Difference Between Hot-Rolled Steel Sheet Pile and Cold-Formed Steel Sheet Pile
Steel sheet piles are essential structural elements used in civil engineering for retaining walls, cofferdams, and foundation systems. Two primary manufacturing methods dominate the production of steel sheet piles: hot-rolling and cold-forming. These processes yield products with distinct characteristics, affecting their mechanical properties, dimensions, and applications. This document provides a detailed comparison, including parameter tables, dimensional data, scientific analysis, and relevant formulas, to elucidate the differences between Hot-Rolled Steel Sheet Piles (HRSSP) and Cold-Formed Steel Sheet Piles (CFSSP).
1. Overview of Manufacturing Processes
1.1 Hot-Rolled Steel Sheet Piles
Hot-rolled steel sheet piles are produced by heating steel billets or slabs to temperatures exceeding 1,700°F (approximately 927°C), above the steel’s recrystallization temperature. The heated steel is then passed through a series of rollers to form the desired profile, typically Z-shaped, U-shaped, or straight-web sections. The high-temperature process enhances the steel’s ductility, allowing complex shapes and tight interlocks (e.g., Larssen or ball-and-socket) to be formed directly during rolling. After shaping, the steel cools gradually, normalizing its microstructure and reducing internal stresses.
1.2 Cold-Formed Steel Sheet Piles
Cold-formed steel sheet piles begin as hot-rolled steel coils, which are cooled to room temperature before further processing. These coils are then fed through a mill at ambient temperature, where they are bent or rolled into profiles such as Z-shapes, Omega-shapes, or U-shapes. The cold-forming process does not involve additional heating, relying instead on mechanical deformation to achieve the final shape. This results in looser interlocks (e.g., hook-and-grip designs) and a uniform thickness across the section.
2. Parameter Comparison Table
| Parameter | Hot-Rolled Steel Sheet Pile | Cold-Formed Steel Sheet Pile |
|---|---|---|
| Manufacturing Process | High-temperature rolling (>1,700°F) | Room-temperature forming from coils |
| Interlock Type | Larssen, ball-and-socket (tight) | Hook-and-grip (loose) |
| Thickness Range | 6–25 mm | 2–10 mm |
| Yield Strength (MPa) | 240–500 (EN 10248) | 235–355 (EN 10249) |
| Section Modulus (cm³/m) | Up to 5,000 | Up to 2,500 |
| Watertightness | High (tight interlocks) | Low (loose interlocks) |
| Maximum Length (ft) | Up to 60 (special orders possible) | Up to 100 |
| Rotation Angle (degrees) | 7–10 | Up to 25 |
| Recycled Content | ~100% | ~80% |
3. Dimensional Comparison Table
The dimensions of steel sheet piles vary based on profile type and manufacturer. Below is a representative comparison of typical Z-profile sections for HRSSP and CFSSP.
| Profile | Type | Width (mm) | Height (mm) | Thickness (mm) | Weight (kg/m²) | Section Modulus (cm³/m) |
|---|---|---|---|---|---|---|
| AZ 18-700 | Hot-Rolled | 700 | 420 | 8.5 | 74.6 | 1,800 |
| PAZ 7050 | Cold-Formed | 857 | 340 | 5.0 | 50.2 | 1,200 |
| AZ 26-700 | Hot-Rolled | 700 | 460 | 10.5 | 95.7 | 2,600 |
| PAZ 8070 | Cold-Formed | 857 | 400 | 7.0 | 65.8 | 1,800 |
4. Scientific Analysis
4.1 Mechanical Properties
The mechanical properties of HRSSP and CFSSP are influenced by their manufacturing processes. Hot-rolling at high temperatures allows recrystallization, reducing residual stresses and enhancing ductility. The yield strength of HRSSP typically ranges from 240 to 500 MPa (per EN 10248), reflecting a robust grain structure. Conversely, cold-forming work-hardens the steel, increasing its yield strength (235–355 MPa per EN 10249) but introducing residual stresses that may affect fatigue performance.
The modulus of elasticity (E) for both types is approximately 210 GPa, as it is a material property of steel unaffected by processing. However, the section modulus (W), which measures resistance to bending, is generally higher for HRSSP due to thicker flanges and optimized profiles.
4.2 Interlock Performance
The interlock is a critical feature of sheet piles, determining watertightness and structural integrity. HRSSP’s tight interlocks (e.g., Larssen) provide superior resistance to seepage, making them ideal for marine and cofferdam applications. The interlock strength can be modeled as a shear capacity:
F_s = τ × A_interlock
Where:
- F_s = Shear force capacity (N)
- τ = Shear strength of steel (approximately 0.6 × yield strength)
- A_interlock = Cross-sectional area of the interlock (mm²)
For HRSSP, the tighter interlock increases A_interlock, enhancing F_s. CFSSP’s looser hook-and-grip interlocks have a smaller A_interlock, reducing shear capacity and watertightness.
4.3 Bending Resistance
The bending resistance of a sheet pile is governed by its moment capacity (M), calculated as:
M = σ_y × W
Where:
- M = Moment capacity (kNm/m)
- σ_y = Yield strength (MPa)
- W = Section modulus (cm³/m)
HRSSP typically exhibits higher W values (e.g., 2,600 cm³/m for AZ 26-700) compared to CFSSP (e.g., 1,800 cm³/m for PAZ 8070), resulting in greater M. However, CFSSP’s work-hardening may offset this slightly with higher σ_y in some cases.
4.4 Local Buckling
CFSSP often falls into Class 4 sections per EN 1993-5 due to thinner walls, making them susceptible to local buckling. The critical buckling stress (σ_cr) is given by:
σ_cr = k × (π² × E) / [12 × (1 - ν²) × (b/t)²]
Where:
- k = Buckling coefficient (depends on boundary conditions)
- E = Modulus of elasticity (210 GPa)
- ν = Poisson’s ratio (0.3)
- b/t = Width-to-thickness ratio
HRSSP’s thicker sections yield lower b/t ratios, increasing σ_cr and reducing buckling risk.
5. Applications and Suitability
HRSSP is preferred for heavy-duty applications like deep cofferdams, load-bearing foundations, and permanent retaining walls due to its robustness and watertightness. CFSSP suits lighter applications, such as temporary walls, riverbank reinforcements, and small retaining structures, benefiting from its flexibility and cost-effectiveness
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