Box-beam or I-beam question

[Aussiebushman]

I'm working on my own so lifting and bolting a steel beam into place would be difficult and potentially dangerous, also welding in this shed is not an option due to the fire hazard. Construction of an engineered timber beam will be simple because the lower section will be bolted into place first, then the vertical web(s) and upper beam added.

I'd appreciate it if one of the engineering experts here can advise whether a timber box beam or I-beam would be the better choice.

Dimensions are overall length 5 metres (15') depth 300 mm (see below) and the beam would be used to support a chain block lifting approximately 300 Kg (660 lb) shackled onto a welded steel "trolley" moving on wheels along the upper beam surface.

The box-beam option would have internal frames made of 75 X 120mm (3" X 5") Douglas fir with a 9mm ply skin either side.​

The I-beam alternative would be easier to build with a single 9mm ply strut rebated into the same sized top and bottom frames as above. It would be possible to increase the depth of the ply strut to say, 450mm as there is plenty of space to do this. I would epoxy the ply into the rebates.​

As said above, comments from engineers about the relative component sizes would be much appreciated

Alan

 

[Baby Grand]

"Better" in what sense?
Easier to make, easier to install, highest strength/weight, lowest cost? Easier to run electrical/plumbing/HVAC service around?

When you ask a group of engineers a question, be prepared for a lot of annoying questions in reponse.

Based on your description, both beams are relying on the plywood as a shear panel for bending strength. It's important that this panel is continuous (one piece) over it's entire length for it to function as a shear panel. From what you have stated, I'd go with the box section. It has twice as much shear panel and would less apt to buckle.

You have decided to use wood/wood composite instead of steel. Why not also consider a combination of these materials? Considered using a flitched beam - this seems like a good situation to use one.
-Jim

 

[Egon]

The box beam will have better torsional resistance.

I'm not an engineer.

 

[Argosy]

One thing I would be really concerned about is the tall narrow section with the trolley on top. If your lift isn't perfectly vertical each and every time it will twist the beam.

 

[PILOON]

I would laminate 3/4" plywood strips (12" wide), joints staggered glued and screwed from both sides.
to make up a 4" x 12" beam. (maybe 6" wide for stability)
Top the beam with a metal plate for wear.

This approach is similar to a commercially available laminated beam only 'made in place'.
I know that 4 x 12 spanning about 12 ft is sufficient to support a house.
We did a 40" long house and specs were engineered that 2 posts were more than adaquate for the task. ie foundation at ends + 2 jack posts.

 

[john4153]

You may want to reconsider the grain direction for the web pieces, if you want maximal strength. The loads (tension and compression) are carried by the top and bottom members. The purpose of the web is to hold those two structures together. OSB is often used. Sometimes, vertical grain is used. Longitudinally laminated as shown in your drawing is probably not the strongest design. For reference, look at wood spar design for aircraft.

John

 

[evo803]

I would recommend using a Micro-Lam built up beam they 1 3/4" wide x whatever depth needed starting from 7 1/4" and you can bolt together multiple beams " in place " so you are only lifting the weight of one beam at a time. These are very common for structural ridge beams for cathedral ceilings they are very strong and easy to work with and secure in place. The biggest one I had to deal with was 6 pieces 36" tall x 40' long.

 

[Travelover]

One thing I would be really concerned about is the tall narrow section with the trolley on top. If your lift isn't perfectly vertical each and every time it will twist the beam.

+1 . When you use these type of beams in the construction of a house, you are assured that the load is purely vertical. When used for a trolley, there can be a lateral component prior to the load being free hanging. Making the top and bottom elements wider would increase the lateral strength, as well, assuming the trolley could span them.

 

[LD1]

I would seriously reconsider the use of a steel beam.

Not that it wont work, but wood is not an Ideal method for overhead lifting.

If I am reading your post correctly, you are wanting to span 15 feet and lift 660lbs. Is this correct?

If so, you can get by with one of the lightest wide flange beams. A W6x9 would be more than enough. That beam means 6" deep and 9 pounds per foot. So you are only talking 135lb beam. I am sure You could figure a way to set it by yourself or even one other person.

With the span you have, you are allowed a deflection of 1/2". A 660lb load on that beam would only deflect it about 3/16". A 1000lb load would be .25" and a 2000lb load would be the limit @ .5". So it will be more than strong enough for the loads you intend. And I am sure you can come up with a way to support/anchor/bolt it without welding.

