CYPECAD Foundation Design: Spread Footings, Pile Caps, and Mat Foundations per Eurocode 7

CYPECAD Foundation Design: Spread Footings, Pile Caps, and Mat Foundations per Eurocode 7

Foundation design in CYPECAD is something I've come to rely on for Eurocode 7 projects. The integration with the superstructure model means you don't have to export reactions to a separate tool — everything stays in one project. I've used it for isolated footings, pile caps, and mat foundations on projects in Spain and Portugal. Let me walk you through the workflow.

Soil Parameters

Defining Soil Profile

1. Foundations > Soil Profile
2. Set:
   • Bearing capacity (Rd): Allowable bearing pressure (e.g., 250 kN/m²)
   • Soil type: Sand, clay, or rock
   • Groundwater level: Depth below surface (e.g., 2.5m)
   • Soil layers: Multiple layers with different properties
3. For pile design:
   • Shaft friction: Per soil layer (kN/m²)
   • End bearing: Base resistance (kN/m²)
   • Pile type: Driven, bored, CFA

Eurocode 7 Design Approaches

1. Set design approach per EN 1997-1:
   • DA1 (UK, recommended): Combination 1 (1.35G + 1.5Q) and Combination 2 (1.0G + 1.3Q)
   • DA2 (France): Factor actions and ground resistance
   • DA3 (Netherlands): Factor ground properties
2. CYPECAD applies the selected approach automatically

Isolated Footing Design

Creating an Isolated Footing

1. Foundations > Isolated Footing
2. Select column (at base level)
3. Set:
   • Shape: Square, rectangular, or circular
   • Initial dimensions: e.g., 2.0m × 2.0m × 0.5m
   • Depth below ground: e.g., 1.5m
   • Concrete: C25/30
   • Reinforcement: B500S
   • Cover: 50mm (foundations)

Bearing Capacity Check

1. CYPECAD calculates bearing pressure:
   • Centric load: p = N / (b × l)
   • Eccentric load: p = N/(b×l) ± 6M/(b×l²) ± 6M'/(b²×l)
2. Check per EN 1997-1:
   • Serviceability: p ≤ Rd (allowable bearing)
   • No uplift: pmin ≥ 0 (no tension on soil)
3. If pressure exceeds Rd: increase footing dimensions

Structural Design

1. One-way shear (at distance d from column face):
   • Vu = p × (tributary area)
   • VRd,c = 0.18/γc × ξ × (100 × ρl × fck)^(1/3) × b × d
   • Check: Vu ≤ VRd,c
2. Punching shear (at perimeter d/2 from column):
   • Vu = p × (area outside punching perimeter)
   • VRd,c = 0.18/γc × ξ × (100 × ρl × fck)^(1/3) × u × d
   • Check: Vu ≤ VRd,c
3. Flexural reinforcement:
   • Mu = p × (cantilever length)² / 2
   • As = Mu / (fyd × z), z ≈ 0.9d
   • Minimum: As,min = max(0.26 × fctm/fyk, 0.0013) × b × d

Footing Output

| Parameter | Value | |-----------|-------| | Dimensions | 2.5m × 2.5m × 0.6m | | Bearing pressure (max) | 210 kN/m² < 250 ✓ | | One-way shear | Vu=280 < VRd,c=350 ✓ | | Punching shear | Vu=520 < VRd,c=680 ✓ | | Reinforcement | Ø16 @ 150mm both ways | | Steel weight | 85 kg |

Combined Footing Design

When to Use Combined Footings

• Two columns too close for separate footings
• Column at property line (eccentric loading)
• Bearing capacity insufficient for isolated footings

Creating a Combined Footing

1. Foundations > Combined Footing
2. Select two or more columns
3. Set:
   • Shape: Rectangular or trapezoidal
   • Dimensions: Width and length
   • Thickness: 600-1000mm
4. CYPECAD analyzes as a beam on elastic foundation:
   • Soil modeled as Winkler springs
   • Subgrade modulus: ks (kN/m³)
   • Calculates pressure distribution, shear, and moment

Design Checks

1. Bearing pressure: Uniform or trapezoidal ≤ Rd
2. Beam shear: At column faces
3. Punching shear: At each column
4. Flexural design: Top and bottom reinforcement
5. Development length: Bars must extend past critical sections

Pile Cap Design

Pile Definition

1. Foundations > Piles
2. Set:
   • Pile type: Bored, driven, or CFA
   • Diameter: 600mm, 800mm, 1000mm
   • Length: e.g., 15m
   • Capacity: Compression, tension, lateral
   • Shaft friction: Per soil layer
   • End bearing: Base resistance

