STRUCTURAL ENGINEERING FORUM OF INDIA [SEFI]

sathyace · ... Joined: 04 Jun 2011 Posts: 78

Hi All,

How to calculate the punching shear in eccentric footing(column located at the edge) ?

Please refer the attachment and clarify how the punching shear behaviour in plan-1 & plan-2 footing?

Thank you.

Regards,
Sathya.

es_jayakumar · Posted: Fri Oct 25, 2019 9:29 am Post subject:

First of all, edge or corner columns on an isolated footing is theoretically unstable, as soil will develop tension on the farther side. Hence the proposed arrangement is never advisable to adopt.
For academic interest : In the first case, there is a stiffener beam. Hence, there will be no punching action. In the 2nd case, the punching shear will act at d/2 from the face of the column. The attached Work sheet will be handy for calculations in this connection.

E S Jayakumar

sathyace · ... Joined: 04 Jun 2011 Posts: 78

Thank you sir for the valuable reply.

Practically,we get both case of eccentric footing since the column has to be placed on the site boundary or closer to site boundary.

In this case,if we do not provide the stiffner beam how do we design the eccentric footing in first case?Also, how to design the second case eccentric footing?

Is it advisable to provide strap beam in eccentric footing and connect to the near by isolated footing? Please refer the attachment.

Kindly clarify which is the efficient method to design both case eccentric footing

Sathya.

es_jayakumar · Posted: Sat Oct 26, 2019 4:21 am Post subject:

You are welcome, Er. Sathya.... You have found the solution on your own ! Strap footing or Combined footing is the solution. Never attempt the proposals you had envisaged earlier, which is atrocious, at least theoretically !

E S Jayakumar

es_jayakumar · Posted: Sat Oct 26, 2019 7:27 am Post subject:

I wish to add that, in the 2nd case, you make a strap / combined footing by combining the column existing in the diagonal direction, if it is a must that the column has to rest on the corner of the footing..

E S Jayakumar

sathyace · ... Joined: 04 Jun 2011 Posts: 78

Thank you sir,

Now clearly understood the concept.

Analysed the strap beam as simply supported beam, here i have attached the strap beam staad file for reference.

Kindly check and let me know if any corrections.

Thank you.
Sathya.

es_jayakumar · Posted: Sat Oct 26, 2019 2:52 pm Post subject:

This is not the method to analyse Strap footings. You can refer books "Design of Reinforced Concrete Foundation" by Varghese (contains a number different cases / examples) or "Design of Reinforced Concrete Structures" by Gambhir, for guidance. If the distance of the column in question to the adjacent column is not much, you can better go for a combined footing.

E S Jayakumar

sathyace · ... Joined: 04 Jun 2011 Posts: 78

Thank you sir.I will refer those books.

Regards,
Sathya.