The correct answer is A. 18.
The modular ratio is a dimensionless number that is used to determine the amount of reinforcement required in a reinforced brick masonry structure. It is defined as the ratio of the modulus of elasticity of the reinforcement to the modulus of elasticity of the masonry. The recommended value of the modular ratio for reinforced brick masonry is 18. This means that for every 1 unit of stress in the reinforcement, there should be 18 units of stress in the masonry.
The modular ratio is important because it ensures that the reinforcement and the masonry work together as a unit. If the modular ratio is too low, the reinforcement will be overstressed and may fail. If the modular ratio is too high, the masonry will be overstressed and may fail.
The modular ratio is determined by the type of masonry, the type of reinforcement, and the expected loads on the structure. The recommended value of the modular ratio for reinforced brick masonry is 18. This value is based on extensive research and testing. It is important to use the recommended value of the modular ratio to ensure the safety of your structure.
The other options are incorrect because they are not the recommended value of the modular ratio for reinforced brick masonry.