If the depth of actual neutral axis of a doubly reinforced beam

ANS:D - all the above.

The neutral axis of a reinforced concrete beam is the line within the beam's cross-section where the bending stress is zero. In doubly reinforced beams, both tensile and compressive reinforcements are used to increase the load-carrying capacity and control deflections. Let's analyze the statements:

1. If the depth of the actual neutral axis of a doubly reinforced beam is greater than the depth of the critical neutral axis:
   • This implies that the compression zone is larger than expected, which means the concrete is experiencing higher compressive stresses. As a result, the concrete will attain its maximum stress earlier.
2. If the depth of the actual neutral axis of a doubly reinforced beam is less than the depth of the critical neutral axis:
   • This suggests that the compression zone is smaller than expected, causing the steel in the tensile zone to experience higher tensile stresses. Therefore, the steel in the tensile zone will attain its maximum stress earlier.
3. If the depth of the actual neutral axis of a doubly reinforced beam is equal to the depth of the critical neutral axis:
   • This indicates that the compression and tension zones are as expected, and both the concrete and steel will attain their maximum stresses simultaneously.

So, based on these analyses, the correct answer is: "all the above." In doubly reinforced beams, the actual depth of the neutral axis relative to the critical depth affects the distribution of stresses in the concrete and steel, which in turn influences when they reach their maximum stresses. Therefore, all the provided statements are valid outcomes depending on the relationship between the actual and critical neutral axis depths.