A simple bridge of three triangular elements spans a river and is carried by the foundation at and in the diagram. The connecting lines between the points correspond to steel girders, each of which can bear a maximum tensile and compressive load of 10 tons.
What is the minimum angle needed so that a truck with a weight of 10 tons can safely cross the bridge?
Hints:
Note: for every point of the polygon, the sum of all forces must be zero.