Fall Restraint Beam

[begstr]

Existing structure needs a fall restraint beam added. There are 2 rows of several floor openings. There will be 2 fall restraint beams spanning between roof frames. Owner wants 3 people to be able to be tied off each side. I know that the design impact load is 5 kips. Is there a reduction that can be taken for multiple people? Looking at the frame, it seems I should design for worst case 15 kips each side. The probability of 6 people falling at the exact same time cannot be very high. It just seems like overkill.

Any literature on structural design for fall restraint?

 

[JStephen]

I believe you're also allowed to use lanyards that limit the fall force, and then design for a multiple of that, which should reduce the design load considerably.

 

[jberg]

In a previous job (fall protection designer), we used lanyards that had a Maximum Arresting Force of 900#. If you read through OSHA, the criteria is actually 5000# or with a factor of safety of 2.0, designed by a "competent" person. We would design with 1800# per person (F.S. = 2.0) and design with the AISC specifications. That gives you an even larger factor of safety.

So, by limiting the lanyard force, you can reduce the required loads. 5.4 kips is much easier to work with than 15 kips.

Joel Berg

 

[jberg]

Oh, I forgot to mention, if it is truly a "fall restraint" beam (meaning the lanyard is short enough that the user can not fall off of the exposed edge, you do not need to design for the Maximum Arrest force. In the past, for fall restraint, I have used the weight of the user (say 300# or so) and double it for your factor of safety of 2.0.

Fall Arrest beams are where the lanyard is long enough that the user can fall off the exposed edge.

This is the best demo of the differences I have found:

http://www.latchways.com/default.aspx?item=34

Hopefully that helps.

Joel Berg

 

[begstr]

That does help! Thank you.

 

[RockEngineer]

Our fall protection "competent person" also take another reduction. Since it is almost impossible even if all three people fell that their impact would be at the same instant, you can design for two hanging (300 lb weight eacg) and one impact force.

The impact force is modified based on the type of lanyards used so you are usually well under the 5000 lb you mentioned.