Code of Practice for Planning and Design of Ports and Harbours, Part III: Loading

IS 4651 Part 3 (1974) - Scope: Key Dimensions & Specifications

The code provides standard dimensional data for various ship types based on Dead Weight Tonnage (DWT) or Gross Registered Tonnage (GRT). These serve as reference for structural design and safety.

Key Tables Summary:

Example: Bulk Carrier Dimensions by DWT

IS 4651 Part 3: Ship Characteristics Summary

1. Ship Dimensions (Clause 3.2 & Appendix A)

• Bulk Carriers (Dead Weight Tonnage - DWT)

• Mixed Cargo Freighters

• Passenger Ships

• Fishing Vessels

| GRT (Tons) | Displacement (Tons) | Overall Length (m) | Width (m) | Draught (m) | |------------|---------------------|--------------------|-----------|

IS 4651 Part 3 — Dead and Live Loads: Key Points

1. Dead Loads (Clause 4.1)

• Include all permanent loads on dock and harbour structures.
• Examples: self-weight of structure, fixed equipment, paving, and utilities.
• Must be fully assessed and incorporated in design.

2. Vertical Live Loads (Clause 5.1)

• Include loads due to temporary forces like cargo, vehicles, and personnel.
• Live loads vary with berth use and ship size.

3. Load Combinations (Clause 6.1)

• Design loads = Dead Load + Vertical Live Load + one of:
  • Berthing Load
  • Line Pull (refer Table 4 for limits)
  • Earthquake Load
  • Wave Pressure
• Use worst-case combination for safety.

Ship Dimensions for Load Assessment (Appendix A)

Typical Load Combination Formula

[ \text{Design Load} = D + L + \max(B, P, E, W) ]

Where:

• (D) = Dead Load
• (L) = Vertical Live Load
• (B) = Berthing Load
• (P) = Line Pull
• (E) = Earthquake Load
• (W) = Wave Pressure

Summary

• Assess all dead loads carefully.
• Use vertical live loads per berth activity.
• Combine loads conservatively using Clause 6.1.
• Refer to ship dimension tables for berthing load and line

Berthing Energy & Impact Loads (IS 4651 Part 3)

1. Berthing Energy Formula (Clause 5.2.1):

[ E = \frac{W_0 \times V^2 \times C_m \times C_e \times C_s}{2g} ]

• (E) = Berthing energy (Joules)
• (W_0) = Displacement or virtual weight of vessel (N)
• (V) = Berthing velocity normal to berth (m/s)
• (C_m) = Mass coefficient (see below)
• (C_e) = Eccentricity coefficient
• (C_s) = Softness coefficient
• (g) = Acceleration due to gravity (9.81 m/s²)

2. Mass Coefficient (C_m) (Clause 5.2.1.2):

For vessels with length >> beam or draft (usually >20,000 DWT):

[ C_m = 1 + \frac{\pi}{4} \times \frac{D^2 \times L_u}{W_D} ]

• (D) = Draft (m)
• (L_u) = Length of vessel (m)
• (W_D) = Displacement weight (N)

3. Berthing Velocity (Clause 5.2.1.1):

Mooring Loads & Wind Forces (IS 4651 Part 3 - 1974)

Mooring Loads

• Formula for Wind Force on Ship (Clause 5.3.2):
  [ F = C \times A \times P ] where:

  • (F) = Wind force (tonnes)
  • (C) = Force coefficient (depends on shape and exposure)
  • (A) = Exposed area on broad side (m²)
  • (P) = Wind pressure (kN/m²)

• Bollard Pulls (Table 4, Clause 5.3.4):

• Notes:
  • Increase line pull by 25% for ships ≥ 50,000 t at quays with strong currents.
  • Main bollards at river structures: 250 t for ships ≤ 100,000 t, double values for larger ships.

Wind Forces

• Wind loads are considered lateral loads acting on the ship, influencing mooring line tension.

Summary Diagram: Mooring Load Components

flowchart LR
    WindForce[Wind Force (F = C*A*P)] --> MooringLines[Mooring Lines Tension]
    MooringLines --> BollardPull[Bollard Pull (from Table 4)]
    CurrentForce[Current Force] --> MooringLines
    MooringLines --> ShipPosition[Ship Held Against Forces]

Use Table 4 values as baseline for bollard design considering ship displacement and environmental factors.

