A concrete slab-on-ground cast monolithically with the footing shall be permitted to locate _____ as an alternative to placement at the footing top and bottom?

The correct option indicates that either one number 5 bar or two number 4 bars can be placed in the middle third of a concrete slab-on-ground cast monolithically with the footing. This option is aligned with standard reinforcement practices, allowing for flexibility in reinforcement design while maintaining structural integrity.

Reinforcement in concrete slabs serves to control tensile stresses and cracking, particularly in areas where the slab is subjected to bending due to load or settlement. The middle third of the slab is considered an effective location for placing reinforcement because it is where tensile stresses are typically greatest. Using either one number 5 bar or two number 4 bars provides sufficient tensile strength, enabling the slab to handle loads effectively.

The mention of a specific middle third location is significant, as it reflects a design concept that helps distribute loads evenly across the slab and enhances performance. Essentially, reinforcing in this manner adheres to the principles of good engineering practice by optimizing both strength and material usage.

The other options do not align with typical reinforcement practices or proper engineering standards for this type of construction. They either provide insufficient reinforcement or do not take into consideration the optimal loading distribution necessary for effective slab performance.