How do I make a Paper bridge that can hold up to 10KG using only paper and tape?

I'm no structural engineer... but your question seems to be missing something to me.

The 10kg... How is that applied? What's the surface area being displaced? How long does your bridge have to be? Tall? The string being "optional"... does it have a limit or use? You could wrap the string around you columns and use it for ties to the bridge.

That's going to make a BIG difference in your design.

You mean to tell me, You can't figure it out? Really.................!

Tip;

Use a sheet of newspaper, roll it up into a tube which has

a cross-sectional area of, 5" using the strongest shape in Nature

configure the tube into ones say, 3" tall as many as you can over its'

full length. Repeat 4times and then construct a platform for the supports

tie together as req' d..........Job Done ! 10 out of 10.