DEFLECTION OF DETERMINATE STRUCTURES
1.Why is it necessary to compute deflections in structures?
Computation of deflection of structures is necessary for the following reasons:
a. If the deflection of a structure is more than the permissible, the structure will not look
aesthetic and will cause psychological upsetting of the occupants.
b. Exessive deflection may cause cracking in the materials attached to the structure. For
example, if the deflection of a floor beam is excessive, the floor finishes and partition
walls supported on the beam may get cracked and unserviceable.
2.What is meant by cambering technique in structures?
Cambering is a technique applied on site, in which a slight upward curve is made in the
structure/ beam during construction, so that it will straighten out and attain the straight shape
during loading. This will considerably reduce the downward deflection that may occur at later
3.Name any four methods used for computation of deflections in structures.
1. Double integration method
2. Macaulay’s method
3. Conjugate beam method
4. Moment area method
5. Method of elastic weights
6. Virtual work method- Dummy unit load method
7. Strain energy method
8. Williot Mohr diagram method
4. State the difference between strain energy method and unit load method in the determination of
deflection of structures.
In strain energy method, an imaginary load P is applied at the point where the deflection is
desired to be determined. P is equated to zero in the final step and the deflection is obtained.
In unit load method, an unit load (instead of P) is applied at the point where the deflection is
5.What are the assumptions made in the unit load method?
1. The external & internal forces are in equilibrium.
2. Supports are rigid and no movement is possible.
3. The materials is strained well with in the elastic limit.
6.Give the equation that is used for the determination of deflection at a given point in beams and
Deflection at a point is given by,
I = l Mx mx dx
where Mx = moment at a section X due to the applied loads
mx = moment at a section X due to a unit load applied at that point I and in the direction
EI = flexural rigidity