Inspection and Maintenance of the Orthotropic Deck of Avonmouth Bridge

Inspection and maintenance of the orthotropic deck of Avonmouth Bridge

B.I. Frey Mott MacDonald, Bristol, UK

ABSTRACT: Avonmouth Bridge is a twin steel box girder bridge with 20 spans, an orthotropic deck in the three main spans and a concrete deck which is acting compositely in the approach spans. The bridge has been widened to accommodate four lanes of traffic in each direction resulting in asymmetrical loading. The orthotropic deck is suffering from recurring cracks and is inspected and repaired annually. Access is provided by gantries and a mezzanine floor inside the box girders. The repaired welds are improved by carrying out partial penetration welds instead of fillet welds; the deck stiffness has also been improved by a new guss-asphalt surfacing.

1 DESCRIPTION OF THE STRUCTURE 6.5m to 18.3m long. In the approach spans the deck is a 220mm reinforced concrete deck which acts Avonmouth Bridge carries the M5 motorway over compositely with the steel box girders. In the main the River Avon, A4 Portway, the Severn Beach span (the river span and the two adjacent spans) the railway line and the industrial estates of Avonmouth. deck is an orthotropic steel deck. The bridge is an- The M5 motorway is the major link of the Southwest chored against longitudinal movements at both to the rest of England. The bridge was originally de- abutments. Movement is accommodated by flexure signed by Freeman Fox Ltd. and first opened to traf- of the piers and the expansion joint adjacent to pier fic in 1974. In the 1990s the bridge was strengthened 10 connecting the orthotropic steel deck and the to accommodate an additional fourth lane of traffic composite northern approach span. The piers and on both carriageways. The bridge is approximately abutments are made of reinforced concrete and have 1.4km long and has 20 spans varying in length be- spread footing foundations, except for piers 6, 7 and tween 30m to 174m with a vertical clearance of 30m 8 which are supported on piles. The strengthening over the river (Figure 1). Balfour Beatty Mott Mac- consisted of external post-tensioning above the river Donald are the Highways Agency’s maintaining piers and some areas of the approach spans, im- agents for Area 2 in the Southwest of England. provement of the steel knuckle bearings, and instal- The superstructure consists of two continuous lation of additional stiffeners and web plates in the steel box girders connected by steel cross girders box girders. Access to the bridge is provided by two which in turn support the deck. The box girders it- centre and eight cantilever gantries (Figure 2). self are divided into 83 box sections each between

Figure 1. Photo of Avonmouth Bridge, looking North.

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Figure 2. Cross section of Avonmouth Bridge indicating the alignment of centre and cantilever gantries. 3 THE ORTHOTROPIC BRIDGE DECK

Avonmouth Bridge has two box girders instead of 2 MAINTENANCE REQUIREMENTS OF open main girders (Figure 3); this provides more tor- AVONMOUTH BRIDGE sional stiffness but does not change the function of the orthotropic deck. The distance between the webs Due to the high importance of Avonmouth Bridge of each box is 5.942m and 18.436m between the for the UK infrastructure a maintenance team is boxes. The cross girders connect the webs every permanently based at the Avonmouth Bridge Unit 3.660m and continue under the cantilevers. The lon- (ABU) close to the bridge. This enables maintenance gitudinal deck stiffeners are of a V-shape trough tasks to be carried out on a day to day basis and profile at 0.610m centres outside the boxes and greatly simplifies the logistics for scheduled works 0.572m centres inside the boxes. and inspections. The trough stiffeners run continuously through The inspection regime for Avonmouth Bridge is the cross girders with cope holes cut around the bot- risk based depending on the criticality of the particu- tom and the longitudinal welds of the stiffeners. lar element of the structure. Each element is graded The increased loading after the widening lead to an as high, medium or low risk. High risk elements are increased risk of fatigue in the orthotropic deck; inspected every 12 months, medium risk elements several measures have been undertaken to deal with every 24 months and low risk elements every 36 this challenge including a stringent inspection re- months. gime, installation of gussasphalt surfacing, installa- All components of the orthotropic deck are con- tion of fatigue sensors and improving the weld detail sidered to be high risk. This includes the welded for repairs. connections between trough stiffeners and deck plate and cross girder; the trough stiffener splices; the deck plate splices; and the deck plate to web connections. The inspections of the orthotropic deck are “Close Visual Inspections” in accordance with BS EN 970. When a weld defect is suspected non- destructive testing is carried out, usually magnetic particle inspection. If a weld defect is confirmed repairs are promptly carried out. Weld repairs usually take place at night when the traffic volume is lower and lane closures on the bridge are possible. In order to repair a dam- aged weld the existing weld is removed along the length of the crack plus an extra 100mm on either end of the crack. After surface preparation the new weld is carried out with close supervision to ensure good workmanship.

