Port Pavement Design Guide

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DISCLAIMER

This Design Guide was prepared for the sole purpose of providing general information on the selected subject matters. However, this Design Guide is only intended to provide general guidance related to container terminals and intermodal rail yard operational areas, and this information, is not intended for use for any specific project. The use of this Guide for actual projects should only be done in conjunction with the services of a qualified engineer or consultant to assure that specific project circums tances are taken into consideration. While all reasonable care has been taken in the preparation of this Design Guide, Moffatt & Nichol does not guarantee the correctness of the data or information contained within, and disclaims any responsibility or liability in connection with its use.

Photographs and drawings of equipment used in this publication are for illustration only and do not imply preferential endorsement of any particular manufacturer by Moffatt & Nichol and their contributors.

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CONTAINER TERMINAL AND INTERMODAL RAIL YARD

OPERATIONAL AREA CONSIDERATION FOR PAVEMENT DESIGN

Executive Summary

Traffic disruptions and the cost associated with rehabilitating and maintaining distressed or failed

pavements in container terminals signifies the importance of optimizing pavement design

procedures within these facilities. This pavement design guide aims at providing general

concepts and instructions on the pavement design of the heavily loaded conditions encountered

in container terminals and intermodal rail facilities. The guide stresses the importance of the

coordination between the pavement designer and terminal planner; this is because the design

guidelines are greatly dependent on the loading conditions associated with the different terminal

operation schemes.

The guide starts by giving an overview of typical container terminal areas focusing on the

different operational loading conditions and their significance on the pavement design. The

different container terminal operational areas are: the wharf, the container storage yard, the

intermodal rail yard, the truck gate facility, and the buildings and automobile parking. With the

modernization of container terminals, several options became available to accomplish the

required tasks in each of these areas. The loading conditions in each sector vary with the type of

equipments used and the nature of commodities handled.

Section 2 of the guide describes the equipment configuration, motion, and usage in the terminal.

It classifies the terminal operational options according to the different equipment used within

each area. For the container yard operations, three options are presented: the use of rubber tire

gantry (RTG’s), front-end loaders (FEL’s), or straddle carriers. The usage conditions along with

the corresponding truck motion are discussed for each of these options. Similar analyses

portraying the operation scenarios for the RTG’s and FEL’s in the intermodal yard are presented.

Section 2 also describes the machinery loads involved in operating wheeled container yards and

gate areas. Having configured the terminal usage and operation schemes, the next step is

calculating the corresponding pavement loads.

Section 3 provides a guide for calculating the design loads and design load repetitions in a

container terminal. The pavement is subject to both dynamic loading from container handling

equipment and static loading from corner castings on containers and either dolly wheels or sand

shoes on the chassis. Different equipment types, container load distributions, tire loads, axle and

tire configurations, and repetition of loads are considered for different areas. Typical

specifications for different makers are provided for each equipment type. An analysis procedure

for determining the container weight distribution is presented. Depending on the container

terminal operational area and equipment used, typical load repetition calculations are derived.

Two approaches for computing load repetitions are discussed; the first requires converting the

various loads and repetitions to equivalent single axle loads (ESAL), and the second

characterizes the loads directly by the number of axles, configuration, and weight. Equipment

weight distribution and wheel loads are stated as seen in the British Port Association 1982 Heavy

Duty Pavement Manual. Accounting for the contact stress and wheel loads, damages to the

pavement are quantified using PAWL’s (Port Area Wheel Load). Section 3 concludes by

presenting a comprehensive example to demonstrate the analysis schemes discussed in the

chapter.

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Section 4 of the manual details the process of site investigation. Proper site investigation is

essential for enabling an economic pavement design and safety and predictability during the

construction operations. Typically, site investigation is carried out by geotechnical consultants,

and it aims at determining the properties of the soils within the influence zones below the

underside of the pavement. Different options and approaches for improving the ground soil

conditions, in order to reduce the consequences of the problems experienced in port facilities, are

discussed in this section.

Section 5 discusses the influence of the subgrade on the pavement type, section and performance

for a particular type of operation. Failure to characterize the subgrade properties can result in

high maintenance costs or premature pavement failure. This section sets out the material

characteristics that affect the pavement performance, and the test methods that can be used to

determine design values. It details the classification of soils as either fine or coarse grained,

granular or cohesive soils. The section also describes the soil mass volume relationships,

different classifications, and moisture density relationships. In-situ and lab testing procedures for

determining these properties are also presented in this section.

Building on the acquired knowledge about the terminal operation and subgrade properties, it is

up to the designer to select a suitable pavement design. Three pavement designs are presented in

this guide: hot mixed asphalt (HMA), Portland cement concrete pavement (PCCP) and roller

compacted concrete pavement (RCCP). The design selection is based on the designer’s vision as

to how the pavement will perform. Generally, the site environmental conditions, the traffic loads

and speed, the pavement structure, and the design life/cost play a major role in determining the

performance of the pavement. Not all pavement options are suitable for all operational areas.

HMA pavement is not usually considered in areas subject to heavy wheel loads. While PCCP

(jointed or continuously reinforced) are considered applicable for most operational areas, RCCP

is best suited for large contiguous areas subject to heavy loading conditions.

Section 6 stages the details of the design, construction, and quality assurance of HMA. The HMA

design yields a flexible pavement that is both rut resistant and durable. Three major design

procedures for HMA mix design are discussed in this section: Marshall, Hveem, and Superpave.

All three procedures share common steps:

1) materials selection;

2) selection of the design aggregate structure;

3) determination of the optimal asphalt content;

4) evaluation of moisture sensitivity.

The primary difference between the three approaches is the laboratory compaction method and

the effort used in the determination of the optimal asphalt content.

The layered elastic analysis theory, Section 7, is used for the analysis of the thickness of the

HMA pavement. It is based on the fact that the stresses and strains, which develop in the

pavement and subgrade due to a wheel load application on a flexible pavement, are distributed

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according to the elastic properties of the various layers. A pavement design software, Kenlayer,

can be used to analyze the pavement sections and develop strains at critical points in the

pavement. It analyzes elastic multilayer systems under circular loads and superimposes values

for multiple loads. It also has some iterative capabilities for the analysis of nonlinear viscoelastic

layers. The section concludes by presenting a design example for flexible pavements using the

methods discussed in section 6.

Section 8 provides the design guidelines for PCCP, a system of subgrade soil, base course

material, and the surface course of Portland cement concrete. The concrete used for PCCP must

meet the combined requirements of durability under repeated heavy loads, dimensional stability

to minimize shrinkage and curling, and non-reactivity of its constituent material. Joints are

typically used in non-reinforced concrete pavements to limit warping and curling stresses which

are due to temperature and moisture gradients through the slab, prevent control cracking due to

volume changes, prevent damage to immovable structures, and facilitate construction. The

thickness of the designed pavement is based upon provid ing a sufficient structural capacity. The

key structural design factors include:

1) slab thickness;

2) slab concrete flexural strength;

3) foundation support (from base and subgrade);

4) wheel loads and repetition loads.

