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Practical Technical Queries of Concrete.

 
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Cyrus Pithawalla
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Joined: 08 Mar 2012
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PostPosted: Sat Nov 24, 2012 4:51 am    Post subject: Practical Technical Queries of Concrete. Reply with quote

I would appreciate , the reply of our esteemed Consultants , regarding the below queries from basically users point of view , arising out of my practical site experience of 37 years , as given below :
1- Views about providing horizontal and vertical joints in footings and large raft foundations , especially for large footings of depths 1.5m & above.
2-Effectivenessof providing Shrinkage strips in place of expansion joints in buildings more than 45m in length , as compared to a expansion joint.
3- How important is re proping in case of PT slabs ?
4- Preferred location of lap in columns, especially from earthquake requirements point of view , but also practically possible , to be implemented.

5- Out of tapered and parallel threaded couplers for rebars which one is better and why , instead of conventional lapping of rebars , especially in
columns ?
6- What is the permissible diff. in grades of concrete for slabs and columns , especially for concreting at the column beam or column slab junction?
7- How significant is effect of size and shape of paver blocks on its compressive strength. Is it that smaller paver blocks say 100mm x 100mm, have lesser strength as compared to large size pavers , say 200mm x 200mm , which is the stand taken by Paver blocks suppliers.
8- Quality and effectiveness of curing compounds ( Curing compound confirming to ASTM C 309 and ASTM C 1315 ) available in india and its suitability for residential buildings & commercial bldgs.
9- What should be permissible diff. intheoroticaland actual quantity of concrete consumed in case of cast in situ piles ?
10- Can we consider 56 days compressive strength of concrete instead of 28 days in case of foundations , since the load is directly transferred to ground , as compared to a regular slab?
11- For residential buildings with slab cycle speed of 12 days, what should be deshuttering criteria for Flat slab ( say 200mm thick) having M40 grade of concrete?
12- Is it true that providing two layers of 9" soling below footing improves SBC of soil ?
13- Any technology available to improve properties of marine clayey soil so that marine clayey soil becomes suitable for back filling ?
14- What is the diff. between shear wall and column design & how do we diffentiate between a column & shear wall ?
15- What is the correct values of loading to be considered for podium with 40 M.T. Fire Engine load & stilt/ car parks having normal cars / suvs?
16- What is the most economical way to design say 7m to 10m high RCC retaining wall , as compared to a rubble masonary wall ?
17- Selecting unbonded and bonded method of PT. Which one is more economical for commercial buildings & also from point of view of earthquake?
18- Any special precautions to be taken for Passive type rock anchors system , to be implemented on site ?
19- Few structural consultants do not given any rebar in column cap bottom in case of Flat slab design. How correct it is ?
20- What is the life of slabs strengthened withfiberwrapping ?
21- In case if structural columns ofresidentialbuildings are coming in Ug tanks provided within buildings, what precautions one must take for such columns , especially to avoid rusting of rebars , resulting in cracking of concrete?
22- Any cost saving achieved when Cellular light weight blocks ( AAC blocks) used in place of hollow concrete blocks ?
23-Which is better way of designing residential building with podium around i.e conventional beam slab or flat slab ??.
a) podium should be connected with main building or
b) podium should not be connected to main building ?
24- In case of buildings with dry cladding as facade, how suitable is solid concrete block masonary from connecting clading frame with block masonary using anchor fastener or it is better to have a RCC shear wall designed to take load or a non structural shear wall ??.
25- Effect of wind pressure on hollow concrete block masonary in case of multistorey buildings, any design calculations / thumb rule/practicesavailable to find out correct thickness of block masonary ?

Regards
C K Pithawalla
Director Engineering
Hiranandani Constructions
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thirumalaichettiar
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PostPosted: Sat Nov 24, 2012 6:40 am    Post subject: Reply with quote

Er.Pithawalla ,

While going through your 25 questions I prefer to put only the questions and doubts related to TALL BUILDINGS since the E-Conference is for it. I find that many are  general types to be put in General discussions.

It will be easy and convenient to reply anybody if less numbers as the E-Conference has limited period.

T.RangaRajan
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MIHIRKUMAR JOSHI
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PostPosted: Sat Nov 24, 2012 8:05 am    Post subject: Practical Technical Queries of Concrete. Reply with quote

Dear Mr C K Pithawalla.

Your all points are vey important, and i am also waiting for expert reply of your points, especially of points nos 4, 12 & 13.

