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M1 in West Yorkshire. Bridges

ON THIS PAGE:
Introduction - Tinsley Viaduct - M1 - Lofthouse interchange - Tinsley Viaduct Construction -
The Strengthening of Tinsley Viaduct - The Calder Bridge - M1


Introduction

A total of 120 bridges and subways were constructed on this length of the M1 Motorway. This represents approximately one quarter of the construction cost. Ten contractors and sub-contractors have been directly concerned with the construction of these bridges.

Five of these bridges formed part of the Lofthouse Interchange and two railway bridges were constructed in advance of the roadworks, having decks incorporating steel beams; all of the remaining structures were constructed in reinforced and/or prestressed concrete. Over 4,000 reinforced and prestressed concrete beams were used and these were manufactured as far afield as Scotland, Teesside, Nottinghamshire, Stamford and Norfolk, and involved Costain, Dowmac, Kingsbury Concrete, Ferro Concrete & Stone and Anglian Building Products.

The largest beams manufactured off site were used on Morthern Hall Bridge which carries the northbound carriageway of the Thurcroft Link over the Motorway.

These beams were 116ft. 6in. long and weighed approximately 75 tons. For this bridge 44 beams were brought from Stamford to Sheffield by special train and then transported out to site by road.

Almost the entire length of this motorway passes over land subject to mining subsidence and this gave the bridge designers special problems. When mining takes place not only can differential settlement occur but horizontal ground strain also. This can be particularly severe when the mining is shallow.

The structures have, in general, been designed to accommodate a differential settlement of 18 inches (45mm) and ground strains of 3mm/metre tension and 6mm/metre compression. The possibility of subsidence, of course, meant that structures with continuous decks could not be built.

The bridges have either jacking pockets provided on the abutments and piers to enable the deck to be lifted up to its new level or jacking pockets provided on the abutments and provision made for the pier walls to be jacked up from their base together with the deck.

To accommodate the horizontal ground strains an elaborate expansion joint is necessary and to avoid providing one of these at each pier the decks have been joined together so that all the movement is accommodated in one abutment of the bridge.

To allow this movement to take place, in the case of square crossings the bridge piers are hinged (in effect they act as giant rocker bearings) and in skew crossings where the piers cannot be hinged, the deck is carried on the piers by means of bearings which incorporate a layer of polytetrafluoroethylene (PTFE) which slides on a stainless steel plate.

In addition to these measures, a layer of sand or gravel had to be placed between the footings - abutments, piers and retaining walls - and the foundation whenever rock was encountered to prevent the ground strain being transmitted into the footings of the structure."

To simplify and cut the costs of both design and construction a series of standard prestressed concrete beams were produced for the motorway for use in conjunction with standard bridges. The large amount of design calculation undertaken by computer assisted in reducing design time.

A Standard Overbridge

The road users had been in mind throughout the design stages and the aesthetics of all structures carefully examined. Every opportunity has been taken to relieve driver monotony by providing where possible variety in the type of structures, relieving large areas of concrete with features and by giving further variety with the various coloured plastic fascias. The majority of the bridge types were submitted to the Royal Fine Arts Commission for approval.

Notwithstanding the standard of aesthetics obtained, the bridgeworks costs compare favourably with those of any motorway bridges built in this country to date.

The standard overbridges have four spans, the decks being formed of pre-cast post-tensioned I-beams and with in situ concrete cast over and/or between the top flanges of these beams to form a series of T-beams.

Rainstorth Bridge

The underbridges generally have three spans but in certain cases single span bridges have been adopted. The decks are formed either as for the standard overbridge or with pre-tensioned prestressed inverted T-beams placed side by side and with the voids between beams filled with in situ concrete to form a solid slab.

Where the road to be carried over the motorway has a steep gradient it was found that the standard overbridge was not aesthetically satisfactory due to the extremely unbalanced side spans and the lack of parallelism between the deck soffit and the motorway.

To overcome these objections Rainstorth Bridge was evolved. This bridge is constructed entirely of reinforced concrete and consists of a series of simply supported spans of varying depth and each having a short cantilever at the piers. This design which provides a soffit line parallel with the motorway, has been partially copied for three other bridges. A full scale load test was carried out at the manufacturer's works on one beam to test the adequacy of the half joints.

