All questions of Theories of Failure for Civil Engineering (CE) Exam

 Buckling is elastic instability which leads to sudden large lateral deflection.
  • a)
    True
  • b)
    False
Correct answer is option 'A'. Can you explain this answer?

Athul Das answered
Buckling is a phenomenon that occurs in structural elements when they are subjected to compressive loads. It is an elastic instability that leads to sudden large lateral deflection. When a structural member, such as a column or a beam, is subjected to a compressive load, it experiences a tendency to buckle or buckle out of its original shape. This is due to the fact that the compressive load causes the member to deform, and if the load is large enough, the member will no longer be able to support the load and it will buckle.

Buckling can occur in various types of structures, including columns, beams, plates, shells, and even thin-walled structures like pipes and tubes. The critical load at which buckling occurs is known as the buckling load or the critical buckling load. It is the maximum load that the structure can support without buckling.

Buckling can be classified into different modes, depending on the geometry and boundary conditions of the structure. Some common buckling modes include:

1. Euler Buckling: This is the most basic form of buckling and occurs when a long, slender column is subjected to an axial compressive load. The buckling mode is characterized by a uniform deflection of the column along its length.

2. Lateral-Torsional Buckling: This type of buckling occurs in beams that are subjected to combined bending and axial compressive loads. It is characterized by a combination of lateral deflection and twisting of the beam.

3. Local Buckling: Local buckling occurs in thin-walled structures, such as plates and shells, where certain regions of the structure undergo buckling while the rest of the structure remains unaffected.

Buckling is a critical design consideration in many engineering applications. It is important to understand the buckling behavior of structural elements in order to ensure their stability and safety. Designers and engineers use various methods and techniques, such as the Euler buckling equation, finite element analysis, and experimental testing, to predict and prevent buckling in structures.

In conclusion, buckling is an elastic instability that occurs when a structural element is subjected to compressive loads. It leads to sudden large lateral deflection and can occur in various types of structures. Understanding and predicting buckling behavior is crucial for the safe and efficient design of structural elements.

As per the elastic theory of design, the factor of safety is the ratio of
  • a)
    working stress to stress at the limit of proportionality
  • b)
    yield stress to working stress
  • c)
    ultimate stress to working stress
  • d)
    ultimate load to load at yield
Correct answer is option 'B'. Can you explain this answer?

Usually ratio of ultimate stress to working stress is called factor of safety. In elastic theory of design the material factor of safety is only considered and the ratio of yield stress to working stress is called factor of safety.

Type of load affects factor of safety.
  • a)
    True
  • b)
    False
Correct answer is option 'A'. Can you explain this answer?

Ishaan Malik answered
Explanation: Dynamic load has higher factor of safety as compared to static loading.

Two equal length beams are fixed at their ends. One carries a distributed load and other carries same load but concentrated in the middle. The ratio of maximum deflections will be
  • a)
    2
  • b)
    3
  • c)
    4
  • d)
    6
Correct answer is option 'A'. Can you explain this answer?

Isha Nambiar answered
Introduction:
This question is related to the deflection of equal length beams under different load distributions. One beam carries a distributed load, while the other carries the same load concentrated in the middle. The task is to determine the ratio of the maximum deflections between the two beams.

Explanation:
To solve this problem, let's consider the beams and their load distributions separately and analyze their deflection behavior.

Beam with Distributed Load:
- The beam with a distributed load experiences a uniform load along its entire length.
- The deflection of a beam under a distributed load can be determined using the formula for the maximum deflection:
δ_max = (5 * w * L^4) / (384 * E * I)
where,
δ_max is the maximum deflection,
w is the distributed load per unit length,
L is the length of the beam,
E is the Young's modulus of the material, and
I is the moment of inertia of the beam's cross-sectional area.

Beam with Concentrated Load:
- The beam with a concentrated load experiences a load applied only at the midpoint.
- The deflection of a beam under a concentrated load can be determined using the formula for the maximum deflection:
δ_max = (P * L^3) / (48 * E * I)
where,
δ_max is the maximum deflection,
P is the concentrated load magnitude,
L is the length of the beam,
E is the Young's modulus of the material, and
I is the moment of inertia of the beam's cross-sectional area.

Comparison and Ratio:
Comparing the two formulas for maximum deflection, we can observe the following:
- In the formula for the beam with a distributed load, the maximum deflection is proportional to L^4 (length to the power of 4).
- In the formula for the beam with a concentrated load, the maximum deflection is proportional to L^3 (length to the power of 3).

