Millennium Bridge & St Paul's

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This is a beautiful photograph from low down on the deck of the Millennium Bridge looking down Peter's Hill pedestrian walkway and Sermon Lane to St Paul's Cathedral. The colour and lighting are fabulous and the image exhibits three-dimensional characteristics as our eye is drawn over the bridge and down the walkway between the rows of buildings and there at the end of Sermon Lane is the majestic cathedral, looking resplendent.

Dome

Wren drew inspiration from Michelangelo's dome of St Peter's Basilica, and that of Mansart's Church of the Val-de-Grâce, which he had visited. Unlike those of St Peter's and Val-de-Grâce, the dome of St Paul's rises in two clearly defined stories of masonry, which, together with a lower unadorned footing, equal a height of about 95 feet. From the time of the Greek Cross Design, it is clear that Wren favoured a continuous colonnade (peristyle) around the drum of the dome, rather than the arrangement of alternating windows and projecting columns that Michelangelo had used and which had also been employed by Mansart. Summerson suggests that he was influenced by Bramante's "Tempietto" in the courtyard of San Pietro in Montorio. In the finished structure, Wren creates a diversity and appearance of strength by placing niches between the columns in every fourth opening. The peristyle serves to buttress both the inner dome and the brick cone which rises internally to support the lantern.

Above the peristyle rises the second stage surrounded by a balustraded balcony called the "Stone Gallery". This attic stage is ornamented with alternating pilasters and rectangular windows which are set just below the cornice, creating a sense of lightness. Above this attic rises the dome, covered with lead, and ribbed in accordance with the spacing of the pilasters. It is pierced by eight light wells just below the lantern, but these are barely visible. They allow light to penetrate through openings in the brick cone, which illuminates the interior apex of this shell, partly visible from within the cathedral through the ocular opening of the lower dome.

The lantern, like the visible masonry of the dome, rises in stages. The most unusual characteristic of this structure is that it is of square plan, rather than circular or octagonal. The tallest stage takes the form of a tempietto with four columned porticos facing the cardinal points. Its lowest level is surrounded by the "Golden Gallery" and its upper level supports a small dome from which rises a cross on a golden ball. The total weight of the lantern is about 850 tons.

Millennium Bridge, London

The Millennium Bridge, officially known as the London Millennium Footbridge, is a steel suspension bridge for pedestrians crossing the River Thames in London, England, linking Bankside with the City of London. It is owned and maintained by Bridge House Estates, a charitable trust overseen by the City of London Corporation. Construction began in 1998, and it initially opened on 10 June 2000.

Londoners nicknamed it the "Wobbly Bridge" after pedestrians experienced an alarming swaying motion on its opening day. The bridge was closed later that day and, after two days of limited access, it was closed again for almost two years so that modifications and repairs could be made to keep the bridge stable and stop the swaying motion. It reopened in February 2002.

The bridge is located between Southwark Bridge and Blackfriars Railway Bridge. Its southern end is near the Globe Theatre, the Bankside Gallery, and Tate Modern, while its northern end is next to the City of London School below St Paul's Cathedral. The bridge's alignment is such that a clear view (i.e. a "terminating vista") of St Paul's south facade is presented from across the river, framed by the bridge supports.

Design

The design of the bridge was the subject of a competition organised in 1996 by the Southwark council and RIBA Competitions. The winning entry was an innovative "blade of light" effort from Arup Group, Foster and Partners, and Sir Anthony Caro. Due to height restrictions, and to improve the view, the bridge's suspension design had the supporting cables below the deck level, giving a very shallow profile. The bridge has two river piers and is made of three main sections 81 m (266 ft), 144 m (472 ft), and 108 m (354 ft) (north to south) with a total structure length of 325 m (1,066 ft); the aluminum deck is 4 m (13 ft) wide. The eight suspension cables are tensioned to pull with a force of 2,000 tons against the piers set into each bank — enough to support a working load of 5,000 people on the bridge at a time.