The PCCP thickness analysis, warping stress analysis, temperature reinforcement analysis, and

dowel bar analysis are demonstrated in two design examples at the end of section 8.

Section 9 provides the guidelines for the design of roller compacted concrete pavements. RCC is

a zero-slump concrete consisting of dense graded aggregates, cement and water. Because of its

low water content, it is usually placed using asphalt pavers and densified by compacting with

vibrating rollers. The design philosophy of RCC pavements is based on limiting the stresses in

the pavement to a level such that it can withstand repeated loadings of this stress magnitude

without failing in fatigue. The critical stress is the maximum tensile stress at the bottom of the

concrete slab. Several methodologies for calculating this stress are well developed and

documented in the literature. Knowing the expected traffic expressed in terms of wheel loads,

load configuration, and number of load applications expected over the design period, the

designer varies the following parameters to optimize the flexural strength of the RCC pavement:

1) modulus of subgrade reaction;

2) flexural strength of the concrete mix;

3) thickness of concrete slab.

Design examples are provided at the end of the section to demonstrate the design methodology

discussed in this section.

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Section 10 of this guide introduces the Pavement Management System (PMS). PMS is a decision

making tool that assists the engineer, budget director, and management to make cost

effective-decisions regarding maintenance and rehabilitation for a pavement network. Section 11 present

some of the PMS software packages currently used for pavement management.

The following flow chart is designed to enable the user to smoothly navigate through this design

manual.

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Determine Container

Terminal Operation:

Terminal Planner

(Section 2)

Calculate Wheel Loads

and Load Repetitions

(Section 3)

Site Investigation &

Subgrade Properties:

Geotechnical Engineer

(Sections 4 & 5)

Pavement Design, Thickness Analysis

Hot Mixed

Asphalt, HMA

(Section 6)

Layered Elastic

Analysis

(Section 7)

Portland cement

Concrete, PCC

(Section 8)

Roller Compact

Concrete

(Section 9)

Pavement Management

(Sections 10 & 11)

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1. Introduction... 1-1 1.1 Description of the Pavement Design Guide ... 1-1 1.2 Container Terminal Operation Area... 1-1 1.2.1 Wharf Area...1-3 1.2.2 Container Storage Yard...1-3 1.2.3 Intermodal Rail Yard ...1-4 1.2.4 Truck Gate Facility ...1-5 1.2.5 Buildings and Automobile Parking ...1-5

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1. Introduction

1.1 Description of the Pavement Design Guide

Pavement is one of the most important facility in container terminals and occupies a significant amount of the costs for container terminal constructions and maintenance. This pavement design guide, prepared for the Port of Los Angeles (POLA), provides general concepts and instructions on pavement design but tailored for the intensive loading conditions encountered in container terminals and intermodal rail facilities. Detailed design examples are also included to illustrate those concepts. Targeted at a United States audience, this guide is intended to provide a comprehensive reference of alternative design procedures and material options available to the engineers undertaking the design of pavement for such a facility, both inside and outside the pavement community. After coving these pavement concepts, you should, in general, be able to:

− Describe the concept of container terminal and intermodal rail yard operations;

− Describe the pavement concept covered;

− Describe the typical equipment, methods and procedures used for pavement design;

− Implement typical pavement design analysis for container terminals;

− Develop a number of appropriate solutions for economic analysis;

− Apply these concepts and methods into practice;

In this pavement design guide, the following topics will be covered:

− State of the art container terminal and intermodal rail pavement design;

− Container terminal and intermodal rail yard operational area;

− Container terminal operational options;

− Typical container handling equipment and the load repetition analysis;

− Site investigation to determine characteristics of subgrade materials;

− Subgrade test and analysis to determine design values;

− Flexible pavement design;

− Layered elastic analysis and the Asphalt design example;

− Rigid Pavement Design and the Portland Cement Concrete (PCC) pavement analysis examples;

− Roller Compacted Concrete (RCC) pavement design;

− Pavement management and Pavement Management System (PMS) software;

The rest of this chapter describes typical container terminal operational areas and the importance of identifying these areas in the pavement design.

1.2 Container Terminal Operation Area

Pavement designer has to consider dividing the container yard area into various operational areas based on the anticipated variety of type of traffic and wheel loads. This will allow optimizing the pavement cost by providing appropriate pavement thickness for each operational area. Identifying the limits of each operational area for current and future operation would require the pavement designer to work closely with the container terminal planner.

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Container terminal complex includes wharf, container storage yard, intermodal rail yard, truck gate facility, container handling equipment parking areas, buildings, and automobile parking areas. These operational areas are identified on a typical container terminal layout in Figure 1-1.

Figure 1-1 - Typical Container Terminal Layout

Containe r facilities buildings include administration, maintenance buildings, and various service facilities. Intermodal rail facility includes area for working tracks (loading and unloading of containers), area for storage tracks (storing loaded or empty cars), container storage area, and some times a separate truck gate facility. The intermodal facility operational areas are shown on Figure 1-2.

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Pavement designers need to work closely with the container terminal and intermodal facility planners to understand the startup operationa l areas and future possible changes within the operational areas. Since the operational changes can be made by just changing yard striping, the pavement designer needs to understand the possible changes and provide an appropriate pavement section that would allow changes in mode of operation in the future.

1.2.1 Wharf Area

Wharf is where the transfer of containers from ship to shore and from shore to ship occurs. The most common method employed in moving containers from ship to shore and shore to ship is using a container gantry crane that handles one or two 20-foot containers or a single 40 foot container. However, some container terminals have started to deploy container cranes that can lift four 20 foot or two 40 foot containers. These cranes are available with different capacities, different outreach and inreach, and leg spread. Most of the current cranes have 100 ft. leg spread.

There are several methods of moving containers from the storage area to the wharf or from the wharf to storage area. The most common methods are chassis with yard tractors and straddle carriers. In addition three truck traffic lanes and hatch cover storage area are required on the land side of the crane rail. Hatch covers range in sizes from 30 to 55 feet. Typical wharf area is presented on Figure 1-3.

Figure 1-3 - Typical Wharf Area

1.2.2 Container Storage Yard

Container storage yard is where containers are stored for duration prior to leaving the terminal on ship, rail, or truck. Transporting within the container yard are used for chassis with yard or road tractors, and straddle carrier. In smaller terminals and as a backup top loader type of equipment can be used to transport containers. In automated terminals containers are transported using automated guided vehicles (AGVs) or automated lifting vehicles (ALVs).

