Lateral loads near the top of a masonry wall

[Tim Watts]

Yeah - I have a bit of a paranoia about lateral forces on tops of walls. Just wondered if anyone could see any problems with this:

View of wall (plan, from top)

D | | C_____|A xxx| xxx| |__________E B

xxx is a 390mm deep wall mount network cabinet (6U or 9U) weighing

12-15kg and carrying another 30-ishkg of load from switches etc.

All walls are single thickness brick and the cabinet will mount near the top of the wall which stops at the ceiling.

BD is a main load bearing wall so does have the weight of the dormer floor above on it. AC and BE do not have any top load.

BD is topped with a conventional wooden wall plate.

Point B near enough also has a pillar supporting part of the dormer roof on top

Planning on screwing into the 2nd or 3rd course of brick from the top.

So if xxx is screwed to AB, it benefits from both the kicks in the adjoining walls and some load on top.

Lateral force at the top of the cabinet pulling out the screws will be

180-240N depending.

Another way of phrasing the question: would you hang a boiler up there? Because this is a less heavy but it's not trivially light either.

Cheers - Tim

Working:

I reckon the top bolts on the cabinet will have a lateral pull out force of around 243N or 24kg-f

(450N acting in the center of the cabinet 0.2m from the wall and assuming a 6U cabinet which is 0.37m high)

450*0.2/0.37=243

reducing to 180N or 18kg-f for a 9U cabinet.

[John Rumm]

Short answer, I can't see it being a problem - especially with the top load and the lateral support from the adjacent wall.

For extra peace of mind, stick in a 12U cabinet - it will convert more of the load to shear, and you know you will always run out of cabinet sooner or later :-)

[Tim Watts]

I like the cut of your jib :)

Can't go wrong with 12U...

It's a really good location too - hall (easy access, bothers no one), great throughway above bewteen the joists), power socket below it (might stick a small Eaton MEM UPS on the floor as we get a *lot* of power cuts, like about 15 in one day last weekened.

Cheers,

Tim

[John Rumm]

Well with hindsight I could have got a 16 in :-)

Yup I did similar:

(right down to the MEM UPS on the floor).

I modified a 1U cable tidy by snapping off the rings, and mounting it on the rear rack struts to support the back of that shelf - since a 1U shelf was not really upto 2 NAS units!

[The Natural Philosopher]

A little engineering theory may help you here.

Lateral loads on masonry have long been understood - mediaeval buttresses are there for that reason.

The problem is that masonry is way better at compressive loads than tensile ones, and has very low elasticity, and that means its liable to failure by buckling with asymmetric loads.

The approach that fundamentally solves this is by ensuring that the thrust vector of the load falls inside the walls. Buttresses achieve this by effectively widening the base of the wall but another approach for a given lateral thrust is to increase the total vertical load on the wall.

That 'bends' the resultant combined vector inside the base.

A wall piled with lead weights on top is harder to push over than the same wall without..

[Tim Watts]

I have a Nas, a miniITX pfSense router and a couple of other widgets - I like the idea of shoving these inside.

How do you find MEM?

Good idea :)

I'm going for tool-less keystone jacks for my wall outlets and panel.

Cat5e, 6 or 6a I am undecided. Under 55m runs, but the sheilding in 6a might be beneficial with all the mains stuff and dimmers nearby. Depends how much of a mare the cable is to route. If it's too horrible, Cat5e will be sufficient for my needs.

Already have a Ubiquiti PoE switch and Wifi AP which have far outperformed anything I've had before - well pleased with those.

[Tim Watts]

In theory I have at least 1-2kN load from the pillar that supports the dormer flat roof, bearing down on the corner and through the wallplate.

And probably quite a lot from the floor above which sits on that wall.

[The Natural Philosopher]

there you go then. I think it will be FINE.

I mounted a CRT telly on a swinging arm brcket affixed to a true single (4") brick outside wall. Apart from the brick falling in half when drilling leaving a gaping hole to the outside, a bit of mortar stuck it all back together and the wall and the telly stayed up..

[John Rumm]

Ordered online - on the doorstep next day :-)

In use? Well it seems to do what it says on the tin. Its a fairly slim unit so not much battery space in it, and that is reflected in the run time. I have a relatively light load on it (I have not counted but certainly less than 100W), and so could probably get 20mins of run time or more. I have it wired to the main NAS via USB so that can do an orderly shutdown after 10 mins (i deliberately leave some spare capacity should I find the need to manually power up later during an extended power cut).

Not had that one there long enough to comment on battery longevity. Hopefully its kinder to its batts than the APC unit it replaced (that was physically too big for this application)

With hindsight, buying a more sturdy shelf in the first place might have been a good move.

I ran CAT5e everywhere - but then again that was over ten years ago now. So for gig ethernet everywhere seems to cope with any needs I have at the moment. Screening wise I have not had any issues, and analogue audio on the various phone extensions seems clean.

I used decent enough patch panels and mid priced sockets at the wall ports. With hindsight, its not worth economising on the wall jacks - since while in low churn applications like mine they hold up just fine, they are much less pleasant to install than the Excel stuff I use these days:

(only marked in 568B colours so less metal effort required when wiring, and they grip the wires nicely prior to punchdown. The domed faceplates allow a little more cable space when wiring)

Yup they make some nice kit.