S.Marcello Pistoiese

The suspension

bridge, in Lower Mammiano bet

ween the municipality

of S. Marco Pistoia, and the City

of Piteglio, is  a pedestrian

walkway that connects the two

sides of the river Lima.

Wher e is it?

Who built it?

Opened in June 1923, it was built following the idea of Vincenzo Scotti Douglas, Count of San Giorgio della Scala, director of

the Lower Mill Mammiano Italian Metallurgical Society.To carry out the work, Count Vincenzo Scotti Douglas

instructed the foreman Filiberto Ducci, who had the responsibility for the achievement of the works for the mechanical part,

while the building works and support were handled by Vannucci Cesare, head of the brick layers.

Why it was  built?

It would be used to allow the passage of workers from Popiglio, who had to go to work in factories located on the opposite

side: without such a structure, in fact, the workers would have to walk about 6 kilometres to reach the workplace.

The work, which has lost its original function, has undergone over the years, important maintenance and consolidation. Recent works, dating back to 2004, allowed to secure the bridge and make it more stable and durable through the complete replacement of cables, side of the walkways and guards, with more dura

ble and lightweight material.

The history of the bridge

Works began in 1920 with the help of about thirty workers, who fixed the cables. At that point it was possible to build a predestrian bridge, made of planks and wire mesh attached by hinges to the supporting structure, which connected the two opposite banks of the river Lima with no intermediate support

It was made by structures and

supported by four steel cables.

Kept in tension, measuring 227 metre

s long, 36 metres height on the bed

of  the river and 1.3 metres wide.

How was it built?

It is a first generation Bridge. This generation includes a number of truss deck bridges, built in large numbers especially in the U.S., between the end of the first half of the ’800 and ‘900. This type of bridge has ‘’lights’’ typically ranging from a few hundred meters to a few more than 1000 metres, in which the deck is suspended by steel roads to the supporting cables arranged in a certain bend, supported by other piers. The costruction of a bridge - a problem that for its usefulness has raised interest for ages - requires, in somes cases, the use of a high-technlogy and often the solution found, was completed only later on.

General features

The curve obtained by fixing the two ends of a cable without any weight, is called catenary, and at first sight it might seem the curve along which the cables of our bridge

are placed. In reality, taking into account the forces acting on the cables, due to the weight of the deck, we will show how these are arranged along  parabolic curves .

To simplify we can outline the situation given, the deck is as a rigid rod and we can make the following assumptions:-The rods are equal in number and are equally spaced (long distance is

called the deck between two consecutive rods)-Wires and rods are perfectly flexible and inextensible

-The bridge is symmetrical to the line perpendicular to the deck,  passing through its midpoint.

Each of the cable will form a broken line ¬ whose vertices are the points where  rods  welded the cables, and this broken line has  the central part placed

horizontally, for reasons of symmetry.So we fix a reference system with the y-axis and x-axis that respectively coincide with the 

deck and the axis of symmetry. So it is sufficient to consider the positive x-axis points.

Aereolastic effects in the suspensive bridge

The response of a structure to an 'external action depends in general on its type and its specific characteristics that define

it (materials, constraints, etc.). In the case of suspension bridges, the answer of the wind essentially depends on the aerodynamic

behaviour of the scaffold , and less on that  of the towers and the suspension system (cables, hangers).  As the first element of the structure, the deck transmits loads (weight, loads of users, wind

action) to its cables, strongly influencing the size. For this reason, the deck is the key element of the project which a large part of the theoretical and experimental study is focused on. In that content to

minimize the wind resistance and maximize the air elastic stability of the deck play an important role , on which also depends  the overall

stability of the suspension bridge. The aerodynamic characteristics can be summarized by the coefficients of

resistance, power and time, and this allows to set actions on the general aerodynamic section. The forms of instability that can be generated depends on the aerodynamic derivatives, that is from the

coefficients of wind power and time, relative to the incidence of  and deck, as well as the parameters of Quasi-

Static Theory Correct.