"Many bridges are designed with trusses deployed on the two sides of the structure. These trusses in turn are fabricated from many bars or rods connected together at bolted or welded joints. We analyze these rods and bars using the same equations established for wire rope and cables. The difference is that the rods and bars are sufficiently stiff to support compressive stresses. Large structures like bridges are fabricated from many small structural elements. There are several reasons for constructing big structures from small components. First, manufacturing facilities limit the size (width and the thickness) of structural elements that are produced. The rolls used in steel and aluminum mills to form the shape of bars, plates and sheets usually are only six to eight feet long. Even more limiting is the requirement for transport from the manufacturing facility to the construction site. If highways are used both the width and length of the structural elements are limited by state law. As structural elemenys, rods and bars subjected to axial loading have a significant advantage. They are subjected to a uniform state of stress over their cross sectional area. Also, if they are two-force members loaded at their two ends, the stresses are uniform over their length. Thus, the entire volume of the rob or bar is subjected to the same stress, which is the optimum state for minimum weight design." p6-1

AREA
A MEASURE OF SURFACE SIZE

BUCKLING

CENTER OF GRAVITY

CENTROID
A CENTER POINT OF A SHAPE

FIRST MOMENT OF AN AREA

GRAVITY
THE ATTRACTIVE FORCE BETWEEN ANY TWO MASSES

MOMENT
A FORCE APPLIED TO AN OBJECT AT SOME DISTANCE FROM THE ROTATION AXIS THAT MAY CAUSE THE OBJECT TO ROTATE. THIS IS THE SAME AS A TORQUE. THE MOMENT IS CALCULATED AS THE PRODUCT OF A FORCE TIMES THE DIRSTANCE OF ITS POINT OF APPLICATION FROM THE AXIS OF ROTATION.

TRUSS