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Tunnel and Bridge AssessmentsEastern ZoneAssessment of the Effects of Tunnel Induced Settlement On Oxestalls Roadbridge Structure No. BR414Doc Ref: 9.15.106

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Thames Tideway Tunnel Thames Water Utilities Limited

Application for Development ConsentApplication Reference Number: WWO10001

Assessment Report Page 1 03/01/2013

Thames Tunnel Detailed Bridge Assessments

List of contents Page number

1 Executive Summary ......................................................................................... 3

2 Introduction ...................................................................................................... 5

3 Structure Details .............................................................................................. 6

3.1 Superstructure ......................................................................................... 6

3.2 Substructure ............................................................................................ 6

3.3 Articulation ............................................................................................... 7

3.4 Spans ...................................................................................................... 7

3.5 Parapet .................................................................................................... 7

3.6 Surfacing ................................................................................................. 7

3.7 Drainage .................................................................................................. 7

3.8 Services ................................................................................................... 7

3.9 Record information .................................................................................. 7

3.10 Maintenance and Modifications ............................................................... 8

4 Inspection for Assessment Findings ........................................................... 10

4.1 Purpose ................................................................................................. 10

4.2 Methodology .......................................................................................... 10

4.3 Superstructure ....................................................................................... 10

4.4 Substructure .......................................................................................... 10

4.5 Foundations ........................................................................................... 11

4.6 Conclusions and Recommendations ..................................................... 11

5 Assessment Methodology ............................................................................. 12

5.1 Analysis of Structure .............................................................................. 12

5.2 Calculation of Settlement Trough .......................................................... 13

5.3 Application of Settlement ....................................................................... 13

5.4 Calculation of Section Capacities .......................................................... 14

5.5 Utilities & Drainage ................................................................................ 14

6 Assessment Results Summary ..................................................................... 15

6.1 Superstructure & Substructure .............................................................. 15

6.2 Utilities ................................................................................................... 16

7 Discussion of Results and Conclusions ...................................................... 17

7.1 Superstructure & Substructure .............................................................. 17

7.2 Utilities & Drainage ................................................................................ 18

8 Recommendations ......................................................................................... 19

APPENDIX 1 – Approval in Principle ...................................................................... 1


APPENDIX 2 – Inspection Report ............................................................................ 2

APPENDIX 3 – Predicted Settlement Troughs ....................................................... 3

APPENDIX 4 – Assessment Calculations ............................................................... 4


1 Executive Summary

AECOM has been commissioned by Thames Tunnel to carry out an assessment of the effect the proposed tunnel would have on Oxestalls Road Bridge. This detailed bridge assessment is part of the Sub-Package 3c contract works for impact assessment of the proposed Thames Tunnel project.

Oxestalls Road Bridge is a single-span steel girder and composite concrete deck bridge with a rising approach structure on each side. Constructed in the late 1960’s, the bridge deck is reinforced concrete and is supported by 13No. longitudinal castellated girders at regular spacing. These have 4No. sections of cross bracing at intervals along their span. The outermost girders on either side of the span are skewed relative to the others. Details missing from archive information have been retrieved from site measurements, or an estimate was used. The approach structures feature a reinforced concrete deck slab and a series of reinforced concrete columns. Pad Foundations are founded on concrete piles.

The inspection for assessment (doc. No. 314-RI-TPI-BR414-000001, see Appendix 2) was carried out on the 28th February 2012. The structure was found to be in a fair condition. Surface corrosion was found to be wide spread over the steel sections of the structure, no section loss was observed. The carriageway surfacing is in poor condition over the structure, this is especially prevalent on the East approach. Some spalling was observed to the superstructure and substructure concrete; however, this is considered to be minor. A condition factor of 1.0 will be applied to all structural members in the assessment of Oxestalls Road Bridge.

This assessment has been undertaken in accordance with the Approval in Principle document No. 314-EA-TPI-BR414-000001 (see Appendix 1). The load effects, for the main span, have been determined by modelling the structure as a grillage in LUSAS, using linear elastic methods, and by using hand calculations. The approach structures have been modelled as a linear elastic plane frame in SAM.

Settlement applied to the structure was in a form of displacements and rotations of the foundation supports induced by the settlement of the soil. The effect of these displacements on the modelled members of the structure was compared against their sectional capacities (calculations in Appendix 4), i.e. utilisation = applied stress / ultimate stress.

The maximum main span effect was due to axial compression of the longitudinal girders, caused by friction at the bearings resisting the induced movements. This temporary effect caused a utilisation of 4.66% which is below the 10% threshold outlined in the Approval in Principle for a volume loss of 1.0%. The approach structures were found to be over 170% utilised for HA, dead load, and super imposed dead load in the hogging regions of the structure. This indicates these sections are cracked under normal working load and the structure is acting as if each span is simply supported, and hence, would not be affected by settlement effects. A number of services were identified in the North footway. These were assessed qualitatively not to be at risk of applied settlements.


The only recommended mitigation measure resulting from this assessment is standard routine monitoring, as per any tunnelling construction project, before, during and after the Thames Tunnel construction to ensure actual movements are less than those used in this assessment.


2 Introduction

AECOM has been commissioned by Thames Tunnel to carry out an assessment of the effect the proposed tunnel would have on Oxestalls Road Bridge. This detailed bridge assessment is part of the Sub-Package 3c contract works for impact assessment of the proposed Thames Tunnel project.

The main objective of the project is to identify any structural or serviceability implications that may result from proposed tunnelling works in the vicinity of the existing infrastructure.

Oxestalls Road Bridge is the most recent bridge to be constructed over the Grand Surrey Canal. It was constructed downstream from the entrance lock of the canal. The bridge and surrounding estate were built in the 1960's, when the canal was still in use. The canal beneath the bridge has been filled in since construction of the bridge and the land has been reclaimed.

Oxestalls Road Bridge is a single-span castellated steel plate girder and composite concrete deck bridge with a rising approach structure on each side. The bridge deck is reinforced concrete and is supported by 13No. longitudinal castellated girders, mostly, at regular spacing. These have 4No. sections of cross bracing at intervals along their span. The outermost girders on either side of the span are skewed relative to the others. The approach structures are formed from reinforced concrete piles and columns supporting a reinforced concrete slab. The approach columns are placed in rows of three with varying spacing between reinforced concrete abutment walls, spanning the full width of the slab.

Archive information has been provided for the structure from the London Borough of Lewisham. Some structure details have not been sourced for the assessment so details, such as pile depth, have used a ‘best estimate’ approach. After reviewing these details an inspection for assessment was performed (see the inspection report in Appendix 2) to verify the condition of the structure.

The settlement of the ground due to the proposed tunnel was calculated using a Greenfield Settlement analysis. The calculated settlements were taken from the analysis and applied directly to the computer model. The resulting structural effects were then compared against the sectional capacity of the affected members.


3 Structure Details

3.1 Superstructure

Oxestalls Road Bridge is a steel and concrete composite structure, consisting of a reinforced concrete deck and 13 No. simply supported pre-cambered longitudinal castellated steel main girders. There are four transverse cross-bracing trusses, formed from 90° steel angle sections. The main I section girders have an overall dimension of 927mm by 312mm. The bridge has a span of 21.2m and is founded on elastomeric bearings which sit on top of a reinforced concrete abutment and bearing shelf, which totals 3.4m in height and 16.5m in width. Joints are located in the concrete deck slab at each end of the span, above each bearing shelf. The metallic parapet railings are founded on concrete upstands.

The approach structures to the East and West are of reinforced concrete construction. The deck slab is supported by rows of three circular columns measuring approximately 450mm diameter each. The approach end is supported on a reinforced concrete abutment wall spanning the width of the slab. The approach structure has masonry infill panels.

Photograph 1 Oxestalls Roadbridge looking North

3.2 Substructure

The structure abutments are of reinforced concrete composition. The West abutment sits on a concrete footing which is founded on two rows of 7No. concrete piles spaced at 2.59m centres. The East abutment sits on a concrete footing which is founded on 17No. staggered concrete piles spaced at 1.22m centres. The approach structures are founded on a


series of concrete footings and concrete piles located under the supporting columns.

3.3 Articulation

The main bridge span is simply supported with expansion joints at either end. The main girders are free to expand and contract on the steel plate bearing system installed between each girder and the bearing shelf. The bearing plates measure 300mm by 350mm by 50mm. The approach span deck is continuous over the column supports, with expansion joints at either end.

Asphaltic plug joints are located in the road surface above the deck joints.

3.4 Spans

The bridge appears square to both the East and West abutments and has a span of 21.2m. The two way spanning approach spans curve on plan up to the main deck span. The West approach spans over 8 rows of columns and the East approach spans over 6 rows of columns.

