Hi,
I am working on my final year engineering project and project aims of using polypropylene fiber in concrete. I am aiming at replacing/minimizing the steel reinforcement in manhole covers with polypropylene fibers without affecting the engineering properties.

Please suggest the design criteria for manhole covers using steel reinforcement and test carried out on it.

Thanks and Regards,
Sachin.

Whatever you do, make it Round. So it doesn't fall down the hole.
Probably the only 2 shapes that won't fall down the hole is round, and trianglular. Triangle is not practical.
Have you checked out fiberglass rebar?

COMPOSITES AND CONCRETE: COMPOSITESWORLD.COM (http://www.compositesworld.com/articles/composites-and-concrete.aspx)