Old AISC Light Beam (B) Section Properties

[whyun]

I have an old structure and the existing structural drawing calls for a beam section 18B40. I have looked into my AISC STeel Manual 6th Edition and found that it is not listed under the "light beam" section nor the WF section. In fact, I was unable to find any 18" beams with 40 plf weight.

Could the existing beam call out be in error?

I would like to know if 18B40 are equivalent to modern W18x40.

Thanks to all in advance.

 

[VirtualEngineer]

whyun,

AISC Design guide 15 covers historical sections.

Printed out, the design guide is over 300 pages long.

From previous experience with historical sections, I'd say 18B40 sounds like a correctly called out section size.

This is a link to the download page, but you have to be an AISC member to download for free.

http://www.aisc.org/Template.cfm?Se...aggedPageDisplay.cfm&TPLID=21&ContentID=22619

It helps to know the approximate year the building was built to tie down the correct section properties.

Regards,

JPJ

 

[JAE]

AISC Design Guide 15 has no 18" deep 40 plf beam listed. How old is the structure?

 

[whyun]

JAE: Construction documents indicate 1961 and 1962. Probably designed to Fifth Edition of AISC. I do not have a copy.

I do have a sixth edition. The wide flange sizes for the 18" deep sections starts with 18WF45. The largest B section in the manual is 16B31. The drawing calls for 18B40.

I've compared 16B31 and W16x31 and found that the dimensions are roughly equivalent and S and I are "very" close. Thus, my educated guess would be that 18B40 and W18x40 can assumed to be the same.

VirtualEngineer: Thanks for the link. Unfortunately, I am not a member of AISC. I do have a AISC Sections Database CD that came with LRFD 3rd edition. I will look there.

Thank you, both.

 

[SlideRuleEra]

I have a Fifth Edition AISC (1947), the smallest 18" is 18WF50. Also have 1934 Bethlehem Manual and 1923 Carnegie Pocket Companion - nothing there of that size or nomenclature. Could this beam have been manufactured outside the USA?

http://www.SlideRuleEra.net

 

[whyun]

Thank you, SlideRuleEra. It was sort of peculiar to me since I was unable to locate 18B40 in all references I have. As-built drawings indeed say 18B40.

I will go home and look for my AISC shape database CD and find out. Thank you all for reassuring me that I am not overlooking something.

 

[whyun]

That size did not exist in the database. The database has sections from ASD 9th all the way back to the 5th edition. Anything prior to that was classified under Historical Section produced by various fabricators.

Perhaps it is a mistake in the existing drawing (?)

How was it ever approved??

Anyways, thanks everyone.

 

[VirtualEngineer]

You may be able to go out and measure the beam.

Usually when I field measure a member, Depth, Flange Width and Flange Thickness is enough to identify the section.

For an older shape, take notice if the flanges are sloped.

It was very common for older section web thicknesses and flange thicknesses to vary considerably from the design thickness, generally on the conservative side.

Best of Luck,


JPJ

 

[unclesyd]

Look at the first publication.

http://www.steeljoist.org/publications/