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VETRIKARASI ...
Joined: 03 Dec 2012 Posts: 63 Location: Puducherry
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Posted: Wed Jul 17, 2013 6:32 am Post subject: how to find the weight of truss |
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Dear SEFIans,
In general Can we calculate the weight of roof truss without designing?
If so what is the procedure & Why is done so?
Thanks & Regards,
Vetrikarasi |
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thirumalaichettiar Silver Sponsor
Joined: 26 Jan 2003 Posts: 3554
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Posted: Wed Jul 17, 2013 10:01 am Post subject: |
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Selvi Vettrikarasi,
Did you download the article "TRUSS" which was put long time ago in the forum? In that there are many formulae given to get the self weight of turss.
Are you so smart to ask further 2 questions?
Do not you know we need the self weight to find the reaction and BM along with other forces? That is the purpose. This is fundamental of civil Engg.
There is no procedure and I do not know why you are asking so many basic questions?
T.RangaRajan. |
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abhy_vivek Silver Sponsor
Joined: 26 Jan 2003 Posts: 690
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Posted: Sun Jul 21, 2013 6:56 am Post subject: Re: how to find the weight of truss |
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Dear Er. Vetrikarasi
Probably you want to know the weights (without design) for Qty estimation purpose / budgeting / tender estimate. To know the weight of truss without design (thumb rule) you need to first perform enumerable designs of trusses with different spans and purposes. Then yourself make a chart / curve from this data.
The truss wt largely changes based on the purpose and configuration. You need to first Identify a purpose of Truss - viz. Temporary steel Shed, Permanent Truss, Factory shed with EOT Girders, etc. The span and C/C spacing also contribute in the weight per unit area. Say two closely spaced trusses will require smaller size purlin, whereas if the trusses are spaced at far the purlin wt will increase. Thus while fixing the C/C distance you may consider the total weight of truss + purlin and then finalise the spacing. The type of section used 'Angle' / 'Channel' / 'Z-Purlin' / small truss as purlin / castelated beam etc. should be kept in consideration.
Also the geographical location decides the wind load on the roof. The inclination of the roof can be finalized accordingly. Usually the designer do not pay attention to temperature and snow loads. But in locations like Rajasthan / Kashmir these factors play a big role to finalize the member sizes, slopes, configurations etc.
The inception of PEB concept has changed all the set thumb-rules developed for trusses with the standard rolled steel sections. Even use of cold-formed steel tubes, innovative use of Std. Cup-lock system at construction sites etc. generate a new thumb rule.
So in conclusion you can not expect a short-cut with out elaborate design and detailing. You may check SP.38 and SP.40 also. Generate the charts based on your need. Tata steel - tube division has developed a software which gives 'Optimised' design for given spans and loadings, but this works only for the section supplied by them. Long back I tried to compare it with the tonnage estimated using the std. rolled sections, but they are not directly comparable.
Now a days many people prefer use a two inclined Joist instead of a truss. In this the material required could be slightly more but the fabrication cost and time is drastically reduced.
Even if there is any restriction on the depth of the truss, the tonnage may change.
Further modern shapes like curved roof etc. increases the fabrications cost. Use of circular pipe section may reduce material cost and give good architectural look, but the fabrication (joints) is difficult. In case there is an opening to be left in the truss, incase any member subjected to locable bending etc. will influence the wt.
Hope this is more than sufficient for you to start with developing charts for your own requirements.
Regards
Vivek Abhyankar
Mumbai
VETRIKARASI wrote: | Dear SEFIans,
In general Can we calculate the weight of roof truss without designing?
If so what is the procedure & Why is done so?
Thanks & Regards,
Vetrikarasi |
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Back to top |
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VETRIKARASI ...
Joined: 03 Dec 2012 Posts: 63 Location: Puducherry
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Posted: Mon Jul 22, 2013 9:26 am Post subject: |
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Dear Vivek sir,
Thank you very much sir.
Its really very useful sir
Thanks & Regards,
Vetrikarasi |
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