The major equipment used for storing containers in container yard are wheeled (container on chassis), rubber tire gantry (RTG), straddle carrie r, top loader or other similar equipments, and rail mounted gantry (RMG). Terminals may use combination of RTG and top picks to store containers.

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Most terminals have designated import, export, and empty container storage areas. In the US where the chassis are owned by the shipping industries the container terminals have designated chassis storage areas as well. Typical container terminal storage yard is presented on Figure 4.

Figure 1-4 - Typical Container Terminal Storage Yard

1.2.3 Intermodal Rail Yard

An intermodal rail facility is used to stage, load and unload containers to and from the ports. Double stack trains are loaded and unloaded by standard container handling equipment. A typic al intermodal facility consists of working tracks, storage tracks, arrival and departure tracks, and a run around track. The pavement designer needs to work with the terminal planner to identify the tracks that will be paved and all possible affected operational modes such as: top picks, RMGs, RTGs, reach stacker. They will also need to identify areas designated for pre-staging inbound and outbound containers. Typical container storage yard is presented on Figure 1-5.

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1.2.4 Truck Gate Facility

Container terminal and Intermodal rail gate facilities have very similar functions. They are used to obtain information on the incoming and outgoing container trucks for operational and security purposes. Prior to implementation of technologies, incoming trucks would be stopped by security, followed by a transaction process via communication pedestals, and finally a physical inspection of container and chassis by mechanics. Some or all of the processes have been automated and/ or eliminated. However, even the most automated gates require trucks to stop for processing.

The Pavement designer should make assumptions that the gate will be operating 7 days a week with very limited tolerance for maintenance during its operation. The stop and go nature of the gate operation should also be considered in selecting the pavement material as well as the over all pavement thickness. A typical Gate facility is presented on Figure 1-6.

Figure 1-6 – Typical Gate Facility

Most of the container handling equipment is located near the maintenance and repair facility areas. The current and future types of equipments that would be stored in this area should be identified prior to designing the pavement system.

1.2.5 Buildings and Automobile Parking

Typical container terminals and Intermodal rail require administration buildings, maintenance and repair facilities and other operational buildings that have designated employee and visitors parking areas. Prior to development of pavement sections pavement designer should work closely with the terminal planner in identifying current and possible future use of these areas.

The following chapters will discuss: operational options, pavement subgrade, flexible and ridge pavements, and pavement management.

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2. Container Terminal Operational Options ... 1

2.1 Grounded Container Yard Operations with RTGs ... 1

2.1.1 Equipment Motions ...1

2.1.2 Container Truck Motions ...2

2.1.3 Usage...3

2.2 Grounded Container Yard Operations with Front-End Loaders ... 4

2.2.1 Machine Configuration ...4

2.2.3 Truck Motions ...7

2.2.4 Usage...8

2.3 Grounded Container Yard Operations with Straddle Carriers ... 9

2.3.3 Strad-Truck Interchange ...11

2.3.4 Usage...12

2.4 Intermodal Yard Operations with RTGs or Travelifts... 13

2.4.3 Truck Motions ...14

2.4.4 Usage...14

2.5 Intermodal Yard Operations with Front-End Loaders ... 14

2.5.3 Truck Motions ...15

2.5.4 Usage...16

2.6 Wheeled Container Yard Operations ... 16

2.6.2 Truck Motions ...18

2.6.3 Usage...18

2.7 Gate Areas with Highway Tractors and Chassis ... 19

2.7.1 Configuration ...19

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2. Container Terminal Operational Options

This section describes typical operational options in the modern container terminals.

2.1 Grounded Container Yard Operations with RTGs

Figure 2.1 shows a typical modern rubber-tired gantry crane in container yard operations.

Figure 2-1 Rubber-Tired Gantry Crane in Container Yard Operations Deltaport, Vancouver, British Columbia

The typical modern RTG spans a space that includes six container stacks and a truck travel lane, and has a gage of about 77 feet. Other widths are common. RTG height is expressed in terms of the maximum effective stack height, plus the pass-over space. The machine in Figure 2-1 has a “one-over-four” configuration. Other heights, up to one-over-six, are common.

The most common machine has eight wheels, such as that shown in Figure 2-1. Some older machines have four wheels, one wheel on each leg. A few machines have sixteen wheels, in eight dual-wheel trucks. Each truck can be rotated 90°.

2.1.1 Equipment Motions

The following equipment motions are defined: Hoist: Vertical motion with the main hoist drive.

Trolley: Horizontal motion perpendicular to the gantry runway, with the trolley drive. Gantry: Horizontal motion parallel to the gantry runway, with the gantry drive.

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Virtually all container handling is done with only the hoist and trolley motions. Gantrying with a container is not generally done, because unequal weight distribution makes precise steering difficult.

Gantry motion perpendicular to the runways is possible in dedicated areas. There are three ways to traverse an RTG perpendicular to its runway:

Spin Trucks: Spin all trucks 90°, traverse to a new position, and spin trucks back to their original position.

Turn Around Truck : Spin all trucks but one, so that their rotation axes pass through the static truck. Turn the entire RTG 90° about the static truck, spin the trucks back, traverse, and repeat.

Turn Around Center: Spin all trucks, so that their rotation axes pass through the RTG center-point. Turn the entire RTG 90° about the center-point, spin the trucks back, traverse, and repeat.

All three of these motions generate high friction loads on the pavement, and are frequently done at embedded metal plates. The “Spin Trucks” method is the most common.

2.1.2 Container Truck Motions

Container trucks commonly traverse the entire length of the RTG block in a single lane, with a bare chassis part of the way, and a loaded chassis the rest of the way. In many terminals, adjacent RTG blocks are laid out to create some weaving and bypass room for trucks, as shown in Figure 2-2 and Figure 2-3.

Runway Runway Runway Runway Stacks Access Lane Bypass Lane RTG Truck

Figure 2-2 Truck Access and Bypass Lanes for RTGs RTGs in Same Orientation

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Runway Runway Runway Stacks Access Lane Access Lane RTG

Truck Bypass Lane

Figure 2-3 Truck Access and Bypass Lanes for RTGs RTGs in Opposing Orientation with Shared Bypass

Where weaving and bypass lanes are available, trucks will generally use them only if the access lane is obstructed downstream.

2.1.3 Usage

RTGs are used in conditions requiring high storage density and frequent container re-handling between adjacent stacks. The need to re-handle means that some empty slots will always be needed.

Figure 2-4 depicts the empty spaces required to accommodate re-handling containers. The container in the white slot labeled “T” is the target for retrieval. The containers in the grey slots labeled “1”, “2”, etc., need to be moved to the corresponding white slots, which need to be left empty. This reduces the effective stacking height.

