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Re: double angle vs starred (cruciform) angle

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Site welding is not, really, a no, no in the USA. It is a chore to weld on galvanized steel, which is very common in industrial facilities. It requires an elaborate procedure to ensure that the iron worker is not exposed to the toxic fumes that arise from welding a galvanized item. Therefore, all attempts are made to prevent site welding, if the steel is galvanized. All said and done, it is the bottom line. If the cost of site welding is cheaper than any pother alternatives, site welding will be done.  There is no rule to proscribe welding a painted steel.

In my opinion, a standard, non-compunded section would be economical than using a cruciform section or any other compund section. Unless I am pressured by a, headstrong, architect I will avoid any form of compunded section. Cruciform will be the last in my list of choices from consideration of cost and aesthetics.

In the US, rolled section conforming to A992 may be cheaper than one conforming to A36!

Rajendran

G Vishwanath <gvshwnth(--nospam--at)yahoo.com> wrote:

Sometime ago, I had posted a copy of my reply to a
member in the steel-detail(--nospam--at)yahoogroups.com list.
He wanted to know which was better , WT or Double
angle.
I had discussed starred angles too in my reply.


Starred angles using two angles (not four) were
popular with us in India when designing compression
bracing members between columns in industrial
buildings.

They offer better Radius of gyration properties than
angles back to back.
Hence they have a better compression load carrying
capacity.
They are better than back to back angles for another
reason viz all the surfaces are accessible for
painting. In a back to back angle you can't repaint
the space between the back to back legs.

Using starred angles, you can reduce the number of
angles to be procured. You can have a single angle,
double angle back to back, double starred angle from
the same angle section procured to suit three
different situations. In our country, where the
variety of shapes available is considerablly less,
this is an advantage. 4 angle configuration is not
efficient. The Radius of gyration will reduce. Too
much thickness collects near the cg of the section.

The disadvantage with starred angles is that you need
longer stitch plates and they are needed in both legs.
This adds to labour costs of cutting and welding the
plates.

Secondly when clearances are an issue, a back to back
angle is more compact at least in one direction. The
starred angles need double the space. This can be an
issue in case of bracings located close to a wall or
where the bracings have stairs or pipes or other
structures located close to the plane of the bracing.

I used starred angles extensively in my designs for
Industrial buildings in India.
I have noted that no one uses them in USA for the type
of structures that we are now detailing for them.

Other differences in preferences:
The end plate connection is hardly ever used by
American engineers. British engineers prefer them.
Shear plates are preferred by the West coast engineers
in USA. The Easterners prefer double clips.

Americans prefer bolting to welding. Indians prefer
welding to bolting.
Site welding is a strict no no to American engineers.
They use it only if unavoidable.
Site welding is welcomed in India. It compensates for
all the fabrication errors. Fabrication in India is
done in open yards at the site and not in
sophisticated and well equipped shops as in USA. The
quality of fabrication here cannot match American
standards. Labour is cheap. Material is costly here,
unlike in USA.

A992 steel costs the same as A36 steel in USA (Please
correct me if I am wrong). In India high strength
steel is costlier and not used unless really required.
Most of time we use steel conforming to IS:2062 Grade
A and the nearest American equivalent is A36.

Regards

Vish




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