justcichlids Posted July 21, 2007 Share Posted July 21, 2007 i have a massive rack holding a number of tanks in my fish room. i have a 6 and half foot space between posts and 1 section is sagging about 10mm, at the front only as i have a support post in centre at the back. the beam is made from 4 x 1 treated pine. apart from the obvious what can happen if it gets worse? and has anyone got any first hand experience with this happening to them. cheers jd Link to comment Share on other sites More sharing options...
gingerbeer Posted July 21, 2007 Share Posted July 21, 2007 Assuming that it is structural timber - how long has the rack been up. If it has just gone up within the last month or so the bad news is that long term it will go twice as much as the timber creeps. If that is the case I would panic! I am guessing that you have 2foot deep by 2 foot wide tanks on there. Based on this you could reasonably expect around 12-15mm deflection midspan - and the member is about 21% overstressed - that is carrying 20% more load than it is theoretically strong enough to carry. If that is the fase I would panic slightly. You need a post to break the span before you have heartache. Either a broken stand or too much deflection leading to cracked tanks. HTH Steve Link to comment Share on other sites More sharing options...
robdog013 Posted July 21, 2007 Share Posted July 21, 2007 definitely brace the stand or rebuild one out of steel. sounds scary, imagine all the water Link to comment Share on other sites More sharing options...
Stuart74 Posted July 21, 2007 Share Posted July 21, 2007 a 6ft span between uprights, that can only end with I would rebuild your stand as others have suggested otherwise you could end up with a massive clean up Link to comment Share on other sites More sharing options...
justcichlids Posted July 22, 2007 Author Share Posted July 22, 2007 thanks everyone for your replies! somehow i don't think they'll help me sleep at night. to answer a couple of questions the tanks are 6' x 18" x 18" the stand has been up since feb and most of the sag happened straight away and seems to be stable for a couple of months now. re building is not an option so a brace will have to made. the main reason for my design having such large spaces between post was not to obstruct vision into the tanks and also i can remove the tank from the front if needed. i thought by using large 4 x 1 it would be strong enough. cheers JD Link to comment Share on other sites More sharing options...
andrew8710 Posted July 22, 2007 Share Posted July 22, 2007 Your best bet with the brace would be to use 4x4 and check it in 2 inches (half thickness) into every level of your stand and then run it tight into the ground that should hold it. Personally to build a stand with that span even using 6x2 probably isn't strong enough, I personally would be looking at 6x3 or something around that section size. Link to comment Share on other sites More sharing options...
gingerbeer Posted July 22, 2007 Share Posted July 22, 2007 You could look at jacking up and stiffening by fixing another 4 x 2 (maybe F27 hardwood) alongside with batten screws. At the end of the members you would need to support it directly. Steve Link to comment Share on other sites More sharing options...
Ash Posted July 22, 2007 Share Posted July 22, 2007 should have used steel for that one beam to get around the span width- I'd think nice thick walled RHS in the same dimensions as the timber would be strong enough* (6x2 aka 150x50 3mm wall min) * I am not a gingerbeer or any thing, but it would have to be better than the wood you have now that WILL break your tanks very soon Link to comment Share on other sites More sharing options...
Josh Posted July 22, 2007 Share Posted July 22, 2007 I have a rack that hold the same size tank and its made from 50x50x3 steel and bows at most 5mm over the same span (6ft) I have also seen timber racks (baZ racks) made from 90x45 timbers that dont bow but have three spans across that base of the tank, one at the front one in the middle and one at the rear. I couldnt think of anything worse then the "obvious' happening. Josh Link to comment Share on other sites More sharing options...
Colfish Posted July 22, 2007 Share Posted July 22, 2007 JD i'd certainly be looking at adding some strenght to that front beam. just because it hasn't sagged any more since built, it's only a matter of time before the silicone lets go, at best, a split seam. worst case, ??? the front beam on my 72x18, two 40x40x2.5 rhs stitch welded together 72" is a long span of GLASS. maybe a post in the middle that can be removed when you want to take the tank out. might not look the best, but it would look better than the risk your're taking hth; Link to comment Share on other sites More sharing options...
BaZ Posted July 22, 2007 Share Posted July 22, 2007 How difficult is it going to be to remove the tank so you can make some repairs to the rack? If you could do this you could replace the 4x1 with a 6x2 or even bigger (but I think I'd be happy with 6x2 if it was my tank). Link to comment Share on other sites More sharing options...
justcichlids Posted July 22, 2007 Author Share Posted July 22, 2007 man............ i'm not sleeping very well at the moment.............. what do you guys think about using maybe a form ply sheet under the tank and jacking and srewing the beam to it?............if you get my drift.... removing the tank is not a huge drama but the stand is 6 mtrs long and the beam is one long 6 mtr peice. basically if i can modify what is there already. the stand is all batten screwed and and painted and it holds 4 six foot tanks and 2 four foot tanks so pulling tthe stand apart is not really an option. taking one tank out is ok but not 6. Link to comment Share on other sites More sharing options...
BaZ Posted July 23, 2007 Share Posted July 23, 2007 What condition is the rest of the 6m piece in? Is it supporting smaller tanks over smaller spans? I'd still be inclined to replace that beam, or even just the section of it that is over a large span with a bigger bit of timber. 4x1 just isn't enough in my opinion. Does it have a centre beam that runs the full length of the tank too? Link to comment Share on other sites More sharing options...
