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Top and bottom reinforcement in isolated footing
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logeshcivil
SEFI Member
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Joined: 07 Aug 2017
Posts: 10
Location: Coimbatore

PostPosted: Fri Aug 10, 2018 11:10 am    Post subject: Design of bi axially loaded isolated footing Reply with quote

Hello sefians

i have a huge problem while deigning an isolate footing.I received the horizontal and vertical reactions for a PEB structure which is resting on a RCC column. I have a formed a 2D frame of the structure for calculating the reactions and moments at the bottom node.

The reactions are
x = 0
y = 484 kN
z = -501 kN

The moment are

x= 0
y = 3257 kNm
z = 26.59 kNm

Here in this the moment is predominant and so the minimum bearing pressure is negative. So please help me in solving the problem

Thank You in advance

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Logesh
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sakumar79
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Joined: 18 Apr 2008
Posts: 663

PostPosted: Fri Aug 10, 2018 1:17 pm    Post subject: Reply with quote

Dear Sir,
    When you have large horizontal force at base of PEB structure, you can consider a plinth beam along the force direction and two stub columns at either end with a pedestal for the PEB stanchion at the centre. This will make it into a Portal structure. The moment will cause an uplift to one column and downward force in the other but the force will reduce as you increase the distance between the two columns.

Yours sincerely
S Arunkumar
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logeshcivil
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Joined: 07 Aug 2017
Posts: 10
Location: Coimbatore

PostPosted: Sat Aug 11, 2018 4:09 am    Post subject: Design of bi axially loaded isolated footing Reply with quote

Dear Arun Kumar,
Thank you for your suggestion.

If i were to do as your suggestion I have to provide plinth beam along the direction of horizontal force which is 50 m, which i think is not economical.Is there any other solution.

I hove also few more doubts.


  1. How do i calculate loss of contact area if minimum bearing pressure is negative and also eccentricity is outside the footing.
  2. Can i omit negative bearing pressure and proceed the calculation with positive bearing pressure only.If not , then please suggest me a solution.


I have attached a picture for you reference.
Thanks in advance


sakumar79 wrote:
Dear Sir,
    When you have large horizontal force at base of PEB structure, you can consider a plinth beam along the force direction and two stub columns at either end with a pedestal for the PEB stanchion at the centre. This will make it into a Portal structure. The moment will cause an uplift to one column and downward force in the other but the force will reduce as you increase the distance between the two columns.

Yours sincerely
S Arunkumar



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Logesh
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sakumar79
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Joined: 18 Apr 2008
Posts: 663

PostPosted: Sat Aug 11, 2018 7:27 am    Post subject: Reply with quote

Dear Er Logesh,
   I think you misunderstand me. I am not talking about a 50 m long Plinth Beam. I am talking about a Plinth Beam may be 3 to 5 m long depending on your forces (half inside and half outside the building). This will be somewhat similar to a Two Pile Pilecap system.

Hope that helps,
Arunkumar
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Jayant Lakhlani
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Joined: 26 Jan 2003
Posts: 190
Location: Rajkot, Gujarat, India

PostPosted: Sat Aug 11, 2018 7:30 am    Post subject: Top and bottom reinforcement in isolated footing Reply with quote

Dear Logesh

There seems to be something wrong with magnitude of Y moment, i.e. 3257 kN-m. Suggest to review the analysis.

Regards.

Jayant Lakhlani
For
Lakhlani Associates


From: logeshcivil [mailto:forum@sefindia.org]
Sent: 10 August 2018 16:41
To: general@sefindia.org
Subject: [SEFI] Re: Top and bottom reinforcement in isolated footing



Hello sefians

i have a huge problem while deigning an isolate footing.I received the horizontal and vertical reactions for a PEB structure which is resting on a RCC column. I have a formed a 2D frame of the structure for calculating the reactions and moments at the bottom node.