3.5 Parapet

The parapets comprise steel railings founded on a concrete upstand at the edge of the deck slab. The parapet is 1.04m total height and the upstand is 170mm high.

3.6 Surfacing

Asphaltic surfacing layers are placed directly upon the concrete deck slabs. It is not possible to determine any depth or materials of the various layers.

3.7 Drainage

The drainage system comprises a series of drain holes adjacent to the road kerb line, these pass through the deck slab, it’s not clear where the drainage system directs the collected water.

3.8 Services

Utility records indicate that two 8” steel low pressure gas mains, a 8” water main and two 4” steel electricity service pipes (General Post Office and London Electricity Board) are located in the North footway of the bridge and are packed in sand.

3.9 Record information

Record information has been provided as follows;


Drawing Number

Drawing Name

1 Road Location Plan

2 Longitudinal Profile and Finished Levels

3 Cross-profiles of road and bridge

4 Section Sheet 1 (West)

5 Section Sheet 2 (East)

6 South elevation

7 North elevation

8 Foundation Location Plan and Drainage

9 Piling Layout

10 Retaining wall 1

11 Retaining wall 2

12 Retaining wall 3

13 Retaining wall 4

14 Retaining wall 5

15 Retaining wall 6

16 West abutment

17 East abutment

18 Ground slab and foundations under West approach road

19 Ground slab and foundations under East approach road

20 West approach road cols and pile caps sheet 1

21 West approach road cols and pile caps sheet 2

22 East approach road cols and pile caps

23 Canal profile to East abutment

24 West approach road general arrangement

25 West approach road bottom steel

26 West approach road top steel

27 East approach road general arrangement

28 East approach road bottom steel

29 East approach road top steel

30 Main span general arrangement

31 Main span slab reinforcement


32 Main span layout of bridge steelwork

33 Main span details of castella beams

34 Petrol interceptor pit and catchpit details

35 Balustrade details

36 Brick manhole details

BE10364-1 Oxestalls road bridge (void beneath W. Approach ramp deck)

BE10364-2 Oxestalls road bridge (void beneath W. Approach ramp deck)

BE Survey 1 Bridgeguard

BE Survey 2 Oxestalls road bridge general arrangement

Table 1. List of drawings to be used in the assessment

3.10 Maintenance and Modifications

Maintenance history has been provided as follows;

- General Assessment Report, 14th July 2009


4 Inspection for Assessment Findings

4.1 Purpose

AECOM has been commissioned by Thames Tunnel to carry out an Inspection for Assessment of Oxestalls Road Bridge. This detailed bridge assessment is part of the Sub-Package 3c contract works for impact assessment of the proposed Thames Tunnel project.

4.2 Methodology

Inspection of the bridge was undertaken by AECOM on the 28th February 2012.

The main objective of the project is to identify any structural or serviceability implications which may result from proposed tunnelling works in the vicinity of the existing infrastructure. The inspection for assessment has been focused specifically at the elements that could potentially be affected by the proposed Thames Tunnel construction, however inspection of other elements was undertaken as well and observations included for the asset owner’s consideration.

Below a brief summary of the inspection is presented. More details relating to observations made during the inspection work are included in Appendix 2.

4.3 Superstructure

Generally, the bridge was in fair condition, with some signs of deterioration throughout.

A large amount of surface corrosion is visible on some of the outer longitudinal span girders and their bearing plates. Surface spalling on the structural concrete of the superstructure elements was observed in several locations. This surface breakaway has resulted in the exposure of reinforcement steel in many places. Concrete spalling and efflorescence was observed adjacent to some of the weep holes in the concrete structure, where water runoff is also evident.

The carriageway and footways were observed to be in poor condition. Excessive cracking was found on the Asphalt surface of the road and in the paving slabs of the footway. Large transverse cracks in the carriageway are visible at the location of joints in the concrete of the superstructure. Significant cracking and breakup of the road surface is particularly evident on the East approach to the bridge. Large pot holes are forming in this area due to the surface deterioration. The underside of the approach structures could not be viewed due to the masonry infill panels surrounding the structure.

4.4 Substructure

Some degradation of the abutments was evident in the form of spalling of the concrete face. This appears to have been caused by water permeating through the joints in the deck at the positions of the span supports. Water runoff has caused staining of the abutment faces. It is promoting the


growth of organic material and the deposition of minerals on the face of the concrete.

4.5 Foundations

The foundations are buried and could not be inspected. At present the structure is showing no signs of distress that could be attributed to a failure or excessive movement of the foundations.

4.6 Conclusions and Recommendations

The structure was found to be in fair condition. Even though surface corrosion was found to be wide spread over steel sections of the structure, no section loss was observed. The carriageway surfacing is in poor condition, this is especially prevalent on the East approach. Some spalling was observed to the superstructure and substructure concrete, this seems to be a result of water ingress into the concrete. The exposed reinforcement appears to be very close to the surface of the concrete, indicating poor design/construction.

Based on the condition of the structural members inspected a condition factor of 1.0 will be applied to all structural members in the assessment of Oxestalls Road Bridge.


5 Assessment Methodology

This assessment has been undertaken in accordance with the Approval in Principle document No. 314-EA-TPI-BR414-000001-AC, included in Appendix 1. Ground movements calculated from the Greenfield settlement analysis are applied at the bearing support of the modelled structure. The resultant load effects on the structure are compared against sectional capacities of the relevant members. Where this approach is not possible empirical methods will be used.

5.1 Analysis of Structure

The main span load effects have been determined by modelling the structure as a grillage in LUSAS, using linear elastic methods, and by using hand calculations.

Figure 1 Main span Grillage in LUSAS

The approaches have been modelled by creating a linear elastic plane frame model, of a section though the east approach, in SAM and using hand calculation methods. The alignment of the tunnel will affect longitudinal and vertical members in the permanent case, so a two dimensional analysis was used.

Figure 2 Approach Plane Frame in SAM

As the main span is simply supported there will be no permanent stresses induced. The deck will slide at the bearings to accommodate the movement of abutments induced by the tunnelling action. Before the deck can slide, the friction due to the dead loads between the bearing plate and the bed stones must be overcome. As the friction prevents the deck from sliding, it will cause the deck to shorten creating an axial stress.

The stress will be relieved either by continued movements of the abutments or vibrations of the deck from the live load. At some point the


friction required to resist the movement of the deck will be overcome by the rotation of the abutments. Alternatively, the vibrations caused by the live load passing over the structure may ‘bounce’ the deck allowing movement at the bearings.

All 13 girders have been modelled using dimensions taken from the site inspection, material properties have been taken from archive information, or where not available, assuming standard 1960’s values. The deck slab has been given conservative or ‘worst case’ properties from supplied archive information. Where possible, members are placed at the centre line of the section they represent. Member connections have been assumed to be rigid. Conservatively, the connection between the bearing plate and girders has been assumed to be fully fixed for a moment check, meaning an unrealistically high force will be induced in the elements. The foundation piles have been omitted from the analysis and a nominal footing has been assumed. This approach mitigates some of the uncertainty about the structure and is conservative.

The approach spans have been assessed using the east approach, inner radius, dimensions. The plane frame model has been assigned section properties to represent the full width of the structure. Therefore, the deck elements are modelled with a 15m wide and 355mm deep section and each column member represents 6 columns. Rigid offsets have been used at deck level to represent the spreading action of the coned support columns, and the tops of the columns are given a relatively higher stiffness to represent the top cone detail. The calculated ground settlements are applied directly to the column bases.

All members will be modelled using beam elements with appropriate section and material properties assigned. The calculated settlements are applied as displacements and rotations to the member supports. The force induced in the members as a result of this displacement and rotation is then calculated and compared against a calculated section capacity.

5.2 Calculation of Settlement Trough

Site ground conditions were identified from borehole logs obtained from the British Geological Society. This information was used along with the proposed tunnel size and alignment in a Greenfield settlement analysis to produce the settlement troughs (see Appendix 3).

5.3 Application of Settlement

Load applied to the structure was in a form of displacements and rotations of the girder supports induced by the settlement of the soil. The calculated displacement and rotation applied to the main span supports takes account of the lever arm formed from the offset from the bearing shelf to the foundation bases where the settlement has been calculated. As the tunnel alignment runs close to the centre of the span the rotation and displacement of the foundations will be the same on each abutment.

The transverse settlement, or bow wave effect, causes the whole structure to deflect away from the tunnel as it approaches and then settle back to a horizontal position in the permanent case. As the main span is a simply


supported, transversely stiff, section this will have little to no effect on the bridge elements. Hence these effects have not been considered.

5.4 Calculation of Section Capacities

When calculating the ultimate capacity of a section, the factor γf3 = 1.1 has

been included for all elements along with the appropriate γm for the material (from BD 56).

A condition factor of γc = 1.0 has been assumed in the assessment of all elements. This is justified as the structure is, in general, without any major signs of distress. For the Inspection Report refer to Appendix 2.

