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Last floor column design
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gautam chattopadhyay
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Joined: 17 Feb 2009
Posts: 128

PostPosted: Fri Nov 30, 2012 1:53 pm    Post subject: Last floor column design Reply with quote

Dr. N S has supported my views. Thanks Dr.

On Fri, Nov 30, 2012 at 6:49 PM, Dr. N. Subramanian <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Dear Dr Channakeshava,

It is a very good point. Many do not consider the construction stage analysis. We discussed about it earlier, in the context of loading on slabs and removal of props. Concrete international has a few papers on this aspect.

Thanks for reminding. Another important aspect is the design if corner columns, which are critical in the 0.9WL combination, have to be designed carefully. Though the load may be less compared to other columns, they are subjected to bi axial bending and even torsion. I believe they are not researched properly.

Regards,
Subramania


      cckeshav wrote:                Dear SEFIans:

As mentioned elsewhare in my mail, every floor is a last floor during construction. This can be verified by a construction stage analysis. As such reinforcement required for the construction stage governs for end and side columns. Otherwise, specific decentering schemes should be provided which ensures that all the beams in the lower two levels are supported (not repropped) until the current floor is cured.

C.Channakeshava


Subject: [E-CONF] Re: Last floor column design
From: forum@sefindia.org (forum@sefindia.org)
Date: Wed, 28 Nov 2012 21:52:31 +0530
To: econf34289@sefindia.org (econf34289@sefindia.org)

There are two ways - either provide higher reinforcement for top most story column or while analyzing assign top joint as hinged. However by doing so there are chances that the inter story drift for the top most story exceeds the limit. - from Vodafone
From: "vijaydshah"
Date: Wed, 28 Nov 2012 18:18:27 +0530
To:
ReplyTo: econf34289@sefindia.org (econf34289@sefindia.org) (econf34289@sefindia.org (econf34289@sefindia.org))
Subject: [E-CONF] Last floor column design

Dear sefians It has been observed from the experience that for all buildings when we do space frame analysis the reinforcement of the last floor is quite high compared to lower stories . This is specifically for the end columns where moment distribution is not possible due to discontinuity of the columns. Providing this reinforcement through out the height of the building do not justify the economy. Can any one throw light on this subject ?.
vdshah
     
     



     


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Dr. N. Subramanian
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PostPosted: Fri Nov 30, 2012 4:06 pm    Post subject: Re: Last floor column design Reply with quote

Dear Er Gautam,

You are welcome! Smile

I am giving below the reference to the construction stage analysis paper. A few more papers should be there in ASCE Structural Div. also

Liu, X.L., H. M. Lee, and W. F. Chen, Analysis of Construction Loads on Slabs and Shores by Personal Computer,     Concrete International
Vol.      10, No. 6, June 1988
Another Ph.D Thesis Abstract (guide Prof. W F Chen) is given below;
Construction loads and load effects in concrete building construction by Mosallam, Khalid Homoud, Ph.D., Purdue University, 1991, 195 pages; AAT 9132480

Summary


The most critical stage of a structure's lifetime is that of construction. Many, perhaps most, construction disasters occur as a result of the failure of temporary structures, and far more disasters occur during construction than after completion of projects. The most serious deficiency in formwork design is in the consideration of lateral loads. Also, a great deal of damage and loss of property during construction are caused by wind. Consequently, determination of load distribution during construction is one of the critical factors in assessing the structural safety during the construction of reinforced concrete structures.

Herein, realistic models of the structure in the construction phase are developed. A practical method to check the slab adequacy during construction is presented. Extensive numerical studies of the distribution of construction loads between multistory framed structures and the shoring and reshoring systems are made, using the computer models developed. A simplified procedure to include the construction live load in the analysis of construction loads is proposed. Furthermore, a simple modification of the popular simplified method for calculating the load distribution during construction is presented. Also, a precise method for assessing wind loads to be used in the design of temporary lateral bracing for open frame buildings is given. Furthermore, a three-dimensional computer model capable of simulating the concrete construction process is developed. The effect of construction process in the analysis of multistory concrete buildings is investigated.

