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Roof Purlins Design

 
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rajneesh_jindal
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Joined: 18 Dec 2010
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Location: Chandigarh

PostPosted: Thu May 26, 2011 6:51 am    Post subject: Roof Purlins Design Reply with quote

Hi All..
In the Design of Roof Purlins, can we design with Factored Load Combinations as 1.0*(DL+WL) considering Limit State of Serviceability, Instead of 1.5*(DL+WL).
Please Help.

Regards
Rajneesh Jindal
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rajancivildesign@gmail.co
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Joined: 26 Jan 2011
Posts: 537

PostPosted: Thu May 26, 2011 7:30 am    Post subject: Load combination for Roof purlin Reply with quote

For analysis of roof purlin in steel truss following load combination has to be considered:
(1) 1.5 DL+1.5LL
(2) 1.12DL +1.12LL+1.12WL (increase 25% allowable stress in steel for wind load)
(3)0.9DL+1.5WL

V.M.RAJAN.
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rajneesh_jindal
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Location: Chandigarh

PostPosted: Thu May 26, 2011 8:24 am    Post subject: Re: Load combination for Roof purlin Reply with quote

rajancivildesign wrote:
For analysis of roof purlin in steel truss following load combination has to be considered:
(1) 1.5 DL+1.5LL
(2) 1.12DL +1.12LL+1.12WL (increase 25% allowable stress in steel for wind load)
(3)0.9DL+1.5WL

V.M.RAJAN.

Dear Sir

Could you give justifications for using factors 1.5 , 0.9  and 1.12..
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PostPosted: Thu May 26, 2011 9:49 am    Post subject: Design of steel purlin load combination Reply with quote

Dear Rajneesh Jindal,
I have indicated the load combination based on my experience. Kindly refer  Table 4 of latest IS 800-2007 for correctness of the design. Generally 1.5 is used for DL+WL combination. For purlin stability check of 0.9DL+1.5WL is not necessary. For stress increase there are two methods of analysis. One is reduce the load by 25% of ultimate load and apply. Accordingly I mention 0.75*1.5 =1.12. Another method is analysis as it is and consider the interaction ratio of less than  1.0  for steel member check as 1.33. I am not expert in Steel design. Kindly comment on this issue by any expert in steel structures.

V.M.RAJAN.
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