Josh Posted July 23, 2007 Share Posted July 23, 2007 I would place a brace under each beam at each leg then run a center brace the whole length. Check out the Baz rack on the SCP. That way you should only have to remove the top tank Link to comment Share on other sites More sharing options...
gingerbeer Posted July 23, 2007 Share Posted July 23, 2007 I acutally have a problem with the three beams one at each side and one down the middle approach. Say the beams are 300 aprt for a 600 tank total. What happens to a load is that 150mm will go to the front beam, 150 to the back beam and 300 to the middle beam. Hence the middle beam will deflect about twice as much. Now that doen't happen as the aquarium tends to act to distribute the loads and so kinda works - until tank warps. I prefer a nice big front and back beam and then trimmers between the front and back to support the bottom of the glass. Lot more work making a stand that way. Shoot some pictures up and lets have a look and see if we can figure the best way to strenthen the stand. Understand the parameters - need picture of how you fixed to the support leg and space around the beam. I am still leaning towards a nice bit of hardwood screwed to the inside of the run of the beam. But we need to support at the end to make it want to take the load. And the beam will need to be jacked up to get it straight again - when you take load of a beam there is some residual deflection that will not come out without application of force. Steve Link to comment Share on other sites More sharing options...
gingerbeer Posted July 23, 2007 Share Posted July 23, 2007 I actually have a problem with the three beams one at each side and one down the middle approach. Say the beams are 300 aprt for a 600 tank total. What happens to a load is that 150mm will go to the front beam, 150 to the back beam and 300 to the middle beam. Hence the middle beam will deflect about twice as much. Now that doen't happen as the aquarium tends to act to distribute the loads and so kinda works - until tank warps. I prefer a nice big front and back beam and then trimmers between the front and back to support the bottom of the glass. Lot more work making a stand that way. Shoot some pictures up and lets have a look and see if we can figure the best way to strenthen the stand. Understand the parameters - need picture of how you fixed to the support leg and space around the beam. I am still leaning towards a nice bit of hardwood screwed to the inside of the run of the beam. But we need to support at the end to make it want to take the load. And the beam will need to be jacked up to get it straight again - when you take load of a beam there is some residual deflection that will not come out without application of force. Steve Link to comment Share on other sites More sharing options...
justcichlids Posted July 23, 2007 Author Share Posted July 23, 2007 ok i'll take a few pics tonight and hopefully post them tomorrow. i like the gingerbeer approach and have discussed it with a mate who came up with the same idea, jacking it up has some logistical problems that hopefully some pics will show what i mean. thanks to everyone for the advice Link to comment Share on other sites More sharing options...
BaZ Posted July 23, 2007 Share Posted July 23, 2007 I actually have a problem with the three beams one at each side and one down the middle approach. Say the beams are 300 aprt for a 600 tank total. What happens to a load is that 150mm will go to the front beam, 150 to the back beam and 300 to the middle beam. Hence the middle beam will deflect about twice as much. Hi Steve What you have said makes sense to me, but I have a question if you don't mind since you are obviously qualified in this area and I am just a backyard hack Would you see a problem with this design if all the beams are oversized anyway? (shorter spans and lighter tanks). You have me looking at my setup now and wondering Link to comment Share on other sites More sharing options...
fishdance Posted July 23, 2007 Share Posted July 23, 2007 Why dont you stiffen the front beam with extra wood? I know adding extra support from the upright beams is best but the stand is holding well apart from the front bow isnt it? I would do a simple experiment like, drain one tank to remove the front bow. Add an extra length of wood to the front beam (4x1 is what you used isnt it?) but simply clamp it in place with 3 or 4 sturdy clamps. Then refill the tank for a week to see how much bowing this removes. If it is only the bow then strengthening the front beam by thickening will work. If this is not sufficient then you will have to add the extra side supports. This is the simplest and most practical method to me. Cheap and fast way to see what will work since even a negative result is useful. I prefer to work all in wood but a steel strengthener would be smaller and easy to screw on/behind. Link to comment Share on other sites More sharing options...
justcichlids Posted July 24, 2007 Author Share Posted July 24, 2007 http://s205.photobucket.com/albums/bb234/justcichlids/ Link to comment Share on other sites More sharing options...
justcichlids Posted July 24, 2007 Author Share Posted July 24, 2007 hey folks. see previous post for some pics, let me know what you think thanks justin Link to comment Share on other sites More sharing options...
gingerbeer Posted July 24, 2007 Share Posted July 24, 2007 Your right Baz the more oversized the members - or the lighter the load - or the more the members are oversized the less deflection occurs. Hence differetial deflection is less. For a 4 x2x2 tank stand the deflection of the sticks is only about 1/5 of the deflection of 6 x 2 x 2 tank stand However in this case as the one member at the front is overloaded - putting another in the middle will not fix the problem in my opinion - only move the location or creat a false condition until more problems occur. Will look at the photos later and gie some ideas on fixing. Steve Link to comment Share on other sites More sharing options...
justcichlids Posted July 24, 2007 Author Share Posted July 24, 2007 thanks steve and baz. i'm emptying the tank tonight and getting a high lift jack tomorrow so i'll talk to guys then cheers Justin Link to comment Share on other sites More sharing options...
justcichlids Posted August 3, 2007 Author Share Posted August 3, 2007 just in case anyone cares i've fixed the problem of sagging now what i did was using a peice of 2 mtr long 60mm steel angle 6mm thick $30.00 (serious bit of steel) and a high lift jack (like those ones yoy see on the back of real 4 wheel drives) bolted it through with 5 x 3/8 bolts problem solved. cheers JD Link to comment Share on other sites More sharing options...
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