Since the mid-1980s the design of bridges has changed quite dramatically with architects becoming more directly involved in the process.
Architectural involvement in bridge design has increased significantly in recent years. To some extent this has been due to the influence of bridge designs by architect/engineer Santiago Calatrava. Examples of his work and that of other contemporary innovative bridge designers are given below.
The Felipe II / Bach de Roda Bridge, Barcelona, 1985-87, designed by Santiago Calatrava, uses four tied arches to carry the road deck over a multi-track railway line.
Of total length 129m, the 46m main span of the Felipe II / Bach de Roda Bridge, in Barcelona, is 8m above railway tracks and skewed at 30º. Its steel and concrete composite deck is suspended by steel tension rods, at 1.85m centres, from four triangular, welded, box-section steel arches, that rise 10m above the roadway. The two main tied arches and their associated sets of paired tension rods run parallel to the outer kerb lines of the carriageways. Secondary inclined arches are supported from inclined and moulded concrete stairways that provide direct access to the bridge from the low-level, landscaped parks adjacent to the tracks. These secondary arches are connected by ribs to the outer face of each main arch, thus providing lateral support.
Felipe II / Bach de Roda Bridge detail of steel arches
Situated behind a large building adjacent to the local railway station, La Devesa Bridge, Ripoll, Spain, 1989-91 (Architect/Engineer: Santiago Calatrava) spans the River Ter with a highly elegant example of modern footbridge design. The main supporting arch, inclined at 65º to the horizontal is offset to one side of the deck.
The geometry of La Devesa is influenced by the topography of the site, as the ground is higher on the station side of the river by around 5 metres. Calatrava exploits this difference in level to some advantage, by using a horizontal arch-supported deck of 44m maximum span which continues beyond the centre line of the foundation at the lower bank to give a total length of 65m.
The main supporting tied arch is offset to the upstream side of the deck and is also inclined at 65º to the horizontal in the same direction. Torsion, which is normally avoided by engineers wherever possible, becomes a major consideration in the design of the cross-section. The 2.44m wide bridge deck of hardwood timber boards is supported on steel ribs cantilevered to one side of the 508mm diameter, 20mm thick, tubular steel tie beam. A 244mm diameter tube, of 10mm wall thickness links the remote ends of the cantilevers and this is set at 3.25m from the centre of the main tube. Cross-bracing runs between the two tubes in each bay between cantilevers to produce a rigid horizontal truss to resist lateral forces. Rising up to 6.5 metres above the tie, the arch is formed using a 267mm diameter steel tube, of 16mm wall thickness. This is linked to the tie/torsion beam by tapered arms that serve to transmit load (in tension) from the deck to the arch, prevent buckling of the arch and to permit the self-weight of the arch to balance the self-weight and load on the deck to some extent.
La Devesa Bridge, Ripoll, Spain
The Alamillo Bridge, Seville, Spain, 1987-92, (Architect/Engineer: Santiago Calatrava) forms a dramatic landmark, pointing the way to the site of the 1992 Seville Exposition. A single inclined pylon removes the need for backstays in the asymmetrical cable-stayed solution.
Traversing the Meandro de San Jerónimo of the Rio Guadalquivir in Seville, the 250m long Alamillo Bridge is perhaps the most controversial and dramatic of Calatrava's bridges to date. Originally conceived as one of a symmetrical pair of bridges approximately 1.5 km apart, the 142m high steel and concrete inclined pylon marks one of the main entrances to Cartuja Island, site of the Seville Expo'92. The germ of the idea for the structural system of the bridge can be seen in Calatrava's sculptures, such as Toros (1985), which he uses to explore statical problems. Here the dead weight of the inclined pylon counter-balances the weight of the bridge deck to which it is attached by cable stays.
