anybody ever tried to lift two bents at once? towards each other. maybe a braced pole in the middle?

Mo, I'd question the wisdom of the idea. I've had designs where multiple, long span trusses were set two at a time including the inter-connected structural bridging because the two trusses - thus connected - were stable when set on their supports. Then the next pair was set and so on. Then the missing bridging was installed in the spaces between the each set of two trusses. So, in this instance there is a compelling reason for the erection scheme. Your questions begs others: Why, for what purpose? Bents are often assembled stacked usually due to limited floor area. So, obviously, you'd need two cranes. Then you'd need to consider the economic efficiency, safety, etc. Unless there is some compelling reason for doing what you're proposing, I'd stick to the "one at a time" approach. And, if you'll be more specific, then perhaps there are other issues to consider. Hope this is helpful.

Yr Frndly Engrg Svnt, David

Hi Mo,

If you built a 2 bay frame and provided ground sills then you could add foot braces on the centre frame which would then provide a relatively stable atandalone frame that could then be used to pull up the two adjacent frames in tandem which would keep the whole lift in balance. In effect you would be using the centre frame as a gin frame and lifting could be done using winches and pulleys rather than needing to employ a crane. You might need more people to help control the lift and guide the post tenons into the sill mortices.

Regards

Ken Hume

Ken, have you ever actually pulled one up this way?

While it is theoretically possible, I'm not sure I see a good reason.

We've had raisings where a bent was lifted, braced off, the second bent was lifted and held by the crane while a second crane or other lifting mechanism set the connecting members.

But to manually raise 2 bents toward each other at the same time from a central lifting mechanism -- you'd need to be really, really good to pull it off. Col. Mullen could do it and a few others I know, but anyone else would be tempting fate.

Mo, tell us what you're thinking about.

Hi Mo,

Many years back I bought a copy of "Timber-Frame Houses" a compendium of articles first published by Fine Homebuilding (1992).

On pages 31 - 33 there is a very interesting article by Ross Kirk on "Solo Timber-Raising". In this article Ross examines the possibility of devising a safe way in which he could go about raising his timber frame workshop without the need to call upon the usual (for the time) army of helpers or crane.

Ross's main motive lifting power was to be nothing more than that of his tractor & come-a-longs also using pulley blocks and rope. I was inspired by this article and as I do not own a tractor I wondered if it would be possible to do an equivalent lift without the aid of the tractor using nothing more for motive power than muscle and 4 off x 2 ton come-a-longs purchased from Home Depot to raise my own Sobon type timber framed shed.

The flaw in Ross's proposed method was that the ropes being pulled by the tractor might not only raise the frame but also due to the blocking plates that he had clamped to the end of the long sills to stop the frame sliding off the sills could also potentially result in the whole floor being pulled off its foundation. Thus if a way could be devised to help balance frame rasing forces then the raising would be safer and more reliable and any potenetial for sill sliding would also be eliminated.

Its not impossible to manually raise and stabilise the centre frame of a Sobon type timber framed shed (12' x 16') with the aid of a few friends especially when the floor has been laid to provide a good solid working platform, but its not so easy (or safe) to raise the end frames when the whole frame is standing above ground level on a dwarf wall foundation whilst at the same time dealing with the demands posed to align and connect the side girts. This got me thinking about how this could be more safely achieved and hence the method that I outlined above.

I agree with Gabel that Mo should now more clearly define his challenge and maybe Mr Hourdequin PE Yr Friendly Hvy Tmbr Engr NY,PA,MD,OH, WV,VA,NC,TN,GA,AL,FL (did I get them all ?) can be challenged to put all that scrambled egg to work ! Who knows maybe even Colonel Mullen might be encouraged to put in a rare appearance on this Forum.

What's the challenge Mo ?

Regards

Ken Hume P.Eng.

Hi All,

David, Ken, and Gabel, thank you for the good insight.

Here is my line of thinking.

I have to bents that are connected by two plates and a ridge. (you can see an image in the topic cypress info)
It is an exhibit that needs to be raised and lowered with efficiency. There is no deck to use for post placement, and due to time constraints was thinking of a way to place posts without lay-out. These bents are modest in scale and could probably be lifted by a small team of 5 or 6.

I tried to run the numbers for three people to raise but you don't know how green the cypress will be.

That being said,



Now, this is a scheme. If this is plausible, I still no nothing of the mechanisms used to lift towards each other. Comealongs, pulley system? it seems the pulley would be faster with a good enough ratio.

Another problem, The plates can be lifted off ladders, but the ridge would probably be cumbersome. In my drawing the pole is centered in a pyramidal braced frame. This would be in the way of ridge placement and it seems that if the pole was offset on the y-axis (in relation to the picture plan) it would skew the bent raising.

I thought about scrapping the pyramidal braces in place of two braces in the x-axis so the pole could lean to avoid this problem, but then realized guys would be needed to do this. Don't want to have to do this, for reasons stated above.

I'm all ears.

Thanks,

Mo

If you are going to build the crane, why not just build a bracing platform? Raise B1, then deadman the plates (posssibly using your brace platform). Raise B2 into the awaiting plates. Come along together.

Ridge - design the joinery so it drops in from the top. Bolt or clamp a 4x or 2x to the top face that is longer than the distance from B1 to B2. If you can lift the plates on a ladder you can lift the ridge to the same height. Slide the ridge up the rafters (using that extra material you bolted on...) - roll into place.

Snug everything up. Be sure to through peg so you can take it all apart.

Dismantle your bracing / working platform.

Seems that by the time you built the tower structure (assuming you had enough hands to get it in position) - you could have the structure standing.

I'm also assuming this is what - 10' - 12' or so square?
Is this a display booth?

I've put up and taken down dozens of various timber display booths. All with 3-4 guys. All with a similar king post bent on the end. Some were recycled material, others were green fir or pine. It is work. Never needed use of a crane (even human powered) - but we have used an exhibit hall fork lift on one occasion for take down.

Hey bmike,

Plan, 12' x 14' in wall direction, 17' in wall direction with projection of plates and ridge. both ridge and plates drops onto four mortises. for the ridge: two kingpost tenons and two braces. for the plates: two post tenons and two braces. both plates and ridge overhang and have to drop onto connection.

Will a bracing platform still work for this, and if yes, can you explain it further for me.

Thanks,

Mo

Do you have a drawing somewhere else on the forum? I need to understand how the plates and ridge work?

A bracing platform - basically something you can lean one of the bents against while you deadman the plates... it can be your shipping crate or you can frame up some triangles that are attached across the frame.

But it seems like the plates drop over the top of the posts? How does that work with the rafters?

If the plates extend beyond and they sit on top of the posts - you need to raise this as a wall and infill the shorter ties and rafters... no?

Post a pic of the frame (3d model?) so I can see what you are trying to get up.

If posts sit on top of plates, assemble and raise W1, brace off.
Deadman the short tie (that the KP sits on).
Raise W2 (already assembled) into the ties. Come along to stabilize.

Now it depends on how your king posts work -

If you can - set the ridge on the ties.
Then insert king posts into ridge (with braces).
Raise the ridge section just like a wall, dropping into the ties.
Block up off the tie a bit and insert rafters (depending on how you design the joinery...)


-Mike