Input Parameters
Use effective movement length between fixed points. Enter strains in microstrain (µε). Set restraint factor to reflect fixity or bearing guidance.
Formula Used
The calculator combines a thermal component and a time-dependent strain component. A restraint factor scales movement to reflect fixity or bearing guidance, then a safety factor is applied.
How to Use This Calculator
- Enter the effective movement length between fixed points.
- Provide the thermal coefficient and the temperature rise and drop.
- Enter creep, shrinkage, and any shortening strain in microstrain.
- Set a restraint factor to reflect guided or fixed behavior.
- Add construction tolerance and an optional safety factor.
- Click Calculate to view component movements and totals.
- Download CSV or PDF for your design documentation.
Example Data Table
| Case | L (m) | α (µε/°C) | +ΔT (°C) | −ΔT (°C) | Creep (µε) | Shrink (µε) | R | Tol (mm) | γ | Factored demand (mm) |
|---|---|---|---|---|---|---|---|---|---|---|
| A | 60 | 12 | 30 | -25 | 200 | 300 | 1.00 | 5 | 1.10 | ≈ 37.84 |
| B | 90 | 11 | 35 | -30 | 250 | 350 | 0.85 | 8 | 1.15 | ≈ 59.18 |
| C | 40 | 12 | 25 | -20 | 150 | 250 | 1.00 | 3 | 1.05 | ≈ 23.31 |
1) Why longitudinal movement matters
Longitudinal movement demand governs bearing travel, expansion joints, and clearances at abutments and piers. If demand is underestimated, joints can open or crush, seals may fail, and unintended restraint forces may develop. This calculator reports thermal and time‑dependent components for transparent design notes.
2) Effective movement length selection
Choose the effective length between points that restrain translation, such as a fixed bearing, integral abutment, or diaphragm tied to substructure. For continuous decks, the controlling length is often from the fixed point to the nearest movement joint. Use the same definition across cases for consistency.
3) Thermal input data and temperature range
Thermal movement scales with the maximum absolute temperature change. Expansion coefficients for common bridge materials often fall near 10–13 µε/°C, while seasonal ranges can exceed 40 °C depending on installation temperature and climate. The tool uses the larger of rise or drop for control.
4) Time‑dependent strains: creep and shrinkage
Concrete shortening from creep and shrinkage can be several hundred microstrain. As an example, 200 µε creep plus 300 µε shrinkage equals 500 µε (0.0005). Over 60 m, that is about 30 mm before restraint factors, tolerances, and safety factors are applied.
5) Restraint factor and real behavior
Guides, friction, shear keys, and integral connections may reduce free translation or redirect movement to other locations. The restraint factor scales movement to reflect expected degrees of freedom. Use values below 1.0 only when the resulting restraint forces are checked and the detailing intent is clear.
6) Tolerances and construction effects
Fit‑up, bearing setting, and fabrication tolerances create practical movement demand beyond ideal calculations. Adding a tolerance in millimeters helps cover seating and alignment variability. This is especially important for short bridges where theoretical movement is small, but installation variability can dominate joint performance.
7) Factoring and documentation
Some projects apply a factor to address uncertainty in temperatures, staging, and long‑term behavior. The factored demand provides a single value for joint selection and bearing travel limits. CSV and PDF outputs support peer review by keeping inputs, assumptions, and component results in one place.
8) Interpreting results for detailing
Use the factored movement to set joint capacity and check bearing travel. Compare expansion and contraction components when setting joint gaps at installation temperature. Confirm guide clearances, keeper plates, and approach slab details accommodate the same travel, and reconcile any assumed restraint with substructure capacity.
FAQs
1) What length should I enter for L?
Use the effective distance between the fixed point and the location where movement is released, such as an expansion joint or guided bearing line. For continuous decks, this may be the distance from fixed pier to the nearest joint.
2) Should I use temperature rise, drop, or both?
Enter both when known. The calculator uses the larger absolute change to compute the controlling thermal component, while also reporting separate expansion and contraction values for joint gap checks.
3) What are typical thermal expansion values?
Common values are roughly 10–13 µε/°C for many bridge materials. Use project material specifications when available, especially for composite systems or special alloys.
4) How do I estimate creep and shrinkage strains?
Use project design documents, material test data, or accepted prediction models for the concrete class and exposure. Enter results as microstrain totals representing the expected long‑term shortening over the movement length.
5) When should I reduce the restraint factor?
Reduce it only if the structural system truly limits translation, and you have evaluated the associated restraint forces and load paths. Otherwise, keep it at 1.0 for conservative movement capacity selection.
6) Why add construction tolerance?
Tolerances represent real fit‑up and seating variability that can shift joint gaps and bearing positions. Adding a few millimeters helps prevent under‑design when calculated theoretical movement is small.
7) Is the PDF output acceptable for submissions?
The PDF is a concise summary for internal documentation and review. For formal submissions, copy the inputs and results into your project calculation template and reference the governing standard and assumptions.