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Erik Soderberg, President and MichaelJordan, Chief Structural Engineer, LiftechConsultants Inc., provide an overview ofsome effects of ULCVs on existing STScranes and wharf infrastructure.

ltra large container vessels (ULCVs) with capacities around 20,000 TEU have arrived and more are coming.

ULCVs are wider and slightly longer than theprevious generation of 12,000 TEU to 15,000TEU vessels and have significantly higher container stacks on deck: ten instead ofseven containers high. (See Figures 1 and 2).

A lift height above the rail of about 50m isrequired for servicing ULCVs. The lift heightwill vary depending on the vessel, crane railand water elevations, and desired clearancesbetween containers on the vessel and thelifted container.The outreach is about 60mbeyond the fender face to the centre of thetrolley.The outreach will vary, depending onthe vessel and desired trolley overrun distance. For a more detailed understandingof the factors involved in deciding outreachand lift height, see: http://www.liftech.net/wp-content/uploads/2014/09/OutreachLiftHeightGuidelines.pdf. Relative to most existing STScranes commissioned in the last ten years,ULCV’s require additional lift height of 5m ormore, necessitating crane raise modifications(See Figure 3). Most cranes built in the lastten years have adequate outreach, but somemay require small extensions or localisedmodifications to trolley or trolley rail systemto extend travel. Costs of modifying existing

cranes vary significantly depending on thescope of modifications, location, and locallabour.The scope of modifications can varysignificantly and include mechanical, electrical,and other modifications, such as to ropedrums, trolley cable reel, machinery houseservice cranes, cabling, lighting, access stairsand walkways, new wire rope, etc. Estimatedcosts per crane vary from about USD1.5million for a short raise with low labourcost, to about USD5 million for a tall raisewith a boom extension and high labour costand improvements to the crane structure’sseismic performance.

Today’s ULCV lengths are not much longerthan those of the previous generation,however some existing wharves will requireadditional length - a costly option. A lesscostly option, if practical, is to add a mooringdolphin beyond the wharf so the vessel canbe located closer to the end of the wharf(see Figure 4). Another option to consider isproviding mooring systems that do notrequire mooring lines. These systems willdecrease the required space between vesselsand allow for the ends of vessels to extendbeyond the end of the wharf.The constructioncost of a new mooring dolphin with accessstructure, lighting, and capstan is approximatelyUSD 500,000 to USD 750,000, depending onlocation,water depth, soil conditions, construction,and required operations coordination. Some

additional crane travel distance can often beobtained at little cost by installing more compact crane stops and relocating the stops closer to the end of the wharf.

Required fender energy capacity is primarilydue to vessel displacement and approachvelocity normal to the wharf. ULCV displacements are significantly larger thanearlier vessels; however, the approach velocityis less.Typically, fenders with more energycapacity than existing fender systems arerequired to meet industry guidelines.

However, it is often reasonable to continueusing existing fender systems with acceptable risk of damage to the fender system, wharf,and vessel structure.The cost of replacing current fender systems is usually not justifiedby the risk of improbable future damage.Berthing data for the larger vessels indicatethat the berthing velocity and angles are significantly less than recommended in designguidelines.Additionally, contacting only a singlefender is significantly less probable than forsmaller vessels. If replacing fender systems, ifpractical, replace with deeper fenders to limitthe fender reaction on the wharf and vessel.If larger fender reactions result, confirm thatthe wharf structure is adequate.Typically, onlylocal wharf strengthening is required at moderate cost.Wharf strengthening costs willvary significantly depending on the capacityof the existing structure - from a fraction of

The effect of ultra largecontainer vessels on cranes and infrastructure

This technical paperwas presented by ErikSoderberg at thePort & TerminalTechnology Conferenceearlier this year inNorfolk, Virginia,United States.

STS crane requirements

Figure 1: CMA CGM Benjamin Franklin at Port of Long Beach

U

Wharf berthing space

Figure 2: Vessel size progression

Berthing fenders

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the fender system cost to more than thefender system cost. If strengthening the existingstructure for ULCVs is impractical, for instanceif a stronger crane girder is also needed onealternative is replacing or extending thewaterside of the wharf with new structure.Again, the risk of significant single fenderloading is usually small.A study should bemade of the berthing conditions and expectedberthing velocities and angles before decidingon upgrades.