The load effects from the analysis are translated into maximum stresses and forces induced in the relevant sections and compared against the ultimate stress or force of the relevant section. The elements are checked for bending, and where required axial effects and shear. The utilisation check is a comparison and does not reflect the actual value of stress in the section but simply the change in stress.

5.5 Utilities & Drainage

Utility information has been provided by Thames Tunnel and the London Borough of Lewisham for the structure, and as a result, two 8” steel low pressure gas mains, a 8” water main and two 4” steel electricity service pipes have been identified in the North footway. Due to the age of the structure it’s unlikely that any sensitive services are carried by the bridge i.e. cast iron pipes. From drawing No.8 no drainage pipes cross the span.


6 Assessment Results Summary

6.1 Superstructure & Substructure

The following table summarises results obtained during the assessment process for the main span superstructure. Detailed calculations are included in Appendix 4 of this report.

The utilisation shown below expresses the ratio of a factored load effect to the ultimate capacity of the element and is derived from the following equation:

Utilisation = FactoredLoadEffect

UltimateLimitStateγ�∗ γ

��

=FactoredLoadEffect

ULSCapacity

The results shown below, in Table 1, are utilisations of the main steel girders when subjected to permanent tunnel settlements at 1.0% volume loss. The applied bending moment has been extracted from the LUSAS model and compared to a bending capacity calculated for the beam only, ignoring composite action, using BS5400-3 and BD56/10. The 1.67% utilisation is minimal considering many conservative assumptions have been made in the assessment.

Location Effect Applied Max Utilisation

Main Girder Axial 9.96 213.85 4.66%

Main Girder Bending 34.19 2049.64 1.67%

Table 1; Utilisation of Main Girders at 1.0% Volume Loss

The applied axial stress has been calculated empirically using the dead load of the structure. This applied axial stress represents the maximum axial stress which can be achieved in the main girders before they slip on their bearing plates. As the calculated settlement causes a theoretical stress higher than that required to cause bearing slippage, the movement caused by the inward rotation of the abutments in the permanent case will be relieved by movement of the bearing plates.

The load effects above are not coincident with live loads on the bridge which will have the effect of relieving the loads built up from the abutments settling.

The calculated settlement was applied to the column bases in the plane frame model of the East approach structure, this lead to an unrealistically high bending utilisation in the deck section. It was noted that the deck does not meet current design requirements for minimum steel reinforcement content. Dead loads and superimposed dead loads were applied to the structure and HA loading was applied over two spans. It was found that the hogging utilisation in the deck slab for this loadcase was over 170% in the hogging region. This indicates the deck concrete has cracked in the hogging regions. The cracking will ultimately mean the deck behaves as a series of simply supported spans, and hence, no moment will be induced as a result of the differential settlement of columns.


6.2 Utilities

As the bridge is simply supported, and the tunnel is aligned close to mid-span, the effect of tunnel induced settlements on the carried services will be negligible. There was no evidence of further services during the inspection of the structure. However, due to the age of the structure it’s unlikely that any sensitive services are carried by the bridge i.e. cast iron pipes.


7 Discussion of Results and Conclusions

7.1 Superstructure & Substructure

As Oxestalls Road Bridge is simply supported the effects of settlement will not add to the permanent stresses in the structure. As the bridge has a relatively short span, and abutment height, the settlement and rotation of the abutments is relatively small.

Theoretically there will be no stresses induced in the main span by the settlement as the bridge deck allows for longitudinal movements and rotations. This allowance comes from the bearing plates located between the girders and bearing shelf and expansion joints in the reinforced concrete deck. In reality the friction between the bearing plates and the bed stones will resist a certain amount of movement. The coefficient of friction used between these two surfaces in the assessment is conservative.

Once the longitudinal movement exceeds that which can be resisted by the friction at the supports, or live load travels over the bridge, the deck will move at the bearings and the stresses will be relieved. The stress in the bridge deck is dependent on the maximum friction force at the bearings and not the amount of movement induced by the settlement. Therefore, the maximum axial stress will be the same for all values of volume loss. It is also worth noting that the level of longitudinal movement experienced by the bridge deck is less than two and a half millimetres for each abutment.

For low volume losses the longitudinal movement induced by tunnelling will be less than the maximum strain that can be realised in the bridge deck before bearing slippage. In this case, the induced stresses will be lower than those calculated in Appendix 4. As the maximum friction force is never achieved, the maximum strain and hence stress is never reached in the deck. As the friction is not overcome the bridge deck will not move due to the settlement alone. The stress will be relieved by the effect of vibrations of the live load that will ‘bounce’ the bridge deck free.

As a conservative check the supports were fixed on the grillage model, and the rotations induced in the abutments as a result of 1.0% volume loss were applied at the base of the girders. The induced bending moment from the LUSAS model was compared with the bending capacity calculated for the section using BS5400 and BD56/10. The utilisation found was 1.67%. Conservatively, no composite action was taken into account when calculating the ultimate capacity of the section. This means that in the highly unlikely case of the bearing plates seizing solid the girders would still be able to accept the induced moment at 1.0% volume loss. The curvature of the girders has been ignored for this assessment. It is considered this would have a minimal effect of the results.

The initial calculations found the longitudinal girders above the proposed tunnel route to be stressed below the first acceptance criteria of 10%. It was assumed that the strains caused by the friction force were evenly applied to all four of the longitudinal girders.


The calculated settlements were applied to the East plane frame column supports for a 1% volume loss. This action set up an unrealistically high bending utilisation for the differential settlement experienced. In order to gauge the level of stress in the approach deck under working loads, HA, dead load and super imposed dead load were applied to the model. Resulting in a utilisation for bending in the hogging region of over 170%. This indicates the concrete in the hogging region must be cracked from working loads on the structure. As the structure is cracked in this region there will be no moment carry over from one span to the next. In effect a pinned support has been created. If the approach spans are treated as simply supported, individual spans, then settlement effects will not induce a stress due to differential settlement of the column foundations. The percentage of steel in the concrete deck is low compared with modern standards and wouldn’t meet current minimum steel requirements. Based on these assumptions the reinforced concrete approach structures will not be affected by the tunnel induced soil settlements.

7.2 Utilities & Drainage

As the tunnel runs close to mid-span of the bridge (no differential settlement between abutments) and the span is relatively small, the effect of tunnel settlements on carried utilities will be negligible. The indicated steel services in the North footway run the entire length of the span and the East and West approach structures. Any settlements experienced at mid-span will be gradual across the length of the approach structures. No further services were identified during the inspection. However, due to the age of the structure it’s unlikely that any sensitive services are carried by the bridge i.e. cast iron pipes.


8 Recommendations

The stress increase we have identified in this assessment is less than the threshold value stated in the Approval in Principle document. It is worth noting that the stresses only represent a change in stress and do not relate to the actual level of stress in the members. The increase in stress is also not coincident with live load so it is safe to say that the additional stress does not exceed the dead plus live load stress level of the bridge.

Given the low value of stress induced in the bridge deck and the temporary nature of these effects it is highly unlikely that the proposed tunnelling will have an impact on the structure. It is also worth noting that the findings of this report are based on conservative values of volume loss structure geometry and coefficient of friction between the bridge bearing plates and bed stones.

The only recommended mitigation measure resulting from this assessment is standard routine monitoring, as per any tunnelling construction project, before, during, and after the Thames Tunnel construction to ensure actual movements are less than those used in this assessment.

Assessment Report Appendix 1 03/01/2013

APPENDIX 1 – Approval in Principle

Document No. 314-EA-TPI-BR414-000001-AC


APPENDIX 2 – Inspection Report

Document No. 314-RI-TPI-BR414-000001-AB


APPENDIX 3 – Predicted Settlement Troughs

Graphs are provided for vertical and horizontal settlement, as well as, ground slope and tensile strain at 1.0% and 1.7% volume loss. Each of the above cases will be provided at base of the foundation level and at ground surface level.

Each case begins with a layout plot which depicts the depth to tunnel centre line and its location relative to the foundation footprint. If the tunnel is located at mid-span, then only a single foundation will be shown for clarity. The second graph shows settlement and horizontal movement from the tunnel centre line. This graph can be used to read off horizontal and vertical movements at various distances from the tunnel axis. The third graph depicts the slope of the settlement trough and the horizontal tensile strain, which can be read off at various distances from the tunnel central axis. The final graph shows a detailed view of the vertical settlement and values at points of interest, such as edges of foundation.

