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Confused about how to model Prestressing?

Prestressing concrete provides internal compression, which counteracts the tension caused by loads coming onto it. It can be internal or external, pre-tensioned or post-tensioned, straight or curved. But the important thing is the application of appropriate prestressing load in the proper location along the length of the girder/beam.

Through this eBook, you can understand different tendons, various profile generation techniques and appropriately predicting the various long-term and immediate losses in midas civil. Examples are used for the calculation and verification of the losses in midas civil. Some key tips/notes are provided along the way for better modeling.

Key Points

1. What is prestressing?

Prestressing is the process by which the concrete element is compressed by means of wires, strands, etc. Concrete is a compression resisting material and its tension resisting capacity is very poor. So, the ultimate purpose of prestressing is that most of concrete remains in compression even after the load is applied.

This can be achieved via 3 methods:

01-1. Internal Pre-tension
01-2. Internal Post-tension
01-3. External Post-tension

2. Losses in Tendons

They are mainly divided into 2 categories: Immediate loss and long-term loss.

3. How to Apply Prestressing in midas Civil?

03-1. Tendon Property

03-1-1. Total Tendon Area

03-1-2. Duct Diameter

03-1-3. Strand Diameter

03-1-4. Relaxation Coefficient

03-1-5. Curvature Friction Factor

03-1-6. Wobble Friction Factor

03-1-7. External Cable Moment Magnifier

03-2. Tendon Property

03-2-1. Typical Tendon

03-2-2. Debonded Length

03-2-3. Reference Axis

03-2-4. Profile Insertion Point

03-2-5. Point of Symmetry

03-2-6. X-axis Direction

03-3. Tendon Prestress

4. Methods of Defining a Tendon Profile

04-1. Simple Beam

04-2. Curved Tendon Profile

04-3. Beam in X-Y Plane

04-4. PSC Section with Inclined Web

04-5. Copying of Tendon

5. Loss Verification

05-1. Immediate Loss

05-1-1. Elastic Shortening Loss

05-1-2. Anchorage Slip

05-1-3. Friction Loss

05-1-4. Creep & Shrinkage Loss

05-1-5. Relaxation Loss

6. Common Mistakes While Modeling Tendons

Common mistakes while modelling the tendon in midas Civil occurs while defining the tendon profile.