www.sefindia.org

STRUCTURAL ENGINEERING FORUM OF INDIA [SEFI]

 Forum SubscriptionsSubscriptions DigestDigest Preferences   FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups  RegisterRegister FAQSecurity Tips FAQDonate
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log in to websiteLog in to websiteLog in to websiteLog in to forum 
Warning: Make sure you scan the downloaded attachment with updated antivirus tools  before opening them. They may contain viruses.
Use online scanners
here and here to upload downloaded attachment to check for safety.

Why do we oly consider service loads while designing footing

 
Post new topicReply to topic    www.sefindia.org Forum Index -> Freshers' Zone
View previous topic :: View next topic  
Author Message
Siddhartha_Balakrishnan
SEFI Member
SEFI Member


Joined: 11 Nov 2014
Posts: 1

PostPosted: Wed Nov 12, 2014 4:19 pm    Post subject: Why do we oly consider service loads while designing footing Reply with quote

While designing footings we consider the service load combinations whereas while designing a beam or column we take factored load combinations ?? I am also confused about why we must consider service load combinations ( limit state of servicibility ex: 1.2D.L +0.9L.L) when we are applying bigger factors like 1.5D.L + 1.5L.L ( limit state of collapse ) ?? It is our choice between how safe and how economic design we want  ??
Back to top
View user's profile Send private message
stharish
SEFI Member
SEFI Member


Joined: 20 Aug 2010
Posts: 5

PostPosted: Sun Aug 09, 2015 1:24 am    Post subject: Service loads used to determine bearing capacity Reply with quote

Factored loads need to be considered for the design of footings, base plates, punching shears and for providing reinforcement.

Only for bearing stress you consider allowable loads. This is because...

Geotechnical engineer provides you allowable bearing capacity. In USA, a safety factor of 4 is provided for soil bearing stresses i.e. Ultimate bearing stress / allowable bearing stress = 4.


Regards,
Harish


Last edited by stharish on Sun Aug 09, 2015 12:47 pm; edited 1 time in total
Back to top
View user's profile Send private message
B.V.Harsoda
General Sponsor
General Sponsor


Joined: 19 Jan 2009
Posts: 2329
Location: RAJKOT,GUJARAT, INDIA

PostPosted: Sun Aug 09, 2015 4:17 am    Post subject: Re: Service loads used to determine bearing capacity Reply with quote

Your explanation is correct, I agree with you. In India factor of safety 3 is taken to calculate the  S.B.C. of soil.


stharish wrote:
Factored loads need to be considered for the design of footings, base plates, punching shears, and providing reinforcement.

Only for bearing stress you consider allowable loads. This is because...

Geotechnical engineer provides you allowable bearing capacity. In USA, a safety factor of 4 is provided for soil bearing stresses i.e. Ultimate bearing stress / allowable bearing stress = 4.


Regards,
Harish
Back to top
View user's profile Send private message
Zia
SEFI Regulars
SEFI Regulars


Joined: 28 May 2015
Posts: 33

PostPosted: Mon Aug 10, 2015 6:45 am    Post subject: Reply with quote

Hi Siddhartha,

You can also use limit stage design for the geotechnical design of footings.  

In the strength limit state design, the geotechnical design strength taken as a geotechnical strength reduction factor times the ultimate geotechnical design strength shall be greater than the ultimate loads (i.e. design action effect).  The geotechnical strength reduction factor depends on a number of factors and can range from 0.4 to 0.8.

Similarly in the serviceability limit state design, a suitable modulus reduction factor can be used in calculating settlements of footings for serviceability loads.

Regards,
Zia
Back to top
View user's profile Send private message
es_jayakumar
General Sponsor
General Sponsor


Joined: 24 Nov 2011
Posts: 1408
Location: Cochin

PostPosted: Sun Oct 10, 2021 2:04 am    Post subject: Reply with quote

In continuation to the comments by Er.Zia, an article of me on the "Geotechnical Design of Foundations by LSD" published in the current CE&CR Magazine (excerpt attached) is expected to throw more light on this topic.

E S Jayakumar



Warning: Make sure you scan the downloaded attachment with updated antivirus tools  before opening them. They may contain viruses.
Use online scanners
here and here to upload downloaded attachment to check for safety.
Article.pdf
 Description:

Download
 Filename:  Article.pdf
 Filesize:  164.56 KB
 Downloaded:  1300 Time(s)

Back to top
View user's profile Send private message
vikram.jeet
General Sponsor
General Sponsor


Joined: 26 Jan 2003
Posts: 3835

PostPosted: Sun Oct 10, 2021 2:56 am    Post subject: Reply with quote

The FOS for bearing strata (soil/rock) is higher  since :
Testing is done at  few locations , it is not done at each foundation location.
Heterogeneous nature of soil /rocks
Water table assessment is at time of testing
In small projects SBC is either taken from nearby sites OR even assumed
Pressure bulb beneath footing depends upon nature of  bearing (strata type /rock )as also foundation system. But in design uniform
pressure is taken under foundation ,for working out bearing area.


Therefore , I think , in terms of Limit stage , The load factor for foundation bearing area requirement is 3.0 or  2.5  as per soil. Whereas Load Factor for structure design of structural components is about half since  heterogeneity and other  factors are not imperative in structure work.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topicReply to topic    www.sefindia.org Forum Index -> Freshers' Zone All times are GMT
Page 1 of 1

 

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


© 2003, 2008 SEFINDIA, Indian Domain Registration
Publishing or acceptance of an advertisement is neither a guarantee nor endorsement of the advertiser's product or service. advertisement policy