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AXIAL DEFORMATION OF COLUMN IN TALL STRUCTURES
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thirumalaichettiar
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PostPosted: Sun Nov 25, 2012 8:09 am    Post subject: Reply with quote

Dear Er.P.K.Mallick,

I appreciate your hard word and efforts to teach Sefians on this topic. I have one suggestion:

Why do not you complete all your write up and put it in PDF format and attach as an attachment so that one who needs to read will go through by down loading it one time  rather than browsing the web site and read in a piece meal.

This is only a suggestion. Up to you to continue further.

T.RangaRajan.
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P.K.Mallick
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PostPosted: Sun Nov 25, 2012 8:48 am    Post subject: Reply with quote

LIMITATION OF METHOD DEVELOPED BY M.FINTEL & F.R.KHAN:

This solution for creep and shrinkage of columns were prepared during late sixties based on state of art in that era. Hence the limitation in the procedure is apparent.

a) Effect of relative humidity on creep is not considered.

b) Effect of water/cement ratio on creep is not considered.

c) Creep also depends on fine aggregate to total aggregate ratio. This effect is not taken into account in the analysis.

d) Similarly percent of air content in concrete has pronounced effect on creep and this method is silent on this aspect.

Further ,the method to predict basic creep (without testing) from elastic modulus of elasticity is based on results of limited tests on normal weight concrete conducted at Bureau of Reclamation in Denver.

----------------------------------------
TO BE CONTINUED.
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P.K.Mallick
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PostPosted: Sun Nov 25, 2012 8:54 am    Post subject: Reply with quote

thirumalaichettiar wrote:
Dear Er.P.K.Mallick,

I appreciate your hard word and efforts to teach Sefians on this topic. I have one suggestion:

Why do not you complete all your write up and put it in PDF format and attach as an attachment so that one who needs to read will go through by down loading it one time  rather than browsing the web site and read in a piece meal.

This is only a suggestion. Up to you to continue further.

T.RangaRajan.


Sir
This site has a limitation to PDF file size for general Sefians. May be I am wrong but that is my experience.Many times I have failed to upload a PDF file in SEFI due to size issue. That is why I am putting up the article by sub-dividing it.
Warm Regards.

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PostPosted: Sun Nov 25, 2012 9:42 am    Post subject: Reply with quote

METHOD DEVELOPED BY M.FINTEL,H.IYENGER AND S.K.GHOSH:

This method is an extension of method-1. However,the procedure has been computerized to ease the burden of meticulous arithmetical calculation and extensive book keeping of data.

The developed computerized procedure is applicable to concrete,steel and composite structure and consider separately the elastic and creep component due to gravity loads and also shrinkage shortening.

Since structural effects result from differential distortions caused by column shortening after slab has been installed,the procedure separates the shortening of supports that occur after slab installations.

Computer utilization is particularly significant because consideration of shrinkage and creep requires extensive computation and summations as every story -high column segment in a multistoried building is loaded as many increments as there are stories above and for each loading increment of each column segment has now new time dependent properties ,modulus of elasticity,creep coefficients ,shrinkage coefficients,changing column sizes i.e. volume to surface ratio and varying reinforcement ratios.

Since the method is similar to method-1, this does not necessitate a detailed discussion.

--------------------------------------------------
TO BE CONTINUED.
---------------------------------------------------------

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thirumalaichettiar
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PostPosted: Sun Nov 25, 2012 10:36 am    Post subject: Reply with quote

P.K.Mallick wrote:
thirumalaichettiar wrote:
Dear Er.P.K.Mallick,

I appreciate your hard word and efforts to teach Sefians on this topic. I have one suggestion:

Why do not you complete all your write up and put it in PDF format and attach as an attachment so that one who needs to read will go through by down loading it one time  rather than browsing the web site and read in a piece meal.

This is only a suggestion. Up to you to continue further.

T.RangaRajan.


Sir
This site has a limitation to PDF file size for general Sefians. May be I am wrong but that is my experience.Many times I have failed to upload a PDF file in SEFI due to size issue. That is why I am putting up the article by sub-dividing it.
Warm Regards.


Dear Mr.Mallick,

In that case you have 4 options.

1. You can send to Er.Sanjeev through mail who will upload it.
2. Load it in some uploading web site like Rapidshare etc.
3. Split the PDF as PDF1,PDF2 and attach to to lesser capacity.
4, If you still find difficulties this is the approach.

Best of luck.

