16ft long structural joists made from honeycomb or Saerfoam

[pbmaise]

I have to span a distance of 16ft between my two aka. This will cover my rear trampoline areas with a solid deck. If this was wood, 2"x12" joists 16" OC is fine.

I find almost no advice or rules of thumb to use core and fiberglass and vinyl ester.

I am in Malaysia and have access to 3 thickness of PPE honeycomb and a new product called Saerfoam

Saerfoam is available 20mm and 30mm

https://www.saertex.com/en/products/saerfoam
According to their website...SAERfoam replaces conventional core materials such as PVC, PET and balsa in an innovative manner: Ultralight foam (PU/PE/PIR) is combined with 3D glass reinforcements.

Their website claims it is far stronger.


I have been thinking of building one beam and testing with a 200kg load in the center. If it breaks I will build it stronger.


Advice is greatly appreciated.

I am thinking of making core beams 12" tall using one of these constructions. They will be set about 14" OC.


A. Honeycomb....4 layers of 12mm overlapped joints no scarf

• 200g/m2 woven
• 400g/m2 woven
• 450g/m2 chop
• 12mm honeycomb
• 400g/m2 woven
• 12mm honeycomb
• 400 g/m2 woven
• 12mm honeycomb
• 400g/m2 woven
• 12mm honeycomb
• 450 g/m2 chop
• 400 g/m2 woven
• 200g/m2 woven

B. Honeycomb 2 layers of 25mm with off set 12/1 scarf at joints

• 200g/m2 woven
• 400g/m2 woven
• 450g/m2 chop
• 450g/m2 chop
• 25mm honeycomb
• 400 g/m2 woven
• 400 g/m2 woven
• 25mm honeycomb
• 450g/m2 chop
• 450 g/m2 chop
• 400 g/m2 woven
• 200g/m2 woven

C. Saerfoam 1 layer 30mm with 12/1 scarf and extra fiberglass over scarp area. This product is so much more expensive that I am thinking more along the lines of a creating an I-Beam. The type of beam, when in wood, is solid timber on the top and bottom and plywood between.

Top and bottom boards solid fiberglass 1/2" thick and 4" wide glassed onto the "plywood" vertical section made from Saerfoam.

• 200g/m2 woven
• 400g/m2 woven
• 450g/m2 chop
• 450g/m2 chop
• 30 mm Saerfoam
• 450 g/m2 chop
• 450g/m2 chop
• 400 g/m2 woven
• 200g/m2 woven

.................................................. .

If anyone also wants to comment on the deck above these joists I would greatly appreciate it.

I am not really looking for a smooth top surface and will be painting with deck paint.

• 400g/m2 woven
• 450g/m2 chop
• 450g/m2 chop
• 400g/m2 woven
• 19mm honeycomb
• 400 g/m2 woven
• 19mm honeycomb
• 400 g/m2 woven
• 400g/m2 woven

[Benz]

I had occasion to make a long beam as you describe a while back. We used Coosa board, epoxy, and carbon fiber biax. There was an upper flange (kind of like a half I-beam), but the real deal-maker was that it was slightly cambered.
The real stiffener in I-beam construction is the vertical component between top and bottom. I'd be comfortable with 1" Divinicell and four layers of 1708 glass on either side. You could build a cambered jig, stand up the corefoam on it, and laminate over it, extending the glass outward in a flange where it met the jig. One jig with mold release on it would build as many identical beams as you wanted.

[GRIT]

When you make a beam, glass in the centre of the beam is wasted. You want the core in the middle, and glass on the outsides.

Glue your core to the thickness you want, then glass the full length. Be sure to use some uni if you want to use it as I think you do.

If you're using epoxy, the chopped strand mat is a waste of resin, and weight. Take it out of the recipe.

If I'm imagining your use case properly, I'd use at least 50% unidirectional, and up to 70%, with the remainder in biax.

You'll have to build test pieces, and decide how much of a compromise you want to make, in stiffness vs weight.

Cheers.
Paul.

[pbmaise]

Originally Posted by GRIT

When you make a beam, glass in the centre of the beam is wasted. You want the core in the middle, and glass on the outsides.

Glue your core to the thickness you want, then glass the full length. Be sure to use some uni if you want to use it as I think you do.

If you're using epoxy, the chopped strand mat is a waste of resin, and weight. Take it out of the recipe.

If I'm imagining your use case properly, I'd use at least 50% unidirectional, and up to 70%, with the remainder in biax.

You'll have to build test pieces, and decide how much of a compromise you want to make, in stiffness vs weight.

Cheers.
Paul.

Thanks for the input. I read yesterday that vinyl ester has a shelf life even when not open that is just 3 months. Since this is Malaysia, I am worried about how old the vinyl ester is. So I am thinking of changing to iso polyester.

My purpose of having fiber between layers of core is mainly to increase bonding between the two surfaces. Each of the 14 beams is only about 1.5m2 so it is really not that much weight or cost.

I am no leaning towards option B. With following changes.

1. I decided to extend the I beam concept to this option and build a solid fiberglass top and bottom 4 inches wide that is glassed onto the vertical piece.

2. At the two ends of the beam I am will beef up the fiberglass layers since this is where the entire load has to be transferred.

Note: I have not mentioned all of these beams rest upon another beam that is then epoxied onto the aka. Since the boat is epoxy the beams that support these 16ft beams will be made from epoxy. I then have to grind off all the paint where these beams attach to the aka and add fresh epoxy and a layers of glass before attaching the beams using epoxy and temporary bolts that have to be later removed and filled.