ANS:C - 4%

In the design and construction of reinforced concrete beams, the amount of tension reinforcement plays a crucial role in ensuring the structural integrity and performance of the beam under various loading conditions. The maximum allowable percentage of tension reinforcement is typically governed by engineering standards, design codes, and considerations related to structural behavior, material properties, and construction practices. Reinforced concrete beams are subjected to bending stresses due to applied loads, and the tension reinforcement, usually in the form of steel rebars, is essential for resisting these tensile forces. However, providing too much tension reinforcement can lead to undesirable consequences such as excessive cracking, reduced ductility, and difficulties in construction. Among the options provided—0.15%, 1.5%, 4%, and 1%—the selection of the correct maximum allowable percentage of tension reinforcement depends on several factors:

1. Design Codes and Standards: Engineering standards and design codes, such as those provided by organizations like the American Concrete Institute (ACI) or the Eurocode, often specify the maximum allowable percentage of tension reinforcement based on extensive research, empirical data, and safety considerations.
2. Structural Behavior: The amount of tension reinforcement influences the structural behavior of the beam, including its strength, deflection characteristics, and crack control. Higher percentages of tension reinforcement can enhance the beam's capacity to carry loads and improve its behavior under serviceability and ultimate limit states.
3. Construction Considerations: Practical aspects of construction, such as placing and anchoring reinforcement, maintaining proper concrete cover, and ensuring constructability, also influence the maximum allowable percentage of tension reinforcement. Excessive reinforcement may lead to congestion, making it challenging to achieve proper concrete compaction and cover.
4. Material Properties: The properties of the concrete and steel used in the beam, including their strengths, ductility, and compatibility, affect the maximum allowable percentage of tension reinforcement. Balancing the properties of these materials is crucial for achieving a durable and robust structural system.

While a maximum allowable percentage of 4% for tension reinforcement may seem unusually high in typical reinforced concrete beam designs, there may be specific cases or design requirements where such a value is warranted. These could include specialized structural configurations, seismic design considerations, or exceptionally heavy loading conditions that necessitate higher levels of reinforcement. In summary, the determination of the maximum allowable percentage of tension reinforcement in reinforced concrete beams involves a careful balance of structural, material, and construction considerations, guided by engineering standards and design codes to ensure the safety, durability, and performance of the structure.