To support the bridge deck a torsionally rigid hexagonal box girder spine 200m long runs along the centre. This carries the pedestrian footway, on its top flange, above the level of the two carriageways that are supported on steel ribs, 12.5m long, cantilevered from the central spine. There are openings between the ribs to separate the carriageway decks and the main spine beam thus allowing the twin stay cables to be attached at low level to both sides of the box spine and light to penetrate through the deck. More transparency is achieved by cutting away a triangular section of each rib web adjacent to the box spine, thus separating completely the tension and compression zones of the cantilevers. A tie element within the box spine joins the tensile flanges of the ribs and the compressive flanges are connected by the lower flange of the box girder.
Trinity Bridge, Salford
Trinity Bridge, Salford, 1993-1995 (Architect/Engineer: Santiago Calatrava), named after the nearby Trinity Church, spans the River Irwell between Salford and Manchester.
As an asymmetric single-masted cable-stayed bridge Trinity Bridge has certain similarities with Calatrava's Alamillo Bridge in Seville. However, in this case, backstays are provided to resist the horizontal pull of the deck stays. In fact, two sets of backstays are provided fanning out along the two curved approach spans arcing back from the river bank on both elevations of the bridge. The mast inclination here is used to reduce the axial force within it as the mast takes up a more equitable position between the mainstays and backstays. There is also approximately 5m difference in level between the two river banks, as at Ripoll, and again an asymmetric solution is adopted to reflect this, although here the bridge deck also slopes at 4º along its length.
Overall length of the bridge is 78.5m, with a maximum span of 54m over the river. The cigar-shaped, 41m long mast is inclined at an angle of 62º to the horizontal and is formed from a tube of diameter varying from 0.55m at the base to a maximum of 1.2m around the anchor point of the second lowest cables. It has a wall thickness of 40mm. The mast sits atop a 5m high sculpted reinforced concrete pillar, inclined at the same angle, which rests on piled foundations. A single fan of eight cables, 30mm in diameter, spring from the mast at angles varying from 16º (the lowest cable) to 39º (the highest) to support the triangular cross-section steel box girder mainspan. Backstays (a further eight 30mm diameter cables to each side of the mast) provide restraint for the horizontal component of the mainspan stay forces. At their lower end the backstay cables are anchored to the outer face of the curved approach spans to each side of the mast. An unusual feature of the bridge is that the upper cable anchorages to the mast are partially concealed, being recessed into the tube.
Merchants Bridge, Manchester, 1995, (Whitby Bird and Partners) links Slate Wharf with Catalan Square on the southwest side of the Bridgewater Canal in the Castlefield conservation area.
Described as "Curved in every possible direction with only the handrail supports vertical" the 67m long Merchants Footbridge is a hybrid comprised of a slender "wedge-shaped" box girder, up to 3m wide and only 475mm deep, and an inclined arch. The inclined arch stiffens the box girder whilst the torsional strength of the girder, in turn, provides restraint to prevent buckling of the arch. Similarity to Calatrava’s Ripoll bridge is acknowledged by Whitby Bird. However, in this case the concept of the inclined arch is developed further as it is also curved in plan. Elements fabricated in the workshop were assembled by bolting and site welding on the bank adjacent to the bridge site and the complete 50m main span was lifted into place in 40 minutes, by an 800 tonne capacity mobile crane.
"Merchants Bridge represents state of the art design in a location that is rich in engineering history. Our proposal took contemporary technology for bridge analysis, documentation and machine fabrication and combined them to create a unique form. The bridge epitomises a new confidence in engineering that is flowing from fast developing technologies and is now designated a Design Council Millennium Product.
Users are responding enthusiastically to the new bridge. The counterbalanced curves not only transport but cradle pedestrians in a manner that suggests they should linger and enjoy the spectacle.
Situated in an industrial heritage site, the bridge has become a focus and symbol of the regeneration of the area. Essential to the project's success was the client's vision in establishing the competition brief that created this opportunity"
Merchants Bridge, Manchester
Challenge of Materials Footbridge, Science Museum, London, 1997 (Architect: Wilkinson Eyre, Architects; Engineer: Whitby Bird and Partners) was part of the winning design in a 1995 competition for a major new gallery at The Science Museum -The 'Challenge of Materials Gallery'.
