Some basic Structural Engineering terms
This article will deal with some basic structural engineering terms that are required to understand the structural analysis. Terms such as Supports of a structure, Degrees of freedom of a support, Support Reactions, Load types, Section Properties, internal forces like Axial force, Shear force, Moment and Deflections, Stresses, etc. will be the subject of discussion.I will explain these terms in such a practical way that even the people with limited knowledge will also be able to understand it. Mostly civil engineering students or those who want to learn Civil/ Structural engineering will get benefit from this article at most.
Structural Engineering: Structural engineering is a branch of civil engineering. Structural engineering deals basically with load carrying capacity of the structure. Apart from structural engineering, Hydraulic structures, Roads and Railways and Surveying, etc. are also major branches of civil engineering.
Different structures are designed to carry special type of loading.
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| Structural Engineering Terms |
Beam: Beam is a simplest forms of structures. Beam supports load and transfers it to its supports where it rests. The support of a beam can be mostly a wall or a column. The wall or column further transfers the received forces on to its foundation.
Load: Load is something that presses against the support structures. This is right also in case of pulls. Weight of people, weight of machines, weight of wall, etc. Loads are also called Actions. Loads can be classified in different ways. Considering the way how they are treated in structural analysis the loads can be of two types- Dead load and Imposed load.
Dead load is weight of load supporting structure such as self weight of a beam, weight of wall, weight of flooring, etc. Position of dead load is always fixed. Dead load is also called a self load.
Loads other than Dead load is called an Imposed load. Imposed load includes weight of people on the floor, weight of a heavy equipment, etc. Vehicle, Wind, Snow, Temperature, etc. are also forms of imposed load. Therefore an imposed load is a Live load. Position of imposed load is not always fixed.
From its stability point of view loads can be divided into two basic groups-Static and Dynamic. All the loads that do not move are static loads. Best example for a static load is self load.
Loads that move are dynamic loads, such as vehicles, dancing people, operating machines, force caused by a dropping body, etc.
Dynamic loads cause additional impact on the supporting structure. Depending on its movement and stopping phenomena, the moving mass can pose impact not only in the vertical direction but also in lateral direction.
This impact is additional to
its static load. Depending on its dynamic behaviour amount of impact can be a
significant which needs to be considered in the load calculations.
Considering its intensity and orientation, loads can also be classified as Point Load, Line Load, Uniformly Distributed Load, Triangularly Varying Load, Area load, etc. Area load is a load that spreads over an area, such as 3.0 kN in one square meter of area.
More explanation about these loads will be provided later in the upcoming article that deals with Structural Analysis.
Cross Section: When we cut
a support structure, such as beam or column, in perpendicular direction to its
longitudinal axis we get a cross section of the support structure. Cross
section of a solid timber beam is a rectangle or a square. Following are some typical
cross sections of a support structure.
Cross Sectional Properties of supporting structure: Cross sectional properties plays major role in load carrying capacity of a support structure. Major cross sectional properties of a plane figure are, Depth, Width, Major Axis, Minor Axis, Centre of Gravity, Cross sectional area (A), Moment of Inertia (I), Radius of Gyration (r), etc.
Following figure shows some of the cross sectional properties of a rectangle:
Slab: Slab is a thinner but much wider version of a beam. Slabs can have continuous supports on its all sides where as beams and rods have supports on its ends. Depending on type of support the slabs can have one support to number of supports that is equal to its sides.
Slabs can carry all kind of loads in three direction that includes area loads.
Supports: Supports are where a support structure rests. Support defines how the ends of a support structure is connected to a supporting body or foundation. In the example shown above the beam is resting on a hinge support on one end and on roller support on other end.
Hinge supports do not allow end of the above mentioned beam to move (displace) in any direction. However, it allows the same end to rotate. The roller support, on the other end allows the beam end to move upward and in the longitudinal direction.
On the beam column system, the columns have fixed supports. Foundation of a regular column is a fixed support.
The fixed support of the columns do not allow the fixed end move neither in any direction nor rotating about any axis.
Movement and rotation possibilities of the support is called Degrees of Freedom. There are altogether six degrees of freedom for a support.
Internal Forces: When we apply a load on a support structure, the support structure transfers the load to its supports. During this process a certain set of forces develop inside the support structure when the load gets transferred to the supports.
In practice these internal forces are called
only forces in the structural engineering. Forces can be mostly of two types, i.e. an
Axial force and Shear force.
Axial forces act along the longitudinal axis of the support structure. For example, along the longitudinal axis of the columns as shown in the above mentioned beam column structure.
Axial forces can be a Compression or
Tension depending on it pushes or pulls the support structure.
Shear force: Shear forces are the forces that develops in the direction perpendicular to its longitudinal axis.Refer article Bending Moment-Shear Force -Axial Force for more details.
Arm: Arm is a shortest distance between support or a point or interest to the force. This distance is always perpendicular to the force. In the example above, "L" is arm for the load "F"
Bending moment: Bending moment is a moment that bends the support structure.Refer article Bending Moment-Shear Force -Axial Force for more details.
Shear Stress equals to Shear force/cross section
area, t =V/A
Bending Stress, sb = M.y/I
Deflection: Due to application of a load, shape of the
support structure changes. Amount of this change is called a deflection or deformation.
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