Set initial joint gaps for any installation temperature. Compare closure and opening limits quickly. Export results for submittals, inspections, and field crews daily reports.
| Case | L (m) | α (µm/m/°C) | Tinstall (°C) | Tmin (°C) | Tmax (°C) | gmin (mm) | gmax (mm) | Recommended ginstall (mm) |
|---|---|---|---|---|---|---|---|---|
| Bridge deck joint | 10 | 12 | 20 | -5 | 45 | 5 | 35 | 20.00 |
| Long slab panel | 15 | 11 | 25 | 0 | 50 | 6 | 40 | 22.12 |
| Steel walkway | 8 | 12 | 15 | -10 | 40 | 4 | 30 | 17.20 |
Thermal length change is computed using: ΔL = α · L · ΔT
Convert ΔL to millimeters and treat warming as joint closure and cooling as joint opening. The installation gap ginstall must satisfy:
Accurate gap settings protect joints through every season today.
Expansion joints are movement devices. As temperature rises, restrained length shortens the free gap by thermal closure; as temperature drops, the gap opens. If the joint closes below the minimum, seals crush and debond; if it opens beyond the maximum, seals stretch, tear, and allow water ingress and debris packing.
The restrained length between fixed points is the largest multiplier of movement. Typical coefficients of thermal expansion are about 10–12 µm/m/°C for concrete and about 12 µm/m/°C for carbon steel. Service temperature ranges often span 30–60°C depending on climate, solar heating, and elevation.
Movement is computed using ΔL = α·L·ΔT. For example, a 10 m run with α = 12 µm/m/°C across 50°C produces about 6.0 mm of total movement. A 20 m run under the same conditions produces about 12.0 mm, which can quickly exceed tight seal limits.
The calculator finds an allowable installation-gap band that keeps the joint within your minimum and maximum limits at both temperature extremes. Choosing the mid-point of that band balances risk, providing margin against field measurement tolerance, sawcut variability, and installation temperature drift.
Manufacturer data typically specifies a minimum seal compression and a maximum extension. Common target working gaps for small slab joints may be 5–35 mm, while bridge deck glands may require different limits. Always align gmin and gmax with the specific joint system and anchorage details.
If the permissible installation range collapses (lower bound exceeds upper bound), the selected joint limits cannot accommodate the thermal movement for the given length and temperatures. Solutions include reducing panel length, increasing movement capacity, using multiple joints, or revising the temperature envelope.
Record the measured installation temperature, gap readings at multiple stations, and any restraint breaks or construction joints. The CSV/PDF exports provide calculation backups for submittals, inspections, and quality records, especially when joints are tied to waterproofing or durability warranties.
Use member temperature rather than shaded air temperature when possible. Confirm whether the length is truly restrained; partially free ends reduce effective movement. Consider solar heating on dark decks and seasonal extremes. Re-check gaps after curing shrinkage if the joint is in new concrete.
Use the effective restrained distance between fixed points. If movement is relieved by an isolation layer or free end, the effective length can be shorter than the physical panel length.
Choose the coefficient for the element controlling movement at the joint. Concrete commonly ranges 10–12 µm/m/°C, and steel is often near 12 µm/m/°C. Use project specifications when provided.
Warming reduces the gap (closure), while cooling increases the gap (opening). Both extremes must stay within allowable limits to avoid seal crushing, loss of adhesion, tearing, and leakage.
Feasible means there is at least one installation gap that keeps the joint between your minimum and maximum allowable gaps at both Tmin and Tmax for the entered length and coefficient.
It is the mid-point of the permissible installation range. This balances available movement capacity and provides practical tolerance for measuring, cutting, and setting the gap in the field.
Yes, if you input the correct restrained length and the joint’s allowable working gap range. Always verify limits with the joint manufacturer and consider additional movements like creep, shrinkage, and bearing slip.
Increase movement capacity (larger gmax or smaller gmin), reduce effective length, split the run into more joints, or revise the temperature range using site-specific environmental data.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.