What Is Truss?
A truss is a structure consisting of various members arranged in rectangles, squares, triangles—the various members attached to the truss act as one object. Trusses are commonly used in railways, bridges, roofs, and towers.
The member of the truss feels compression load, dead load, and live load. Now the part of the truss that feels pressure in the member is usually called the strut. Similarly, the truss part in which the member is carrying a dead load and live load is called a tie member.
The truss is expensive to use. It is often more economical where there is a long span. Each member of the truss can be easily inspected. The repair work of the truss can be done easily. Using a truss-like North light keeps the air fresh.
Compression force and tension forces are generated in each member of the truss. Therefore compression force and tension force should be calculated for each member of the truss.
Methods to Find Stresses in the Members of Truss
The forces generated in the member of the truss can be found in the following way.
- Method of joint
- Graphical method
- Method of section
Method of Joint
The method of joints is the process used to resolve the various forces applied to different truss members. This method focuses on the joints between the members. And the fastest and easiest way to calculate all the unknown forces in a truss structure.
In this method, the forces applied at each point of the truss are balanced below its effect on the joint.
A free-body diagram is drawn for the joint. And the members associated with the joint are counted.
In this method, the free body diagram of the joint is drawn. It should not be accompanied by members with more than two unknown forces.
The reaction near the support is then calculated. Equilibrium conditions are taken into account for calculating the reaction. The conditions of equilibrium are as follows.
ΣH =0, ΣV=0, and ΣM=0.
The forces generated in each member of the truss are decomposed in vertical and horizontal directions. And the forces generated in it are found according to the conditions of equilibrium.
Zero Force Member
In the construction of a truss, a zero force is applied to the member of the truss.
In truss construction, zero force is applied to the member in the case of the truss. It can therefore be assumed that no force is felt on the member.
The position of the truss is such that no stress load is felt on any member of the truss. Or there seems to be no compression load.
Basic Zero Force members analyze the forces acting individually in a non-charged physical figure. Solid trust is completed by zero-force members.
If two non-collinear members in the truss meet in an unloaded joint, both are zero-force members.
Similarly, if three members meet in an unloaded joint that has two colonies, the third member is a zero-force member.
Reasons for Zero-Force Members in a Truss System
These members are used for long-span members under compressive forces. It also contributes to the stability of the constitution by providing buckling prevention.
These truss members can also carry loads when there is event variation. And the external loading configuration can be changed due to the zero-force member.
Examples
Find the forces generated in different members of the cantilever truss shown in the figure by the joint method.
First, the free diagram of joint A is drawn, which is shown in the figure.
Now the force in member AD and AD is generated by FAB and FAD, respectively. Now the tension force in FAB and compression force in FAD are assumed, as shown in the figure.
In the traverse member, the calculation FAB sin60◦ will be done in the upward direction of FAB in the AB members. And in the same way, its calculation in the horizontal direction is FABcos60◦.
According to the condition of equilibrium, ΣV=0,
FAB sin60◦ – 60 = 0,
FAB = 60/sin60◦ = 60/0.866
FAB = 69.28 KN(Tension).
Doing the same in the horizontal direction
Lets ΣH =0,
FAD – FABcos60◦ = 0,
FAD = FABcos60◦ = 69.28 x 0.5
FAD =34.64 KN (Compression).
Joint B
The free diagram of joint B is drawn, which is shown in the figure.
ΣV=0,
FBD sin60 –FAB sin60 =0
FBD = FAB
FBD =69.28 KN(compression).
Doing the same in horizontal direction,
Lets ΣH =0,
FBD cos60 + FAB cos60 –FBC = 0
FBC = FBD cos60 + FAB cos60,
FBC = 69.28 cos60 + 69.28 cos60,
FBC =69.28 KN(Tension).
| Sr No | Member | Force (KN) | Nature Of Force |
| 1 | AB | 69.28 | Tension |
| 2 | AD | 34.64 | Compression |
| 3 | BD | 69.28 | Compression |
| 4 | BC | 69.28 | Tension |
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