Figure 3. Isometric view of an orthotropic deck.

366 3.1 Changes in the course of the strengthening works The strengthening works were carried out in order to accommodate an additional fourth lane in each direction. This resulted in the central reserve being moved from the centre line of the bridge by 2.037m towards the west and the closure of the west side cycle track. The steel box girders were strengthened to accommodate 40t vehicles which also led to strengthening of the cross girders in the main span and the addition of flat stiffeners on the orthotropic deck inside and between the box girders in the mid- dle of the river span. Figure 4. Crack between stiffener and deck plate.

3.2 Fatigue This type of crack however is not an immediate threat to traffic safety and the integrity of the deck In spite of the strengthening Avonmouth Bridge be- because loads can redistribute after a crack has came more heavily loaded since the widening mak- formed; it is also the most common type of weld de- ing it more vulnerable to fatigue – which by defini- fect on Avonmouth Bridge. tion is progressive and localised structural damage caused by fluctuations of stress. It occurs when a 3.2.2 Cracks in the welded trough splice structure is subjected to cyclic loading; in the case of Splicing of the troughs is carried out after the pre- road bridges the primary cause is traffic loading (De fabricated box sections are assembled. This is done Jong 2004). Structural damage can appear without by fitting short sections of trough profile between the peak stress reaching the ultimate tensile stress the preassembled trough stiffeners with backing limit and may also be below the yield stress limit. strips to allow for welding (Figure 5). Three different types of cracks have been detected in The reasons for this type of crack are bending the orthotropic deck of Avonmouth Bridge. moments in the troughs due to local wheel loads and the associated stress ranges. The quality of the weld 3.2.1 Cracks in the stiffener to deck welded connec- is of crucial importance, for this form of defect (De tion Jong 2004). Cracks of this type can appear in any part of the Provided the crack dimensions are limited, cracks trough to deck connection except at the intersection of this type do not pose a threat to safety of the with a cross girder. The crack initiates at the root of structure as load redistribution is possible. Cracks of the weld and first grows towards the surface of the this type have only seldom occurred on Avonmouth weld and then spreads longitudinally along the fillet Bridge because the splices are located at quarter weld (Figure 4). points. If the deck is viewed in cross section between the box girders, the deck plate functions as a continuous 3.2.3 Cracks in the welded connection between beam with each of the stiffener webs acting as a trough and crossbeam support. Depending on the exact location of a local In this connection cracks originate around the cope wheel load, each section between the stiffeners is holes and spread in either the trough stiffener or the subject to constant upward or downward bending. cross girder (Figure 6). Hence these deformations cause bending moments Cracks in this area are due to poor quality weld- in the deck and stiffener webs. The stress caused by ing. However cracks of limited dimension are not the bending moments in the trough web is the main crucial to traffic safety as loads are sufficiently re- cause for cracks in the fillet welds between trough distributed (De Jong 2004). Again, cracks of this stiffener and deck plate. type have only seldom been recorded on Avonmouth A thick asphalt layer can help to prevent the for- Bridge. mation of this type of crack as thicker surfacing dis- tributes local wheel loads over a larger area. The quality of the weld has a significant influence on the growth rate of the crack. It is assumed the fatigue behaviour can be improved by avoiding a gap between trough profile and deck plate and executing the connection as a full penetration weld instead of a fillet weld (De Jong 2004).

Figure 5. Crack in the trough splice.

367 The spray applied waterproofing was installed by Stirling Lloyd and the gussasphalt surfacing by Aes- chlimann. The gussaphalt layer was laid by a paver running on rails, thus ensuring uniform thickness and density in addition to an even surface finish. This creates a smoother ride for vehicles and like- wise reduces impact loads on the steel deck. For the steel orthotropic deck gussasphalt was preferred over epoxy surfacing because of lower associated costs. Both options need to be resurfaced