It has been found that the simplified method is adequate for predicting the construction location of the maximum slab and shore loads. However, it generally overestimates the actual load ratios. Furthermore, it is concluded that ACI-347 minimum requirement for horizontal loads can underestimate design wind loads by as much as 50%. It is also found that the effect of lateral loads on the construction load distribution is very small and can be neglected for practical purposes. In addition, it is found that neglecting the construction process in an elastic analysis of multistory buildings leads to a significant error in stresses due to dead loads.

Regards
NS


gautam chattopadhyay wrote:
Dr. N S has supported my views. Thanks Dr.

On Fri, Nov 30, 2012 at 6:49 PM, Dr. N. Subramanian <forum> wrote:
Quote:
            Dear Dr Channakeshava,

It is a very good point. Many do not consider the construction stage analysis. We discussed about it earlier, in the context of loading on slabs and removal of props. Concrete international has a few papers on this aspect.

Thanks for reminding. Another important aspect is the design if corner columns, which are critical in the 0.9WL combination, have to be designed carefully. Though the load may be less compared to other columns, they are subjected to bi axial bending and even torsion. I believe they are not researched properly.

Regards,
Subramania


      cckeshav wrote:                Dear SEFIans:

As mentioned elsewhare in my mail, every floor is a last floor during construction. This can be verified by a construction stage analysis. As such reinforcement required for the construction stage governs for end and side columns. Otherwise, specific decentering schemes should be provided which ensures that all the beams in the lower two levels are supported (not repropped) until the current floor is cured.

C.Channakeshava


Subject: [E-CONF] Re: Last floor column design
From: forum@sefindia.org (forum@sefindia.org)
Date: Wed, 28 Nov 2012 21:52:31 +0530
To: econf34289@sefindia.org (econf34289@sefindia.org)

There are two ways - either provide higher reinforcement for top most story column or while analyzing assign top joint as hinged. However by doing so there are chances that the inter story drift for the top most story exceeds the limit. - from Vodafone
From: "vijaydshah"
Date: Wed, 28 Nov 2012 18:18:27 +0530
To:
ReplyTo: econf34289@sefindia.org (econf34289@sefindia.org) (econf34289@sefindia.org (econf34289@sefindia.org))
Subject: [E-CONF] Last floor column design

Dear sefians It has been observed from the experience that for all buildings when we do space frame analysis the reinforcement of the last floor is quite high compared to lower stories . This is specifically for the end columns where moment distribution is not possible due to discontinuity of the columns. Providing this reinforcement through out the height of the building do not justify the economy. Can any one throw light on this subject ?.
vdshah
     
     



     


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surya_prakash_k
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PostPosted: Sat Dec 01, 2012 2:02 am    Post subject: Last floor column design Reply with quote

Dear Dr. Chennakeshava,

During analyses carried out earlier, the dead load induced moments for this construction stage are safe to be taken by columns for last slab condition as long as dead load is not exceeding apprx 40 per cent of total load. However, for light live load structures like car parks and long span structures special analyses need to be done.

Thanks & Regards

K Suryaprakash
From: cckeshav <forum@sefindia.org>
Date: Fri, 30 Nov 2012 18:32:54 +0530
To: <econf34289@sefindia.org>
ReplyTo: <econf34289@sefindia.org>
Subject: [E-CONF] Re: Last floor column design


Dear SEFIans:

As mentioned elsewhare in my mail, every floor is a last floor during construction. This can be verified by a construction stage analysis. As such reinforcement required for the construction stage governs for end and side columns. Otherwise, specific decentering schemes should be provided which ensures that all the beams in the lower two levels are supported (not repropped) until the current floor is cured.

