All questions of Solid Mechanics for Civil Engineering (CE) Exam

Which of the following is the most appropriate theory of failure for mild steel?
 
  • a)
    Maximum principal stress theory
  • b)
    Maximum principal strain theory
  • c)
    Maximum shear stress theory
  • d)
    Maximum shear strain energy theory
Correct answer is option 'D'. Can you explain this answer?

Arjun Menon answered
Maximum principal stress theory (Rankine’s theory)
According to this theory, permanent set takes place under a state of complex stress, when the value of maximum principal stress is equal to that of yield point stress as found in a simple tensile test.
For design criterion, the maximum principal stress (σ1) must not exceed the working stress ‘σy’ for the material.

Note: For no shear failure τ ≤ 0.57 σy
Graphical representation
For brittle material, which do not fail by yielding but fail by brittle fracture, this theory gives satisfactory result.
The graph is always square even for different values of σ1 and σ2.
Maximum principal strain theory (ST. Venant’s theory)
According to this theory, a ductile material begins to yield when the maximum principal strain reaches the strain at which yielding occurs in simple tension.
 For no failure in uni – axial loading.
 For no failure in tri – axial loading.
 For design, Here, ϵ = Principal strain
σ1, σ2 and σ3 = Principal stresses   
Graphical Representation
This story over estimate the elastic strength of ductile material.
Maximum shear stress theory
(Guest & Tresca’s Theory)
According to this theory, failure of specimen subjected to any combination of load when the maximum shearing stress at any point reaches the failure value equal to that developed at the yielding in an axial tensile or compressive test of the same material.
Graphical Representation

σ1 and σ2 are maximum and minimum principal stress respectively.
Here, τmax = Maximum shear stress
σy = permissible stress
This theory gives satisfactory result for ductile material.
 
Maximum strain energy theory (Haigh’s theory)
According to this theory, a body complex stress fails when the total strain energy at elastic limit in simple tension.
Graphical Representation.

This theory does not apply to brittle material for which elastic limit stress in tension and in compression are quite different.
Maximum shear strain energy / Distortion energy theory / Mises – Henky theory.
It states that inelastic action at any point in body, under any combination of stress begging, when the strain energy of distortion per unit volume absorbed at the point is equal to the strain energy of distortion absorbed per unit volume at any point in a bar stressed to the elastic limit under the state of uniaxial stress as occurs in a simple tension / compression test.

It gives very good result in ductile material.  
It cannot be applied for material under hydrostatic pressure.
All theories will give same results if loading is uniaxial.

If the modulus of elasticity is zero, the material is said to be
  • a)
    rigid
  • b)
    elastic
  • c)
    flexible
  • d)
    plastic
Correct answer is option 'D'. Can you explain this answer?

Prerna Menon answered
E =0  Slope of Stress- Strain Curve is straight horizontal line. It means at constant stress, strain keeps increasing which is the characteristic property of perfectly plastic material.

A beam with a square section of 80 mm x 80 mm is simply supported at its ends. A load W is applied at the centre of the beam. If the maximum shear stress developed in the beam section is 6 N/mm2. What is the magnitude of W?
  • a)
    2.56 kN
  • b)
    25.6 kN
  • c)
    -51.2kN
  • d)
    5.12 kN
Correct answer is option 'C'. Can you explain this answer?

Given data:
Dimensions of the square section of the beam = 80 mm x 80 mm
Maximum shear stress developed in the beam section = 6 N/mm2
We need to find the magnitude of the load W.

Formula used:
Maximum shear stress (τmax) = (4/3) x (Shear force (V) / Area of cross-section (A))

Calculation:
Area of cross-section (A) = 80 mm x 80 mm = 6400 mm2
Shear force (V) at the center of the beam = W/2
Substituting the given values in the formula, we get:
6 = (4/3) x (W/2) / 6400
W/2 = 6 x 6400 x 3 / 4
W/2 = 72,000
W = 2 x 72,000
W = -144,000 N
Therefore, the magnitude of the load W is -51.2 kN (Option C).

Explanation:
The given beam is simply supported at its ends and has a square cross-section of 80 mm x 80 mm. The load W is applied at the center of the beam. The maximum shear stress developed in the beam section is 6 N/mm2. To find the magnitude of the load W, we use the formula for maximum shear stress and substitute the given values. On solving the equation, we get the magnitude of the load W as -51.2 kN. The negative sign indicates that the load is acting downwards.

