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Top and bottom reinforcement in isolated footing
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yusushah
SEFI Member
SEFI Member


Joined: 25 Jun 2018
Posts: 1

PostPosted: Sat Aug 11, 2018 9:30 am    Post subject: Top and bottom reinforcement in isolated footing Reply with quote

Dear All
Usually the base condition for PEB rafter over RCC column is pinned at one end and roller at the other
Please discuss with your supplier to check the design and revert.
Yusuf
From: Jayant Lakhlani <forum@sefindia.org>
Sent: Saturday, August 11, 2018 1:13 PM
To: general@sefindia.org
Subject: [SEFI] Re: Top and bottom reinforcement in isolated footing  

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 (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





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rakeshhumty
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Joined: 25 Aug 2014
Posts: 1

PostPosted: Sat Aug 11, 2018 9:30 am    Post subject: Top and bottom reinforcement in isolated footing Reply with quote

Review your loads which you have assigned..


Regards
Rakesh Kalburgi
Structural consultant

On 11 Aug 2018 1:15 p.m., "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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logeshcivil
SEFI Member
SEFI Member


Joined: 07 Aug 2017
Posts: 16
Location: Coimbatore

PostPosted: Sat Aug 11, 2018 2:30 pm    Post subject: Top and bottom reinforcement in isolated footing Reply with quote

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sachinselot
SEFI Member
SEFI Member


Joined: 24 Aug 2012
Posts: 3

PostPosted: Sat Aug 11, 2018 2:30 pm    Post subject: Top and bottom reinforcement in isolated footing Reply with quote

Dear logesh, Review the analysis once again, somewhere major error.


On Sat 11 Aug, 2018, 1:15 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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sangeeta_wij
...
...


Joined: 21 Apr 2016
Posts: 51

PostPosted: Sun Aug 12, 2018 8:30 am    Post subject: Top and bottom reinforcement in isolated footing Reply with quote

You may use a pin connection only if the drift on top is in permissible limits; usually for large spans and large height structures, this maynot be a good idea as the displacements on top maybe very high in wind load combinations. Besides, if you use a Pin joint, the connection has to be designed carefully so that it stays a Pin and does behave like one.




Best Regards
Sangeeta Wij
President,WISE India
Managing Partner
SD Engineering Consultants LLP
Vice President(North),Indian Association of Structural Engineers,
Fellow and Chartered Engineer, Institution of Engineers
H333 New Rajinder Nagar(Lower Ground Floor),
New Delhi-110060
Ph:9811776210;01145128530


From: Solanki Dimpesh [mailto:forum@sefindia.org]
Sent: 11 August 2018 19:39
To: general@sefindia.org
Subject: [SEFI] Re: Top and bottom reinforcement in isolated footing



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:
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saikiran gone
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Joined: 22 Apr 2016
Posts: 217

PostPosted: Sun Aug 12, 2018 11:36 am    Post subject: Re: Top and bottom reinforcement in isolated footing Reply with quote

suresh_sharma wrote:
To all Sefians

From the design consideration bottom reinforcement is worked out by
the designer for RCC isolated footing. I have observed from the design of
some designers and I too am practising to provide some reinforcement
in the top layer of the isolated footing say 0.12% of the section
distribted both ways. In almost all the design books the top layer of
the footing is shown as inclined. But I do not favour this approach as
it becomes difficult to vibrate the concrete in inclined state.
Further the RMC having higher slump will flow away in course of
vibration from the inclined surface.My senior is asking me to convince
him about the top layer of reinforcement. My feeling is that it is
very difficult to predict the exact behavior of footing, hence it is
advisable to provide minimum reinforcement in the top layer too so
that entire footing behaves as one unit of concrete. I seek your help
in this regard to enable me to convince my senior with adequate
justification.



Hi Suresh,

I addition to below many valued points , I add one more point . The top reinforcement in isolated footing is provided to take care of temperature stresses.

Regards,
Saikiran Gone.
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logeshcivil
SEFI Member
SEFI Member


Joined: 07 Aug 2017
Posts: 16
Location: Coimbatore

PostPosted: Mon Aug 13, 2018 8:29 am    Post subject: Design of bi axially loaded isolated footing Reply with quote

Dear all

We have designed the column and footing using pinned support.

Thank you all for your valuable suggestion and advice.

Thank you one again

_________________
Yours
Er. S.Logesh
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Dr. N. Subramanian
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General Sponsor


Joined: 21 Feb 2008
Posts: 5299
Location: Gaithersburg, MD, U.S.A.

PostPosted: Tue Aug 14, 2018 4:04 am    Post subject: Re: Top and bottom reinforcement in isolated footing Reply with quote

I agree with the views expressed by Er Sangeeta Wij!

Regards
NS
sangeeta_wij wrote:
You may use a pin connection only if the drift on top is in permissible limits; usually for large spans and large height structures, this may not be a good idea as the displacements on top maybe very high in wind load combinations. Besides, if you use a Pin joint, the connection has to be designed carefully so that it stays a Pin and does behave like one.




Best Regards
Sangeeta Wij
President,WISE India
Managing Partner
SD Engineering Consultants LLP
Vice President(North),Indian Association of Structural Engineers,
Fellow and Chartered Engineer, Institution of Engineers
H333 New Rajinder Nagar(Lower Ground Floor),
New Delhi-110060
Ph:9811776210;01145128530


From: Solanki Dimpesh [mailto:forum@sefindia.org]
Sent: 11 August 2018 19:39
To: general@sefindia.org
Subject: [SEFI] Re: Top and bottom reinforcement in isolated footing



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:
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