Doubly reinforced beams are structural members commonly used in construction to support loads and resist bending. These beams are reinforced with both tension steel (usually in the form of bars) and compression steel (usually in the form of stirrups or hoops).

The given statement asserts that a doubly reinforced beam is considered less economical than a singly reinforced beam because the compressive steel is under-stressed. Let us discuss this in detail:

1. **Tensile steel requirement**: One of the main reasons why doubly reinforced beams are considered less economical is that they require a higher amount of tensile steel compared to a singly reinforced beam. This increased requirement is due to the need to provide additional reinforcement to resist the tensile forces that develop in the beam. In a singly reinforced beam, the tension steel is sufficient to resist the bending moment and the tensile stresses in the beam. However, in a doubly reinforced beam, additional tension steel is required to counteract the increased tensile stresses caused by the larger bending moment.

2. **Shear reinforcement**: Shear reinforcement refers to the additional steel provided in the beam to resist the shear forces that develop parallel to the plane of the beam. In doubly reinforced beams, the shear reinforcement may need to be increased to accommodate the larger bending moment and ensure the beam's structural integrity. This increased requirement for shear reinforcement can contribute to the higher cost of construction and, therefore, reduce the overall economy of the beam.

3. **Concrete stress**: Doubly reinforced beams are designed to ensure that the concrete is not stressed to its full capacity. This is done to prevent the concrete from reaching its ultimate compressive strength, which could result in concrete failure. By limiting the stress in the concrete, the beam's overall safety and reliability are ensured. However, this also means that the full strength of the concrete is not utilized, which can be seen as an inefficient use of the material.

4. **Compressive steel**: The compressive steel in a doubly reinforced beam is generally under-stressed compared to a singly reinforced beam. This is because the primary purpose of the compression steel is to prevent the concrete from failing in compression. In a singly reinforced beam, the concrete itself is responsible for resisting the compression forces, while in a doubly reinforced beam, the compression steel provides additional support. As a result, the compressive steel in a doubly reinforced beam is typically not stressed to its full capacity, leading to a perception of inefficiency.

In conclusion, the given statement is correct in stating that a doubly reinforced beam is considered less economical than a singly reinforced beam because the compressive steel is under-stressed. However, it is important to note that the decision to use a doubly reinforced beam depends on various factors such as the design requirements, load conditions, and cost considerations.