The 'Challenge of Materials' gallery was opened to the public in May 1997. Inspired by the desire to produce a contemporary version of a rope bridge and the postcard image of a sculpture (Suspended Stone Circle II, by Ken Unsworth), this 16m span bridge has a laminated glass deck suspended by a filigree of fine cables. The balustrade infill panels are also of laminated glass so that a very transparent quality is achieved. Changing load patterns in the bridge are monitored and the electrical signals produced are transposed into an ever changing sound and light show.
"At the heart of the gallery a dramatic and innovative new bridge spans the atrium at mezzanine height floating across the space to provide a visual focus and a marker for the gallery form the adjacent spaces. Comprising of few elements and limited material the bridge is minimal in the extreme. Designed to the limits of technical feasibility if offers a clear demonstration of material capability. Aiming to be almost imperceptible the bridge comprises a deck formed by 828 abutted glass planks suspended by an array of ultra fine stainless steel wires. By channelling these wires through stress gauges and incorporating acoustic devices and lighting systems by the artist Ron Geeson, the bridge becomes an interactive exhibit, challenging materials to the limit and consequently challenging visitors to cross."
(Courtesy: Wilkinson Eyre Architects)
"This bridge in the Challenge of Materials Gallery in the Science Museum solves the problem of providing the lightest possible link across the atrium of the building. The bridge has now been designated a Design Council Millennium Product.
The bridge celebrates the structural properties of steel and glass, illustrating the challenge raised by the gallery. Piano wire technology, which has very simple detailing, is used in a cable stay arrangement. The wires are finely spaced, creating a filigree fan of cables cradling the bridge.
The stresses of the bridge are linked to a computer such that its behaviour is animated in light and sound, making the bridge both a visual exhibit and a means of demonstrating stress patterns in the deck. The deck is formed from vertically laminated annealed glass - the first time the material has been used in this way."
In 1998, the Challenge of Materials Gallery gained an RIBA Award for Architecture and a Design Week Award for Exhibition Design (exhibition design and lead consultant: Jasper Jacob Associates). In the same year, the Challenge of Materials Footbridge was a finalist in the Glassex Industry Awards and was awarded Millennium 'Product Status'.
Suspension anchorage detail
South Quay Footbridge, Canary Wharf, London (Architect: Wilkinson Eyre Architects, Engineer: Jan Bobrowski and Partners) was the winning entry in a competition for the design of an opening bridge to span West India Dock between South Quay and Heron Quays in London's Docklands. It was completed and opened in May 1997.
The competition brief for this 170m long footbridge across West India Dock specified that one part should be permanent and the other temporary and capable of relocation to a position about 100m to the east. It also had to incorporate an opening for the passage of small boats and be capable of being shortened to accommodate a proposed future narrowing of the dock. The solution adopted complied with both present and future requirements. It features a bridge deck of variable width, having an 'S' shape in plan and being curved in elevation. This is split into two identical lengths, one of which is fixed and the other a swing bridge. Each half of the bridge is cantilevered from the side of a 914mm diameter tubular edge beam which is, in turn, suspended by 75mm diameter cable stays from a 32m high raking and tapered elliptical steel pylon. The opening section rotates on a bearing located at the pylon base. In the initial configuration the bridges span diagonally across the dock, with the southern half opening. However, eventually the northern section will be relocated and the southern section will be swung into a new alignment.
The inclined pylons and 'S' shape of the deck creates a twisted plane of cables that adds visual interest to the crossing. Along one side there is a shaped stainless steel wind-screen to offer some protection to pedestrians. On the other there is a balustrade incorporating an illuminated elliptical hand-rail, the light from which reinforces the 'S' geometry at night. The mast profile is ovoid in response to the directional line of the rake and is fabricated by welding together two matching segments cut from cylindrical sections.
