Answer: B. Depth of neutral axis increases
As the percentage of steel increases, depth of neutral axis increases.
As the percentage of steel increases, the depth of the neutral axis increases. A balanced section will have a larger carrying capacity for tensile stress if the area of steel is increased. The neutral axis must descend in order to counteract or generate equivalent compressive stress or force.
In a rectangular beam segment that is singly reinforced,
xu/d = 0.87fyAst/0.36fckbd
Implies that , xu ∝ Ast
Which means as the percentage of steel increases, depth of the neutral axis also increases.
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