The reactions are
x = 0
y = 484 kN
z = -501 kN

The moment are

x= 0
y = 3257 kNm
z = 26.59 kNm

Here in this the moment is predominant and so the minimum bearing pressure is negative. So please help me in solving the problem

Thank You in advance




Yours
Logesh

Posted via Email



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snsdec
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Joined: 07 Aug 2010
Posts: 1

PostPosted: Sat Aug 11, 2018 8:30 am    Post subject: Top and bottom reinforcement in isolated footing Reply with quote

Dear logesh,




Pl check moment y I think something wrong in analysis


Thanks

On Sat 11 Aug, 2018, 1:14 PM Jayant Lakhlani, <forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
           Dear Logesh

There seems to be something wrong with magnitude of Y moment, i.e. 3257 kN-m. Suggest to review the analysis.

Regards.

Jayant Lakhlani
For
Lakhlani Associates


From: logeshcivil [mailto:forum@sefindia.org (forum@sefindia.org)]
Sent: 10 August 2018 16:41
To: general@sefindia.org (general@sefindia.org)
Subject: [SEFI] Re: Top and bottom reinforcement in isolated footing



Hello sefians

i have a huge problem while deigning an isolate footing.I received the horizontal and vertical reactions for a PEB structure which is resting on a RCC column. I have a formed a 2D frame of the structure for calculating the reactions and moments at the bottom node.

The reactions are
x = 0
y = 484 kN
z = -501 kN

The moment are

x= 0
y = 3257 kNm
z = 26.59 kNm

Here in this the moment is predominant and so the minimum bearing pressure is negative. So please help me in solving the problem

Thank You in advance




Yours
Logesh
     



     
Download Attachments:
~WRD000.jpg





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perumal12379
SEFI Member
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Joined: 05 Mar 2017
Posts: 2

PostPosted: Sat Aug 11, 2018 8:30 am    Post subject: Top and bottom reinforcement in isolated footing Reply with quote

While designing the single frame, if you are using staad then analysis in plane not in space.

On Sat, Aug 11, 2018 at 10:43 AM, Jayant Lakhlani <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Dear Logesh

There seems to be something wrong with magnitude of Y moment, i.e. 3257 kN-m. Suggest to review the analysis.

Regards.

Jayant Lakhlani
For
Lakhlani Associates


From: logeshcivil [mailto:forum@sefindia.org (forum@sefindia.org)]
Sent: 10 August 2018 16:41
To: general@sefindia.org (general@sefindia.org)
Subject: [SEFI] Re: Top and bottom reinforcement in isolated footing



Hello sefians

i have a huge problem while deigning an isolate footing.I received the horizontal and vertical reactions for a PEB structure which is resting on a RCC column. I have a formed a 2D frame of the structure for calculating the reactions and moments at the bottom node.

The reactions are
x = 0
y = 484 kN
z = -501 kN

The moment are

x= 0
y = 3257 kNm
z = 26.59 kNm

Here in this the moment is predominant and so the minimum bearing pressure is negative. So please help me in solving the problem

Thank You in advance




Yours
Logesh
     



     
Download Attachments:
~WRD000.jpg





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nimal ranasinghe
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Joined: 27 May 2009
Posts: 3

PostPosted: Sat Aug 11, 2018 8:30 am    Post subject: Top and bottom reinforcement in isolated footing Reply with quote

Unless the column is fully cantilevered and having a eccentric crane girder fixed with a heavy pay load this moment is unrealistic. Kindly check your 2D model and assumptions for the connectivity and cross check with a manual calculation with simple distribution coefficients

Nimal

Sent from my iPhone

On Aug 11, 2018, at 1:13 PM, Jayant Lakhlani <forum@sefindia.org (forum@sefindia.org)> wrote:


Quote:
           Dear Logesh

There seems to be something wrong with magnitude of Y moment, i.e. 3257 kN-m. Suggest to review the analysis.

Regards.

