This may not be totally LEGO legal, but hey it works. And even after all most a year of being built I could find no damage to my bricks. SO make these types of designs at your own risk, I take no responsibility if you stress your bricks too far and damage them.
This was my 2nd version of a pre-stress concrete style bridge that I made, but my favorite. Something you will not see in the LDraw file or any pictures was some lift arms within the bridge, attached to the bottom. The purpose of the lift arms is to keep the bridge compressed and not allow the bottom to stretch out.
