1. What is a Prestress Drop Calculator?

Definition: This calculator estimates the loss of prestress force in tendons due to strain changes in prestressed concrete members.

Purpose: It helps structural engineers determine the reduction in prestressing force that occurs over time in prestressed concrete structures.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( \Delta f_p \) — Prestress drop (MPa)
• \( E_s \) — Modulus of elasticity of steel reinforcement (MPa)
• \( \Delta \varepsilon_p \) — Change in strain (%)

Explanation: The modulus of elasticity is multiplied by the change in strain (converted from percentage to decimal) to calculate the prestress drop.

3. Importance of Prestress Drop Calculation

Details: Accurate calculation of prestress loss is crucial for ensuring the long-term performance and safety of prestressed concrete structures.

4. Using the Calculator

Tips: Enter the modulus of elasticity (default 200,000 MPa for steel) and change in strain (as percentage). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is typical modulus of elasticity for prestressing steel?
A: Typically around 200,000 MPa, but can vary slightly depending on the specific steel alloy used.

Q2: What causes strain changes in prestressed tendons?
A: Factors include concrete creep, shrinkage, elastic shortening, and tendon relaxation.

Q3: How significant is prestress drop in design?
A: It can account for 15-30% of initial prestress force and must be considered in design calculations.

Q4: Should the strain be entered as percentage or decimal?
A: Enter as percentage (e.g., 0.05% not 0.0005), the calculator handles the conversion.

Q5: Does this include all types of prestress losses?
A: No, this calculates only the loss due to strain change. Other losses (friction, anchorage slip) need separate consideration.

Prestress Drop Calculator© - All Rights Reserved 2025