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RTG 6 Wide, 1+6 High

5.2 Effective Height

RTG 6 Wide, 1+4 High

3.5 Effective Height

T

5

4

3

2 1 5 4 3 2 1

T

3

2 1 3 2 1

Figure 2-4 Container Rehandling Space for RTGs

A typical work sequence for an RTG retrieval operation would be as follows:

− Truck arrives adjacent to target storage location with a bare chassis.

− RTG is assigned, and gantries to truck’s location.

− RTG re-handles obstructing containers to other stacks without gantrying.

− RTG retrieves target container, and sets it on the truck chassis.

− Truck departs with loaded chassis.

Export loads are typically arranged to mimic the ultimate ship stowage pattern. In many RTG terminals, a single set of adjacent export stacks would have a single common ship-stowage designation. Import loads are typically arranged in the order they are retrieved from the ship, since the order of delivery to the gate is unknowable. These patterns minimize the number of gantry moves required during ship operations, but maximize the number of gantry moves required during gate operations.

The need to keep open slots for re-handling, along with the tendency to sort containers within RTG blocks, tends to limit overall RTG space utilization. When calculating annual truck trips through RTG operating areas, this reduced utilization needs to be taken into account.

2.2 Grounded Container Yard Operations with Front-End Loaders 2.2.1 Machine Configuration

“Front-end loader” (FEL) is a generic term for a broad class of equipment. All types of FEL pick up a container in a position cantilevered outside and in front of the machine’s wheelbase. FELs come in three common configurations:

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Top-Pick (TP): The spreader is mounted on a vertical mast. The container is picked up by its four top corner castings. The machine is used for both loads and empties. Top-picks frequently have a forklift attachment that allows picking up loaded 20-foot containers by their bottom forklift slots.

Side-Pick (SP): The spreader is mounted on a vertical mast. The container is picked by the two top corner castings closest to the FEL. The machine is used for empties only.

Reach-Stacker (RS): The spreader is mounted on a hydraulically-lifted, extensible boom. The container is picked up by its four top corner castings. The machine is used for both loads and empties, and can handle containers at some distance from the machine.

Figure 2-5 shows a typical top-pick. Figure 2-6 shows a typical side-pick. Figure 2-7 shows a typical reach-stacker.

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Figure 2-6 Typical Side -Pick FEL Serving 7-High Stack

Figure 2-7 Typical Reach-Stacker FEL with Spreader at 20'

All FELs having rotating rear trucks and are fairly maneuverable. The following motions are defined: Hoist: Vertical motion along the mast on TPs and SPs, or vertical motion of the boom on RSs

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Extend: Extension of the boom on RSs. Travel: Straight-line motion of the FEL.

Turn: Spinning of the rear truck, and rotation about one of the front trucks.

Most container handling is done without turning, simply traveling forward and backward perpendicular to a storage stack.

TPs and SPs can only access the top-most container in the outer-most stack in any container block. If re-handling is required, the obstructing container must be moved to an adjacent block. This requires the FEL to do the following:

− Load re-handled container

− Back up

Turn

Traverse to the next block Turn

Align to the block

Set the re-handled container Back up

Turn

Traverse to the original block Turn

Align to the block

− Load target container

Reach stackers have some ability to handle containers into the stack second from the front, but re-handling is usually done the same as for TPs and SPs.

This sequence takes quite a bit of time, and so most FELs are restricted to operations involving simple fore-and-aft motions.

2.2.3 Truck Motions

Trucks commonly traverse the entire length of the FEL block in a single lane, with a bare chassis part of the way, and a loaded chassis the rest of the way. The gap between adjacent FEL storage blocks is fairly large, frequently 65’ or more, so there is usually room for maneuvering. However, simultaneous access of both adjacent FEL blocks can reduce this flexibility. Figure 2-8 shows a common FEL and truck traffic configuration.

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Access Lane Access Lane

FEL

FEL Tire Path

Truck

Figure 2-8 Truck Access for FELs Working Adjacent Blocks

Note the intersection of the FEL and truck tire paths in Figure 2-8. This area is subject to numerous repetitions, since the FEL must retreat each time to clear the truck access la ne, then advance all the way to the face of the container stack.

In grounded CY operations, the stacks are in fixed locations, and so the FEL tire wear patch does not vary over time.

2.2.4 Usage

FELs are used in conditions requiring high storage density, in which container re-handling is expected to be rare or non-existent. The long cycle time for re-handling between blocks makes re-handling very expensive and unproductive.

A typical work sequence for an FEL retrieval operation is as follows:

− Truck arrives, and stops short of the FEL travel path.

− FEL arrives, aligns to the block, and advances across the truck access lane to the face of the block.

− FEL picks the container, and retreats to clear the truck access lane.

− Truck advances, aligning to the FEL.

− FEL advances, and sets the container on the truck.

− FEL retreats or hoists to clear the truck.

− Truck departs.

A typical work sequence for an FEL storage operation is as follows:

− Truck arrives, and aligns to the stack.

− FEL arrives, and aligns to the truck.

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− FEL retreats or hoists to clear the truck.

− Truck departs.

− FEL advances across the truck access lane to the face of the block.

− FEL sets the container atop the stack.

− FEL retreats to clear the truck access lane.

TPs are commonly used to handle pre-sorted export loads. RSs are less-commonly used. SPs are commonly used to handle empties. FELs are almost never used to handle import loads, because the randomness of retrieval order generates a high re-handle incidence. In facilities where FELs are used to handle imports the stack height and width is kept at two or less containers.

As with RTGs, export loads are sorted in FEL blocks according to ship stowage designations. During ship load-out operations, all of the containers in a block will be considered logically interchangeable, so that the FEL can always work the most accessible container and avoid re-handling.

Empties in FEL blocks are sorted according to their physical type and ownership. During delivery of empties to the ship or a trucker, all of the containers in a block will be considered logically interchangeable, minimizing the need for re-handles. Some physical types, e.g., “dry 40-foot standard cubes” are quite common, and generate large, full blocks. Some physical types or ownership categories are rare, and generate poorly utilized blocks.

The need to avoid re-handling in FEL blocks places a practical limit on the utilization of these areas. Utilization will vary from terminal to terminal, based on local commercial patterns. These utilization patterns need to be considered when calculating annual FEL and truck trips.

2.3 Grounded Container Yard Operations with Straddle Carriers 2.3.1 Machine Configuration

Figure 2-9 shows a typic al modern straddle carrier.

Straddle carriers (strads) combine the ability to stack and transport containers over long distances. Most straddle carriers are eight-wheeled machines, with the steering of the wheels coordinated to generate a tight turning radius. Most strads are built for “one-over-two” operations. Some terminals are now using “one-over-three” straddle carriers. One high strads are also available as transporters only.

