stmp add3_243011-f3-c3-tn01 - loading for tram structures rev_b[1]

Technical Note No. TN01 Loading for Tram Structures

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Surface Transport Master Plan

Addendum 3 – Transit Corridor Safeguarding

Mott MacDonald

Technical Note

May 2009

Loading for Tram Structures

Issue and Revision Record

Rev Date Originator Checker Approver Description

A 31-03-09 S. Luke T. Watson J. Forbes First Issue – for Comment

B 27-05-09 J. Gomez B. Duguid S. Luke Second Issue

This document has been prepared for the titled project or named part thereof and should not be relied upon or used for any

other project without an independent check being carried out as to its suitability and prior written authority of Mott

MacDonald being obtained. Mott MacDonald accepts no responsibility or liability for the consequence of this document

being used for a purpose other than the purposes for which it was commissioned. Any person using or relying on the

document for such other purpose agrees, and will by such use or reliance be taken to confirm his agreement to indemnify

Mott MacDonald for all loss or damage resulting therefrom. Mott MacDonald accepts no responsibility or liability for this

document to any party other than the person by whom it was commissioned.

To the extent that this report is based on information supplied by other parties, Mott MacDonald accepts no liability for any

loss or damage suffered by the client, whether contractual or tortious, stemming from any conclusions based on data

supplied by parties other than Mott MacDonald and used by Mott MacDonald in preparing this report.


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Contents

Ch Section/Title Page

1 INTRODUCTION 3 1.1 Purpose of the Technical Note 3 1.2 Source data 3 1.3 Definitions & Acronyms 4

2 STANDARDS 6 2.1 Technical Standards 6 2.2 Abu Dhabi Tramway Planning Guidelines 6 2.2.1 Lighting Requirements Error! Bookmark not defined. 2.2.2 Geometric Requirements 6 2.2.3 Electrical Requirements 7 2.2.4 Drainage Requirements 7 2.2.5 Ducting and Utilities 7 2.2.6 Trackform 7

2.3 Technical approvals 9

3 TRAM LOADS 10 3.1 Vertical loads from passenger trams 10 3.1.1 Review of LRVs 10 3.1.2 Summary of vertical loads 11

3.2 Horizontal loads from passenger trams 12 3.2.1 Lurching 12 3.2.2 Nosing 13 3.2.3 Centrifugal 13 3.2.4 Summary of horizontal loads 13

3.3 Longitudinal loads from passenger trams 14 3.3.1 Deceleration 14 3.3.2 Acceleration 15 3.3.3 Summary of Longitudinal Traction Loads 16

3.4 Fatigue loads for passenger trams 17 3.4.1 Load intensity 17 3.4.2 Load frequency 18

3.5 Accidental loads for passenger trams 18 3.5.1 Vertical loads from derailed LRV 18 3.5.2 Horizontal loads from derailed LRV 19 3.5.3 Horizontal loads from impact of other vehicles 20

3.6 Loads from freight trams 20 3.6.1 Vertical loads for freight trams 21 3.6.2 Horizontal loads for freight trams 21


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3.6.3 Longitudinal loads for freight trams 21 3.6.4 Fatigue loads for freight trams 21 3.6.5 Accidental loads for freight trams 21

4 MAINTENANCE AND CONSTRUCTION VEHICLE LOADS 22 4.1 Vertical loads for maintenance and construction vehicles 22 4.1.1 Assumed vehicles 22 4.1.2 Summary of vertical loads 24

4.2 Horizontal loads for maintenance and construction vehicles 24 4.3 Accidental loads for maintenance and construction vehicles 25

5 OTHER LOADS 26 5.1 Highway vehicles 26 5.2 Pedestrian loading 26 5.3 Wind loads 26 5.4 Temperature loading 26

6 REFERENCES 27


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1 Introduction

1.1 Purpose of the Technical Note

In September 2007 the Abu Dhabi Government published “Plan Abu Dhabi 2030: Urban Structure

Framework Plan”, also known as Vision 2030, which is a plan for the development of the City of Abu

Dhabi to guide planning decisions for the next quarter of a century.

In February 2008, Mott MacDonald was appointed by the DOT to prepare the STMP. This was to

develop the conceptual transportation strategy outlined in Vision 2030 into a detailed master plan and

prepare the implementation programme.

The STMP includes an ambitious plan to introduce over 340km of tramway into Abu Dhabi. Some

elements of the tram system will be retrofitted into the existing urban fabric whilst other elements will

be provided within new development areas. In these new development areas the tramway might be

implemented in parallel with, earlier or later than other development. In all instances however it will

be necessary for the functional requirements of the tramway to be provided. One aspect of this is that

any new or existing structures that interface with the tramway should take into account the loading and

other design criteria related to the tram system.

The objective of this Technical Note is to detail the required considerations for tramway structures and

other structures integrated or related to the proposed and likely alignment.

The Technical Note considers vertical, horizontal, fatigue and accidental loadings, and design criteria

including headroom clearances, deflection and vibration. The Technical Note will propose appropriate

standards for the system.

Loading and design criteria for structures other than tram structures are not covered by this Technical

Note.

Text in bold type is intended as a mandatory requirement and all structures supporting the tramway

must demonstrate compliance.

1.2 Source data

The information consulted in preparation of this Technical Note comprises, but is not limited to the

following documents:

• Design Manual for Roads and Bridges (DMRB) – UK Highways Agency publication (Ref. 1);

• Roadway Design Manual – Road and Bridges (Abu Dhabi Municipality) (Ref. 2);

• Load appraisal report for Merseytram , Mott MacDonald, 2004 (Ref.3);

• Design loads & spatial parameters – Technical Note. Cross River Tram, Mott MacDonald,

2008 (Ref. 4);

• Report on loading and design criteria for tram structures. Nottingham Express Transit, Mott

MacDonald, 2008 (Ref. 5);

• Manufacturer specifications and publish data for information on low floor trams. Collated in

May 2009 by Mott MacDonald.