"The elegance of the bridge is derived from these relatively few elements: the lines of the deck; the visual counterpoint of the raking masts and the splay of the cables. The appeal of the curved deck lies in the compound nature of the curves. The width of the decks varies along their length to provide visual weight opposite the masts and to narrow as they reach out towards the landings and the centre of the bridge. This accentuation gives both the impression of visual lightness as well as being an actual expression of where the weight in the bridge is minimised. There are numerous comparables for the 'S' shape that occur in the visual arts, in science, in nature and in sport. William Hogarth's 'The Analysis of Beauty' (1753) compares various 'S' curves, concluding with the definition of his 'line of beauty'." (Courtesy Wilkinson Eyre Architects)
"The lyrical and romantic curved forms and slender proportions of the bridge act in contrast to the bulk and uniformity of the surrounding buildings. The kinetics of the design provide the excitement which promotes the bridge as a visual focus and an experience rather than just a functional crossing." (Courtesy Wilkinson Eyre Architects)
The bridge design has been awarded the following honours:
Inclined mast, South Quay Footbridge, Canary Wharf, London
Gateshead Millennium Bridge, Gateshead, which is currently under construction (Architect: Wilkinson Eyre Architects, Engineer: Gifford and Partners) was the winning entry in a 1997 competition for a major new crossing over the Tyne.
The Millennium Bridge, which is promoted by Gateshead Metropolitan Borough Council, will form a link between the newly developed Newcastle Quayside and the new Visual Arts Centre at the Baltic Flour Mills and the Northern Regional Music Centre currently under development in East Gateshead. The bridge consists essentially of two arches of 100m span. One arch is inclined slightly from the vertical and the other, which is almost horizontal, forms the curved bridge deck that is suspended from it. Both arches have a common springing point on which they pivot, allowing the bridge deck to be raised by the action of a series of hydraulic rams. In the open position the cables joining the two arches lie horizontally, leaving a clearance of 25m for the passage of boats on the River Tyne (ref. Curran). This configuration complies very well with the competition brief, which required a clear channel for shipping and a low level crossing for pedestrians and cyclists to be provided. The bridge spans between new islands, formed from caissons that run parallel to the quaysides.
"The opening motion of the design is both its generator and its highlight. Bridges that open offer a spectacle, yet are rarely spectacular. This bridge in contrast has visual daring and elegance in its closed position, giving way to theatre and power in operation.
The idea is simple; a pair of arches, one forming the deck, the other supporting it, pivot around their common springing point to allow shipping to pass beneath. The motion is efficient and rational, yet dramatic beyond the capabilities of previously explored opening mechanism. The whole bridge tilts, and as it does the composition undergoes a metamorphosis into a 'grand arch' of great width and grace, in a operation which evokes the action of a closed eye slowly opening.
The scheme is wholly informed by the need for a legible integration with the Tyne's existing bridges and with its particular context. The design is a mix of the robust, as befits its lineage, combined with an overall lightness to contrast the visual mass of the Baltic Flour Mill. A soaring arch provides instant visual reference to the Tyne Bridgebeyond, but presents a slender profile against the skyline, interpreting and updating the structural and aesthetic order of its neighbour."
The design received a Royal Academy AJ/Bovis Grand Award in1997.
Neckarstrasse Footbridge, Stuttgart, 1989 (Architect: Hans Kammerer, Engineer: Jörg Schlaich), has a slender reinforced concrete deck that hangs from steel cables attached to the façade of the Hotel Intercontinental.
The Neckarstrasse Footbridge in Stuttgart is one of many innovative bridges designed by engineer, Jörg Schlaich. In this case the 280mm depth of the concrete bridge deck was constrained by headroom restrictions over the dual carriageway below and the level of the first floor slab of the Hotel Intercontinental to which it is attached. As space for intermediate supports was severely restricted, a cable-supported span of 45.15m was proposed, anchored to large columns on the façade of the building itself. This resulted in a very slender and elegant solution with the main cables curved in plan as well as elevation. To reduce maintenance costs all nodes and anchorages were made from a stainless steel alloy, which is resistant to chloride attack from the road de-icing salts.