Straddle carriers can drive equally well, forward or backward. The operator’s cab is at the top, at one end. The driver is typically on a swivel chair, and can orient to see either direction of travel. However, many drivers prefer to drive longer distances with the cab forwards, because visibility and safety are improved. Many terminals have operating rules that dictate this behavior.

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Figure 2-9 Typical Straddle Carrier, One -Over-Two

The hoist and spreader move vertically, with some limited ability to adjust spreader position for fine alignment to stacks.

Long-distance travel is supposed to be done with the container in the lowered position, so that stability is increased. There is usually a transition between long-distance travel over the open roadway and motion over container stacks. During this transition, the spreader is raised and the strad slows down to ensure proper alignment.

There is limited clearance between stacked containers and the inner face of the drive equipment. Travel speed over stacks is reduced, and the driver must take some care to avoid striking the stacked containers. It has been found that when traversing long strad stacks, the driver’s attention may wander, increasing the probability of collision. Any irregularities in the pavement may cause the strad to wander, further increasing the probability of collision. To minimize collision probability, the length of strad stacks is generally limited to twelve or fourteen 20-foot slots.

Figure 2-10 shows a typical stack configuration in a straddle carrier storage area. It is important to note that adjacent blocks of containers share strad tire paths, so that strads may not pass one another in adjacent blocks. This is done to maximize storage density. It affects the number of tire passes over any one tire path.

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Stacks Strad

Tire Paths

Figure 2-10 Typical Strad Stack Configuration

Storage run positions are painted onto the pavement, and do not vary much with time. The strad tire wear paths can stay in one place for years, concentrating load repetitions in fairly tight bands.

2.3.3 Strad-Truck Interchange

Strad-based terminals have an interchange area where trucks and straddle carriers can exchange containers. This area is generally laid out for maximum safety and visib ility, because of the hazards inherent to the operation. The layout of this area will vary considerably between terminals, depending on local safety practices, truck-driver skill, and strad-driver skill.

Figure 2-11 shows the interchange area at Portsmouth Marine Terminal in Virginia.

Figure 2-11 Strad/Truck Interchange Area Portsmouth Marine Terminal, Virginia

Figure 2-12 shows the layout of a typical strad/truck interchange area. The layout of the area allows strads to simultaneously serve adjacent trucks. The tire paths between adjacent interchange slots are not

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shared. Depending on local safety rules, trucks may either be backing into the interchange slot, or driving forward into it from inside the strad work zone. “Herringbone” configurations are also common.

Strad Truck Interchange Slot Driver Zone Tire Paths

Figure 2-12 Strad/Truck Interchange Area 2.3.4 Usage

Strads are used in conditions requiring moderate storage density and high productivity. Strads are capable of effective re-handling. Figure 2-13 shows the empty spaces required to accommodate re-handling of containers in 1-over-3 and 1-over-2 configurations. Terminal operators typically want to limit the distance a strad driver needs to move to find an open slot for a rehandled box. This requires that a certain number of slots be kept clear, reducing the effective stacking height.

1

1 Strad 1+2 High

1.75 Effective Height

Target

2 Strad 1+3 High

2.50 Effective Height

1

2

1

Figure 2-13 Container Rehandling Space for Strads

Strads are used for both loaded and empty container operations, although many terminal operators prefer to keep the bulk of their empty containers in side-pick configurations for higher density.

Each container storage or retrieval operation typically requires that the strad traverse the entire length of the storage run.

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Export loads are typically sorted in runs corresponding to ship stowage patterns, so re-handles are relatively rare. Re-handling is more common in import load areas, and the additional strad motions up and down the run need to be considered in calculating load repetitions.

2.4 Intermodal Yard Operations with RTGs or Travelifts 2.4.1 Machine Configuration

Figure 2-14 shows an RTG serving an intermodal double -stack rail car.

Figure 2-14 RTGs Serving Intermodal Doublestack Car

The configuration of the machine is similar to that used in grounded container yard operations. One common difference is the presence of a stabilizer system that restricts the side-sway of the spreader. This stabilizer system is critical in the handling of trailers, as it allows the rapid attachment of trailer kingpins to support stanchions on piggyback cars. Stabilizer systems are more common in inland intermodal yards, where domestic trailer operations are more common. Maritime intermodal yards frequently use standard, non-stabilized, wire-rope RTGs.

The motions of the RTG are similar to those described in Section 2-1.1 for grounded container yard operations using RTGs.

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Trucks commonly traverse the length of the RTG run along bypass lanes, because of the great length of many of the rail car “cuts”. See Figure 2-15 below. The trucks weave into the loading access lane just upstream of the target location, and weave back to the bypass lane when they are clear of the RTG.

2.4.4 Usage

Figure 2-15 shows one common layout for high-density intermodal working tracks, using RTGs. There are many variations on this theme, based on the dimensions of the RTGs, the nature of the truck and rail traffic, and the configuration of the site.

Runway Runway Runway Runway Access Lane Access Lane Bypass Bypass RTG Rail Car Truck Tracks Tracks

Figure 2-15 Typical RTG Intermodal Rail Layout

The amount of gantrying by the RTGs is much less than in grounded container yard operations, because the RTGs are generally working in a systematic way from one end of the track to the other. There are, of course variations between terminals, but most RTG assignments are pretty well-organized.

The utilization of double -stack rail equipment is fairly high, so it is reasonable to assume, for the purposes of traffic counts, that cars arrive loaded and depart loaded.

2.5 Intermodal Yard Operations with Front-End Loaders 2.5.1 Machine Configuration

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Figure 2-16 Front End Loader Serving Intermodal Car

Top-picks and reach-stackers are commonly used on intermodal operations. Side-picks are not commonly used.

Reach-stackers have the advantage of being able to reach a second track, by extending the boom. This is particularly useful in serving tracks set against a terminal boundary.

FELs are capable of serving curved working tracks, while RTGs are not.

The motions of FELs in serving rail cars are similar to those described in Section 2.2.2 for ground container yard operations. The FEL typically moves fore and aft, turning frequently to move from car to car. The area of pavement immediately adjacent to the track sees a great deal of traffic, as depicted in Figure 2-17.

In grounded CY operations, the stacks are in fixed locations, and so the FEL tire wear patch does not vary over time. In intermodal operations, the alignment of cars is not constant, as each train has different mixture of car and platform lengths and positions. The tire wear patch shifts constantly, spreading the repetitions over a much greater area.

Trucks generally traverse the length of the working track segment along the access lane, as shown in Figure 2-17. The access lane thus sees the combined traffic of trucks running parallel to the track, and FELs moving back and forth perpendicular to the tracks.

