Prestress Drop given Stress in concrete at Same Level due to Prestressing Force Calculator

Prestress Drop Formula:

\[ \Delta f_p = \frac{E_s \times f_{concrete}}{E_{concrete}} \]

Modulus of Elasticity of Steel Reinforcement:

MPa

Stress in Concrete Section:

MPa

Modulus of Elasticity Concrete:

MPa

Tolerance:

Prestress Drop (MPa):

1. What is Prestress Drop?

Definition: Prestress Drop is the reduction in applied prestress force due to strain in tendons when accounting for concrete stress at the same level.

Purpose: This calculation helps engineers determine the actual prestress force remaining after accounting for concrete strain effects.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \Delta f_p = \frac{E_s \times f_{concrete}}{E_{concrete}} \]

Where:

\( \Delta f_p \) — Prestress drop (MPa)
\( E_s \) — Modulus of elasticity of steel reinforcement (MPa)
\( f_{concrete} \) — Stress in concrete section (MPa)
\( E_{concrete} \) — Modulus of elasticity of concrete (MPa)

Explanation: The formula calculates the stress loss in prestressing steel due to the strain compatibility between steel and concrete.

3. Importance of Prestress Drop Calculation

Details: Accurate calculation ensures proper design of prestressed concrete members, accounting for stress losses that affect long-term performance.

4. Using the Calculator

Tips: Enter the modulus of elasticity of steel, concrete stress, concrete modulus of elasticity, and tolerance percentage. All values must be > 0 except tolerance which can be 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical modulus of elasticity for prestressing steel?
A: Typically around 200,000 MPa for steel strands, but varies by material.

Q2: Why include a tolerance percentage?
A: The tolerance accounts for material variations and construction tolerances (±5% is common).

Q3: How does concrete modulus of elasticity affect results?
A: Lower concrete modulus results in higher prestress drop as the concrete deforms more under load.

Q4: When would I use this calculation?
A: During design of prestressed concrete beams, slabs, or other members where prestress loss is critical.

Q5: Does this account for all prestress losses?
A: No, this only calculates elastic shortening losses. Other losses (creep, shrinkage, relaxation) need separate consideration.