The following settlement cases are provided in this report;

1. West Ground Level at 1.0% Volume Loss

2. West Ground Level at 1.7% Volume Loss

3. West Foundation Level at 1.0% Volume Loss

4. West Foundation Level at 1.7% Volume Loss

5. West Datum Level at 1.0% Volume Loss

6. West Datum Level at 1.7% Volume Loss

7. East Ground Level at 1.0% Volume Loss

8. East Ground Level at 1.7% Volume Loss

9. East Foundation Level at 1.0% Volume Loss

10. East Foundation Level at 1.7% Volume Loss

11. East Datum Level at 1.0% Volume Loss

12. East Datum Level at 1.7% Volume Loss


APPENDIX 4 – Assessment Calculations

Project Thames Tunnel Detailed Bridge Assessments Sheet A1

Section Oxestalls Bridge - Utilisation Summary Rev

Made by BTB Date

Reference Calculations Output

Results Summary

1.0% Volume Loss

East Approach Frame

Main Girder Bending 34.19 2049.64



02/01/2013

1.67%


Deck Slab Hogging 75.61 43.64 173.24%

CALCULATION SHEET

Project Thames Tunnel Detailed Bridge Assessments Sheet 1

Section Oxestalls Road Bridge - Introduction Rev

Made by BTB Date


Contents Page

Introduction 2 - 2

Modelling 3 - 3

Material Strength 4 - 4

Section Properties 5 - 6

Shape Limitations 7 - 8

Bending Capacity 9 - 10

Dead Load of Span 11 - 12

Axial-Friction Check 13 - 14

DL + SDL + HA Loading Calculation 15 - 15

East Approach Section Check 16 - 16

02/01/2013

CALCULATION SHEET


Section Oxestalls Road Bridge - Introduction Rev

Made by BTB Date


Objective

To assess the change in stresses in the members of the bridge caused by the settlement of the

foundations in accordance with the calculated settlements. The settlements used are calculated at ground

level, the underside of pile cap and datum level assuming a volume loss due to the proposed tunnel of 1.0%

(Details in AIP).

Relevant Documents

314-EA-TPI-BR414-000001-AC AIP Oxestalls Road Bridge

BD 21/01 The Assessment of Highway Bridges and Structures

BD 56/10 The Assessment of Steel Highway Bridges and Structures

BS 5400-3:2000 Code of Practice for Design of Steel Bridges

BS 5400-5:2005 Code of Practice for Composite of Steel Bridges

Structural Analysis

The structure is assessed assuming rigid connections between all members. The effect of the settlement

has been calculated using a two dimensional grillage model for the main span of the bridge and plane frame

for the approach spans. The force output from the models have been applied to individual sections and their

utilisation of capacity has been checked.

Loadings

Settlements taken from the calculated settlement troughs are applied directly to the structure at

02/01/2013

CALCULATION SHEET

foundation level. When required, to gain an understanding of the working loads of the structure, dead loads,

super imposed dead loads and HA live loading will be calculated and applied to the models.


Section Oxestalls Road Bridge - Modelling Rev

Made by BTB Date


Modelling

The grillage model created in LUSAS to model the effects of the settllement on the main span is shown below.

As the tunnel passes under the structure, at close to 90 degrees, the volumne loss will cause the abutments

to rotate and settle down, and inward pitch toward the tunnel centre line. Conservatively, the main girders have

been assumed to be rigidly connected at their supports, this will induce excessive moment into the girders.

The bow wave effect will cause the the whole structure to rotate toward the approaching tunnel and, once

it has passed, level out again. As this is a simply supported structure on single abutments, and the tunnel

runs centrally to the foundations, this will have no effect on the span in question. For this reason only

longitudinal permanent effects will be considered.

LUSAS Grillage Model Diagram

General View of LUSAS Grillage Model

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CALCULATION SHEET

The East approach was modelled using a linear elastic plane frame. The column spacing was taken from the

inner line of columns, which gives the smallest spacing of columns, meaning the lowest hogging moment

will be calculated to check for cracking. If cracking is found in the hogging regions of the deck slab then

the approach structures will be shown to act as a series of simply supported spans. If the hogging regions

are not cracked, then then spacings will be increased to the outer column line spacing, this will create the

largest spacing, and the calculated settlement effects will be applied to the column bases and a utilisation

calculated for the deck members. A simply supported span will mean that the approach spans are not affected

by long-term tunnel settlements.

The plane frame will be given the properties of the full width of the structure. Therefore, each column will

represent six columns and the deck will have the geometric properties of of a 15m wide slab. Rigid offsets

will be used between the deck beams, representing the cone column support, to reduce the action of moment

peaking. A relatively stiffer section will be applied to the tops of the columns to represent the column flare.

General View of SAM Plane Frame Model


Section Oxestalls Road Bridge - Material Strength Rev

Made by BTB Date


Material Strengths

BD21/01 Steel

Annex C - 1960's construction, conservatively assume yield strength of: 247 N/mm^2 σy = 247

Table C2 - (Minimum for flange thicknesses less than 38mm, BS15 Revision September 1961) (fk)

BD21/01 Concrete

4.7 - Concrete cube strength assumed to be: 26 N/mm^2 (Archive information) fcu = 25.5

(fk)

BD21/01 Partial factor for Material Strength

Table 3.2 - Ƴmc 1.5 ULS for concrete Ƴmc = 1.5

BS5400-3:1990 - Ƴms ULS for steel Ƴms = 1.05

Table 2

4.2.3 - Ƴf3 1.1 for ULS Ƴf3 = 1.1

Table 3.1 - Ƴfl 1.5 for Live Loading Ƴfl = 1.5

BD21/01 Condition Factor from Inspection for Assessment = Fc = 1

3.10 Assessment Load Effects

- SA* = Ƴf3(Ƴfl*Qk)

1.05

1.00

02/01/2013

CALCULATION SHEET

3.11 Assessment Resistance

- RA* = (fk/Ƴm)*Fc

3.20 Verification of Structural Adequacy

- RA* ≥ SA*


Section Oxestalls Road Bridge - Section Properties Rev

Made by BTB Date


Section Properties

Main Steel Girders

NOTE;

Dimensions used are measurements taken from site inspection

Second moment of area, Ixx

b d yi

312 29 912

15 868 463

312 29 15

∑

y = ∑Ayi = 463 mm Ixx = ∑Ai (y-yi) + ∑Ic = mm^4

∑A

y-yi A(y-yi)^2

02/01/2013

Section A Ic Ayi

T Flange 9048 634114 8247252 -448.5 1820025558

Web 13020 817465040 6028260 0 0

B Flange 9048 634114 131196 448.5 1820025558

31116 818733268 14406708

4.459E+09

3640051116

CALCULATION SHEET

∑A

Calculation of elastic modulus, S

Sx = I / Y = mm^3 = cm^3

Calculation of plastic modulus, Z (symmetrical section)

Z = Sum of the first moments of area about the central axis

b d yi

312 29 449

15 434 217

15 434 217

312 29 449

∑

Z = mm^3 = cm^3

Shape Factor = S / Z

= 1.1

1.094E+07 10941

9630204 9630

4058028

15558 10941396

Web/2 6510 1412670

Section A Ayi

T Flange 9048 4058028

B Flange 9048

Web/2 6510 1412670


Section Oxestalls Road Bridge - Section Properties Rev

Made by BTB Date


Second moment of area, Iyy

b d yi

29 312 156

868 15 156

29 312 156

∑

y = ∑Ayi = 156 mm Iyy = ∑Ai (y-yi) + ∑Ic = mm^4

∑A

Calculation of elastic modulus, S

Sy = I / Y = mm^3 = cm^3

Torsional constant, J (approx)

J = [(2(tf^3)b + (tw)^3 d]/3 cm^4 = mm^4

Radius of gyration

ry = SQRT(I/A) = 69 mm

rx = 379 mm

6114662611.466

T Flange 9048 73397376

B Flange

A(y-yi)^2

1.470E+08

0

0

02/01/2013

Section A Ic Ayi y-yi

1411488 0 0

Web 13020 244125 2031120 0 0

942557

9048 73397376 1411488 0

31116 147038877 4854096

943

CALCULATION SHEET


Section Oxestalls Road Bridge - Shape Limitations Rev

Made by BTB Date


BS5400-3 Shape Limitations

AND Main Steel Girders

BD56/10 APP A NOTE;


6.6

E = N/mm^2 σy = 235 N/mm^2 L = 21 m

G = N/mm^2 A = mm^2 Le = 4.8 m

ʋ = 0.3 Ixx = mm^4 hs = 868 mm

y = 463 mm ts = 10 mm

BS5400 Design of Beams ds = 110 mm

9

9.2.1.2 Effects to be Considered in Design of I Beams

02/01/2013

205000

80000 31116

4.5E+09

CALCULATION SHEET

a) Flexure, shear, torsion

b) Axial load

c) Creep, shrinkage and differential temperature

d) Settlement of supports

9.2.1.3 Effects that may be Neglected in Design of I Beams

a) Shear lag

b) restraint of torsional warping

9.3.2.1 Flange Outstands in Compression

An unstiffened outstand should limit bf0/tf0 to 12SQRT(355/σy)

bf0/tf0 = 11 and, 12SQRT(355/σy) = 15 Therefore; Okay

A stiffened outstand should limit bf0/tf0 to 14SQRT(355/σy)

bf0/tf0 = 11 and, 14SQRT(355/σy) = 17 Therefore; Okay

9.3.2.1A No reason to downgrade strength due to bf0/tf0 limit, due to historical use