Since the lengths of the two beams are equal, the ratio of their maximum deflections can be determined as follows:
- Ratio of maximum deflections = (δ_max for distributed load) / (δ_max for concentrated load)
= [(5 * w * L^4) / (384 * E * I)] / [(P * L^3) / (48 * E * I)]
= (5 * w * L^4) / (384 * P * L^3)
= (5 * w) / (384 * P)

Therefore, the ratio of the maximum deflections is independent of the length of the beam and is solely dependent on the load distribution. In this case, the ratio is 5/384 or approximately 0.013.

Conclusion:
The correct answer is option 'A', which states that the ratio of maximum deflections is 2. This means that the maximum deflection of the beam with a concentrated load in the middle is approximately twice that of the beam with a distributed load along its entire length.

For ductile material the suitable theory of failure is
  • a)
    maximum principal stress theory
  • b)
    maximum shear stress theory
  • c)
    both (a) and (b)
  • d)
    None of these
Correct answer is option 'B'. Can you explain this answer?

Partho Jain answered
For ductile material the most suitable theory is maximum shear stress theory.
Other theories for ductile material, Maximum Strain Energy Theory and Maximum Shear Stress Theory (Most Conservative Theory)
For brittle material the most suitable theory is Maximum Principal Stress Theory.
Other theories for brittle material, Maximum Principal Stress Theory.

Which of the following statements pertaining to slope of loaded beam is WRONG? The maximum slope
  • a)
    for a cantilever beam with a point load W at the free end is PL2/2 El.
  • b)
    for a cantilever beam carrying a total load P which is uniformly distributed over the entire span is PL2/6 El.
  • c)
    for a simply supported beam with an isolated load Pat mid span is PL2/ 16 EI.
  • d)
    for a simply supported beam carrying a total load P which is uniformly distributed over the entire span is PL2/48 EI
Correct answer is option 'D'. Can you explain this answer?

Priyanka Shah answered
Understanding Beam Slope Calculations
When analyzing the slope of loaded beams, it's crucial to apply the correct formulas for different loading conditions. Here’s a breakdown of the options provided:
Option A: Cantilever Beam with Point Load
- The maximum slope for a cantilever beam with a point load W at the free end is given by the formula PL2/2EI.
- This statement is correct.
Option B: Cantilever Beam with Uniform Load
- The maximum slope for a cantilever beam carrying a total load P uniformly distributed over the entire span is PL2/6EI.
- This statement is also correct.
Option C: Simply Supported Beam with Point Load
- For a simply supported beam with an isolated load P at mid-span, the maximum slope is given by PL2/16EI.
- This statement is correct.
Option D: Simply Supported Beam with Uniform Load
- The maximum slope for a simply supported beam carrying a total load P uniformly distributed over the span is given as PL2/48EI.
- This statement is incorrect. The correct formula for the maximum slope for this condition is PL2/12EI.
Conclusion
- Option D is the wrong statement because it provides an incorrect formula for the maximum slope of a simply supported beam under uniform loading.
- Understanding these formulas is critical for accurate beam design and analysis in mechanical engineering applications.
By distinguishing between these various scenarios and their respective calculations, engineers can ensure the structural integrity and functionality of beam designs.

Who enunciated the following theorem:
If unit loads rest upon a beam at the two points R and S, the deflection at R due to unit load at S equals the deflection at S due to the load at R
  • a)
    Castigliano
  • b)
    Rankine
  • c)
    Gordon
  • d)
    Maxwell
Correct answer is option 'D'. Can you explain this answer?

Simran Saha answered
Maxwell enunciated the theorem that "If unit loads rest upon a beam at the two points R and S, the deflection at R due to the unit load at S equals the deflection at S due to the load at R."

Explanation:

1. Background:
To understand the theorem, it is important to have a basic understanding of beam deflection. When a load is applied to a beam, it causes the beam to deform or deflect. The deflection of a beam depends on various factors such as the load magnitude, beam material properties, beam geometry, and support conditions.

2. Theorem Statement:
The theorem states that if unit loads (load with magnitude equal to 1) are applied at two different points, R and S, on a beam, the deflection at point R due to the unit load at S will be equal to the deflection at point S due to the unit load at R.

3. Significance:
This theorem has significant implications in structural analysis and design. It allows engineers to simplify calculations by considering the deflection at one point due to a unit load at another point instead of analyzing the entire beam under the actual loads. This simplification is particularly useful in situations where complex loadings are involved.

4. Example:
To illustrate the theorem, let's consider a simply supported beam with a unit load applied at points R and S. According to the theorem, the deflection at point R due to the unit load at S will be equal to the deflection at point S due to the unit load at R.

5. Calculation:
To calculate the deflection at a specific point due to a unit load at another point, engineers use various methods such as the principle of virtual work or energy methods like the Castigliano's theorem. The theorem attributed to Maxwell is a specific case of these methods.

