When was the medway bridge built

In the civil parish of Rochester. In the historic county of Kent. Modern Authority of Medway. Medieval County of Kent. Rochester Medway Bridge has been described as a certain Fortified Bridge.

Description Chapel with offices of the Rochester Bridge Fund. Chapel built and endowed as a chantry by Sir John de Cobham in at the S end of the bridge he and Sir Robert Knowlles built across the Medway demolished ; it fell into ruin and was restored and partially rebuilt in TQ , no trace remains. PastScape By them it appears, that this antient bridge was made of wood, and that it consisted of nine piers, which made ten intermediate spaces in the length of the bridge, and from one end to the other was about twenty-six rods and an half, equal to four hundred and thirty-one feet, which corresponds nearly to the present breadth of the river, where this bridge stood, in a direct line with the high-street of Rochester, and that of Stroud.

And that towards the reparation and maintenance of it, different persons in respect of their manors, and lands in the adjacent neighbourhood were bound to bring certain materials, and to bestow both cost and labour in laying them, which duty grew either by tenure or custom, or perhaps by both, and it seems, that according to the quantity and proportion of the land to be charged, the materials found were either more or less.

Lambarde's Perambulation, p. The owners of the manors and lands, chargeable with the repairs of this bridge, were used by antient custom to elect two men from among themselves to be wardens, or overseers of the repairs of it, at which time there was a wooden tower erected on the bridge, with strong gates, and it was probably near the east end of it, and was used as a fortification for the defence of this passage into the city.

Hasted In c. AD a new bridge was built over the Medway to replace the Romano-British one, with local lords, the king, the bishop of Rochester and the archbishop of Canterbury being responsible for its upkeep.

Nine stone piers with ten arches supported a timber superstructure c. The late Saxon timber bridge was still in use at the Norman Conquest, although it may have been restored in the early eleventh century. As there seem to have been neither balustrade nor handrail, crossing the bridge could be hazardous, and there are numerous twelfth and thirteenth century records of people falling into the river and drowning.

When the city was besieged in there was an unsuccessful attempt to burn the bridge and its defensive tower, and in the west end of the bridge was extended with a barbican and drawbridge.

Repairs were carried out on the ever more fragile bridge at least nineteen times between and , but it was swept away in February Between and a new stone bridge was erected on a new site closer to the castle, with ferry boats plying the river while it was under construction.

The new bridge was carried on twelve piers with eleven openings, all arched except the seventh which had a drawbridge and a winding house above; its carriageway was of ragstone and was c. This gave greater design efficiency due to the superior load-sharing properties but, by minimising the box width and maximising the deck cantilever lengths, also created the appearance of a lighter structure. The viaduct approaches, with spans up to 83 m, were constructed span-by-span with a maximum span to depth ratio of 24 which adds to the structure's light appearance.

They are supported on twin hollow piers that were designed to be as slender as possible. The superstructure is monolithic with the river piers piers 6 and 7 , which are of twin cell box construction. The viaducts have fixed bearings at piers 3, 4 and 5 on the west viaduct and at pier 8 on the east viaduct. The remaining bearings are guided longitudinally.

The pier concrete was grade 50 to give adequate axial capacity from the relatively slender box walls. The viaduct twin piers share a common pilecap foundation. The site geology generally consists of made ground overlying terrace gravels and upper chalk. In the river, there was soft alluvial clay and silt of up to 3 m in depth. The remaining foundations are founded on bored piles, mm in diameter with the exception of those for the main river piers which were mm in diameter due to the need to resist ship impact.

Typical pile lengths vary from 21 to 29 m. Load tests were conducted on trial piles in the chalk and the results were used to refine the detailed design of subsequent piles to be less conservative than an initial design using CIRIA Report Since the bridge is externally post-tensioned, BD58 2 was used in conjunction with BSPart 4 3 in the design. The bridge was designed to satisfy all the specified code serviceability and ultimate limit state SLS and ULS criteria with one tendon having been removed for a replacement operation.

Analysis of the bridge was performed using a spaceframe global model with separate shear flexible grillage analysis to determine the transverse distribution. Finite element models were used in the design of local elements.

The construction sequence had a significant effect on the load effects to be built up and this is discussed further later. Externally prestressed bridges are less efficient than internally prestressed ones in flexure at ULS because the eccentricity of the tendons is likely to be less.

Furthermore, the strain in the tendons does not increase at the same rate as the strain in the adjacent concrete at the section being checked, as the tendons are not bonded to the concrete. On the new Medway Bridge, the box was sufficiently deep that the loss of eccentricity from placing tendons next to the flanges was not significant.

The lack of strain increase however was very significant and this led to ULS flexure governing the design as expected. Typically, it might be assumed that the tendon force does not increase at ULS as any strain increase results only from the overall deflections of the structure and not from local high strains.

BD58 2 allows a small strain increase without proof for mid-span regions of cables which do not extend beyond the supports, but most of the Medway Bridge tendons did not comply. The design therefore considered strain increases more rigorously since all increases had a significant impact on reducing reinforcement quantities in such a large structure.

Strain increases were calculated by an iterative procedure considering the nonlinear material behaviour of reinforcement, concrete and tendons, with the increase in length of the cable obtained by strain integration along the axis of the cable. Both hand and computer methods were used to check behaviour. Generally all the strain increase took place on the elastic part of the tendon stress—strain diagram due to the losses from creep, shrinkage, draw-in and friction.

