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

Sep 24 2023

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:

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

Procedure:

Ensure that the truss remains in a vertical plane during the observation
Note the initial reading on the scale of spring balance.
Mark the position of thread with the help of mirror on paper and join all the points.
Place the known masses at speciﬁed joints (here they are three)
Note the changed readings on the scale of spring balances
Change the loads at these joints and record the corresponding readings of spring balance scale
Take at least FIVE or more sets of observations and tabulate them
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., R_A +R_B =W₁ +W₂ +W₃

and

ΣM_A= o

R_B= (W₁L₁ + W₂L₂ +W₃L₃)/L

Then R_A =(W₁ +W₂ +W₃)-R_B

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–S_A	% error in R_A R_A-R'_A/R_A X100	Experimental Reaction R’_B =S”_B –S_B	Analytical Reaction R_B	% error in R_B R_B-R'_B/R_B X100
1
2
3
4
5
6

Result:

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

Precautions:

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

Viva Questions:

1.What is a perfect frame?