TECHNICAL USER MANUAL CONARCH OVERBRIDGE STANDARD DESIGNS

(1)

TECHNICAL USER MANUAL

for

CONARCH OVERBRIDGE STANDARD DESIGNS

(2)

Summary

This Technical User Manual is applicable to the reconstruction of masonry arch overbridges using precast concrete conarch units. It provides guidance on the selection and application of Network Rail’s Suite of Standard Drawings. The Standard Designs and Details within these drawings will generally be used for reconstruction of existing structures; however they can be used for new-build applications.

Issue record

This Technical User Manual will be updated when necessary by distribution of a complete replacement.

A vertical black line in the margin will mark amended or additional parts of revised pages.

Revision Date Comments

(3)

Content

Section Description Page

1. Introduction 7

1.1. Conarch Suite Documents 7

1.1.1. Technical User Manual 7

1.1.2. Standard Design Inner & Edge Precast Concrete Unit Drawings 7

1.1.3. Standard Design Parapet Beam Precast Concrete Unit Drawings 8

1.1.4. Standard Detail Precast Concrete Unit Drawings 8

1.1.5. Standard Detail In-situ Concrete Drawings 8

1.1.6. Standard Details Drawings 8

1.1.7. Conarch Calculator 8

1.2. Use of Network Rail Standard Designs and Details 9

1.3. Safety/CDM and Environmental 9

1.3.1. General 9

1.3.2. Possession Plan 10

1.3.3. Design Risk Assessment 10

1.4. National Design Codes 10

1.4.1. General Design Requirements: 10

1.4.2. Actions and loadings: 10

1.4.3. Concrete design: 10

1.4.4. Abutment strength: 10

1.4.5. Geotechnical design 10

1.4.6. Bar bending schedule: 10

1.5. Network Rail Approval Documents 11

2. Executive Summary 12

2.1. Benefits of using the Standard Designs 12

2.1.1. At Each Bridge Location 12

2.1.2. Scheme Specific Designer 12

2.1.3. Precast Concrete Manufacturer 12

2.2. Geometrical Envelope 13 2.2.1. Span 13 2.2.2. Skew 13 2.2.3. Rise 13 2.2.4. Bridge Width 13 2.2.5. Construction Depth 13 2.3. Road Profile 13 2.3.1. Vertical Profile 13 2.3.2. Horizontal Profile 13 2.4. Gauge Clearances 14 2.5. Conarch Calculator 14 2.5.1. Layout Design 14

2.5.2. Reinforcement Scheduling Tool 15

3. Design Assumptions and Restrictions 16

3.1. Structural Analysis modelling & Actions 16

3.1.1. Structural Models 16

3.1.2. Actions 16

3.1.3. Verifications 17

4. Background of the Conarch Standard Design and Details 18

(4)

4.1.1. Conarch Unit Widths 18 4.1.2. Edge units 18 4.1.3. Inner units 18 4.1.4. Tie Bars 18 4.1.5. Parapet Beams 19 4.1.6. Parapet panels 19 4.1.7. Construction Depth 19 4.1.8. Capping Slab 20

4.1.9. Rear Vertical Saw Tooth Profile to Backfill Concrete 20

4.1.10. Concrete Specification and Nominal Cover to Reinforcement 20

4.1.11. Couplers 20 4.2. Existing Substructure 21 4.2.1. Abutment Thickness 21 4.2.2. Abutment Strength 21 4.2.3. Loading on Abutments 21 4.2.4. Substructure Restrictions 21

4.3. Main Railway Related Details 21

4.3.1. Soffit Profile & Clearances 21

4.3.2. Curvature and Clearance Requirements 22

4.3.3. Standard vehicle gauges 22

4.3.4. Analysis 23

4.3.5. Envelope profile 23

4.3.6. Electrical protection, earthing and bonding 23

4.3.7. Protection from stray currents 25

4.4. Ancilliary Railway Related Details 25

4.4.1. OHLE Fixings 25

4.4.2. Bridge ID Plates 25

4.5. Main Highway Related Details 25

4.5.1. Existing Masonry Bridge Widths 25

4.5.2. Existing Masonry Overbridge Reconstructions 25

4.5.3. Proposed New Overbridges 25

4.5.4. Internal Bridge Width 26

4.5.5. Road Restraint Systems 27

4.5.6. Highway Alignment and Cross Fall Criteria 28

4.5.7. Road Surfacing Material 30

4.5.8. Asphaltic Plug Joints 30

4.5.9. Footpath Construction 30

4.5.10. Road Drainage Details 30

4.5.11. Sub-Surface Drainage 31

4.6. Ancilliary Highway Related Details 31

4.6.1. Service Duct Size and Location 31

4.6.2. Lighting Columns Fixings 31

4.7. Conarch calculator 31

4.7.1. Input Data 31

4.7.2. Layout Design 32

4.7.3. Reinforcement Scheduling Tool 32

4.8. Standard Drawings & Details 32

4.8.1. Standard Design Precast Concrete Unit Drawings 32

4.8.2. Standard Design Parapet Beam Precast Concrete Unit Drawings 33

(5)

5. Site Construction Methodology 35

5.1. Construction Guidance 35

5.2. Conarch Unit Weights 36

5.3. Temporary Restraint Ties and Beams 36

5.3.1. Temporary Restraint Ties 36

5.3.2. Temporary Restraint Beams 37

5.4. Trial erection 37

5.5. Site Installation 37

5.5.1. Cill Units & Bearings 37

5.5.2. Inner and Edge Units 37

5.5.3. Shear Key Joints 38

5.5.4. In-situ concrete and waterproofing 38

5.5.5. Existing Wing Walls 39

5.5.6. Abutment Backfill 39

5.5.7. Transition Parapet Slabs & Parapets 39

5.5.8. Kerbs, Road and Pavement Surfacing and Drainage 39

6. Scheme Specific Design Process 40

6.1. Background Data 40

6.2. Initial Feasibility Flow Chart 40

6.3. Site Surveys 41

6.4. Feasibility Study 41

6.5. Conarch Calculator 42

6.6. Further Site Surveys 43

6.7. Detailed Design 43

6.8. Re-use of existing sub-structure 44

6.8.1. Criteria 1 44

7. Scheme Specific Designers Responsibilities 47

7.1. Scheme Specific details 48

7.2. Standard Designs and Details 48

7.2.1. Conarch Calculator 48

7.2.2. Standard Design Precast Concrete Unit Drawings 48

7.2.3. Standard Detail Precast Concrete Unit Drawings 48

7.3. Site Specific Form A 49

7.3.1. Contents Summary 49

ANNEXE 1 Schedule Of Standard Drawings

ANNEXE 2 Standard Vehicle Gauges & Profile Envelope Sketches

ANNEXE 3 Excel Spread Sheet For Envelope Profiles

ANNEXE 4 Conarch Structure Details

ANNEXE 5 Conarch Bridge Span Variance Sketch

ANNEXE 6 Conarch Bridge Deck Width Variance Sketch

ANNEXE 7 Construction Sequence

ANNEXE 8 Road Vertical Profile Envelopes

ANNEXE 9 Design Risk Assessment

(6)

Definitions

Span: clear distance between inside face of precast units, on elevation

Clearance: clear distance between inside face of parapet panels,

perpendicular to the road

Carriageway: distance between kerbs, road width

Conarch calculator: active design spreadsheet

Tunnel: soffit profile of precast units

(7)

1. INTRODUCTION

A library of Standard Designs and Details for the reinforced concrete Conarch Units for masonry arch overbridge reconstructions has been produced. This document contains guidance on the use of these standard drawings, including advice on the following:

• The elements and options contained within the Suite of Standard Designs and

Details.