9.3.4 Stiffeners to Webs and Compression Flanges

For Flat stiffeners hs SQRTσys should be less than 10 = 71 Not Okay

ts 355

Annex C Or ds/ts should not exceed 1.7 SQRT(E/(σys+σa)), conservative to assume σys = σa

= 35 ds/ts = 11 Okay


Section Oxestalls Road Bridge - Shape Limitations Rev

Made by BTB Date


Note: The slenderness of the web stiffeners is not of importance in this case due to the lateral cross bracing fixed

at each stiffener

9.3.7 Compact Section Check , where m = 0.5

9.3.8.2A The depth between plastic neutral axis and 28tw * SQRT 355 =

compression edge of web should not exceed; σy

Web is compact

9.3.7.3 The projection of the compression outstand, bf0, should not exceed;

7tf0* SQRT[355/σy] = 249 mm bf0 = 149 mm Flange is compact

Note: as this section is castellated it will be treated as a non-compact section

9.4 Effective Section for Global Analysis

9.4.2.2 - Shear lag effects not considered

9.4.2.3 - Effective area of tension flange = 1, no holes in tension flange

9.4.2.4 - Effective area of compression flange = 1, no holes in compression flange

9.4.2.5.1 - Effective web for beams with effective longitudinal stiffeners, twe = tw

(beams without longitudinal stiffeners check)

twe = tw if yc/tw SQRT(σyw/355) ≤ 68 = 24 therefore twe = tw

02/01/2013

515.952

CALCULATION SHEET


Section Oxestalls Road Bridge - Section Capacity Rev

Made by BTB Date


BS5400-3 Section Capacity

AND Main Steel Girders

BD56/10 APP A NOTE;


6.6

E = N/mm^2 σy = 235 N/mm^2 L = 21 m

G = N/mm^2 A = mm^2 Le = 4.8 m

ʋ = 0.3 Ixx = mm^4 (distance between lateral restraints)

y = 463 mm

9.7.1 Plastic Moment of resistance

Mpe = σyZ = Nmm = kNm2573833154 2574

02/01/2013

205000

80000 31116

4.5E+09

CALCULATION SHEET

Elastic Moment of resistance

Me = σyS = Nmm = kNm

9.8 Limiting moment of Resistance

Using;

λLT SQRT(σyc*Mult/355Mpe)

Where,

- Mult = Mpe for compact sections or Me for non-compact sections = kNm

- σyc = 235 N/mm^2

9.7.2 - λLT = (le/ry)K4 η V

- η = 1

9.7.1 - lw = Half wave length of buckling = 4.8 m between intermediate bracing

- λf = (lw tf/ry D) =

9.7.2A - V = [{4i(1-i)+0.05λf^2+ψi^2}^0.5 + ψi]^-0.5 =

i = 0.5 when flanges are equal

ψi = 0 (when ic ≤ It)

9.7.2A - Cw = (df^2 tft tfb Bft^3 Bfb^3)/12(tft Bft^3 + tfb Bfb^3) = mm^6

df = 897 mm

9.7.2A - K4 = [Iy Zpe^2 (1-(Iy/Ix))/A^2 Cw]^0.25 = (symmetrical about major axis)

- K4 = [4 Zpe^2 (1-(Iy/Ix))/A^2 h^2]^0.25 = (symmetrical about minor axis)

- λLT = 39

2265390811 2265

2.9528E+13

0.595

0.594

2265

2.164

0.949


Section Oxestalls Road Bridge - Section Capacity Rev

Made by BTB Date


9.8 - Mult = Mpe (compact sections), Me (non-compact sections) = kNm

9.8A

Figure 11a - λLT SQRT(σyc*Mult/355Mpe) = 34

Reading off figure 11a MR/Mult =

Figure 11a

0.95

02/01/2013

2265

CALCULATION SHEET

MR = kNm Factored moment of resistance = kNm

Utilisation

Factored applied 1.0% moment from SAM model = kNm (1.5 LL factor applied)

Bending Utilisation 1.0% = 1.7 % Okay

20502152

34.19


Section Oxestalls Road Bridge - Dead Load Reaction Rev

Made by BTB Date


Conservative calculation for self weight of deck elements

Main Girders

927mm by 308mm symmetrical steel girders with 29mm thick flanges and 15mm web;

CSA = mm^2 Unit weight = 79 kN/m^3 Span = 22 m

Weight of each I section = 53 kN Number of girders = 13

02/01/2013

31116

CALCULATION SHEET

Minus wight of web holes = 0.2 m^2 each 31No. = 7.2 kN

Total weight of I sections in deck = 676 kN

Web stiffeners

807mm by 140mm by 5mm web stiffeners, total volume = m^3

12 per inner girder and 6 per outer girder, total number of = 144

Total weight of web stiffeners in deck = 6.4 kN

Cross Bracing (4x12 units, i.e. 48 trusses)

80mm by 80mm by 5mm angle sections across 4 transverse bracing trusses

length of top and bottom elements = 1.5 Total number = 96

Length of diagonal elements = 1.7 Total number = 96

Weight of top and bottom cords = 8.9 kN

Weight of diagonals = 10 kN

End span channel sections, 180mm by 80mm by 80mm by 5mm, 1.48m in length *24 = 5 kN

Total weight of bracing in deck = 24 kN

675.5

6.4

0.00056

24.3


Section Oxestalls Road Bridge - Dead Load Reaction Rev

Made by BTB Date


Bearing Plates

300mm by 350mm by 50mm plates under each end of the main girders = 9.2 kN

Concrete Deck

580mm deep reinforced concrete deck 20m wide and 22m length = kN

unit weight of concrete = 24 kN/m3

Concrete Coping

170mm by 620mm deck coping over 22m*2 length = 111 kN

Steel Parapet (assumed)

Top cord 250mm by 100mm by 5mm volume over 22m = 0.2 m^3

Upright members, assume 8 per metre, 20mm by 30mm by 2.5mm over 22m= 0.1 m^3

Bottom cord 30mm by 5mm by 22m = m^3

Total weight of parapet on deck = 20 kN 20

02/01/2013

9.2

6124.8 6124.8

111.3

0.0066

CALCULATION SHEET

Footways and Carriageway

160mm depth over 3m width on South and 6.3m on North for 22m span = 33 m^3

Assume carriageway is 250mm thick over total area of the deck = 110 m^3

Unit weight of surfacing = 23 kN/m3

Total weight of surfacing on deck = kN

BD21/01 Table 3.1 The partial load factors the dead loads and the ultimate dead loads are given below.

Material γγγγm

Steel

Concrete

Surfacing

Total weight of deck = kN kN

3282.933282.93

1.10

1.75

13376 13376.5

1.05


Section Oxestalls Road Bridge - Friction Rev

Made by BTB Date


Assume each main girder carries a thirteenth of the total weight of the deck.

Main Girder Load: 13376/13 = kN / Girder

Reaction at each main girder support = kN

Assume the coefficient of friction between the bearing plate and the bedstone, μ = 0.5

The friction force at each support, F = μ.R (where R is the reaction at each support)

Friction at each main girder support = kN

The maximum total friction force at each end of the bridge due to dead loads = kN

This is the force that must be carried axially in the longitudinal girders before slip occurs.

Maxium axial at 1.7% = kN per girder Slippage Occurs at 1.7%

Maxium axial at 1.0% = kN per girder Slippage Occurs at 1.0%

The minimum cross section of the longitudinal girders is at web openings;

1028.96

514.481

257.24

3344.12

02/01/2013

1793.64

1055.08

CALCULATION SHEET

The cross sectional area (CSA) of the longitudinal girders at the web openings is:

Main girder: 2 x[(312 x 29) + (15 x 258)] = mm2

The total CSA for the longitudinal girders at web openings = 13 x (25836) = mm2

As the CSA is a minimum at the the web openings, σa, is a maximum.

σa = F / A = 3344124 / 335868 = N/mm2

(stress at which bearing slippage will occur)

The ultimate longitudinal resistance stress in the section, σy = 247 N/mm2 / (γm x γf3)

σy = 247 / (1.05 x 1.1) = N/mm2

213.9

25836

335868

9.96


Section Oxestalls Road Bridge - Friction Rev

Made by BTB Date


Check that the movement experienced by the bridge deck due to the settlement is greater than the shortening

of the bridge deck caused by the friction forces applied at the bearings.

