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sub IS 167700 / 2017

 
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k.gangadharan
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PostPosted: Wed Mar 14, 2018 7:19 am    Post subject: sub IS 167700 / 2017 Reply with quote

to econf@sefindia.org (econf@sefindia.org)
sub: econference on IS 16700 / 17
The very title of the code ' structual safety of Tall Concrete building means that it is only for concrete tall structures. Does this mean that another code will be forth coming for steel buildings & for tall composite bldgs.
Many of the super tall buildings built today in Shangai and beijing and other parts of the world like Taipei 601, Shanghai Financial tower or Incheon tower in S. korea are steel buildings with concrete metal deck floorings.Did the code formulators of IS.16700 consider this aspect while writing this code.
Even the terrorists attacked world Trade centre whose design was prepared by world renowned structural engineer Leslie Robertson, , & the Sears Tower ( now Willy's tower) whose structural design was prepared by structural genius Fazlur R khan, are steel Buildings. The only exception we can quote is Khalifa Tower in Dubai designed by William F. Baker Of SOM . Even in this building, of 828 m height, the top portion is steel structure.
Cl. 3.13, 3.14 &3.15 super tall towers above 250 m height.
Transfer structures are are suggested forthese buildings
When it is not possible to have continuous columns from bottom to roof, Transfer structures are suggested.
There are different types of transfer structures like transfer beams, Transfer Trusses & even very thick Transfer slabs . Where ever these are applicable and the limitation of each at different types of buildings are nor clearly specified.There are limitations for each according to the type of superstructures coming over it.
Cl.5.12 -Ht limit for type of structures
Limitations of ht. and slendernes ratio is given in Table.no.1 & Table 2
Moment frames are not allowed in EQ zones IV & V.
There are many buildings constructed In Zon IV & V voilating this clause and voilating this slenderness ratios in many parts of India. Generally the general architectural plans are conceived by the architets , as per the size of the plot available and structural designer cannot do much on this. In such cases , what precautions must be taken in the structural design of such buildings shall also be given.
Cl. 7.13 and Fig. IA & fig 1
Multiple tall Building connected by a common podium
Sensitivity analysis & stiffness parameters are given in this clause. upper bound & lower bound values adopted are also given.
Does this mean two different analysis should be done for these type of systructures. Also, generally the sizes of beams & columns reuired in certain locations and places of bldgs for beams & columns will be insisted by  
architects and stiffness parameters as required under code may not be possible as stipulated in the code . Such limitation may be difficult to implement inn actual design practice.
When there are no expansion joint in the podium connecting more than one tower, the towers may be different in ht. and floor pattern & also in use pattern and layout may be different resulting in different natural frequency and time period of the two towers .Will this not, in such a situation , affect behaviour of connecting members of the podium structure. The Collector beams in fig 2 is not clearly understood regarding their function ,different from other beams in podium structure. kindly give further clarification on this.
regards& thanks
Gangadharan .K  
structural Consultant



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hemalmistry
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PostPosted: Wed Mar 14, 2018 7:31 am    Post subject: Reply with quote

China have steel tall building code also JGJ-99_2015 like JGJ-3_2010 for concrete tall building.
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sangeeta_wij
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PostPosted: Wed Mar 14, 2018 8:07 am    Post subject: sub IS 167700 / 2017 Reply with quote

Dear Alpa
It maybe worthwhile to actually go clause by clause, especially for section 8, for Buildings with Single/multiple towers and explain the intent behind each clause, and the possible implications. It really does look scary to try and carry out multiple tower integrated analysis(will be a software and hardware challenge for all, especially with 50+ floors) and then compare it with the results of deformation compatibility analysis for Non Tower area columns manually. Similarly, carrying out two sets of such analysis, one with Wind and 2%damping and other with 5% damping and Earthquake and then carrying out the above task will be a garangutan task.

