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RE: Fall Protection System - Loading

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I, too have had problems designing to these requirements.  We had some
existing buildings that were being re-roofed and the contractor wanted
to use tie-offs.  We didn't have anything in the structure capable of
supporting the loads prescribed in OSHA.  Instead, the contractor
eventually used railing or one of the other options.  The bottom line
was that he saw the engineer as being unable to do something that common
sense says should be easy.

One interesting side issue, since there seems to be a concurrent thread
concerning cables...we tried using a long cable running parallel with
the edge of the building.  The workers were going to tie-off to it.  Bad
idea.  Just a small lateral force on a cable produced enormous end
reactions.  Try it sometime.  It got into an iterative process of 1) how
much does the cable elongate; and 2) what is the resulting geometry (of
the triangle).  Then with that geometry, what is the force in the cable
and how much does it elongate.  It got silly after a while.  It appears
a lot of sag would be required in the initial cable design just to make
it feasible.

Michael Ritter, PE

> -----Original Message-----
> From:	RajSTC(--nospam--at) [SMTP:RajSTC(--nospam--at)]
> Sent:	Tuesday, November 16, 1999 10:36 AM
> To:	seaint(--nospam--at)
> Subject:	Fall Protection System - Loading
> Recently, I was involved with the design of a fall protection system,
> for 
> personnel engaged in activities on top of trucks in petroleum product
> loading 
> rack.  I was asked to follow OSHA guidelines.  According to OSHA,
> "Lifelines 
> shall be secured above the point of operation to an anchorage or
> structural 
> member capable of supporting a minimum dead weight of 5,400 pounds".
> Design 
> based on this requirement resulted in lot of structural steel, which
> seems to 
> me to be an overkill.  The project was on a fast track, so I could not
> do 
> enough research before sketching the details.
> Now that the project is behind me (except for comments from all those 
> self-styled structural engineers, like "which idiot designed this ?")
> I can 
> get to the bottom of the design philosophy.  I am curious to know the
> basis 
> on which OSHA came up with their recommendation.  Yes, it is a dynamic
> problem, but what assumptions or tests led to the 5,400 load?  Am I
> justified 
> in stressing the steel members to their yield limit, considering the
> loading 
> to be extraordinary?  Is it possible to get theoretical basis for the 
> recommendation etc.  I am looking forward to some lively discussions
> on the 
> topic.  Thanks, in advance.
> Raj.