(i.e. that the maximum stress calculated is realised)

σ = E.ε δ = ε.L δ = σ . L δ = = mm

E

As this is smaller than the actual expected movement of the bridge the deck will experience the stresses.

Horizontal movement due to tunnel settlement = 2.2 mm

Therefore, as the movement required to cause the girders to slip on the bearings is lower than the

worse case applied horizontal movement due to settlement of the tunnel no significant increase

in axial force will be observed in the main girder, as the girder will slip on its bearing plates.

i.e. Limiting the applied axial force

Stresses in the Longitudinal Girder (N/mm2)

As slippage occurs at both 1.0% and 1.7% volume loss, the maximum axial stress in the girders will be the

same for both cases.


9.96 x 21.2/205000 1.02918


02/01/2013

CALCULATION SHEET


Section Oxestalls Road Bridge - Loading Calculations Rev

Made by BTB Date


Calculation of Loading for Crack Check

If approach slab is shown as cracked over the supports, then it may be treated as simply supported

with no hogging moment over supports.

Live Load

37/01 Loaded Length Two Spans = m

6 HA UDL = 336(1/L)^0.67 for Loaded lengths upto 50m;

HA UDL = 36(1/L)^0.1 for Loaded lengths over 50m;

HA UDL = kN/m

BD21/01

5.24 HA Lane Factors

Loaded length = m First Lane Factor = 1 ; Second Lane Factor = 1

6.2.2 Nominal knife edge load = 120 kN per lane

6.5.1 Nominal Pedestrian Live Loading Over 5.94m total width

6.5.1.1 Loaded length = m Pedestrian Live Loading = kN/m^2

5.2 Reduction Factor K, Medium Traffic Flow, Poor surface = 0.9

5.23 Adjustment Factor = 4.27

10.47

02/01/2013

10.47

69.66

10.47 5.00

CALCULATION SHEET

5.1 Dead Loading (Design loads = Loads * ƳfL * Ƴf3)

Assume 15.09m wide and 355mm depth slab at 24kN/m^3 = 128.5kN/m

5.2.2 Superimposed dead Loading

Assume 15.09m wide road and 200mm depth surfacing at 23kN/m^3 = 69.4kN/m

Maximum Hogging Moment from SAM plane frame model under LL + DL + SDL = kNm

Maximum sagging Moment from SAM plane frame model under LL + DL + SDL = kNm

1140.62

-873.74


Section Oxestalls Road Bridge - East Approach Rev

Made by BTB Date


Calculation of East Approach Slab Hogging Moment Capacity

Section Properties

Width of section mm Es N/mm^2

Depth of Section mm es

Concrete, Fcu N/mm^2 gm

Steel, Fy N/mm^2 gm

Concrete Properties

Depth to NA mm

Area of Concrete mm^2

Gross conc comp force N

34.0458

34045.8

347268

02/01/2013

1000 200000

355 0.00107

25.5 1.5

247 1.15

CALCULATION SHEET

Max conc strain

Depth of conc comp block mm

Calculation of Forces in section

No.

6

3

Calculation for removal of steel area from concrete

Conc F lost due to steel N

Conc M lost due to steel Nmm

Conc comp M less-steel Nmm

ULS Capacity

Fcc (inc steel reduction) N

Fst N

ULS Axial Force N

ULS Moment Nmm 44 kNm

Highest applied moment due to DL + SDL + LL = kNm (hogging)

Moment appiled per meter = kNm

Therefore utilisation of deck slab = 173 % Therefore slab will crack in hogging over columns

giving the effect of pinned supports.

1.1E-06

4.4E+07

1140.62

75.6078

0

0

6502658

347268

383818

-0.02827 -214.783 -127939 3.5E+07 6750.92 -1856194

-184.102 -219328 1963899 13501.8 -120898

15.9 198.557 595.67 309 -274.954

15.9 198.557 1191.34 43

Dia Bar Area T Area d NA-d

-0.00092

Strain

-8.95416

0.0035

Mconc

30.6413

Stress Force Mx Fconc

314-RI-TPI-BR414-000001 | AB


Inspection for Assessment Report Oxestalls Road Bridge Structure No. BR414

THIS REPORT INCLUDING THE DRAWINGS AND OTHER SUPPORTING DOCUMENTATION IS PROVIDED FOR THE PURPOSE OF IDENTIFYING AND AGREEING THE LIKELY EFFECTS OF THE CONSTRUCTION OF THE THAMES TUNNEL ON THE ASSETS AND INFRASTRUCTURE OF THE PARTY IN RECEIPT OF THIS REPORT AND FOR THE PURPOSE OF SECURING APPROVAL IN PRINCIPLE TO THE DESIGN OF THE THAMES TUNNEL. THE REPORT IS CONFIDENTIAL TO THAMES WATER AND THE INTENDED RECIPIENT AND THEIR CONSULTANTS [APPOINTED WITH THE AGREEMENT OF THAMES WATER]. THE REPORT SHALL NOT BE PROVIDED TO ANY THIRD PARTY WITHOUT THE EXPRESS WRITTEN PERMISSION OF THAMES WATER UTLIITIES LIMITED.

314-RI-TPI-BR414-000001 | AB

Inspection for Assessment Report 11/07/2012


Inspection for Assessment Report

Name Data

Document no 314-RI-TPI-BR414-000001

Status APP/PUB

Document type Report

WBS DE.03.3P

Authors Ian Ó Dubhghaill

Keywords Oxestalls, Bridge, Assessment, Inspection Report

Contents amendment record

This document has been issued and amended as follows:

Revision Date Issued for/Revision details Revised by

AA 10/04/2012 First Issue I ÓD

AB 11/07/2012 Second Issue BTB

Required approval

11/07/2012

George Lawlor – Project Manager

Date

314-RI-TPI-BR414-000001 | AB

Inspection for Assessment Report Page 1 11/07/2012


Inspection for Assessment Report

List of contents

Page number

1 Summary ........................................................................................................... 2

2 Introduction ...................................................................................................... 3

2.1 Purpose of Inspection .............................................................................. 3

2.2 General Inspection Methodology ............................................................. 3

2.3 Inspection Details .................................................................................... 3

3 Description of Structure .................................................................................. 4

3.1 Location Plan ........................................................................................... 5

3.2 Substructure ............................................................................................ 5

3.3 Superstructure ......................................................................................... 5

3.4 Spans ...................................................................................................... 6

4 Inspection & Maintenance History .................................................................. 7

5 General Observations ...................................................................................... 8

5.1 Substructure ............................................................................................ 8

5.2 Superstructure ......................................................................................... 9

5.3 Joints ..................................................................................................... 17

5.4 Surfacing ............................................................................................... 20

5.5 Drainage ................................................................................................ 24

5.6 Services ................................................................................................. 24

5.7 Parapets ................................................................................................ 26

5.8 Ancillary ................................................................................................. 27

6 Conclusions .................................................................................................... 28

7 Recommendations ......................................................................................... 29

314-RI-TPI-BR414-000001 | AB


1 Summary

AECOM has been commissioned by Thames Tunnel to carry out an

Inspection for Assessment of Oxestalls Road Bridge for Sub-package 3c

of the Detailed Bridge Assessment contract.

Oxestalls is a single-span steel castellated girder and composite concrete

deck bridge with rising approach structures on both sides. It appeared as

though the existence of a smaller span to the West of the visible span is

possible. However, the brickwork concealing areas of the bridge under its

deck level prevented confirmation of this.

The inspection comprised of a visual survey to check for corrosion,

cracking, water seepage and other defects. It was conducted during

daytime hours and in accordance with the approved method statement

(Doc. No. 314-PE-TPI-BR414-000001-AB). The bridge shows some

deterioration but was found to be in fair condition overall.

Parts of the structure were concealed behind a brickwork facade that has

been constructed since the closure of the canal. The abutment walls and

the superstructure of the span were visible at the time of the inspection.

Some degradation of these abutments was evident in the form of spalling

of the concrete face. This appears to have been exacerbated by water

permeating through joints in the deck at the positions of the span supports.

Water runoff has caused staining of the abutment faces. It is promoting the

growth of organic material and the deposition of minerals on the face of

the concrete.

A large amount of surface corrosion is visible on some of the outer

longitudinal span girders and their bearing plates. However, no section

loss was observed.

Spalling of the surface of the structural concrete of the superstructure

elements was observed in several locations. This surface breakaway has

resulted in the exposure of reinforcement steel in many places. Surface

breakaway of the concrete and efflorescence of surfaces was observed at

the locations of two of the weep holes of the concrete structure, where

water runoff is evident.

The carriageway and footways were observed to be in poor condition.