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1.3 Definitions & Acronyms

DKE Developed Kinematic Envelope, defined as per the UK’s Office of Rail Regulation

(ORR) “Guidance on Tramways” (Ref. 6), clause 107: “The DKE should be

established by enlarging the kinematic envelope to take into account all the possible

effects of curvature, including superelevation of the track, and end and centre throw

of the tram. It too is speed dependent, but is unique to the particular location at given

speed.” Refer to additional Clauses 108-109 for further information.

DoT Department of Transport

ESZ Area within which, there may be a risk of electrocution from the OLE.

LRT Light Rail Transit

LRV Light Rail Vehicle

OLE Overhead Line Equipment

RL Reduced loading for use on passenger rapid transit systems on lines where main line

locomotives and rolling stock do not operate.

RU Standard railway loading and allows for all combinations of vehicles running or

projected to run on railways in the UK.

STMP Surface Transport Master Plan.

TCS Transit Corridor Safeguarding.

Tramway As per the ORR “Guidance on Tramways” (Ref. 6), clause 16: “…a system of

transport used wholly or mainly for the carriage of passengers, employing parallel

rails which provide support and guidance for vehicles carried on flanged wheels, and

in respect of which:

the rails are laid in a place to which the public have access; and

on any part of the system, the permitted speed of operation of the vehicles is limited

to that which enables the driver on any such vehicle to stop it within the distance he

can see or be clear ahead…”

Refer to additional Clauses 108-109 for further information.

Tramway Path As per the ORR “Guidance on Tramways” (Ref. 6), clause 85: “…the area reserved

for a moving tram in its environment. It is derived from the DKE by adding the

minimum appropriate clearance as specified within this document…It therefore

depends upon the DKE and upon the nature of the operational environment and the

structures and features within it.” Refer to Clause 86 for further information.


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UIC Union Internationale des Chemin de Fer or International Union of Railways.


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2 Standards

2.1 Technical Standards

A number of different technical standards are routinely used in the United Arab Emirates (UAE) for

various purposes. For example, British Standards are used in building design, and AASHTO standards

for road and bridge design. There are no recognised national or international standards for LRT

structures. In the UK, the Highways Agency’s Design Manual for Roads and Bridges (DMRB) (Ref.

1) together with UIC 776-3R (Ref. 7) are often combined for LRT Structures.

We have developed on other schemes a set of LRT structures requirements and recommend a similar

approach is adopted for STMP-TCS. However, it should be open to developers to use other standards

where they can demonstrate that the requirements of this Technical Note will be fully satisfied. In

particular, structures supporting both LRV and highway loads may need to comply with the Abu

Dhabi Municipality Roadway Design Manual (Ref. 2), which incorporates AASHTO Standards.

Structures supporting the tramway shall be designed in compliance with the Highways Agency’s

Design Manual for Roads and Bridges (DMRB) (Ref 1), with the addition of UIC 776-3R

(International Union of Railways) (Ref. 7) to address vibration issues and deflection constraints.

Alternative standards may be adopted subject to prior demonstration that they are at least

equivalent to these standards, and that their use shall satisfy the other requirements set out in

this Technical Note.

2.2 Abu Dhabi Tramway Planning Guidelines

The DoT have commissioned the preparation of Tramway Planning Guidelines and this

Technical Note should be read in conjunction with these guidelines.

2.2.1 Geometric Requirements

Provision for sufficient height clearance to the OLE will be required (the desirable minimum

wire clearance is 6.2m above top of rail). If a tram only section runs under a structure, this may

be locally reduced to an absolute minimum height of 5.2m above platform/street level providing

that there is sufficient longitudinal separation to the nearest section of on-street track to achieve

the minimum clearance of 6.2m at that point. An absolute minimum of height of 4.8m and 4.2m

shall apply to off street and subway sections where there is no public access.

The Electrical Safety Zone (ESZ) extends 2m beyond the outer rails of the tramway once the

tramway is operational.

Buildings shall be located and designed such that areas physically accessible to occupiers are a

minimum 2.75m clear of the ESZ to reduce the risk of electrocution.

The layout of the development boundaries should allow for maintenance of the development

without the need for possessions of the tramway. It should be noted that possessions of the

tramway could have significant cost implications.


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No obstructions shall be placed within the tram DKE. Obstructions greater than 0.5m in length

shall additionally be located at least 0.9m beyond the DKE to allow clear space for evacuation of

passengers in an emergency.

2.2.2 Electrical Requirements

Stray current issues stem from the fundamental design of electrified rail transit systems. Electric

current from the OLE is returned to substations via the running rails. The magnitude of stray current

flow in the ground conductor will increase as its resistivity decreases. Steel reinforcement to concrete

and any metallic structure buried in ground of this nature will also tend to “attract” stray current. The

risk of corrosion to the metallic elements is therefore increased.

Stray current monitoring and management are therefore required to prevent structural damage of

structures.

Structures supporting the tramway shall be electrically isolated from the trackform.

For example, an electrically inert membrane shall be placed on any structural floor slab below the

proposed tramway trackform (see below).

Developers shall have regard to the possibility of electromagnetic interference with sensitive

equipment (e.g. computing and communication equipment) placed in the close vicinity of the

tramway’s electrical system. Measures to address such interference are the developer’s

responsibility (e.g. relocation of equipment).

2.2.3 Drainage Requirements

All new or altered drainage should direct surface water away from the tramway. Proposals to drain

water onto, or connect into, the tramway track drainage shall not be permitted.

Tramway drainage is expected to be incorporated into the trackform, comprising longitudinal drain

channels and carrier drains.

On long structures, developers may be required to provide for tramway drainage outfalls at

suitable intervals, to be incorporated into the structure’s design.

2.2.4 Ducting and Utilities

Provision shall be made for tramway related ducting. The location of utilities shall take into

account the requirements of the Tramway planning Guidelines.

2.2.5 Trackform

Various track forms are currently in use on modern tram schemes. These are:

Ballasted track, without stray current collection measures but incorporating insulated rail fastenings.

