FOS for Scaffold 2

[andriver]

I work for a large construction company, and we outsource our scaffolding to a very large scaffolding company. Per my company policy I need to review all 3rd-party engineered plans.

Recently I reviewed a plan to use 6x6 timber to span 17.5' (16in OC). I found an error in that they were using repetitive member factors and size factors that were only applicable for 2"-4" thick members not the 6x6 members being used. Consequently the FOS is 1.85 and not 4.0.

In talking with the company and our superintendents, this is a very big deal because the material is on site and they were going to begin assembling it this week, the area is a very large area so that this will impact quite a bit of material.

The EOR states that he does not need to reach a 4.0 FOS because this is an engineered system, and as EOR he can state what the capacity is. The 4.0 is more for people who don't know what they are doing.

Either way I am just a junior engineer grunt, it will not be up to me whether we accept this design. I wanted to know the consensus on his statement that engineered scaffolding does not require 4.0 FOS.

 

[andriver]

Archie, we could absolutely purchase more and I suspect that is what's going to happen. This back and forth is only occurring because the Director of Engineering for their regional branch is pushing back on me, a junior engineer. I will have a project manager who controls the purse strings take it from here, I just checked the numbers, and they weren't good. Now they can decide on a resolution, which I will check again.

 

[SlideRuleEra]

Archie264 - Thank you.

andriver - You may be a "junior engineer", but it appears you are doing a credible job representing your company's interests. Be sure to return and let us know how this comes out.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[andriver]

Just wanted to give you guys an update. We had a meeting and decided that we would not "bend" the criteria for this specific area. My boss summed it up quickly in his email to the director.


I have reviewed the conversations in the email string and the design proposed by _____ for the ____.

The project decking design criteria for this area is the following:
1. Deck load rating of 25psf
2. FOS per OSHA as described in the email string “…capable of supporting, without failure, its own weight and at least 4 times the maximum intended load applied or transmitted to it.”

Based on the above design criteria, the 6x6 timber members in the current design are inadequate as mentioned in the email string. Please revise the design and submit to ____ and myself for our final review to close this out.

 

[BadgerPE]

Way to stand your ground!

Houston Scaffold Collapse

 

[SlideRuleEra]

andriver - Great! For future reference, southern pine 6 x 6's make really terrible beams. It's where a 6 x 6 comes from in the tree - the center. The wood around the center develops longitudinal splits (checking). Also, since this member is from the center, limbs (knots) can be on all four sides... sometimes simultaneously. A better choice is an appropriate number of southern pine 4 x 6. We used only 4 x 6 for falsework of cast-in-place bridge slabs and high-pressure concrete forms (such as tall overpass crash-walls adjacent to railroad tracks).
See this link for information on 6 x 6s... so called "dog boards": Link

When designing with southern pine for temporary structures, I suggest sticking with the values for #2 grade. These days, there are few southern pines that are old enough to provide higher grades.

BadgerPe - Very appropriate and timely link.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[IFRs]

Excellent thread.
I'm proud of you for finding this and respectfully sticking to your guns.
I'm really happy about the excellent advice you got - just what this site is all about.
I'm pleased that your boss backed you up.
The fact that this is a "large" job is MORE reason to pursue it, not less.
Money and human life are not in any way shape or form comparable.

GO ENGINEERS !!!