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2.5.4 Usage

Figure 2-17 shows one common layout for high-density intermodal working tracks, using top-picks. There are many variations on this theme, based on the nature of the truck and rail traffic, and the configuration of the site. Note the differing car alignments, and their impact on the location of FEL tire wear paths. Track Track Track Track Access Lane Access Lane Access Lane Access Lane FEL

FEL Tire Path

Truck Rail Car

Figure 2-17 FEL and Truck Access for Inermodal Operations

2.6 Wheeled Container Yard Operations 2.6.1 Machine Configuration

Figure 2-18 shows a typical wheeled storage row.

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In wheeled container storage, containers are mounted and parked on street-capable chassis. While parked, the chassis are sitting on their landing legs, which can be retracted for travel. The pads on the landing legs generate a high ground pressure, frequently causing local pavement damage.

Street chassis have twist locks at each corner to secure the container for road travel. Chassis for 40’ containers are just over 40’ long. They have a “gooseneck” which mates to a well built into the underside of the standard container. Chassis for 20’ containers are generally 28’ or longer, to avoid exceeding highway axle load limits.

Containers may also be mounted on dedicated terminal chassis, known as “bomb carts”. Bomb carts are not generally street-legal, because they are wider than 8 feet. They are equipped with flare guides at each corner, making container mounting faster and easier. Bomb carts are typically 40’ or 45’ long, and can hold two 20’ containers with a total rated load of 48 long tons. Figure 2-19 shows the rear flare guides on a typical bomb cart.

Figure 2-19 Rear Flare Guides on a Bomb Cart

A mixture of in-terminal tractors, and off-terminal, or “street”, trucks typically accesses wheeled container storage. The configuration of street trucks varies considerably. Terminal tractors are much more uniform, and differ from street trucks in a number of ways:

− Shorter wheel base

− Hydraulically-liftable “fifth wheel”

− Tighter turning radius

− Single rear axle

The hydraulic -lift wheel on termina l tractors allows them to back under a parked chassis, pick the chassis up off its landing legs using the fifth wheel, hook up the brakes and electrics, and drive away. The

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terminal tractor can park chassis just as quickly. The act of lowering the chassis using the fifth wheel increases the impact load under the landing leg pads, exacerbating pavement damage.

A typical terminal tractor is shown in Figure 2-20.

Figure 2-20 Typical Terminal Tractor 2.6.2 Truck Motions

Removing a chassis from storage is a fairly simple truck motion.

Placing a chassis into storage generally requires some maneuvering, especially for street tractors. Parking slots are typically ten feet wide, and long-wheelbase tractors have some difficulty backing a 40-foot chassis gracefully into this width.

The access aisles running between rows of parked containers frequently double as general traffic circulation roads for the terminal. As such, the number of truck repetitions is not directly related to just the storage and retrieval operations within a row. Truck repetitions within a row will depend on the overall traffic layout of the terminal. If the terminal is amply supplied with dedicated arterial circulation roads, traffic will be diminished in the storage rows.

2.6.3 Usage

Wheeled storage is used where low storage density is acceptable, and high container accessibility is required. Wheeled storage is used for import and export loads, and for empties. Wheeled storage is commonly used for reefer containers, since plugging, unplugging, and servicing reefers is easier when they are mounted and accessible.

Peak storage utilization is typically very high, because re-handling is not required in any circumstance. When utilization is high, drivers may have to search a bit to find an empty slot to park a chassis in. This increases driving time, and increases the number of pavement load repetitions.

When wheeled storage is in use, bare chassis can make up a considerable portion of the total storage demand. At times, the high population of bare chassis mandates that their storage be densified. Figure 2-21 shows a typical high-density storage area for bare chassis. Note these chaises are stacked to save yard spaces.

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Figure 2-21 High Density Bare Chassis Storage

2.7 Gate Areas with Highway Tractors and Chassis 2.7.1 Configuration

There are many different configurations in use for gate complexes. In general, however, they have in common a number of basic components:

Queuing Lanes: In-stream queuing space for trucks waiting for processing.

Remote Processing Stations: Locations where the truck driver can interact with terminal staff through telecommunications equipment, without leaving the truck cab.

Scales: Weigh scales.

Inspection Stations: Locations where the truck is visually inspected, and paperwork is exchanged.

Holding Areas: Locations where trucks are parked awaiting resolution of problem transactions, or are otherwise out of the main gate traffic stream.

Only street tractors pass through terminal gates, and only with street-legal chassis. Neither terminal tractors nor bomb carts are suitable for open-road use, and they are generally not registered as such. The configuration of street trucks varies widely, based on local commercial conditions.

A typical gate can process about 20 to 25 trucks per hour, per lane. The number of gate lanes is established through queuing analysis based on the exact nature of the gate process.

2.7.2 Usage

A typical truck process through a gate requires many stops and starts, within queuing areas, at processing and inspection stations, at stop-lines established to protect pedestrians, and around holding areas.

Gate traffic tends to be concentrated at the interfaces between the gate and road, and gate and container yard. Within the gate, truck traffic is diffused across many processing lanes, spreading the repetition load out to a considerable degree.

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3. Typical Container Handling Equipment Wheel Load Calculation... 3-1 3.1 Container Handling Tires and Pressures ... 3-1 3.2 Yard Equipment... 3-2 3.2.1 RTG’s ...3-2 3.2.2 Straddle Carriers ...3-3 3.2.3 Top Picks ...3-3 3.2.4 Side Picks...3-4 3.2.5 Reach Stackers...3-5 3.2.6 Yard Hustlers...3-6 3.3 Container Distribution... 3-6 3.4 Static Loads ... 3-8 3.5 Typical Load Repe tition Analysis for Container Terminals and Intermodal Facilities . 3-8 3.5.1 Entrance Gate ...3-9 3.5.2 Wheeled Storage Area ...3-9 3.5.3 Side/Top Pick and Truck Operations ... 3-10 3.5.4 RTG and Truck Operation ... 3-11 3.6 Equipment Weight Distribution and Wheel Loads ...3-14 3.6.1 RTG ... 3-14 3.6.2 Side or Top Pick ... 3-15 3.6.3 Yard Trucks ... 3-17 3.7 Pavement Damage ...3-18 3.7.1 Damage ... 3-18 3.7.2 Proportional Damaging Effect ... 3-19 3.7.3 Average Damage... 3-19 3.7.4 Critical Damage... 3-19 3.7.5 Total Damage of a Plant and Wheel Proximity Factors... 3-20 3.8 Equivalent Load Repetitions ...3-21 3.8.1 RTG ... 3-21 3.8.2 Yard Trucks ... 3-21 3.8.3 Side and Top Picks... 3-22 3.9 A Comprehensive Wheel Load Calculation Example ...3-22 3.9.1 Key Notations ... 3-23 3.9.2 RTG Operation – RTG Repetitions ... 3-23 3.9.3 RTG Operation – Truck Repetitions ... 3-24 3.9.4 Side/Top Pick Repetitions ... 3-24 3.9.5 Damage – Top Pick ... 3-25 3.9.6 Damage –RTG ... 3-31 3.9.7 Design Summary ... 3-33

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3. Typical Container Handling Equipment Wheel Load Calculation

One important function of the pavement on the container handling equipment runways is to distribute repetitive load into earth structures. Therefore, calculation of design load and design load repetitions (Load Repetition: Number of time that an area undertaking a certain amount of load.) plays an important role in the pavement design. This section provides a guide on calculation of design load and design load repetitions in a container terminal. Different equipment types, container load distribution, tire load, axle and tire configuration, and repetitions of loads are considered for different areas such as RTG runways and top pick operation area. At the end of the section, a comprehensive example is presented to illustrate the described concepts and methods.

