## Allowable Stress Formula / Equation #

## Allowable Stress Formula / Equation #

(OP)

Guys,

Sorry to ask these questions. With your help I am trying to understand the code & learn the calc procedure.

On one reference calcs i have it says:

Questions :

1. On the underlined formula, I believe that 0.85 is got to do something about the 85% of the allowable stress. Not sure what the 1.33 is? I couldn't find which of the equation#/formula was used to develop 18000 x 1.33 x 0.85.

2. I believe in the table 6-1 & 6-2 of LTS-6 there is 3 different stresses on the table. Tension, Compression, Shear & bearing. Which of these 4 should be used for Bending?

3. On 6-1 & 6-2 I did not see 18ksi(18000 psi) any where for 6063 alloy. Any idea how this might have obtained?

Thanks

GC

Sorry to ask these questions. With your help I am trying to understand the code & learn the calc procedure.

On one reference calcs i have it says:

*ALLOWABLE UNIT STRESSES - 6063-T6 Aluminum Alloy*

Allowable Bending Stress: Within 1" of weld

Allowable Bending Stress: Greater than 1" from weld

Fa =18000 x 1.33 =23940 PSI

Allowable Bending Stress: Within 1" of weld

__Fa = 18000 x 1.33 x 0.85 = 20349 PSI__Allowable Bending Stress: Greater than 1" from weld

Fa =18000 x 1.33 =23940 PSI

Questions :

1. On the underlined formula, I believe that 0.85 is got to do something about the 85% of the allowable stress. Not sure what the 1.33 is? I couldn't find which of the equation#/formula was used to develop 18000 x 1.33 x 0.85.

2. I believe in the table 6-1 & 6-2 of LTS-6 there is 3 different stresses on the table. Tension, Compression, Shear & bearing. Which of these 4 should be used for Bending?

3. On 6-1 & 6-2 I did not see 18ksi(18000 psi) any where for 6063 alloy. Any idea how this might have obtained?

Thanks

GC

## RE: Allowable Stress Formula / Equation #

## RE: Allowable Stress Formula / Equation #

Link

Link

Even in 2013 (LTS-6) also these tables remain same.

## RE: Allowable Stress Formula / Equation #

The allowable bending stress is your 18ksi or whatever you adjust it by. It's not the other four.

The 18ksi would be 0.6*Fy so roughly 0.6*31=18.6ksi. Hope this helps.

## RE: Allowable Stress Formula / Equation #

Its now clear why we multiply by 1.33. I recognized this on the table 3.4.1 - Group load combination.

GL2 & GL3 require 133%. Thanks for directing me.

Based on this, Fa = (0.6 Fy) x 1.33 x 0.85

Am I right?

I wish there was a equation reference number. (I would like documenting it while calculating for debugging)

I am putting one together. But, just checking, if any of you have a spread sheet available.

## RE: Allowable Stress Formula / Equation #

Like I said I'm doing this from memory, but I don't believe you need the 0.85. I think that's more of a book keeping issue. For instance if you have a calc set up that always allows for the 33% increase you don't need the 0.85 but if you have an load case where the increase isn't allowed then you need to use the 0.85 to offset the increase.

I think the 0.85 corresponds to an increase of 15% and 0.75 is for a 33% increase.

## RE: Allowable Stress Formula / Equation #

_{y})After a bit more reading, here is what I understood so far.

I believe that 0.85 is got to do with 85% of allowable stress. This is applicable to only 1" from the welded connection though.

There are 4 types of stress to calculate & check.

- Allowable Bending stress within 1" of weld. F
- Allowable Axial Compressive stress within 1" of weld. F
- Allowable Shear stress within 1" of weld. F
- Allowable Shear stress greater than 1" from weld. F

0.85 (85%) reduction of allowable stress is applicable to only the 1-3. The last one will used the allowable stress as-is._{B}_{A}_{v}_{v}One thing I didn't follow is that the Shear stress is tied to "h/t <= 39 ratio". Not sure how to do this. Is this height of the total pole/ thickness of the pole. This doesn't make sense. if the pole is 10 ft tall with 0.25in wall. Thats will be

120in/0.25in = 480

I am sure that I am not doing this right. Any reference / example to read about this.

Thanks

GC

## RE: Allowable Stress Formula / Equation #

## RE: Allowable Stress Formula / Equation #

When you have a moment, can you see if I am doing this right, please.

At this point, I am concerned only about h/t. There are 2 segments of pole :

Pole drawing :

Thanks,

GC