• Instruction on configuring a design using the Standard Designs and Details.

• Specific design restrictions and design assumptions.

• Advice on circumstances when the Standard Designs and Details may not be used.

• Installation guidance.

• Safety/CDM/environmental issues.

The library will be maintained and distributed by Network Rail to its stakeholders and key external suppliers for adoption across the network at a national level.

1.1. CONARCH SUITE DOCUMENTS

The conarch suite of Standard Designs and Details includes the following documents:

1.1.1. Technical User Manual

This document provides the following information:

• Details of the design process to be followed.

• Details of the standard designs and how they are to be incorporated into the

Scheme Specific Design.

• Details of the standard details and how they are to be incorporated into the Scheme

Specific Design.

• Instructions on the use of the ‘Conarch Calculator’ during the scheme specific design

process.

1.1.2. Standard Design Inner & Edge Precast Concrete Unit Drawings

General arrangement and reinforced concrete detailed drawings for the Inner and Edge Units for the following spans and skews:

• 7.4 metre span

o Square span

o 15° skew span both left and right skew

• 8.4 metre span

o Square span

• 9.4 metre span

o Square span

(8)

1.1.3. Standard Design Parapet Beam Precast Concrete Unit Drawings

General arrangement drawings for the Parapet Beams between a curved and horizontal top profile for the following spans and skews:

• 7.4 metre span

o Square span

• 8.4 metre span

o Square span

• 9.4 metre span

o Square span

Reinforcement layout drawings for the Parapet Beams for the following spans and skews:

• 7.4 metre span

o Square span

• 9.4 metre span

o 45° skew span right skew

1.1.4. Standard Detail Precast Concrete Unit Drawings

Generic general arrangement and reinforced concrete detailed drawings for the Parapets, Transition Parapet Edge Upstand Beams and Cill Units.

1.1.5. Standard Detail In-situ Concrete Drawings

Generic general arrangement and reinforced concrete detailed drawings for the Backfill Reinforced Concrete, Capping Slab Reinforced Concrete and Transition Parapet Slab Reinforced Concrete.

1.1.6. Standard Details Drawings

Generic general arrangement drawings for the following elements:

• Construction Sequence

• Concrete Finishing Details

• Lifting Details

• Waterproofing details

• Road Surfacing details

• Transition Parapet layout details

1.1.7. Conarch Calculator

The Conarch Calculator is an active spread sheet to assist the Scheme Specific Designer with the detailing of the replacement bridge structure. The spread sheet has two sections as follows:

(9)

This section allows the scheme specific designer to input the data of the existing structure and will then provide layout details of the proposed conarch structure components.

• Precast Reinforced Concrete Scheduling Tool

This section will then provide the reinforcement schedules for the Inner Units, Edge Units, Parapet Beams, Parapet Panels and Cill Beams as generated from the layout calculator.

1.2. USE OF NETWORK RAIL STANDARD DESIGNS AND DETAILS

The following flowchart demonstrates the use of the Technical User Manual and Standard Design and Standard Detail Drawings. The Designer should analyse the constraints and requirements that exist for the specific project site. This information should be used in conjunction with the design advice contained within the Technical User Manual, to decide which elements can be taken from the Suite of Standard Designs and Details and which items, if any, need bespoke design. This Designer output, and the series of standard drawings can be combined to produce the final overbridge solution.

1.3. SAFETY/CDM AND ENVIRONMENTAL

1.3.1. General

The general (non site specific) risks associated with the bridge design, construction and operation are listed in the Designer Risk Assessment, Appendix 9. In addition there may be others arising from site-specific considerations, such as the presence of Overhead Line Equipment (OHLE) or vulnerable services.

Environmental issues can only be determined on a site by site basis but should include looking into the effect the additional land required for the ramp will have on the locality, whether the protective coating needs to be changed to avoid the possibility that its renewal may contaminate watercourses and the aesthetic effect of the bridge’s presence, which may have requirements for bridge colouration or other details.

Technical User Manual Scheme Specific Designer Input Conarch Design Solution Conarch Calculator Specific Site Requirements Standard Details Standard Drawings

(10)

The effect of renewing the protection scheme on the environment, particularly any watercourses, should be taken into consideration during the selection of the elements of the protection scheme.

1.3.2. Possession Plan

Availability and lengths of possessions will vary from site to site. The longest single element of the reconstruction works will be the demolition of the existing structure and it is anticipated that a minimum possession length of 26 hours will be required for the demolition of a single span two lane bridge. The reconstruction process can be undertaken with individual or a number of Conarch Units being erected in a series of short Rules of Route Possessions, or all the conarch units erected in a single long possession if available.

1.3.3. Design Risk Assessment

The generic design risk assessment of the Standard Designs and Details is included in Annex 9 of this document. It is for the Scheme Specific Designer to take responsibility for the document and amend the document by adding site specific risks or deleting risks as they designed out.

1.4. NATIONAL DESIGN CODES

The design was carried out to Euro Code (EC) and to EC National Annexes (EC NA) using the following documents:

1.4.1. General Design Requirements:

• EC0 and EC NA0 Basis of structural design were used.

1.4.2. Actions and loadings:

• EC1 1.1 and EC NA1 1.1 Densities, self-weight, imposed loads for buildings

• EC1 1.3 and EC NA1 1.3 Snow loads

• EC1 1.4 and EC NA1 1.4 Wind actions

• EC1 1.5 and EC NA1 1.5 Thermal actions

• EC1 1.6 and EC NA1 1.6 Actions during execution

• EC1 1.7 and EC NA1 1.7 Accidental actions

• EC1 2 and EC NA1 2 Traffic loads on bridges

1.4.3. Concrete design:

• EC2 1.1 and EC NA2 1.1 General rules and rules for buildings

• EC2 2 and EC NA2 2 Concrete bridges, Design and detailing rules

1.4.4. Abutment strength:

• EC6 1.1 and EC NA6 1.1 General rules for reinforced and unreinforced masonry

structures

1.4.5. Geotechnical design

• EC7 1 and EC NA7 1 General rules

1.4.6. Bar bending schedule:

(11)

1.5. NETWORK RAIL APPROVAL DOCUMENTS

The following Network Rail documents form part of the design approval process:

• Network Rail Form A document signed by DPE Bridges on 24th September 2008

• Tony Gee Addendum to Form A Document no. L109004/501/Addendum No.1 –

Alternative Conarch Design dated 26th

May 2009.

• Tony Gee Addendum to Form A Document no. L109004/501/Addendum No.2 –

Eurocode Requirements dated 18th

(12)

2. EXECUTIVE SUMMARY

To improve the efficiency in terms of time scales and driving down the costs of the reconstructions of masonry arch overbridges required as part of gauge enhancement and overhead electrification schemes, the Conarch Unit Standard Design Project has developed in addition to a Suite of Standard Drawings and Details a site specific design procedure that will suit a large range of bridge geometrical layouts. The site specific design procedure includes an active design spread sheet (Conarch calculator) that the Scheme Specific Designer uses to determine the basic structural layout parameters and the reinforcement schedules of the main precast units required for each structure.

