FRP Bridge Decking vs. Metal Grating 2

[MJB315]

Hey all,

I've been reading about work done trying to bring FRP composite materials to the transportation / bridge world. It claims that since the costs of composites are dropping, efficient FRP sections are now practical in replacing deteriorated concrete bridge decks and corroded metal grating-- especially decks on movable bridges.

I can see the possible usefulness of an FRP bridge deck over a normal weight concrete deck (lighter dead weight = more allowable truck loading, corrosion resistant materials, etc) but what advantages does it have over metal grating?

Can FRP sections compete?

MJB

 

[Qshake]

I've had numerous coursework on composites and am myself aways looking to use my knowledge and products in the heavy infrastructure and marine industry I work in.

The FRP industry has to overcome the following to make a very solid introduction into the civil infrastructure market. And from my vantage point (various committees I serve on) I do see some of these happening...just slowly.

1. Cost
2. UV degradation
3. lack of in-situ performance data
4. lack of testing data, especially durability or longevity and resiliance
5. poor impact resistance.
6. lack of codes and standards applicable to the civil industry.
7. lack of knowledge on the part of current engineers in the civil industry to understand the design applications.
8. Where applicable adhesion studies and limitations. Which leads to the question..."to mechanical fasten or not" to existing infrastructure.
9. Well understood failure modes. Composite failures are anything but ductile.
10. Control of large displacements that grow with time.

I'll stop there.

Item 1 is pretty easy. There are some appilcations (FRP rebar, FRP decking, concrete repair, etc.) but it is no where near what it needs to be to compete with conventional materials. I recently designed a pedestrian crossing as an addition to a major river crossing. Three alternates were designed for use: Concrete deck, steel deck and composite plating. If it were not for the contractor's not wanting to use light weight concrete in cold weather the composite would not have seen the light of day. However, the contractor was pushed in this direction by schedule and his desire to avoid cold weather concrete over a major river. So he used the composite. It saved time and money only when adding up all the necessities of cold weather work such as blankets, salamanders, etc. Had his schedule worked and concrete was placed in the summer he would not have given composite decking a second look.

Much of the rest has to do with how we engineers design structures now and how we'll need to change to use composites. High strengths are a given for composites but in our industry strength will rarely control for these very thin applications. Delections and stability are bigger issues. Moreover deflections are exacerbated over the years and grow into larger deflections. In the aerospace industry these composite elements are typically plates or shells with stiffening elements attached to them. These composite shells and plates are mainly loaded in the in-plane direction. In the civil industry we load nearly everything for gravity and that is in out-of-plane direction for most applications. So there is a paradigm shift.

Last thing I'll mention is the old performance data or even testing data question. CLients love to hear what you noted, lighter weight deck translates to higher vehicle loads for same structural skeleton. It's a miracle they've been waiting for they say. Then they ask, who else has done this and what testing data is avaialble and what's the warranty? When the client finds out that he's the new guy providing data sets for someone else the smile fades. When he finds out that the specific test data doesn't fit this application but something close, the smile is gone and when he finds out there is no warranty (no warranty with concrete or steel) he's upset.

I'd love to work with the material in our industry but we need some more time.

You might check out John Hillmann who developed a composite girder. Made the cover of ENR.

There are also composite prestressing strands available.

And ASCE publishes a journa for Composites in Construction where you'll find more exciting ideas.





Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.