with the same frequency but the surfacing and wa- Figure 6. Crack between cross beam and stiffener. terproofing costs for epoxy surfacing are higher than gussasphalt and associated waterproofing costs. Fur- ther, the epoxy surfacing is more difficult to remove 3.3 Weld defects and repairs from the deck making it more expensive and time Since 2006 regular weld inspections have been car- consuming to replace when it has worn out. ried out on the orthotropic deck of Avonmouth The gussasphalt surfacing significantly increases Bridge. The vast majority of the weld defects are the stiffness of the steel deck plate and therefore im- cracks in the welds between trough and deck plate. proves fatigue behaviour. Due to composite action Inspections have found most weld defects occur between steel deck and surfacing, any bending in the on the east side between the box girders with the relatively elastic deck is also forced on the surfacing. majority located at the two troughs corresponding to Therefore the surfacing needs to be considered as a the wheel tracks of the southbound lane 2. During load bearing component of the deck plate and stress- the inspection carried out in March 2010 more es from composite action taken into account. The cracks were detected west of the centre line of the surfacing material is generally visco-elastic to elastic bridge than east. The increase of weld cracks on the in low temperatures, as the effective Young’s Modu- west side was caused by the resurfacing works lus is highly dependant on the temperature (Wolchuk which were carried out on the northbound carriage- 2007). way at the end on 2009. The new defects, both east Bituminous surfacing is very sensitive to temper- and west of the centre line of the bridge, mainly de- ature and tends to become soft and ductile at high veloped at trough to deck welds underneath the temperatures and hard and brittle at low tempera- wheel tracks of lane 1. tures. The stiffness of surfacing materials further de- The new cracks on the west side occurred related pends on the strain deformation under loading; it is to surfacing works as a result of higher loads due to therefore stiffer under short term loading than per- traffic management and less stiffness due to the manent loading. temporary lack of surfacing. The surfacing can significantly increase the stiff- As described above, cracks in the weld between ness of the orthotropic deck system, depending on trough stiffener and deck plate are not crucial to traf- composition, thickness and temperature dependant fic safety. Provided the dimension of the crack is young’s modulus, significantly reducing the stress in limited, stresses in the deck plate are redistributed. It the deck plate in cold temperatures. At higher tem- can therefore be summarised that the cracks in the peratures the same surfacing becomes soft and as its orthotropic deck, as long as regularly inspected and Young’s Modulus decreases, the contribution to the repaired, do not present a major hazard to the struc- composite stiffness becomes insignificant. In hot ture. climates this temperature dependence of the Young’s Modulus is problematic, as the contribution of the surfacing to the composite action cannot be 3.4 Gussasphalt Resurfacing relied on. However, this does not present a signifi- In 2008 and 2009 the southbound and northbound cant problem for Avonmouth Bridge as sufficiently carriageways of Avonmouth Bridge were resurfaced high temperatures only seldom occur in the south- in two phases. Both the orthotropic deck and the west of England. concrete deck were surfaced with a spray applied In 1997 an assessment of the composite action waterproof membrane, a single layer of gussasphalt between the previous surfacing and steel deck of and pre-coated chippings in the surface layer. The Avonmouth Bridge was carried out (Cuninghame 1997). This project included measurements of the thickness of the gussasphalt layer varied depending surfacing temperature for 11 weeks between June on the location on the bridge deck. This surfacing and October 1995 and highlighted that during the type was chosen after a whole life costing analysis hottest four weeks the mean deck temperature did was carried out by Mott MacDonald (2007). not exceed 29°C.

368 The new gussasphalt surfacing of Avonmouth Bridge is expected to significantly contribute to the fatigue resistance of the steel deck. The waterproofing bonding layer was finished to a high standard, a good composite action of the steel and the asphalt surfacing can therefore be assumed. As summer temperatures tend to be relatively mild, even the re- duced Young’s Modulus of the gussasphalt adds stiffness to the combined system of steel deck and surfacing.

