North of the first Bosphorus road bridge
Opened in 1988, the Fatih Sultan Mehmet Bridge was Istanbul's second road bridge across the Bosphorus. It connects Hisarüstü on the European shore with Kavacık on the Asian shore, approximately five kilometres north of the first Bosphorus bridge, which opened in 1973. By 1987, annual average daily traffic on the first bridge had reached approximately 130,000 vehicles, making an additional crossing an urgent need.
The new bridge was linked to construction of the O-2 ring road and the Trans-European Motorway system, connecting road networks on the European and Asian sides. The General Directorate of Highways' engineering record lists 29 May 1988 as the date construction was completed and 3 July as the inauguration marking the start of operation. Completion and formal opening were thus separate stages.
Designers, builders and a single large span
Britain's Freeman Fox and Partners designed the second Bosphorus bridge. A bridge data sheet from the US National Cooperative Highway Research Program listed Ishikawajima-Harima Heavy Industries, Mitsubishi and Nippon Kokan as its superstructure contractors. The table distinguished the design organization from the superstructure builders, reflecting the international division of engineering work.
The steel suspension bridge has a main span of 1,090 metres, a total deck width of 39.4 metres, a box section approximately three metres deep, and a midspan deck elevation approximately 64 metres above mean sea level. The terrain places the tower foundations near the elevation of the deck ends, so the bridge lacks the long deck approach spans used on the first bridge. Roads enter from the high banks while the main span crosses the strait, leaving navigational space below.
Steel box girders, main cables and hangers
The deck uses stiffened orthotropic steel plates and a streamlined closed box girder, while the towers are rectangular steel box structures. Main cables pass over the tower tops and are anchored on shore at both ends; hangers transfer deck loads to the main cables. This interconnected system carries both traffic and the structure's own weight.
The 39.4-metre cross-sectional width is not entirely roadway: the box itself is 33.8 metres wide, with a 2.8-metre projection on each side. The relatively shallow box girder spans a very long distance, and its geometry also serves wind-resistance requirements. Deck, cables and towers must therefore be studied as a whole; roadway width alone does not convey the bridge's scale.
From shore-side assembly to closure in the air
Sixty-two steel deck units were welded at the Küçüksu assembly yard, with welds inspected by X-ray. Barges carried the units beneath the bridge. Thirty-six units over water were lifted directly into place; another twenty-six above the shores were first lifted from the water and then shifted laterally between the hangers in stages. Transport, lifting and lateral movement thus formed a continuous sequence.
Construction also continually changed the structure's loading. In a 2012 study, Murat Günaydin and colleagues used design drawings to build a staged finite-element model incorporating geometric nonlinearity and steel relaxation, and compared calculations for sequential erection with those for the entire bridge formed at once. Differences in deck displacement, bending moments and horizontal tower displacement showed that construction order was itself an analytical problem. The durations assigned to stages in the paper were model assumptions, not actual site completion periods.
The bridge and changing employment geography
Transport effects extended beyond the bridge approaches. Pelin Alpkokin and colleagues used Istanbul's transport-planning data from 1985 and 1997 to study relationships between employment centres and commuting. Across the two surveys, average morning-peak motorized journey time fell from 53 to 41 minutes. The authors associated the change both with completion of the second Bosphorus bridge and with polycentric urban growth, which brought some suburban residents closer to jobs.
Car ownership in the surveys nearly doubled, reaching 98 cars per thousand people in 1997, but the modal split did not change comparably: approximately 29 percent of journeys used cars, while about 65 percent relied on public buses, private service buses and minibuses. The new bridge was therefore embedded in an urban transport system shaped jointly by public transport, roads and employment locations.
References: [5]
Measured vibrations during operation
Nurdan Memişoğlu Apaydın of Turkey's highways administration and Yavuz Kaya of Boğaziçi University's Kandilli Institute organized ambient-vibration tests in 2007. Responses under heavy traffic were recorded on 12 July. Early on 19 July, they first recorded light traffic, then briefly closed the deck to obtain data without vehicles. Five measuring points simultaneously recorded longitudinal, lateral and vertical acceleration.
The researchers compared the records through spectral analysis and calculated velocity and displacement from acceleration. Response amplitudes were markedly smaller without vehicles, while those under light and heavy traffic were similar. Such observations connected actual vehicle effects with idealized structural models, allowing the bridge that opened in 1988 to remain an engineering object subject to continuing examination during operation.
References: [6]