Ballast-less paved track, with the rails flush with the road surface and continuously supported by and

embedded in an elastomeric insulating material.


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Ballast-less non-paved track, with discrete rail supports incorporating full insulation as part of the rail

fastenings.

Grass-track which is a modification of one of the ballast-less track forms (generally not proposed for

Abu Dhabi because of watering requirements).

Typical Ballast-less paved track slab arrangement adopted in the UK is shown in Figure 1.

For situations where the track slab is placed directly onto a podium, it would be expected that

reinforced concrete elements of the track slab could be placed directly onto the podium structure, with

electrical separation.

Developers shall allow in their designs for the dead weight of the tramway track slab and

platforms where required including all ancillary fixed items (e.g. OLE support columns,

platform shelters and the like).


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Figure 1: Typical track slab detail

2.3 Technical approvals

We recommend that the Department of Transport obtains assurance from developers and contractors

that their structures and other design features comply with this Technical Note and Tramway Planning

Guidelines, prior to commencement of construction.

In other jurisdictions, this assurance is obtained by means of a Technical Approval process whereby

designers submit their proposals for “Approval in Principle” at the preliminary design stage. While

this offers the greatest assurance that developments will be compliant, it requires the approval body to

have appropriate technical expertise and devote considerable resources to technical review of design

proposals.

Typical UK Standards for such a Technical Approval process include:

• BD 2/05 – Technical Approval of Highway Structures (Ref. 8);

• NR/SP/CIV/003 – Technical Approval of Design, Construction and maintenance of Civil

Engineering Infrastructure (Ref. 9).

• 1-538 – London Underground (Ref. 17)

The fundamental objectives of the Technical Approval procedures are to give increased assurance for

the required construction, refurbishment or demolition so that the proposals are safe to implement.

Also, that any new structures procured are serviceable in use, economic to build and maintain, comply

with the objectives of sustainability, have due regard for the environment, and that they satisfactorily

perform their intended functions.

Additionally, Technical Approval gives the Department of Transport the assurance that structures built

by others can safely support the future tramway with a minimum of alteration.

Developers shall submit preliminary details of their structural proposals, and an accompanying

design statement demonstrating how their design meets the requirements of this Technical Note

and Tramway Planning Guidelines. The developer shall obtain the Department of Transport’s

acceptance of this submission before finalising the design of the structure.


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3 Tram Loads

3.1 Vertical loads from passenger trams

3.1.1 Review of LRVs

There are currently no national or international standards for tram loading. Therefore, information on

low floor (full or partial) trams was collated in May 2009 from manufacturer and published data. This

data has been reviewed and the relevant results are shown on Table 1. This information is preliminary

and may not reflect all LRVs on the market satisfying the requirements set by the Abu Dhabi Surface

Transport Masterplan on tram characteristics.

We are aware that trams have historically tended to become heavier as improvements are made and

extra pieces of equipment added. For example, different manufacturers may choose to deal with the

temperature extremes of Abu Dhabi in different ways, adding solar gain shields, additional fans or

additional air-conditioning units among the possible solutions. Therefore, it would seem prudent to

add a margin for future flexibility and location specific requirements.

Vehicle

Maker

Vehicle

Type

Location

(City)

Length

(m)

Vehicle

Weight

(Empty)1

Loaded

Crush2

(6pass./m2)

Equivalent

UDL-6p

(kN/m)

Loaded

Crush

(8pass./m2)

Equivalent

UDL-8p

(kN/m)

Tramways

CAF Streetcar Edinburgh 45.850 55.8t 79.040t 16.91 84.920t 18.17

Bombardier Flexity

Outlook Berlin 40.550 51.5t 74.005t 17.90 79.780 19.30

Bombardier Flexity

Outlook Brussels 43.394 52.5t 76.160t 17.22 82.320t 18.61

Siemens3

Combino

Plus Almada 36.360 50.5t 72.270t 19.50 77.800t 20.99

Guided Buses

Bombardier Tram-on-

Tires Nancy 24.500 25.5 39.710t 15.90 43.280t 17.33

Table 1 Comparison of Low-floor Light Rail Vehicle Loads

We have compared the above vehicle loads against reference standards for light rail loading. Chapter

8.0 of the design code BD 37/01 (Ref. 10) describes two types of railway loading, RU and RL loading.

RL loading is a reduced loading for use on passenger transit railway systems where mainline

1 Vehicle weight (empty) does not include cooling units or similar.

2 Assumed passenger weight is 70kg per person

3 Siemens provides a second version of the Combino Plus tramway for Budapest, with a vehicle length of 53.990m;

however, at the time of the production of this Technical Note, we do not have tare weight data for this model.


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locomotives and rolling stock do not operate, and can be used for LRV loading, although this is

conservative.

In accordance with clause 8.2.2 of BD 37/01, the most onerous of the following is used for nominal

(un-factored) RL loading:

• A single 200 kN concentrated load coupled with a uniformly distributed load (UDL) of

50 kN/m for loaded lengths up to 100 m, and for loaded lengths in excess of 100 m a UDL of

50 kN/m for the first 100 m reducing to 25 kN/m for lengths in excess of 100 m;

or

• Two concentrated loads of 300 kN and 150 kN, spaced at 2.4 m along the track, placed at a

point along the deck to give the most severe result.

With the exception of the two concentrated loads of 300 kN and 150 kN, which are deemed to include

dynamic effects (clause 8.2.2 of BD 37/01), a dynamic factor for RL loading shall be taken as 1.4 for

un-ballasted tracks and 1.2 for ballasted tracks (clause 8.2.3.2 of BD 37/01) (Ref. 10).

Mott MacDonald has previously carried out research work in the UK, investigating both LRVs and

maintenance vehicles. Our load appraisal reports for Merseytram (Ref. 3), Cross River Tram (Ref. 4),

and Nottingham Express Transit (Ref. 5), concluded that a value of 0.5 x RL was generally suitable to

represent current and future tram loads on those schemes.

The tabulated UDLs range between 17.33 kN/m and 20.99 kN/m and would be within a proposed

loading of 0.5 x RL, which equates to 25 kN/m. This provides a margin typically 20% above the most

onerous tram considered for this load model.

