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How to avoid Expansion joints in a high rise rcc building(150×150×103m) with geometrical irregularity in plan?

 
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Bindu Sunil
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PostPosted: Wed Jan 01, 2020 8:42 am    Post subject: How to avoid Expansion joints in a high rise rcc building(150×150×103m) with geometrical irregularity in plan? Reply with quote

Dear SEFIANs,
Wishing everyone here a very happy New year.
We have a high rise apartment building to be designed, without expansion joint as per client requirement.
4 towers of 31 floors ,connected up to 4 levels for parking space.
Overall dimensions 150m x 150m in plan, tower dimensions approx 50x 55m in plan.
We proposed 3 expansion joints initially.
Client says they absolutely do not want an expansion joint, design accordingly.
We have designed rcc buildings with plan dimensions up to 100m x 80m  with 60m height without expansion joints, with Thermal analysis done.
However, there was not much geometric irregularity in plan.
In this project under discussion, there's vertical irregularity and horizontal irregularity and hence,we preferred expansion joints.
Since the client does not want such joints, we are in the process of modelling the building without joints.
I request all SEFIANs to please advice/guide us on how to do this, whether this is advisable, if not ,Why.
If yes, how to proceed, what to refer, etc.
Are there any case studies we can refer?



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es_jayakumar
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PostPosted: Thu Jan 02, 2020 7:36 am    Post subject: Reply with quote

In my opinion, it will be safe for you to go by the recommendations of the Coded IS 3414 : 1968 & IS 4326 : 2013, which advocates the provision of expansion joints in various circumstances. Which is the location (place) of this building ? If the seasonal temperature variation in the locality is not extreme, the effect of temperature stresses will be less.
The clients should not be made to dictate terms (technical) !


E S Jayakumar
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Bindu Sunil
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PostPosted: Thu Jan 02, 2020 9:51 am    Post subject: Reply with quote

Dear Jayakumar sir,
Thank you for the reply.
I do agree with what you said.
Providing joints as recommended by the codes is safer.
The location is in coastal area of Kerala, temperature variation is less there ,comparatively.
If there's a requirement to avoid such joints in a building of these dimensions, what should we do, technically?
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es_jayakumar
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PostPosted: Thu Jan 02, 2020 10:07 am    Post subject: Reply with quote

I have once read somewhere an article that tells if the temperature difference is not substantial, expansion joints can be dispensed with, for concrete bridges or so. I am not sure, if the same can be applied to tall irregular building structures like that of yours. I know that the temperature variation is moderate in Kerala, as I am situated in Ernakulam. I advise you to convince the client of the importance of the expansion joints, citing the Codal stipulations.

Best wishes,
E S Jayakumar
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Balaji K S
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PostPosted: Wed Jan 08, 2020 8:09 am    Post subject: Reply with quote

Hi

You can provide shrinkage strips at required intervals and avoid expansion joints.
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Bindu Sunil
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PostPosted: Wed Jan 08, 2020 8:59 am    Post subject: Reply with quote

Thank you sir, for this advice.
Actually, we have used shrinkage strips (pour strips) in building exceeding 45m length.
But, from analysis point of view, we didn't consider these strips as expansion gaps.
And , there were not much structural irregularity in those buildings.
From your answer, I take it that, shrinkage strips, separating two large slab areas can be provided, to take care of the effects of temperature, isn't it?

For analysis, can we model each tower seperately, or , should we model the whole structure together?
Can we take these shrinkage strips as if we've provided an expansion joint,  is my doubt.
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es_jayakumar
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PostPosted: Thu Jan 09, 2020 5:52 am    Post subject: Reply with quote