Can we request you to please spare some time and explain the whole of section 8, clause by clause.I know it’s asking for too much but this will really help everyone a lot!
Best regards
Sangeeta Wij

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From: k.gangadharan (forum@sefindia.org)
Sent: 14 March 2018 12:52
To: econf@sefindia.org (econf@sefindia.org)
Subject: [E-CONF] sub IS 167700 / 2017


to econf@sefindia.org (econf@sefindia.org (econf@sefindia.org))
sub: econference on IS 16700 / 17
The very title of the code ' structual safety of Tall Concrete building means that it is only for concrete tall structures. Does this mean that another code will be forth coming for steel buildings & for tall composite bldgs.
Many of the super tall buildings built today in Shangai and beijing and other parts of the world like Taipei 601, Shanghai Financial tower or Incheon tower in S. korea are steel buildings with concrete metal deck floorings.Did the code formulators of IS.16700 consider this aspect while writing this code.
Even the terrorists attacked world Trade centre whose design was prepared by world renowned structural engineer Leslie Robertson, , & the Sears Tower ( now Willy's tower) whose structural design was prepared by structural genius Fazlur R khan, are steel Buildings. The only exception we can quote is Khalifa Tower in Dubai designed by William F. Baker Of SOM . Even in this building, of 828 m height, the top portion is steel structure.
Cl. 3.13, 3.14 &3.15 super tall towers above 250 m height.
Transfer structures are are suggested forthese buildings
When it is not possible to have continuous columns from bottom to roof, Transfer structures are suggested.
There are different types of transfer structures like transfer beams, Transfer Trusses & even very thick Transfer slabs . Where ever these are applicable and the limitation of each at different types of buildings are nor clearly specified.There are limitations for each according to the type of superstructures coming over it.
Cl.5.12 -Ht limit for type of structures
Limitations of ht. and slendernes ratio is given in Table.no.1 & Table 2
Moment frames are not allowed in EQ zones IV & V.
There are many buildings constructed In Zon IV & V voilating this clause and voilating this slenderness ratios in many parts of India. Generally the general architectural plans are conceived by the architets , as per the size of the plot available and structural designer cannot do much on this. In such cases , what precautions must be taken in the structural design of such buildings shall also be given.
Cl. 7.13 and Fig. IA & fig 1
Multiple tall Building connected by a common podium
Sensitivity analysis & stiffness parameters are given in this clause. upper bound & lower bound values adopted are also given.
Does this mean two different analysis should be done for these type of systructures. Also, generally the sizes of beams & columns reuired in certain locations and places of bldgs for beams & columns will be insisted by
architects and stiffness parameters as required under code may not be possible as stipulated in the code . Such limitation may be difficult to implement inn actual design practice.
When there are no expansion joint in the podium connecting more than one tower, the towers may be different in ht. and floor pattern & also in use pattern and layout may be different resulting in different natural frequency and time period of the two towers .Will this not, in such a situation , affect behaviour of connecting members of the podium structure. The Collector beams in fig 2 is not clearly understood regarding their function ,different from other beams in podium structure. kindly give further clarification on this.
regards& thanks
Gangadharan .K
structural Consultant

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hemalmistry
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PostPosted: Wed Mar 14, 2018 9:26 am    Post subject: Reply with quote

References for Backstay effect

http://www.tallbuildings.org/PDFFiles/2014-LATBSDC-CRITERIA.pdf

http://peer.berkeley.edu/tbi/wp-content/uploads/2010/09/PEER-ATC-72-1_report.pdf

Regards
Hemal
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imteyaz_ahmad
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Joined: 07 Apr 2014
Posts: 10

PostPosted: Wed Mar 14, 2018 2:17 pm    Post subject: sub IS 167700 / 2017 Reply with quote

In section 8, Structural design, this code dictates to have staircase to be included in 3D model.My query is that do a designer need to model and design this staircase as an area element (shell/membrane) or a linear element? As for staircase we have been designing waist slab considering it as a line element of unit width for gravity loads only.
As i understand code wants designer to study overall stiffness behavior of building by modelling staircase and also effect of lateral load (Stresses) on staircase. In such cases should there be a change in detailing too for such elements? What if the axial stress on section is higher than 01fck? should we detail this element too as column?


Further modelling a staircase on columns will have effect on column design which will reflect high probable shear (Cl 6.3.3 IS13920) due to less effective height of column with addition to midlanding levels and will demand more material (say in Etabs).
Do designer have a choice to neglect such effect and produce calculation best suited in terms of economy and safety?










On 14 March 2018 at 14:56, hemalmistry <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           References for Backstay effect

http://www.tallbuildings.org/PDFFiles/2014-LATBSDC-CRITERIA.pdf

http://peer.berkeley.edu/tbi/wp-content/uploads/2010/09/PEER-ATC-72-1_report.pdf

Regards
Hemal
     



     


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