Construction

Ordinarily, bridges across the River Thames require an Act of Parliament. This bridge avoided that requirement because the Port of London Authority granted a license for the structure and the City of London and London Borough of Southwark granted planning permission. Construction began in late 1998 and the main works were started on 28 April 1999 by Monberg & Thorsen and Sir Robert McAlpine. The eventual cost was £18.2 million (£2.2m over budget), primarily paid for by the Millennium Commission and the London Bridge Trust.

Opening

The bridge opened on 10 June 2000, two months late.

Unexpected lateral vibration due to resonant structural response caused the bridge to be closed on 12 June for modifications. Attempts were made to limit the number of people crossing the bridge, which led to long queues but were ineffective in damping the vibrations. The closure of the bridge only two days after opening attracted public criticism as another high-profile British Millennium project that suffered an embarrassing setback, akin to how many saw the Millennium Dome.

The vibration was attributed to an under-researched phenomenon whereby pedestrians crossing a bridge that has a lateral sway have an unconscious tendency to match their footsteps to the sway, exacerbating it. The tendency of a suspension bridge to sway vertically when troops march over it in step was well known, which is why troops stop marching in stride together as a unit when crossing such a bridge. An example is London's Albert Bridge, which has a sign dating from 1873 warning marching ranks of soldiers to break step while crossing.

Resonance

The bridge's movements were caused by a positive feedback phenomenon, known as synchronous lateral excitation. The natural sway motion of people walking caused small sideways oscillations in the bridge, which in turn caused people on the bridge to sway in step, increasing the amplitude of the bridge oscillations and continually reinforcing the effect; the maximum sway was around 70mm. On the day of opening, the bridge was crossed by 90,000 people, with up to 2,000 on the bridge at a time.

Resonant vibrational modes due to vertical loads (such as trains, traffic, or pedestrians) and wind loads are well understood in bridge design. In the case of the Millennium Bridge, because the lateral motion caused pedestrians to inadvertently exacerbate the motion, the designers had not anticipated the vibrational modes. When the bridge lurches to one side, the pedestrians must adjust to keep from falling over, and they all do this at the same time. The effect is similar to soldiers marching in lockstep but horizontally instead of vertically.

The risks of lateral vibration in lightweight bridges are well known. Any bridge with lateral frequency modes of less than 1.3 Hz, and sufficiently low mass, could witness the same phenomenon with sufficient pedestrian loading. The greater the number of people, the greater the amplitude of the vibrations. Other bridges which have seen similar problems are:

• Auckland Harbour Bridge, with a lateral frequency of 0.67 Hz during a 1975 demonstration
• Birmingham NEC Link bridge, with a lateral frequency of 0.7 Hz

Mitigation

Engineers at Arup, the company that designed the bridge, researched the unexpected oscillation they called synchronous lateral excitation. The first laboratory studies used pedestrians on moving platforms at the University of Southampton and Imperial College London. Later in 2000, one span of the bridge was instrumented and tested with crowds of up to 275 people.

They concluded that making the bridge stiffer, to move its resonant frequency out of the excitation range, was not feasible as it would greatly change its appearance. Instead, the resonance was controlled by retrofitting 37 viscous fluid dampers to dissipate energy. These include 17 chevron dampers — long V-shaped braces under the deck panels — to control lateral movement, 4 vertical-to-ground dampers to control lateral and vertical movements, and 16 pier dampers to control lateral and torsional movements. Additionally, 52 tuned mass dampers add inertia to control vertical movement. The work took from May 2001 to January 2002 and cost £5 million. After a period of testing, the bridge was reopened on 22 February 2002 and has not been subject to significant vibration since. In spite of the successful cure, the "wobbly bridge" (sometimes "wibbly-wobbly") epithet remains in common usage among Londoners.