2.1. BENEFITS OF USING THE STANDARD DESIGNS

2.1.1. At Each Bridge Location

The major benefits at each bridge location are as follows:

• Increased railway gauge clearance beneath the structure for both gauge enhancement

and OHLE electrification schemes with minimum road profile changes across the structure.

• Flexible geometry:

• Existing bridge spans between 7.4 and 9.4 metres

• Existing skews between 0 to 45º, both left and right hand

• Existing internal bridge widths between 4.5 and 12.5 metres

• High containment parapets (H4a) are provided for each structure with standard

details for the approach parapet transitions.

• Significant reduction in design time associated with the use of the standard designs

for the precast units and associated standard details which can be generated utilising the Conarch Calculator.

2.1.2. Scheme Specific Designer

The major benefits to the Scheme Specific Designer are as follows:

• Initial feasibility of the overbridge reconstruction using the conarch units can be

undertaken in a short timescale utilising the Conarch Calculator.

• All precast conarch units have been designed with available reinforcement schedules

available for the Inner Units, Edge Units, Parapet Beams, Parapet Panels and Cill beams which can be generated utilising the Conarch Calculator.

• Significant reduction in design time associated with the use of the standard designs

for the precast units and associated standard details.

2.1.3. Precast Concrete Manufacturer

The major benefits to the precast concrete manufacturer are as follows:

• Units have a common central curved Soffit ‘Tunnel’ Profile perpendicular to the

tracks with the two support legs formed with straight vertical and sloping sections. The span range is achieved by varying the height of the vertical and the length of the sloping components of the legs.

• For all spans the common central curved Soffit Tunnel Profile is utilised for a length

of 7.4 metres perpendicular to the track.

• For spans between 7.4 and 9.4 metres extension straight side Soffit Shutters formed

of vertical and sloping sections are added to the main soffit tunnel unit to suit the specific site geometry.

(13)

• High degree of standardisation on reinforcement layouts and details.

2.2. GEOMETRICAL ENVELOPE

The project allows for the conarch units to be produced within the following parameters:

2.2.1. Span

Internal face of unit span range is between 7.4 and 9.4 metres.

2.2.2. Skew

Skew range is between 0º (square) and 45º both right and left hand.

2.2.3. Rise

Rise from foot of unit to crown of arch is 2.2 metres.

2.2.4. Bridge Width

The internal width at road level between parapets can extend from a minimum width of 4.500 metres (14ft 9¼in), up to any required width by varying the width of the Inner Units (900 to 1250mm) except for a small zone between 5.220 metres (17ft 1½in) and 5.360metres (17ft 7in). If a bridge width is required in this zone then the scheme specific designer will need to consider a small increase in the bridge width with the cill units extending over the end of the abutments by up to 70mm.

2.2.5. Construction Depth

The minimum construction depth at the crown of the arch is 575mm which is formed of the following items:

• Road surfacing 100mm

• Waterproofing & Protection 25mm

• Capping slab concrete 150mm

• Conarch unit 300mm

2.3. ROAD PROFILE

2.3.1. Vertical Profile

The minimum road vertical curve radius is 20.670 metres with the minimum construction depth at the crown for all the square spans. For the skew spans the minimum vertical curve will be dependent on both the internal width of the bridge and the skew. For internal bridge widths between the parapets of 7.620 metres the minimum vertical curve for varying skews are as follows:

• 15º 31.000 metres

• 30º 48.700 metres

• 45º 86.000 metres

To achieve a constant section of road surfacing material across the structure, the difference between the underside of the road material profile and the top of the conarch units is made up by varying the thickness of the capping slab.

2.3.2. Horizontal Profile

It is assumed that at most bridges there will be no requirement for any major changes to the highway horizontal alignment except for minor local changes to suit the run on to and the run off from the bridge.

(14)

The ideal alignment is expected to be straight across the bridge deck, but any existing curvature can be replicated within the existing width of the bridge.

2.4. GAUGE CLEARANCES

The Conarch Soffit Tunnel Profile has been designed to suit a double track railway (standard 1970mm sixfoot) and be clear of the gauge envelopes for both straight and curved track using the following parameters from GE/RT8073:

• The dynamic vehicle profiles listed in GE/RT8073 have been enlarged to include for

the end and centre throw from a 360 metre radius curve.

• The straight track is set out about the centre line of the structure, with the curved

track translated side ways to include for the cant and the curvature through the opening.

• The versine (offset) for a 360 metre curve through the maximum bridge width of

12.5 metres is 54mm.

• The dynamic vehicle profiles are shown with 150mm of track cant.

• The clearance required to the dynamic vehicle envelopes for both the curved and

straight track are to have the normal clearance of 100mm plus an additional 50mm to include for future track lifting and or slewing.

• In addition an OHLE electrification envelope profile with 4640x1435mm pantograph

is added.

• This gives a minimum headroom from the highest rail to the crown of the arch as

follows:

o Non–OHLE electrified track 4455mm

o OHLE Electrified track 4790mm

The Scheme Specific Designer has the opportunity to change any of the above defined criteria which will have any affect on the highest rail to crown of the conarch dimension as follows:

• If the tracks pass through the bridge opening offset to the centre line then the

vertical distance will increase.

• If the track curvature is reduced (radius is increased) and the cant reduced then the

vertical dimension will reduce.

• If the track curvature is increased (radius is reduced) and the cant maintained then

the vertical dimension will increase.

• If the sixfoot is reduced then the vertical height will reduce, likewise if the sixfoot

dimension is increased the vertical height will increase.

2.5. CONARCH CALCULATOR

The Conarch Calculator is an active spread sheet to assist the Scheme Specific Designer with the detailing of the replacement bridge structure.

2.5.1. Layout Design

The Conarch Calculator is used to produce the following layout data which will be used by the Scheme Specific Designer to layout the proposed bridge structure on the detailed design drawings:

• The number required and widths of the Inner Conarch Units and the size of the gaps

between.

• A section through the bridge perpendicular to the tracks showing the proposed

railway gauge relative to the conarch.

(15)

• A section through the bridge showing the highway vertical longitudinal profile across

the bridge.

• A cross-section through the bridge showing the layout of the carriageway and

verges.

• An elevation of the parapet beam taking into consideration the bridge skew.

• Lifting details for the main units including the location of the cast in lifting anchors

and unit tie bar requirements.

• Abutment loading from the new structure.

2.5.2. Reinforcement Scheduling Tool

The Conarch Calculator is used to produce the reinforcement schedules to suit the span and skew of the scheme specific bridge for the following units:

• Edge Units

• Inner Units

• Parapet Beam And Parapet Panels

• Cill Units

• Transition Parapet Edge Upstand Beams

The Conarch Calculator provides reinforcement details to suit the span and skew of the scheme specific bridge for the following elements:

• Shear key joints

• Backfill concrete including the rear vertical saw tooth profile

• Capping slab

(16)

3. DESIGN ASSUMPTIONS AND RESTRICTIONS

3.1. STRUCTURAL ANALYSIS MODELLING & ACTIONS

3.1.1. Structural Models

3.1.1.1 LUSAS model

LUSAS, a three dimensional structural analysis programme was used to undertake the structural analysis of the conarch models.

