Plan bridge deck slab depth with preliminary checks. Compare criteria, dead loads, and live loads. Get fast sizing guidance for safer early structural decisions.
Enter project assumptions for a rapid bridge deck slab sizing study.
This estimator blends several preliminary checks and chooses the largest required depth before applying an exposure margin.
1. Span proportion check:
hspan = L / (span-depth ratio)
2. Deflection control check:
hdeflection = L / (deflection ratio)
3. Durability check:
hdurability = top cover + bottom cover + 2.5 × bar diameter + wearing surface + tolerance
4. Factored strip load:
wu = [1.25 × (self-weight + superimposed dead)] + [1.75 × live load × impact] × distribution factor
5. Factored strip moment:
Mu = continuity factor × wu × L² / 8
6. Flexural depth approximation:
d = √[Mu / (φ × b × K)] where K depends on assumed steel ratio, concrete strength, and steel strength.
7. Recommended thickness:
hrec = ceil(max(hspan, hdeflection, hdurability, hstrength, hminimum) × exposure factor)
Use this tool for early sizing only. Final bridge deck design must follow the governing code, load model, distribution rules, crack control, fatigue, and detailing provisions.
For conservative concept studies, increase the exposure factor or practical minimum thickness. For alternate structural systems, update continuity and distribution factors to reflect the actual behavior.
Sample concept-level values for comparing likely deck slab depths across common bridge deck conditions.
| Case | Girder Spacing (m) | Concrete Strength (MPa) | Live Load (kPa) | Impact Factor | Practical Minimum (mm) | Estimated Thickness (mm) |
|---|---|---|---|---|---|---|
| Urban overpass | 2.70 | 35 | 8.50 | 1.25 | 180 | 205 |
| Heavy truck route | 3.20 | 40 | 10.00 | 1.30 | 200 | 235 |
| Marine exposure deck | 3.00 | 45 | 9.00 | 1.30 | 210 | 250 |
| Pedestrian bridge deck | 2.20 | 32 | 5.50 | 1.10 | 160 | 180 |
It estimates a preliminary bridge deck slab thickness using span, load, cover, material, and practical construction assumptions. It is meant for concept sizing, not final code design.
No. Final design needs code-based analysis, lane loading, distribution rules, reinforcement design, crack checks, fatigue review, detailing, and project-specific approval.
Girder spacing controls the deck strip span. Larger spans usually increase bending demand, serviceability concerns, and the empirical depth needed for a practical slab.
The impact factor amplifies live load effects to reflect dynamic action from moving vehicles. Higher impact usually increases factored load and required slab depth.
The tool uses an assumed reinforcement ratio to approximate flexural strength depth. This helps early sizing before detailed bar design is completed.
It adds conservative margin for severe environments such as deicing salts, marine spray, or aggressive weathering where thicker slabs may improve durability.
Yes, for quick comparisons. However, rehabilitation decisions should also consider existing reinforcement, deterioration, overlays, remaining section, and construction staging limits.
The estimate rounds up to the next 5 mm after margin is applied. That makes the recommendation easier to communicate and more practical to detail.
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.