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Design of liquid retaining structure

 
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dubeyratnesh
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PostPosted: Sat Jun 04, 2022 4:30 pm    Post subject: Design of liquid retaining structure Reply with quote

Dear seniors
As per new codal provison of is 3370 2021
We have to design water retaining   structure based on LSM method only.my doubt is when code permits permisible stress in steel  in tension for hysd bars about 130-135 n /mm2.we know stress in tension in steel is taken as 0.87fy.  Does it means the value of yiel strength will  be used as (permisible stress/0.87) time for design.and same will be used in software ?
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vikram.jeet
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PostPosted: Tue Jun 07, 2022 6:47 am    Post subject: Reply with quote

Yet to see revised  (latest ) IS 3370 ,various parts.

Permissible stress of 130 mpa is to be used for STRENGTH DESIGN ,as per 2009 version, but it is WSM . Working Stress Method also permitted to be used  as alternative to LSM in 2009 v.
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dubeyratnesh
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PostPosted: Tue Jun 07, 2022 7:13 pm    Post subject: Design of liquid retaining structure Reply with quote

Dear sir
Is it a correct way to use staad model to find stresses other than approximate methods which require moment coeeficients for vaious condition?

Also new code ask to satisfy crack width criteria by limiting stresses in steel both in mild as well as hysd bars.also it limits spacing of bar for crack width criteria.
If we are calculating reinforcemnt by Lsm method than how we can limit tensile stresses in steel? What is the procedure for that? Also how one can same apply in software ?
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vikram.jeet
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PostPosted: Wed Jun 08, 2022 6:08 am    Post subject: Reply with quote

Er dubey naresh

Not seen new version so far.

For  liquid retaining structures , I always used WSM which was only method till 2009 version . Even afterwards used WSM as it was never prohibited. But as per yr post reg newer version , have to see .
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vikram.jeet
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PostPosted: Wed Jun 08, 2022 6:12 am    Post subject: Reply with quote

When computers were not there , IS 3370 tables were used in design Offices . IS 3370 covers limited cases . MOODY TABLES COVERS more edge conditions and we're also used alongside IS 3370 part 4.

But in computers exact results can be achieved if modelling is ideal.
You can have liberty to compare them with MOODY TABLES / Is 3370 results .
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akuc007
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PostPosted: Wed Jun 08, 2022 9:10 am    Post subject: Reply with quote

Er dubey naresh


It's happy to here that we received revision in code. I havn't seen this recent version.


However from the detail you mentioned, the new code restrict stress in the rebar and spacing in the rebar.


This could be the same as ACI 350 - Code for Environmental structure. Which does not have crack width check as serviceability criteria, instead the stress in the rebar shall be limited to allowable stress for static service cases and spacing of rebar must be within allowable spacing.


Also The factored moment to be multiplied by Durability factor. This implementation in IS code need to be checked.


Arun
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dubeyratnesh
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PostPosted: Wed Jun 08, 2022 11:19 am    Post subject: Reply with quote

dear seniors
following new code i have attached here please give some guidance after going through it regarding design and permissible stress criteria



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akuc007
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PostPosted: Wed Jun 08, 2022 1:21 pm    Post subject: Reply with quote

Er. Dubay,

following may be the short practice step of design.

1. Design the section using IS 456 for the load combinations given in table-1 of IS 3370:2021.

2. Option-1 Calculate the crack width for service bending moment due to serviceability cases (static cases only) if the crack width < Limiting crack width. section and rebar are satisfied. Limiting width based on water tightness classification (table-4) shall be increased by 0.05mm if the high of water (operating) H / t  thickness (gross) of element at consideration is less than 20. (for thicker section section limiting crack width shall increased by 0.05, but not greater than 0.2 in any case. This would be helpfull for deeper tanks. at sections where the alternate rebars are planed for curtailment, the spacing of rebar increase. so a relaxation of crackwidth by 50% is really going to help)

Option:2 calculate the stress in the tensile steel for service bending moment due to serviceability cases (static cases only) using working stress method. If the stress in steel and spacing are equal or less than mentioned in Table-3 (not table-2), section and rebar are satisfied. No need to calculate the crack width.

The haunch bar detailing (above ground) in section 8.3 is good.
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dubeyratnesh
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PostPosted: Thu Jun 09, 2022 9:28 am    Post subject: Reply with quote

Dear seniors
thanks for your valuable reply
further crack width calculation is quite tedious process as per given code ,where as ACI formula suggested in a post by our seniors was quite easy. can you provide any simplified calculation approach for crack width calculation?
also any approach to calculate reinforcement for plate results obtained after analysis and detailing as i find it little confusing that BM for plate direction and providing reinforcement in a particular direction.?
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