NCIDQ IDFX Practice Exam

In pre-cast concrete systems, what happens to the high-strength steel cables during the process?

1. They are cut after the concrete sets

2. They are stretched before the concrete is poured

3. They are used only for aesthetic purposes

4. They are not needed for structural integrity

The correct answer is: They are stretched before the concrete is poured

In pre-cast concrete systems, high-strength steel cables, known as tendons, are stretched before the concrete is poured, which is a key step in the process of prestressing. This technique allows the concrete to be designed more efficiently, as it helps to counteract tensile forces that can lead to cracking. By tensioning the cables prior to the pouring of the concrete, the structure benefits from increased bearing capacity and improved performance under load. This method takes advantage of the high compressive strength of concrete and the tensile strength of steel. When the concrete hardens around the cables, the tension in the cables induces a compressive force in the concrete itself. As a result, the finished precast element is stronger and can span greater distances or carry heavier loads than non-prestressed concrete elements. The other options do not reflect the established practices in pre-cast concrete systems. Cutting the cables after the concrete sets would not provide the intended benefits of prestressing, and using tendons solely for aesthetic purposes overlooks their critical structural role. Lastly, high-strength steel cables are essential for maintaining structural integrity in precast concrete applications. They are integral to ensuring that the concrete can withstand various forces, demonstrating the importance of their proper installation and usage.