With Warm regards,
T.RangaRajan.
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bijay sarkar
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PostPosted: Sun Nov 25, 2012 12:36 pm    Post subject: Reply with quote

Dear Sir,

At the end of this discussion,

i) Can we get a consolidated step by step procedure for calculating all the deformations to reach at ultimate deformation quantity of vertical members. What are test data required for that.

ii) Also, please discuss, how the stress in the core members and out rigger perimeter columns are kept same to avoid differential deformation effects in tall buildings.

with regards,

bijay sarkar
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P.K.Mallick
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PostPosted: Sun Nov 25, 2012 2:57 pm    Post subject: Reply with quote

bijay sarkar wrote:
Dear Sir,

At the end of this discussion,

i) Can we get a consolidated step by step procedure for calculating all the deformations to reach at ultimate deformation quantity of vertical members. What are test data required for that.

ii) Also, please discuss, how the stress in the core members and out rigger perimeter columns are kept same to avoid differential deformation effects in tall buildings.

with regards,

bijay sarkar


Sir

When I discuss Prof Samra's method which is the latest  method,I would try to write step by step. But only problem I find in writing long mathematical formula but still I will try.
Warm Regards.

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Dr. N. Subramanian
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PostPosted: Sun Nov 25, 2012 3:22 pm    Post subject: Reply with quote

Dear All,

I also appreciate the postings by Er Mallick on a subject which is very important and has not been discussed. Axial shortening of columns will also result in malfunctioning of cladding attachments.  As suggested rightly by Er Rangarajanji, I also suggest Er Mallick to put everything in PDF file and send it to Er Sanjeev, who will upload it. In that way it is easy to accommodate the complicated equations.

I am also happy that Er Rangarajan has given a link to an useful PPP by Shapour Mehrkar-Asl. It is interesting to note that Er Ranjith Chandunni, who was involved in the design of 360m high Almas Tower in Dubai, UAE, has also responded.

Er R.Chandunni and F. Berahman, have explained the different aspects of the structural design of Almas Tower, Dubai, UAE,in their paper, including the axial shortening of column (see Fig. 7 and Cool This paper is available at
http://www.atkinsglobal.com/~/media/Files/A/Atkins-Global/Attachments/sectors/buildings/library-docs/technical-papers/the-structural-design-of-almas-tower-dubai.pdf
Incidentally Dr. Shapour Mehrkar-Asl is the Former Head of Structural Engineering, WS Atkins & Partners Overseas, Dubai, where Er Chandunni  worked as an Associate Structural Engineer, and authored a similar paper (now I think he is in Buro Happold, as I see from his posting)- see http://www.mehrkar.com/shapour/PDFs/almas-tower.pdf

Dr Taranath 1998, developed a formula to calculate the axial shortening of column at height z, in one single step. He also provides an example and procedure for column shortening verification during construction. Jayasinghe and Jayasena (2004) provide a set of guidelines so that the effect of axial shortening of column could be taken into account approximately, especially at the preliminary design stage and also during the construction phase.

References:

  • Jayasinghe, M.T.R., and W.M.V.P.K. Jayasena,  Effects of Axial Shortening of Columns on Design and Construction of Tall Reinforced Concrete Buildings, Practice Periodical on Structural Design and Construction, ASCE, Vol. 9, No. 2, May 2004, pp. 70-78.
  • Tatanath, Steel, Concrete & coposite Design of tall buildings, 2nd ed., McGraw Hill, 1998, pp. 882-897.
  • ACI Committee 209, Prediction of Creep, Shrinkage & Temperature Effects in Concrete Structures.  1997.
  • Fintel, M., Ghosh, S.K., and Iyengar, H. Column Shortening In Tall Structures - Predictions & Compensation, 1987, Portland Cement Association, Illinois.


Best wishes,
Subramanian
P.K.Mallick wrote:
METHOD DEVELOPED BY M.FINTEL & F.R.KHAN-Continued.

In continuation to explanation of above method let us look into the rest of the issues associated with the method.

Effect of Member size on Creep:

Creep is less sensitive to member size than shrinkage since only the  drying creep component of total creep is affected by size and shape of members,where as basic creep is independent of size and shape. It appears from a laboratory investigation that drying creep has its effect only during the initial three months.Beyond 100days,the rate of creep is equal to basic creep.