Pile Cap Creation

1. Foundations > Pile Cap
2. Select column
3. Set:
   • Number of piles: 2, 3, 4, 5, 6, 9
   • Pile spacing: 3 × diameter minimum
   • Cap dimensions: Thickness, width, length
4. CYPECAD arranges piles and designs the cap

Pile Load Check

1. CYPECAD calculates pile loads:
   • Axial per pile: N/n ± My × x/I ± Mx × y/I
   • Maximum pile load: ≤ pile capacity
   • Minimum pile load: ≥ 0 (no tension) or ≤ tension capacity
2. If maximum load exceeds capacity:
   • Add more piles
   • Increase pile diameter
   • Increase pile length

Pile Cap Structural Design

1. Punching shear: At column and at individual piles
2. Beam shear: Between piles
3. Flexural reinforcement: Top and bottom mats
4. Detailing: Bars must anchor around piles

Mat Foundation Design

Creating a Mat Foundation

1. Foundations > Mat Foundation
2. Set:
   • Plan area: Covers entire building footprint
   • Thickness: 800-2000mm
   • Soil model: Winkler springs (ks) or soil profile
   • Mesh: Auto-mesh or manual

Mat Analysis

1. CYPECAD models the mat as FEM plate elements:
   • Element type: 4-node or 8-node plate
   • Mesh size: 0.5m × 0.5m to 1.0m × 1.0m
   • Soil springs: One per node (ks × tributary area)
2. Apply column loads at node locations
3. CYPECAD calculates:
   • Pressure distribution: Varies across the mat
   • Plate moments: Mx, My, Mxy per element
   • Shear: At column perimeters
   • Settlement: Total and differential

Mat Design Checks

1. Bearing pressure: Maximum ≤ Rd at all locations
2. Settlement: Total and differential within tolerable limits
3. Punching shear: At each column
4. One-way shear: At critical sections
5. Flexural reinforcement: Based on plate moment output

Mat Reinforcement

1. From plate moment output:
   • Mx: Reinforcement in X direction
   • My: Reinforcement in Y direction
   • Top mat: For hogging moments (near columns)
   • Bottom mat: For sagging moments (mid-span)
2. Calculate As per meter:
   • As = Mu / (fyd × z), z ≈ 0.9d
3. Select bar size and spacing:
   • Typical: Ø20 @ 200mm both ways, top and bottom
   • Extra reinforcement at column locations

Retaining Wall Design

Basement Walls

1. Walls > Retaining Wall
2. Set:
   • Wall type: Cantilever, propped, or anchored
   • Height: e.g., 4.0m (basement depth)
   • Soil properties: φ (friction angle), c (cohesion), γ (unit weight)
   • Surcharge: e.g., 10 kN/m² (traffic load)
   • Water pressure: Hydrostatic if applicable
3. CYPECAD calculates:
   • Active earth pressure: Ka × γ × H (Rankine or Coulomb)
   • Surcharge pressure: Ka × q
   • Water pressure: 0.5 × γw × H²
   • Total lateral force: E = earth + surcharge + water
4. Design checks:
   • Overturning stability: resisting moment / overturning moment ≥ 1.5
   • Sliding stability: resisting force / driving force ≥ 1.5
   • Bearing capacity: Under footing
   • Structural design: Wall stem and base reinforcement

Foundation Drawings

Automatic Drawing Generation

1. Drawings > Foundation Drawings
2. CYPECAD generates:
   • Foundation plan: Footing/pile cap layout with dimensions
   • Footing details: Section views with reinforcement
   • Pile cap details: Plan and section with bar layout
   • Mat reinforcement plan: Top and bottom reinforcement layout
   • Retaining wall details: Section with stem and base reinforcement
3. Export to DXF/DWG for CAD integration

Common Foundation Issues

Bearing Capacity Exceeded

Cause: Footing too small or soil capacity overestimated. Fix: Increase footing dimensions, verify soil report, use piles, or improve soil.

Excessive Settlement

Cause: Soft soil, heavy loads, or large footing area. Fix: Increase footing depth, use piles to stiffer strata, or use mat foundation.

Pile Capacity Insufficient

Cause: Pile too short, too small, or soil friction overestimated. Fix: Increase pile length, increase diameter, add more piles, or use end-bearing piles.

Differential Settlement

Cause: Variable soil or uneven loading. Fix: Use mat foundation, adjust footing sizes to equalize pressure, or use piles to uniform strata.

Wrapping Up

Foundation design in CYPECAD is efficient because it's integrated — no exporting reactions to a separate tool. The Eurocode 7 design approaches (DA1, DA2, DA3) are all supported, and the software handles the partial factor combinations for you. My advice: get the soil parameters right from the geotechnical report, and don't forget to check differential settlement — it's the thing that causes the most problems in practice.