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AXIAL DEFORMATION OF COLUMN IN TALL STRUCTURES
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P.K.Mallick
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PostPosted: Mon Nov 26, 2012 5:10 pm    Post subject: Reply with quote

Dr. N. Subramanian wrote:
Dear Er Rangarajanji,

The paper New Analysis for Creep Behavior in Concrete Columns by R.M. Samra,  Journal of Structural Engineering, Vol. 121, No. 3, March 1995, pp. 399-407, referred by Er Mallick contains an example.


Respected Sir

Over a period of time I have lost the original article of Prof Samra and my memory does not help me too. I need a confirmation from you . In the worked out example ,has Prof Samra  assumed the creep coefficient and ultimate shrinkage or he derived those by method outlined in ACI 209 R ?

I had solved the same problem of Prof Samra's article by using method outlined in ACI 209 R for  creep coefficient and ultimate shrinkage. If Prof Samra has used ACI 209 R for  creep coefficient and ultimate shrinkage and has not assumed the data,then I will not discuss the problem as anybody can see the worked out example in Prof Samra's article .

In case he has assumed the data,then I will discuss the problem.
Please confirm.

Warm Regards.

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PostPosted: Tue Nov 27, 2012 10:11 am    Post subject: AXIAL DEFORMATION OF COLUMN IN TALL STRUCTURES Reply with quote

Effect of creep on columns may appear to be an academic query but I feel it has got a practical sense in case of multi storeyed buildings, 50 and above. By definition creep is deformation under sustained loading. A column is always under compression whose magnitude varies with change of live load at different floors. In case of a column we know axial deformation is the only deformation a column can undergo. In case of small and medium high buildings we do not pay any attention to the axial deformation of columns but in a high rise building this phenomenon may affect the entire structural system. So long I have not seen any formula for assessing effect of creep categorized for structural elements like column, beam or slab. We consider concrete loses strength due to creep. We can start from this premises and consider that after 100 years the column will function in its residual strength only.  On Mon, Nov 26, 2012 at 9:00 PM, Dr. N. Subramanian <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Dear Er Rangarajanji,

The paper New Analysis for Creep Behavior in Concrete Columns by R.M. Samra, Journal of Structural Engineering, Vol. 121, No. 3, March 1995, pp. 399-407, referred by Er Mallick contains an example. The abstract of the paper is given below:
     This paper presents a new rational approach for the evaluation of the effects of creep on reinforced-concrete axially loaded columns at sustained service stresses. The analysis involves a straightforward computation based on a closed form procedure and the assumption of linear elastic materials for both concrete and steel. The analysis may be easily extended to cover the case of reinforcement at yield. The results of the proposed approach may be superposed with those from a shrinkage model presented by Park and Paulay in 1975, and the overall behavior of column axial shortening and stress transfer from concrete to steel may be described using the combined approach. The process involved is very convenient to use from an engineering view point since it requires few input parameters, which are easy to estimate or measure experimentally, such as the modulus of elasticity of concrete and the creep coefficient. The results of the theoretical approach correlate well with experimental tests conducted on specimens in the laboratory and with deformations of columns measured in the Water Tower Place and Lake Point Tower in Chicago.

As I already informed Dr Taranath discusses these effects in his book- These effects should be considered when the no. of stories exceed 30. Taranath discusses about steel columns, the same can be applied to concrete also, which creeps more than steel. Prof. Samra's method is more refined for RCC.

Regards,
NS
      thirumalaichettiar wrote:                As Er.Bijay sarkar has asked in his posting on 25-11-12 may I request you on behalf of all Sefians the following:

At the end of your write up can you put the concluding remarks in a nutshell with the notes:

a. What is the Creep and shrinkage effect on Column?

b. When it is important i.e from how many floor level it is important?

c. Is this phenomenon is applicable to all materials?

d. How to calculate with example specially with respect to R.C.C with the latest ( new method as per your previous statement)method using the necessary equations in SI units?

e. Is there any software as per your knowledge available?

f. If not is there any method that can be used with any of the available commercial software?

g. Can you list out the few important reference articles and books on the above subject?

Hope you will do for the sake of interested Sefians?

T.RangaRajan.[/color:426367a801]     
     



     


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PostPosted: Tue Nov 27, 2012 2:32 pm    Post subject: Re: AXIAL DEFORMATION OF COLUMN IN TALL STRUCTURES Reply with quote


The beauty of Prof.Samras method is that it separates the issue of the prediction of creep coefficient and ultimate shrinkage from the main problem of calculation of axial shortening. Therefore, one can use the codal provision of his own country or the output of latest research findings to calculate creep coefficient and ultimate shrinkage. This flexibility is not available other two methods discussed (Method developed by M.Fintel & F.R.Khan and the Method developed by M.Fintel, H.Iyenger & S.K.Ghosh.)
For solving axial deformation problem by Prof.Samras method, I prefer to use the code of ACI 209R-92(Reapproved in 1997)-PREDICTION OF CREEP, SHRINKAGE AND TEMPERATURE EFFECTS IN CONCRETE STRUCTURES for calculation of creep coefficient and ultimate shrinkage.