I would suggest you IS-13920 for Preferred location of lap in columns CL-7.2.1 AND FIG-10.

I WOULD LIKE TO KNOW WHAT PRACTICAL PROBLEMS ARISE IF WE GO AS ABOVE.

Regards.

Mihir Joshi.
Design Engr (Civil)
GSFC Vadodara.


From: Cyrus Pithawalla (forum@sefindia.org)
Sent: Saturday, November 24, 2012 11:04 AM
To: econf34289@sefindia.org (econf34289@sefindia.org)
Subject: [E-CONF] Practical Technical Queries of Concrete.




I would appreciate , the reply of our esteemed Consultants , regarding the below queries from basically users point of view , arising out of my practical site experience of 37 years , as given below :
1- Views about providing horizontal and vertical joints in footings and large raft foundations , especially for large footings of depths 1.5m & above.
2- Effectiveness of providing Shrinkage strips in place of expansion joints in buildings more than 45m in length , as compared to a expansion joint.
3- How important is re proping in case of PT slabs ?
4- Preferred location of lap in columns , especially from earthquake requirements point of view , but also practically possible , to be implemented.

5- Out of tapered and parallel threaded couplers for rebars which one is better and why , instead of conventional lapping of rebars , especially in
columns ?
6- What is the permissible diff. in grades of concrete for slabs and columns , especially for concreting at the column beam or column slab junction?
7- How significant is effect of size and shape of paver blocks on its compressive strength. Is it that smaller paver blocks say 100mm x 100mm, have lesser strength as compared to large size pavers , say 200mm x 200mm , which is the stand taken by Paver blocks suppliers.
8- Quality and effectiveness of curing compounds ( Curing compound confirming to ASTM C 309 and ASTM C 1315 ) available in india and its suitability for residential buildings & commercial bldgs.
9- What should be permissible diff. in theorotical and actual quantity of concrete consumed in case of cast in situ piles ?
10- Can we consider 56 days compressive strength of concrete instead of 28 days in case of foundations , since the load is directly transferred to ground , as compared to a regular slab?
11- For residential buildings with slab cycle speed of 12 days, what should be deshuttering criteria for Flat slab ( say 200mm thick) having M40 grade of concrete?
12- Is it true that providing two layers of 9" soling below footing improves SBC of soil ?
13- Any technology available to improve properties of marine clayey soil so that marine clayey soil becomes suitable for back filling ?
14- What is the diff. between shear wall and column design & how do we diffentiate between a column & shear wall ?
15- What is the correct values of loading to be considered for podium with 40 M.T. Fire Engine load & stilt/ car parks having normal cars / suvs?
16- What is the most economical way to design say 7m to 10m high RCC retaining wall , as compared to a rubble masonary wall ?
17- Selecting unbonded and bonded method of PT. Which one is more economical for commercial buildings & also from point of view of earthquake?
18- Any special precautions to be taken for Passive type rock anchors system , to be implemented on site ?
19- Few structural consultants do not given any rebar in column cap bottom in case of Flat slab design. How correct it is ?
20- What is the life of slabs strengthened with fiber wrapping ?
21- In case if structural columns of residential buildings are coming in Ug tanks provided within buildings, what precautions one must take for such columns , especially to avoid rusting of rebars , resulting in cracking of concrete?
22- Any cost saving achieved when Cellular light weight blocks ( AAC blocks) used in place of hollow concrete blocks ?
23-Which is better way of designing residential building with podium around i.e conventional beam slab or flat slab ??.
a) podium should be connected with main building or
b) podium should not be connected to main building ?
24- In case of buildings with dry cladding as facade, how suitable is solid concrete block masonary from connecting clading frame with block masonary using anchor fastener or it is better to have a RCC shear wall designed to take load or a non structural shear wall ??.
25- Effect of wind pressure on hollow concrete block masonary in case of multistorey buildings, any design calculations / thumb rule/ practices available to find out correct thickness of block masonary ?

