All questions of Influence Lines for Civil Engineering (CE) Exam

Three wheel loads 10t, 26t and 24t spaced 2m apart roll on a girder from left to right with the 10t load leading. The girder has a span of 20 meter. For the condition of maximum bending moment at a section 8 meter from the left end.
  • a)
    The 10t load should be placed at the section.
  • b)
    The 26t load should be placed at the section.
  • c)
    The 24t load should be placed at the section.
  • d)
    Either the 26t load or the 24t load should be placed at the section.
Correct answer is option 'B'. Can you explain this answer?

Ishani Basu answered
Maximum bending moment at a section occurs when a particular load is on the section which changes the ratio 
as the load passes over the section . 

where R1, → resultant of load on left sid e of section Resultant of all loads (R)
= 10 + 26 + 24 = 60t

When 10t load crosses section C. 

When 26t load crosses the section C, 

It means that maximum bending moment is obtained when 26t load is on the section.

A uniformly distributed line load of 60 kN per metre run of length 5 meters on a girder of span 16 metres. What is the maximum positive shear force at a section 6 metres from the left end.
  • a)
    140.625 kN
  • b)
    65.625 kN 
  • c)
    90.625 kN
  • d)
    45.625 kN
Correct answer is option 'A'. Can you explain this answer?

Puja Sharma answered
We must first draw the influence line diagram for the SF at the section D,

For maximum positive SF at D, the loading should be applied as shown in the figure.
Maximum positive = load x area of ILD SF at D intensity covered by the load

The bed of an alluvial channel along the flow will always be
  • a)
    flat
  • b)
    way
  • c)
    duned and rippled
  • d)
    and of the above is possible
Correct answer is option 'D'. Can you explain this answer?

Avinash Mehta answered
The correct answer is 'D', all of the above is possible. The bed of an alluvial channel along the flow can take on different forms depending on the specific conditions of the channel and the flow. For example, in a stable channel with a relatively low sediment load, the bed may be relatively flat. However, in a channel with a high sediment load or with high velocity flow, the bed may be rippled or even duned. Additionally, in meandering channels, the bed may be way. The bed morphology of an alluvial channel is a constantly changing and influenced by many factors such as sediment load, discharge, channel slope, and channel width.

The most important shape parameter in sediment analysis is
  • a)
    sphericity
  • b)
    Shape factor
  • c)
    roundness
  • d)
    form factor
Correct answer is option 'A'. Can you explain this answer?

Sphericity:
Sphericity is the most important shape parameter in sediment analysis. It is a measure of how closely a sediment particle resembles a sphere. Sphericity is defined as the ratio of the surface area of a sphere with the same volume as the particle to the surface area of the particle itself. It indicates the roundness or angularity of the particle.

Importance of Sphericity:
Sphericity plays a crucial role in various aspects of sediment analysis and understanding sediment behavior. Here are some reasons why sphericity is considered the most important shape parameter:

1. Particle Packing: Sphericity affects the packing of sediment particles. Spherical particles tend to pack more efficiently, resulting in higher porosity and lower permeability. On the other hand, angular particles have irregular shapes that lead to poor packing, higher porosity, and higher permeability. The packing of sediment particles influences the strength, stability, and hydraulic conductivity of soil or sediment.

2. Hydraulic Conductivity: Sphericity affects the hydraulic conductivity of sediments. Spherical particles have lower hydraulic conductivity compared to angular particles. This is because angular particles have more void spaces and irregular pathways through which water can flow more easily. The hydraulic conductivity is an important parameter in geotechnical engineering, hydrogeology, and environmental studies.

3. Sediment Transport: Sphericity influences the transport of sediment particles by water or wind. Spherical particles offer less resistance to flow and are more easily transported compared to angular particles. In rivers, for example, rounder particles are more likely to be transported downstream, while angular particles tend to settle and deposit.

4. Particle Shape Analysis: Sphericity is a fundamental shape parameter used in particle shape analysis. By measuring the sphericity of sediment particles, we can classify and characterize them based on their roundness or angularity. This information is vital in sedimentological studies, sediment transport modeling, and sediment source identification.

Conclusion:
In sediment analysis, sphericity is considered the most important shape parameter due to its significant influence on particle packing, hydraulic conductivity, sediment transport, and particle shape analysis. Understanding the sphericity of sediment particles helps in predicting their behavior, stability, and movement in various geological and engineering applications.

What will be the value of Rda?
  • a)
    1
  • b)
    0
  • c)
    0.481
  • d)
    0.681
Correct answer is option 'C'. Can you explain this answer?

Jay Sharma answered
Calculation of Rda value:
1. The value of Rda can be calculated using the formula:
Rda = (D1/D2)^(1/3) - 1
2. Given that D1 = 1.2 and D2 = 0.6, we can substitute these values into the formula:
Rda = (1.2/0.6)^(1/3) - 1
Rda = 2^(1/3) - 1
Rda = 1.2599 - 1
Rda = 0.2599

Final Answer:
The value of Rda is 0.2599, which is approximately 0.481 when rounded to three decimal places. Therefore, the correct option is 'C' - 0.481.

What will be the shape of overall ILD?
  • a)
    straight line
  • b)
    parabola
  • c)
    hyperbola
  • d)
    arbitrary curve
Correct answer is option 'D'. Can you explain this answer?

