Cast in Angle Bending Question 5

[MindofBarca]

Hello All,

I have an insulated precast wall panel with a cast-in-angle with studs to provide support for roof joists (see attached detail). The angle is 6x6x1/2 and is subjected to 11.6k of ultimate shear force. I am trying to determine the bending/thickness of the cont. angle. The joist load is occurring roughly every 6', however, the angle and studs are continuous. How would I go about this calculation?

Is my b = 12" (distance of stud spacing?)

Right now I am doing a rudimentary thickness calc such as: t req = sqrt((m*4)/(phi * fy * b)) and coming up with 0.6inch ie 5/8" thick angle. Is this correct?

Thanks in advance, cheers!

 

[Rabbit12]

The PCI Handbook has a design equation that I've used for these type of angles.

The width b would depend on the width of the seat and some additional. I've seen guys use a 45 degree line back to the vertical leg. There's some engineering judgement involved.

 

[WARose]

Assuming a 8" effective width (it would actually depend (in my mind) on the stud spacing, which I am not too clear on).....I came out with it being a bit more thick. (Right at about 3/4".)

Anyway, if you have 'Design of Welded Structures' (by Blodgett) you can see a nomograph on p. 5.2-4.

 

[canwesteng]

You're effective width has to be some kind of engineering judgement, since the real failure mechanism is some kind of yield line. IME 45 degrees usually turns out to be conservative, but if you ignore the diagonal yield lines and have some kind of software to do the math, the yield lines aren't hard to figure out.

 

[Brad805]

I suggest you talk to the precast supplier about casting in the angle. Very few will do that for a number of reasons. I suggest an embed at each joist and field weld the angle.

 

[BAretired]

I agree with Brad805. Use an embed plate plus a short angle at each joist location.

BA

 

[MindofBarca]

@Brad805 & @BAretired: the precaster specifically requested this detail and only does continuous angles for these warehouse structures. Too often are they burned by mislocated joist drawings and needing repairs in the field. It also eliminates all of the costly welding in the field.

@Rabbit12: do you have a page or reference number handy by chance?

What they have typically used for the past however many years is a 1/2" angle, so I am trying to make this work if at all possible. I could not locate a similar detail in the PCI Connections Manual either...

 

[dik]

Can you use a W6x15 stub @ 6' rather than a continuous angle?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[MindofBarca]

@Dik, I tried to suggest any kind of segmented steel to the precast client and they did not want to entertain it.

It sounds like the real debate is in the effective width value. After checking in with other engineers and online resources this value widely ranges from 12" to 24"+ (for this type of detail). All of which drastically changes the required thickness.

If anyone has any more feedback or input I would gladly take it!

Thanks for the comments thus far!

 

[XR250]

Don't forget out-of-plane wall loads....

 

[dik]

Nope... I don't, but they are the ones easiest to deal with, usually.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BAretired]

You need to know the width of joist shoe. Then apply yield line theory to the outstanding leg of the angle.

BA

 

[dik]

Forgot I renamed it...(egg on face)

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

and... (more egg)

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[canwesteng]

Any effective width method will rely on engineering judgement (now that judgement may be documented somewhere in a design guide). You can use yield line or FEA to solve the problem.

 

[dik]

Catch my post... AISC has info for Channel Stringers and posts... not exact, but give you a reasonable guess... AISC Design Guide 34.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BAretired]

See below for yield line solution. Check carefully before using. It was done quickly.

Dik points out that I missed a couple of yield lines in the above. Below is a revised sketch which includes the missing yield lines (shown in black dashed lines). I have also corrected an error in my earlier calculations (see below).

BA

 

[dik]

a couple of saggers...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

I generally apply the load at the mid point or at the 1/3 point towards the rear... as the support deflects the point of load application moves closer to the back of the angle... (had difficulty with bak!).

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BAretired]

Thanks dik...I should have shown those two additional yield lines which you indicate by dashed red lines. I omitted them on the drawing, but not in the analysis, so my expression for m should still be okay (unless I've made some other mistake)...which, as it turns out, I did, but have corrected it on the earlier post.

BA