Cock Inn Bridge

Similarly Cock Inn Bridge carries Pilley Lane over the motorway (at a 1 in 10 gradient) at Birdwell. This bridge has reinforced concrete abutments, a row of raking columns which support a deck formed of post-tensioned prestressed concrete box beams.

The three span footbridges, Smithy Wood, Birdwell Quarry and Stainborough, which incorporate the principles of the Wichert Truss are the first bridges of their type to be constructed in concrete in this country, and the first use of concrete tri-hinges.

The principles involved provide continuity over the piers as in a continuous design structure but permit differential settlement and accommodate the movements associated with mining subsidence."

The first concrete tri-hinges

From tests carried out at Sheffield University using a 200 ton Amsler testing machine it was found that the unreinforced hinge throat could be replaced to effect repair and that the detail of the anti-bursting reinforcement required modification.

Birdwell Quarry Footbridge was perhaps the most elegant of the three constructed on M1 having side spans of 95 ft. to accommodate entry and exit slip roads at the Tankersley Interchange. The main span is 119 ft.

The construction sequence required the spans to be cast 5 in. high at the bearings and lowered into their final position after pre-stressing had been completed.

The lowering operation was carried out on a Sunday afternoon. First the eastern span was jacked up to remove the packing and lowered it onto its fixed bearings. The operation took less than 15 minutes. The operation was repeated on the western span with the weight on the jacks and packings removed, the balk of timber, beneath the jack on one corner crushed and the side span slid laterally 3 in. Fortunately the movement was stopped by the kicker upstand and there was no immediate danger.

Needle Eye Bridge

To correct the problem, the bearings were turned through 90 degrees, the span jacked down and the span slid sideways into its correct position, the bearings were lifted and put in their correct alignment and the span lowered into its final position. The operation was completed without any complications.

Considerably adding to the aesthetics of the motorway, three concrete arches built over the motorway are notable. Approaching from the South the motorist is presented with a panoramic view of Leeds City framed by Urn Farm (213ft. between springing and 320ft. overall length), located just to the south of Stourton Interchange. Needle Eye Bridge (290ft. between springings and 434 ft. overall length), is immediately south of Dodworth Interchange.

Dropping Well footbridge

Dropping Well Footbridge, a reinforced concrete three pin arch, (169ft. between springings) is particularly interesting as the approach on the west side is by means of a spiral ramp. The east springing is sited behind the top of an attractive retaining wall and is 8 m above the western springings, which have split legs at motorway level. On each side of the arch there are two suspended spans.

The density of property also required the construction of a 1,500 ft. long retaining wall, over 40 ft. above the road at its highest point, adjacent to Grange Mill Lane.

This together with other locations, was used by West Riding engineers in their study of earth pressures and strain gauges were built into the wall for this purpose.

A second wall at Meadowhall was built to retain a housing estate and enabled the cutting to be taken out for the motorway. The wall comprised 120 bored piles, 48 in. in diameter sunk to depths of up to 60 ft. Following excavation in front of the piles an in situ L-shaped wall, connected by reinforcement shear connectors to the piles was constructed. This wall has a striking appearance having a face of 12 in. deep tapering corrugations. The piling catered for short term earth pressure effects and the composite wall those anticipated in the longer term. The above footbridge springs from this wall.

Bramley Lane Viaduct which carries a local road over the motorway and the slip roads leading to the Wooley Edge service area is a pleasing simple 8 span structure."

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Lofthouse Interchange

Lofthouse Interchange

This is a three level roundabout type interchange at the junction with the Lancashire-Yorkshire Motorway. Considerations of traffic loading and cost dictated its adoption and hence the high level curved bridges which are now familiar to users of the M1 between Wakefield and Leeds. The M62 Motorway is carried over the M1 Motorway by a 4 span bridge having reinforced concrete multi-cellular deck.

The north and south bridges, carrying the roundabout over the M1 have four spans of 91 ft. 6 in. average length at a mean radius of 420 ft. The smaller east and west bridges, crossing the M62 motorway have four spans of about 70 ft. All the spans are simply supported because there was a slight risk of differential settlements of the foundations due to old mine workings in the area.