3.1.1.2 Model Geometry

Twelve models were constructed and analysed to cover the following span and skew options as detailed below:

• 7.4 metre span, with square span, 15º skew, 30º skew and 45º skew.

Each model was formed of two conarch Edge Units 1725mm wide and four conarch Inner Units 1250mm wide to provide a bridge arrangement that provided a nominal width between the parapets of 7.62 metres (25 feet).

3.1.2. Actions

3.1.2.1 Dead Load & Superdead Load

The dead load densities of the conarch structure were taken as follows:

• Reinforced concrete 28kN/m³

• Asphalt 24kN/m³

• Masonry 25 kN/m³

3.1.2.2 Wind Load, Thermal Action and Snow Load

The following wind loads and thermal loads cover the worst conditions in the UK up to an altitude of 452 metres at the Druimachdar summit on the line between Perth and Inverness and represent one hundred and twenty year return period.

• The maximum wind map velocity has been taken as 30m/s given in EC1 1.4: Figure

NA.1; exposure factor as 4.2 given in EC1 1.4: Figure NA.7 and wind load factor as 4.0 given in EC1 1.4: NA.2.49.

• Minimum and maximum air shade temperatures have been taken as -21°C and

+35°C given in EC1 1.5: Figure NA.1 & NA.2.

• Snow load may generally be ignored in the UK as EC0 NA.2.3.3.3.

3.1.2.3 Traffic Load

• Load Model 1: Tandem System (TS) in Lane 1 300kN, Lane 2 200; UDL System in

Lane 1 9.0 kN/m2

, other lanes 2.5 kN/m2

given in EC1 2: 4.3.2.

• Load Model 2: Single Axle (SA) 400kN given in EC1 2: NA.2.15.

• Load Model 3: Special Vehicle (SV) as VS196, 1500 kN given in EC1 2: NA.2.16.

• Load Model 4: crowd loading as 5.0 kN/m2 given in EC1 2: 4.3.5.

• LM1, LM2, LM3 and LM4 were applied to the model.

(17)

3.1.2.4 Accidental Actions

• Vehicles on footway: 200kN axle load given in EC1 2: 4.7.3.1.

• Collision force on kerbs: 100kN load given in EC1 2: 4.7.3.2.

• Collision to vehicle restrain system: 600kN transverse, 100kN longitudinal and 175

vertical force given in EC1 2: NA.2.30.

• Load Model 2: Single Axle (SA) 400kN given in EC1 2: NA.2.15.

• Load Model 3: Special Vehicle (SV) as VS196, 1500 kN given in EC1 2: NA.2.16.

3.1.2.5 Differential Settlement – Lateral Displacement

Each model allowed for long term rearward movement of a total of 15mm at each abutment.

3.1.3. Verifications

3.1.3.1 Ψ Factor

Combinations of actions were defined as given in EC0: NA.2.3.6.

3.1.3.2 Ultimate Limit State

• EQU : Loss of static equilibrium of the structure or any part of it considered as a

rigid body given in EC0: 6.4.1.

• STR: Internal failure or excessive deformation of the structure or structural

members given in EC0: 6.4.1.

• GEO: Failure or excessive deformation of the ground where the strengths of soil or

rock are significant in providing resistance given in EC0: 6.4.1.

• FAT : Fatigue failure of the structure or structural members given in EC0: 6.4.1.

3.1.3.3 Serviceability Limit State

(18)

4. BACKGROUND OF THE CONARCH STANDARD DESIGN

AND DETAILS

4.1. CONARCH UNIT DETAILS

The conarch units have been designed to suit overbridge clear square spans of between 7.4 and 9.4 metres with a skew up to 45°, with a rise at the crown of 2.2 metres. Sections through the 7.4, 8.4 and 9.4 metre spans for both the Inner and Edge Units are shown on a sketch in Annexe 6 of this document.

The Soffit Profile perpendicular to the tracks has been designed so that the centre section which extends 3.7 metres either side of the centre line is common for the whole span range.

This section covers the full width of the smallest span of 7.4 metres and to complete the 7.4 metre span conarches vertical legs are provided on each side.

The spans are increased up to 9.4 metres by extending the ends of the central sections tangentially downwards on a slope in conjunction with reducing the height of the vertical leg to provide the constant arch rise. The intermediate span of 8.4 metres has legs which have the upper section inclined and the lower section vertical. The maximum span of 9.4 metres has the majority of the leg inclined with a small vertical section at the bottom.

This means that a single soffit shutter, Tunnel Profile, supporting the central common section can be constructed by the precast concrete manufacturer, with varying leg shutters at each end to suit the bridge span being cast. See sketch in Annexe 5 of this document.

4.1.1. Conarch Unit Widths

The width of the Edge and Inner Arch Units have been sized to suit the bridge widths identified in Section 4.4.1, taking into consideration the effect that the unit weight will have on the delivery to site, craneage and erection methodology.

4.1.2. Edge units

The Edge Units are of a constant width of 1745mm and have been developed to accommodate a separate parapet beam which supports either a masonry sandwich or reinforced concrete high containment parapet (H4a).

The Edge Units will be manufactured off site and brought to site as a single unit and lifted in to place.

4.1.3. Inner units

The Inner Units have been designed with a maximum width of 1250mm with standard reinforcement schedules to suit this width, but to allow the flexibility of varying bridge widths the site specific designer can specify widths down to 900mm. There is no required change to the reinforcement schedules except that (i) the external links which are formed from two ‘U’ bars decrease in length and increase in number and (ii) the longitudinal reinforcement will need to be displaced side ways and re spaced to suit the revised width.

4.1.4. Tie Bars

Temporary tie bars are required to be provided to the edge and inner units to maintain their geometry until the units have been erected.

(19)

4.1.5. Parapet Beams

Dependant on the span, the Parapet Beam and Parapets can be transported to site as a single unit and lifted in or for the larger spans the Parapet Beam can be transported to site as a single unit, set up on the ground adjacent to the bridge allowing the Parapets to be constructed before being lifted into place. For either situation the parapet beam needs to be supported for its full length when the parapet panels are constructed.

The Parapet Beam is designed to be supported off a return wall directly above the abutments with the spandrel wall set back to the inside face of the Parapet Beam. This alleviates the problem of match casting the Parapet Beam onto the Edge Unit and allows the Parapet Beam to be cast separately from the Edge Unit. A standard shear key joint will be provided between the Parapet Beam and the Edge Unit central section. In addition reinforcement couplers will be provided at close centres along the top of the inside face of the parapet beam. This is to allow site transverse reinforcement to be fixed as part of the in-situ capping slab over the Inner Units to transfer the high transverse loads from the high containment parapets into the main bridge structure.

The Parapet Beams have been designed to support a high containment Parapet up to a maximum height of 1.850 metres above the adjacent verge/footpath level, with the road longitudinal profile varying from the minimum radius up to a horizontal profile. To suit the horizontal road longitudinal profile, the Parapet Beam is increased in depth at the ends.

4.1.5.1 Infill concrete top profile

The top profile of the lower surface on the parapet beam will be designed to match the top profile of the infill concrete and capping slab, which in turn is determined from the design vertical road alignment and surfacing for each individual site.

