blakesteel
Structural
- Mar 25, 2017
- 2
I was reading this thread about how regular pipe does not satisfy the load requirements of the standard specs used:
I meant to just reply in that thread but it is closed.
My supplier has been selling me HSLA pipe that has a much higher stress yield and therefore satisfies the standard load requirements.
If one looks over how NAAMM handles the calculations for this thing:
One sees on page 19 of that manual (page 22 of the PDF) that the pertinent equations are:
And for the 1-1/4" sched-40 ASTM A500-13 HSLA Grade 50 round tube that I am buying it has a stress yield of 70,371 psi. So one can use an Fb of (0.72 * 70.371) ksi = 50.667 ksi for this round tube.
This 1-1/4" round tube has a wall thickness of 0.13" and not the standard 0.14" of the Grade B tube. And therefore its sectional modulus is 0.222 in^3 - not 0.235 in^3.
So if one were to make a 42" high guardrail out of this round tube and needed to satisfy a uniform load requirement of 50 lbs/ft, you could space the posts:
For a round tube with only a 30 ksi Fb (50 ksi stress yield) you could only have a maximum post spacing of 40.29" = less than what is normally done. That is what that thread is talking about there. This HSLA tube is fine for standard post spacings though.
where P is the load applied to any post in lbs (a percentage of the required load depending on the geometry of how that load applies).
For the 42" high guardrail of this material, it could handle 100% of:
Therefore, one can just use HSLA round tube for pipe rails and avoid the problems brought up in that thread.
This is important info to know because everyone has come across this problem of standard pipe not meeting spec. HSLA pipe meets spec and is only about 5 cents a ft (about 2 cents a lb) more in cost.
I meant to just reply in that thread but it is closed.
My supplier has been selling me HSLA pipe that has a much higher stress yield and therefore satisfies the standard load requirements.
If one looks over how NAAMM handles the calculations for this thing:
One sees on page 19 of that manual (page 22 of the PDF) that the pertinent equations are:
Code:
1. For uniform loads:
w * l * h = 12,000 * S * Fb
where
w = uniform load requirement to satisfy in lb/ft (usually 50 lb/ft)
l = post spacing in inches
h = height of rail in inches
S = section modulus of post in in^3
reference = [URL unfurl="true"]https://en.wikipedia.org/wiki/Section_modulus[/URL]
Fb = bending stress in ksi
= 0.72 * Fy according to footnote 1 on the previous page
where Fy = yield stress
My supplier gets the HSLA pipe I buy from Bull Moose Tube:
[URL unfurl="true"]http://www.bullmoosetube.com/references/documentation[/URL]And for the 1-1/4" sched-40 ASTM A500-13 HSLA Grade 50 round tube that I am buying it has a stress yield of 70,371 psi. So one can use an Fb of (0.72 * 70.371) ksi = 50.667 ksi for this round tube.
This 1-1/4" round tube has a wall thickness of 0.13" and not the standard 0.14" of the Grade B tube. And therefore its sectional modulus is 0.222 in^3 - not 0.235 in^3.
So if one were to make a 42" high guardrail out of this round tube and needed to satisfy a uniform load requirement of 50 lbs/ft, you could space the posts:
Code:
l = (12,000 * 0.222 * 50.667)/(50 * 42) = 64.28"
= more than what people usually make the post spacing (about 5 ft o/c)For a round tube with only a 30 ksi Fb (50 ksi stress yield) you could only have a maximum post spacing of 40.29" = less than what is normally done. That is what that thread is talking about there. This HSLA tube is fine for standard post spacings though.
Code:
2. For a concentrated load, that NAAMM manual uses the equation:
P * h = 1,000 * S * Fbwhere P is the load applied to any post in lbs (a percentage of the required load depending on the geometry of how that load applies).
For the 42" high guardrail of this material, it could handle 100% of:
Code:
P = (1,000 * 0.222 * 50.667)/42 = 268 lbs
= well within a spec of 200 lbs even if ALL applied to the post considered.Therefore, one can just use HSLA round tube for pipe rails and avoid the problems brought up in that thread.
This is important info to know because everyone has come across this problem of standard pipe not meeting spec. HSLA pipe meets spec and is only about 5 cents a ft (about 2 cents a lb) more in cost.