Three other bridges form part of the interchange complex. The first which carries Longthorpe Lane B6135 over the M1 immediately adjacent to the north roundabout bridges. The other two bridges are 3 span reinforced/prestressed concrete structures which carry the two northernmost slip roads over Longthorpe Lane.

Unusual problems arise with long curved bridges due to the change in curvature with temperature change. This was aggravated in this case by the decision to adopt simply supported spans and by the height of the piers, about 40 ft. in the case of the north and south bridges.

The solution lay in the unique system of articulation which enables the decks and piers to move around the curve without transmitting excessive horizontal loads and resultant bending moments to the piers. Taking a side span, the inside corner is anchored to the abutment and the far end is anchored to the pier in two places. The pier has three spherical bearings, allowing rotation at the top and bottom of this prop and at the base of the sloping leg. The deck and pier thus form a rigid, but statically determinate and hence stable frame. Each successive deck is anchored to its neighbour in the same way.

The decks consist of curved box beams. The inner beams are rectangular in section - 4 ft. deep by 2 ft. wide. The edge beams are trapezoidal with the outer web sloped to enhance the appearance of the structure. A 9 in. thick concrete deck slab connects the beams and acts compositely with the steel work in resisting bending moments.

Mild steel is used throughout as the savings in weight which could have been achieved with a high yield steel were largely cancelled out by extra width and labour costs in cutting the curved plates. This would have been necessary to remove local hardening caused by the cutting process.

The behaviour of the structure under concentrated loads was investigated with the aid of a grillage programme at Leeds University. This technique was then relatively new. A programme was developed in the department to establish the forces on the links between the deck and the piers for a large number of different load combinations.

At the time of the preliminary Merrison Report (discussed later) these structures were thoroughly checked for panel distortion and the calculations were checked against the Steel Box Girder Appraisal Rules and in both cases they were found to be entirely satisfactory.

The piers are believed to be unique and consist of an inverted "L" shaped member which is supported on the outer face by a cruciform shaped column."

The 'banana' shaped piers

The "banana" piers, as they became known, also presented a problem to the contractor in the placing of the concrete due to the heavy concentration of steel reinforcement. The contractor proposed to prestress these structures using strand cables to overcome their problems. This was accepted.

There was concern over the production of prestressed beams at various manufacturers. Sub-contracts for beams were always placed after the main contract had been let. Usually there were considerable delays between ordering, casting and delivery to site. Abutments to receive the beams often standing completed many weeks before their arrival. Additionally beams, because of the rate of production and despite deploying inspectors to the production factories, were found to have repaired honeycombed areas, often being rejected on site.

For these reasons, the concept of a "bulk beam contract" with beams produced, on the shelf, to be available when the main contracts were let was put to the Ministry. This idea found favour with them and West Riding Engineers later produced such a contract for the supply of the beams for many of the contracts on the M62.

With the opening of the motorway, the West Riding bridge engineers could claim to have built with their contractor colleagues 120 bridges in just over three years and in the finished work they feel justly proud, of a job well done."

Two structures initially included in the brief of the West Riding engineers, Tinsley Viaduct and the Calder bridge, did not have such a happy story and were designed by consulting engineers.

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Tinsley Viaduct - M1

The site at Tinsley presented an extraordinary challenge: a structure had to carry a six-lane motorway and a four lane trunk road over the congested and heavily industrialised Don Valley, crossing the Sheffield-Keadby Canal, the River Don and three railways; a method of erection had to be devised which would permit industrial activity to continue below the structure; the line had to be S-curved to thread a way through industrial complexes such as the power station cooling towers; condensation from these towers and the proximity of the river and canal generally kept relative humidity above the corrosion threshold of 80%; with this humidity, the precipitation of over 29 tons of sulphur dioxide each day from the power station and the fumes from a nearby sulphuric acid plant gave what was regarded as the most corrosive atmosphere in Britain; the Don geological fault system crosses the site; the soil survey gave evidence of ancient uncharted 'pillar and stall' mine-working, entailing a risk of sudden subsidence; benchmark levelling had revealed settlements of up to 15 in. since 1935.