4.1.5.2 Parapet beam top profile

The parapet beam top profile (upper top surface) forms the interface with the parapet panels. For any given bridge, the profile is a constant height above the infill concrete top profile, but the height adopted can vary dependent on the following::

• The width and cross fall on the verges/footpaths

• Increase in depth (maximum 95mm) of verges/footpaths to accommodate service

ducts.

4.1.6. Parapet panels

The conarch superstructure is designed to support high containment parapets (H4a) up to a maximum height of 1825mm above the adjacent footpath/verge level

4.1.6.1 Type of parapet

The conarch suite provides typical details of masonry sandwich or reinforced concrete parapets.

4.1.6.2 Length and Number of panels

The length and the number of Panels is dependent on the total length of the Parapet Beam.

4.1.7. Construction Depth

The minimum construction depth at the crown of the arch is 575mm which is formed of the following items:

• Road surfacing 100mm

(20)

• Capping slab concrete 150mm

• Conarch unit 300mm

4.1.8. Capping Slab

For the square span structures with the minimum road curvature the capping slab has a constant thickness of 150mm across the conarch units, with a constant section through the road surfacing material. For all the other road profile conditions, to achieve a constant section of road surfacing material across the structure, the difference between the underside of the road material profile and the top of the conarch units is made up by varying the thickness of the capping slab.

4.1.9. Rear Vertical Saw Tooth Profile to Backfill Concrete

To provide adequate horizontal restraint to the ends of the conarch units parallel to centre line of the units from the abutment backfill material a vertical saw tooth profile is required. The rear face of the in-situ concrete saw tooth profile is set perpendicular to the centre line of the conarch units and is the same width as the conarch unit, with the depth of the side surfaces increasing with the skew. At the acute corners of skew bridges the transverse tie bars from the parapet beams are turned down into the back fill concrete to provide the appropriate anchorage.

4.1.10. Concrete Specification and Nominal Cover to Reinforcement

The reinforced concrete grade and cover has been derived as follows:

4.1.10.1 Concrete Specification

The concrete specification for all precast concrete units and insitu concrete is to be:

• Class C40/50

• Nominal maximum aggregate size 20mm

• Maximum water/cement ratio 0.45

• Minimum cement content 360kg/m³

4.1.10.2 Nominal Cover to Reinforcement

The nominal cover to the reinforcement is in accordance with BS EN 206-1. Exposure classes are as follows:

• XC1 – Nominal Cover 30mm

• XD1 – Nominal Cover 40mm

• XF2 – Nominal Cover 60mm

The nominal cover includes a fixing tolerance as follows:

• Precast concrete +/- 5mm

• Insitu concrete +/- 10mm

4.1.11. Couplers

Reinforcement couplers are required to be used for the continuity of the main transverse reinforcement in the top of the capping slab from the parapet beams. It is proposed to use full strength parallel threaded screwed couplers such as Ancon Bartec Type A couplers or similar approved in the central area where the connecting bars can be rotated and Ancon Bartec Type B couplers or similar approved at each end where the connecting bars cannot be rotated.

(21)

4.2. EXISTING SUBSTRUCTURE

The following assumptions have been made with regard to the existing abutments:

4.2.1. Abutment Thickness

It has been assumed that the minimum abutment thickness is 1200mm for a square span increasing proportionally up to 1750mm for a 45º skew span. It is for the site specific designer to verify the thickness of the abutments through coring, see section 6.8.

4.2.2. Abutment Strength

It has been assumed that the existing masonry abutments have a minimum strength of clay masonry units with M6 mortar.

4.2.3. Loading on Abutments

The following schedules identify the loading from the twelve analysis models at the underside of the cill units.

The Scheme Specific Designer will need to check the interpolated value taken from the table below to suit the site specific span and skew against the calculated capacity of the existing abutments on site including the overall stability. See section 6.8.

The following table defines the load required to be transferred into the abutments for the twelve structural models. The table shows the GEO loading, which is “failure or excessive deformation of the ground where the strengths of soil or rock are significant in providing resistance” (EC0 6.4). In simplistic terms: safety factor of dead load is 1.00; the live load is 1.15; wind 1.45 and thermal actions 1.30.

Skew 7.4m Span 8.4m Span 9.4m Span

GEO Vertical load (kN) Horizontal load (kN) Vertical load (kN) Horizontal load (kN) Vertical load (kN) Horizontal load (kN) Square 2,988 3,137 3,145 2,983 3,463 2,932 15º 3,095 3,087 3,255 2,916 3,575 2,624 30º 3,294 2,867 3,495 2,480 3,922 2,976 45º 3,760 2,198 4,141 2,993 4,335 3,336 4.2.4. Substructure Restrictions

Actual substructure restrictions will need to be determined by the Scheme Specific Designer as following:

• Comparing the existing masonry arch bridge loading on to substructure with that

identified in this document for the new structure.

• Any available ground investigation information.

• General condition of existing bridge.

4.3. MAIN RAILWAY RELATED DETAILS

4.3.1. Soffit Profile & Clearances

The soffit profile of the conarch unitss perpendicular to the tracks has been developed in consultation with the Network Rail Gauging Engineer at York to be clear of all the vehicle profiles detailed in Railway Group Standard GE/RT8073 and the minimum headroom

(22)

required for future electrification of 4640mm as defined in section A.8.1a Notes on Standard Structure Gauge of the Track Design Handbook NR/L2/TRK/2049 issue 11. All eleven standard vehicle gauges have been reviewed and an envelope produced for both straight and curved track.

4.3.2. Curvature and Clearance Requirements

Gauge envelopes have been developed for both straight and curved track using the following parameters:

• The dynamic vehicle profiles listed for straight track have been generated from the

railway standard.

• The dynamic vehicle profiles for the curved track are based on the straight track

profiles enlarged to include for the end and centre throw from a 360 metre radius curve.

• The clearance required to the dynamic vehicle envelopes for both the curved and

straight track are to have the normal clearance of 100mm plus an additional 50mm to include for future track lifting and or slewing.

The above envelopes were then plotted on bridge openings with the following parameters:

• Two tracks 3405mm apart (1970 sixfoot), for both straight and curved track.

• The minimum curve radius of 360m was plotted with the maximum cant of 150mm.

• The straight track is set out about the centre line of the structure, with the curved

track translated side ways to include for the cant and the curvature through the opening.

• The versine (offset) for a 360 metre curve through the maximum bridge width of

12.5 metres is 54mm.

• Electrification envelope profile with 4640x1435mm pantograph.

• Range of span from 7.4m to 9.4m.

• Height of concrete conarch unit 2.2m.

This gives a minimum headroom from the highest rail to the crown of the arch as follows:

• Non–OHLE electrified track 4455mm

• OHLE electrified track 4790mm

4.3.3. Standard vehicle gauges

The eleven available vehicle gauges are given in GE/RT8073’s Appendices. The coordinates are given for static and dynamic cases, incorporating with 35m/s side wind load, and the overthrows’ formulas on curved track are given for each different profile.