3.1 Container Handling Tires and Pressures

Container handling equipment, including FELs, RTGs, strads, hustlers with bomb carts, hustlers with chassis, and street legal trucks with chassis, is typically used in container terminals and intermodal rail facilities. Table 3-1 lists typical tire pressures for different makers and different tire sizes of container handling equipment.

Table 3-1. Typical Tire Pressures

Tire Pressures

Maker

Size

psi.

bars

Goodyear 11R22.5 144 9.9 Nokian 14.00-24 161 11.1 Goodyear 14.00-24 144 9.9 Kalmar spec. 14.00-24 138 9.5 AVE 14.00-24 148 10.2 Goodyear 16.00-25 152 10.5 Nokian 16.00-25 131 9.0 Nokian 16.00-25 170 11.7 Kalmar spec. 16.00-25 116 8.0 AVE 16.00-25 142 9.8 Goodyear 18.00-25 131 9.0 Goodyear 18.00-25 167 11.5 Paceco spec. 18.00-25 139 9.6 Nokian 18.00-25 165 11.4 Kalmar spec. 18.00-25 131 9.0 AVE 18.00-25 147 10.1 Nokian 18.00-33 145 10.0 Goodyear 18.00-33 144 9.9 AVE 18.00-33 145 10.0 Goodyear 21.00-25 112 7.7 Kalmar spec. 21.00-25 116 8.0 AVE 21.00-25 114 7.9 Other manufacturers: Michelin General Tire

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3.2 Yard Equipment

This section presents various yard equipments, such as RTGs, straddle carriers, top picks, side picks, reach stackers, and yard hustlers. Pictures, typical dimensions, and typical specifications for different makers are provided for each equipment type.

3.2.1 RTG’s

Figure 3-1 A typical RTG

Kalmar 402315-2045C

• 16 wheels, 5+1 lift, 40.6t max lift, 125.6t dead weight, 16.00-25 tires.

• 8 wheels, 5+1 lift, 40.6t max lift, 127.8t dead weight, 18.00-25 tires. PACECO PTD 200503

• 8 wheels, 5+1 lift, 40.6t max lift, 126.0t dead weight, 18.00-25 tires. Other manufacturers:

Noel (Gottwald) PMC

Taylor Fantuzzi

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3.2.2 Straddle Carriers

Figure 3-2 A typical Straddle Carrier

Kalmar CSC

• 8 wheels, 4 container stack capacity, 50t max lift, 74.95t dead weight, 16.00-25 tires. Kalmar Shuttle Carrier

• 4 wheels, 2 container stack capacity, 50t max lift, 45t dead weight, 18.00-33 tires. Other manufactures: Belotti Nelcon Noel (Gottwald) MHI 3.2.3 Top Picks

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Kalmar DCF450CSG

• 6 Wheels, 5 container stack capacity, 100,000 lbs. max container weight, 165,000 lbs. dead

weight, 18.00x33 tires. Kalmar DCF410CSG

• 6 wheels, 5 container stack capacity, 90,000 lbs. max container weight, 154,000 lbs. dead weight, 18.00x33 tires.

Taylor 954

• 6 wheels, 4 container stack capacity, 95,000 lbs. max container weight, 157,800 lbs. dead weight, 18.00x25 tires.

Other manufacturers: Hyster

Fantuzzi

3.2.4 Side Picks

Figure 3-4 A typical Side Pick Kalmar DCE80-45 E8

• 6 wheels, 7/8 (9.5’/8.5’ containers) container stack capacity, 17,600 lbs. max lift, 81,600 lbs. dead weight, 12.00x24 tires.

Kalmar DCE100-45 E8

• 6 wheels, 7/8 (9.5’/8.5’ containers) container stack capacity, 25,400 lbs. max lift, 92,400 lbs. dead weight, 12.00x24 tires.

Kalmar DCD70-40 E5

• 6 wheels, 5 container stack capacity, 15,400 lbs. max lift, 68,100 lbs. dead weight, 12.00x20 tires. Other manufacturers:

Taylor Hyster Fantuzzi SMV

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3.2.5 Reach Stackers

Figure 3-5 A typical Reach Stacker Kalmar DRF4000C-450C

• 6 wheels, 5-4-3 (9.5’) 5-5-4 (8.5’) stacking capacity, 99,200 max lift, 194,000 dead weight,

18.00x25 tires. Kalmar DRS4527-4531

18.00x25 tires. Kalmar DRD450-80S

21.00x35 tires. Other manufacturers: Taylor Hyster Fantuzzi SMV

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3.2.6 Yard Hustlers

Figure 3-6 A typical Yard Hustlers

Ottawa 50

• 6 wheels, 63,300 maximum capacity, 14,500 dead weight, 11R22.5 tires Ottawa DOT/EPA 60

• 6 wheels, 62,000 maximum capacity, 18,000 dead weight, 11R22.5 tires Kalmar YT-50

• 6 wheels, 63,300 maximum capacity, 14,500 dead weight, 11R22.5 tires

Other manufactures Magnum

Capacity of Texas

3.3 Container Distribution

Heaviest load will cause most damage but may only make up less than one percent of the containers transported. Therefore, to accurately analyze heavily loaded port pavements it is important to understand the weights of cargoes that will be handled. Such container distribution will be used to calculate proportional damage effect, as seen in section 3.7.2.

Typical container weights range from approximately 10,000 to 67,000 pounds. Containers over 67,000 pounds are within a very small percentage and generally overweight for highway transport. A vessel discharge report summarizing all containers sizes and weights discharged and loaded during a vessel call in representative month can be obtained from a container terminal operator. A simplified tabulation of the combined import/export container distribution for a container terminal in the northwest is shown in Table 3-2 below. Figure 3-7 shows the comparison between measured and assumed container distributions. It should be noted that container weight distributions are highly sensitive to changes in the types of commodities handled. Therefore, the pavement designer should work closely with terminal planners to understand possible changes to commodities types in the region.

