Design Beam For Fall Arrest Anchorage

[cdi12]

In this thread thread507-84756 "SlideRuleEra" suggested that we compare the failure load of harness parts (5,000 lb) to one measure of the failure load of the steel member (the load at 36 ksi yield strength) and "haggis" came up with C4x5.4 spanning 9 ft. Is this correct approach? For 9 ft span and 5,000 lbs at middle I am getting C8x18.75 (Mmax=5*9/4=11.25 ft-kips, bending stress fb=11.25*12/11.00=12.27 ksi, allowable bending stress Fb=13.68 ksi for unbraced length Lb=9ft).

Other question: I couldn’t find any document related to direction of 5,000 lbs. Does this load have to be applied in vertical direction only?

Thank you,
IV

 

[kslee1000]

Q1: Without check into details, C4 seems odd to me for the 9' span. Please note that the 5,000# is the OSHA requirement on strength for personal fall arrest devices such as harness and lanyard. However, if I remember correctly, the design force for anchorage point - beams, wire ropes, connections, shall be 10,000# (SF = 2).

Q2: Depending on the type of application (for example: fall from a ladder vs fall from the free edge of a runway beam with limited edge distance), the direction of force may deviate from vertical, and for which, it is likely to produce the maximum reactions on the subject under consideration.

Please check latest OSHA provisions on "Fall Protection" for more information.

 

[IFRs]

I thought that the 5000 pounds was the minimum failure load of the support structure. If you want to add an additional FOS, feel free.

The fialure direction is the one that the safety line will pull in when a worker is suspended by it. If that could be in more than one direction, so be it.

 

[Galambos]

per OSHA's website...

"(10) Anchorages to which personal fall arrest equipment is attached shall be capable of supporting at least 5,000 pounds (22.2 kN) per employee attached, or shall be designed, installed, and used as part of a complete personal fall arrest system which maintains a safety factor of at least two, under the supervision of a qualified person."

Since it does not appear that you meet the qualifications of a 'qualified person', as designated by OSHA, you need to design for 5,000 lbs, IMHO. it is possible to design for less.

as far as i know, OSHA does not specify an angle for the reaction. I have used 30 degrees from vertical in the past. I would feel uncomfortable using a channel and even moreso using a C4. it seems it would be very sensitive to any eccentricity.

also, the 10,000 lbs minimum factored design force has been eliminated from AISC's specification and is not necessary.

 

[geoffdale]

From the majority of fall arrest systems we have looked at, there ends up being as much horizontal load as vertical loads. For this, I would suggest a hss section. Would you also not have to look at torsion?

We end up for the most part giving them travel restraint rather than fall arrest for these reasons.