Q1: Steel beam theory is used for

ANS:C - doubly reinforced beams ignoring compressive stress in concrete

Steel beam theory is used for doubly reinforced beams ignoring compressive stress in concrete is incorrect. Steel beam theory is not typically applied to doubly reinforced beams or beams where the compressive stress in concrete is ignored. Instead, steel beam theory is primarily used for the design of simple steel beams, as previously mentioned. Simple steel beams are beams primarily composed of steel and are supported at two points, such as at their ends or on columns. They are subjected to loads that induce bending moments and shear forces. Doubly reinforced beams, on the other hand, are reinforced concrete beams that have steel reinforcement in both the tension and compression zones. These beams are designed to withstand both tensile and compressive forces, utilizing steel reinforcement in addition to the concrete's compressive strength. The design and analysis of doubly reinforced beams involve more complex considerations, including the interaction between concrete and steel, compatibility of strains, and equilibrium of internal forces. This typically requires different design methods and theories compared to those used for simple steel beams. In doubly reinforced beams, the compressive stress in concrete is a critical component of the beam's behavior and must be considered in the design process. Ignoring the compressive stress in concrete would result in inaccurate calculations and could lead to unsafe designs.