The correct answer is: C. Less than 2.
A deep beam is a beam whose effective span-to-depth ratio is less than 2. This means that the beam is relatively short and deep, which can lead to problems with deflection and cracking. Deep beams are often used in situations where there is a need for a large amount of load-bearing capacity, such as in bridges and other long-span structures.
The effective span of a beam is the distance between the supports, while the overall depth is the distance from the top of the beam to the bottom. The effective span-to-depth ratio is calculated by dividing the effective span by the overall depth.
If the effective span-to-depth ratio is less than 2, the beam is considered to be a deep beam. Deep beams are more likely to deflect and crack than shallow beams. This is because the bending stresses in a deep beam are concentrated near the top and bottom of the beam, which can lead to these problems.
Deep beams can be designed to overcome these problems, but they require special attention from the engineer. The engineer must select the appropriate materials and reinforcement to ensure that the beam can withstand the loads without excessive deflection or cracking.