Hence let me explain the provisions of ACI 209R-92(Reapproved in 1997).
CALCULATION OF CREEP COEFFICIENT BY ACI 209R 92 (REAPPROVED IN 1997) METHOD

     This code expresses the creep coefficient (t, t o ) as a function of time
      (t, t o) = X/Y (∞ (t o ))

     X= (t- t o  ) 0.6

              Y= 10 + (t- t o )0.6

Where creep coefficient is the ratio of specific creep C (t, t o ) at age t due to a unit stress applied at the age t  to a unit stress applied at the age t o , where age   t o is measured in days.  
Since the initial elastic strain under a unit stress is equal to the reciprocal of the modulus of elastically Ec (t0)

     (t, t o  ) = C (t, t o )  x    Ec(t0)

     (t, t o  ) is the time since application of load and  ∞ (t, t o )     is the ultimate creep coefficient, which is given by

∞ (t, t o )      = 2.35 K1 K2 K3 K4 K5 K6  

For age at application of load greater that 7 days for moist curing, or greater that 1 to 3 days for steam curing, the coefficient K1 is estimated from:

For moist curing:
K1 = 1.25 t o  -0.118
For steam curing:
K1 = 1.13 t o -0.095

The coefficient k2 is dependent upon the relative humidity h (percent)
K2 = 1.27 0.006h
For h ≥ 40

The coefficient K3 allows for member size in terms of volume/surface ratio, V/s which is defined as the ratio of the cross sectional area to the perimeter exposed to drying.  For values of V/s smaller that 37.5mm, K3 is given below.

Value to Surface Ratio (mm)                    Coefficient (K3)
     12.5                                   1.3
     19.0                                   1.17
     25.0                                   1.11
     31.0                                   1.04
     37.5                                   1.0

When V/s is between 37.5 and 95mm, K3 is given by:
For (t-to) ≤ 1 year:
     K3 = 1.14 0.00364 v/s
For (t-to) > 1 year:
     K3 = 1.1 0.00268 v/s
When v/s ≥ 95mm
K3 = 2/3 [1+1.13e-0.0212(v/s) ]       
     
The coefficients to allow for composition of concrete are K4, K5.
Coefficient K4 is given by :

K4 = 0.82 + 0.00264S
Where S = slump of fresh concrete.

Coefficient K5 depends on the fine aggregate/total aggregate ratio, Af/A, in percent and is given by :
K5 = 0.88 + 0.0024(AF/A)

Coefficient K6 depends on the air content a (percent)
K6 = 0.46 + 0.09a ≥1

The elastic strain plus creep deformation under a unit stress is termed the creep function , which is given by:
   (t, t o ) = [1/Ec(t0)]* [1 + (t, t o )]

Where Ec (t0) is related to the compressive strength of test of cylinders.  If the strength at age t0 is not known, it can be found from the following relation
Fcy (t0) = (t0/(X+Yt0)) * (fcy28)

Where fcy28 is the strength at 28 days and X and Y are given below in table:

Type of cement      Curing condition     Constant
                                                         X     Y
Ordinary Portland           Moist                4       0.85
Cement

                                      Steam                1       0.95



Rapid hardening
Portland cement            Moist                    2.3     0.92
Stream

                                      Steam                   0.7     0.98


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

-----------------------------------------------------------------

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PostPosted: Tue Nov 27, 2012 5:20 pm    Post subject: Re: AXIAL DEFORMATION OF COLUMN IN TALL STRUCTURES Reply with quote

I would request ADMIN to transfer this topic to General discussion Forum

Thanks and Regards.

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PostPosted: Tue Nov 27, 2012 7:32 pm    Post subject: Re: AXIAL DEFORMATION OF COLUMN IN TALL STRUCTURES Reply with quote

Dear Er Mallick,

Why do you want to transfer it to General discussion Forum? Axial deformation of columns is a problem only in Tall Buildings!

Best wishes & Regards,
NS
P.K.Mallick wrote:
I would request ADMIN to transfer this topic to General discussion Forum

Thanks and Regards.
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PostPosted: Wed Nov 28, 2012 1:27 am    Post subject: Re: AXIAL DEFORMATION OF COLUMN IN TALL STRUCTURES Reply with quote

Dr. N. Subramanian wrote:
Dear Er Mallick,

Why do you want to transfer it to General discussion Forum? Axial deformation of columns is a problem only in Tall Buildings!