Latest developments in tram technology include ground-powered trams using the PRIMOVE

(Bombardier) and APS (Alstrom) systems. We have no evidence to anticipate that the load imposed by

these systems is much more onerous than the vehicles explored in Table 1. Other technologies, such as

Bombardier’s MITRAC system, for storing energy released when braking, can add to the empty

weight of vehicles by approximately one tonne. This increase to the tare weight has minimal effect on

the equivalent UDL, hence, the proposed 0.5 x RL remains acceptable.

In a climate such as Abu Dhabi, we have estimated conservatively that for a 7 section, 40 metre long

tram, 2 drivers cab air conditioning modules would be required (1 module per cab), combined with

approximately 7 separate saloon air conditioning modules (1 in each vehicle section). These modules

would increase the tare weight of vehicles by approximately 2.5t. The tabulated UDLs range would

then be between 18.70kN/m and 21.66kN/m. Under this loading, the proposed 0.5 x RL provides a

margin typically 15% above the most onerous tram and, therefore, still acceptable.

We recommend that the design should allow for a maximum static axle load of 12.5 tonnes. This

would result in a revised load model of two 175 kN axles, spaced anywhere from 1.6 m to 1.9 m,

whichever is most onerous.

3.1.2 Summary of vertical loads

To summarise, the proposed design vertical LRV loads for Abu Dhabi tramway shall be as

follows:


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• 0.5 x RL for normal vertical loading. This comprises a uniformly distributed load (UDL)

of 25 kN/m with a concentrated load of 100 kN for loaded lengths up to 100 m, both of

which shall be increased with a dynamic factor of either 1.2 for ballasted track or 1.4 for

non-ballasted track.

or

• Two 175 kN axle loads spaced 1.6 m to 1.9 m apart to represent the likely maximum

concentrated load of current or planned trams.

These loads are illustrated in Figure 2.

Figure 2: Proposed nominal vertical LRV loads

3.2 Horizontal loads from passenger trams

3.2.1 Lurching

Lurching is an effect that results form the temporary transfer of part of the live loading from one rail to

another, whilst the total load remains unaltered.

Clause 8.2.7 of BD 37/01 provides the following factors to account for lurching, which results from

the temporary transfer of part of the live loading from one rail to the other with the total track load

remaining unaltered.

0.56 of the track load shall be considered to act on one rail concurrently with 0.44 of the track load

acting on the other. The total load per track will continue to be based on 0.5 x RL UDL loading. The

effect of lurching will only be considered on one track where structural members support two tracks.

100 kN

25 kN/m

Proposed Condition No. 1

Proposed Condition No. 2

Up to 100m

1.6m to 1.9m

175 kN

175 kN


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3.2.2 Nosing

The nosing effect is caused by discontinuities on the rails. The gaps between the rails and the wheel

flanges due to lateral construction tolerances will cause the vehicles to apply a lateral force onto the

rails.

Clause 8.2.8 of BD 37/01 provides an allowance of 100 kN for lateral loads applied by trains to the

track. Where elements support more than one track a single load is deemed sufficient to represent this

effect.

The origin of this value is unclear, however the structural design shall include provision for this

100 kN horizontal load applied at right angles to the track.

The vertical effects of this load on secondary elements such as bridge bearings shall also be

considered.

3.2.3 Centrifugal

Clause 8.2.9 of BD 37/01 provides an equation for calculating centrifugal forces, only applicable to

tracks which are curved in plan. The centrifugal force is dependent on the greatest speed envisaged on

the curve, the radius of the curve and the static equivalent uniformly distributed load for bending

moment when designing for RU loading. In this clause, a value of P for static uniformly distributed

load of 40 kN/m is given for RL loading. However for the reasons given in section 3.1.1 of this

Technical Note, we propose to use 0.5 x RL, i.e. 25 kN/m, for calculating centrifugal forces. For the

purposes of these calculations, we propose that the speeds for Abu Dhabi Tramway are limited to

80 km/h generally, with 30 km/h restrictions at sections with adjacent passenger walkways or

platforms. Different speeds may be adopted at individual structures with prior approval from a

competent technical authority to suit site specific restrictions.

3.2.4 Summary of horizontal loads

To summarise, the proposed design horizontal LRV loads for Abu Dhabi tramway shall be as

follows:

• For lurching effects, 0.56 of the track load shall be considered to act on one rail

concurrently with 0.44 of the track load acting on the other. The total load per track will

continue to be based on 0.5 x RL UDL loading. The effect of lurching will only be

considered on one track where members support two tracks.

• For nosing effects, a single nominal load of 100 kN, acting horizontally in either direction

at right angles to the track at rail level and at such point in the span as to produce the

maximum effect in the element shall be applied.

• The centrifugal load shall be calculated with the following equation:

r

vF

t

c

×

+×=

127

)10(25 2

; where the centrifugal load (Fc)is given in kN/m, the greatest speed

(vt) is given in km/h and the radius (r) is given in metres.


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3.3 Longitudinal loads from passenger trams

3.3.1 Deceleration

Tram braking systems are often composed of 3 different types of brakes. These are dynamic, disc and

magnetic, and are designed especially for service braking, parking and emergency braking

respectively.

• Service braking is often via the regenerative use of the AC traction motors. It is common for

them to provide a retardation rate of about 1.3 m/s2 from the maximum permitted speed of

operation. This braking force will be applied at the powered bogies.

• The friction brake is used when the tram is in a park position.

• Trams are normally required to have hazard brakes fitted to provide a retardation rate of at

least 2.5 m/s2 and a maximum instantaneous retardation rate of between 3 and 4 m/s

2. This is

achieved through the use of electromagnetic braking. In this situation a 'shoe' either side of a

bogie, can apply over 5 tons of pressure onto the track, causing rapid deceleration. Magnetic

track brakes are intended to be primarily used for emergency applications.

