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DEL2000 (Structural) (OP)
28 Dec 04 17:45
Anybody know where to find out how much of a radius different HSS shapes have at their corners.  I know this depends on the thickness of the tube wall.  In the welded joint tables, the flare bevel weld shows that the radius C is three times the thickness, which could be 1-1/2" for a 1/2" thick wall.  Is this right?  I haven't seen a lot of half inch wall tubes to recollect how big of a radius it had on them.  Is there any where you can find this information?

I have wanted to know this radius several times over the last couple of weeks, so thought I would finally ask.
krus1972 (Structural)
28 Dec 04 19:01
DEL2000,

In the green AISC Steel Construction Manual (1989 ASD) take a look at the Tubing Dimensions and Properties on pages 1-94 - 1-103.

If you look at the very bottom of every page you will see a note that says "** Properties are based upon a nominal OUTISIDE corner radius equal to two times the wall thickness". If you notice this is used for ALL TUBE properties they have listed in all of these tables. (Area, Moment of Interia, Section Modulus, Polar Moment of Interia, and Z.)

Although the green 1989-ASD is a code that is still used by many engineers the dimensions and properties for all of the structural tubing should still be the same in the LRFD codes that now specify the same tubing with a HSS designation.

I hope this helps.

Jeffrey A, Krus P.E.

    
krus1972 (Structural)
28 Dec 04 19:15
DEL2000,


As a follow-up to my earlier post you may want to also look at page 1-155. This is the allowable mill tolerances permissable.

On the right hand side toward the middle of the page you will see:

Radius of Corners - For a square or rectangular structural tubing, the radius of any outside corner of the section shall not EXCEED three times the specified wall thickness.

Based on this and my previous post would suspect that using 2 times the wall thickness for engineering calculations would be reasonable.

If you are doing some sort of fit up or clearence job you can expect the outside radius to be 2 times the wall thickness and no larger then 3 times the wall thickness. This is where you need to use your judgment depending on what you are doing.

Jeffrey Krus P.E.
UcfSE (Structural)
28 Dec 04 22:37
I believe the AISC HSS Connections manual says to use 3t for the corner radius if the true radius is not known.
LPPE (Structural)
29 Dec 04 13:18
One other - the TS shapes in the ASD manual and the HSS shapes in the LRFD manual ARE NOT THE SAME!  Wall thicknesses of HSS shapes are thinner than TS shapes - BE VERY CAREFUL WHEN DESIGNING COLUMNS WITH TS PROPERTIES AND CALLING THEM OUT AS HSS ON YOUR DRAWINGS!!!!

Also, you may not want to design anything using TS properties, as I'm not sure they're even manufactured anymore.
UcfSE (Structural)
29 Dec 04 15:29
HSS shapes are not different than TS shapes.  The ASTM 500 that governs rectangular tube steels allows manufactured thicknesses to be a percentage less than the nominal thickness, since products will have variance.  Because many manufactured tubes were being consistently produced about 93% of the nominal thickness, the HSS designation takes care of that reduced thickness in section properties and other calculations.  You will notice that the TS and HSS counterparts still have the same weight per foot.  The self weight would be different if the two were truly different sections.  They are not different shapes, but rather a new designation to recognize that the delivered thickness is in many cases less than the nominal.
LPPE (Structural)
29 Dec 04 17:30
I respectfully disagree.  Yes, they are not different shapes.  An HSS8x8 and a TS8x8 are still 8 inches square.  And yes, the material is still the same.  However, the design properties are not the same.  Open your books and put them side by side.  The areas, I, S, and Z are all different.  Not by alot, but it can make a difference.
Do you neglect the different K values for W shapes from the ASD to 3rd ed. LRFD?  No, you cant.  The weights are the same, but if you're detailing, you'd better be using the properties out of the 3rd ed. LRFD.

A HSS/TS example-

HSS8x8x1/4
A = 7.10
I = 70.7
S = 17.7
Z = 20.5

TS8x8x1/4
A = 7.59
I = 75.1
S = 18.8
Z = 21.9
JAE (Structural)
29 Dec 04 17:45
LPPE - I think if you read UcfSE's post you'll see that you really don't disagree with what is stated....The shapes are different in that the HSS properties are reduced to account for the ALLOWED variation in the thicknesses that were becoming a reality with current fabrication techniques.

The shapes are both fabricated under the same ASTM - it is because of the TREND in fabbricating these things closer to the lower bound thickness that AISC felt that the phi factor was not adequately accounting for the allowed variation - so they created the HSS shape to deal with it.

When you say that "the thickness of the TS shapes and the HSS shapes is not the same" - you should be saying "the thickness of rectangular tube sections fabricated some years ago varied in the + and - allowables, but now the rectangular shapes tend to be fabricated in the - zone only and AISC has adjusted the properties to give us a better measure of strength to reflect that."

A fabricator could make a rectangular shape and call it EITHER a TS or an HSS and still meet the ASTM requirements.  Its just a name change to reflect a need to adjust calculations - its not a name change that required any different fabrication methods.

krus1972 (Structural)
29 Dec 04 19:02
Everyone here has some valid points and the debate is valid, however, I believe DEL2000 was looking for simple answer to what the radius is.

The Green ASD book is STILL a valid code to use for design but its becoming outdated and will soon be updated with the new LRFD/ASD steel manual release in 2005.

Until the 2005 book is released the green 1989 ASD and the 2000 LRFD codes are valid. I've stated in my earlier post word for word with page numbers taken directly from the green 1989 ASD manual.

Since I do not use the LRFD method, can anyone provide the SAME information word for word (as I did for ASD) with page numbers from the 2000 LRFD Manual?

By doing this DEL 2000 can make his own educated decision with references to BOTH codes.

Jeffrey Krus P.E.
 

 
krus1972 (Structural)
29 Dec 04 19:06
Correction to my previous post:

2000 LRFD should be 1999 LRFD with 2001 LRFD Errata suppliment.

I cannot wait until the 2005 manual is released it will save lots of confusion between these codes.

Jeffrey Krus P.E.

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