Upper gauge: Table A.2

Lower gauge: Table A.3

W6a

Overthrow: 3.2.3.1

Upper gauge: Table B.2

Lower gauge: Table B.3

W7

Overthrow: 3.3.3.1

Upper gauge: Table C.2

W8

(23)

Overthrow: 3.4.3.1

Upper gauge: Table D2

Lower gauge: Table D.3

W9

Overthrow: 3.5.3.1

Upper gauge: Table E.2

Lower gauge: Table E.3

W9+ Overthrow: 3.6.3.1 Gauge: Table F.3 W10 Overthrow: 3.7.3.1 Gauge: Table G.3 W11 Overthrow: 3.8.3.1 Gauge: Table H.3 W12 Overthrow: 3.9.3.1

Upper gauge: Table I.6 & I.7

Lower gauge: Table I.4

WC1

Overthrow: 3.10.3.1

Upper gauge: Table J.2

Lower gauge: Table J.3 & J.4

WC1-Appendix A Overthrow: 3.11.3.1 Gauge: Table L.2 Locomotive Overthrow: 3.13.3.4 4.3.4. Analysis

A calculating Excel spread sheet has been made to determine the envelope of the profiles for both straight and 360m radius curved track including dynamic effect and overthrow where appropriate. The spread sheet is included in Annexe 3 of this document.

4.3.5. Envelope profile

Sketches in Annexe 2 of this document show the available clearances from the design envelopes for both straight and curved track, with and without the requirement for clearances to provide OHLE equipment through the bridge opening. Please note the clearance between the two vehicles with a standard sixfoot of 1970mm on curved track, is very tight but there is still enough space for the 100mm passing clearance.

4.3.6. Electrical protection, earthing and bonding

A draft copy of NR/L2/CIV/020 Design of Bridges & Culverts identifies the following issues with regards to electrical protection, earthing and bonding that need to be considered.

(24)

A Bridge carrying or passing over electrified lines shall comply with the electrical protection and bonding requirements of Railway Group Standard GE/RT8025: Electrical Protective Provisions for Electrified Lines.

Earthing and bonding systems for a Bridge, its metal parts and supported metal services shall comply with NR/SP/ELP/21085: Design of Earthing and Bonding Systems for 25kV A.C. Electrified Lines. As required by NR/SP/ELP/21085, the Design of such systems shall be in accordance with BS EN 50122-1: Railway Applications – Fixed Installations – Part 1: Protective Provisions Relating to Electrical Safety and Earthing and with all other relevant standards.

The electrical protection of the Bridge shall take into account the structure itself, any supported/attached equipment, any dual purpose issues, the surroundings and adjacent buildings or structures.

Where electrical protection is achieved by physical separation or isolation, the Design of any earthing or bonding systems shall not compromise this protection.

Bonding/earthing studs shall be fitted to the Bridge as required by Network Rail.

Bonding that is required exclusively for signalling purposes is outside the scope of this standard.

Consideration shall be given to maximising the use of metalwork or reinforcement in substructures for earthing, taking into account requirements for low resistance and low impedence.

Where required, remote earth test-points shall be provided for in the Design.

Where metal fences are attached to a Bridge, the electrical protection of the Bridge and fences, including gates, shall be considered as a whole. Consideration shall be given to using non-conducting fencing.

Trays or ladders which support electrical cables and are attached to a Bridge shall be earthed to the Bridge.

In D.C. electrified areas, Bridges shall not be bonded to the negative return rail unless otherwise agreed with Network Rail.

Where a Bridge carries or passes over an overhead line electrified railway, consideration shall be given to providing effective electrical bonding as follows:

• uniformly spread over a width of 2.6 m as above bonding a metal Underline or

Overline Bridge to the traction return rail or earth wire,

• connecting the components of a metal Bridge by welding or by substantial, clean

metal-to-metal bolted or riveted joints,

• connecting together and bonding as above any exposed metal parts of an Underline

or Overline Bridge (e.g. parapets, handrails and bearings of a concrete Bridge),

• bonding as above concrete reinforcement (including prestressing anchorages) if it is

accessible or if it is electrically connected to accessible metalwork,

• attaching a bonded metal plate to the underside of a concrete, timber and masonry

Overline Bridge, in certain cases where required by Network Rail,

• using non-metallic embedded service ducts in the Bridge.

Where a railway signal structure or any other railway equipment or equipment support structure that is required to be bonded to the traction return rail are attached to a Bridge, the interface between the Bridge and the attached equipment or support structure shall be designed so that all metal parts form a continuous electrical whole.

Where a Bridge crosses over an overhead electrified railway, consideration shall be given to waterproofing the Bridge and to managing any run-off to avoid potential damage through dripping water causing flash over.

(25)

4.3.7. Protection from stray currents

A draft copy of NR/L2/CIV/020 Design of Bridges & Culverts identifies the following issues with regards to protection from stray currents that need to be considered.

Where third rail D.C. electrification, or dual overhead A.C. and third D.C. electrification is present, consideration shall be given to the risk of stray current corrosion arising due to high current flows through the earth.

Railway Group Standard GL/RT1253: Mitigation of DC Stray Current Effects identifies the process requirements concerning stray currents. Where applicable, details shall be agreed with Network Rail as to the requirements of GL/RT1253 are to be included in the Design of the Bridge.

Consideration shall be given to special protection, or measures to mitigate the rate of corrosion, such as electrical isolation of substructure reinforcement cages, electrical screening, sacrificial zinc electrodes, or cathodic/anodic protection. Where applicable protective provisions shall be in accordance with BS EN 50122-2: Railway Applications – Fixed Installations – Part 2: Protective provisions against the effects of stray currents caused by D.C. traction systems.

4.4. ANCILLIARY RAILWAY RELATED DETAILS

4.4.1. OHLE Fixings

If there is a requirement to fix OHLE equipment to the underside of the Soffit of the bridge, the fixing should be located within the joints between the conarch units. No drilling into the actual soffit of the conarch units will be permitted. It will be the responsibility of the Scheme Specific Designer to check the capacity of the fixings of OHLE equipment.

4.4.2. Bridge ID Plates

Bridge ID plates are to be provided at track level on both sides of the bridge.

4.5. MAIN HIGHWAY RELATED DETAILS

4.5.1. Existing Masonry Bridge Widths

Historically, the Acts of Parliament that the original railway routes were built under required the majority of the road over rail bridges to be constructed with either 15 feet (4.57m) between the parapets for small country public roads and accommodation access routes or 25 feet (7.62m) for main roads. Typically the parapets on these bridges were 18 inches thick (457mm).

4.5.2. Existing Masonry Overbridge Reconstructions

As the 4.57 metres (15ft) and 7.62 metres (25ft) width between parapet masonry arch bridges are the most common widths that will require to be reconstructed, the conarch units have been sized so that common Edge Units can be used with varying numbers of Internal Units which also can vary in width from 900 to 1250mm to make up the bridge widths. A sketch showing the proposed units layouts for the 4.57 metres (15ft) and 7.62 metres (25ft) width between parapet bridges are included in Annexe 6 of this document.

4.5.3. Proposed New Overbridges

The most likely use of the arch units in new bridge constructions is for a new bridge to carry a road diversion allowing an existing level crossing to be closed. It would be expected that the bridge would need to carry a new two lane highway with a footpath on one side

(26)

and a verge on the other. A sketch showing the proposed units layout for these bridge width is included in Annexe 6 of this document.