C.Channakeshava


Subject: [E-CONF] Re: Last floor column design
From: forum@sefindia.org (forum@sefindia.org)
Date: Wed, 28 Nov 2012 21:52:31 +0530
To: econf34289@sefindia.org (econf34289@sefindia.org)

There are two ways - either provide higher reinforcement for top most story column or while analyzing assign top joint as hinged. However by doing so there are chances that the inter story drift for the top most story exceeds the limit. - from Vodafone
From: "vijaydshah"
Date: Wed, 28 Nov 2012 18:18:27 +0530
To:
ReplyTo: econf34289@sefindia.org (econf34289@sefindia.org) (econf34289@sefindia.org (econf34289@sefindia.org))
Subject: [E-CONF] Last floor column design

Dear sefians It has been observed from the experience that for all buildings when we do space frame analysis the reinforcement of the last floor is quite high compared to lower stories . This is specifically for the end columns where moment distribution is not possible due to discontinuity of the columns. Providing this reinforcement through out the height of the building do not justify the economy. Can any one throw light on this subject ?.
vdshah





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mtamil
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PostPosted: Sat Dec 01, 2012 4:16 am    Post subject: Reply with quote

Dear Sirs,

Elsewhere in this thread, it has been mentioned that the corner columns can be considered as hinged. During a recent discussion with one of my senior colleague, I heard similar argument. Is this ok?

Even for a single story building the column sizes working out to  be higher & mainly attributed to biaxial moments in the corner columns.

My argument is that, release of moment(s) at the corner column amount to 100% moment redistribution and moment redistribution is not allowed as per IS:13920.

But in case, shear wall is provided, columns in the plane of the shear wall can be considered as axially loaded. (this is from sefi gen. discussions).

May senior sefians through some light on the above!!

Reagrds
Tamilarasan
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Manoharbs_eq
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PostPosted: Sat Dec 01, 2012 4:25 am    Post subject: Reply with quote

I don't agree with assigning any support to any structural element other than at the bottom @ foundation level. I suggest we should design the structure as it is (A cantilever) above ground.


we have passed the stage where we use to idolize the structure support as simply fixed, pinned or hinge. At this stage we can model the structure nearest to field condition and even soil springs at bottom to consider SSI.


Rgds
Manohar
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gautam chattopadhyay
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PostPosted: Sat Dec 01, 2012 4:54 am    Post subject: Last floor column design Reply with quote

A column will act as hinged or not depends on detailing. If the reinforcements be provided full anchorage length with footing they will act as fixed columns. If hinge detail be deliberately provided, they will act as hinged columns. Russians used to provide hinged columns to reduce moment and horizontal forces on footing. This may not be true for tall buildings. I myself have doubt on generalisation of such provision.

On Sat, Dec 1, 2012 at 9:46 AM, mtamil <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Dear Sirs,

Elsewhere in this thread, it has been mentioned that the corner columns can be considered as hinged. During a recent discussion with one of my senior colleague, I heard similar argument. Is this ok?

Even for a single story building the column sizes working out to be higher & mainly attributed to biaxial moments in the corner columns.

My argument is that, release of moment(s) at the corner column amount to 100% moment redistribution and moment redistribution is not allowed as per IS:13920.

But in case, shear wall is provided, columns in the plane of the shear wall can be considered as axially loaded. (this is from sefi gen. discussions).

May senior sefians through some light on the above!!

Reagrds
Tamilarasan
     



     


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gautam chattopadhyay
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Joined: 17 Feb 2009
Posts: 128

PostPosted: Sat Dec 01, 2012 4:59 am    Post subject: Last floor column design Reply with quote

thanks dr. i shall go through the papers you sent. right now i am quarrelling with concessionaire.  My daily routine. I now enjoy the discussions and webinars since I am now far from design works, mainly on management.


On Fri, Nov 30, 2012 at 9:36 PM, Dr. N. Subramanian <forum@sefindia.org (forum@sefindia.org)> wrote:
[quote]            Dear Er Gautam,

You are welcome!

I am giving below the reference to the construction stage analysis paper. A few more papers should be there in ASCE Structural Div. also

Liu, X.L., H. M. Lee, and W. F. Chen, Analysis of Construction Loads on Slabs and Shores by Personal Computer,     Concrete International
Vol.      10, No. 6, June 1988
Another Ph.D Thesis Abstract (guide Prof. W F Chen) is given below;
Construction loads and load effects in concrete building construction by Mosallam, Khalid Homoud, Ph.D., Purdue University, 1991, 195 pages; AAT 9132480

Summary

The most critical stage of a structure's lifetime is that of construction. Many, perhaps most, construction disasters occur as a result of the failure of temporary structures, and far more disasters occur during construction than after completion of projects. The most serious deficiency in formwork design is in the consideration of lateral loads. Also, a great deal of damage and loss of property during construction are caused by wind. Consequently, determination of load distribution during construction is one of the critical factors in assessing the structural safety during the construction of reinforced concrete structures.