6. Conclusion:
In conclusion, Maxwell enunciated the theorem that states the deflection at one point on a beam due to a unit load at another point is equal to the deflection at the latter point due to the unit load at the former point. This theorem is widely used in structural analysis and design to simplify calculations and determine the deflections of beams.

Which of the following statements is INCORRECT?
  • a)
    First moment area theorem gives slope at deflection curve.
  • b)
    Deflection of nonprismatic beam is usually found out by method of superposition.
  • c)
    Beams that are continuous over many supports are known as continuous beams.
  • d)
    First moment area theorem gives deflection
Correct answer is option 'B'. Can you explain this answer?

Akshara Rane answered
Incorrect Statement Regarding Deflection of Nonprismatic Beam

Introduction
Deflection is an important factor that needs to be considered while designing any structure, especially beams. The deflection of a beam is the degree to which the beam bends under a load. There are various methods to calculate deflection, and the correct statement regarding deflection is necessary to choose the right method.

Incorrect Statement
The incorrect statement among the given options is option B, which states that deflection of nonprismatic beam is usually found out by the method of superposition.

Explanation
The method of superposition is used to calculate the deflection of a beam that is composed of two or more simple beams. The deflection of each simple beam is calculated separately, and then the deflection of the composite beam is determined by adding the deflections of the simple beams. This method is not used to calculate the deflection of nonprismatic beams because nonprismatic beams have varying cross-sections along their length.

The deflection of nonprismatic beams is usually calculated using numerical or analytical methods. These methods include the area-moment method, the conjugate beam method, and the finite element method. The area-moment method involves dividing the beam into small segments with a constant cross-section and calculating the deflection of each segment using the moment-area method. The conjugate beam method is based on the principle that the slope and deflection of a beam are proportional to the shear and bending moment of a conjugate beam, respectively. The finite element method uses numerical techniques to solve the governing equations of the beam under loading conditions.

Conclusion
In conclusion, the incorrect statement among the given options is option B, which states that deflection of nonprismatic beam is usually found out by the method of superposition. The deflection of nonprismatic beams is usually calculated using numerical or analytical methods, such as the area-moment method, the conjugate beam method, and the finite element method.

A support is said to be non-yielding if
  • a)
    it can take any amount of reaction
  • b)
    it is frictionless
  • c)
    it holds the beam firmly
  • d)
    the beam has zero slope at the support
Correct answer is option 'D'. Can you explain this answer?

Kajal Tiwari answered
Non-Yielding Support in Structural Engineering

A non-yielding support is an important concept in structural engineering. It is a support that does not deflect or move in response to loads or forces applied to the structure. This type of support is also sometimes referred to as a fixed support.

Definition of Non-Yielding Support

A non-yielding support is a support that is rigid and does not move or deflect in response to loads or forces applied to the structure. It is often used to anchor one end of a beam or other structural member, and is typically made of a material that is stronger than the member it is supporting.

Characteristics of Non-Yielding Support

A non-yielding support has several important characteristics that distinguish it from other types of supports. These include:

- It does not deflect or move in response to loads or forces
- It provides a high level of support and stability to the structure
- It is typically made of a strong material such as concrete or steel
- It is often used to anchor one end of a beam or other structural member

Importance of Non-Yielding Support

Non-yielding supports are important in structural engineering because they provide a high level of support and stability to the structure. They are often used to anchor one end of a beam or other structural member, which helps to prevent the structure from collapsing or becoming unstable.

Conclusion

In conclusion, a non-yielding support is an important concept in structural engineering. It is a support that does not deflect or move in response to loads or forces applied to the structure. Non-yielding supports provide a high level of support and stability to the structure, and are often used to anchor one end of a beam or other structural member.

What is deflection at A of the following cantilever beam with two different moments of inertia?
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'D'. Can you explain this answer?

Sahana Dey answered
Deflection of A due to bending is AB as a cantilever beam:

Part CB also behaves as a cantilever and contributes to the deflection of point A.


Additional deflection

Total deflection of free end,

The deflection is found out by method of superposition is very useful for finding deflections of nonprismatic beams.

The ratio of the area under the bending moment diagram to the flexural rigidity between any two points along a beam gives the change in
  • a)
    deflection
  • b)
    slope
  • c)
    shear force
  • d)
    bending moment
Correct answer is option 'B'. Can you explain this answer?

Amrita Chauhan answered
Explanation:

To understand the given statement, we need to understand the terms mentioned in it. Let's define each term first:

Bending Moment Diagram: It is a graphical representation of the bending moment variation along the length of the beam.

Flexural Rigidity: It is a measure of a beam's resistance to bending deformation under load.

Deflection: It is the displacement of a point on the beam from its original position when it is subjected to a load.

Slope: It is the angle between the tangent to the deflected beam and the horizontal axis.

