2005 AISC Seminar Handout 1

[miecz]

About a year ago, I attended an AISC seminar on the 2005 Specification. At this seminar, a booklet was handed out to participants. I'm reviewing the material for composite beams.

On sheet 4.16, Example 2, they calculate a Nominal Moment Strength of 1730 ft-kips. I cannot duplicate this result. I get 1381 ft-kips for this shape, by breaking it into 5 areas.

I wonder if anyone else has followed this example, and has verified AISC's result.

 

[JAE]

I just did the numbers. I think the calcs they show aren't exactly correct in that they take force moments about the interface between the slab and the beam. This is incorrect as they should be taking moments about the PNA which is in the top flange (down .209" below the top)

I re-did their numbers and I got 1723 ft-kips instead of their 1730. Not a big difference...I believe they just cheated a bit by using the top flange as the PNA instead of .209 inches below it.

Here's some of my numbers:

Area of beam below the PNA = 30.12 sq. in.
Area of flange above the PNA = 2.58 sq. in.

Force in slab = 1380 kips (.85 x 3 x 120 x 4.5)
Moment arm - slab NA to PNA = 2.459 in.

Force in top flange above the PNA = 129 kips (.209 x 12.34 x 50)
Moment arm - upper steel to PNA = .1045 in (.209/2)

Force in rest of beam below the PNA = 1506 kips (30.12 sq. in x 50)
Moment arm - lower steel to PNA = 11.47 in.

Mn = 1506(11.47") + 129(.1045") + 1380(2.459") = 20,681 in-kips

Mn = 20,681/12 = 1723 ft-kips.

 

[miecz]

JAE

Thank you. Your break down helped me find that I was using a web thickness of 0.17".