3.5 Fatigue Sensors

In order to examine the fatigue behaviour CrackFirst fatigue monitoring sensors and data loggers were in- Figure 7. Photo of CrackFirst fatigue sensor (Strainstall 2010). stalled on the underside of the orthotropic deck in 2008. This type of sensor consists of a steel coupon The repair procedure increases the fatigue (Figure 7) that needs to be attached adjacent to a strength from BS5400, class F, to class D in the web critical joint. The sensor is then subjected to the of the trough at 15mm from the deck plate. same loading history as the structure and can provide an accurate record of cumulative weld fatigue damage. 4 ACCESS AND EGRESS PROCEDURE Twenty four sensors altogether have been installed in both the east and the west box and between The importance for maintenance and inspection es- the box girders of the Avonmouth Bridge in the cen- pecially of the orthotropic deck has been outlined tre of the river span and close to a river pier, Pier 8. above. In order to assure safe access to all parts of This distribution ensures that fatigue stresses can be the bridge, internal walkways and mezzanine floors picked up in both the hogging and sagging zones of have been installed and an external walkway de- the bridge deck. The installation of sensors on both signed. The box girders of Avonmouth Bridge are the east and west side of the bridge was necessary as accessible via hatches in the box webs and a door in the bridge is no longer symmetrically loaded since each east and west box in both the north and south the strengthening works. The shift of the central re- abutment. serve to the west has caused a different road layout The hatches in the outer web are accessible via on the east and west sides. Further, the east and west two cantilever gantries from both the east and west sides of the bridge also have been strengthened to cantilever on either side of the expansion joint. The different degrees, therefore the load distribution var- distance between adjacent inner web hatches is ies. spanned by a centre gantry on either side of the ex- The sensors are positioned adjacent to the splice pansion joint (Figure 2). welds of the deck plate and therefore detect fatigue stresses that would be crucial for the structural integrity of bridge deck. As one sensor can only monitor 4.1 Standard access and egress procedure via fatigue stresses in one direction the alignment de- gantries pends on the orientation of the monitored butt weld. The standard procedure for entering the box girders Since the installation of the fatigue sensors, no fa- is via the gantries. The east cantilever gantries are tigue damage has been detected, nor have any de- accessible from the foot and cycle path. fects been found in the splice welds of the deck In order to access a cantilever gantry, an access plate. walkway from either of the two access towers needs to be lowered over the cycle track parapet and a lad- der extracted. The two access towers assure that 3.6 Improvement of weld detail even in case the gantry is parked in line with a street To further improve the performance of the ortho- lighting column, access is available via at least one tropic deck all weld repairs in the trough to deck of the towers. connection are carried out as partial penetration The east cantilever gantries are generally parked welds rather than fillet welds. This procedure is at docking stations a short distance from the hatch based on a research project carried out by the locations. The docking stations provide an additional Transport and Road Research Laboratory (TRRL) mesh around the parapets to discourage unauthorised on the fatigue life of the Severn Crossing. access to the gantries. The cantilever gantry is then moved to line up with the relevant hatch. As a further security measure the hatches in the outside web

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Figure 8. Photo of ACN gantry lined up with west cantilever gantry. of the east box are equipped with a padlock on the The mezzanine floor was installed in 2010 by outside. Turner Access and is integrated in the access walk- In order to reach the west box the standard proce- way. Before 2010, inspection and maintenance of dure is to step from the east box, through an inner the orthotropic deck had to be carried out using mo- web hatch, onto the centre gantry and enter the west bile scaffolding. The downside of this procedure was box through the adjacent hatch in the inner web of only small areas could be inspected at a time; plus the west box (Figure 8). The west box cantilever the scaffolding had to be taken down at the end of gantries are generally only used for access to the each shift so as not to obstruct the walkway to other west cantilever. parts of the internal box section. The mezzanine On either side of the expansion joint a centre gan- floor is installed in both box girders in the vicinity of try is located, the Steel Centre South (SCS) gantry the river piers where the box girders are of increased south of the expansion joint and the Aluminium height. The constraints for the dimension of the floor Centre Gantry (ACN) gantry on its northern side were the location of the post tensioning cables and (Figure 9). They are functioning as both mobile sufficient headroom underneath the mezzanine floor. working platforms with access to the underside of The mezzanine floor was constructed using the the bridge deck between the boxes, and bridging the Safespan system which is a patented working plat- gap between the adjacent inner web hatches of both form developed in the USA in 1996. It consists of box girder sections. Both centre gantries are usually three principal components: cables in horizontal and parked relatively close to the expansion joint, or are vertical direction; profiled steel sheeting; and special positioned wherever works are in progress. clips. The horizontal ropes along the longitudinal bridge axis are suspended first, then vertical hangers 4.2 Access inside the box sections – internal are installed along each cable which are then at- walkway and mezzanine floor tached via clamps to the bottom flange of the cross girders. Between each vertical hanger the longitudi- A wooden walkway is provided in most areas of the nal cable forms a catenary. This supports the pro- internal box section to minimise tripping over stiff- filed steel sheeting which spans transversely be- eners in the bottom flange. In the main span area of tween longitudinal cables. The vertical cables are the bridge the wooden walkway has been exchanged attached to the longitudinal cables via steel clips. for an access walkway which was installed by The deck and all elements above the sheeting are Turner Access in 2008. The internal walkway pro- inspected from the platform. The longitudinal ca- vides much quicker and safer access to the box gird- bles, connections and underside of the sheeting will ers as it eliminates the risk of tripping over stiffeners be inspected from the underside. Turner Access car- on the bottom flange. Further improvements are its ries out annual inspections; before and after any ma- greater width and a raised floor level which enables jor works qualified Avonmouth Bridge personnel in- a continuous walkway uninterrupted by transverse spect the mezzanine floor. Access to the mezzanine floor is provided by two stiffeners. staircases per section integrated into the access