And since I-beams are ususally priced by the lb @ anywhere from .50-$1.00 per pound (depending on where you go), that is not going to cost you a lot of money either. End result will probabally be cheaper, easier, stronger, and lighter overall. This is assuming there is no other load on the beam like overhead storage/loft, etc.

If you can manage the 135lbs, that is the route I'd go.

 

[Argosy]

You could tie a couple of trusses or rafters together and use a chain fall or come a long to lift 135 lbs. That would be easier than building a beam (in place?) out of wood.

 

[Shield Arc]

For that kind of weight, at that span you and a buddy could easily carry an S-shape up ladders into place.

 

[BruceWard]

To me this type of wooden truss seems easier to manufacture

Open Web Floor Truss

 

[Aussiebushman]

Thanks guys advice much appreciated. I expected to get a few different views so apologies to those who feel their particular suggestion has been overlooked. You have all been very helpful and have provided ideas that together make up a solution that seems to meet most of the criteria:

• The steel web or pre-made trusses are tempting, but transport over 90 Km to the farm from the fabricators then lifting it on my own pretty well rules these options out

Laminating ply 12 deep X 6 wide with staggered joints is possible but hard to do it in situ and too heavy to lift on my own once assembled. The Micro-Lam option would be easier to build up a piece at a time but more costly than a box-beam.

• A box-beam structure is the easiest of the lot to build and certainly better than an I-beam because it doubles the shear panel
• By making the box structure of timber, then adding an internal web of steel plates to handle tension and compression loads it should be should more than adequate in strength and easier than getting the ply grain vertical
• A steel plate on top is a great idea to prevent wear from the traveller, but also to stop any lateral bending if the lift is slightly out of vertical

If I have got anything badly wrong, please yell. Otherwise, thanks again.

Alan

 

[LD1]

Yes, what you plan on doing will no doubt handle the load just fine. But I still think you are way over-complicating things. We are only talking a 135 pound steel beam to set and give you a saftey factor 3x's. If you cant set it yourself, you dont have even one person that can help you:confused2:

 

[tommu56]

Steel I beam a couple of comealongs and some rigging you should be able to get it up yourself

a pair of jacks and big pile of cribbing would get you their too

If you are like me I got more time than money I would invest in the steel.

tom

 

[o2batsea]

My thoughts:
Lifting; with the right rigging there is no reason why you as one person could not lift a steel beam into place. It may not go fast or be very pretty but a combination of lifting tackle or chain hoist each end, and leverage should be the ticket. You'll need a ladder at each end and a good supply of coffee or Red Bull.
I think you could also do it with two small bottle jacks. A jack post with holes for a cross brace every 6 inches? Keep moving the peg up one hole at a time as the end of the beam comes up....dunno...lotsa ways. Just wouldn't go too fast.

Wood beam; if you choose to build in place do a bit of prep work to the structural components to assure it will be a one time one shot deal. Pre assemble everything on the ground "dry" with no fasteners to be sure you have all the parts. Coat everything with at minimum two coats of thinned epoxy resin mix. This will encapsulate the wood against rot and insects and will give you a firm base for the next step which will utilize a thickened epoxy glue.
Assemble all the parts with epoxy thickened to peanut butter consistency with wood flour or fumed silica. Use removable stainless deck screws to hold the parts together for clamping force. Using stainless will allow you to leave the fasteners in there. With the frame built, install the sides with more thickened epoxy glue. The result will be a structure that is as strong as a solid beam without the weight. The epoxy encapsulation and glue is the trick

 

[Aussiebushman]

Yes "o2batsea" you are talking to the converted. I am also a boatbuilder so I'm working with epoxy all the time - in fact building a 22' strip/timber trimaran right now, which the reason the beam is needed - to lift the main hull off the trailer, then lower it onto old inner tubes where it can be rolled/turned to make the glassing and fairing easier, before lifting it back onto the trailer.

As well as coating the timber and ply with epoxy, the joints will be filleted with thickened epoxy. This is probably all overkill. I'm nearing seventy so the beam will outlast me by a considerable margin, even without the epoxy!

Alan

 

[TGF]

go steel.

 

[crazyal]

Sounds like maybe years ago steel would have been an option but if I was close to 70 I'm not sure if I would want to do some of the things I've done. If you are going wood have you thought about building it in place?

 

[chickenman]

it would help to see a pic or sketch of the installation