edge of RC Wall  Fig. 7 Rain Water Pipe Hidden in a Hollow Box Section Outside Column’s Section (Attached to column) Fig. 8 Rain Water Pipe Outside Column’s Section Passing Through Corner of The Slab Covered In Hollow Box Section JURNAL KEJURUTERAAN AWAM (JOURNAL OF CIVIL ENGINEERING) Vol. 15 No. 2  2002  15                         Fig. 9 Plan View of RC Wall Showing The Drain Pipe Positioned At The Centre of The Section of Wall 

A critical review of the reinforced concrete columns and walls concealing rain water pipe in multistorey buildings

http://eprints.utm.my/3769/1/WahidOmar2002_ACriticalReviewoftheReinforced.pdf

A critical review of the reinforced concrete columns and walls concealing rain water pipe in multistorey buildings

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