I don't know if it's cheating but I used a dirty trick to make my bridge longer on the Challenge part. What I did was this, whenever I put the steel bars into the grassy areas they would pop out again. So what I did was to find ways so is would pull back instead of pop out. --- Here's my plans. See? It looks like the weight is too heavy and should just drop this part down:
Here's where it looks like it will fall:
But it gets pulled taught instead:
---- So there are different ways to lift the weight of my bridge and get it stronger so I could build longer bridges that way. Also more bars pull better than single ones if you have enough of money.