London Bridge: The New Bridge of 1973 and Staged Reconstruction

London Bridge's history as a crossing of the Thames long predates the present concrete bridge. The foundation's official annual report dates completion of the first stone bridge to 1209 and attributes the replacement of 1831 to John Rennie the Elder's design. The Historic American Engineering Record further explains that, after the elder Rennie's death, his son of the same name completed the working drawings and supervised construction. These bridges form a historical succession, rather than a single structure surviving unchanged.

Completion of the modern bridge must also be distinguished from its ceremony. The annual report records construction completion in 1972 and an opening led by Elizabeth II in 1973. The 1973 milestone therefore identifies the new bridge's formal opening, not the first time London possessed a river crossing. When considered alongside the transfer of old bridge stonework to the United States, the places and structures involved must be clearly distinguished.

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By the 1960s, the nineteenth-century bridge again faced inadequate capacity for traffic. A contemporary Building report recorded that Mott, Hay & Anderson was initially commissioned to examine widening it. Investigations found the existing foundations heavily loaded, with continuing settlement accompanied by cracks in the arches and elsewhere. In 1965, engineers instead recommended a new bridge to avoid adding further loads to hazardous foundations.

The City of London obtained parliamentary authorization in 1967, awarded the demolition and construction contract to Mowlem, and began work on 6 November. Rebuilding involved more than replacing a deck: foundations, river piers, navigation openings and road traffic had to be planned together. Superstructure engineer Michael Leeming later recalled that existing roads and buildings at both ends constrained the bridge's form, while the architectural demand for a slender appearance encouraged the choice of prestressed concrete.

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The new bridge used three spans, with a central span of 340 feet, an overall width of 107 feet and two piers in the river. Its superstructure consisted of four parallel concrete box girders, each capable of being built independently before final transverse connection. Width, navigational clearance and the routes that had to remain available during construction jointly determined this form. Its simple appearance concealed a set of interdependent engineering constraints.

Staged construction first used space alongside the old bridge to build the outer new girders and divert some traffic onto them, then progressively removed the old bridge and inserted the middle sections. In his oral account, Leeming described four bridges finally joined into one. The old bridge did not disappear completely before the new one began working; old and new structures simultaneously served different transport and construction functions during the transition.

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Leeming recalled that almost no usable space existed at the bridgeheads. Precast components were made downstream at Surrey Docks and transported to the site by barge. An elevated steel truss spanning the river helped lift new components and dismantle the old stone bridge block by block. Moving manufacture off-site eased pressure on land space without removing the difficulties of construction organization.

Barges had to contend with tidal currents, and differences between the old and new pier positions complicated water flow; some operations could proceed only at suitable tides. Maintaining traffic also requires precise description. Leeming stressed that the team preserved the crossing, while the contemporary report explained that limited nighttime or weekend arrangements were permitted. The objective was to maintain specified traffic capacity, not to eliminate construction effects everywhere and at every moment.

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Another part of the old bridge's history unfolded in the United States. Contemporary reporting recorded that in April 1968 the City sold the exterior stonework to McCulloch Properties. Leeming said the stones had to be numbered before shipment, and that some exported pieces were only a layer cut from the face of an original block. The site, foundations and all load-bearing material were not transferred intact.

The National Park Service's 1999 engineering history explains that the bridge in Lake Havasu City uses concrete arches faced with old granite, preserving the appearance of the corbelled parapets. It was constructed using sand forms on dry land, with a channel excavated only after completion, turning the former peninsula into an island. It was rededicated on 10 October 1971. Serving local tourism and urban development, it was a project connected to, but distinct from, the staged rebuilding of London Bridge over the Thames.

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The new London Bridge formally opened on 16 March 1973. The engineering report published that day corroborates Leeming's firsthand recollections of the Queen presiding at the ceremony and presenting commemorative medals. The report also stated that the City's Bridge House Estates fund paid for the project, supporting bridge affairs through revenue including property rents.

This institutional background carries the bridge's history beyond completion. The official 2023 annual report still identified maintenance of London Bridge and four other river crossings as the foundation's primary purpose, with property and financial investments as its main income sources. Rebuilding renewed the load-bearing structure and coordinated pedestrians, vehicles and shipping; lasting usefulness depends on continued investment in maintenance and management after construction.

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