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Wind Load calculation as per IS 875 Part-3

 
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rahulranjan_31
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PostPosted: Thu Sep 02, 2021 6:32 am    Post subject: Wind Load calculation as per IS 875 Part-3 Reply with quote

Dear SEFIans,
For a foot over bridge I want to calculate the wind force over the purlin, but as per table-6 (External pressure coefficients for pitched roofs of rectangular clad buildings) for h/w ratio i am confused if i should take the height from ground level or from top of girder level (i.e. walkway level).
Any suggestion would be highly appreciated and thank you in advance.
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Dr. N. Subramanian
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PostPosted: Thu Sep 02, 2021 8:16 pm    Post subject: Re: Wind Load calculation as per IS 875 Part-3 Reply with quote

rahul_ranjanprasad wrote:
Dear SEFIans,
For a foot over bridge I want to calculate the wind force over the purlin, but as per table-6 (External pressure coefficients for pitched roofs of rectangular clad buildings) for h/w ratio i am confused if i should take the height from ground level or from top of girder level (i.e. walkway level).
Any suggestion would be highly appreciated and thank you in advance.

Dear Er Rahul

In Table 6 of IS 875(Part 3): 2015, h is taken from the GL only and is clearly indicated in the drawings.

Best wishes
NS
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vikram.jeet
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PostPosted: Sun Sep 05, 2021 8:48 am    Post subject: Reply with quote

The height at which roof spring level is located from GL is height h to be taken . It is already made clear by Dr NS  Sir.

Confusion to you occured , I think , due to foot bridge deck and roof forming a sheltered formation.

But it seems a case of open roof  without wall cladding and exterior wind coefficient needs to be plus/minus 0.7 as per IS.
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vikram.jeet
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PostPosted: Sun Sep 05, 2021 12:29 pm    Post subject: Reply with quote

Minor slip in earlier post , inconvenience regretted

The internal wind pr coefficient needs to be plus/minus 0.70 , as roof is open , no cladding from sides except railing posts and roof posts in a foot over bridge.
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rahulranjan_31
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PostPosted: Mon Sep 06, 2021 4:26 am    Post subject: Reply with quote

Thank you so much for your response sir. Actually that is the confusion which i am not clear about. Since bridge deck comes in between GL and roof truss level then why should we consider height from the GL for calculating external wind pressure coefficient.
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vikram.jeet
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PostPosted: Mon Sep 06, 2021 4:57 am    Post subject: Reply with quote

The bridge deck is also subject to external and internal wind pressure based on height h of deck from ground surface .

The stability of overall bridge structure under wind case , will get uplift force  (by summing up) from (I) wind pressures on deck (ii) wind pressure on walkway A type sloping roof.


rahul_ranjanprasad wrote:
Thank you so much for your response sir. Actually that is the confusion which i am not clear about. Since bridge deck comes in between GL and roof truss level then why should we consider height from the GL for calculating external wind pressure coefficient.
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