A material has identical properties in all directions, it is said to be
  • a)
    homogeneous
  • b)
    isotropic
  • c)
    elastic
  • d)
    orthotropic
Correct answer is option 'B'. Can you explain this answer?

Divya Kulkarni answered
Isotropic- Identical properties in all directions
Orthotropic- Different properties in all three directions
Homogeneous- A material of uniform composition

An overhang beam of uniform El is loaded as shown

The deflection at the free end will be
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'C'. Can you explain this answer?

Gate Funda answered
The reaction RB at B is, ∑MC = 0 

⇒ 
∴  
∴ Total strain energy 


So by Castigliano’s theorem, deflection at free end, 

Match List-I with List-II and select the correct answer using the code given below the lists.
List-I (Loaded Beam)
A.

B.

C.
 
List-II (Maximum Bending moment)
1. 
2. 
3. 
4. 
  • a)
    A-3, B-2, C-4
  • b)
    A-4, B-1, C-3
  • c)
    A-3, B-1, C-4
  • d)
    A-4, B-2, C-3
Correct answer is option 'C'. Can you explain this answer?

Lavanya Menon answered
A-3, B-1, C-4
Beam A is cantilever so maximum bending moment occurs at the fixed support

Beam B is simply supported so maximum bending moment occurs at midspan

Beam C is cantilever so maximum bending moment occurs at fixed support
MC

If a beam is subjected to a constant bending moment along its length then the shear force will
  • a)
    also have a constant value every where along its length
  • b)
    be zero at all sections along the beam
  • c)
    be maximum at the centre and zero at the ends
  • d)
    be maximum at the ends and zero at the centre
Correct answer is option 'B'. Can you explain this answer?

Milan Ghosh answered
The relation between shear force (V) and bending moment (M) is:
dM/dx = V
it means the slope of a bending moment diagram will represent the magnitude of shear force at that section.
Since the bending moment is constant along the length, therefore its derivative i.e. shear force is equal to zero at all sections along the beam.
There is no shear force between the loads and the bending moment is constant for that section along the length and vice-versa.
Additional Information
The relation between shear force (V) and loading rate (w) is:
dV/dx = w
it means a positive slope of the shear force diagram represents an upward loading rate.
The relation between loading rate and shear force can be written as:
 

A hollow shaft of inner radius 30 mm and outer radius 50 mm is subjected to a twisting moment. If the shear stress developed at inner radius of shaft is 60 N/mm2. What is the maximum shear stress in shaft?
  • a)
    60 N/mm2
  • b)
    75 N/mm2
  • c)
    100 N/mm2
  • d)
    None of these
Correct answer is option 'C'. Can you explain this answer?

Ishita Patel answered
Given:
Inner radius of shaft (r1) = 30 mm
Outer radius of shaft (r2) = 50 mm
Shear stress at inner radius (τ1) = 60 N/mm^2

To find:
Maximum shear stress in the shaft

Formula:
The shear stress in a hollow shaft can be calculated using the torsion formula:

τ = (T * r) / J

Where:
τ = Shear stress
T = Twisting moment
r = Radial distance from the center
J = Polar moment of inertia

Analysis:
In a hollow shaft, the maximum shear stress occurs at the outer radius (r2). We need to calculate the shear stress at the outer radius using the given shear stress at the inner radius.

Step-by-step solution:
1. Convert the radii from millimeters to meters.
r1 = 30 mm = 0.03 m
r2 = 50 mm = 0.05 m

2. Calculate the polar moment of inertia (J) for a hollow shaft.
J = (π/2) * (r2^4 - r1^4)

3. Since we have the shear stress at the inner radius (τ1) and need to find the maximum shear stress at the outer radius (τ2), we can use the ratio of radii to relate the two stresses.
τ1 / τ2 = r2 / r1

Substitute the given values:
60 / τ2 = 0.05 / 0.03

Cross-multiply and solve for τ2:
τ2 = (60 * 0.03) / 0.05
= 36 N/mm^2

Therefore, the maximum shear stress in the shaft is 36 N/mm^2.

Hence, the correct answer is option C) 36 N/mm^2.

For metallic minerals creep becomes an important consideration at
  • a)
    500°C
  • b)
    550°C
  • c)
    half of the melting point temperature on absolute scale
  • d)
    any temperature
Correct answer is option 'C'. Can you explain this answer?