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Table 3-2. Container Weight Distribution

0% 5% 10% 15% 20% 25% 30% 35% 0-10,000 10,001 - 25,000 25,001 - 35,000 35,001 - 40,000 40,00 1 - 45 ,000 45,001 - 50,000 50,001 - 55,000 55,00 1 - 60 ,000 60,001 - 65,000 65,001 - 70,000 72,501 - 100 ,000

Container Weight (pounds)

Percentage of Inventory

Measured Vessel Distribution Assumed Yard Distribution Figure 3-7 Measured vs. Assumed Container Distribution

Using the assumed container distribution discussed above, container handling equipment wheel loads, tire contact pressure, and tire contact radius (Typical pavement design generally assumes the tire loads is uniformly distributed over a circular area.) for each load increment can be tabulated. A typical table for straddle carrier is shown in Table 3-3. Empty container handler wheel loads, with and without an empty refrigerated container are shown in Table 3-4.

Container Weight Range (pounds) Container Weight (pounds) Container Weight Distribution 0 – 10,000 10,000 (empty box) 25% 10,001 – 25,000 25,000 17% 25,001 – 35,000 35,000 12% 35,001 – 40,000 40,000 7% 40,001 – 45,000 45,000 8% 45,001 – 50,000 50,000 8% 50,001 – 55,000 55,000 8% 55,001 – 60,000 60,000 7% 60,001 – 65,000 65,000 6% 65,001 – 70,000 70,000 1% 72,501 – 100,000 100,000 1%

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Table 3-3. Kalmar CSC-350 Straddle Carrier Wheel Loads Container Weight

(pounds)

Single Wheel Load (pounds)

Tire Contact Radius (inches)

Tire Contact Pressure (psi) 0 17,088 6.12 145 10,000 18,338 6.34 145 25,000 20,213 6.66 145 35,000 21,463 6.86 145 40,000 22,088 6.96 145 45,000 22,713 7.06 145 50,000 23,338 7.16 145 55,000 23,963 7.25 145 60,000 24,588 7.35 145 65,000 25,213 7.44 145 70,000 25,838 7.53 145 100,000 29,588 8.06 145

Table 3-4. Taylor TEC-155H Wheel Loads With or Without An Empty Container

Container Weight (pounds) Front Axle Dual Wheel Load (pounds) Front Axle Single Tire Contact Radius (inches) Front Tire Contact Pressure (psi) Rear Axle Single Wheel Load (pounds) Rear Axle Single Tire Contact Radius (inches) Rear Tire Contact Pressure (psi) 0 22,000 5.40 120 11,900 6.15 100 11,000 31,167 6.43 120 8,233 5.12 100 3.4 Static Loads

In addition to dynamic loading from container handling equipment, port pavements are typically subjected to static loading from corner castings on containers and either dolly wheels or sand shoes on chassis. Corner castings measure 7-inches by 6 3/8-inches and project approximately ½ -inch below the container base. While containers may be stacked in a block arrangement up to four high, it is unlikely that all containers in the stack will be fully loaded. Two high container stacks exert an average load of approximately 120,950 pounds and a contact stress of 677 pounds per square inch. Chassis dolly wheels are typically 4-inches wide by 9-inches diameter. The contact area of each wheel is approximately ½-inch by 4-inches and generates a stress of 5,600 psi. Sand shoes are typically 6-inches by 9-inches and exert a contact stress of 280 psi.

3.5 Typical Load Repetition Analysis for Container Terminals and Intermodal Facilities

Different areas in container terminals may have different equipment and subject to different load repetitions. This section presents formulas of typical load repetition calculation for different areas in a container terminal.

Areas of the yard that can be converted to other use, such as the conversion of wheeled parking to side-pick empty storage or top-side-pick storage to RTG storage, need to be designed for more severe loading

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condition. In order to achieve the maximum flexibility, some terminals use a uniform design for the majority of the pavement.

Typically, there are two approaches to compute load repetitions of vehicles. One approach is to convert various loads and repetitions to an equivalent number of standard or equivalent loads. This is called ESAL (Equivalent Single Axle Loads) approach. The most common equivalent loads used in the U.S. is the 80 kN (18,000 lbs). Another more complex but more accurate approach characterizes loads directly by number of axles, configuration and weight. No conversion to ESAL is involved. In the following sections, both approaches are discussed.

3.5.1 Entrance Gate

Obtain the estimated throughput capacity per year for the terminal in Twenty Equivalent Units (TEUs) and a conversion factor from lifts to TEUs from terminal planners. Also obtain the assumed percentage (%) of the total throughput going through the gate (DT). If there is no on-dock rail intermodal facility the 100% of the throughput would go through the gate. Use the following equation to compute Equivalent Single Axle Loads (ESAL).

Given:

C4 = TEU/Lift (typical number of TEU per lift between 1.7 to 1.85)

C5 = Transactions/Lift (typical number of truck transaction per lift between 1.5 to 2)

DD =50 % (directional split, 50% in and 50% out)

DL = 90% (% of traffic in the preferred lane)

DT = % (% of lifts moved by truck – 100% for no on-dock intermodal facility)

TF = 3 ESAL/Trans (estimated number of ESAL per transaction)

YC = total annual terminal capacity in TEUs

We have:

Design Lane ESAL’s = YC / C4 • C5 • DT • DD • DL • TF (3-1)

3.5.2 Wheeled Storage Area

Given:

PS = estimated number of wheeled storage slots

C5 = 2 Transactions/Slot (typical number of truck transaction per slot)

TF = 3 ESAL/Trans (estimated number of ESAL per transaction)

SU = estimated slot utilization – between 70 to 90%

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We have:

Design ESAL’s = PS • SU • 365 / DW • C5 • TF (3-2)

3.5.3 Side /Top Pick and Truck Operations

It is assumed the containers will be delivered using truck and stacked using side or top-picks. Assuming that the storage area has the configuration as shown in the Figure 3-8, the calculations are as follows:

In the Side/Top Pick yard, the heaviest traffic will be directly in front of the first row. At this location there are two types of traffic - Side/Top Loader and Truck traffic. The Side/Top Pick traffic is limited to the number of boxes in the first row, while the truck traffic is defined by the size of the whole stack, because the trucks follow each other along the length. For Side/Top Picks, the storage area can be accessible from only one side or two sides. If Side/Top Picks and trucks can access both side, the repetitions will be decreased to a half. In the calculation, the variable, "Number of accessible sides (C7)", is added for this purpose.

Given:

SU = estimated slot utilization – between 70 to 90%

DW = assumed average container dwell time in days

C4 = TEU’s per lift (typical number of TEU per lift between 1.7 to 1.85)

C5 = trips per box (2 for Side/Top Pick area)

C6 = moves per trip

C7 = number of accessible sides (1 or 2)

L = length of the stack in TEU’s

W = width of the stack in TEU’s