Cable resonance

An artistic expression of the higher-frequency resonances within the cables of the bridge was explored by Bill Fontana's Harmonic Bridge exhibition at the Tate Modern in mid-2006. This used acoustic transducers placed at strategic locations on the cabling of the Millennium Bridge and the signals from those transducers were amplified and dynamically distributed throughout the Turbine Hall of the Tate by a programme that Fontana entered into the sound diffusion engine of the Richmond Sound Design AudioBox.

Millennium Inclinator

A short inclined lift, known as the Millennium Inclinator, is next to the northern end of the Millennium Bridge. It was opened in December 2003 to allow pedestrians to surmount the steep slope (13.6°) of Peter's Hill from the riverside to the entrance to the Millennium Bridge without using the alternative flight of steps. The lower end of the lift is on Paul's Walk next to the Thames, and the top end is 26.85 metres (88.1 ft) further up Peter's Hill on the terrace which is level with the deck of the bridge. It was primarily installed for use by those who cannot easily manage the steep steps, such as people with disabilities and parents with pushchairs.

The lift carriage was originally powered by an electric traction motor, manufactured in Italy by Maspero Elevatori, with a speed of 0.5 metres per second (1.6 ft/s) and a maximum capacity of 0.7 metric tons (0.77 short tons; 0.69 long tons). However, by 2010 the City of London Planning and Transportation Committee decided that the level of service was unacceptable because the inclinator was frequently out of service due to mechanical breakdowns and vandalism. So the Committee agreed it would be replaced at a cost of up to £750,000 in time for the 2012 Summer Paralympics.

A major renovation project was undertaken in 2012, and the lift was reopened in time to be used by people attending the Thames Diamond Jubilee Pageant of 3 June 2012, which took place about a month before the 2012 Summer Olympics. The new lift was manufactured by the company Hütter Aufzüge of Glinde, Schleswig-Holstein, Germany, a lift manufacturer which was taken over by the Otis Elevator Company in 2013. Installation was by Axis Elevators. Following the redevelopment of the area in 2021 the lift was closed and will be replaced by a platform lift.

St Paul's Cathedral

St Paul's Cathedral is an Anglican cathedral in London and is the seat of the Bishop of London. The cathedral serves as the mother church of the Diocese of London. It is on Ludgate Hill at the highest point of the City of London and is a Grade I listed building. Its dedication to Paul the Apostle dates back to the original church on this site, founded in AD 604. The present structure, dating from the late 17th century, was designed in the English Baroque style by Sir Christopher Wren. Its construction, completed in Wren's lifetime, was part of a major rebuilding programme in the city after the Great Fire of London. The earlier Gothic cathedral (Old St Paul's Cathedral), largely destroyed in the Great Fire, was a central focus for medieval and early modern London, including Paul's walk and St Paul's Churchyard, being the site of St. Paul's Cross.

The cathedral is one of the most famous and recognisable sights in London. Its dome, surrounded by the spires of Wren's City churches, has dominated the skyline for over 300 years. At 365 ft (111 m) high, it was the tallest building in London from 1710 to 1963. The dome is still one of the highest in the world. St Paul's is the second-largest church building in area in the United Kingdom, after Liverpool Cathedral.

Services held at St Paul's have included the funerals of Admiral Lord Nelson, the Duke of Wellington, Winston Churchill, and Margaret Thatcher; jubilee celebrations for Queen Victoria; an inauguration service for the Metropolitan Hospital Sunday Fund; peace services marking the end of the First and Second World Wars; the wedding of Prince Charles and Lady Diana Spencer; the launch of the Festival of Britain; and the thanksgiving services for the Silver, Golden, Diamond, and Platinum Jubilees and the 80th and 90th birthdays of Queen Elizabeth II. St Paul's Cathedral is the central subject of much promotional material and images of the dome surrounded by the smoke and fire of the Blitz. The cathedral is a working church with hourly prayer and daily services. The tourist entry fee at the door is £21 for adults (Summer 2022, cheaper if booked online), but no charges are made to worshippers attending advertised services.

The nearest underground station is St Paul's, which is 130 yards (120 m) away from St Paul's Cathedral.

From Wikipedia, the free encyclopedia.