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How Tall is Tall?

 
This forum is locked: you cannot post, reply to, or edit topics.This topic is locked: you cannot edit posts or make replies. Thank Post    www.sefindia.org Forum Index -> E-Conference on Tall Buildings
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PostPosted: Sun Nov 25, 2012 3:54 pm    Post subject: How Tall is Tall? Reply with quote

Dear Colleagues:

"How tall is tall?" is an interesting question... Excellent inputs were given by our participants of the eC so far...

One way of regulating the development of tall buildings is by placing a cap on their absolute height, specified as a certain number of meters or in terms of number of storeys (assuming a standard height of each storey). This physical limit is imposed by countries or municipal authorities largely based on a number of factors, including:
(1) Capability on the method of assessing within the municipality (or through a committee structure) the safety of a building of a certain height;
(2) Confidence in the norm of a designer of the country to be able to comfortably (with less approximations) design buildings of a certain height;
(3) Capability of the construction industry to be able to reach tall heights with ease;
(4) Confidence on the behaviour of materials (e.g., creep in concrete structures) subjected to large stresses; and
(5) Level of knowledge available in the country in academia and in practice, to deal with large uncertainties related to all aspect of planning, design and construction of the building, especially geophysical investigations, geotechnical issues, modeling nonlinear actions in soil-foundation-structural system, understanding implications of structural design of the building that is likely to enter nonlinear domain of behaviour, and understanding behaviour of non-structural elements, like facades.

Another way of controlling the development of tall buildings is through their lateral stiffness. Buildings become flexible as they go tall, but too much of lateral sway is not desirable. Hence, an upper limit can be placed on the lateral stiffness of the buildings through their lateral inter-storey and overall drift. When a country has one limit for wind effects and another for earthquake effects, the issue of stiffness gets mixed up. But, since
(a) earthquake shaking imposes displacement loading on the building, and not force loading like wind, and
(b) design earthquake lateral load is only a fraction of the actual lateral force that is induced in the building during strong earthquake shaking. The actual inelastic displacements in buildings (if it is allowed) can be at least 300-500% more.
This suggests that it is not being consistent when the lateral drift limits specified for these two effects are compared without knowing the force levels for which these lateral drifts are specified. When the lateral force effects are same, only then the comparison is meaningful. Thus, some countries have a single specification for lateral drift (for both wind and earthquake effects) to remove this confusion.

This lateral stiffness of a building can be specified in the code in two ways:
(1) by specifying at least a minimum the structural plan density (sum of areas of vertical structural elements/ plinth or floor area) at different levels. When Chile wanted to regulate the structural system, it adopted this path; or
(2) by specifying an upper limit of the fundamental lateral natural period of the building. This is yet to find acceptance for inclusion in codes.

Hence, it seems that the limiting height after which a building may be termed as TALL, will remain subjective, and is only likely to be revised upwards as the knowledge level grows in that country. For instance, Japan restricted the building height to 10 storeys in the early 1920s after the Great Kanto earthquake, and released this ceiling after 40 years of research and development, in the 1960s. These 40 years were years of hard work and confidence building for the engineers and academia of Japan. Can we take a leaf off the book of experiences related to development of tall buildings in Japan?

with warm regards...C.V.R. Murty

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bharati.umekar
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PostPosted: Mon Nov 26, 2012 7:06 am    Post subject: Base Isolation for Tall Buildings. Reply with quote

Dear Sir,

Thank you for this very informative topic.

Two Questions,
1. Is Base Isolation possible for Tall Structures?
2. If Possible, than how effective could it be?

As you have mentioned, Japan took almost 40 years to release the Ceiling for the No.  of Storeys, and I feel they are the pioneers in the Base Isolation Techniques,  is this Technique effective, as Japan is the most vulnerable Earthquake prone Country.

Warm Regards,

Bharati.
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sarfaraj.husain
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PostPosted: Mon Nov 26, 2012 7:32 am    Post subject: How Tall is Tall? Reply with quote

no doubt base isolation is very effective technique......but it is very costly.....i doubt any building in india is having this facility...(not sure one newly constructed hospital in ahmedabad having this)...


sarfraj



From: "bharati.umekar" <forum@sefindia.org>
To: econf34289@sefindia.org,  
Date: 11/26/12 12:51 PM
Subject: [E-CONF] Re: How Tall is Tall?



Dear Sir,

Thank you for this very informative topic.

Two Questions,
1. Is Base Isolation possible for Tall Structures?
2. If Possible, than how effective could it be?

As you have mentioned, Japan took almost 40 years to release the Ceiling for the No. of Storeys, and I feel they are the pioneers in the Base Isolation Techniques, is this Technique effective, as Japan is the most vulnerable Earthquake prone Country.

Warm Regards,

Bharati.





-- ญญ

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suraj
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PostPosted: Mon Nov 26, 2012 7:41 am    Post subject: Regulating development of tall buildings Reply with quote

Regulating development of tall buildings

Respected Eng
C.V.R. Murty



  1. Thanks for conclusive comments about required regulatory provisions

  2. Capability from all disciplines should be analysed, studied & decided

  3. Concept, design, soil data, prosecution procedures & executive management should all dictate production of tall buildings, in case at all tall buildings are required to be produced keeping abreast whatever necessity it could be

  4. In ours, missing disciplines generally, are safety/HSE & quality management

  5. Neither industry nor engineering & nor state have done anything on improving existing practice to top up to defined levels

  6. Howsoever, good designs may be , substandard work shall pull down all efforts of engineering designers

  7. Without total & comprehensive management particularly, for basic engineering deliveries, proposals for tall buildings should not take off

  8. Emphasis should be included within detailed explanations on all specifications & philosophies, which practice is yet to start with

  9. Even drawings & design documents are not well delivered giving required clarifications & for clear understanding by site line management

  10. An overall improvement is required for quality building engineering, while, structural engineer & prosecution engineers should not keep themselves in isolation from inter disciplines for interface resolutions in office as well as on site during carrying out activities


  11. An exclusive dependence on architecture shall not support smooth production & delivery of buildings

  12. Such requirements should hold good for all buildings

  13. Tall buildings areas should be meant for tall buildings only, without any mix up

  14. Even, city vistas & ekisticks require such proposals for rythm & harmony

  15. Cluster of all type of buildings do not pose a good sense of view

_________________
Thanks & Warm Regards
IntPE(India)Suraj Singh FIE Civil
Engineering & Arbitration

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Manoharbs_eq
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PostPosted: Wed Nov 28, 2012 5:14 am    Post subject: Reply with quote

You can find more information at:
http://www.earthquakeprotection.com/product2.html andhttp://www.earthquakeprotection.com/triple_vs_single_pendulum.html (from the company that has the patent of triple friction pendulum bearings)
http://www.scribd.com/doc/65934006/28/TRIPLE-PENDULUM-BEARINGS (a very important PhD thesis)
http://vimeo.com/10000748 (a video shows how it works)



please find this useful.


Rgds
Manohar
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