The magnitude of increases in the cable strain possible led to the conclusion that, for Medway Bridge, it was generally not possible to increase the tendon force significantly past the stress at which the tendon stress—strain relationship first becomes non-linear, except for the shortest cantilevering tendons.

In the course of the calculations, it became clear that the majority of the deformation, and thus strain increase, occurred in relatively small regions where the reinforcement was yielding. Therefore a considerable time-saving could be achieved by only integrating the strain in these plastic regions. Normally in design it is safe to ignore tension stiffening. However, when calculating strain increases in external tendons this is unsafe as a tension-stiffened section will not undergo as much deformation as a fully cracked section.

Where the tensile stresses did not exceed the tensile strength of the concrete, the section was deemed not to be cracked and the gross elastic cross-section stiffness was used. Where stresses exceeded this value, section stiffness was calculated from a cracked analysis using the stress—strain curves for reinforcement and concrete given in BSPart 4.

For the typical reinforcement content on the Medway Bridge, it was expected that tension stiffening would have little effect on sections where the steel strain from a fully cracked analysis exceeded 1 millistrain.

A departure from standards was sought to use Eurocode 2. The depth of the main bridge box was varied parabolically so that the soffit was theoretically on an approximately constant radius.

The soffit was however formed from a series of chords. The continuity tendons have to follow the bottom flange profile via a series of deviators which gives rise to a series of concentrated downward forces. These forces must be resisted by the flange and deviator spanning transversely between webs.

A similar additional downward force arises from the longitudinal tension reinforcement in the flange required for ultimate bending capacity. This was a significant force as the largest soffit bars were T After looking at test results for straight bars lapping and by considering the possibility of bars shearing out, it was considered that small T6 links should be placed around the lapping bars where their size exceeded T It was noted that Eurocode 2 5 would have required links around the larger bars even if they had been lapped straight.

The most slender bridge piers see Fig. The stiffness of the pier sections was determined from the stress—strain relationships in Figs 1 and 2 of BSPart 4. It is noted that Eurocode 2 now gives a method very similar to this. Initial imperfections were applied to the modelled piers. The piers with free bearings were modelled individually with a simple lean imperfection. Elastic critical buckling analysis was used to investigate the buckling mode shapes for the system comprising monolithic and pinned piers and similar imperfections were applied to this complete system.

On site, the construction was limited to a tolerance on verticality of half this design value. The lateral deflections under load found by the non-linear analysis were considerably less than those found to BS Part 4 3 and a large saving on reinforcement was produced.

There appears to be far greater freedom in placing tendons in an externally prestressed bridge as the whole space within the box can be used as long as access is still provided and the tendons do not have to be confined within the concrete outline. The disadvantage however is that the tendons cannot be gradually deflected throughout the span by the encasing concrete, as can be done with internally prestressed bridges, and physical deviators have to be provided.

Tendons in a typical viaduct span were anchored at an anchor beam ahead of the pier see Fig. The tendons then deviate downwards from the top of the pier diaphragm to a span deviator see Fig.

Tendons are thus lapped over the piers when the subsequent span is completed so one main constraint on tendon positioning was to ensure that these two sets of cables missed each other at diaphragms see Fig. The other main constraint was to ensure that a clear walkway was still provided throughout the box so tendons move back towards the webs from their spaced positions at the piers.

The tendons must also keep clear of the drainage. Typical prestressing arrangement in viaduct spans dimensions in mm. Viaduct cable routing—in-span deviator and anchor beam during construction. Viaduct cable routing—typical diaphragm at pier during construction. There were greater difficulties, however, with the balanced cantilever section because of the necessarily large number of tendons.

There is effectively less width available for routing the cantilevering tendons than for an internally prestressed design since they cannot be run out into the box cantilever flanges. Consequently the cantilevering cables would not all fit within one layer and a double layer was necessary between the main piers Fig. Double layer of balanced cantilever tendons at main pier diaphragm. Deviation and anchorage of the balanced cantilever tendons. Between segment 8 and the pier, each newly anchored tendon has to pass through the anchorage blister in the previous segment and the one prior to that.

From their end anchorages, the tendons set off at a small horizontal angle into the box such that the tendon misses the bursting reinforcement and anchorage for the previous tendon at the blister in front. Each newly anchored tendon has to pass through the blister in the previous segment, because it is too close to the previous tendon to pass outside the blister and allow sufficient cover to its reinforcement. The tendons must then also be deviated at the segment previous to this to avoid clashes as they come together towards the pier.

The longer tendons, from the ninth segment onwards, were all in the upper layer and were straight between the main piers and the segment 8 deviator. As these later segments are longer and the plan angle of the tendons is smaller, the tendons only needed to pass through the previous one blister, without deviation, until they reached the main deviator beam at segment 8 see Fig.

The setting out of these deviator pipes was crucial both to ensure that tendons did not clash and also to guarantee a smooth profile without potentially damaging kinks at pipe entries and exits. Current lightbox. Live chat. Narrow your search:. Cut Outs. Page 1 of 8. Next page. Recent searches:. Create a new lightbox Save. Create a lightbox Your Lightboxes will appear here when you have created some. Save to lightbox.