The solution agreed with the Ministry of Transport after examining a range of options was for a 3,400 ft. long two level viaduct substantially in prestressed concrete, with some structural steel members which had a specially high specification from corrosion. The viaduct designed had twenty simply-supported spans of up to 163 ft. length, allowing for thermal and subsidence movement at each span end, and incorporating jacking facilities at each support for rectifying gross settlements.

The design involved 4,500 sheets of calculations, the writing of three computer programs, five structural analyses by computer, 176 drawings and 239 pages of specification and bills of quantities. A 12 ft. long detailed model of the viaduct and surrounding roads and buildings was commissioned.

Two models of the joints between the structural steelwork and the concrete of the composite Warren truss girder were tested at the Cement and Concrete Association in March 1964 and showed no signs of distress.

Pre-tender drawings were issued 9 months before the tender period to enable prospective contractors to view the design and assess requirements, and to give the opportunity to comment or make suggestions during the design stage; no amendments to the basic form of the viaduct were suggested.

Drawings and contract amendments were issued to five selected contractors in February 1964, inviting tenders at the end of April.

When the five tenders were opened, that from the Cleveland Bridge and Engineering Company was accompanied by a separate lump sum quotation for an alternative steel box-girder viaduct; the quotation was just over 1 million cheaper than the lowest tender of about 6 million, and was accompanied by 8 pages of description with welding and painting specifications and 5 outline drawings prepared by consulting engineers Freeman, Fox and Partners.

The alternative design was for the upper and lower levels to be carried independently of each other by steel twin box-girders running continuously throughout the two thirds of a mile, 20 span length of the viaduct.

A report recommended acceptance of the lowest tender for the West Riding design and rejection of the alternative. But in spite of these protests and a clear indication that this solution would, in the long term increase, rather than decrease costs, the Ministry accepted Freeman Fox's view that "a continuous form of structure rather than simple supports or other form of articulation should be adopted for this structure", and was convinced that there was still about half an million pounds advantage in adopting the alternative.

The Council resigned their Agency for Tinsley Viaduct on behalf of the Ministry who invited re-tenders on contractor's own designs based on changed requirements: the degree of live load to be allowed for was reduced; the viaduct was to be 5 ft. narrower; construction operations would be easier because of the Ministry's purchase of land under and around five of the spans.

The lowest tender received was for 4,344,000 for a simply supported prestressed concrete viaduct similar to the West Riding design (two of the other three tenders were also for simply supported structures). Nevertheless, the Ministry awarded the contract to Cleveland Bridge and Engineering Company, whose tender for their continuous steel structure was 272,000 higher. The Ministry appointed Freeman Fox and Partners as Engineer to supervise the contract.

One could only speculate on the reasons for the outcome. It is hard to believe that it was to save money; if it was important to have a steel structure at Sheffield or that such a prestigious structure should be designed in the private sector, then such matters should have been resolved earlier.

The Ministry was home and dry. The Minister received a deputation from the County Council but told them he was not prepared to ignore the saving offered, and moreover did not propose to invite the County to continue as his agent for the Tinsley Viaduct.

In December 1971, the Department of Environment confirmed that the need for strengthening to meet "Merrison box girder safety standards".

A brief record is included of the design and construction of Tinsley Viaduct one of the first instances of a motorway being carried through a densely populated urban area and also the first steel structure in Britain to carry road traffic on two tiers.

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Tinsley Viaduct Construction

Some 12,500 tons of mainly high tensile steel and about 80,000 tons of concrete were used in the construction of this 3,400 ft. viaduct. Gas, electricity and water supplies being carried in service bays on the lower deck.

The factors most affecting the design were the two tier requirement, the S-shape alignment (only five of the twenty two spans of the upper deck are straight) and possible mining subsidence due to uncharted mine workings. The viaduct is flexible enough to take settlement and provision is made for jacking at the main bearings.

Tinsley viaduct

Each deck is continuous and of composite construction - a reinforced concrete slab on two main longitudinal box girders with cross girders and cantilevers transversely at about 10 ft. centres carried on 17 pairs of steel columns spaced across the Don Valley. Each deck is anchored longitudinally to its abutment at the north end of the viaduct and expansion is allowed to take place along the full length of the structure by a Demag expansion joint at the southern abutment, the range of movement being more than 2 ft. All the intermediate supports are of the rocker type allowing independent thermal movement of the decks. The main box girders are on roller bearings at the south end.

