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- Subject: More on "Quick Help" thread
- From: G Vishwanath <gvshwnth(--nospam--at)yahoo.com>
- Date: Tue, 24 Nov 2009 03:53:33 -0800 (PST)
- Cc: steel steel <steel-detail(--nospam--at)yahoogroups.com>, misc misc <misciron-detail(--nospam--at)yahoogroups.com>
Subject: Re: Quick Help
From: David Topete
I don't believe the point of load application matters as much as the
stresses in the beam. if you sit a post on a beam or hang a load from the
bottom flange, the top flange will still be in compression while the bottom
flange is in tension. therefore lateral bracing points are still to be
added to avoid the buckling. unless I am missing something in the
While it is easy to appreciate that once the position of the load along the span of the beam is fixed, the point of application of a concentrated load (top flange or bottom flange) does not influence the BM and therefore the stresses, the Indian codes do make a distinction, while computing the allowable stresses.
May be the presence of concentrated local stresses has got something to do with it.
This local stress is unfavorable if applied to the top flange which is in a more "undesirable" stress state viz compression.
I am not sure. May be academics can explain better?
Thanks. This is interesting. We do work all over the world and indigenous=
design and construction practices are of interest to me.
It has been my experience in many countries a lot of heavy industrial steel structures are constructed of plate shapes that are welded to form a similar shape that
generally conforms to US=2C British or Japanese shapes.
Is that practice used in India?
The reason for Indian designers to use plated sections extensively is simply because in Industrial structures, the loads and stresses are so high that the deepest available rolled sections (24" in India) are just not adequate.
Besides the great lengths you in the US go to minimize labor makes you avoid any kind of fabrication work. But labor is cheap in India. The ratio of material cost to labour cost in India is perhaps the reverse of what it is in USA.
Another reason is that the cost difference between rolled sections and plates is marginal. Plates can be ordered to 50 ksi strength if necessary unlike rolled sections.
Besides plates are easier to transport. They can be stacked neatly and more of it can be accommodated in a truck or wagon.
They can be used and shared between the various buildings in a project and there is great flexibilty in apportioning steel between the various buildings/units of a project. Due to urgency a particular plate section can be "borrowed" from the the procurement made for another unit of the project which is scheduled later, and the quantity can be made up later.
This would not be possible with rolled sections.
Fabricators would rather buy just plates and cook up the sections they want using three plates and submerged arc welding. This reduces the inventory list and the BOM list.
Designers also greatly value the freedom they have in sizing the members. Normally they use 16, 20 and 25 mm thick plates for the flanges and 8, 10 and rarely 12 mm for the webs. Unlike you in the US, we don't have to live with pre-determined flange widths, thicknesses etc. of the available rolled sections.
Left over Plates can be more readily reused by the fabricator or the client in other projects.
Waste pieces left over from cut plates can be used for gussets/packs/shims etc and finally the scrap steel commands a fairly good price (about half the cost of new steel).
Also one must remember that In India rolled sections are supplied in standard lengths and not in exact cut lengths as in USA.
This increases wastages of rolled steel sections at site. Plates too are supplied in standard lenghts but the wastage can be controlled better.
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