Not all the types of braking systems are located on all bogies. Regenerative/rheostatic electric brakes

are often located on the motorised bogies, although electromagnetic emergency brakes are often

located on all bogies.

As the emergency braking gives the critical braking loads it will be assumed for Abu Dhabi Tram that

the brakes are located on every bogie. This means that the braking load has been assessed relative to

the entire tram loading.

The most severe braking forces are produced when the emergency braking is applied. This is often

achieved through a combination of the available braking methods. The magnetic brakes are applied to

all axles and are used as an emergency brake.

Due to the effectiveness of magnetic brakes and the lightness of the tram vehicles, the rates of

acceleration and deceleration are often higher than for other rail vehicles. For this reason, the

longitudinal loads are assessed specifically for tram vehicles.

(a) Braking efficiency

In BD37/01, both the RL and RU longitudinal braking loads are calculated as 25% of the load on the

braked wheels.

As force is a product of mass and acceleration, the deceleration that occurs from a braking system of

25% can be calculated as 0.25g = 2.453 m/s2. Therefore, BD37/01 assumes a rate of deceleration of

approximately 2.5 m/s2.

The maximum braking speed allowed for trams by the Railway Safety Principals and Guidance (Ref.

11) is 4 m/s2. Estimates have been made that the maximum permissible emergency deceleration is

0.47g for forward facing seated passengers, and 0.41g for side-facing seated passengers (Ref. 12).

These are equal to 4.61 m/s2 and 4.02 m/s

2.


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Location Service Braking

(m/s2)

Hazard Braking

(m/s2)

Nottingham Express Transit 1.3 -

Edinburgh-Proposed prototype 1.5 3.3

Sheffield -Stagecoach Supertram 1.5 3

Manchester Metrolink 1.3 3.93

Croydon Tramlink 1.2 3.15

Table 2 Rates of retardation achieved on British tram systems

The maximum deceleration rates of trams are currently around 3m/s2. Table 2 shows some examples

of braking systems that are in use or have been proposed in Britain. As braking systems are constantly

being developed and improved, it is assumed that the tram braking system is only limited by human

factors. Therefore the loads will be calculated assuming a deceleration rate of 4m/s2. This value takes

into account possible future developments in braking technology.

(b) Adjusted Braking Loads

A new set of braking loads shall be calculated for the tram loading using the following assumptions:

• Vertical loading = 0.5 x RL, limited to a maximum tram length of 80m

• Load on braking wheels is equal to total vertical loading over loading length

• A deceleration rate of 4m/s2

Longitudinal Force = Total mass acting on loading length x Acceleration

= (0.5 x RL loading / 9.81) x 4

Loaded Length RL Loading RL Braking Load Tram Braking Load

Up to 8m 400 kN 64 kN 150 kN

From 8 to 15m 50 kN/m 8 kN/m 150 kN

From 15 to 80m 50 kN/m 8 kN/m 10 kN/m

From 80 to 100m 50 kN/m 8 kN/m 800 kN

Over 100m 5000 kN 800 kN 800 kN

Table 3 Calculation of RL braking loads and Adjusted Tram braking loads

A minimum braking load is set for short spans to allow for the possible case where only a single

braking bogie is supported by the structure.

3.3.2 Acceleration

(a) Driving units

The standard tram designs have a set of 4 motors fitted to the two, two axle power bogies at the outer

ends. The central bogies are generally un-powered. As the topography in Abu Dhabi is relatively flat


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and the tramway planning guidelines have placed limits on the tramway vertical gradient it has,

therefore, been assumed that only the front and back bogies will be powered.

The document BD 37/01 uses a reduced value for the weight on the driving wheels. This is to allow

for the fact that not all the bogies have motors. As it will be assumed that some of the bogies will be

un-powered, the reduction factor used in BD37/01 RL Traction loading will be used in the evaluation

of Tram traction loading.

(b) Rate of acceleration

The assumed rate of acceleration for the tram under full RL loading used in BD37/01 may be

calculated in a similar way to the rate of retardation, using a factor of 0.30

Longitudinal traction force = Load on driving wheels x 0.30

Therefore assumed acceleration = 0.3 g = 2.943m/s2

Location Rate of acceleration

(m/s2)

Nottingham Express Transit 1.3

Edinburgh-Proposed prototype 1.5

Sheffield -Stagecoach Supertram 1.3

Manchester Metrolink 1.3

Croydon Tramlink 1.2

Table 4 Rates of acceleration achieved on British tram systems

Current rate of acceleration for trams tend to range from about 1 m/s2 to 1.5 m/s

2. Therefore, this is

safely within the values taken in BD37/01.

Acceleration capabilities are constantly being developed. A potential development is that it may be

possible to develop electromagnetism further so that it can be used to enhance both the acceleration

and the deceleration. It may be that acceleration capabilities increase so that the maximum acceleration

is governed by human comfort factors. As mentioned in the previous section, humans can take

accelerations up to 4 m/s2. However, it is only intended for a value this high to occur in emergency

braking and not in general use. Therefore, a maximum acceleration of 3 m/s2 is an acceptable value to

be assumed for tram loadings.

3.3.3 Summary of Longitudinal Traction Loads

The above concludes that a higher rate of retardation should be used when calculating braking loads

for trams. New values of these longitudinal loads have been calculated using a deceleration rate of 4

m/s2. These are summarised in Table 5.

The following longitudinal loads shall be used in design of structures supporting the tramway. It

shall be assumed that traction can occur on one track simultaneously with braking on any one

other track.


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Loaded Length LRV Braking Loads LRV Traction Loads

Up to 15m 150 kN 112.50 kN

From 15 to 80m 10 kN/m 7.5 kN/m

Over 80m 800 kN 600 kN

Table 5 Adjusted values for Braking and Traction Longitudinal Loads

3.4 Fatigue loads for passenger trams

All steel structures will be designed for fatigue loading in accordance with BS5400: Part 10 (Ref.

13).

Clause 9.0 provides two methods for assessing fatigue and the choice of method depends on the

information available. In this case, the information available for loadings and loading frequency

enables the use of Miner’s summation (clause 9.3.1) to be used for assessing fatigue.