Best wishes & Regards,
NS
P.K.Mallick wrote:
I would request ADMIN to transfer this topic to General discussion Forum

Thanks and Regards.



Respected Sir

I will not be able to complete the discussion by the time the E -conference is over.Topics will be locked for discussion once the E-conference is over.That is why ,I want,it should be transferred to General forum.
Warm Regards.

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PostPosted: Wed Nov 28, 2012 2:09 am    Post subject: Re: AXIAL DEFORMATION OF COLUMN IN TALL STRUCTURES Reply with quote

Dear Sirs,
Glad to inform we have planned to extend the e-conf till Dec 5. We expect to make formal announcement shortly.
Regards
Admin

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

Why do you want to transfer it to General discussion Forum? Axial deformation of columns is a problem only in Tall Buildings!

Best wishes & Regards,
NS
P.K.Mallick wrote:
I would request ADMIN to transfer this topic to General discussion Forum

Thanks and Regards.



Respected Sir

I will not be able to complete the discussion by the time the E -conference is over.Topics will be locked for discussion once the E-conference is over.That is why ,I want,it should be transferred to General forum.
Warm Regards.
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PostPosted: Wed Nov 28, 2012 2:14 am    Post subject: AXIAL DEFORMATION OF COLUMN IN TALL STRUCTURES Reply with quote

Hi everybody,

As it is mentioned below by Mr. Ranjith, the spread sheets may have some restrictions regarding the height of the building, but there is a software called MIDAS(GEN) to model and predict the column shortening effects. I have used this software to model a 70 storeys building in Dubai.


Regards,
Jayakumar K
email: ejk.iitb@gmail.com (ejk.iitb@gmail.com)




On Sun, Nov 25, 2012 at 8:09 AM, Ranjith.Chandunni <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           To add to the response:

The presentation by Dr. Shapour is based on his works on a project in Dubai and the method of assessing column shortening is adopted from PCA publication by Mark Fintel, S.K. Ghosh and Hal Iyengar titled Column shortening in tall structures Prediction and compensation published in 1986. This book is still by far one of the most comprehensively covered paper on the subject. The complete methodology of assessing columns shortening is explained in detail with examples and refers to ACI publications for many of the parameters. I am not sure if a computer programme is available but one can be easily produced. A spread sheet can also be developed with macros to do a few iterations required in the analysis.

Another easy to use tool to assess column shortening is the spread sheet TCC55 by Reinforced Concrete Council (RCC, BCA), UK which is based on Euro Code. The main limitation is it can only be used for 12 levels (updated to 24 levels perhaps now). However, for a high rise building, floors can be clubbed together in to 12 or 24 groups in order to use this yet get a fairly good assessment of axial and differential shortening of columns. RCC spread sheets are shareware and can be distributed freely but should not be used commercially.

Ranjith Chandunni
Buro Happold



From: P.K.Mallick [mailto:forum@sefindia.org (forum@sefindia.org)]
Sent: 24 November 2012 16:40
To: econf34289@sefindia.org (econf34289@sefindia.org)
Subject: [E-CONF] Re: AXIAL DEFORMATION OF COLUMN IN TALL STRUCTURES



thirumalaichettiar wrote:
In response to Er.P.K.Mallick's article on the above topic I could find a presentation on

Presentation on Column Shortening in Tall Buildings from the internet. By Shapour Mehrkar-Asl

Since it is not stated as copy righted one I am posting for the benefit of all.

CONTENT:About the presentation:[/color:e03acba3a1]


The Event was held on 26 September 2012 at the Abu Dhabi Mens College, Abu Dhabi, UAE.


The design of tall buildings normally leads to columns in the exterior with a higher average compressive stress compared to that of the interior columns/cores elements. In buildings of normal height, 30 to 40 floors, this would not normally cause any issues. However, in taller buildings this difference leads to a different vertical elevation for the exterior columns compared to interior columns/cores, normally referred to as Column Shortening even though it is actually a relative shortening.

The consequence of that are sloping of the floor towards the edges of the building, cracking in the partitions and cladding. Other non-structural elements such as piping may get affected.
Column shortening calculation on steel structures is slightly different to concrete structures mainly because of the properties of the steel and concrete.

Concrete is subject to creep and shrinkage. In addition, age of concrete affects its properties such as Elastic Modulus, basic Creep and Shrinkage behaviors. As these parameters are functions of time then movements become function of time bringing the construction sequence into play. In steel structures even though the construction sequence is important the time intervals in the construction sequence become less important as material properties are relatively constant.

The presenter explains the effects as described by the authors of the original publication of PCA by Fintel et al. In addition he shows the results of such an application on a 71 floor building with the help of a computer program he had developed in 2005 based on the approach given in the publication.