walkway: close to the shallow end of the mezzanine

floor; in the deepest section next to the diaphragm

over the river pier.

370 would need to be moved to extend the underslung section is approximately 40m which takes up to 60 minutes to cover. In order to provide a quicker escape route Mott Macdonald have designed an escape walkway to be installed outside the east box girder in the areas of increased box girder height. Generally the four west cantilever gantries are only used for access to the cantilever as the gantry access walkways lead on to the hard shoulder of the west carriageway. In order to accommodate a fourth lane on each carriageway the west cycle path has been removed and both hard shoulders narrowed. Descending from the west cantilever gantries should be strictly avoided as it means entering a live carriageway; this procedure is reserved for emergencies when it is not safe to walk inside the bridge. Utilization of the abutment doors, at the ends of the box girders, for exiting the bridge is also restrict- ed to emergencies. The area adjacent to the abut-

ments is classified as confined space for a number of Figure 9. Existing gantry arrangement. reasons: the space between box girder end and abutment wall is very narrow with uneven and wet Since the construction, the mezzanine floor has ground; the drainage is of an open trough type; and been used for inspections of the orthotropic deck and from the abutments a steep rubble slope is the only maintenance purposes. way down to ground level. Access to the bridge The trough-to-deck welds are now easily accessi- through the abutment doors is not possible as they ble allowing for weld inspections and potential re- are permanently bolted from the inside. pairs without scaffolding. The maintenance and in- Two studies have been undertaken by Balfour spection of the fatigue sensors also has become Beatty Mott MacDonald analysing alternative means easier. of access and egress from Avonmouth Bridge in case of emergencies, which can include damage to the centre and west cantilever gantries; accidents on 4.3 Access and egress procedures in case of the carriageway leading to hazardous substances en- emergencies tering the drainage system of the bridge, or other in- Both centre gantries are fitted with an underslung cidents that restrict access to certain parts of the section that extends underneath the box girder. The bridge. As mentioned above the SCS gantry plays a SCS gantry has a single underslung section that can vital role in providing full access to the bridge. The be moved underneath either the east or west box considered options of improving the accessibility in girder. The ACN gantry possesses two underslung case of a gantry failure in an emergency were: instal- sections which can be extended simultaneously un- lation of an emergency generator or external power derneath both box girders. If the underslung section supply; installation of a powered escape cradle; in- of a centre gantry is lined up with the gondola sec- stallation of a manual escape cradle; extensively tion of a cantilever gantry – a vertical extension of a training the operatives to enable insitu replacement cantilever gantry below the main floor level – it is of engine or generator parts that are susceptible to possible to transfer from cantilever to centre gantry failure; rope descent; permanent escape walkway. without setting foot into the box girder. Using the The installation of backup generators was deemed underslung sections however is more time consum- not to be feasible due to access restrictions. Neglect- ing than walking through the box girder especially if ed was also the installation of a powered or manual tools and equipment need to be carried across. For escape cradle due to the high costs in the case of a this reason the underslung sections are only used if powered cradle, and long traveling times in case of a the centre gantries are immobile. manual escape cradle; plus the potentially hazardous The box girders gradually increase from 2.3 to access procedures. 7.6 m in height above the river piers, which means In spite of being able to carry out minor bogie in- the underslung sections cannot be extended in these spections the Avonmouth Bridge operatives are not areas. In the case of a breakdown of the SCS gantry electrically trained and therefore not qualified to if could be moved manually to the closest hatch. manipulate the gantry’s electrical drive system. This however requires six operatives using manual Rope descent is currently the only option for winding handles and continuously moving braking egress from the SCS gantry if stranded in the areas clamps. The maximum distance the SCS gantry of increased box girder height. However, this means

