STRUCTURAL ENGINEERING FORUM OF INDIA [SEFI]

vaisakhg · Posted: Mon Dec 22, 2008 7:28 amPost subject: Moment transfer columns to slabs

Sir,
I came across a confusion whether the moment transfer from slabs to columns is to be considered in case of checking the punching shear. In usual practice, as i know, only the axial load is considered. But from literatre, i came across the fact that some portion of the moment is transfered by the eccentricity of shear. if that is the case that had to be added to the shear stress. Can you please give me a guidance?
Yours truly,

Vaisakh G
+971 50 6844981

Posted via Email

pankajgrai at gmail.com · Guest

Dear Vaisakh,

According to me best solution is to design Column strip as an foundation and apply all the checks.

On Mon, Dec 22, 2008 at 1:36 PM, vaisakhg forum@www.buonovino.com)> wrote:

sahi · SEFI Member Joined: 02 Oct 2008 Posts: 4

ADD to shear as you said. At least it will be conservative.

On 12/22/08, vaisakhg wrote:

rahulganguli29 · ... Joined: 10 Dec 2008 Posts: 63 Location: Kolkata

Dear Vaisakh,
Actually, if you considered the slab as beam, (since both are flexure member) so as per laws of equilibrium, the beam moment should equalise by coloumn in case of both are riigid together. Therefore this moment should be considered to design coloumn. Again on the other hand compressive load on coloumn should not act in center of coloumn cross section properly, distance between acting position of load and c.g. of coloumn is called ecentricity, and a moment is induced on coloumn due to this ecentricity. If you considered a free body diagram of this moment performance, you can understand this much better.

- Rahul

On Mon, Dec 22, 2008 at 1:36 PM, vaisakhg forum@www.buonovino.com)> wrote:

vaisakhg · Posted: Tue Dec 23, 2008 7:31 amPost subject: Moment transfer columns to slabs

Dear Sefians,

My question is not about the moment that is caused in the columns by the eccentricity of loads. But it was about the transfer of unbalanced moments at the slab - column intersection. I had seen in literature and in ACI 318-05 about this. It is said that arround 40% of the unbalanced moment is transfered by the eccentricity of shear, which means the shear stress at the critical section is the sum due to the normal punching shear and the extra stresses said above.

This was exactly my question.
Yours truly,

Vaisakh G
+971 50 6844981

On Tue, Dec 23, 2008 at 11:06 AM, rahulganguli29 forum@www.buonovino.com)> wrote:
[quote] Dear Vaisakh,
Actually, if you considered the slab as beam, (since both are flexure member) so as per laws of equilibrium, the beam moment should equalise by coloumn in case of both are riigid together. Therefore this moment should be considered to design coloumn. Again on the other hand compressive load on coloumn should not act in center of coloumn cross section properly, distance between acting position of load and c.g. of coloumn is called ecentricity, and a moment is induced on coloumn due to this ecentricity. If you considered a free body diagram of this moment performance, you can understand this much better.

- Rahul

On Mon, Dec 22, 2008 at 1:36 PM, vaisakhgforum@www.buonovino.com(forum@www.buonovino.com))> wrote:
--auto removed--

Posted via Email

naveen · Posted: Wed Dec 24, 2008 5:13 amPost subject: Moment transfer columns to slabs

Dear Mr. Vaisakh, Please refer " Reinforced Concrete : Mechanics and Design- James G. Macgregor" . This topic has been dealt in this book by neat sketches.

Regards
Naveen.

On Tue, Dec 23, 2008 at 1:30 PM, vaisakhg forum@www.buonovino.com)> wrote:

ksant26 · SEFI Member Joined: 03 Jun 2008 Posts: 1

Dear all,

Yes we do required to transfer unbalanced bending moments in columns by taking care of punching shear. Please do refer CP110 for the formulation of punching shear check, as indian code is very silent on it. This is perhaps very critical check most of the engineer do forgot to check.

I like to ask all of you guys.
DO FLAT SLAB TAKES PARTICIPATION IN TRANSFERING SEISMIC LOADS?
IF YES ARE WE DESIGNING FOR THE SAME.
METHOD OF DISTRIBUTION OF FORCES AS PER STIFNNES OF MEMBERS TRANSFERS HEAVY FORCES ON SHEAR WALLS, AND THE COLUMNS JUST ACTS AS A PROPED ONE,. FOR HOW MUCH ACCURACY THIS PHENOMENON IS VALID?

CORRECT ME IF I'M WRONG.
AS PER MY THINKING GOES, EVERY FLOOR SLAB TRANSFER LOAD ON COLUMNS ON WHICH IT IS RESTING. SO THERE IS TRANSFER OF BENDING MOMENTS ALSO APART FROM VERTICAL LOAD. FLAT SLAB ALSO TAKE PART IN TRANSFERING LATERAL LOADS, I.E SHEAR AND BENDING MOMENTS. WE REQUIRED TO CHECK FOR THE SAME WHILE DESIGNING. AS MOST OF THE CONSULTANTS DESIGN THE FLAT SLAB ONLY FOR VERTICAL LOADS AND NOT FOR LATERAL LOADS.

THE POST TENSIONING FIRMS ALSO DESGIN SLABS FOR VERTICAL LOAD.
WE REQUIRED TO TRANSFER MOMENTS CONTOURS TO THEM FROM ETABS OR SIMILAR SOFTWARES TO ACCOMMODATE LATER FORCES OR CRTICAL BENDING MOMENTS AND SHEEAR.

REGARDS
SANTOSH KADAM

--- OnTue, 12/23/08, naveenwrote:
[quote]
From: naveen
Subject: [ECONF] Re: Moment transfer columns to slabs
To:econf@www.buonovino.com
Date: Tuesday, December 23, 2008, 9:40 PM

Dear Mr. Vaisakh, Please refer " Reinforced Concrete : Mechanics and Design- James G. Macgregor" . This topic has been dealt in this book by neat sketches.

Regards
Naveen.

On Tue, Dec 23, 2008 at 1:30 PM, vaisakhgforum@www.buonovino.com)> wrote:
--auto removed--

Posted via Email

Kedar · Posted: Sun Dec 28, 2008 3:22 pmPost subject:

Hi

Vaisakhg

你能请分享参考资料吗m where u got
info regarding moment in column due to shear?for PT slab.

regards
Kedar

ibarua · General Sponsor Joined: 26 Jan 2003 Posts: 1039

30 Dec 2008

For Mr Kedar:

You can get details in RCC Design Handbook by Mark Fintel & others. But do use the formulae given in IS:456 rather than those given in the ACI Code. You can easily write a spreadsheet to solve your problem.

Happy New Year.

Indrajit Barua.
On Sun, 28 Dec 2008 Kedar wrote :

vaisakhg · Posted: Tue Dec 30, 2008 1:40 pmPost subject: Moment transfer columns to slabs

it is there in ACI 318-05
but i was not talking about the moment caused by shear but about the moment transfer between slabs and columns.
Also it is in referance to flat slab in general and not in particular referance to PT slabs
Yours truly,

Vaisakh G
http://vaisakhg.googlepages.com
http://www.orkut.com/Profile.aspx?uid=7580923768115555776
+971 50 6844981

On Sun, Dec 28, 2008 at 7:22 PM, Kedar forum@www.buonovino.com)> wrote: