In 1502 the Sultan of the Ottoman Empire wanted a bridge built at Galata on the Golden Horn of the Bosporus in order to unite the two sides of the city Constantinople. Leonardo da Vinci came up with an incredibly revolutionary design that his contemporaries were highly sceptic and believed it was unfeasible. Leonardo’s bridge would have leapt the water in a single gigantic arch that would have spanned 240m.

If it had been built it would have been the largest masonry bridge in the world. The current record is the AdolpheBridge in Luxemburg built in the 20^th century and it is 85m, this is only 1/3 of Leonardo’s bridge.

Sketched survive in the Codex Leicester, the sole Leonardo manuscripts remaining in private hands, they are currently owned by Bill Gates.

• Most obvious is the enormous central arch which would have presented major technical difficulties for the builders during construction
• Not a constant width. It is extremely wide at the ends and narrows dramatically in the middle

Leonardo would have been limited by the diversity of the materials available to him. Stone and wood were the most common materials. Neither of these is entirely satisfactory for the construction of long beam spans. Stone being to heavy and brittle and wood would lack strength and sag over short distances. This problem could have been overcome by using shorter beams and more piers however this would have restricted the size of the vessels able to pass underneath. Therefore Leonardo chose an arch bridge. An arch is inherently stronger then a beam of equal span since all of the voussoirs experience compressional forces. An arched bridge would require fewer supports and allow larger vessels to pass underneath. The 40m height of his designs would have been sufficient for vessels used even in the 18^th and 19^th centuries.

The flatter the arch the greater the outward thrust, this has to be counteracted by a greater inwards counter-thrust.

A semi-circular arch would have produced less outward thrust however considering the great span a semi-circular arch would have produced too high a gradient for horse pulled carts to climb.

1. enormous outward thrust
2. need to stiffen the length of the arch so it would not buckle or flex under loads

Enormous outward thrust solution:

The usual method would have been to create massive abutments. This would have taken up lots of land and materials which would be very expensive.

Leonardo’s solution was to have flaring abutments. Therefore the outwards force of the arch would radiate outwards from the centre of the span along the curving path of abutments. Each metre square of abutment is subjected to a smaller amount of outward force and needs to push back with a corresponding weaker force. This would be a more economically viable solution and create an attractive structure.

Stiffen the arch solution:

A piece of stone located near the centre of the arch exerts a much greater load than an equivalent sized stone closer to the pier.

In Leonardo’s bridge the centre of the arch is some 135m from the footing. Therefore reducing the amount of material closer the centre of the arch would reduce the strain on the arch. Hence the middle is more slender in width and depth. However as an arch becomes more slender it loses rigidity and becomes more vulnerable to flexing, buckling and complete collapse.

Flexing is a consequence of loads being placed on bridges such as traffic and wind, the latter would push the structure sideways (see TayBridge).

A slender bridge is less capable of resisting the sideways pressure. Hence Leonardo designed for a pair of arches, one on either side of the main arch, to lean inwards towards the centre of the bridge and touch the keystone of the main arch (pushing in and up). The inward force of each arch is counteracted by the forces of its opposite number. This would restrain the main arch moving sideways by wind.

This is a mixture of engineering and aesthetics.

No one has ever attempted to build a masonry bridge on the scale of Leonardo’s design as masonry bridges are rarely constructed nowadays. This is due to:

• cost of materials
• skilled labour
• they have become obsolete-modern materials and construction techniques permit alternative bridge designs which are lighter, stronger and cheaper

• 2001
• 135m pedestrian bridge
• architect – Vebjorn Sand
• futuristic structure belying it 16^th century origins
• modern materials-laminated wood (strength, flexibility, durability and can be moulded into complex shapes found in modern architecture)
• inspired by Leonardo-pair of inward leaning arches supporting the main arch
• vertical metal piers instead of solid masonry