Wave Forces on Structures (IS 4651 Part 3: Clause 5.7)

Key Formulas

1. Dynamic Pressure at Still Water Level
   [ P = 101 - 26 (D + d) \frac{L_D}{D} H_w d ]

• (P): Dynamic pressure (kg/m²)
• (H_w): Wave height at breaking (m)
• (w): Unit weight of water (kg/m³)
• (d): Water depth at structure (m)
• (D): Deeper water depth (m)
• (L_D): Deeper water wavelength (m)

2. Hydrostatic Pressure

• At still water level and depth (d), hydrostatic pressure (P_h = w \times d)

3. Wave Forces on Vertical Cylindrical Piles (Clause 5.7.5.1)

Total force (F) = Drag force + Inertia force

[ F_{DM} = C_D \times \rho \times D \times H \times K_{DM} ] [ F_{IM} = C_M \times \rho \times D^2 \times H \times K_{IM} ]

• (F_{DM}): Drag force (kg)
• (F_{IM}): Inertia force (kg)
• (C_D): Drag coefficient (suggested 0.53)
• (C_M): Inertia coefficient (from graphs or literature)
• (D): Diameter of pile (m)
• (H): Wave height (m)
• (K_{DM}, K_{IM}): Correction factors (from graphs/publications)

Design Recommendations

• Use (C_D = 0.53) for drag coefficient.
• Calculate maximum crest elevation, wavelength, and overturning moments using accepted graphs/publications.
• Combine drag and inertia forces for total wave force on piles.

Diagram: Components of Wave Force on a Pile

graph LR
A[Wave Force on Pile] --> B[Drag Force (F_DM)]
A --> C[Inertia Force (F_IM)]
B --> D[Depends on velocity]
C --> E[Depends on acceleration]

Summary: Use

Earthquake Forces as per IS 4651 Part 3 (1974)

• Horizontal seismic force ( F_e ) is taken as a fraction of gravity acceleration times the weight at the center of gravity:

  [ F_e = k \times W ]

  where:

  • ( k ) = seismic coefficient (fraction depending on seismic intensity per IS 1893-1970)
  • ( W ) = total weight = Dead Load + 0.5 × Live Load

• Seismic coefficient ( k ) is selected based on the seismic zone from IS 1893-1970 (Zones II to V).

• Weight ( W ) includes:

  • Dead Load (structure self-weight)
  • Plus half the Live Load (occupancy or imposed loads)

• Note: No exact formula for forces due to broken waves; approximate methods are in Appendix D.

Summary Table for Earthquake Force Calculation

Additional Notes:

• Use IS 1893 for seismic zone classification and ( k ) values.
• Combine earthquake forces with other loads as per Clause 6 (Combined Loads).
• For wave and current forces, refer to Clauses 5.6 and 5.7 respectively.

flowchart LR
    A[Load Calculation] --> B[Dead Load + 0.5 Live Load = W]
    B --> C[Select seismic coefficient k from IS 1893]
    C --> D[Calculate Earthquake Force: F_e = k × W]
    D --> E[Apply horizontal force at structure's C.G.]

This approach ensures earthquake resistant design consistent with IS 4651 Part 3 and IS 1893.

Forces Due to Current (IS 4651 Part 3 - Clause 5.6)

• Pressure due to current acts on the vessel area below waterline when fully loaded.
• Approximate formula for pressure per square meter:

[ P = \frac{w \cdot v^2}{2g} ]

where:

• ( P ) = pressure (tonnes/m²)

• ( w ) = unit weight of water (tonnes/m³, approx. 1.0 for fresh water)

• ( v ) = velocity of current (m/s)

• ( g ) = acceleration due to gravity (9.81 m/s²)

• The force on the vessel is:

[ F = P \times A ]

where ( A ) = submerged area exposed to current (m²).

• Ships are generally berthed parallel to current; for strong currents or non-parallel berths, use recognized hydrodynamic methods for force calculation.

Summary Table for Current Force Calculation

flowchart LR
    V[Current Velocity (v)]
    W[Unit Weight of Water (w)]
    G[Gravity (g)]
    V -->|Calculate| P[Pressure P = w v² / 2g]
    P -->|Multiply by Area A| F[Force F = P × A]

This formula provides a quick estimate of current forces on marine structures per IS 4651 Part 3. For complex cases, detailed hydrodynamic analysis is recommended.

Key Specifications & Formulas for Design of Fendering Systems (IS 4651 Part 3):

1. Fender Capacity (Clause 2.30)

• At jetty ends:
  • 2.30 tonne-metre per 1000 DWT (yield stress basis)
  • 1.52 tonne-metre per 1000 DWT (working stress basis)
• Fender reaction force:
  • Max 500 tonnes (for 2.30 tonne-metre energy)
  • Approx. 300 tonnes (for 1.52 tonne-metre energy)
• Thrust distribution: Over hull length ≥ spacing between transverse frames.

2. Berthing Energy (Clause 5.2.1)

The kinetic energy ( E ) absorbed by the fender system is:

[ E = W \times V^2 \times C_b \times C_c \times C_s / (2g) ]

Where:

• ( W ) = displacement of vessel (tonnes)
• ( V ) = berthing velocity (m/s)
• ( C_b ) = softness coefficient (0.9 to 0.95)
• ( C_c ), ( C_s ) = correction factors (usually provided by manufacturer)
• ( g ) = acceleration due to gravity (9.81 m/s²)

3. Fender Reaction & Deflection (Clauses 5.2.1.4 & 5.2.2.1)

• Use deflection-reaction diagrams from fender manufacturers to find reaction force and energy absorption.
• Fender system = fenders + berth structure; reaction force is common to both.

