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Daily Digest Tue Nov 25 23:00:02 2003

This forum is locked: you cannot post, reply to, or edit topics.This topic is locked: you cannot edit posts or make replies.    www.sefindia.org Forum Index -> Past Discussions Year 2003
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SEFI Member
SEFI Member

Joined: 26 Jan 2003
Posts: 7

PostPosted: Wed Nov 26, 2003 11:58 am    Post subject: Daily Digest Tue Nov 25 23:00:02 2003 Reply with quote

Dear Mr.Rajendra,
If the footing is two or more Piles, combined footing/raft or if the soil is Rock the boundary condition is taken as fixed. For individual footing on compressible soil the boundary condition is to be taken as hinged. It is because of the
rotation of the foundation due to the compressible soil(see for full discussion of this in French,S.E., Introduction to Soil Mechanics and Shallow foundations Design, Prentice Hall pp.187-197 which also gives methods to find degree of fixity
at the base of the column). As stated by Mr.Abhyankar, if the soil has medium compressibility(in between Rock and soft soil), you may have to consider soil structure interaction by considering soil stiffness by means of soil springs. But it
requires soil data which are normally not found in soil reports! The above idealization is not onlt valid for STAAD but for any analysis. In the draft IS 800, we have included such guidelines for the benefit of designers(also see Draft IS

general@sefindia.org wrote:

From: ABHYANKAR@hccindia.co.in
Subject: Answer to query raised by Mr. Rajendra about STAAD-support condit      ion
Date: 25/11/03
Time: 09:09:37
To, Mr. Rajedra,

In STAAD analysis the results vary as per the support condition i.e. fixed
or pinned. But to specify the type of support for any base of the column one
must know the following data:
1) Type of soil at the site - sandy / clayee or rock
2) Type of foundation system - Raft / Isolated footing / Pile foundations

Usually for very tall buildings, structural engineers require pile
foundation (subject to type of strata). Even the piles are classified as -
flexible / rigid. Based on this data one may define the support condition.
But in practice hardly one get the above data. Hence he may proceed with
'FIXED' support condition in case of pile foundations.

In case of Isolated footing if it is to be designed for axial load in
addition to the bi-axial moments then the size required may be higher. Hence
there is a tendency to reduce down the design moment on the isolated
footing. The lower design moments are obtained by specifying the support as
'PINEED'. You question that are we designing the footing as unsafe. The
answer is 'NO' because when we define the isolated footing as 'PINNED' the
same time the design moments in the column increase than the 'FIXED'
condition. Thus the overall safety is unaffected.

Note that this whole process is a matter of 'PROPER JUDGEMENT AND
EXPERINCE'. While seating in office we may not be able to do this task
correctly. Hence in case of important projects we must consult

In case of flexible strata ; flexible footings one may have to go for
'SPRING' type of footing. The results are very sensitive to the type of

V. G. Abhyankar
(Design Engineer-HCC)

From: Rajendar
To: admin@sefindia.org
Sent: 24 November, 2003 10:17 AM


How can  have to give support conditions for multistoried buildings(Fixed or
hinged) at footing and column joint,using STAAD Analysis.please give reply
any one knows, because I am new for STAAD.


Hindustan Construction Company, Mumbai, India
Sent using PostMaster by QuantumLink Communications Pvt Ltd


From: rajeshpatnaik2001@yahoo.co.in
Subject: Searles Spiral
Date: 25/11/03
Time: 09:43:07
Does anybody has any information regarding Searles Spiral (calculating method, construction procedure,...) . It is an old surveying technique used in railroad surveying in which a spiral is aproximated by curved segments.
Rajesh patnaik


From: mutyalanaidu@rediffmail.com
Subject: doubt
Date: 25/11/03
Time: 19:48:46

Respected sirs,
I have few doubts, plz clarify them
1) why do we prefer hyperbolic shape to the cooling towers? why not other
2) while designing a r.c.c beam if we get the reinforcement calculated is less than the minimum we will provide minimum reinforcement, my question will it not become over reinforced as we are providing more reinforcement than the required?
3)What is the cretria to be followed to determine the height of the truss in industrial buildings? some the books giving span/5 or some thing if so what is the technical explanation behind it?



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