Section 3 Design loads and combinations

3.1.1 When loaded, all bridges and ramps are to be considered for the worst possible in-service combination of loads, inclinations, and support arrangements arising from the following forces:

1. Self-weight.

2. Applied vehicle loadings.

3. Dynamic forces due to vehicle movement including braking, skidding and cornering effects.

4. Static and dynamic forces due to inclination, twist and movement of the pontoon or other buoyant support.

5. Operational environmental loads (e.g. wind, wave and current), including those acting on a berthed ship which can be transferred to the linkspan structure.

6. Forces transferred to the linkspan due to motions of the berthed ship.

3.1.2 When unloaded and out-of-service all bridges and ramps are to be considered for the worst possible combination of loads, angles and support arrangements arising from the following forces:

1. Self-weight.

2. Static and dynamic forces due to inclination and movement of the pontoon or other buoyant support.

3. Extreme environmental loads (e.g. wind, wave and current) appropriate to the location.

3.1.3 For raising or slewing manoeuvres the bridges and ramps are to be considered with respect to the following forces:

1. Self-weight.

2. Dynamic forces due to hoisting/slewing.

3. Static and dynamic forces due to inclination and movement of the pontoon or other buoyant support.

4. Environmental loads.

5. Loads due to ship motions transmitted through any ship to linkspan connection, as appropriate.

3.2.1 The self-weight load, L _w, is to be taken as the weight of the ramp or bridge for all design conditions, except when it is being mechanically raised or lowered, in which case it is to be multiplied by a dynamic factor of 1,1.

3.2.2 The applied load, L _c, is the static load on the ramp or bridge due to vehicles and is to be multiplied by a factor of 1,1 to take account of vehicle movement.

3.2.3 Environmental loads, L _e, need not be multiplied by any factor.

3.2.4 HA and HB vehicle loading already contain an allowance for impact and need not be further factored.

3.3.1 Ramps and bridges are to be designed to operate safely and efficiently when accommodating any inclination or dynamic movement of the pontoon or other buoyant structure from which they derive their support.

3.4.1 Ramps and bridges are to be considered for the design loadings resulting from the following load cases:

1. Case 1: Loaded operational in-service condition.

2. Case 2: Unloaded, out of service, survival condition.

3. Case 3: Manoeuvring condition when unloaded (if appropriate), i.e. when being mechanically hoisted or lowered.

Case 1. The bridge or ramp is to be considered with respect to self weight plus the applied load multiplied by 1,1, together with any horizontal, vertical and rotational forces resulting from pontoon movement and slope of the bridge/ramp, together with any loads imposed by the ship and any environmental loading. This is represented by the following expression:

where the above loads are added vectorially, and where:

Case 2. The bridge or ramp is to be considered with respect to the direct forces resulting from the extreme environmental conditions (generally 1 in 50 year return case) and from the corresponding forces acting on the self weight resulting from the accelerations due to pontoon motions and static inclination resulting from the same severe environmental conditions.

Case 3. The bridge or ramp is to be considered with respect to its self weight multiplied by 1,1 together with any additional vertical, horizontal and rotational forces resulting from pontoon motions, see Pt 3, Ch 5, 3.3 Forces due to motion of the pontoon or other buoyant support 3.3.1.

For ramps which are unloaded during manoeuvring this is represented by the following expression:

where the above loads are added vectorially.