Summary Table

flowchart LR
    Vessel[Kinetic Energy of Vessel]
    Vessel -->|Berthing velocity V| EnergyCalc[Calculate Berthing Energy E]
    EnergyCalc --> FenderSystem[Fender System (Fenders

Load Distribution on Piers and Jetties (IS 4651 Part 3 Highlights)

1. Equivalent Surcharge Load on Retaining Structures (Clause 5.1.7)

• When live loads act on fill behind structures (e.g., sheet pile wharves), design for an equivalent uniform surcharge = 0.5 × value in Table 1, Column 3.
• For higher expected loads, use actual surcharge values.

2. Mooring Loads & Bollard Pulls (Clause 5.3.4, Table 4)

• Notes:
  • Increase by 25% at quays with strong currents for ships ≥ 50,000 T.
  • Main bollards at river berths: 250 T for ships ≤ 100,000 T; double for larger ships.

3. Berthing Load & Eccentricity Coefficient (Clause 5.2.1.3)

• Eccentricity coefficient, ( C_e ):

[ C_e = 1 + \frac{1}{r} \sin^3 \theta ]

Where:

• ( r = \frac{l}{R} ), ratio of distance from CG to contact point ( l ) over radius of gyration ( R ).
• ( \theta ) = approach angle (default 10°, 20° for small vessels).
• ( R \approx \frac{L}{4} ) (rotational radius).
• ( l \approx \frac{L}{4} ) (quarter point contact).

Wave Pressure Calculations (IS 4651 Part 3)

1. Dynamic Pressure (Breaking Waves)

[ P = 101 - 26 (D + d) \frac{L_D}{D} H_w w d ]

• P = Dynamic pressure (kg/m²)
• H_w = Height of breaking wave (m)
• w = Unit weight of water (kg/m³)
• d = Water depth at structure (m)
• D = Deeper water depth (m)
• L_D = Deeper water length (m)

Note: (L_D) and (D) are computed by accepted wave theory methods.

2. Hydrostatic Pressure

• At Still Water Level (SWL):
  [ P = w \times d ]
• At depth (d):
  [ P = w \times d ]

3. Force and Moment on Low Height Walls (Clause 2.3)

• For wall height < wave height, forces are calculated by assuming wall higher than wave crest.
• Use force polygon area AFBSC (Fig. 5) for resultant force and moment.

4. Minikin's Method (Appendix C)

• Used for breaking wave force calculation.
• Wave pressure diagram given in Fig. 6.
• Non-breaking wave forces are hydrostatic; Sainflou method applies (Appendix B).

Summary Table: Pressure Components

flowchart TD
    A[Wave Height \(H_w\)] --> B[Dynamic Pressure \(P\)]
    C[Water Depth \(d\), Deeper Depth \(D\)] --> B
    B --> D[Total Wave Pressure]
    D --> E[Force on Structure]
    E --> F[Moment Calculation]

References: IS 4651

IS 4651 Part 3 — Appendix D: Broken Waves

Key Points from Appendix D (Clause 5.7.4.1)

• Broken waves occur when waves break before hitting the structure (e.g., seawalls seaward of shoreline).
• No exact formula exists for forces due to broken waves; approximate methods based on assumptions are provided.
• Minikin’s method (detailed in Appendix C) is used for actual breaking wave pressures.

Approximate Method Highlights (Appendix D)

• Wave pressure on seawalls seaward of shoreline is reduced due to wave breaking.
• Forces are estimated by reducing the wave height and pressure coefficients compared to unbroken waves.
• Typical assumptions:
  • Wave height after breaking, ( H_b ), is less than the original wave height ( H ).
  • Pressure coefficients are adjusted to reflect energy dissipation.

Minikin’s Method (Appendix C Reference)

• Calculates wave pressure ( P ) as:

[ P = \rho g H_b \cdot C_p ]

Where:

• ( \rho ) = density of water (≈ 1000 kg/m³)
• ( g ) = acceleration due to gravity (9.81 m/s²)
• ( H_b ) = wave height at breaking
• ( C_p ) = pressure coefficient depending on structure geometry and wave conditions

Summary Table: Wave Pressure Estimation for Broken Waves

flowchart LR
    A[Incoming Wave Height \(H\)] --> B[Wave Breaks Seaward]
    B --> C[Reduced Wave Height \(H_b\)]
    C --> D[Apply Minikin's Method]
    D --> E[Calculate Pressure \(P = \rho g H_b C_p\)]
    E --> F[Estimate Forces on Structure]

Note: For detailed design,