Identifying Pre-stressing Systems by Anchoring Method

Pre-stressing is a technique used in concrete structures to introduce internal stresses that counteract the stresses caused by external loads. This helps to improve the strength, durability, and performance of concrete members. Different pre-stressing systems employ various types of tendons and anchoring methods.

The question asks about a specific pre-stressing system that utilizes high tensile bars with threads at their ends. Let's examine the systems provided in the options:

• Lee-McCall system: This system, also known as the Macalloy bar system, uses high tensile alloy steel bars as tendons. These bars are typically threaded at both ends. Nuts are screwed onto these threads against bearing plates or anchor blocks to grip and anchor the bar after tensioning. This directly matches the description given in the question.
• Gifford-Udall system: This system generally uses parallel wires that are stressed one by one. The anchorage typically involves split cones or similar gripping devices that bear against a plate, not threads on the wire ends.
• Magnel-Blaton System: This system employs cables formed by stacking high tensile wires in layers within a rectangular sheath. The anchorage involves wedge-shaped plates and shims to grip the wires, not threaded bar ends.
• Freyssinet system: This is a widely used system that utilizes high tensile steel wires, typically grouped into cables. The anchorage relies on conical wedges or cones that are forced into a conical cavity to grip the bundle of wires. It does not use bars with threads at the ends.

Based on the characteristics of these systems, the one that specifically employs high tensile bars with threads at the ends for anchoring is the Lee-McCall system.

Therefore, the pre-stressing system described is the Lee-McCall system.