Its possible to create a Pratt truss bridge combined with su

Solution

it consists of an upper chord, in compression, and a lower chord, in tension, connected by vertical and diagonal members. The loads w are applied to the truss at the panel joints, and the reactions R are applied at the ends. The principal job of the vertical posts is to keep the chords apart and brace them. The end posts carry only tension, but the others are designed as compression members. The diagonal members resist the shearing forces between the chords that arise when the loads tend to cause the centre of the span to sink. In the centre panel, there are diagonals in each direction, although only one direction is in tension at any one time, the other being slack. The reason is that a moving load is not applied evenly across the bridge, and as it moves one set or the other of the diagonals will find itself in tension. These counters are generally used in one or more of the central panels.