Herein, realistic models of the structure in the construction phase are developed. A practical method to check the slab adequacy during construction is presented. Extensive numerical studies of the distribution of construction loads between multistory framed structures and the shoring and reshoring systems are made, using the computer models developed. A simplified procedure to include the construction live load in the analysis of construction loads is proposed. Furthermore, a simple modification of the popular simplified method for calculating the load distribution during construction is presented. Also, a precise method for assessing wind loads to be used in the design of temporary lateral bracing for open frame buildings is given. Furthermore, a three-dimensional computer model capable of simulating the concrete construction process is developed. The effect of construction process in the analysis of multistory concrete buildings is investigated.

It has been found that the simplified method is adequate for predicting the construction location of the maximum slab and shore loads. However, it generally overestimates the actual load ratios. Furthermore, it is concluded that ACI-347 minimum requirement for horizontal loads can underestimate design wind loads by as much as 50%. It is also found that the effect of lateral loads on the construction load distribution is very small and can be neglected for practical purposes. In addition, it is found that neglecting the construction process in an elastic analysis of multistory buildings leads to a significant error in stresses due to dead loads.

Regards
NS


      gautam chattopadhyay wrote:                Dr. N S has supported my views. Thanks Dr.

On Fri, Nov 30, 2012 at 6:49 PM, Dr. N. Subramanian wrote:
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kapildingare
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PostPosted: Sat Dec 01, 2012 6:30 am    Post subject: Reply with quote

Resp. Dr Channakeshava,

                     Thank you very much for your advice and views on load conditions (.9DL+1.5 EL)

                               Thank you.

                                                         Kapil Dingare
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S.KANTHIMATHINATHAN
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Joined: 09 Jun 2012
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PostPosted: Sat Dec 01, 2012 6:31 am    Post subject: Last floor column design Reply with quote

Dear Sirs,

In my opinion, top of all columns in the top floors can be considered as hinged.

With kind regards,
S.Kanthimathinathan
Structural Engineering Consultant,
Tiruchy Engineering Consultancy House,
1/1-A.Nariyan Street,
Srirangam, Tiruchy-620006
( Courses offered:- Design & Detailing of steel & R.C.C Structures)



Subject: [E-CONF] Re: Last floor column design
From: forum@sefindia.org
Date: Sat, 1 Dec 2012 09:46:13 +0530
To: econf34289@sefindia.org

           Dear Sirs,

Elsewhere in this thread, it has been mentioned that the corner columns can be considered as hinged. During a recent discussion with one of my senior colleague, I heard similar argument. Is this ok?

Even for a single story building the column sizes working out to be higher & mainly attributed to biaxial moments in the corner columns.

My argument is that, release of moment(s) at the corner column amount to 100% moment redistribution and moment redistribution is not allowed as per IS:13920.

But in case, shear wall is provided, columns in the plane of the shear wall can be considered as axially loaded. (this is from sefi gen. discussions).

May senior sefians through some light on the above!!

Reagrds
Tamilarasan

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mtamil
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PostPosted: Sat Dec 01, 2012 6:48 am    Post subject: Reply with quote

Dear Manohar

I have used "Hinged" in the sense, 100% moment released and not a hinged support. No way!!.

Can you pl. share your opinion with this correction!!

regards
tamilarasan



Manoharbs_eq wrote:
I don't agree with assigning any support to any structural element other than at the bottom @ foundation level. I suggest we should design the structure as it is (A cantilever) above ground.


we have passed the stage where we use to idolize the structure support as simply fixed, pinned or hinge. At this stage we can model the structure nearest to field condition and even soil springs at bottom to consider SSI.


Rgds
Manohar
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