Regards
C K Pithawalla
Director Engineering
Hiranandani Constructions
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suraj
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PostPosted: Sat Nov 24, 2012 9:06 am    Post subject: Practical Technical Queries of Concrete. Reply with quote

Practical Technical Queries of Concrete.
Part replies-Remaining to be replied later


  1. Large footings to be designated as massive blocks or thick members do not require vertical defined joints. Question is not explicitly clear. What size & volume of footing is questioned?
  2. Current practice is for massive blocks, concreting is effected using 70 % GGBS replacement or a combination fo GGBS/PFA, so called SCMs replacement of cement
  3. Vertical joints are conducted by virtual stepping mode concreting in sequences, so that cold joints are allowed
  4. Differential thermocouples are inserted to monitor thermal gradient
  5. Normal curing is not carried out, but thermal curing
  6. In case, of vertical joint, limitation for concrete volume is required & if so agree for joint formation, vertical joint is formed using metallic shutters at intermediate division with reinforcing bars continuity
  7. Question about re-proping pertinent PT slab is not clear. PT slabs can directly be put on cast in situ beams for slab formation & used as permanent forms, on which diaphragm constituent of cast in concrete is placed
  8. Columns started bars are placed from stub column followed, but full length bar covering up to floor zero BM location avoiding moment area
  9. Couplers should be used for bar more than T 25 conveniently, since it is difficult to work on for higher dia. bars, yet prior to deciding about inclusion of couplers, practical test for tension should be conducted by a specific testing equipment
  10. Couplers can be used in both compression as well as, in tension bars without problems, but staggering should be effected
  11. Practically, contemplating, only one grade should be included for whole floor from control view point. Use of different grade do cause delivery issues & column cap concrete variation
  12. Concrete Paver/interlocks block should be 49 N according to codes 80 mm for traffic areas & 60 mm for walking areas
  13. Curing compound is a good replacement for water, but should be selected with caution
  14. Two types of compound used to be available. Wax based & water based. Wax based forms a gelatinous layer on concrete surface, which takes about 6 month for natural degradation or scraped is used to deteriorate it, when plastering or rendering is required earlier
  15. Water based curing compound is partly effective only, since it evaporates easily
  16. Prior to use of compound, water should be sprinkled on vertical surface, so that it retains within formed gelatinous layer
  17. Actually, curing compound is never 100 % effective. On horizontal members that are accessible during curing duration, in addition to curing compound, water curing should be supplemented. Compound should be used only for avoiding initial cracks formation
  18. Not only, on cast in situ piles, but on all cast in situ concrete, reinforcing bars quantity,  for all concrete ordering purposes should be deducted from theoretical quantity, but for estimation purpose, no such deductions is permissible. A % variation should be conducted for perimeter surfaces for piles depending on soil nature
  19. Compressive characteristics strength is object for standard strength measurement for practical approval of concrete, but testing can be conducted on whatever number of days. 56 days age of concrete is a must for load testing purpose
  20. In certain cases, when striking shutter is required on an earlier basis, even 3 days testing can be conducted
  21. Cycle of 12 days can be achieved with no issues irrespective of consideration of 40 N, depending on availability of resources & strength of working team & allied services coordination & inspection issues
  22. Certainly soling with grading below foundations, improved bearing capacity & also, acts as filter as well as protection as it is isolated from effect of soil
  23. In such cases, when water soil mobility occurs, it does not harm concrete to considerable an extent
  24. Clay soil can be used for filling purpose in combination with desert fill & sand soils so that keeping liquid limit within 35 & plasticity index below 6. It is suggested that non plastic soil should be used for filling purpose
  25. Columns are designed for direct loads as well as for moments, while shear wall is meant for primary lateral loadings

_________________
Thanks & Warm Regards
IntPE(India)Suraj Singh FIE Civil
Engineering & Arbitration

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arungiriyan634@gmail.com
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PostPosted: Wed Nov 28, 2012 5:18 am    Post subject: Practical Technical Queries of Concrete. Reply with quote