Excessive cracking was found on the Asphalt surface of the road and in

the paving slabs of the footway. Large transverse cracks in the

carriageway are visible at the locations of joints in the concrete of the

superstructure. Significant cracking and breakup of the road surface is

particularly evident on the east approach to the bridge. Large pot holes are

forming in this area due to the surface deterioration.

314-RI-TPI-BR414-000001 | AB


2 Introduction

2.1 Purpose of Inspection

AECOM has been commissioned by Thames Tunnel to carry out an

Inspection for Assessment of Oxestalls Road Bridge. This forms a part of

the Sub-package 3c of the Detailed Bridge Assessment contract for impact

assessment of proposed tunnelling works for the Thames Tunnel project.

The main objective of the project is to identify any structural or

serviceability implications that may result from proposed tunnelling works

in the vicinity of the existing infrastructure. The inspection for assessment

has been focused specifically at the elements which could potentially be

affected by the proposed Thames Tunnel construction.

2.2 General Inspection Methodology

The proposed Thames Tunnel will pass underneath the structure

potentially causing settlement of the soil structure beneath the foundations

of the bridge. The line of the proposed tunnel passes close to the centre

line of the span.

All visible elements of the structure affected by the proposed tunnel were

inspected. The inspection took place from the bridge deck and from areas

surrounding the bridge. All major defects were recorded and

photographed. Procedures were in accordance with the method statement

for the inspection for assessment of Oxestalls Roadbridge (Doc. No. 314-

PE-TPI-BR414-000001-AB) and followed the relevant sections of BD62/07

(As Built, Operational and Maintenance Records for Highway Structures)

and BD63/07 (Inspection of Highway Structures).

2.3 Inspection Details

Inspected by: AECOM Ltd.

B. Burney, I. Ó Dubhghaill

Equipment Used: Digital Camera

Date of inspection: 28th February 2012

Weather Conditions: Dry, Clear sky and sunny, ambient temperature

approx. 12°C

Access: By pedestrian footways on deck. By use of

footways to the North of the structure, by use of

property yard to South of structure.

Areas not Inspected: Foundations, abutments below ground level or

concealed by brickwork; internal aspects of

structural elements e.g. joints; Superstructure

elements concealed by brickwork

314-RI-TPI-BR414-000001 | AB


3 Description of Structure

Oxestalls Road Bridge is located in the London Borough of Lewisham (OS

ref. TQ 364 784).

The Oxestalls Road Bridge is the most recent bridge to be built over the

Grand Surrey Canal. It was constructed just downstream from the

entrance lock of the canal. The bridge and surrounding estate were built in

the 1960's, when the canal was still in use. The canal underneath the

bridge was filled in since the construction of the bridge and the land

reclaimed.

Oxestalls is a single-span castellated steel girder and concrete composite

bridge. A rising approach structure carries the approach carriageways on

either side of the span.

It appeared as though the existence of a small span to the West of the

visible span is possible. However, the brickwork concealing the structure

of the bridge under its deck level prevented confirmation of this.

Photograph 1: General view of structure – Span, South Elevation

314-RI-TPI-BR414-000001 | AB


3.1 Location Plan

Figure 1: Location Plan of Oxestalls Road Bridge, London

3.2 Substructure

No information is currently available on the substructure of Oxestalls

Bridge. The visual survey found that the abutments were of reinforced

concrete composition.

3.3 Superstructure

Oxestalls is a single-span castellated steel girder and composite concrete

deck bridge with a rising approach structure on both sides.

The bridge deck is a reinforced concrete structure. On the span, the

concrete bridge deck is supported by 13 No. longitudinal castellated

girders at regular spacing. These have 4 No. cross bracings at intervals

along their length. The outermost girders on either side of the span are

skewed relative to the others.

The pre-cambered longitudinal girders of the span are simply supported

on the bearing shelves of the abutment walls. Steel bearing plates sit

between the girder bottom flanges and the bearing shelf. There are joints

in the concrete deck above bearing shelf. There is also a joint in the

concrete slab on the West approach and it is likely that there is a similar

joint on the East approach.

Oxestalls Bridge

314-RI-TPI-BR414-000001 | AB


A small concrete wall sits just proud of the deck level to support the

parapets, which are steel.

A brickwork wall surrounds the structure. It extends from the underside of

the deck down to ground level. This conceals the most of the underlying

structure of the bridge.

3.4 Spans

The structure is a single span. The presence of a separate shorter span

to the east of the structure could not be confirmed.

314-RI-TPI-BR414-000001 | AB


4 Inspection & Maintenance History

The history of inspections and maintenance of the Oxestalls Road Bridge is unknown.

314-RI-TPI-BR414-000001 | AB


5 General Observations

5.1 Substructure

The majority of the substructure was not visible at the time of the

inspection as much of the area underneath the superstructure has been

concealed by brickwork. The abutments of the span were the only sections

of the substructure that were accessible for visual survey.

The abutments were observed to be in fair condition. A large amount of

water runoff was evident on the walls of the abutments. It is likely that the

joints at the abutments are allowing the permeation of water from the deck

level. This appears to be most prominent at the outer edges of the span.

The runoff is causing a large amount of organic growth and the deposition

of minerals on the face of the abutment walls, suggesting that the runoff

had been taking place for some time prior to the inspection. [Photograph

2]

Spalling and cracking of the concrete face of the abutment walls was also

observed, causing the exposure and corrosion of the reinforcement bars

on the East abutment. The bars appear to have been installed with

relatively low concrete cover at the time of construction. [Photograph 3]

Photograph 2: Water runoff and organic growth Western abutment wall

314-RI-TPI-BR414-000001 | AB


Photograph 3: Water runoff and spalling causing exposure and corrosion of reinforcement

5.2 Superstructure

As with the substructure, much of the superstructure is hidden by the brick

wall around the structure. However, the survey of the visible elements of

the superstructure showed them to be in a fair condition overall.

The girders supporting the span decking were observed to be in good

condition generally, showing surface corrosion in places. Generally, this

corrosion is localised to the outer girders and is at its worst on the bottom

flanges of these girders. [Photograph 4, 5]

The bearing plates under the longitudinal girders also show signs of

surface corrosion. This deterioration of the steel is likely to be related to

the water runoff that is evident at the faces of the abutment walls.

[Photograph 6, 7]

Exposed Reinforcement

314-RI-TPI-BR414-000001 | AB


Photograph 4: Surface corrosion of outermost girders of the span

Photograph 5: Corrosion of bottom flange of outer North-Western longitudinal girders

314-RI-TPI-BR414-000001 | AB


Photograph 6: Deterioration of bearing plate due to corrosion – West abutment wall

Photograph 7: Deterioration of bearing plate due to corrosion – East abutment wall

314-RI-TPI-BR414-000001 | AB


Minor misalignment of the bearing plates between the top of the bearing

shelf and the bottom flanges of the longitudinal girders was observed at

one location. [Photograph 8]

Photograph 8: Misalignment of bearing plate – West abutment

The bottom angle plate of the Northern-most transverse bracing between

girders 11 and 12 appeared to be damaged. [Photograph 9]

Photograph 9: Damage to transverse girder bracing

Damage to girder transverse bracing

314-RI-TPI-BR414-000001 | AB


It was observed that, in several locations along the length of the bridge,

spalling had occurred on the outermost faces of the concrete slabs of the

span and the approaches. This spalling has led to the exposure of the

steel reinforcement of the slabs in several locations. Where the

reinforcement bars are exposed, corrosion of the steel is visible. It should

also be noted that, regardless of the effects of spalling, the steel appears

to have been installed with very low concrete cover at the time of

construction, and lies very close to the face of the slab elements in places.

[Photograph 10, 11]

Photograph 10: Spalling concrete exposing corroded steel North wing-wall, West

approach

314-RI-TPI-BR414-000001 | AB


Photograph 11: Exposed steel reinforcement North face of slab, West approach

Water staining is evident in numerous locations on the structure. In many

locations where water runoff and staining are evident, the continual build

up and flow of water is causing deterioration and breakup of the concrete

at the surface of the structural elements. Organic growth is also promoted

in the locations with a regular presence of water. Such breakup and

organic growth was observed at the outlet points for two of the weep-holes

in the concrete. [Photograph 12-14]

314-RI-TPI-BR414-000001 | AB


Photograph 12: Spalling of concrete face due to water runoff at weep-hole outlet point

Photograph 13: Water staining & exposed reinforcement on concrete element soffit

314-RI-TPI-BR414-000001 | AB


Photograph 14: Water staining & efflorescence at weep-hole, Southern wing-wall

The brick wall extends from the underside of the concrete structural

elements to ground level and it is in place in all locations around the

structure, barring the South elevation of the span section. There is a

significant level of mortar loss at the joints between bricks of the facade.

