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Design of Long Span Trusses.
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spsvasan
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Joined: 18 Dec 2008
Posts: 344

PostPosted: Sun May 17, 2020 6:45 am    Post subject: Reply with quote

thirumalaichettiar wrote:
es_jayakumar wrote:
Sir,
For permeability value between 5% & 20% , the set of values is [+0.5 & -0.5]. How can we interpolate them  for any intermediate value between 5% & 20% ?

E S Jayakumar


Er.Jeyakumar,

That is what my question?

if u know kindly explain.

May be we can first take the valor fro 0 to -5 interplaote  and again fro 0 to +5 >
May be wrong or wright must be ponyed out by experts in the forum?

T.RangaRajan.



Dear Er.RangaRajan

I am not an expert on windpressures

Reading IS:875 Part III, it is seen that when the percentage of openings is between 0 and 5%, we have to take Cpi as 0.2. When the percentage of openings is between 5% and 20%, Cpi is to be taken as 0.5 and when the openings exceed 20%, Cpi is 0.7. The code is definitely not suggesting any interpolation

IMHO any deviation from the code should be done only on the basis of carefully conducted wind tunnel tests

Regards
S.P.Srinivasan
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spsvasan
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Joined: 18 Dec 2008
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PostPosted: Sun May 17, 2020 6:48 am    Post subject: Reply with quote

nurat wrote:
Dear Sir,

Please see that C.G. Lines of intersecting members ( detail A ) falls within the Joint to avoid any additional moment at the Joint. Other experts can comment on my statement please.



Dear SEFIan

I agree with you that the centrelines of intersecting members should meet at a point in order to reduce secondary moments

S.P.Srinivasan
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spsvasan
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Joined: 18 Dec 2008
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PostPosted: Sun May 17, 2020 6:54 am    Post subject: Reply with quote

thirumalaichettiar wrote:
Er.Jeyakumar,


After going through your load on 31.5 meter truss I noticed that there are so intersections of vertical and diagonal members in the bottom chord. My point of view is

1. Since the bottom chord is subject to tension,
2. and the SLENDERNESS RATION as per IS-800-2007 -Table 3(v)        is 350  and (vi) is 400.

In the above is it possible to make long length in the bottom chord. I mean the number of diagonal and vertical may be arranged in such a way that the length will be good enough for resisting the forces as well as the SLENDERNESS RATIO.

This is my view in the case of long span trusses.

T.RangaRajan.



Dear Er.Rangarajan

I have two comments.

The bottom chord can be in compression under windload and hence slenderness ratio should be limited further

The verticals and diaganols give lateral support to the bottom chord only against buckling in the plane of the truss. To arrest buckling perpendicular to the plane of the truss tie runners [connecting the bottom chords of the trusses]are needed

Regards
S.P.Srinivasan
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