All questions of Plane Trusses for Mechanical Engineering Exam

Explanation:
The statement in question states that there are no rules for designing a truss, but there are rules for designing bridges. The correct answer is option B, which means that the first part of the statement is false and the second part is also false.

Designing a truss:
A truss is a structural framework that consists of straight members connected at joints. Trusses are commonly used in engineering and construction to support loads such as the weight of a roof or a bridge. While there may not be specific rules for designing a truss, there are certainly principles and guidelines that need to be followed to ensure the structural integrity and stability of the truss. These principles include:

1. Analysis of loads: The first step in designing a truss is to analyze the loads that the truss will be subjected to. This includes considering the weight of the structure, any live loads such as people or vehicles, wind loads, and seismic loads. The truss must be designed to safely support these loads without excessive deflection or failure.

2. Material selection: The choice of materials for the truss is important to ensure its strength and durability. Common materials used for truss construction include steel, timber, and aluminum. The material must be able to withstand the loads and environmental conditions that the truss will be exposed to.

3. Truss configuration: The configuration of the truss, including the arrangement and size of the members and the connections between them, is crucial for its stability and load-bearing capacity. Various truss configurations, such as the Pratt truss, Warren truss, and Howe truss, have different advantages and limitations, and the appropriate configuration should be chosen based on the specific requirements of the project.

4. Structural analysis: Once the truss configuration is determined, it is important to perform structural analysis to ensure that the truss can safely carry the imposed loads. This analysis involves calculations to determine the internal forces and stresses in the truss members, as well as deflections and deformations. Finite element analysis (FEA) software is commonly used for this purpose.

Designing a bridge:
The second part of the statement is also false. There are indeed rules and guidelines for designing bridges. Bridges are complex structures that must safely support the weight of vehicles, pedestrians, and other loads while spanning across rivers, valleys, or other obstacles. The design of a bridge involves several considerations, including:

1. Structural analysis: Similar to truss design, a bridge must undergo structural analysis to ensure its stability and load-bearing capacity. This analysis considers the forces and stresses that the bridge will experience, including dead loads, live loads, wind loads, and seismic loads.

2. Material selection: The choice of materials for the bridge depends on factors such as span length, anticipated loads, and environmental conditions. Common bridge materials include steel, concrete, and composite materials. The material must have sufficient strength, durability, and resistance to corrosion.

3. Bridge type and configuration: Different types of bridges, such as beam bridges, arch bridges, and suspension bridges, have different structural characteristics and requirements. The selection of the appropriate bridge type and configuration depends on factors such as span length, terrain, and budget.

4. Geotechnical considerations: Bridges often require foundations to support their weight. Geotechnical investigations are conducted to assess the soil and rock conditions at the bridge site, which helps determine the appropriate foundation design, such as

Bridge structures are designed to transmit loads from stringers to floor beams and then to joints.

False

Explanation:

Free Body Diagrams:
Free body diagrams are used to represent the external forces acting on a body or a system. These diagrams are used to analyze the equilibrium of the body or system by considering the forces and their directions. In a free body diagram, all forces acting on the body are represented by vectors. These forces can include both translational forces (such as applied loads, reactions, etc.) and rotational moments (such as torques).

Internal Forces:
Internal forces are forces that exist within a body or a system. These forces are not visible from the outside and are responsible for maintaining the equilibrium of the body. When analyzing internal forces using the method of sections, a section is cut through the body or system to isolate a portion of it. The internal forces at the cut section are then evaluated to determine their magnitude, direction, and type (such as tension, compression, shear, etc.).

Rotational Moments:
Rotational moments, also known as torques, are forces that cause an object to rotate about an axis. These moments are typically caused by external forces acting at a distance from the axis of rotation. Rotational moments are important in analyzing the equilibrium of a body or system, especially when considering the rotational motion.

Importance of Rotational Moments:
Rotational moments are essential in analyzing the equilibrium of a body or system. They play a crucial role in determining the stability, balance, and motion of the body. Ignoring rotational moments in free body diagrams or the evaluation of internal forces by the method of sections can lead to incorrect results and an incomplete understanding of the system's behavior.

Conclusion:
In conclusion, rotational moments are indeed counted in free body diagrams and the evaluation of internal forces by the method of sections. These moments are essential in analyzing the equilibrium and motion of a body or system. Therefore, the statement "Rotational moments are not counted in the free body diagrams and the evaluation of the internal forces by the method of sections" is false.

Internal Forces in the Method of Sections

In the method of sections, which is commonly used for analyzing complex truss structures, the internal forces within the members of the structure are determined by applying the principle of equilibrium to a section of the truss. This allows us to calculate the internal forces such as axial forces, shear forces, and bending moments in the members.

External Forces
The external forces are the forces acting on the truss that are not located within the section under consideration. These forces include applied loads, reactions at supports, and any external moments. The external forces are applied to the truss as a whole and are not specifically related to the section being analyzed.

Method of Sections
The method of sections involves cutting the truss into two sections by passing an imaginary line through the desired section. This imaginary line is called the section line. By isolating one of the sections and considering the equilibrium of forces acting on that section, we can determine the internal forces within the members of the truss.

Calculation of Internal Forces
To calculate the internal forces in the method of sections, we consider the equilibrium of forces acting on the isolated section. This includes both external forces and internal forces within the members. By applying the equations of equilibrium, such as the sum of forces in the x-direction and sum of forces in the y-direction, we can solve for the unknown internal forces.

Choice of External Forces
In the method of sections, we only consider the external forces acting on the truss as a whole. This is because the internal forces within the members are a result of the equilibrium of these external forces. By neglecting the internal rotational forces and considering only the external forces, we can simplify the analysis and focus on determining the internal forces within the members.

