This set of Engineering Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Space Trusses”.

1. __________ is a structure made of slender members which are joined together at their end points.

a) Space Truss

b) Pillar

c) Beam

d) Support

View Answer

Explanation: The space 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.

2. As the loading is acting in the three dimensions, that is in multi planes. Thus the calculations involved in the trusses are in 3D.

a) True

b) False

View Answer

Explanation: The loading is acting in a 3D plane. Thus the calculations are done in 3D only. As the equations for 3D are different. The use of vectors can make our task easy. Using 2D can make the calculations but it’s a hectic job. Thus a 3D problem requires using the 3D equations to find the necessary data.

3. Which of the following is correct for space trusses?

a) To know the direction of the unknown force we take assumption of it

b) The direction of the unknown force is known to us already

c) The direction of the unknown can’t be determined

d) The direction of the unknown is of no use, it is not founded

View Answer

Explanation: The direction of the unknown is not known to us. To know the direction of the unknown force we take assumption of it. That is we assume that the particular direction might be the direction of the force and then we do the calculations accordingly.

4. Find the force in the member RQ.

a) 750N

b) 450N

c) 250N

d) 200N

View Answer

Explanation: The direction of the unknown is not known to us. To know the direction of the unknown force we take assumption of it. That is we assume that the particular direction might be the direction of the force and then we do the calculations accordingly. And then we apply the equilibrium equations to the joints.

5. _________ trusses lie on a 3D volume.

a) Planar

b) 2D

c) Linear

d) 3D

View Answer

Explanation: The planar trusses lie on a plane while the space truss in 3D volume. Like for e.g. the trusses in the bridges. These trusses are the main supports of the bridge. They are extended straight vertical and are strong enough to resist various changes in the weather.

6. In case of bridge the load is transferred as:

a) Stringers > floor beams > joints

b) Floor beams > stringers > joints

c) Joints > floor beams > stringers

d) Stringers > joints > floor beams

View Answer

Explanation: The bridge load is transmitted to the stringers first. It is then transmitted to the floor beams. The load from beams is then transmitted to the joints. Thus the transmission of the load of the bridge.

7. To design the space trusses which of the following rules is followed?

a) All the loads are applied by the use of cables

b) The loads are applied at the joints

c) All the loads are not applied at the joints

d) The loads are not applied at all to the joints

View Answer

Explanation: The set of rules which are used to design the trusses are having various rules. To them, one is that the loads are applied at the joints. This is done with the neglecting of the weight of the trusses section.

8. The rules which are used to design the space trusses are having various rules. Of them, one is that the smooth pins are not used to join the members.

a) Statement is correct

b) Statement is incorrect

c) Statement is incorrect because there are no rules

d) Statement is incorrect as the rolling pins are used

View Answer

Explanation: The set of rules used to design the trusses are having various rules. Of them one is that the smooth pins are used to join the members. The joint is generally formed by welding the materials at the ends of the trusses. Which gives strength to the design.

9. In a roof supporting space truss, the load is transmitted as:

a) First to the truss then the joints through purlins

b) First to the purlins then the joints through trusses

c) First to the truss then the purlins through joints

d) First to the joints then the trusses through purlins

View Answer

Explanation: The roof load is transmitted to the truss first. It is then transmitted to the joints. This transmission of the force or the load from trusses to the joints is achieved by the purlins. Thus the distribution of the load.

10. The free body diagram of which part of the section of the space truss is made to make use of the method of joints?

a) Joints

b) Truss

c) The whole structure

d) The combination of joint and the whole structure

View Answer

Explanation: The free body diagram of joints part of the section of the truss is made to make use of method of joints. Various equations of equilibrium are made to do the calculations. The net force acting on the vertical direction is made zero. Also horizontal direction forces are made to be zero.

11. Find the force in the member RQ of the frame shown below.

a) 566N

b) 400N

c) 773N

d) 1090N

View Answer

Explanation: The direction of the unknown is not known to us. To know the direction of the unknown force we take the assumption of it. That is we assume that the particular direction might be the direction of the force and then we do the calculations accordingly. And then we apply the equilibrium equations to the joints.

12. We use the method of a joint to find the forces acting over the joints in the space trusses. In this we start from the joint having at least one known force and at the most two unknown forces.

a) The first part of the statement is false and other part is true

b) The first part of the statement is false and other part is false too

c) The first part of the statement is true and other part is false

d) The first part of the statement is true and other part is true too

View Answer

Explanation: This makes the calculations easy. Also for the solving of any equation one requires equal number of variables as that of equal number of an equation. So to do the calculations easily the above mentioned conditions are followed.

13. As space trusses are used in bridges. When the bridges are extended over long routes or distance then:

a) A rocker or a roller is used at the joints

b) They are not extended to such a long distance

c) The bridges are painted

d) The roads are made narrow

View Answer

Explanation: When the bridges are extended over long routes or distance then a rocker or a roller is used at the joints. This allows the bridge joints to move around. That is when the temperature is raised. The elongations and the contractions of the joints part are not much affected if the rollers and rockers are used.

14. What is after taking the assumption of the direction of the force in space trusses, the direction comes opposite?

a) The assumption made was wrong and the question can’t be solved further

b) The assumptions are not to be taken

c) The direction is in the opposite sense, and hence the direction is known to us

d) The direction will be already given to us, no need of assuming

View Answer

Explanation: The direction is comes opposite, means that the assumption was wrong. But that doesn’t means that the question can’t be solved further. One needs to change the sign of the direction and the question is solved. Thus the calculations of the force direction.

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