4.5.4. Internal Bridge Width

The internal width at road level between Parapets can extend from a minimum width of 4.5 metres (14ft 9¼in), up to 12.5 metres by varying the width of the Inner Units (900 to 1250mm) except for a small zone between 5.120 metres (17ft 1½in) and 5.360 metres (17ft 7in). If a bridge width is required in this zone then the Scheme Specific Designer will need to consider a small increase in the bridge width with the cill units extending over the end the abutments by up to 70mm.

The Conarch Standard Details provide a bridge cross section that is formed from two Edge Conarch Units and multiple numbers of varying width Inner Conarch Units to provide the required road width.

The Edge Units and Parapet Beam with high containment parapets are 1745mm wide and are common for all bridge widths, with the overall width made up of Inner Units which can each be provided with a width between 900 and 1250mm.

A schedule of the unit numbers and widths for varying bridge widths is shown in the table below: Overall Bridge Width (m) Width between Parapets (m) Width between Parapets (ft) Edge unit Width (mm) Inner unit Width (mm) Joint Width (mm) 7.14 4.5 14 ft 9¼in 2 x 1745 2 x 910 3 x 20 7.21 4.57 15 ft 2 x 1745 2 x 945 3 x 20 7.82 5.18 17 ft 2 x 1745 2 x 1250 3 x 20 7.84 5.2 17 ft 0¾in 2 x 1745 2 x 1250 3 x 30

No available combination of Units in range of 5220mm - 5360mm (17 ft 1½in - 17 ft 7in)

8.01 5.37 17ft 7½in 2 x 1745 3 x 900 4 x 10 8.04 5.4 18ft 8½in 2 x 1745 3 x 900 4 x 20 9.09 6.45 21ft 2in 2 x 1745 3 x 1250 4 x 20 9.1 6.46 21ft 2¼in 2 x 1745 4 x 935 5 x 20 10.26 7.62 25ft 2 x 1745 4 x 1225 5 x 20 10.36 7.72 25ft 4in 2 x 1745 4 x 1250 5 x 20 10.38 7.74 25ft 7¾in 2 x 1745 5 x 1000 6 x 20

Any width available beyond 5.4m between parapets by adjusting number and width of Inner units

(27)

4.5.5. Road Restraint Systems

4.5.5.1 TD19/06 Requirement for Road Restraint Systems

TD19/06 describes the requirements for road restraint systems in the area of bridges covering both the approach and departure areas and the bridge parapets. Figure 1.2 defines the vehicle restraint system at bridges as follows:

• Safety fence – road vehicle restraint system either side of the structure

• Transition – Interface between two restraint systems

• Vehicle Parapet – safety barrier installed on the edge of a bridge

The main requirement of TD19/06 is that the Road Restraint Risk Assessment Process is undertaken at each bridge to determine the containment level of the bridge parapet and safety fences. It is the responsibility of the Scheme Specific Designer to undertake this risk assessment.

4.5.5.2 Very High Containment Parapets (H4a)

For new structures over railways TD19/06 requires very high containment parapets (H4a) to be provided, but where parapets on existing structures are to be replaced it requires the highest possible containment to be provided, but not less than normal (N2). It is a Network Rail Policy to provide high containment parapets (H4a) to all public highway bridges with normal containment parapets for accommodation bridges. To reduce the number of structural options the standard conarch designs only provide details of the very high containment parapets which will be used at all locations.

4.5.5.3 Parapet Types

The Conarch Standard Drawings provide details for both very high containment reinforced Concrete Parapets in accordance with BS 6779-2:1991 and very high containment Reinforced Masonry Parapet in accordance with BS 6779-4:1999. The Scheme Specific Designer has the opportunity where the site specific requirements allow, to use other forms of very high containment parapets such as a steel (H4a) parapet or subject to any site specific risk assessments a normal containment (N2) parapet.

4.5.5.4 Parapet Heights

The standard design includes for the high containment parapets up to a maximum height of 1.825 metres above the adjacent verge/pavement level. The Scheme Specific Designer is to set the top level of the parapets on both sides of the road either 1525mm (normal conditions) or 1825mm (bridle paths) above the design footpath/verge profile.

The height of the Parapet Beam is adjusted so that there is a constant parapet height above the design road vertical profile.

4.5.5.5 Parapet Ends

The very high containment parapet ends will be provided square to the road alignment with cast in anchorages for the connections from the adjacent transition parapets section of the approach and departure safety fences. The following Highway Construction Detail drawings are used for this connection:

• SB/151 Connection Bracket

(28)

4.5.5.6 Safety Fences and Transitions

Standard details for the approach and departure safety fences and the transitions on to the very high containment parapets of the conarch structure are based on the Highway Construction Details – Double Rail Open Box Beam Safety Fence Connection to Structure (Verge) as follows:

• GA/84 – Connection to structure

• GA/85 – Connection to HVCB or concrete structure at approach end (Sht 1of 5)

• GA/90 – Connection to HVCB or concrete structure at departure end (Sht 1of 3)

These construction details have been developed for the conarch structure to take into consideration the need to provide an adequate restraint to the transition length of the safety fence directly behind the abutments above the existing masonry wing walls.

It is proposed that a reinforced parapet transition slab is provided over the wing walls to support the transition length of the safety fence on either side. This will extend away from the bridge for a length of 13.8 metres to provide support to all seven 150x150 RHS fence posts. Beyond this point the zed section posts will concreted into the ground as per the construction detail drawings.

4.5.5.7 Transition Parapet Support Slab

The transition support slab is formed of precast concrete Edge Upstand Beams that sit on top of the wing walls, nominally 1500mm wide that support the posts of the Transition Parapet. An in-situ concrete slab is provided between the Edge Upstand Beams to tie them together.

The Scheme Specific Designer will be responsible for determining the dimensions and alignment of these units to suit the site conditions.

4.5.5.8 Transition Parapet Infill

For bridges over OHLE electrified lines, the Steel Transition Parapets are to be enclosed on the front face with a solid steel panel and provided with a solid steeple capping to the same height and profile as the bridge parapets for a distance back from the face of the abutment of 3 metres.

4.5.6. Highway Alignment and Cross Fall Criteria

4.5.6.1 Highway Horizontal Alignment

It is assumed that at most bridges there will be no requirement for any major changes to the highway horizontal alignment except for minor local changes to suit the run on to and the run off from the bridge.

The ideal alignment is expected to be straight across the bridge deck, but any existing curvature can be replicated within the existing width of the bridge.

(29)

4.5.6.2 Highway Vertical Alignment

The largest variable associated with the design of the conarch structures is the longitudinal vertical road profile which has an effect on the construction depth at the crown of the arch and the overall dead load of the structure. The conarch units have been designed to accommodate the loading from the vertical road profile from the minimum radius hog curve tight to the top of the conarch units up to a horizontal profile over the bridge with at least 5 metre horizontal sections before and after the structure (5 metre measured from outside face of 200mm backfill within the following ranges – See also sketches in Annexe 8 of this document:

4.5.6.3 Square Spans

For square spans the longitudinal profile of the road always crosses over the structure perpendicular to the centre line of the conarch tunnel profile. Therefore the minimum radius of the road profile is equivalent to the radius of the top of the conarch units plus the minimum depth of the capping slab and road surfacing.

• Range 1 – Symmetrical Profile

The vertical road profile is assumed to be symmetrical about the centre line of the bridge varying from a minimum radius of 20.670 metres up to a horizontal profile for the full length of the bridge. The minimum construction depth at the crown of the arch is maintained for all profiles.

