What is Truss?
It is defined as, two or more elements like beams or any two or more force members, which when assembled together, behaves like a complete structure or as a single structure. They generally consist of two force member which means any component structure where the force is applied only at two points. The point of contact of joints of truss are known as nodes. They are generally made up of triangular patterns. Nodes are the points where all the external forces and the reactionary forces due to them act and shows whether the force is tensile or compressive. There are various characteristics of trusses and are characterized as Simple truss, planar truss or the Space Frame truss.
Any truss which consists of triangles completely is known as the simple truss. This type of trusses is very common and can be seen in the mechanical components like aircrafts or in cycles. The figure shows the simplest type of truss.
It can be made by adding the links with one another, which are made to form a joint with the pre-existing joint. This type of trusses are considered as highly stable, and their analysis methods are also quite easily achievable than the other kinds.
It is the type of truss which lies only in one plane. These are the type of trusses which are generally used in the parallel form so that they can be used to make roofs as well as bridges. It is proved to be an efficient form of truss whose structure makes it more better form. And this can be seen in its structure like the depth of truss or the length between the two chords i.e., upper and the lower one. A beam or some kind of solid girder is considered to have more cost and more weight in comparison to truss. The figure shows the simplest type of planar truss.
Space frame Truss
It is the three-dimensional framework which is connected at the ends of the pins. The simplest type of the space frame can be seen in the shape of tetrahedron. Large size of planar structures can be composed with the help of tetrahedrons whose edges are common and can be used to make the base for some large structures or some larger bodies.
- Pitched truss: These are the types of trusses which are basic among all and can be easily characterized by its shape i.e., triangular. This type of trusses are used for the construction of roof.
- Warren truss: These are the type of truss in which members when connected, forms the shape like an equilateral triangle and each being alternately up and down.
Statics of Truss
The trusses, whose members or links are connected with pin joints, or which are supported at both the ends with the help of hinge or roller support are considered as statistically determinate. Newton’s law is applied for the whole structure or for each and every node individually. For any node, to be static in space, the sum of all the forces i.e., horizontal or the vertical, as well as the moments which is taking place about the fixed or particular node is considered as zero.
The static indeterminate trusses are the ones which are supported at more than two positions and the member forces are not been defined by Newton’s law.
For a simple truss, to be stable here is the condition which shows whether the given truss is stable or not, i.e.
where m tells the number of members of truss, j tells about the number of joints of truss, and r defines the number of reactions, which is generally equal to 3.
Analysis of Truss
The forces in the main girders of the truss generally exert in the planar frame and hence they are designed as a two- dimensional reference plane. Or else in other cases the structure is designed in the form of three-dimensional space. This is been seen that the forces are applied at the joints or the nodes of the truss members. The members are considered to be longer in size due to which the moments which have been transferred through the joints is also neglected so that these points can be treated as pin joints. Trusses are considered stronger because most of the material can withstand a much larger load either in case of tension or in compression. Trusses can be analyzed by many methods, some of which include, the method of flexibility, direct stiffness method or the method with the help of finite element analysis.
Methods of Solving Truss Involves
- With the help of analytical methods of joints
- With the help of graphical method of Cremona’s diagram
- By the method of sections
Analytical methods of joints
In this process, the analysis starts from the joint where only one load exists and the unknown forces should not be more than two. Then we will be finding out the external reactions which are determined with the help of the equilibrium equations to the complete truss. While doing the analysis of joint, it must be kept in mind that if the arrow is moving away from pin then that means tension, and in case of coming closer in the direction of pin, it means compression.
In this method, all the joints are graphically represented for the equilibrium. In this method, the special feature is that it can transform the various force polygons of different joints into a single force polygon. And that diagrammatic representation is known as Cremona’s diagram.
Method of sections
For a system to be statistically determinate, the equation- m= 2j- 3 should be satisfied. In this method, reactions of the truss should be calculated by passing a section within the three members so that two portions are to be separated. At all the intersections, tensile forces are to be put down, then out of the two portions, select the one which has a smaller number of external loads and with the help of that, draw the free body diagram, then write down the equilibrium equations, solve it further.
Context and Applications
This topic is significant in the professional exams for both undergraduate and graduate courses, especially for
- Bachelors in Science (Biochemistry and Molecular biology)
- Bachelor of Molecular and cellular biology
- Masters in Science- Biological science
- Masters in Science- Bio molecular chemistry
- Masters in Biotechnology
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