3.4.1 Load intensity

Axel load distribution is particular to each tram design and number of bogies on each car. The typical

axle loads depend on the extent of passenger loading under the following conditions:

• Typical off peak period – AW1 (all seats occupied)

• Typical peak period – AW2 (4 persons/m2 standing)

• Crush laden – AW3 (6 persons/m2 standing)

Note that an occupation of 8 persons per square metre is assumed for strength design, but this extreme

condition would not be appropriate for consideration of cyclic loading.

The typical axle loads can be applied to the structure to calculate the worst load effects and therefore

the maximum stress in any given section of the structure. The weight of the vehicles studied for the

purpose of this report show a likely axle load under the following load conditions:

Loadcase Maximum bogie axle load

AW1 (all seats occupied) - Typical off peak period 7.675 t

AW2 (4 persons/m2 standing) - Typical peak period 9.145 t

AW3 (6 persons/m2 standing) - Crush laden 9.880 t

Table 6 Axle loads

The Abu Dhabi design LRV has not been confirmed and the tram fleet is likely to change during the

design life of the structures. Therefore, we recommend allowing flexibility for alternative trams with

potentially heavier loading and modifications due to extreme temperatures as described previously.

Unlike the maximum static axle load (12.5 t) which would be an extreme case, the fatigue loading

considers everyday service operation. A reasonable cyclical loading margin to apply would be a 25%

increase on the most onerous tare (empty) load form the reviewed trams for this study and this is

assumed in the following calculations.


18 ABC

Loadcase Maximum bogie axle load

AW1 (all seats occupied) - Typical off peak period 9.419 t

AW2 (4 persons/m2 standing) - Typical peak period 10.890 t

AW3 (6 persons/m2 standing) - Crush laden 11.624 t

Table 7 Adjusted axle loads

3.4.2 Load frequency

The proposed peak operational service for the Abu Dhabi tramway system is to be 30 trams per hour

per direction, operating during approximately 19 hours per day, from 05.30 am to 00:30 am the

following morning.

A frequency breakdown of peak and non-peak hours has not been provided at the time of issuing this

Technical Note, therefore, we have assumed that all trams, conservatively, carry the full AW3 load at

all times and on all lines.

For fatigue design, the following loads and frequencies will be applied:

• 19-Hour Peak Period (30 trams/ hour/ direction)

19 Hours AW3 loading = 19 x 30 = 570 trams/ day at AW3 per track

The total tram movements over 365 days per year are

• 208,050 trams at AW3/ year (365 x 570) per track

The axle load to apply is 125kN. Assume 8 axles per LRV for passenger trams.

3.5 Accidental loads for passenger trams

Derailment of LRVs can occur in several circumstances, including a steering mechanism failure, a

fault or wear in the rails, or vehicle collision. In the case of collision, it can occur between LRVs or

with other road vehicles, where the road is shared. The support structure needs to be designed for the

vertical load imposed by the LRV in its derailed location, and barriers to contain the LRVs require to

be designed to withstand the appropriate collision forces. Building structures in close proximity to the

tramway may be affected in the derailed condition and as such, they must be designed to withstand

such collision forces as well.

3.5.1 Vertical loads from derailed LRV

In the UK, Clause 8.5 of BD 37/01 (Ref. 10) outlines three conditions to be taken into account to

ensure the stability of the structure under vertical derailment loads.

These three conditions below shall be considered separately and are based on the RL loading specified

in Clause 8.5.2:

Condition (a) – For serviceability limit state, derailed coaches or light wagons remaining close to the

track shall cause no permanent damage.


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Condition (b) – For the ultimate limit state, derailed locomotive or heavy wagons remaining close to

the track shall not cause collapse of any major element, but local damage may be accepted.

Condition (c) – For overturning or instability, a locomotive and one following wagon balancing on the

parapet shall not cause the structure as a whole to overturn, but other damage may be accepted.

The loading applied for each of these conditions shall be as follows:

Condition (a), either a pair of vertical line loads 15 kN/m each, 1.4 m apart, parallel to the track

and applied anywhere within 2 m either side of the track centre line, or an individual

concentrated load of 75 kN applied anywhere within 2 m either side of the track centre line.

Condition (b), for ultimate limit state, four individual concentrated vertical loads each of 120 kN

arranged at the corners of a rectangle 2 m long by 1.4 m wide applied anywhere on the deck.

Condition (c), for overturning or instability, a single line vertical load of 30 kN/m over a 20 m

length applied along the parapet or outermost edge of the bridge anywhere along the span.

3.5.2 Horizontal loads from derailed LRV

The Railway Safety Principles and Guidance (RSPG), Part 2, Section G, Guidance on Tramways

published by the HSE (Ref. 11) has been reviewed for general recommendations for derailment loads.

Although, no specific loads are provided in RSPG to represent the effects of a derailed tram, the

document recommends adequate derailment containment including the provision of longitudinal pits

or drainage channels to contain a stray wheel.

It can be assumed that the trackform will incorporate such derailment containment channels, or

alternative wheel restraint such as a robust structural up-stand or keep rail.

Developers shall assume that derailment imparts a 100kN lateral point load to the trackform, to

be transmitted to the tramway support structure, and applied in conjunction with normal

accidental vertical loads.

Parapets or balustrades do not generally need to be designed to restrain a derailed tram but may

be designed for pedestrian or highway vehicle impact where appropriate.

It is anticipated that the Abu Dhabi tramway will be supported upon podium structures design by

developers, and structural elements from other sections of the buildings will be located near the tram

corridor.

Guidance on containment barriers is given in the text book “Bridge Loads” (Ref. 15). The magnitude

and line of action of a horizontal derailment load on a barrier element is dependant on several factors

including the lateral clearance from the track to the obstacle, and the friction coefficient between the

LRVs and the surface of the physical barrier.