Royal Victoria Dock Footbridge, London, 1999 (Architects: Lifschutz Davidson, Engineer: Techniker), was originally conceived as a "transporter" bridge. It has an innovative form based on an inverted Fink truss.
Originally this 135m span competition winning design was conceived as a "transporter" bridge in which pedestrians were to be carried across the Royal Victoria Dock suspended in an enclosed gondola hanging from the deck above. The glazed pods were designed to pass at levels ranging from just above dock level to immediately below the deck, depending on the presence or absence of yachts in the vicinity of the bridge. However, due to the client's concern about maintenance and operating costs, the final version has lifts to raise pedestrians to deck level where they must cross on foot. The sailing analogy has been taken up in the design of the bridge, which has a continuous, variable depth box girder supported by masts and cables in the form of an inverted Fink truss. The bridge is notable in that it is assembled without the use of any bolts or welding, the structure being simply "pulled together" and therefore fully demountable.
The Butterfly Bridge, over the River Great Ouse, in Bedford (1997), was the winning entry in an open RIBA competition, in 1995, to design an appropriate landmark pedestrian crossing of the Upper River to complement Webster's existing Bedford Suspension Bridge, of 1888.
The bridge, completed in May 1997, spans 30m between willow-lined grassed banks. Two inclined tubular steel arches form the primary structure from which the hardwood timber deck is suspended by means of a system of rod hangers connected to transverse steel bearers that are integral with the balusters supporting the handrails. This is a modern reinterpretation of Webster's Victorian bridge, using contemporary design concepts and material capabilities, therefore fulfilling the objective of the competition, which was described thus: - "Webster's 1888 Suspension Bridge provides a memorable landmark which epitomises Bedford at the end of the 19th century. The aim is to build a bridge which similarly marks the end of the 20th century and the beginning of the 21st".
"Webster's twin arched trusses are re-visited, as high arching parabolas each of a single circular hollow steel section. The arches emanate from a single point on each bank and are canted to form an 'opening' arch form, 16m crown to crown, which alludes to the vision of butterfly wings. The composition is thus vaguely organic, like some mechanical insect landed on the flood meadows. This sense, in addition to the references to its neighbour, locates the bridge in its setting.
In the context of the multiple factors informing the design, the result is functional on many levels. Its reason to be, a level and navigable crossing of the Great Ouse [in contrast to the steeply sloped existing suspension bridge], is a by-product of the more esoteric demands of the design problem. Structurally the composition is at the limits of its capability. Visually it is intentionally arresting and historically it is anchored to its site by reference to the existing. The design is a result of a collaborative application of art and engineering in contrast to Webster's engineering latterly perceived as art."
Butterfly Bridge, Bedford
The Hulme Arch Bridge, Manchester, 1997, (Architect: Wilkinson Eyre Architects, Structural engineer: Ove Arup and Partners) is a landmark structure located in the Hulme regeneration area. The bridge deck is suspended by twenty-two, 51mm diameter spiral-strand cables from a 52m span single diagonal steel parabolic arch of tapering trapezoidal form.
The re-establishment of the former route of Stretford Road over the major road cutting of Princess Road was an important element in the Hulme regeneration programme, reuniting the two halves of this area of south Manchester. A two-stage design competition was initiated, calling for a new road bridge to raise the profile of Hulme. In the opinion of the winning design team (Ove Arup and Partners / Wilkinson Eyre Architects) this was taken to mean that the bridge should act as a landmark, form a gateway and reunite the two halves of Hulme. The principal design reference has been cited to be Eero Saarinen's Gateway Arch, St. Louis built in 1964 (Hussain 1999).
