26.1.1. Materials

Try these first

1. 1.

   What does prestressed concrete aim to prevent?

   Hint

   Think about the purpose of prestressing.

2. 2.

   What is an important property of materials used in prestressing?

   Hint

   Focus on the strength of steel.

3. 3.

   What is the maximum compressive strength of prestressed concrete?

   • 6,000 psi
   • 8,000 psi
   • 10,000 psi

   Hint

   Consider the capacity advantage over traditional concrete.

4. 4.

   True or False: High yield stress steel is used to minimize crack widths.

   • True
   • False

   Hint

   Think about the purpose of high-strength materials.

5. 5.

   A prestressed concrete beam has an initial prestress of 160 ksi but experiences a loss of 25 ksi due to creep and steel relaxation. What is the effective residual stress?

   Hint

   Subtract the losses from initial prestress.

6. 6.

   If a strand composed of 7 wires has an initial stress of 150 ksi and has a relaxation loss of 10 ksi, is the remaining stress sufficient for a design requiring a minimum of 130 ksi?

   Hint

   Keep track of the stress after relaxation to ensure it meets design requirements.