• Range 2 Square Spans – Asymmetrical Profile

It is also acceptable to provide an asymmetrical vertical road profile about the centre line of the bridge varying from a minimum radius of 20.670 metres up to a horizontal profile. The minimum construction depth at the crown of the arch is maintained for all profiles.

4.5.6.4 Skew Spans

For any skew span, the longitudinal profile of the road will not cross over the structure perpendicular to the centre line of the conarch profiles. Therefore the minimum road profile vertical curve across the structure will be dependent on both the internal width of the bridge and the skew, the greater the skew and internal bridge width the greater the minimum radius. The minimum vertical curve radius will now be determined from the extreme positions of the upper haunches of the conarch units on the longest diagonal of the structure. The vertical curve through these two points parallel with the centre line of the road maintaining the minimum capping slab and road construction depth at the haunches will require the construction depth at the centre point of the bridge to be increased. See sketch in Annexe 8 of this document.

• Range 3 Symmetrical Profile

The vertical road profile is assumed to be symmetrical about the centre point of the bridge varying from a minimum radius achieved by increasing the construction depth at the crown of the arch by up to a maximum of 200mm, up to a horizontal road profile with the minimum construction depth at the crown of the arch across the bridge. As the profile radius increases towards the horizontal the increase in construction depth at the arch crown reduces.

With an internal bridge width between the parapets of 7.620 metres the table below shows the minimum vertical curve for varying skews:

Skew 7.4m Span 8.4m Span 9.4m Span

Hog curve radius (m) Hog curve radius (m) Hog curve radius (m)

(30)

Square 20,667 20,667 20,667

15º 32,042 30,987 30,127

30º 51,257 48,717 46,637

45º 91,467 86,052 81,627

• Range 4 Skew Spans – Asymmetrical Profile

It is also acceptable to provide an asymmetrical vertical road profile about the centre point of the bridge varying from a minimum radius on one side up to a horizontal profile on the other. For this range the increase in construction depth at the crown of the arch must be limited to a maximum of 100mm.

4.5.6.5 Camber and Crossfall

The standard deck detail assumes that on a two lane highway there is a crown along the centre of the road with crossfalls of 1 in 40 to the kerb line. Any variance in the level of the bottom of the Parapet on each side of the bridge will be dependant on the width and the crossfall of the verge/footways. The Parapet Beam’s upstand can be raised by maximum of 95mm in order to increase the diameter of service dusts under the verge/footways. The standard Parapet Beam detail assumes that the two beams are identical.

4.5.7. Road Surfacing Material

The road surfacing will have a minimum construction depth of 125mm formed of a regulating road base course 60mm minimum thickness laid on 20mm thick red sand asphalt over the 5mm thick sprayed waterproofing membrane with a 40mm thick wearing course on top.

4.5.8. Asphaltic Plug Joints

Asphaltic plug joints in the road surfacing at the rear of the abutment where the bridge deck meets the Transition Parapet Slab are to be provided for the full width of the road surfacing.

4.5.9. Footpath Construction

The footpath will be formed from compacted Type 6N material behind a precast kerb with 25mm nominal thickness dense macadam wearing course with 6mm aggregate.

4.5.10. Road Drainage Details

4.5.10.1 Curved Vertical Road Profiles

On bridges which have a curved vertical road profile then it is not proposed to provide any surface water drainage across the bridge structure, but the Scheme Specific Designer will need to consider the requirement for drainage gullies on the bridge approaches.

4.5.10.2 Level or near Level Road Profiles

On bridges with level or near level road profiles the Scheme Specific Designer will need to consider the requirement to provide kerb channel drains across the structure to manage the surface water on the deck.

(31)

4.5.11. Sub-Surface Drainage

Sub-surface drainage is to be provided across the deck located on either side of each of the kerb lines. The drainage paths will be formed of 50x50 square perforated aluminium ducts wrapped in a geotextile fixed to the top of the conarch capping slab with a bitumen bedding.

4.6. ANCILLIARY HIGHWAY RELATED DETAILS

4.6.1. Service Duct Size and Location

If service ducts are required across the structure, they will be located within the verge or footpath construction above the main conarch units. The actual alignment and size of duct will be for the Scheme Specific Designer to determine.

By increasing the upstand on the parapet beam will allow the maximum size of the service ducts to be increased. This uplift of the upstand must be less than 95mm.

4.6.2. Lighting Columns Fixings

If lamp posts or other signs are required to be positioned on the bridge deck, a plinth with the appropriate holding down bolts will need to be cast above and connected into the Capping Slab above the conarch units. No connection is to be made into the Conarch Units. The Scheme Specific Designer is responsible for the design of the plinths and holding down bolt arrangement to suit the type of lamp post or sign post.

4.7. CONARCH CALCULATOR

The Conarch Calculator is an active spread sheet to assist the scheme specific designer with the detailing of the replacement bridge structure. An example of the input and output of the calculator is included in Annexe 10 of this document.

4.7.1. Input Data

The following data from the site survey and the layout of the proposed structure is to be input into the Conarch Calculator:

• Bridge location details (ELR, mileage etc)

• Railway data

o Proposed railway vehicle gauge

o Whether line is to be OHLE electrified

o Track details:

Cant

Radius

Sixfoot

o Height from top of highest rail to soffit of proposed conarch units

• Structure data

o Clear perpendicular distance (span) between the inside faces of abutments

o Any sitback of units from face of abutments

o Skew of bridge

o Any uplift of parapet beams upstand

• Highway data:

o Carriageway width and crossfalls

o Verge/footpath widths and crossfalls

o Highway construction thicknesses

o Proposed highway longitudinal vertical curvature

(32)

o Type of parapet panel

o Height of parapet panel

o Number of parapet panels required

• Abutment data:

o Size and number of dowels

o Width of abutment

o Existing loading on the abutment

4.7.2. Layout Design

From the input data the Conarch Calculator produces the following layout data which will be used by the Scheme Specific Designer to layout the proposed bridge structure on the detailed design drawings:

• The number required and widths of the Inner Conarch Units and the size of the gaps

between.

• A section through the bridge perpendicular to the tracks showing the proposed

railway gauge relative to the conarch.

• A plan of the proposed structure.

• A section through the bridge showing the highway vertical longitudinal profile across

the bridge.

• A cross-section through the bridge showing the layout of the carriageway and

verges.

• An elevation of the Parapet Beam taking into consideration of the bridge skew.

• Lifting details for the main units including the location of the cast in lifting anchors

and unit tie bar requirements.

• Abutment loading from new structure.

4.7.3. Reinforcement Scheduling Tool

The Conarch Calculator produces the reinforcement schedules to suit the span and skew of the scheme specific bridge for the following units:

• Edge Units

• Inner Units

• Parapet Beam and Parapet Panels

• Cill Units

The Conarch Calculator provides reinforcement details to suit the span and skew of the scheme specific bridge for the following elements:

• Shear key joints

• Backfill concrete including the rear vertical saw tooth profile

• Capping slab

4.8. STANDARD DRAWINGS & DETAILS

The following drawings have been produced and are detailed in Annex 1 of this document:

4.8.1. Standard Design Precast Concrete Unit Drawings

General arrangement and reinforced concrete detailed drawings for the Inner and Edge Units for the following spans and skews:

• 7.4 metre span

o Square span