huangyhg

fall protection loading
fellers,
i can't remember the dyanmics of this problem? if i have a 500 pound weight falling 6' starting at zero velocity what is the final static loading compared to? this is for a fall protection design system
thanks

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many jurisdictions have their own loading requirements.
dik
one allowable loading is the actual load with an impact factor. i'm hoping to do this in lieu of designing for a 5000 pound load for each person
i think the loading would be very dependent on the arresting distance. that's why the 5000 lbs (probably obtained emperically) is the easy way out.
if you are talking about osha fall protection, your maximum restraining force on the person is limited to 1,800 lbs for a harness and 900 lbs for a hip belt.
as for the anchorage, we are allowed to use an engineered design with a safety factor of 2. so, in lieu of the 5,000 lbs, you can engineer a system for 2 x 1,800 lbs for a harness = 3,600 lbs
you, the engineer are required to determine your own jurisdictional requirments and do your own investigation (do not rely on my info alone).
reference that may help - "fall protection" - j. nigel ellis (and a lot of initials)
5000 lbs if you're under osha'a juridiction.
tdog67:
the increase of the design load is not direct multiple. i couldn't cite the source at this moment, but it goes like for 1 person with free fall limited to 6', the vertical load is 1800#...then for 6 persons, the load is 3000+ pounds. the killer is the horizontal load effect.
kslee
i believe you are referring to a horizontal lifeline system. the diminishing effect of additional persons falling is due to an assumption that the loading any one person will not occur at exactly the same time as the next.
the loading does not usually happen at the same time because of:
horizontal location along the lifeline
height of the person
length of the lanyards being used
etc...
based on limited testing, the diminishing return on multiple persons on a horizontal lifeline winds up being +20% for each additional person on the system.
this is a contentious issue and lifeline engineering companies disagree on what to do regarding this issue (my boss and i had an disagreement on this one)
teguci,
your calculation above ignores the fundamentals of how cables work. the fall load of 1800lb will result in a large horizontal reaction from the cable as well as the reaction in opposition of the applied force.
look up the formula in roarks for calculating the horizontal reactions from cables and you will understand what i mean. you will actually find that the loads on a horizontal lifeline calculated by first principles will be much more than 5000lb.
get the manufacturer of the system to specify for you
csd72
so quick to criticize without much consideration - not very kind.
initial response is replying to tdog67 who doesn't mention anything about a horizontal lifeline.
second response is replying to kslee100 who seems to be looking at a horizontal lifeline. the diminishing return does not apply to fixed vertical anchorages.
in either case, the load that needs to be designed for under an engineered system is the maximum restraining force with a safety factor of 2. it is just that the chance of this dynamic load occuring at exactly the same time on a horizontal line is very slim, hence the diminishing return.
before criticizing them, i would assume that any engineer who can draw a free body diagram to understand that the vertical force on a horizontal line will not equal the horizontal reaction and give them the benefit of the doubt.

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