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.

Modification factor for slab deflection check

 
Post new topicReply to topic Thank Post    www.sefindia.org Forum Index -> SEFI General Discussion
View previous topic :: View next topic  
Author Message
Vignesh_Aravinthan
SEFI Member
SEFI Member


Joined: 25 Jun 2015
Posts: 3

PostPosted: Fri Jun 04, 2021 7:08 am    Post subject: Modification factor for slab deflection check Reply with quote

Hi, I am designing a two way slab and while checking for the deflection I need to calculate the modification factor to take in to account the effect of tension reinforcement on L/d ratio. For which I am getting following values,
fs = 117
Pt = 0.36%
But I am confused on how much should be the modification factore used as shown in Fig 4 of IS 456:2000.
Should I take it as 2 or 0?
What is the meaning of the curve which ends much near to 0.8% tension reinforcement?
Back to top
View user's profile Send private message
vikram.jeet
General Sponsor
General Sponsor


Joined: 26 Jan 2003
Posts: 2760

PostPosted: Fri Jun 04, 2021 8:04 am    Post subject: Reply with quote

Dear Er

For Deflection check , the load factor is 1.0.

However Tension steel is provided in the slab based on Load Factor of 1.5.

Therefore equivalent tension steel at load factor 1.0 needs to be worked  based on M/bd2 using working moment , thereby taking Load factorFas  1.0. The corresponding steel % pt to be seen from table . This steel % to be used in working out deflection.
Otherwise % steel provided in slab can be directly divided by 1.5 , to arrive at  steel % for Deflection calcs.under Load Factor 1.0.

This is my personal opinion and to be ignored if not directly related to yr querryquery.


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


Joined: 26 Jan 2003
Posts: 2760

PostPosted: Fri Jun 04, 2021 2:31 pm    Post subject: Reply with quote

Further in continuation of previous post:

The modification factor as per figure 3 of IS 456 is higher if % tension steel is less.

If at load factor 1.5 reinf. worked is   0.6% say to be actually provided in slab.
For modifications factor , the reinf % of (0.6/1.5*1.0)= o.4 % to be used to see the modification factor  . Load factor = 1.0 is required for Deflection check.

Alternatively it can also be said that at load factor = 1.0, the steel provided in design will have a stress = (0.87 Fy)/1.5
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topicReply to topic Thank Post    www.sefindia.org Forum Index -> SEFI General Discussion 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