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[R L DINESH]

Dear SEFI’s Friends,

We are all know that wind tunnel test can be conducted to study the effect of wind load on tall structures and effect of adjacent structures on wind loading. However  we are not generally do the study of wind load effect on the adjacent structures due to the construction of tall structure closer to the existing structures. My interest in this e-conference is to know the following

1.       Whether Wind load will increase on the existing structures due to the proposed tall structure nearby. If so any guidelines available.

2.       How to safe guard the proposed tall structure from increased wind load effect due to construction of future tall structure closure or near by the presently proposed tall structure.

Expert opinion or any codal provision is available regarding above aspects.

Regards

R L Dinesh

[Manoharbs_eq]

Dear Dinesh,

How can constructing a tall building increase wind load on the existing structure, as per 875-p3 topography for structure suggested is flat terrain (for coastal and open fields) which is the critical K factor but for closely spaced regions K is less.


Please any one give their valuable suggestions and comment with regard to this



Rgds
Manohar

[R L DINESH]

Dear Manohar,
In case of two tall chimneys closely spaced, oscillation will increase due to match of natural frequancies of two adjucant chimneys. Is such effects will occur in tall structures?. If such phenomena isl not occuring or such situation doesn,t arise then there is no problem.

Regards,
R L Dinesh

[Dr. N. Subramanian]

Dear Er Dinesh,

IS 875 is very old, developed in 1987 and needs revision. Please visit the NICEE web site(http://www.nicee.org/IITK-GSDMA_Codes.php). Down load the documents
Indian Code for Wind Loads IS: 875 (Part 3)

       

• IS: 875(Part 3): Wind Loads on Buildings and Structures - Proposed Draft & Commentary
  
•     Wind Storms, Damage and Guidelines for Mitigative Measures
  
•     A Commentary on Indian Standard Code of practice for design loads (other than earthquake): For buildings and structures: Part 3 Wind Loads (Second Revision)
  
•     An Explanatory Handbook on Proposed IS 875 (Part 3) Wind Loads on Buildings and Structures

They discuss the provisions to consider wind interference effects. Similar clauses may be found in ASCE 7-2010.

Best wishes,
NS

[sureshkumar_kumaresan]

Hi ALL,

This is an interesting topic and quite practical as well.

(1) When new structures are coming nearby, the wind loads on the existing structures can increase/decrease depending on many factors such as the spacing between them, dimensions/geometry of the structures, oncoming turbulence, structural properties etc. Note that this influence will exist only for a few angles of attack and generally the built-in factor of safety will cover if any increase in loading.

(2) In another sense, over the years the city is going to get build and then the crowded cities will essentially protect the new upcoming buildings from the full force wind. This means typically upcoming new structures may experience less load than a similar structure getting constructed now.

Suresh

[suresh_sharma]

In  my view, the effect of wind  on the building adjacen to the tall bulding will be less, had there been no tall building near the shorter building. Oscilaation as pointed out is inversely proportional to the square root of mass and directly proportional to the the height. Chimney is altogether a different stucture having very little mass but more height.

[Manoharbs_eq]

Dear Dinesh,

Usually Buildings have more dead weight, and the stiffness is quite higher and also the ground coverage. so the slenderness of the whole structure is not as critical as chimney, of course resonance of buildings to wind is not often found.

There will be no increase in wind load rather there will be few amount decrease if we have closely spaced buildings in form of obstructions.


Rgds
Manoahr

[gautam chattopadhyay]

between two tall buildings in close proximity wind finds a path and create wind tunnel effect. Because of narrow space wind speed increases. For medium high buildings say 6 to 7 storeys any adversity may not occur but very tall buildings of 25 to 30 storeys I feel upper floors will be subjected to wind gust.

On Mon, Nov 19, 2012 at 8:25 PM, Dr. N. Subramanian <forum@sefindia.org (forum@sefindia.org)> wrote:

[Manoharbs_eq]

Dear sir,

Wind gust effect is found to be at the lower levels, however wind tunnel effect would occur for structures above a height of 60m or so and this will induce a drag and pull effect. But there is no provisions in code for this. tunneling effects must be studied by wind tunnel test experimentally. there are no developed empirical equations for this.

please correct me if am wrong

Rgds
Manohar

[Manoharbs_eq]

NOTE 1 - This standard does not apply to buildings
or structures with unconventional shapes, unusual
locations, and abnormal environmental conditions that
have not been covered in this code. Special investigations
are necessary in such cases to establish wind loads
and their effects. Wind tunnel studies may aiso be
required in such situations.
NOTE 2 - In the case of tall structures with
unsymmetrical geometry, the designs may have to be
checked for torsional effects due to wind pressure.

This is what IS 875-3 presents.

Rgds
Manohar