Reviewing W/D Ratio for Concrete Encased Steel

9/15/2017

Daily Discussion (today's anonymously submitted question):

Reviewing the Example 2 on SFPE (4th) page 4-307, could not understand how it is W/D = 0.67 lb/ft-in.

Here is the effort:

Found total cubic inches of the concrete encased W8x28 = (added 1.25 inches on all sides of the column) = [(8.06 + 2.5) x (6.535 + 2.5) x 12] = 1145 cu. in.

Subtracted W8x28 cubic inches = (A x 12) = (8.3 x 12) = 99.6 cu. in.
Got net lightweight concrete cubic inches = 1145 cu. in. - 99.6 cu. in. = 1045.4 cu. in.
Interpolate with 110 lbs per 1728 cubic inches
Got lightweight concrete only weight = 66.55 lbs per foot of the column
Added 28 lbs per foot of the beam to 66.55 = 94.55 lbs
So W = 94.55 lbs total weight of the linear foot of the column

D: As per figure 4-11.10 on page 4-305
D = 2(a + b)
So, Added 2.5 inches to beam flange, a becomes 9.035, and b becomes 10.56
D = 2(9.035 + 10.56)
D = 2(19.595)
D = 39.19 W/D = 94.55 ÷ 39.19 = 2.413

What is not right?

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7 Comments

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9/15/2017 09:46:20 am

W is 28 lb/ft (the second number in 'W8x28').

D is 4*6.535 + 2*8.060 - 2*0.285 = 41.69 in

W/D = 28/41.69 = 0.67 lb/ftin.

Now why did they use contour profile to calculate D? No clue.

Both the SFPE Handbook and Reference Manual are crap for little stuff like this that continually adds up. Don't get me started.

9/15/2017 10:25:56 am

Why hire a competent editor when you can crowd source it.(Busch league)

Jay

9/15/2017 11:03:46 am

Unwelcomed controversy.

This is a healthy discussion and should continue the posts.

9/15/2017 11:17:59 am

Just to be clear, it's only the SFPE materials (Handbook and Reference Manual) which I think are poorly written.

The Meyer Prep Guide, this website, NFPA Handbook, and NFPA Codes/Standards are all very well done.

Joe Meyer

9/15/2017 11:30:39 am

Thanks CJ! That being said I have looked into getting editing support for the 2018 edition of the Prep Guide.

9/15/2017 11:33:27 am

I was referring to the SFPE review manual/handbook not your guide Joe.

9/15/2017 12:49:19 pm

I try my best but no doubt it's difficult to get it all correct - I do see now that I misread your earlier post, but I appreciate the followup!

Reviewing W/D Ratio for Concrete Encased Steel

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