Basic Principles of Structural Analysis: Structural engineering involves an extensive variety of structural systems to deal with such as buildings, bridges, sports stadiums, radio and television towers, arches, storage tanks, aircraft and space structures, concrete pavements, etc.
These structures can vary in size from a single member as is the case of a light pole to buildings or bridges of tremendous size. For example, the Taipei 101 building in Taiwan has a height of 509 m. Also, Among the world’s great bridges are the Humber Estuary Bridge in England, which has a suspended span of over 1410 m.
The point is that to be able to analyze this wide range of sizes and types of structures, a structural
engineer must have a solid understanding of the basic principles that apply to all structural systems. It is unwise to learn how to analyze a particular structure, or even a few different types of structures. Rather, it is more important to learn the fundamental principles that apply to all structural systems, regardless of their type or use. One never knows what types of problems the future holds or what type of structural system may be conceived for a particular application, but a firm understanding of basic principles will
help us to analyze new structures with confidence.
The fundamental principles used in structural analysis are Newton’s laws of inertia and motion, which are:
1. A body will exist in a state of rest or in a state of uniform motion in a straight line unless it is forced to change that state by forces imposed on it.
2. The rate of change of momentum of a body is equal to the net applied force.
3. For every action there is an equal and opposite reaction.
These laws of motion can be expressed by the equation
Σ F = m * a
In this equation, Σ F is the summation of all the forces that are acting on the body, m is the mass of the body, and a is its acceleration.
In structural analysis of static structures, we will be dealing with a particular type of equilibrium called static equilibrium, in which the system is not accelerating. The equation of equilibrium thus becomes:
Σ F = 0
These structures either are not moving, as is the case for most civil engineering structures, or are moving with constant velocity, such as space vehicles in orbit. Using the principle of static equilibrium, we will study the forces that act on structures and methods to determine the response of structures to these forces where response means the displacement of the system and the forces that occur in each component of the system.