Respected sirs,I would like to give my views to the raised points by my practical experience of about many years in this field worked with outstanding consultants .1.Vertical joints in footings are always objected because of compression load makes it fail under shear and spit .2. Shrinkage / expansion and contraction has some what diff meanings in civil subject. The first one happens when water evaporates quickly from the substance than designed time due to abnormal atmos heat and leaves porous and deformation. The second one is due to different thermal coefficients of materials used for the construction of a structure expand in opposite directions . in such case using a shrinkage strip will give one sided effect .on the other side the subject expands will create passage for water .3. Pt slab preferred for reducing no of columns coming in between . design factor says removing props only after full tensioning done subject to the concrete 7days strength tested found 70% and then grout gets started .you can start reprop only after 70% concrete strength and tendons stretched to required values. Lest ,slab will develop cracks. 4. Whenever earthquake happens , impact changes the movement and all columns act as beams. Beams act under compression due to horizontal pull of earth slate and columns fail at nearest joints with the beam. lap provided in the middle zone of the effective column ht with min 50% steel staggered by a lap length.5. Parallel thread is most preferable. In case of conical shaped threading only 45% tip length of the threaded portion gets tightened and the rest does not actually act . In case of parallel thread you can exactly check both ends touch . 6.It should be of max one grade .that is 20-25 or 30-35 . But while preparing water cement ratio should be adjusted in such a way that same mix acts in both with reducing water content to the lower one with increasing admixture . There is a perforated mesh system being suggested in case of much difference but its in preliminary stage. this should be reviewed. 14.If the ratio of width to length is 4 or more .that means L /b gives more than 4 it is considered as a shear wall. Regards. Will continue.Arunagiri.Sent from BlackBerry® on Airtel
From: "Cyrus Pithawalla" <forum@sefindia.org>
Date: Sat, 24 Nov 2012 11:04:19 +0530
To: <econf34289@sefindia.org>
ReplyTo: econf34289@sefindia.org
Subject: [E-CONF] Practical Technical Queries of Concrete.

     I would appreciate , the reply of our esteemed Consultants , regarding the below queries from basically users point of view , arising out of my practical site experience of 37 years , as given below :  1- Views about providing horizontal and vertical joints in footings and large raft foundations , especially for large footings of depths 1.5m & above.  2- Effectiveness of providing Shrinkage strips in place of expansion joints in buildings more than 45m in length , as compared to a expansion joint.  3-  How important is re proping in case of PT slabs ?  4- Preferred location of lap in columns , especially from earthquake requirements point of view , but also practically possible , to be implemented.  5- Out of tapered and parallel threaded couplers for rebars which one is better and why , instead of conventional lapping of rebars , especially in columns ?  6- What is the permissible diff. in grades of concrete for slabs and columns , especially for concreting at the column beam or column slab junction?  7- How significant is effect of size and shape of paver blocks on its compressive strength. Is it that smaller paver blocks say 100mm x 100mm, have lesser strength as compared to large size pavers , say 200mm x 200mm , which is the stand taken by Paver blocks suppliers.  8- Quality and effectiveness of curing compounds ( Curing compound confirming to ASTM C 309 and ASTM C 1315 )  available in india and its suitability for residential buildings & commercial bldgs.  9- What should be permissible diff. in theorotical and actual quantity of concrete consumed in case of cast in situ piles ?  10- Can we consider 56 days compressive strength of concrete instead of 28 days in case of foundations , since the load is directly transferred to ground , as compared to a regular slab?  11- For residential buildings with slab cycle speed of 12 days, what should be deshuttering criteria for Flat slab ( say 200mm thick) having M40 grade of concrete?  12- Is it true that providing two layers of 9" soling below footing improves SBC of soil ?  13- Any technology available to improve properties of marine clayey soil so that marine clayey soil becomes suitable for back filling ?  14- What is the diff. between shear wall and column design & how do we diffentiate between a column & shear wall ?  15- What is the correct values of loading to be considered for podium with 40 M.T. Fire Engine load  & stilt/ car parks having normal cars / suvs?  16- What is the most economical way to design say 7m to 10m high RCC retaining wall , as compared to a rubble masonary wall ?  17- Selecting unbonded and bonded method of PT. Which one is more economical for commercial buildings & also from point of view of earthquake?  18- Any special precautions to be taken for Passive type rock anchors system , to be implemented on site ?  19- Few structural consultants do not given any rebar in column cap bottom in case of Flat slab design. How correct it is ?  20- What is the life of slabs strengthened with fiber wrapping ?  21- In case if structural columns of residential buildings are coming in Ug tanks provided within buildings, what precautions one must take for such columns , especially to avoid rusting of rebars , resulting in cracking of concrete?  22- Any cost saving achieved when Cellular light weight blocks ( AAC blocks)  used in place of hollow concrete blocks ?  23-Which is better way of designing residential building with podium around i.e conventional beam slab or flat slab ??.   a) podium should be connected with main building or  b) podium should not be connected to main building ?  24- In case of buildings with dry cladding as facade, how suitable is solid concrete block masonary from connecting clading frame with block masonary using anchor fastener or it is better to have a RCC shear wall designed to take load or a non structural shear wall ??.  25- Effect of wind pressure on hollow concrete block masonary in case of multistorey buildings, any design calculations / thumb rule/ practices available to find out correct thickness of block masonary ?  Regards     C K Pithawalla Director Engineering Hiranandani Constructions        --auto removed--

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