Example 7.6 Part "e" on Notes on ACI 318-08

[ipswitch]

I was wondering how the 30psf is calculated for wu . I know the 44psf is for the 3.5" slab.

 

[ipswitch]

is the 30psf just an assumed superimposed service DL?

I'll check out ASCE 7 to see if it makes some sense.

 

[McEngr]

6x16x12/1728x150pcf/3=33psf

FWIW, I don't get 30.

 

[ipswitch]

I assume then they rounded the calc for the joist DL down.

 

[McEngr]

I assume then they rounded the calc for the joist DL down.

That's my understanding. There's also the support of the girders' influence on the edges that would reduce the contribution of DL, which might shrink this down.

 

[ipswitch]

They do some arcane stuff in this example. ln for the int. neg. ultimate moment is listed at 27.25' for the joists in example 7.6. They also have ln listed at 28.54' for the int. neg. ultimate moment for the continuous beams in example 7.7.

I have no idea why they're doing this unless they are shortening ln for point of inflection or perhaps think the crtical face for the joist lies 4" beyond the beam face.

 

[ipswitch]

I guess the critical face is taken as d/2 for the slab which has h=3.5" and d=2"? d*2= 4".

 

[ipswitch]

This is stupid. if you take ln= 27.25' or ln= 27.5' it makes a total difference of 0.15" in determing d. Total minutiae.

 

[McEngr]

It seems like minutia until exam day. Chapter 4 has some good practice problems for interpreting section 8.3 of the ACI. Chapter 4 and chapter 6 are fundamental ACI 318 building blocks. I assume you've gone through all of these problems?