Question

A fletched beam composed of two different pieces, each having breath b and depth d, supports an external load. This statement implies that

1. the two different materials are rigidly connected

2. there will be relative movement between the two materials

3. for transforming into an equivalent single-material section under ‘strength’ consideration, the depth is kept constant and only the breadth is varied

Which of the above statement are correct?
1. 1 and 2 only
2. 1 and 3 only
3. 2 and 3 only
4. 1, 2 and 3

Answer 1

Correct Answer - Option 2 : 1 and 3 only

Concept:

The fletched beam is non-homogenous in nature and therefore, flexural formula cannot be directly used. To use this formula, we need to convert the given fletched beam into an equivalent section of either of the material from which fletched beam is made of.

The following assumptions are made while analyzing the fletched beam:

1.  The junctions are rigidly connected.

2. There is no relative movement between both the materials at jointed section.

Note:  The above two assumption ensured that strain in one material at junction is equal to strain in other material at same location (junction).

3.  Total Moment is resisted by the both of the materials. So, the total moment of resistance is the sum of the moment of resistance of both sections.

4. Both materials will bend about common axis, so having equal radius of curvature.

5. For transforming into an equivalent single-material section under ‘strength’ consideration, the depth is kept constant and only the breadth is varied. This makes calculation is easy.