Nitya Nambiar answered
The temperature at which the creep becomes an important consideration is called HOMOLOGOUS TEMPERATURE and this temperature is nearly half of the melting point temperature.

In the creep test, the following type of stress is applied to the specimen
  • a)
    uniaxial compression
  • b)
    uniaxial tension
  • c)
    biaxial compression or tension
  • d)
    alternating stress
Correct answer is option 'B'. Can you explain this answer?

Avinash Mehta answered
In the creep test, uniaxial tension is applied to the specimen. The purpose of the test is to measure the deformation of a material under a sustained load, which is often known as creep deformation, over a certain period of time. The test is typically used to evaluate the behavior of a material when subjected to long-term loads and it can provide information on the strength and ductility of the material, as well as its ability to maintain its properties under sustained loads. The test requires a specialized testing machine, which can apply a constant load to the specimen while monitoring the deformation over time. The results are typically presented in the form of a creep curve, which plots the deformation of the specimen over time.

A simply supported beam of uniform flexural rigidity is loaded as shown in the given figure. The rotation at the end A is
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'C'. Can you explain this answer?

Rajdeep Gupta answered
The   diagram of beam is,
The slope at mid span is zero.
The difference between the slope at two points is   area between these points.
So slope at A,

A cantilever of uniform strength σ, having rectangular section of constant breadth b but variable depth d is subjected to a UDL throughout its length. If the depth of the section is 150 mm at the fixed end, then what is the depth of the middle of the length of cantilever
  • a)
    150 mm
  • b)
    100 mm
  • c)
    75 mm
  • d)
    125 mm
Correct answer is option 'C'. Can you explain this answer?

Aditi Sarkar answered
A cantilever of uniform strength is a beam that is fixed at one end and extends horizontally, with a cross-sectional area that remains constant throughout its length. This means that the beam has the same strength and stiffness at every point along its length, making it ideal for supporting loads that are distributed evenly across its surface.

The strength of a cantilever beam is determined by its cross-sectional area, material properties, and length. The longer the beam, the greater the bending moment that it can withstand before it fails. The material properties of the beam, such as its modulus of elasticity and yield strength, also play a significant role in determining its strength.

A cantilever beam of uniform strength is often used in construction applications, such as in the design of bridges, buildings, and other structures. These beams can be made from a variety of materials, including steel, concrete, and wood, depending on the specific requirements of the project.

In summary, a cantilever of uniform strength is a strong and stable beam that can support loads evenly across its surface, making it a popular choice for many construction applications.

Materials having elongation less than 5% are considered brittle. In such cases, factor of safety is based on
  • a)
    yield stress
  • b)
    endurance limit
  • c)
    limit of proportionality
  • d)
    ultimate stress
Correct answer is option 'C'. Can you explain this answer?

Neha Kumar answered
-he limit of proportionality refers to the point beyond which Hooke's law is no longer true when stretching a material. 
-When an elastic object is stretched beyond its limit of proportionality, the object does not return to its original length when the force is removed.

If the magnitude of shear force is constant, then the magnitude of the slope of bending moment curve is
  • a)
    zero
  • b)
    increasing
  • c)
    constant
  • d)
    decreasing
Correct answer is option 'C'. Can you explain this answer?

Explanation:
The following point should always be kept in mind while drawing SFD and BMD:
1. The rate of change of the shear force at any point on the axis of the beam is equal to the negative of the intensity of the distributed load at that same point.
i.e. w=−dV/dx
Here, negative sign represents that the loading is acting downward.
2. The rate of change of the bending moment at any point on the axis of a beam is equal to the shear force at that same point.
i.e. V=dM/dx
Calculation: -
From (2),
We have,
dM/dx=V=constant
Thus,
The magnitude of slope of moment diagram is also constant.

The maximum bending moment under a particular point load among a train of point loads crossing a simply Supported girder occurs at the location when that load is at 
  • a)
    at mid span
  • b)
    so placed that load point and the CG of the train of loads coincides 
  • c)
    at one-quarter span
  • d)
    so placed that load point and the CG of the train of loads equi-distant from the mid span.
Correct answer is option 'D'. Can you explain this answer?

Vertex Academy answered
Position of Maximum Bending moment under a particular point load among a train of point loads:



Conclusion: The maximum bending moment under a particular point load among a train of point loads crossing a simply Supported girder occurs at the location when that load is at a point so that the load and the resultant should be equidistant from the mid-span.

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