01-07-2013, 04:54 PM
The Basic Principles in Structural Mechanics
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INTRODUCTION
What are structures in civil engineering? Why is it important to understand? Structures can be defined as shapes
or forms such as buildings, bridges, dams, and walls, are designed significantly to resist any applied load (force)
without losing its own strength capacities and appreciable deformation. The fundamental purpose of the structure
is to transmit all applied loads to the support systems and ultimately through the foundations and to the Earth
surface.
Therefore, it is the structural design engineer responsibility to make sure that the required structures to be strong,
durable, stable, and safe. A proper process in design stages must be taken and this includes applying
mathematical concepts to determine the applied forces and the reactions in the structural elements.
Types of Structures
Structures can be categorized in two types namely frame and mass. The frame structures resist the applied loads
by virtue of its geometry, while the mass structures are the type of structures which are able to resist the applied
loads by virtue of its weight. The most common structural elements structural elements are arches, beams,
columns, foundations, trusses, and walls.
The Structural Forms
Large structures are built significantly to safely withstand large loadings. Thus, to be able to transmit the loads
and needed to combine the elementary forms of structural members. For examples, as the span of a beam
increases, it becomes uneconomical to use a solid beam. Therefore, it is necessary to introduce frameworks
composed of straight members connected at their ends to form rigid structures, such as bridges and roof planes.
Trusses
Trusses provide both practical and economical solutions especially in the design of bridges and buildings. If an
entire truss lies in a single plane, it is called a plane truss. Typically, the most simple and stable truss consists of
three straight members (triangle shape) connected together at its ends. As for rectangular configuration, be
advice that the shape is not suitable for a truss because of instability and shape changes without changing the
length of any of the four members, thus swaying will occurred.
Rigid Frames
Another type of structure that is similar to a truss and capable of carrying external loads. The main different is the
way that external loads are applied to them. In frames, members maybe applied at any point of any member. The
consequence of the difference is that not all frame members are two-forces which as a result may subjected of
bending as well. Portal frames and large frames are common types of rigid jointed frames as the joints are stiff,
continuous and moment couples occurred.
Types of Supports
All applied loads on a framed structure will be transferred to the support systems which will then provide the
reacting force (reactions) to maintain equilibrium. Some structures are constrained by supports that do not allow
any rigid-body movement and other support systems resist translational movement but no resistance to rotation.
The behavior of the supports can be a critical effect on the structure proper and therefore cannot be ignored at
the design stage.
In the actual practice, it is necessary to make certain idealized simplifications regarding the nature of supports.
The common types of support are fixed or built-in, pinned and rollers support.