There is little or no published guidance on impact loads from a derailed tram where the primary

derailment containment (channel or up-stand) has been ineffective. The American Concrete Institute

Committee Report ACI 358.1R-92 (Ref. 16) states in lieu of a detailed analysis to adopt a load equal

to 50% of the tram’s total weight, and we propose that this be adopted for particularly vulnerable

structures.


20 ABC

Designers shall assess and identify any structural elements within the vicinity of the tramway,

which, if they were to fail under LRV impact could lead to disproportionate collapse or loss of

life. These would typically include column supports to bridges over the tramway, or to adjacent

building structures.

All vulnerable structural elements located at or closer than 4.5 metres from the running edge of

the track shall be designed for impact loading to resist a point lateral force equivalent to 50 per

cent of a single LRV, acting at a height of 1 metre above floor level, and in any horizontal

direction. For the purposes of this clause, the tram weight may be assumed to be 25kN/m, over a

40m LRV, i.e. 1000kN, giving a 500kN impact force.

3.5.3 Horizontal loads from impact of other vehicles

The local effects of road or rail vehicle collision with supports to the tramway structure (including

piers and columns) and also the tramway deck superstructure require consideration.

Vehicle collision loads on supports to the tramway shall be considered for the design as

secondary live loads. This load shall be applied in combination with the permanent loads and the

appropriate primary live loads associated with it.

Clause 6.8.1 of BD 37/01 (Ref. 10) provides highway vehicle impact loads with their direction and

height of application, acting horizontally on the supports or superstructure. These are appropriate to

high-speed road vehicle impact e.g. where the tramway passes above a public highway.

Heavy rail impact loads shall be as agreed with the appropriate technical authority and applied where

the tramway passes above a heavy rail line.

Designers shall identify elements of the tramway superstructure or substructure that are

vulnerable to impact due to limited headroom (superstructure) or proximity to traffic

(substructure), and design these for appropriate collision loads. Alternatively, suitable barriers

may be located to protect the structure against impact.

In the case of multi-level carriageways, such as those encountered in multi-storey car parks, the

collision loads are to be considered for each level of carriageway separately, not together.

Different methods to determine the collision loading may be adopted at individual structures to

suit site-specific restrictions, subject to prior agreement with Department of Transport.

3.6 Loads from freight trams

At the time of writing this Technical Note it is not clear whether freight trams will run on the system,

and if so, on which parts. Worldwide, few freight tram systems exist, and we have based what follows

on information from the Dresden system summarised in Table 8.


21 ABC

Vehicle

Maker Vehicle Type

Location

(City)

Length

(m)

Vehicle Weight

(Empty)

Loaded Crush

(Fully laden)

Equivalent UDL

(kN/m)

Freight Tramways

Schalke CarGoTram Dresden 59.400 90t 158t 26.09

Table 8 Freight tramway vehicle loads

3.6.1 Vertical loads for freight trams

Due the limited information available on freight trams at the time of writing this Technical Note and

observing the data collected in Table 8, we conclude that LRV loading (i.e. 0.5 RL) is insufficient to

allow for freight trams; particularly if some redundancy is desirable for technological advances in tram

systems and location specific requirements on freight trams such as cooled units. A detailed review of

the tram network usage should be carried as soon as possible in order to identify the sections where it

would be desirable to provide for freight tram operation.

To cover freight vehicles and allow flexibility, we propose a loading of typically 50kN/m to be

appropriate, i.e. RL. For track carrying freight trams we recommend the use of BD37/01 (Ref. 1) for

light rail lines (RL loading).

The design of tramway structures supporting or providing access to freight trams shall allow for

vehicle load equal to full RL loading to BD37/01. RL loading on any two tracks simultaneously

shall be applied to these sections of track.

3.6.2 Horizontal loads for freight trams

For sections of track loaded with RL, the appropriate RL horizontal loads from BD 37/01 will be

applied.

3.6.3 Longitudinal loads for freight trams

For sections of track loaded with RL, the appropriate RL longitudinal loads from BD 37/01 will

be applied.

3.6.4 Fatigue loads for freight trams

Designers shall consider what further analysis for fatigue is required beyond that already stated

for passenger trams.

3.6.5 Accidental loads for freight trams

Derailment loads shall be the same as for RL in accordance to BD37/01.

Accidental loading of a derailed freight tram shall be full RL loading applied as two line loads

1.4m apart anywhere within 2m either side of the track centre line, including consideration of

the alternative RL axle loads (300kN and 150kN) where this gives an effect worse than the

uniform load (50 kN/m).


22 ABC

4 Maintenance and Construction Vehicle Loads

4.1 Vertical loads for maintenance and construction vehicles

4.1.1 Assumed vehicles

Information on vehicles to be used to construct or maintain the tramway is not yet available. We have

therefore drawn on our experience elsewhere in proposing the following requirements. A more

detailed review of system construction and maintenance requirements should be carried out as soon as

possible.

For track sections not involving ballast or access to ballast track, designers may assume

maintenance vehicles are restricted in weight to be no more onerous than passenger trams.

Therefore no further consideration is required.

Rail mounted maintenance could be carried out using a modified LRV, however the loads would be

less than those for a fully laden passenger tram and will therefore not be a governing case.

Maintenance can also be carried out using road/rail vehicles which again give lesser load effects than a

fully laden tram. We have assumed that in non-ballasted areas all heavy maintenance plant will cross

the bridges on rails and be limited to the loading conditions of a crush laden tram. Non rail access will

be limited to LGV class maintenance vehicles with 2 axles and less than 7.5 tonne gross vehicle

weight.

For ballasted track, we have made reference both to BD37/01 (Ref. 1) for light rail lines (RL loading)

and to typical ballast wagons and tamping plant operated in the UK.

Heavy rail ballast wagons (e.g. “Skako” type) impose loads up to 3 or 4 times that of the passenger

trams. We believe it is not economic to design the tramway for this loadcase, and therefore only

restricted plant can be permitted.

