Fall arrest points

[oneintheeye]

Hi I am looking at designing some restraint points (for fall arrest system) in masonry walls. first thoughts have been to provide two plates either side of the double leaf a connected with bolts . Anyone used alternative similar method?

 

[csd72]

I you can, coincide the anchor point with a corner and make the internal bracket an L shape. Then you can engage the perpendicular wall as well.

If this is not possible, you may be able to fit a channels on the flat to the inside of the wall to spread the loads vertically.

These are nasty things to make work in unreinforced masonry particularly to the 5kips or so that OSHA requires.

 

[shin25]

You may try the link below for temporary anchorages-

http://www.millerfallprotection.com.../miller-premium-products/anchorage-connectors

 

[msucog]

been a while, but seems like when i was a contractor, our masons use L-angle iron on each side of the wall with a thread I-bolt going through. the angle was about 5' long (to reach across two grouted/reinforced cells when at a slight angle from the horizontal to cross over say 2-3 courses). you can build the wall, grout it, then hammer drill out the 1/2-3/4" or so hole (probably want to keep the hole smaller than the mortar thickness to keep from messing up the block) for the I-bolt then just add washers then tighten the back side nut (think it was double-nut actually to make sure the first didn't back off). when finished, simply pull everything apart and patch the small hole. i believe they even used this for walls that weren't yet grouted to tie off or to tie off the scaffolds. it was sort of a homemade solution so i'm not completely sure if it would satisfy any particular loading requirement. i would find it hard to believe that a man falling vertical would pull the anchor out of system i describe--even if the wall was still sort of green. i have also seen 2x4 lumber used in a similar way with tie wire bundled up to make a heavy strand of wire...it's readily available on the jobsite and isn't expensive but still works...i see this used most of the time. then if the men need to along the wall, simply string a cable through the points.
not sure if this is what you're looking for but hope it helps.

 

[oneintheeye]

sounds similar to what I'm looking at though the wall is long standing. Basically there will be two points either end of the walkway. Its a double leaf wall. Wondering how I can prove the capacity of the plate bearing on the wall? Sketch detail attached below. Hope this identifies my problem (although you've probably seen better sketches!) am generally happy it'll work, but proving it?

 

[hokie66]

I question the wisdom of attaching fall arrest anchors to an unreinforced cavity wall. If I were the worker whose life depended on the anchor holding, I wouldn't accept a cavity wall as good enough.

 

[oneintheeye]

do you suggest another way? and why exactly are you so against this? the only other possibility is dropping something down off high level roof beams.

 

[csd72]

Do the numbers on the capacity of the masonry and you will see what he means. It is almost impossible to justify the strength of the wall. Also individual bricks can easily break out under the punching shear.

 

[hokie66]

Thanks, csd72. Yes, the punching shear would be my concern. If herewegothen does persist with this approach, he should at least use epoxy screens through the cavity so that both wythes are mobilized.

 

[oneintheeye]

thanks for the replies. Been to site to have another look. There may be a possibility of using a channel from the floor beam and attaching to sheeting rail on the other wall. Or the only other alternative is to drill through and attach to column other side of wall. Client not happy with that though.

 

[theonlynamenottaken]

I designed the attachment of and supervised the installation and testing of ~10,000 fall arrest anchors on 100's of high rise buildings. Humbly, I would consider myself an expert on this subject.

We went around and around on the anchors attached to unreinforced masonry penthouses and always came to the same conclusion... no engineer was comfortable taking responsibility for applying what could potentially be an impact load to an unreinforced wall (no ductility).

If your client is a property manager, I feel your pain. They typically take the, "its a freakin cinder block wall - it can hold anything!" outlook.

 

[msucog]

can there not be tie off points on scaffolding?...secure the scaffolding to the wall since there wouldn't be that much load for a scaffold firmly attached at several points (in a way i describe in my previous post). in other words, the scaffold never has the opportunity to lean out far enough to put much force on the wall. it might be easier/cheaper to just spot vertically reinforced cells where you want hook off points at then secure angles through the wall on either side of the grouted cell.
(just thinking out loud from what i've seen before)

 

[oneintheeye]

can't see them going for any kind of scaffold system. Its relatively congested, by that I mean is there is only about 1.5m walkway at most and some of that area is taken up by a rail hence a trip hazard.Plus they need it in quickly?? Think I'm going to tell them to knock a hole in wall and attach to column other side and if his doesn't like it, well, tough I suppose.