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  1. #1
    Join Date
    Sep 2007
    Location
    Melbourne, Australia
    Posts
    149

    Default Steel grate rhs deflection

    Hey guys
    My cousin has a factory thst has been broken into twice now and they are entering from a hole in a gate. He has asked me to build s large grate which will be mounted between two concrete walls.


    I'll be using 20x20x1.6 rhs and am a bit worried about deflection as it's quite big.


    He doesn't want any horizontal support as they may use it as a step to climb up and over. I wanted to add one half way for strength.


    Will this be ok. Bars are 200mm apart.


  2. #2
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,439

    Default

    Hi Oohsam,

    If they want to break in through that gate, they will just use a car jack to force the bars apart.

    At one premises that I owned, they used a car jack to force open a steel framed door. They crowbarred the bottom of the door away from the frame and then used the car jack to force it open destroying the lock.
    Best Regards:
    Baron J.

  3. #3
    Join Date
    Feb 2013
    Location
    Laidley, SE Qld
    Posts
    1,038

    Default

    3m long 20 x 20 x 1.6 RHS is not very strong, at 200 spacings it could be distorted enough for a person to pass through with little effort, possibly even cut with bolt cutters.

    I'm assuming your cousin is trying to protect his factory with minimal expense - no shame there at all - but for a grate of that size and type to be effective, i.e. people can't readily force their way through it, it needs way bigger sections of RHS. I'd be thinking 100 x 50 or 150 x 50 plus razor wire on top to stop climb overs.

  4. #4
    Join Date
    Dec 2015
    Location
    Melbourne
    Posts
    202

    Default

    I would make the outer frame bigger in section, and increase the vertical bars to something like 30mm or 40mm square 1.6mm.
    you might pay to check out some of the commercially available fence panels. some are similar in construction but have the vertical tube passing all the way passed the top bar and squashed in a press to form a flat section which is then sharpened to a point.

    like this
    Ornamental Steel Fence Panels for Higher Security


    They list there sizes for industrial as 1" (25mm) section size fore lengths up to 8' (just under your 3m). This to me says that 30mm would be the minimum.

    If they really really want to get in they will.

    its a balancing act between effective protection and being a deterrent.

    Ryan

  5. #5
    Join Date
    Jan 2004
    Location
    Mackay North Qld
    Posts
    6,446

    Default

    Oosham,
    No
    20 x 20 x 1.6 over a span of 3 meters, is as weak as, well, you know what !

    Both the height and span of the gate work against you and the dimension of the bars them selves are way , way undersized.

    Bars ( box section ) of greater dimensions is called for, as are heavier wall thickness of box and closer spacing of the box sections.

    Yes it will cost a lot more, and yes it will be heavy but will take substantially longer to break into.

    An alternate design might be a frame with some close spaced heavy mesh ,harder to climb unless one has monkey toes.

    Grahame

  6. #6
    Join Date
    Sep 2007
    Location
    Melbourne, Australia
    Posts
    149

    Default

    Thanks Guys,
    This helps immensely. I will go back to the drawing board.
    I'll beef up the rhs in size and thickness, and will probably weld some mesh to it too.

    As you know, these guys will get in no matter what, its more of a deterrent, and also, make it hard for them to be able to escape with anything of value if they have to climb a 3m fence with razor wire at the top. Hopefully they would rethink it after coming across such an obstacle.

    Will update on progress.

    Thanks guys

  7. #7
    Join Date
    Nov 2012
    Location
    Adelaide
    Posts
    81

    Default

    Oohsam,

    You need to consider an effective way of mounting the grate to the walls as well, otherwise that would also be a weak point.

    I have seen others drill holes in the wall and place solid bar in there, with a corresponding hole through the grate/frame. There are also holes through the frame and it all gets plug welded (not sure if it's the correct term) as a permanent fixture.

