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load combinations considering earth pressure on basement walls

 
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aditya
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Joined: 05 Apr 2008
Posts: 159

PostPosted: Sat Jan 12, 2019 12:11 pm    Post subject: load combinations considering earth pressure on basement walls Reply with quote

Dear Dr. N. Subramanian, Eng. S. Arun Kumar, Eng. S. Jayakumar and fellow Sefians,
I am confused about the load combinations to be used for the modelling, analysis and design of RC Buildings with basement walls. In such cases, the basement walls constructed between RC columns of the frame will have earth pressure acting all the time. IS 1893 Part 1 does not give the list of load combinations or load factors to be used in which earth pressure is included. My queries are:
1) Shall we use load combinations listed below:

1.5*Dead Load+1.5* Earth Pressure+1.5*Live Load
1.2*Dead Load+1.2* Earth Pressure+1.2*Live Load+/-1.2 EQ
0.9*Dead Load+0.9* Earth Pressure+/-1.5 EQ
1.5*Dead Load+1.5* Earth Pressure+/-1.5 EQ

2) Will earth pressure acting on walls contribute towards seismic weight or not:
3) Load combinations indicated in (1) above will affect columns in superstructure also. Is this logical? How to carry out the overall 3d modelling of the building
with regards to all,
Aditya
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es_jayakumar
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Joined: 24 Nov 2011
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Location: Cochin

PostPosted: Sun Jan 13, 2019 2:07 pm    Post subject: Reply with quote

Dear Er.Aditya,


I guess, the Earth Pressure being an almost permanent load, we have to consider it as a Dead Load acting in the horizontal direction. In that case, the Load Combinations indicated by you shall hold good.

Earth Pressure may not contribute to seismic weight, I hope. You may use Dynamic Active Earth Pressure for the calculation of horizontal load on the basement wall under seismic conditions. Reference may be made to the attached article and the book "Analysis and Design of Substructures" by Swami Saran.
The lateral (dynamic) EP will induce additional moments in the basement columns to which the RCC basement retaining walls are connected, which will necessitate increased reinforcement in them. This may not affect the columns in superstructure much, I think.
Experts may please throw more light on this.

Best wishes,
E.S.Jayakumar



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