RL loading covers maintenance vehicles such as those shown in Figure 3, showing the layout and axle

configuration for work trains covered by RL loading. The 20 t hopper is a 7.88 m long vehicle with

two axle loads of 16.3 t (160 kN) at 3.96 m spacing, equating to a UDL of 41 kN/m. The tube battery

car is 16.85 m in length and applies a total axle load of 62.7 t (615 kN), equating to a UDL of

36 kN/m. The steam crane applies a total axle load of 63.2 t (620 kN) over a length of 16.77 m, a UDL

of 37 kN/m. The diesel electric crane applies a UDL of 30 kN/m (total axle load of 46.6 t (457 kN)

over 15.63 m). In addition to these vehicles, allowance for typical tamping plant such us those in

Figure 4 are also likely to be required. Therefore, designing the structure to a capacity of 0.5 x RL

design load would exclude the use of all the work trains described here.


23 ABC

Figure 3: Extract from BD37/01 showing works trains covered by RL loading


24 ABC

Figure 4: Typical tamping plant configuration

4.1.2 Summary of vertical loads

To cover all the vehicles in section 4.1.1 and allow flexibility to also operate alternative plant, we

propose a loading of typically 50kN/m to be appropriate, i.e. RL. However, we propose to adopt full

RL loading on one track coexistent with LRV loading on the other track as this restriction can readily

be implemented during maintenance operations and may lead to some economy in the design.

The design of tramway structures supporting or providing access to ballast track line shall allow

for maintenance vehicle load equal to full RL loading to BD37/01. RL loading on one track

coexistent with LRV loading on any one other track shall be applied to these sections of track.

4.2 Horizontal loads for maintenance and construction vehicles

For sections of track loaded with RL, the appropriate RL horizontal loads from BD 37/01 will be

applied.

Equivalent UDL

20.1 kN/m

Equivalent UDL

21.7 kN/m


25 ABC

4.3 Accidental loads for maintenance and construction vehicles

Derailment loads shall be the same as for the LRV i.e. 100kN applied horizontally.

Accidental loading of a derailed maintenance vehicle shall be full RL loading applied as two line

loads 1.4m apart anywhere within 2m either side of the track centre line, including consideration

of the alternative RL axle loads (300kN and 150kN) where this gives an effect worse than the

uniform load (50 kN/m).


26 ABC

5 Other Loads

5.1 Highway vehicles

Where tramway structures can additionally provide access to highway vehicles, they shall be

designed for both loads.

Generally, design highway loads are given in Abu Dhabi Municipality Roadway Design Manual

(Ref. 2).

Design shall assume whichever of the following gives the most onerous case:

• Highway loads only

• LRV loads only

• Mixed loads but LRV loads not shorter than 40m

Longitudinal and horizontal loads from highway vehicles and LRVs shall be considered

simultaneously.

5.2 Pedestrian loading

All public footways shall be designed for BD 37/01 pedestrian loads. Emergency, cess and

evacuation walkways shall be designed for the same loading unless agreed otherwise in

individual cases.

5.3 Wind loads

The wind loading required to be applied on a structure depends on the geographical location and

structure characteristics. Factors such as the topography and terrain of the surrounding area, and the

horizontal dimensions and cross-section of the structure or element under consideration determine the

loading to be applied.

The method described under BD37/01 or an agreed equivalent standard shall be used to

determine the wind loading to be applied.

For wind load coexistent with live load, designers shall assume trams to be 4m high. Apply wind

load to an assumed 4m high side face over the full length of the structure. This shall be assumed

to be transmitted to the deck by appropriate horizontal and vertical forces applied at each rail.

Further guidance for wind velocity values can be found in Abu Dhabi Municipality Road Design

Manual (Ref. 2) Part 3: clause 201.6, appropriate for this geographical location.

5.4 Temperature loading

Temperature loading on all structures shall be applied in accordance with Abu Dhabi

Municipality Road Design Manual (Ref. 2) Part 3: clause 201.8.

Any structures with an unjointed length greater than 100m shall require special discussion, as

thermal effects may lead to the need for unusual track joints and create difficulties for the future

design of the track and trackform


27 ABC

6 References

1. Design Manual fro Roads and Bridges (DMRB), The Highways Agency, HMSO,

February 2009.

2. Roadway Design Manual: Road and Bridges, Abu Dhabi Municipality, 2009.

3. “Load appraisal report for Merseytram”, ref 205066/205066/L1/STR/00/A, Mott

MacDonald, July 2004

4. “Design Loads & Spatial Parameters”, ref 221214/TNXX, Mott MacDonald, January

2008

5. “Report on Loading and Design Criteria for Tram Structures”, ref

241592/000/REP/003/B, Mott MacDonald, August 2008

6. “Guidance on Tramways: Railway safety publication”, Office of Rail Regulation, UK,

November 2006.

7. UIC Code 776-3R “Deformation of Bridges”, International Union of Railways, 1989.

8. BD 2/05 “Technical Approval of Highway Structures” DMRB Volume 1 Section 1

Part 1, 2005.

9. NR/SP/CIV/003 “Technical Approval of Design- Construction and maintenance of

Civil Engineering Infrastructure”, 2004

10. BD 37/01 “Loads for Highway Bridges”, The Highways Agency, HMSO, August

2002.

11. “The Railway Safety Principles and Guidance, Part 2, Section G, Guidance on

Tramways”, HSE, 2005

12. “Transportation Research Record: Effects of deceleration and rate of deceleration on

live seated human subjects”, Transportation Research Board Business Office, USA,

1977.

13. “Steel, concrete and composite bridges Part 10 – Code of practice for fatigue”, BS

5400 Pt 10, British Standards Institution, 1980

14. “Recommendations for the Design of Bridges”, GC/RC5510, Railtrack, August 2000

15. “Bridge Loads”: O’Connor, Colin and Shaw, Peter, SPON Press, 2000, pg 255.

16. “Analysis and Design of Reinforced and Prestressed Concrete Guideway Structures”,

Report ACI 358.1R-92, American Concrete Institute Committee, 1992.

17. “Assurance” Report 1-538 Issue A1, London Underground, 2008.

stmp add3_243011-f3-c3-tn01 - loading for tram structures rev_b[1]

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