Work on the site began in Spring 1965, the first task was to drill a pattern of 65ft. bore holes over the full area of the bases of all the piers and abutments, no undue settlement due to subsidence was expected.

Underground services caused complications in the construction of the concrete piers: two large sewers had to be temporarily supported across 30ft. wide excavations while the pier footings were constructed underneath, and the footings of several piers were altered in shape to clear other services and to avoid any major diversion works. The 17 piers and 4 abutments are simple reinforced concrete structures on spread footing founded at depths varying between 15 to 30ft. Coal or seat earth at foundation level was removed.

The erection of the steelwork was arranged to minimise use of the land and to avoid interruption of operation of the railways and factories. From its position on the upper deck steelwork over the last pier, a 35 ton derrick lifted into position the next 4 boxes of the lower deck each of which was brought to the working end by a diesel locomotive running along the lower deck that had already been built, and the upper deck was completed to the end of that stage. The derrick then moved forwards to the leading edge of the upper deck and completed the next stage which brought it within reach of the next pier. When the boxes for the last but one section of the lower deck were in position, it extended 165ft. from the last vertical support and the end deflection was 4 ft. To position the last two longitudinal boxes of the section, the weight of the derrick was transferred to jacking beams and the free end of the lower deck was jacked into position: the upper deck was then completed by propping up the boxes from the completed lower deck. Each span was completed in about 11 days.

Concreting of the 8½ in. deck was begun before the steel erection was completed and made composite with the steel members with welded steel shear connectors. To maintain operations clear of the ground, the central service duct under the lower deck was used as a channel through which all shutters were moved. The formwork was designed to be rolled out between the cross girders into position and, after stripping, rolled back into the central duct and forwarded to the next position. Concreting was started in the middle of the viaduct moving both ways so that there were four working faces, and was not placed in areas that would become subject to dead load tensile forces until that dead load had been added thus minimising cracking.

Electric Heating cables were built into the road surface of the top deck because of the viaducts exposed position, and to counteract the possible affects of ice formation as a result of condensation from the nearby cooling towers. The whole system is controlled automatically.

The exterior painting system was micacious iron ore and the interior of the sealed box units given red lead only. This was to prove a costly system to maintain.

The lower deck of the viaduct was opened to local traffic on the 25th March 1968. But the viaduct was not given a complete 'bill of health' until 1980 after further strengthening works described below.

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The Strengthening of Tinsley Viaduct.

The Merrison design check revealed the need for strengthening particularly in the bottom flanges, the columns, the diaphragms in both longitudinal boxes and the supports.

Piers of the upper deck were indirectly strengthened by having an inverted triangular truss built around each one. The trusses spring from each pier's foundations to new cross-boxes laid within a quarter span length of the main cross-box. They comprise two raking steel box struts that each generate a nominal 165t-uplift, and a horizontal tension member to connect the strut heads. Generally eight 40 mm dia. Macalloy bars form this member, but for the extreme north and south pairs of motorway deck piers where greater uplift is required, this number has been increased to 10 and 12 respectively.

Lower deck piers are relieved by steel links between the strut heads above and more new cross boxes under the carriageway. The links develop a nominal 125t tension.

Shear and bending between the new support points are reduced to a level that is sufficient to bring the compressive working stresses within the Merrison limits. By achieving this system at the critical section, bending stresses are automatically reduced over the remaining span length, so that this too meets the Committee's requirements."

The penultimate columns supported at each end of the viaduct on the lower deck abutments have special trusses, of which there are four. The 15 main piers of columns have the truss system described i.e. 30 trusses in all.

The viaduct was re-opened to full traffic in 1980, some 15 years after started.

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The Calder Bridge - M1

Although Tinsley viaduct involved considerable extra costs following its construction, the construction of the River Calder Bridge and its collapse during construction with loss of life was a more tragic affair.

The design of the Calder Bridge was the product of a competition organised by the Ministry of Transport. The competition produced about 110 entries in which the County Bridges Section was involved in drawing up the competition rules and the technical assessment of the twelve entries selected by the judges under the chairmanship of Sir Herbert Manzoni. It is estimated that something like 150 man years of effort went into the competition.