T.RangaRajan[/color:e03acba3a1]



Respected RangaRajan Sir
I had a glance on the presentation by Shapour Mehrkar-Asl. Useful certainly. Though the presentation is as recent as the year 2012,the methodology described is quite old. I wish to go beyond that. Let me try. Warm regards.




P.K.Mallick
pk_mallick1962@rediffmail.com (pk_mallick1962@rediffmail.com) (pk_mallick1962@rediffmail.com (pk_mallick1962@rediffmail.com))
     



     



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PostPosted: Wed Nov 28, 2012 2:26 pm    Post subject: Re: AXIAL DEFORMATION OF COLUMN IN TALL STRUCTURES Reply with quote

CALCULATION OF ULTIMATE SHRINKAGE BY ACI 209-R-92(REAPPROVED IN 1997) METHOD


According to AC I 209.R 92, Shrinkage Sh (t,τo) at time  t(days), measured from the start of drying at τo (days) is expressed as follows:

For moist curing

Sh (t, τo ) =(( t- τo)/(35 + (t τo)))  Sh∞

For steam curing

Sh (t, τo) = ((t- τo)/(55 + (t- τo)))  Sh∞

Where  Sh∞= Ultimate shrinkage and

Sh∞ = 780 x 10-6  K1 K2 K3 K4 K5 K6 K7

For curing times different from seven days for moist cured concrete,

the age coefficient K1 is given below:

Period of moist curing                    shrinkage coefficient (K)
     1                              1.2
     3                              1.1
     7                              1.0
     14                              0.93
     28                              0.86
     90                              0.75

and for steam curing with a period of 1 to 3 days

     K1  = 1

The humidity coefficient K2 is

K2  = 1.4 (0.01)h, where 40 ≤ h ≤ 80

K2  = 3.0 0.3h, where 80 ≤ h ≤ 100

Where h = Relative humidity (Percent)

Coefficient K3  allows for the size of the member in terms of the

Volume / surface ratio V/S.

For values of the V/S <37> 50)

Where Af/A = Fine aggregate / total time aggregate ratio by mass

K6 = 0.75 + 0.00061τ, Where τ = Cement content (Kg/m3 )

K7 = 0.95 + 0.008 A, Where A = Air content (Percent)          



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

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PostPosted: Sat Dec 01, 2012 9:43 pm    Post subject: Re: AXIAL DEFORMATION OF COLUMN IN TALL STRUCTURES Reply with quote

Dear Er Mallick,

I wish to inform you that the current issue(Dec 2012) of ICJ is a spl. issue on Creep and shrinkage and contains the following articles:

  • Factors affecting creep and shrinkage of hardened concrete and guide for modelling
    Mario A. Chiorino and Domingo J. Carreira
  • Evaluation of the structural response to the time-dependent behaviour of concrete: Part 1 - An internationally harmonized format
    Mario A. Chiorino and Carlo Casalegno
  • Evaluation of the structural response to the time-dependent behaviour of concrete: Part 2 - A general computational approach
    Mario Sassone and Carlo Casalegno
  • Costanera Center - Shortenings due to elastic deformation, creep and shrinkage of concrete in a 300-m tall building
    Ren C. Lagos, Marianne C. Kupfer, Simn T. Sanhueza and Francisco V. Cordero


Regards,
NS
P.K.Mallick wrote:
CALCULATION OF ULTIMATE SHRINKAGE BY ACI 209-R-92(REAPPROVED IN 1997) METHOD


According to AC I 209.R 92, Shrinkage Sh (t,τo) at time  t(days), measured from the start of drying at τo (days) is expressed as follows:

For moist curing

Sh (t, τo ) =(( t- τo)/(35 + (t τo)))  Sh∞

For steam curing

Sh (t, τo) = ((t- τo)/(55 + (t- τo)))  Sh∞

Where  Sh∞= Ultimate shrinkage and

Sh∞ = 780 x 10-6  K1 K2 K3 K4 K5 K6 K7

For curing times different from seven days for moist cured concrete,

the age coefficient K1 is given below:

Period of moist curing                    shrinkage coefficient (K)
     1                              1.2
     3                              1.1
     7                              1.0
     14                              0.93
     28                              0.86
     90                              0.75

and for steam curing with a period of 1 to 3 days

     K1  = 1

The humidity coefficient K2 is

K2  = 1.4 (0.01)h, where 40 ≤ h ≤ 80

K2  = 3.0 0.3h, where 80 ≤ h ≤ 100

Where h = Relative humidity (Percent)

Coefficient K3  allows for the size of the member in terms of the

Volume / surface ratio V/S.

For values of the V/S <37> 50)

Where Af/A = Fine aggregate / total time aggregate ratio by mass

K6 = 0.75 + 0.00061τ, Where τ = Cement content (Kg/m3 )

K7 = 0.95 + 0.008 A, Where A = Air content (Percent)          



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