Therefore, the correct answer is option 'D' - External forces.

There is normal component of force acting o the body. though there is bending moment by external force, which is resisted by the normal stress generated by itself. so the answer is 0

The truss is a structure made of slender members which are joined together at their end points. They can be of wooden or steel. But most probably they are made from stainless steel. As they need to support the loadings in various climates.

Explanation:
A truss is a structural framework made up of triangular sections that are connected by straight members. The triangular shape of the truss provides stability and strength to the structure.

Types of Trusses:
There are different types of trusses based on their configuration and the arrangement of their members. These include:

1. Simple Truss: A simple truss is the most basic type of truss structure. It consists of straight members connected at joints to form triangular sections. The members only experience axial forces and are either in tension or compression. This type of truss is commonly used in bridges, roofs, and towers.

2. Complex Truss: A complex truss is a more intricate truss structure that contains additional members, such as diagonals or verticals, to provide additional support and stability. It may have more than one triangular section or incorporate other shapes besides triangles. Complex trusses are used when there is a need for extra load-carrying capacity or when architectural aesthetics require a different configuration.

3. Lateral Truss: A lateral truss is a specialized type of truss that is used to resist lateral loads, such as wind or earthquake forces, in addition to vertical loads. It is designed to provide lateral stability to the structure and prevent it from collapsing or buckling under these loads. Lateral trusses are commonly used in tall buildings, bridges, and other structures that are subjected to significant lateral forces.

Equilateral Truss:
An equilateral truss is not a recognized type of truss. The term "equilateral" refers to a triangle in which all three sides are equal in length. While equilateral triangles are often used in the construction of trusses, it does not define a specific type of truss structure. Trusses can be made up of equilateral triangles, isosceles triangles, or any other combination of triangles, depending on the design requirements.

Therefore, the correct answer to the given question is option 'B' - Simple Truss. The triangular section in a truss refers to the arrangement of members in the shape of triangles, which is a characteristic feature of a simple truss structure.

Shear force
The force acting parallel/tangential to the beam is called shear force. Let's break down the concept in detail:

Definition
Shear force is the force that acts parallel to the surface of a material, such as a beam. It creates a sliding or tearing effect on the material, causing it to deform.

Causes
Shear force is typically caused by external loads applied to a structure, such as bending moments or direct forces. These forces can result in shear stress within the material.

Effects
Shear force can lead to deformation or failure of a material if it exceeds the material's shear strength. It is crucial to consider shear force in the design and analysis of structures to ensure their stability and safety.

Calculation
Shear force can be calculated at any point along a beam using equilibrium equations. It is represented by the symbol V and is measured in units of force (e.g., Newtons or pounds).

Application
Understanding shear force is essential in civil and mechanical engineering, as it influences the design, analysis, and performance of structures like bridges, buildings, and machinery.
In summary, shear force plays a significant role in the behavior of materials and structures. By considering shear force in design and analysis processes, engineers can ensure the safety and reliability of their creations.

Explanation:

First Step:
- The determination of the truss's support reaction is done first.
- This step involves analyzing the external forces acting on the truss structure and calculating the support reactions at the points where the truss is connected to the external supports.
- These support reactions help in determining the stability and equilibrium of the truss structure.

Second Step:
- Then the section is isolated for the method of the section.
- Once the support reactions are determined, the truss structure can be analyzed further by isolating a specific section of the truss.
- The method of sections is used to analyze the internal forces (such as member forces) within the isolated section of the truss.
- This step helps in determining the forces acting on individual members of the truss structure.
Therefore, the correct approach is to first determine the support reactions of the truss and then isolate a section for further analysis using the method of sections. This sequential process ensures a systematic and accurate analysis of the truss structure.

C) The direction of the unknown force cannot be determined

The correct answer is option 'C': The first part of the statement is true and the other part is false.

Explanation:

Method of Joints:
The method of joints is a technique used to analyze trusses by considering the equilibrium of each joint. It allows us to determine the unknown forces acting on the joints of the truss. By applying the principles of statics, we can solve for these unknown forces by considering the forces in equilibrium at each joint.

Method of Sections:
The method of sections is another technique used to analyze trusses. It involves cutting the truss into two sections and analyzing the equilibrium of one of the sections to determine the unknown forces. This method allows us to calculate the forces in members that are not directly connected to the joints.

Correcting the statement:
The first part of the statement is true because the method of joints does help us find out the unknown forces in the truss joints. However, the second part of the statement is false. The method of sections is not used to calculate the direction of the zero members. Instead, it is used to determine the forces in members that are not directly connected to the joints.

The correct statement should be:
"The method of joints helps us to find out the unknown forces in the truss joints. However, the method of sections is used to calculate the forces in members that are not directly connected to the joints, not the direction of the zero members."

In conclusion, while the first part of the statement is true, the second part is false. The method of sections is not used to calculate the direction of the zero members in trusses.

Explanation:

The correct answer is option 'C', which states that the first part of the statement is true and the other part is false. Let's break down the explanation:

- Method of section:
- The method of section is a technique used in structural analysis to determine the internal forces within a truss by cutting the structure into sections and analyzing the equilibrium of the section.

- False Statement:
- The first part of the statement, which says that the whole structure of trusses is cut into a section, is false. In reality, the method of section involves cutting a specific section of the truss where the unknown forces need to be calculated.

- True Statement:
- The second part of the statement, which mentions that at most two forces must be collinear, is true. When applying the method of section, the equilibrium of the section is analyzed by considering at most two unknown forces that are collinear. This simplifies the calculations and makes it easier to solve for the unknown forces.

In conclusion, the method of section is a powerful tool in analyzing truss structures, but it involves cutting a specific section of the truss rather than the entire structure. Additionally, the method requires at most two forces to be collinear for accurate calculations.