The correct answer is: C. 30 m.
Expansion joints are provided in masonry walls to allow for movement due to temperature changes, settlement, and other factors. The length of a wall without an expansion
joint will depend on the type of masonry, the climate, and other factors. However, a general rule of thumb is to provide an expansion joint every 30 m.Option A: 10 m is too short for a wall without an expansion joint. This would likely result in cracking and other damage to the wall.
Option B: 20 m is a common length for an expansion joint in a masonry wall. However, it is important to consult with a structural engineer to determine the appropriate length for a particular wall.
Option C: 30 m is the recommended length for an expansion joint in a masonry wall. This will allow for movement due to temperature changes, settlement, and other factors without causing damage to the
wall.Option D: 40 m is too long for a wall without an expansion joint. This would likely result in cracking and other damage to the wall.