In the winning design, completed in May 1997, inclined cables from a single steel arch, spanning diagonally across both Stretford Road and Princess Road (forming a gateway for both routes), support the bridge deck. Each half of the arch supports eleven cables, which are anchored at their lower ends at equally spaced intervals along one edge of the deck (the other edge being supported by cables from the other half of the arch). The arch is trapezoidal in section and tapers in opposite directions in plan and elevation, being at its widest and shallowest at its crown. The parabolic profile of the arch generates a height of 25m, which is high considering the relatively modest 52m span of the bridge. This adds to the structure's impact as a landmark, as does the aluminium-painted surface finish, which is illuminated at night.
"The two sets of cables, which support either side of the deck, are arranged to interlock and overlap so visually uniting the two banks and the two halves of Hulme. Tensioned cables connecting the bridge deck to the arch fan out in opposing directions to resemble a 'cat's cradle' which changes in complexity and disposition according to the position of the viewer. By positioning the arch and distributing the cables in this manner the structure combines the symmetrical and the asymmetrical. Visual complexity is achieved from geometric simplicity."
The bridge has received the following awards: -
Hulme Arch, Manchester
Corporation Street Footbridge, Manchester (Architect: Hodder Associates, Engineer: Ove Arup and Partners) represents an interesting and innovative solution for a short span pedestrian bridge linking two buildings. The bridge deck is supported by and enclosed in a horizontal hyperboloid glazed tube.
The competition brief for a bridge to replace the original connection (destroyed by an IRA bomb in 1996) between the Arndale Centre and the Marks and Spencer store was seeking a solution that masked the 1.2m difference in first floor levels between the buildings. To achieve this, the winning solution by Hodder Associates/ Ove Arup and Partners encloses a slender sloping bridge deck within a horizontal glazed tube of 18m span. However, the tube's circular cross-section is not of constant radius but is generated by a horizontal hyperboloid surface. This is formed by a network of straight, 110mm diameter, compression tubes and 25mm diameter tension rods, which link offset points on two vertical circles at the supports in both clockwise and anti-clockwise directions. The prefabricated filigree bridge structure was lifted into place in just 40 minutes. Triangular (hurricane-proof) laminated glass cladding panels, reinforced with a polyester interlayer, are supported at their corners with purpose designed stainless steel clamps. (Spring 1999)
On 15 June 1996 a large bomb exploded injuring 220 people and causing immense physical damage to the core of Manchester city centre and its social and economic fabric. The shattered footbridge, which connected two shopping centres across Corporation Street remains one of the most vivid images. The renewal programme is now well underway and in December 1997 the competition for a new footbridge was won. Its reinstatement may be seen as a symbol of the City's recovery.
Contextually Corporation Street is canyon like and is a significant, linear north-south route through the City culminating with the civic space of Albert Square. The footbridge takes the form of a hyperbolic parabloid of revolution and appears as a lightweight glazed membrane stretched across the street. Its transparency is heightened by the arch, which permits uninterrupted aspects and whose symmetry optically redresses the change in level of the boardwalk which threads through from side to side. Outside the membrane are 18 straight stainless steel cables and compression members which spiral in an alternating clockwise and anti-clockwise direction."
Corporation Street Footbridge, Manchester 1999
Oracle Bridge, completed in autumn 1999, consists of two separate 20m span box girder pedestrian bridges across the River Kennet in Reading (Architect and Engineer: Whitby Bird and Partners).
"These two bridges over the River Kennet were the subject of a design competition. Our winning entry took a holistic design approach to the site, seeking to create a new civic space embraced by the bridges. Terraced seating, performance spaces and a canopy have also been designed, forming a public arena in the centre of the new Oracle shopping development in Reading.
The original purpose of the bridges was to provide access across the river between the shops on either side. Our bridges do more than this, forming the boundary of the civic space that crosses the river. Seating on the curved bridge provides an alternative view of the performance space and encourages pedestrians to enjoy the river.
Both bridges are formed from sealed box girders, employing a single tube on one side. The handrail uses tensioned wires with feature lighting set into the standards."
(Courtesy Whitby Bird and Partners)