Er. Bindu Sunil,
Dr.N.Subramanian sir has clarified to my query, in our Whatsapp group “Proud Civil Engineers”, that we can assume the structures to be continuous across the shrinkage strip for analysis, because the strips will be converted eventually. His famous book  “Design of Reinforced Concrete Structures”  has covered “Shrinkage Strips”.  He says therein that, a better alternative to this is the use of “Shrinkage Compensating Concrete” . You may refer this book for detailed  information.
I have also enclosed another useful excerpt on Shrinkage Strips here.
Other responses on this received in the said group, from experts are as follows :
Er.Hemal Mistry : Shrinkage, creep, temperature loads are self straining loads causing volumetric changes in structures with time. Rather than designing structure for such loads, it is better to adopt a suitable crack mittigation technique to control (distribute) cracks occuring due to these loads. One of the options is to provide expansion joint at code specified distance (say 45 m). Generally cracks due to such loads are more and critical where there is more restraining effect from stiff basement walls, shear walls and large columns. For span below 45 m these cracks are not critical. Energy is released by formation of narrow (may be invisible) cracks along span of member. When span is more than 45 m and no expansion joint is available, shrinkage strip (delay strip) shall be provided to allow shortening of concrete member due to these loads. However, these delay (strips) shall be kept open (uncast) for calculated time to allow required shortening. About 90 to 95% of total shortening occurs in 5 years from casting of slab. It is not possible to keep delay strips open for such long time. Basement walls, shear walls etc accommodate shortening of maximum 6 mm. So, from total calculated shortening 12 mm (6mm from each end) shall be deducted and time required to allow remaining shortening shall be calculated. Delay strips shall be kept open for such times. Time varies from 1 month to 2 month and generally contractors/clients are not happy with that. Time vs shortening graphs are also available. Crack mitigation in RC and PT is somewhat different. Basement floors shall be given due care as there is lot of restraing effect of foundation through basement walls, shear walls etc.

Er.Dileep Bhagwat : Just citing from my experience, Jetties are long structures for which this is a possible issue to be addressed. The codes suggest lengths of 75 m.
However, lately we have designed continuous stretches of 125, 150 m length and have considered the resultant forces. We find that shrinkage + temp variation doesn't govern.
Crack widths are checked routinely but not for shrinkage + temp variation.

The domain wisdom says that cracks are prevented because of the continuity of reinforcement, and as a result the structure is required to be designed for corresponding restraining forces that are generated.

Best wishes,
E S Jayakumar



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Dr. N. Subramanian
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PostPosted: Thu Jan 09, 2020 9:20 pm    Post subject: Re: How to avoid Expansion joints in a high rise rcc building(150×150×103m) with geometrical irregularity in plan? Reply with quote

Interestingly another engineer asked a different question about the same structure through LinkedIn!
The building is highly irregular and violate all clauses regarding regularity of IS 1893(Part 1) :2016, and hence not suitable in earthquake zones.

Anyway Er Bindu Sunil may check this: https://www.iitk.ac.in/nicee/wcee/article/14_12-01-0075.PDF

Subramanian


Bindu Sunil wrote:
Dear SEFIANs,
Wishing everyone here a very happy New year.
We have a high rise apartment building to be designed, without expansion joint as per client requirement.
4 towers of 31 floors ,connected up to 4 levels for parking space.
Overall dimensions 150m x 150m in plan, tower dimensions approx 50x 55m in plan.
We proposed 3 expansion joints initially.
Client says they absolutely do not want an expansion joint, design accordingly.
We have designed rcc buildings with plan dimensions up to 100m x 80m  with 60m height without expansion joints, with Thermal analysis done.
However, there was not much geometric irregularity in plan.
In this project under discussion, there's vertical irregularity and horizontal irregularity and hence,we preferred expansion joints.
Since the client does not want such joints, we are in the process of modelling the building without joints.
I request all SEFIANs to please advice/guide us on how to do this, whether this is advisable, if not ,Why.
If yes, how to proceed, what to refer, etc.
Are there any case studies we can refer?
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Bindu Sunil
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Joined: 29 Jun 2014
Posts: 6

PostPosted: Fri Jan 10, 2020 12:12 am    Post subject: Reply with quote

Thank you Jayakumar sir for the detailed reply and interest taken in my query.
These are valuable inputs, information for me.
Thank you Dr. Subramaian sir, for the valuable reply and sharing the link.
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