Jayant Lakhlani
For
Lakhlani Associates


From: logeshcivil [mailto:forum@sefindia.org (forum@sefindia.org)]
Sent: 10 August 2018 16:41
To: general@sefindia.org (general@sefindia.org)
Subject: [SEFI] Re: Top and bottom reinforcement in isolated footing



Hello sefians

i have a huge problem while deigning an isolate footing.I received the horizontal and vertical reactions for a PEB structure which is resting on a RCC column. I have a formed a 2D frame of the structure for calculating the reactions and moments at the bottom node.

The reactions are
x = 0
y = 484 kN
z = -501 kN

The moment are

x= 0
y = 3257 kNm
z = 26.59 kNm

Here in this the moment is predominant and so the minimum bearing pressure is negative. So please help me in solving the problem

Thank You in advance




Yours
Logesh
     



     
Download Attachments:
~WRD000.jpg





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Solanki Dimpesh
SEFI Member
SEFI Member


Joined: 10 Apr 2018
Posts: 1

PostPosted: Sat Aug 11, 2018 8:30 am    Post subject: Top and bottom reinforcement in isolated footing Reply with quote

Hello sir, As PEB are long free span frame structure. The moment at bottom of the column will be very much because of lateral load and high eave height. This is the reason why designer use pin connection instead of fixed connection, which reduce the foundation size. My suggestion would be to use pin support.


Then design the base plate and column pedestal using reactions. The isolated foundation will then have moment because of Fx & Fz and different in level.
















Regards - 
Dimpesh Solanki
+91 9987443194
Techniqes, Mumbai.


On Sat 11 Aug, 2018, 1:16 PM Jayant Lakhlani, <forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
           Dear Logesh

There seems to be something wrong with magnitude of Y moment, i.e. 3257 kN-m. Suggest to review the analysis.

Regards.

Jayant Lakhlani
For
Lakhlani Associates


From: logeshcivil [mailto:forum@sefindia.org (forum@sefindia.org)]
Sent: 10 August 2018 16:41
To: general@sefindia.org (general@sefindia.org)
Subject: [SEFI] Re: Top and bottom reinforcement in isolated footing



Hello sefians

i have a huge problem while deigning an isolate footing.I received the horizontal and vertical reactions for a PEB structure which is resting on a RCC column. I have a formed a 2D frame of the structure for calculating the reactions and moments at the bottom node.

The reactions are
x = 0
y = 484 kN
z = -501 kN

The moment are

x= 0
y = 3257 kNm
z = 26.59 kNm

Here in this the moment is predominant and so the minimum bearing pressure is negative. So please help me in solving the problem

Thank You in advance




Yours
Logesh
     



     
Download Attachments:
~WRD000.jpg





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devendrarathi
SEFI Member
SEFI Member


Joined: 12 Sep 2012
Posts: 3

PostPosted: Sat Aug 11, 2018 8:30 am    Post subject: Top and bottom reinforcement in isolated footing Reply with quote

Please share the staad file so that we can identify if there is any mistake n staad 

On Sat 11 Aug, 2018, 13:15 Jayant Lakhlani, <forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
           Dear Logesh

There seems to be something wrong with magnitude of Y moment, i.e. 3257 kN-m. Suggest to review the analysis.

Regards.

Jayant Lakhlani
For
Lakhlani Associates


From: logeshcivil [mailto:forum@sefindia.org (forum@sefindia.org)]
Sent: 10 August 2018 16:41
To: general@sefindia.org (general@sefindia.org)
Subject: [SEFI] Re: Top and bottom reinforcement in isolated footing



Hello sefians

i have a huge problem while deigning an isolate footing.I received the horizontal and vertical reactions for a PEB structure which is resting on a RCC column. I have a formed a 2D frame of the structure for calculating the reactions and moments at the bottom node.

The reactions are
x = 0
y = 484 kN
z = -501 kN

The moment are

x= 0
y = 3257 kNm
z = 26.59 kNm

Here in this the moment is predominant and so the minimum bearing pressure is negative. So please help me in solving the problem

Thank You in advance




Yours
Logesh
     



     
Download Attachments:
~WRD000.jpg





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