Shear Force: It is the force acting perpendicular to the longitudinal axis of the beam.

Now, let's analyze the given statement:

Ratio of the area under the bending moment diagram to the flexural rigidity:

This ratio represents the total deformation (specifically, the change in slope) caused by the bending moment along the beam.

Change in slope:

The change in slope is the difference between the initial slope and the final slope of the beam when it is subjected to a load. It is measured in radians or degrees.

Thus, the given statement implies that the ratio of the area under the bending moment diagram to the flexural rigidity between any two points along a beam gives the change in slope of the beam between those two points.

This is because the bending moment diagram represents the variation of bending moment along the beam, and the flexural rigidity represents the resistance of the beam to deformation. Therefore, the ratio of these two quantities can be used to determine the amount of deformation (change in slope) that occurs between any two points along the beam.

Conclusion:

Hence, we can conclude that the correct answer is option B, i.e., the ratio of the area under the bending moment diagram to the flexural rigidity between any two points along a beam gives the change in slope.

 Which one of the following graphs represent Von Mises yield criterion?
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'C'. Can you explain this answer?

Janhavi Datta answered
As per Von Mises yield criterion, the equation in the 2-D system is .This equation represents an ellipse.

Which amongst the following methods is/are most commonly used to determine beam deflection?
1. Double-integration method
2. Method of singularity functions
3. Elastic energy methods
4. Moment-area methods
  • a)
    1 only
  • b)
    1 , 2 , 3 and 4
  • c)
    2, 3 and 4
  • d)
    2 and 4
Correct answer is option 'B'. Can you explain this answer?

Kirti Bose answered
Methods for Determining Beam Deflection

There are several methods used to determine beam deflection. The most commonly used methods are:

1. Double-Integration Method: This method involves calculating the second derivative of the deflection equation twice to obtain the deflection equation. This method is commonly used for simple beam configurations.

2. Method of Singularity Functions: This method involves breaking the beam into segments and evaluating the deflection equation for each segment. This method is commonly used for complex beam configurations.

3. Elastic Energy Methods: This method involves using the principle of conservation of energy to determine the deflection of a beam. This method is commonly used for beams subjected to non-uniform loads.

4. Moment-Area Methods: This method involves calculating the area under the moment diagram and using it to determine the slope and deflection of the beam. This method is commonly used for beams subjected to simple loads.

Answer:

The correct answer is option B, which includes all of the above-mentioned methods. These methods are commonly used by mechanical engineers to determine the deflection of beams under different loading conditions. The choice of method depends on the complexity of the beam configuration and the type of load it is subjected to.

Which theory of failure is widely used in machine design dealing with ductile materials?
  • a)
    Maximum principal stress theory
  • b)
    Energy of distortion theory
  • c)
    Maximum shearing stress theory
  • d)
    Maximum elastic energy theory
Correct answer is option 'D'. Can you explain this answer?

Aarav Kulkarni answered
Theory of Failure in Machine Design for Ductile Materials

In machine design, it is important to understand the behavior of materials under stress and strain. When designing with ductile materials, a theory of failure is used to determine the maximum stress that a material can withstand without undergoing permanent deformation or fracture. The theory of failure used in machine design for ductile materials is the Maximum Elastic Energy Theory.

Explanation of Maximum Elastic Energy Theory

The Maximum Elastic Energy Theory is based on the concept that failure occurs when the elastic strain energy stored in a material reaches a critical level. This theory assumes that the material will deform elastically up to a certain point before it begins to undergo plastic deformation. Once the material reaches its yield point, it will begin to deform permanently.

The maximum elastic energy theory states that failure will occur when the elastic strain energy in a material reaches a critical level. This critical level is determined by the maximum elastic energy that the material can store before it begins to undergo plastic deformation. The maximum elastic energy is calculated using the stress-strain curve of the material.

Advantages and Disadvantages of Maximum Elastic Energy Theory

One advantage of the maximum elastic energy theory is that it considers the entire stress-strain curve of a material, not just a single point. This allows for a more accurate prediction of failure. Additionally, this theory can be applied to a wide range of materials, including those that exhibit nonlinear behavior.

However, one disadvantage of this theory is that it can be difficult to calculate the maximum elastic energy of a material. This calculation requires knowledge of the entire stress-strain curve, which may not be readily available for all materials. Additionally, the maximum elastic energy theory assumes that the material will behave in a perfectly elastic manner up to its yield point, which may not always be the case in real-world applications.

Conclusion

In conclusion, the maximum elastic energy theory is widely used in machine design for ductile materials. This theory considers the entire stress-strain curve of a material and predicts failure based on the maximum elastic energy that the material can store before undergoing plastic deformation. While this theory has its advantages and disadvantages, it provides a useful tool for designing safe and reliable machines.

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