Minor spalling of the brickwork was also observed. [Photograph 15]

Photograph 15: Mortar loss and spalling of brickwork – Southern wing-wall, West

approach

314-RI-TPI-BR414-000001 | AB


The Southern wing-wall of the West approach shows signs of previous

repair of the brickwork in several locations. The reason for this

replacement of brickwork is unknown. [Photograph 16]

Photograph 16: Brickwork replacement – Southern wing-wall, West approach

Horizontal separation cracks were observed in the concrete elements on

the East approach, adjacent to the span. [Photograph 17]

Photograph 17: Separation crack in concrete element

5.3 Joints

A joint in the structural concrete is visible on the West approach, and it is

presumed that a similar joint is located on the East approach at the

position of the significant transverse crack in the carriageway surface.

314-RI-TPI-BR414-000001 | AB


Joints in the concrete superstructure are also evident at the positions of

the supports of the simply-supported span.

The joints that were visible at the time of the inspection appeared to be in

fair condition. The silicon-type material used to achieve water tightness at

the joints has deteriorated to the point where it serves to be ineffective.

[Photograph 18]

Photograph 18: Deteriorated water-proofing material at joint

Significant transverse cracking was observed in the carriageway in some

locations. It is likely that much of this transverse cracking is caused by the

relative movement of material at a joint in the main structural elements.

[Photograph 19, 20]

314-RI-TPI-BR414-000001 | AB


Photograph 19: Transverse cracking in carriageway – West approach

314-RI-TPI-BR414-000001 | AB


Photograph 20: Transverse cracking in carriageway – East approach

5.4 Surfacing

The surfacing of the bridge deck was seen to be in poor condition. Both

the carriageway and footway surfaces show significant cracking.

As stated in the previous section, large transverse cracks spanning the full

width of the carriageway were observed in a number of locations. It is

likely that some of these cracks originated and propagated at points where

there are structural joints in the superstructure. Large cracks are evident in

several other areas of the road surface also.

314-RI-TPI-BR414-000001 | AB


There is a large longitudinal crack running just to the South of the centre of

the road. The crack runs the length of the bridge including the approaches.

[Photograph 21]

Photograph 21: Longitudinal crack South of road centre

There is significant cracking on the East approach. Both transverse and

longitudinal cracking of the surface was observed at this location. The

cracks have become large enough to form pot holes in a number of

locations in this area. It appears as though attempts have been made to

repair these in places.

Reinstatement has also been carried out at the Eastern end of the span.

The reinstatement extends transversely across the width of the

carriageway. The Asphalt installed during the reinstatement has since

sunk slightly, forming a crack in the road surface at the point where the

reinstatement Asphalt meets the original surfacing Asphalt.

[Photograph 22]

314-RI-TPI-BR414-000001 | AB


Photograph 22: Transverse reinstatement in roadway

A large amount of surface breakup is also evident around the edges of the

storm water gullies. [Photograph 23]

314-RI-TPI-BR414-000001 | AB


Photograph 23: Road surface breakup around storm water manhole

Cracking of the footway paving slabs was observed over the length of the

bridge and its approach sections. [Photograph 24]. Reinstatement in the

footway has sunk to create a pot hole in the pavement. This is likely to

have been caused by lack of compaction of backfill at a time when the

footway was excavated in this location. [Photograph 25]

Photograph 24: Cracking of paving slabs along South footway

314-RI-TPI-BR414-000001 | AB


Photograph 25: Sinking of reinstated section of footway

5.5 Drainage

There are a number of storm water gullies along the kerb line of the

footways. Most of the gulley pots did appear to be clear of debris, however

one was observed to be blocked due to a build up of silt debris and litter.

Despite the build up of debris within the gulley, no signs of recent flooding

were evident at the time of the inspection.

It was observed that there are a number of weep-holes in the concrete

elements of the bridge. These appear to be unblocked as there is

evidence of water runoff on the surface of the concrete at the locations of

a number of these weep-holes. [Section 5.2, Photographs 12, 14]

5.6 Services

The service hatches on many of the street lamps along the carriageway

were in a state of disrepair. Some of the hatches are merely strapped in

position using cable ties. [Photograph 26]

314-RI-TPI-BR414-000001 | AB


Photograph 26: Damaged lamp post service hatch – North footway, West approach

A service box integrated into the brickwork of the West approach, adjacent

to the span. This presumably houses electric or telecom services

supplying the nearby buildings and street lighting. [Photograph 27]

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Photograph 27: Service box South wing-wall

5.7 Parapets

The parapets were observed to be in fair condition. Some damage to the

Southern parapet is evident on the West approach. It would appear that

the parapets were deformed in places as a result of impact. [Photograph

28]

Photograph 28: Damage to Southern Parapet

314-RI-TPI-BR414-000001 | AB


A number of capping slabs of the base wall of the parapets have become

loose and dislodged from their original positions. These have been

replaced in numerous positions along the wall. [Photograph 28, 29]

Photograph 29: Dislodge capping slabs on parapet base-wall

5.8 Ancillary

Excessive vegetation growth and litter was observed adjacent to the South wing-wall of the West approach. [Photograph 30]

Photograph 30: Vegetation and litter South wing-wall

314-RI-TPI-BR414-000001 | AB


6 Conclusions

The bridge was found to be in fair condition, generally. There were,

however, some signs of deterioration at the time the inspection was

carried out.

From the inspection of the visible areas of the substructure, it was deemed

to be in fair condition. Water runoff is causing spalling of the abutment

walls, exposing the steel reinforcement in the East wall. The exposed

reinforcement shows signs of corrosion. It would appear as though the

bars were installed with very little concrete cover at the time of

construction. A significant amount of organic growth and deposition of

minerals was apparent on the faces of the abutment walls. These are

likely to be the result of water seepage. This water appears as though it is

percolating from the deck level through the outermost sections of the joints

in the superstructure.

The leaking at these joints appears to be leading to surface corrosion of

the bearing plates and simply supported steel girder elements of the span.

These elements are in good condition generally, with the inner girders

showing little to no corrosion. The corrosion appears to be limited to the

surface of the outermost elements for the most part and is at its worst on

the bottom flanges; no section loss is evident.

The surface of the superstructure concrete shows signs of significant

spalling, which is resulting in the exposure of the steel reinforcement.

Similarly here the reinforcement was installed with a very little cover

The breakup of the concrete is prevalent at the locations of the weep holes

in the structure. At these locations, water runoff appears to be causing the

breakaway of the concrete surface as well as organic staining.

The bridge surfacing shows signs of significant degradation, with cracking

widespread across the surface of the carriageway and footways. It is

probable that some of the more prominent transverse cracks in the

roadway are the result of the relative movement of material at joints in the

structure underneath the road surface. Severe breakup of the road surface

was recorded on the East approach. The paving slabs of the footways are

also in poor condition, and cracking of the slabs can be seen along the full

length of the bridge, including the approaches.

The capping slabs of the parapet base-wall are in poor condition and have

been replaced in some locations.

314-RI-TPI-BR414-000001 | AB


7 Recommendations

Based on the condition of the structural members inspected, and that

observed deterioration is only to the surface of the main structural

elements a condition factor of 1.0 will be applied to all structural members

in the assessment of Oxestalls Bridge (Doc. No. 314-RG-TPI-BR414-

000001).

Copyright notice Copyright © Thames Water Utilities Limited September 2013. All rights reserved. Any plans, drawings, designs and materials (materials) submitted by Thames Water Utilities Limited (Thames Water) as part of this application for Development Consent to the Planning Inspectorate are protected by copyright. You may only use this material (including making copies of it) in order to (a) inspect those plans, drawings, designs and materials at a more convenient time or place; or (b) to facilitate the exercise of a right to participate in the pre-examination or examination stages of the application which is available under the Planning Act 2008 and related regulations. Use for any other purpose is prohibited and further copies must not be made without the prior written consent of Thames Water. Thames Water Utilities LimitedClearwater Court, Vastern Road, Reading RG1 8DB The Thames Water logo and Thames Tideway Tunnel logo are © Thames Water Utilities Limited. All rights reserved.

Copyright notice Copyright © Thames Water Utilities Limited September 2013. All rights reserved. Any plans, drawings, designs and materials (materials) submitted by Thames Water Utilities Limited (Thames Water) as part of this application for Development Consent to the Planning Inspectorate are protected by copyright. You may only use this material (including making copies of it) in order to (a) inspect those plans, drawings, designs and materials at a more convenient time or place; or (b) to facilitate the exercise of a right to participate in the pre-examination or examination stages of the application which is available under the Planning Act 2008 and related regulations. Use for any other purpose is prohibited and further copies must not be made without the prior written consent of Thames Water. Thames Water Utilities LimitedClearwater Court, Vastern Road, Reading RG1 8DB The Thames Water logo and Thames Tideway Tunnel logo are © Thames Water Utilities Limited. All rights reserved.

10243-A4P-Copyright-imp-V01.pdf p1 12:03:39 September 21, 2013