1.0 OBJECTIVE
1.1 To observe the effect of redundant member in a structure in a structure and understand the method of analysis type of this structure.
2.1 LEARNING OUTCOME
2.2 The application of the engineering knowledge in practical application
2.3 To enhance technical competency in structural engineering through laboratory application
3.0 THEORY
3.1 In a statically indeterminate truss, static equilibriumalone cannot be used to calculated member force. If we were to try, we would find that there would be too many “unknowns” and we would not be able to complete the calculations.
3.2 Instead we will use a method know as the the flexibility method, which uses an idea know as strain energy.
3.3 The mathe,atical approach to the flexibility method will be found in the most appropriate text books.
Basically the flexibility method uses the idea that energy stored in the frame would be the same for a given loa for a given weather load wheather or not the redundant member wether or not.
In the other word, the external energy = internal energy
In practice, the loads in the frame are calculated in its “released” from (that is, without the redundant member) and then calculated with a unit load in place of the redundant member and remaining members.
There redundant member load in given by:
P= ∑
The remaining member force are then given by:
Member force = Pn+f
Where,
P= Redundant member load (N)
L=Length of member (as ratio of the shortest)
N=Load in each member due to unit load in place of redundant member (N)
F=Force in each member when the frame is release (N)
Figure shows the force in the frame due to the load of 250N . You should be able to calculate these values from experiment. Force in a statically determinate truss
Method of Joints
- Suitable to use in calculating all of the member forces for a truss. - This method entails the use of a free body diagram of joints with the equilibrium