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Home Engineering Mechanics Electrical Machines To determine the support reactions of a given truss and verify it analytically.
Electrical Machines Lab Experiments

To determine the support reactions of a given truss and verify it analytically.



Aim

To determine the support reactions of a given truss and verify it analytically

Theory:

The truss is one of the major types of engineering structures. It provides both a practical and economical solution to many engineering situations, especially in Learning content the design of bridges and buildings. A truss consists of straight members connected at joints. The truss is designed to carry those loads which acts in its plane and thus treated as a two-dimensional structure. The applied loads are at the joints. The load shared by the members of the truss is along their axes. These members are either in tension tend to elongate or in compression tends to shorten. Force analysis in the members of the truss helps in deciding their size. The first step in the procedure of analysis is to determine the reaction on the support.

The aim of the experiment is to find support reaction of a given truss (in the present case it is warren type) and verify analytically considering it simply supported. The truss is loaded at three joints and supported on a frame through spring balances at two joints. The readings on the spring balance show the amount of force on the support.

Apparatus Used:

apparatus
  1. A warren- truss apparatus
  2. A set of slotted masses of known values weights (1 kg, 2 kg, ..... ..)
  3. A measuring tape
  4. Sprit level etc.

Procedure:

  1. Ensure that the truss remains in a vertical plane during the observation
  2. Note the initial reading on the scale of spring balance.
  3. Mark the position of thread with the help of mirror on paper and join all the points.
  4. Place the known masses at specified joints (here they are three)
  5. Note the changed readings on the scale of spring balances
  6. Change the loads at these joints and record the corresponding readings of spring balance scale
  7. Take at least FIVE or more sets of observations and tabulate them
  8. Measure the distance of loads from the left end of support of spring balance (L1, L2, L3 for W1, W2, W3 respectively). Measure the distance L between the spring balance support.

Considering the equilibrium of forces :

ΣV = 0

i.e., RA +RB =W1 +W2 +W3

and

ΣMA= o

RB= (W1L1 + W2L2 +W3L3)/L

Then RA =(W1 +W2 +W3)-RB

Observations and Calculations:

S.no Applied Loads/W1/W2/W3 Final Reading of spring balance/S”A/S”B Experimental Reaction R’A =S”A–SA % error in RA RA-R'A/RA X100 Experimental Reaction R’B =S”B –SB Analytical Reaction RB % error in RB RB-R'B/RB X100
1
2
3
4
5
6

Result:

  1. For ____ sets of observations, the observed percentage error in RA is____________________
  2. For ____ sets of observations, the observed percentage error in RB is____________________

Precautions:

  1. Ensure the loads and the truss are in a vertical plane throughout the observation
  2. Do not put excessive load.
  3. Remove the load as the observations are over.
  4. Clean the apparatus carefully.
  5. Loads should be placed gently.

Viva Questions:

1.What is a perfect frame?

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Q.-2. What are the methods of analysisng a perfect frame?

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Q.-3.Which are the various type of frames?

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Q.-4. What is redundant frame?

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Q.-5. Write expression for perfect frame.

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Q.-6. Which are the assumptions made in the analysis of a perfect frame?

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Q.-7. What is deficient frame?

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