Easy "Big spender" achievement
Spend 100,000 to build a structure below a working bridge, without a connection. Place it so the structure will fall in the water when you start the map.
Easy "Car insignia 'South'" achievement
The actual task to be completed is "Cars can drive on all of Island 3's bridges".
Easy "Monumental structure" achievement
Play one of the canyon stages, for example level 4-1. Create a normal bridge, however make a large concrete pylon as tall as possible. Next, build a number of bridge parts hanging off of the pylon. The pylons cannot break or buckle, allowing you to hang anything off of it all interconnected in a blob of wood or steel that will have no negative effects on the rest of the bridge.
Easy "Stubborn!" achievement
Each failure must be done on the same bridge. To give the bridge a slightly different layout, add a non-structural girder with each attempt. Create a bridge that collapses quickly. Start the simulation, add slightly more wood to the bottom, start it again, wait for it to collapse, then repeat the process as many times as needed.
Easy "Big spender" achievement...