The system in which high tensile alloy steel bars (silica manganese steel) are used as prestressing tendons, is known as

ANS:D - Lee-McCall system.

1. Freyssinet system: Named after its inventor, Eugène Freyssinet, this system utilizes high tensile alloy steel bars, commonly silica manganese steel, as prestressing tendons. These bars are typically installed in ducts within the concrete member and are tensioned to induce compressive forces in the concrete, enhancing its load-carrying capacity. The Freyssinet system is widely used in prestressed concrete construction for bridges, buildings, and other structures.
2. Magnel-Blaton system: Developed by Gustave Magnel and Léonard Blaton, this system also involves the use of high tensile steel tendons for prestressing concrete members. However, unlike the Freyssinet system, the Magnel-Blaton system often utilizes pre-tensioning techniques, where the tendons are tensioned before the concrete is cast around them. This system has been employed in various prestressed concrete applications, including bridges and industrial structures.
3. C.C.L. standard system: CCL (Construction Composite Limited) is a company that specializes in providing post-tensioning and pre-tensioning solutions for concrete structures. The CCL standard system refers to the proprietary prestressing systems and techniques developed and offered by the company. These systems typically involve the use of high-strength steel tendons, either in the form of bars or strands, to impart prestress to concrete members. CCL systems are used worldwide in various construction projects, including bridges, buildings, and infrastructure.
4. Lee-McCall system: The Lee-McCall system is a prestressing method developed by engineers T.Y. Lee and J.G. McCall. This system utilizes a combination of pre-tensioning and post-tensioning techniques to prestress concrete members. It often involves the use of steel tendons, either in the form of bars or strands, which are tensioned either before or after the concrete is cast. The Lee-McCall system has been used in a variety of applications, including bridges, parking structures, and industrial buildings.

Each of these prestressing systems offers unique advantages and may be selected based on factors such as project requirements, structural design considerations, and construction constraints. They all aim to enhance the performance and durability of concrete structures by improving their load-carrying capacity and minimizing the effects of cracking and deflection under load.