Prestressing systems identification in building construction: The system that uses high-tensile alloy steel bars (silico-manganese bars) as prestressing tendons, tightened by nuts and anchor plates, is known as which of the following?

Introduction / Context:
Prestressed concrete can be executed using several proprietary or classical systems. Each system is distinguished by the type of tendon (wire, strand, or bar), the anchorage arrangement, and the stressing method. Recognizing these systems is a common exam objective in civil engineering and structural design.

Given Data / Assumptions:

• The tendon material in question is a high-tensile alloy steel bar, often described as silico-manganese steel.
• The question asks for the name of the system that specifically employs such bars with mechanical anchorage (nuts/anchor plates).
• No numerical calculations are required; this is a factual classification problem.

Concept / Approach:
Classic systems include: Freyssinet (multiple high-tensile wires with conical wedges), Magnel–Blaton (grouped wires with sandwich plates), C.C.L. systems (strands/wires with wedge anchors), and Lee–McCall (high-tensile alloy steel bars stressed by nuts against anchor plates). Matching the tendon type to the system identifies the correct choice.

Step-by-Step Solution:
Identify tendon: high-tensile alloy steel bars (not wires/strands).Map to system: bar tendons with nut-and-plate anchorage correspond to Lee–McCall.Confirm: other systems listed mainly use wires/strands with wedge grip anchors.Select answer: Lee–McCall system.

Verification / Alternative check:
Reference descriptions of historical prestressing methods consistently attribute bar-tendon, nut-anchored techniques to Lee–McCall, whereas Freyssinet and Magnel–Blaton are wire/strand-based systems.

Why Other Options Are Wrong:

• Freyssinet system: uses multiple wires with conical wedge anchorages, not alloy bars.
• Magnel–Blaton system: sandwich plate anchor with grouped wires; not alloy bars.
• C.C.L. standard system: wedge-grip anchors for strands/wires; not a bar-with-nut system.

Common Pitfalls:
Confusing bar tendons with strand/wire systems, or assuming anchor plates imply any system. The key identifier here is the bar tendon stressed by a nut.

Final Answer:
Lee–McCall system