Plastic Beam

[TORCHMAN]

Has anyone ever worked with plastic as a structural material? It seems to me that the industry accepts it in a few applications like exterior decking or roofs for greenhouses. Or in composite applications such as adding fibres to concrete. Though it seems like there is a cut off line where the structural member is not a deck and fully plastic (no beams, columns). Why haven't we made small beams or studs out of recycled polypropylene?

A couple that are out on the market below:

ThruFlow – Premium Decking Solutions

INTRODUCING LEGACY XP 2'X4' PANELS Featuring a 24" span! GO WITH THE FLOW The open architecture of ThruFlow™ allows your dock to fight the power of water's surg

thruflow.com

Shop 5/4 in x 6 in Structural Plastic Lumber

Discover the durability and versatility of our 5/4 in x 6 in HDPE board. Resistant to weather, rot, and fading, it’s perfect for decking, docks, and outdoor projects.

plasticlumberyard.com

JD Composites - JD Composites

We have a vision of a greener future, where we help create a new line of architectural structures using 100% recycled PET plastic bottles.

jdcomposites.ca

 

[Harbringer80]

FRP structural shapes are available. Capacity is of course relatively low. I've used them in telecom work for rooftop screen enclosures where you can't have metal blocking antenna signals. The FRP manufacturers have their own design guides you can use.

I've also specified FRP bar grating in certain corrosive environments.

Structural Shapes and Plate

EXTREN® | SAFPLATE® EXTREN® EXTREN® is the registered trade name for a proprietary line of standard pultruded fiberglass structural shapes and plate produced by Strongwell. The EXTREN® line consist…

www.strongwell.com

 

[SWComposites]

Torchman - by "plastic" do you mean pure unreinforced plastic? or glass fiber reinforced plastic? and if glass fiber reinforced, it is continuous glass fiber or chopped discontinuous glass fiber? Strength and stiffness are highly dependent on the plastic resin, the reinforcement type, and the amount of reinforcement.

Structural fiberglass beams and panels have been used for bridges and bridge decks.

Some articles here: https://www.compositesworld.com/topics/construction

also:

Creative Composites Group acquires United Fiberglass of America

The acquisition helps support critical infrastructure applications.

www.compositesworld.com

CCG marks 10-year anniversary for six-span FRP Massachusetts bridge

Inspection on the state’s oldest moveable steel truss bridge since its renovation project in 2013 reveals CCG’s prefabricated FRP decking is in optimal condition.

www.compositesworld.com

Composites end markets: Infrastructure and construction (2024)

Composites are increasingly used in applications like building facades, bridges, utility poles, wastewater treatment pipes, repair solutions and more.

www.compositesworld.com

CCG FRP panels rehabilitate historic Northamption Street Bridge

High-strength, composite molded, prefabricated panels solve weight problems, safer shared use path, for the heavily-trafficked bridge.

www.compositesworld.com

Great Haywood Marina reconstructed with Dura Composites fiberglass decking

Latest Lakeland Leisure Estates project saw design, supply and installation of 10,000 square meters of durable, long-lasting Dura Composites Mini Mesh Grating.

www.compositesworld.com

Creative Composites Group’s FRP composite bridge decking is sourced for five upcoming projects

CCG seeks to accommodate growing FRP deck installations across the U.S.

www.compositesworld.com

 

[JoshPlumSE]

I swear I've been on a project where they used non-metallic grating before. Same look as metal grating, but with a fiberglass product. You just look at the allowable span for the most part. I didn't see any problem with these products. Though, to be fair, I really don't have much knowledge about them. They seemed like any grating to me.... meaning there is a load and span limit on the product..... The Thru-flow product you linked to seems pretty similar in concept to what I've remember seeing.

That being said for a true deck, there is probably some diaphragm action that you need to look at. Other than that the main beams are generally more conventional products. Composite wood products (Parallams, OSB, etc) are all over the wood industry. I haven't used the type of products you linked to before. But, I feel there has to be some code compliance documents on them if you rely on them for diaphragm behavior.

Lastly, there were some people that were really into Structural - Insulated - Panels awhile ago.... I don't know much about those products, but they seemed similar to the JD composites site you linked to. I kind of remember seeing some articles in Structure or Structural Engineer trade magazines about SIP.

 

[TORCHMAN]

@Harbringer80
Very interesting, I see they use it for heavy structures. I see they have trade marked their product but they explain they are out of vinyl ester resin or Polyester resin. I am fairly ignorant about plastics, are these resins something that could be extracted out of plastic bottles or other commonly used plastics?

@SWComposites
I am interested in both. I am mostly interested in recycling of plastics like polypropylene which is abundant in our consumer market and transforming to a structural application. If it requires some glass fibre to reinforce it that is fine.

 

[enginerding]

Creep. I think the biggest reason to avoid using unreinforced polypropylene beams is the huge creep to be expected under load. It could also be a problem with reinforcement as well if the shear deformation continues to increase through time away from plane-sections-remain-plane assumptions typical for beam design. I am a long way out from my composites courses in grad school, but the best matrices are compatible with the fibers that they encase. I would expect that this could only make sense in very low DL conditions (similar to grating) where creep won't kill you.

 

[Harbringer80]

@Harbringer80
Very interesting, I see they use it for heavy structures. I see they have trade marked their product but they explain they are out of vinyl ester resin or Polyester resin. I am fairly ignorant about plastics, are these resins something that could be extracted out of plastic bottles or other commonly used plastics?

No idea about the raw materials they manufacture them from. I'm sure if they can get the required strength and is economical, they are doing it, similar to Trex deck boards which I've been told are made from recycled milk jugs.

 

[SWComposites]

agree with enginerding
unreinforced polypropylene will creep underload, has relatively low heat distortion temperature, and a relatively high coefficient of thermal expansion. this is why you see a lot of Trek type boards warped and deflected after a few years.

 

[bugbus]

We have used this recycled plastic stuff before as kerbs on boardwalks / golf cart bridges, similar to the below photo.
I have to admit I don't really recall how strong the stuff is, but in those cases the loads were very small.



I've also seen them used as pedestrian barriers, fence palings, bollards, etc. In the hot sun, they warp and bend like crazy though.

 

[MintJulep]

explain they are out of vinyl ester resin or Polyester resin. I am fairly ignorant about plastics, are these resins something that could be extracted out of plastic bottles or other commonly used plastics?

Vinyl ester and polyester resins describe epoxy chemistry.

It might be technically possible to recover some of the needed feedstock from the post-consumer plastic waste stream, but it doesn't seem commercially viable at the moment.

Why haven't we made small beams or studs out of recycled polypropylene?

Because the strength:weight, creep, stiffness and price are inferior to what's currently in use.

Many of the cellular PVC trim boards (Azek, TimberTech, Palboard, etc.) use recycled plastic, and seem a more suitable use since they aren't intended for structural use.