ANS:B - depth of neutral axis increases

As the percentage of steel in a reinforced concrete section increases, several changes occur in the behavior of the section, including the position of the neutral axis and the lever arm. Let's analyze each option:

1. Depth of neutral axis decreases: This statement is generally correct. When the percentage of steel in a reinforced concrete section increases, the neutral axis tends to shift towards the compression face of the section. This means that the depth of the neutral axis decreases, as it moves closer to the top (compression) face of the beam. This occurs because the added steel increases the tensile strength of the section, causing more of the compressive forces to be resisted by the concrete, leading to a lower neutral axis depth.
2. Depth of neutral axis increases: This statement is incorrect based on the typical behavior of reinforced concrete sections. As explained above, an increase in the percentage of steel typically leads to a decrease in the depth of the neutral axis.
3. Lever arm increases: This statement is generally incorrect. The lever arm is the distance between the centroid of the compressive force and the centroid of the tensile force in a reinforced concrete beam. When the percentage of steel increases, the tensile force increases, and the centroid of the tensile force moves upward (toward the neutral axis). Therefore, the lever arm usually decreases rather than increases.
4. Lever arm decreases: This statement is generally correct. As mentioned earlier, the lever arm tends to decrease when the percentage of steel increases due to the upward movement of the centroid of the tensile force towards the neutral axis.
5. None of these: While the depth of the neutral axis decreases and the lever arm usually decreases when the percentage of steel increases, this option does not accurately capture these relationships.