371 of egress is not ideal: it requires continuous training In spite of its vast dimensions of almost one mile of the personnel; if the location of breakdown was in length the accessibility of the internal box girders above the river Avon a rescue boat would need to be of Avonmouth Bridge is very good. Except for the provided by the coastguard. Further, access back on- expansion joint and abutment chambers, both classi- to the stranded gantry to carry out repairs and recov- fied as confined spaces, all areas are accessible via er would be very difficult. at least two different routes – once the external The installation of an external walkway was walkway system is opened for use. hence considered as the best option to assure safe The stringent risk based inspection regime is a emergency access to the SCS gantry and has since cost effective way to assure the serviceability of the been designed by Mott MacDonald; and is now un- structure. The greatest challenge to the integrity of der construction. the orthotropic deck – maintaining the trough to deck welds – has been met by improving the weld detail.

4.4 External Walkway Further, the gussasphalt surfacing significantly Mott MacDonald has designed an external walkway increased the stiffness of the steel deck plate hence which allows safe evacuation from the SCS gantry improving the fatigue behaviour of the orthotropic in all areas where the underslung section cannot be deck which is also monitored by fatigue sensors. extended. Once built, the walkway system will also In turn, the requirement for regular maintenance include a maintenance platform around the bearing and inspection is met by the maintenance team oper- shelves of Piers 8 and 9 which would be accessed ating the gantries, based in close vicinity to Avon- from the SCS gantry or the new external walkway. mouth Bridge. The walkway system will consist of two 113m The internal mezzanine floor and external escape long sections on either side of the river piers on the walkway assure permanent and safe access to all vi- outside face of the inner web of the east box girder tal parts of the structure. and two 4m long sections on the outside face of the This proactive approach to managing Avonmouth inner web of the west box girder. The long walk- Bridge guarantees to maximize the lifespan of the ways on the east box will also have an angled off structure. section running underneath the box girder and connecting the inner and outer web, at either end. This proposed walkway provides a safe escape REFERENCES route from the SCS gantry in case of a breakdown in the vicinity of the deep sections where the under- Cuninghame J.R: Strengthening and refurbishment of Severn slung sections cannot be operated. At both ends the Crossing, Part 4: TRRL research on Severn Crossing. Pro- ceedings Institution of Civil Engineers, Structures & Build- walkway will change direction and cross beneath the ings, 1992, February, pp. 37-49 box girder to provide access to the east cantilever Cuninghame J.R: Avonmouth Bridge: Assessment of Compo- gantry. site Action between Surfacing and Steel Deck. TRL, pre- The bearing inspection platforms will be accessi- pared for Hyder Consulting Ltd., Order no. 017577 ble from the external walkways via permanently in- De Jong F.B.P: Overview Fatigue Phenomenon in Orthotropic stalled ladders. The platforms are designed to go Bridge Decks in the Netherlands. 2004 Orthotropic Bridge Conference, Sacramento, California, USA – August 25-27, around each of the piers 8 and 9 close to the pier top 2004 so the bearings can be accessed easily. Since the Frey, B.I. 2009. Avonmouth Bridge - Bearings Management Avonmouth Bridge was opened to public in 1974, Study. Balfour Beatty Mott MacDonald the areas of the floodplains and riverbed underneath Frey, B.I. 2010. Avonmouth Bridge – Orthotropic Deck Study. the bridge were declared a Site of Special Scientific Balfour Beatty Mott MacDonald Frey, B.I. 2010. Avonmouth Bridge – Feasibility Study – Ac- Interest (SSSI) area. Thus it is no longer possible to cess to and from the bridge. Balfour Beatty Mott MacDon- build scaffolding around the river piers. All bearings ald of Avonmouth Bridge however are rated as high risk Mott MacDonald: M5 Avonmouth Bridge Waterproofing and items and should therefore be inspected every 12 Resurfacing Whole Life Costing. March 2007, Final months. Once the bearing platforms are installed it Pucknell, B. 2008. M5 Avonmouth Bridge Maintenance Manu- will be significantly easier to carry out inspections al. Balfour Beatty Mott MacDonald Strainstall UK Ltd: website http://www.strainstall.coml, down- of the river pier bearings. loaded 15 March 2010 Wolchuk R: Orthotropic Decks – developments and future out- look. Stahlbau 76 (2007), Issue 7 5 CONCLUSION

The improved access methods to Avonmouth Bridge geared to the maintenance and inspection requirements provide an excellent example for maintaining a 40 year old structure under today’s requirements.

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