1. Pre-Stressed Concrete
NT Alice Springs Stuart
Highway Rail Overpass
THURSDAY 4TH DECEMBER – 1:00 PM
By Jad Daet

2. 2Agenda
 What Is Pre-Stressed
Concrete?
 How Does A Pre-Stressed
Concrete Beam Work?
 Example Model Construction of
Pre-Stressed Concrete
 Stressing & De-Stressing
Procedure
 Q & A
Stress Bed Constructed At The Overpass

3. 3What is Pre-Stressed Concrete?
 Method for Overcoming Concrete’s Natural Weakness
 Accomplished In Three Possible Ways:
1. Pre-Tensioned Concrete
2. Bonded Post-Tensioned Concrete
3. Unbonded Post-Tensioned Concrete

4. 4How Does A Pre-Stressed Concrete Beam Work?

5. 5How Does A Pre-Stressed Concrete Beam Work?

6. 6
 Picture of Stop End
 Strands contain massive amounts of force, Overpass strands contain either
147kN or 187kN of force
 Strands are stretched, concrete poured around strands
 Once specified compressive strength is reached, strands are then gradually
released one by one. Thereby transferring force from strands into the
concrete. Thus Compression into the beam.
 Notice the strands at the bottom of the beam, reason being is, not only do we
wish to apply compression, but we want to apply a bending moment, because
the overall position of the strands are eccentric, ie removed from the centre of
the beam, that creates the bending moment which helps to counteract the
loads on the beam itself.
 Once construction is complete of the pre-stressed concrete beam, you will
notice that the beam itself will result in the beam cambering up several
milimetres.
 Beneficial for two reasons, deflection checks for structural steel/concrete
calculations. The other is for the aesthetics, as we do not want to see visual
sagging of the beam itself once the load is applied.
How Does A Pre-Stressed Concrete Beam Work?

7. 7How Does A Pre-Stressed Concrete Beam Work?

8. 8Model Construction of Pre-Stressed Concrete
Step 1 Step 2

9. 9Model Construction of Pre-Stressed Concrete
Step 3 Step 4

10. 10Model Construction of Pre-Stressed Concrete
Step 5 Step 6

11. 11Model Construction of Pre-Stressed Concrete
Step 7 Step 8

12. 12Model Construction of Pre-Stressed Concrete
Step 9 Step 10

13. 13Stressing & De-Stressing Procedure
De-Stress Order:
De-Stress Is Performed In Reverse To Stress Order, A0, A1, B0, B1 etc.
Stressing Order:
D4, D7, C4, C7, B4, B7, D3, D8, C3, C8, B3, B8, D2, D9, C2, C9, B2, B9, D1, D0, B1, B0, A1, A0

14. 14
 Beams are intended to carry flexural and shear forces, however the flexure
which is carried by the beam results in tension in at least one face of the
beam and as we know, concrete is not strong in tension. Thus pre-stress
concrete methodologies are required.
 Therefore, in pre-stressed concrete design, we apply compression to
overcome the tensile stress on the beam due to flexure.
Summary

15. 15Q&A