The wind area of today’s loaded ULCV is significantly greater than the design ship usedfor most existing mooring systems. Forces ofup to 250 t per bollard can occur due tocommon design wind speeds and mooring

line arrangements (t = metric tonne).Additionally, ship captains may have concernsabout relying on older, lower capacity bollards,and they may not be willing to moor theirship at the berth. Consider site-specific wind speeds and directions based on historicaldata when determining required bollardcapacities, as these may justify significantlylower loads. It is also worth considering realistic mooring line arrangements as thesemay differ significantly from optimal arrangements (See Figure 5). When specifyingdouble bitt bollards, be aware that unlessspecified otherwise, each bitt will only havehalf the capacity of the entire bollard.Specifying larger bitt capacities results in littleadditional cost. New bollards with increasedcapacity are relatively inexpensive.

Strengthening the wharf local to the bollard,if needed, is more expensive, with costs varying significantly depending on the existingstructure. Strengthening by drilling holes intothe wharf structure and installing groutedhigh strength reinforcing is often practical.

STS cranes suitable for ULCVs typically havelarger wheel loads than smaller cranes.Wheel loads may exceed the design or ratedcapacity of existing wharf girders. Options toaddress excessive crane girder loads include:

☛ Optimising the crane design to reducecrane reactions and better suit the distributionbetween available landside and watersidegirder capacities

☛ Analysing or load testing the existingstructure and foundation to justify increasingthe rated capacity

☛ Strengthening the existing girders

☛ Replacing girder systems with new,stronger systems

☛ Consider increasing the crane rail gage fornew cranes, which reduces crane loads andpermits additional truck lanes for operationsas well

Optimising a new crane design or a cranemodification design will reduce crane girderloads some, but there are limits.Typically, thisoption is only worthwhile if the existingcrane wheel loads are not significantly morethan the girder’s rated capacities.Analysis orload testing of the existing girder structureto justify additional capacity is usually worthwhile since it is the least costly ofthese options and often yields significantresults. Girders often have more capacitythan stated for the original design loads.See Figure 6 for an example of a strut-and-tiegirder analysis, which can often justify additional girder shear capacity. For moreinformation on this approach, see:http://www.liftech.net/wp-content/uploads/2015/01/PT60_Article_YourWharfMayBeStrongerThanYouThink.pdf.A feasibility study by a structural engineer isa good first step to decide if analysis or testing will probably be a fruitful approach.Feasibility study costs will vary, but are typically less than USD 30,000. If feasible,studies to justify additional capacity, typicallyinvolving one or more types of analyses, are

Mooring bollards

Figure 3: Crane being raised with a jacking frame

Figure 4: Mooring dolphin at IMTT Port of Richmond

STS crane girders

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often USD 50,000 to USD 100,000 and areusually successful. Strengthening or replacinga wharf girder will often require new piling,and costs can be significant. If strengtheningor replacing a wharf girder is required, and ifnew cranes are to be procured, then buildinga new landside girder and using larger gagecranes can limit girder construction costs,reduce crane wheel loads, and increase thetruck lane space between the crane legs.

Today’s ULCVs up to 20,000 TEU will typicallyaffect existing STS cranes and may affectexisting infrastructure. Existing STS craneswill probably require increases to lift heightand infrequently require increased outreach.Increased vessel lengths may require changes

to berthing arrangements, extending the wharf or only the crane girders, modificationsto crane stop locations and structure, addingmooring dolphins, using mooring systemswithout mooring lines, or combinations ofthese. Fender berthing velocities and anglesare typically much less than recommended indesign guidelines. Consider recent data whendetermining berthing energies. If a systemwith increased energy is required, acceptingadditional risk with existing systems is oftenreasonable. Increased mooring forces mayrequire larger, higher-capacity bollards.Installing higher capacity bollards requires relatively little cost unless the wharf structureneeds strengthening, in which case costs canincrease significantly. Consult ship captainsand local pilots to ensure they will be

comfortable with the planned mooring system. Consider site-specific wind speedsand directions, and less than optimal mooringline arrangements when determining bollardloads. Be careful when specifying bollardswith multiple bitts that the bitt has thedesired capacity. Increased crane wheel loadsmay exceed existing rated girder capacities.Engineering analyses or load testing canoften justify additional capacity. Strengtheningexisting or building new girders will be costly. If new structure and cranes arerequired, building a new landside or waterside girder can limit crane wheel loadsand girder construction costs. Finally,consider performing a study to determineyour terminal requirements and the mostcost effective approaches.

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Summary

Figure 6: Strut-and-tie girder analysis

Figure 5: Suboptimal mooring line arrangements - all lines to one bollard

Figure 5: Suboptimal mooring line arrangements - all lines on one bitt

** Costs presented in this paper and article are estimates of construction costs based on recent projects

and do not include other costs. **

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