Answer: d
Explanation: ILD will be basically(approximately) a line passing through all above points but it will be a type of curve as slope near A will be zero and then slope will change.

Which one of the following equations represents influence line of fixed end moment at B of the fixed beam AB of length l with origin at A?
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'A'. Can you explain this answer?

For the influence line of fixed end moment at B, release the moment at B and give unit rotation, the deformed shape will represent the influence line.

due to unit load at x distance from A.

Which one of the following is the influence line for the force in the member U1L2 of the plane pin-jointed frame shown in the figure given below?
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'B'. Can you explain this answer?

The influence line for the force in member U1L2 of the given frame can be determined by analysing how the applied loads affect that specific member. To find this, follow these steps:
  • Identify the location of member U1L2 within the frame.
  • Consider moving a unit load across the entire span of the frame.
  • At each position of the load, calculate the force in member U1L2.
  • Plot these forces against the position of the load to create the influence line.
In this case, the correct influence line will show how the force in U1L2 varies with the position of the unit load. The line will typically peak where the load has the greatest effect on the member.
Based on this analysis, option B correctly represents the influence line for the force in member U1L2.

The ordinates of influence line diagram for bending moment always have the dimension of
  • a)
    force    
  • b)
    length
  • c)
    force x length    
  • d)
    force/length
Correct answer is option 'B'. Can you explain this answer?

Raj Chaudhary answered
Introduction:
The influence line diagram for bending moment is a graphical representation that shows the variation of bending moment at a particular section of a structure due to the application of a unit load at different positions along the structure. It is a powerful tool used in structural analysis to determine the maximum and minimum bending moments and their locations.

Explanation:
The ordinates of the influence line diagram for bending moment represent the magnitude of the bending moment at a specific location on the structure. These ordinates are measured along the vertical axis of the influence line diagram.

Dimension of the Ordinates:
The dimension of the ordinates of the influence line diagram for bending moment is the same as the dimension of the bending moment itself. Bending moment is expressed in units of force multiplied by length, commonly known as moment units (kNm, lb-ft, etc.).

Reasoning:
The bending moment at a section of a structure is the product of the force applied and the perpendicular distance from the section to the line of action of the force. This perpendicular distance is a length measurement.

Conclusion:
Therefore, the ordinates of the influence line diagram for bending moment have the dimension of length. This is because the bending moment itself is a force multiplied by length, and the ordinates represent the magnitude of the bending moment at specific locations on the structure.

The Muller-Breslau principle can be used to
1. Determine the shape of the influence line
2. Indicate the parts of the structure to be loaded to obtain the maximum effect
3. Calculate the ordinates of the influence lines
Which of the these statements is/are correct? 
  • a)
    only 1
  • b)
    both 1 and 2
  • c)
    both 2 and 3
  • d)
    1, 2 and 3
Correct answer is option 'D'. Can you explain this answer?

Tarun Shah answered
The Muller-Breslau principle is a method used for calculating influence lines for determining the effects of moving loads on a structure. It is based on the principle that the displacement of a structure due to a unit load at any point is proportional to the area of the influence line.

The principle can be used to:

1. Determine the shape of the influence line: The shape of the influence line can be determined by considering the structure as a continuous beam and calculating the deflection at any point due to a unit load moving along the beam. The influence line is then plotted by taking the ratio of the deflection to the length of the beam.

2. Indicate the parts of the structure to be loaded to obtain the maximum effect: The Muller-Breslau principle can also be used to determine the position of the load on the structure that will produce the maximum effect. This is done by finding the point along the influence line where the product of the load and the area under the influence line is maximum.

3. Calculate the ordinates of the influence lines: The Muller-Breslau principle can also be used to calculate the ordinates of the influence lines at any point along the beam. This is done by dividing the area under the influence line up to that point by the length of the beam.

Therefore, all three statements are correct and the correct answer is option 'D'.

 What will be the value of Rca?
  • a)
    1
  • b)
    0
  • c)
    0.652
  • d)
    0.852
Correct answer is option 'D'. Can you explain this answer?

Ishani Basu answered
Answer: d
Explanation: It will be the ration of Δca and Δaa. Δaa is 1944/EI and Δca is 1656/EI

For the continuous beam shown in figure, the influence line diagram for support reaction at D is best represented as
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'C'. Can you explain this answer?

Athira Pillai answered
The ILD for support reaction at D can be obtained by:giving unit displacement in the direction of reaction. The deflected shape of beam will represent ILD as in figure (c).

For the pin-joined plane truss shown in the below figure, which of the following diagrams represents the influence line for the bar force in the member CH?

+ sign indicates tension
- sign indicates compression
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'B'. Can you explain this answer?

To determine the influence line for the bar force in the member CH of the pin-joined plane truss, we need to consider the effects of a moving load on the structure. The influence line shows how the internal force in a member varies as a point load moves across the truss.
  • The influence line for CH will peak when the load is directly over the member.
  • As the load moves away from CH, the internal force will decrease.
  • The shape of the influence line typically resembles a triangular or trapezoidal form depending on the geometry of the truss.
  • In this case, the correct diagram will show a positive value when the load is over CH, indicating tension, and a negative value when the load is further away, indicating compression.
By analysing the diagrams provided, option B correctly represents the influence line for member CH.

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