Shrinkage Strains-Adjusted For Column Size:


Shrinkage of concrete is caused by evaporation of moisture from the surface. Similar to creep,the rate of shrinkage is high at early ages,decreasing with increase of age,until the curve becomes asymptotic to final value of shrinkage.Since evaporation occurs only from the surface of members the volume to surface ratio of a member has a pronounced effect on the amount of its shrinkage.
The amount of shrinkage decreases as the size of specimen increases. Much of the shrinkage data available in the literature is obtained on 27.9 cm long prisims of a 7.6* 7.6 cm section. Obviously ,such data can not be applied to usual size columns without considering side effect.  The relationship between the magnitude of shrinkage and the volume-to-surface ratio has been plotted in a curve(we call fig-4). The size coefficient for shrinkage shown in fig-4 is used to convert shrinkage data obtained in 6inch cylinders to any other size columns.

Effect of relative humidity on shrinkage:

The shrinkage specimen should be stored under conditions similar to those for actual structures. If this is not possible ,the shrinkage results of a specimen not stored under field humidity conditions of structure must be modified to account for humidity conditions of structure. The curve developed by C.L.Freyermuth  showing relative humidity percentage and shrinkage humidity correction factor must be used in this regard.

Progress of Creep and Shrinkage with Time:

Both creep and shrinkage have similarity regarding the rate of progress with respect to time. A curve  (we call fig-5) is developed to show ratio of creep or shrinkage at anytime to final value at time infinity. This curve can be used to extrapolate the ultimate creep and shrinkage values from laboratory testing of certain duration time.

Effect of Reinforcement on creep and shrinkage:

Long term test has shown that on columns with low percentage of reinforcement the stress in steel increased until yielding while in highly reinforced columns after entire load had been transferred to steel ,further shrinkage actually caused some tensile stresses in the concrete. It should be noted that despite the redistribution of load between concrete and steel ,the ultimate steel capacity of the columns remains unchanged.

The total creep and shrinkage strains of a non-reinforced column are

Σ = fc Σc + Σs
where
fc =Initial elastic stress in the concrete.
Σc = ultimate specific creep strain of plain concrete
ΣS = Ultimate shrinkage strain of plain concrete.

A curve (we call fig-5) has been developed to determine residual creep and shrinkage strains of reinforced column from the total creep and shrinkage strain of identical column without reinforcement for various percentage of reinforcement,varying specific creep and modulus of elasticity of concrete.

THEREFORE,THE TOTAL STRAIN IN COLUMN DUE TO CREEP AND SHRINKAGE IS SUM TOTAL OF STRAINS CALCULATED DUE TO VARIOUS FACTORS AFFECTING SHRINKAGE AND CREEP.
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TO BE CONTINUED
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PostPosted: Sun Nov 25, 2012 4:57 pm    Post subject: Reply with quote

Dr. N. Subramanian wrote:
Dear All,



Dr Taranath 1998, developed a formula to calculate the axial shortening of column at height z, in one single step. He also provides an example and procedure for column shortening verification during construction. Jayasinghe and Jayasena (2004) provide a set of guidelines so that the effect of axial shortening of column could be taken into account approximately, especially at the preliminary design stage and also during the construction phase.



[/quote]

Respected Sir
Dr Taranath ,I think.only talks of elastic shortening and temperature effect pertaining to Steel structure.
I think he has not dealt with creep and shrinkage associated with concrete structure. I stand corrected if it is otherwise.
Warm Regards.

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PostPosted: Sun Nov 25, 2012 5:19 pm    Post subject: Reply with quote

Dear Er Mallick,
Yes. Taranath's calculations are for steel buildings and based on simple shortening/elongation PL/AE. But the reference by Jayasinghe and Jayasena is for RC columns and they compare the methods originally suggested by

  • Fintel, M., and Khan, F. R.,1969, ‘‘Effects of column creep and shrinkage in tall structures—Prediction of inelastic column shortening.’’ ACI Journal, Vol.66, American Concrete Institute, Detroit, 957–967.
  • Gosh, S. K.,996, ‘‘Estimation and accommodation of column length
  • changes in tall buildings.’’ Large concrete buildings, B. V. Rangan and
  • R. F. Warner, eds., Longmans, London

Regards,
Subramanian

P.K.Mallick wrote:
Dr. N. Subramanian wrote:
Dear All,



Dr Taranath 1998, developed a formula to calculate the axial shortening of column at height z, in one single step. He also provides an example and procedure for column shortening verification during construction. Jayasinghe and Jayasena (2004) provide a set of guidelines so that the effect of axial shortening of column could be taken into account approximately, especially at the preliminary design stage and also during the construction phase.





Respected Sir
Dr Taranath ,I think.only talks of elastic shortening and temperature effect pertaining to Steel structure.
I think he has not dealt with creep and shrinkage associated with concrete structure. I stand corrected if it is otherwise.
Warm Regards.[/quote]
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