The competition was partly in response to criticisms that the younger generation of engineers were not getting an opportunity to apply their talents to design and partly in answer to pressure from the House of Commons following the controversies over the Staines Bridge and Chiswick Flyover.

The joint winning design submitted by A A W Butler and M V Wooley in association with E W H. Gifford was chosen for construction. Subsequently E W H. Gifford and Partners were appointed consulting engineers to the Ministry of Transport for the bridge.

The Ministry took the view at the time that the overall result did not justify them departing from their existing policy of giving bridge design commissions to firms of consulting engineers and the county highway departments.

The bridge was designed to accept ground movements due to mining. A three point support system ensured a statically determinate structure under all conditions of ground movement.

Calder bridge

The decks were made from in situ pre-cast units trapezoidal in section with 6 in. wide concrete joints poured after correct positioning of the units. The completed deck was post-tensioned longitudinally. The bridge built of twin decks has a 240 ft. main span and 60 ft. long cantilevered side spans. The side spans connected to the abutments by 20 ft. beams.

The piers cast integral at the top and sit on a simple steel spherical bearing at the north side and at the south on two single steel roller bearings 22ft apart.

During construction by Costains two of the 250 ton, 30ft long deck units and supporting falsework collapsed and four workmen were killed.

Although the disaster produced shock movements throughout the structure, no movement was found to have occurred at the piers, which were propped and stabilised.

On temporary works it is recorded that "the staging consisted of a series of high tensile steel beams carried on H.T.S. transoms supported on concrete filled 16 in. diameter BSP cased piles, which were driven through the gravel into the mudstone. The piles were toe-driven from a rig mounted on a pontoon, using a 2 ton drophammer, to a set of five blows to one inch. A safe working load of 100 tons, with a factor of safety of 1.5, was indicated by loading a test pile against ground anchors.

Three spans of temporary works were constructed in this fashion over the river, scaffolding being used to support the deck over dry land. Because of the stringent navigational and drainage requirements the pile bents forming the temporary works had to be placed parallel to the stream flow. This highly skewed steel beam system, loaded by rigid concrete sections with joints at right angles to the axis of the bridge and in random relationship to the spans of the temporary works, presented a difficult analytical problem which was made even more complex by the vertical jacking operations required to level the units before final joining. The temporary transoms across the tops of the piles were designed as 18 in. x 6 in. x 55 lb. high tensile steel joists. The materials used on site were second-hand and thus the painted identification marks were no longer visible.

Unfortunately there was also a stock of 18 in. x 6 in. 44 lb. mild steel beams on site. Because of the close similarity in dimension and the lack of identification marking, some of these weaker beams were erroneously used in the work.

This, combined with the underestimate of the loads imposed through the skew framework, produced a web buckling failure of one transom. This led to the collapse of one span of the staging which caused two of the concrete units each weighing 220 tons to fall into the river. When analysing the causes of this accident it was found that very small differences in calculated deflection of the temporary packs between the concrete units and the beams could cause very large differences in the end reactions of the skew beams, primarily because of the great stiffness of the concrete units in comparison with the beams, and the variable flexibility of the beam system at the pack positions. Each of the several analytical approaches that were used revealed the extreme sensitivity of the system to the thickness and stiffness of the packs. Subsequently therefore, plywood packs of a predetermined stiffness were used to support the units in their final position. These packs were proportioned so that they would yield and redistribute the load on any particular beam should it inadvertently reach unsafe proportions at any time.

Some of the packs were required to be tapered and, where units had to be rotated laterally as well as lifted, it was necessary in some cases to do this in stages. All loading cases were computer analysed. The final jacking scheme involved the jacking of one unit off the adjacent unit whilst at the same time keeping the remote ends of both units floating on jacks. This enables the effects of all reactions to be calculable and fully controlled."

Once again lessons were to be learnt about temporary works design, the importance of which was equal to that of the bridge itself.

Although the Darton to Wakefield contract was delayed, the bridge was finally completed and opened to traffic in October 1968, at a cost of 440,000. This graceful bridge crossing over the River Calder now stands as a monument to those who gave their all to its building.

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