You may not ever have given it any thought – BUT – did you know there are four main types of bridges?
One is the beam bridge. If you picture a fallen log across a stream, brook, or river, you are picturing a beam bridge at its simplest. As you picture this fallen log turned beam bridge, you also know at an intuitive level that there is a limit to the distance a beam bridge can span while carrying a load without collapsing. That limit depends upon the weight of the log, the weight of the load that will cross the bridge, and the adequacy of the banks the fallen log rests upon.
If the log is a slender, supple sapling that will bend easily, the load it carries cannot be very heavy. Why? The log is not capable of supporting the “live load.” If the log is a huge oak that is resting upon dry, crumbling banks, the log will also not be able to carry a heavy load without falling into the stream because the weight of the “bridge” itself is already nearing the capacity of the supports. For a bridge of any type to be successful, all of the forces at work – those acting in all directions – must be in balance.
What else can you guess about how beam bridges work?