    Thanks,
    Spiro

  8. #8
    Join Date
    Sep 2007
    Location
    Melbourne, Australia
    Posts
    149

    Default

    Thanks Spiro,
    Yes I'll be welding tabs to the frame to bolt to the two walls and floor with dynabolts, and then i will tack weld the dynabolt to the tab so it cant be undone with a wrench.

    This is the easy part!

  9. #9
    Join Date
    Dec 2015
    Location
    Melbourne
    Posts
    202

    Default

    I have found "weldmesh" with squares around the 40mm size with a is hard to climb and keeps people out, use a razor wire top to it as well, it is however easy to cut so weld some 40mm x 3mm strap to the back of it on 300mm centres and then even if they do cut it with bolt cutters they can not spread it far enough apart to get it.

    Australian Steel & Wire - Weld Mesh Experts 358 High Security Fencing Weld Mesh Rockingham Steel Manufacturer, Galvanised Welded Panels and Fencing Products; Steel Quality Supply Service:

    edited

    maybe more like this
    Australian Steel & Wire - Weld Mesh Experts Weld Mesh Industrial Standard Galvanised Sheet 2.0m X 1.2m 50/50 4mm Rockingham Steel Manufacturer, Galvanised Welded Panels and Fencing Products; Steel Quality Supply Service:

    then back with straps to stop them cutting through it.

  10. #10
    Join Date
    Jun 2010
    Location
    Canberra
    Posts
    1,322

    Default

    Geeze, where are all you people getting razorwire from? I didn't think it was readily available?

  11. #11
    Join Date
    Feb 2013
    Location
    Laidley, SE Qld
    Posts
    1,038

    Default

    Razor wire is $50 or so delivered for a 100m coil from eBay.

    I have seen 400/500 dia spiral duct run along the top of a fence to deter climbers, they can't get a grip or an arm or leg over when they get to the top.

    Check out the fencing at your neighbourhood correctional facility.

  12. #12
    Join Date
    Feb 2003
    Location
    formerly from Sydney (north of The Harbour), NSW, Oz
    Age
    68
    Posts
    306

    Default

    oohsam,
    I think there is a standard specifying the maximum gap between the bars for what you're building -- it would pay to check
    regards from Canmore

    ian

  13. #13
    Join Date
    Dec 2005
    Location
    South Australia
    Posts
    1,656

    Default

    I don't know about VIC. in SA you have to have a almost impossible to acquire permit to install razor wire, usually reqires a second barrier fence plus a warning notice and you are then liable fo any injury to any person.

  14. #14
    Join Date
    Dec 2015
    Location
    Melbourne
    Posts
    202

    Default

    The fences that I have been involved with that have had razor wire on them were government owned

  15. #15
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
    Age
    71
    Posts
    5,942

    Default

    Quote Originally Posted by Ryan in Melbour View Post
    I have found "weldmesh" with squares around the 40mm size with a is hard to climb and keeps people out, use a razor wire top to it as well, it is however easy to cut so weld some 40mm x 3mm strap to the back of it on 300mm centres and then even if they do cut it with bolt cutters they can not spread it far enough apart to get it.
    Nice idea Ryan, but I think the 40X3 strap would flex far to easy, I'd be inclined to use 40 X 40 X 4 RHS 200mm vertically apart, with the mesh welded on the back to prevent the intruders climbing easily, plus if using a cordless saw/grinder it would take a while to cut a hole large enough to enter. The thicker the RHS the longer it should take. To make it even more difficult, drop some round bar about 1.8m long inside the RHS, so that when they go to cut through with a saw the bar rotates slowing down their progress, even an oxy acetylene wouldn't cut this set up to easily, as the bar, I don't think would get hot enough to cut unless they spend more time to cut. I estimate about 15 minutes to cut a hole big enough to get through, using the bar inside the RHS.
    I wouldn't use dyna bolts to mount the section, as someone suggested use some round bar 16mm diameter and about 300mm long welded to the fence to locate it, the deeper into the piers the stronger it would be. Probably only a ram raider would take it down.
    That's the trouble with cordless power tools, a burglars delight.

    Kryn
    To grow old is mandatory, growing up is optional.

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