MIJO VIADUCT BRIDGE AS AN ENGINEERING MARVEL

МОСТ ВИАДУК МИЙО КАК ЧУДО ИНЖЕНЕРНОЙ МЫСЛИ

Лапшин Илья Андреевич

студент, Национально-исследовательский университет Московский государственный Строительный Университет,

РФ, г. Москва

Поленюк Артемий Александрович

студент, Национально-исследовательский университет Московский государственный Строительный Университет,

РФ, г. Москва

Кокотов Степан Иванович

студент, Национально-исследовательский университет Московский государственный Строительный Университет,

РФ, г. Москва

ABSTRACT

This article presents a complete description of the technical characteristics of the world-famous Millau Viaduct bridge, a review of the methods used in the construction and the description of the construction process itself.

АННОТАЦИЯ

В данной статье представлено полное описание технических характеристик всемирно известного моста Виадук Мийо, рассмотрение методов, использованных при возведении и описание непосредственно самого процесса строительства.

Keywords: Millau Viaduct, bridge, construction, supports, structures, roadbed.

Ключевые слова: Виадук Мийо, мост, строительство, опоры, конструкции, дорожное полотно.

One of the unique engineering megastructures is the cable-stayed Millau Viaduct. It spans the valley of the River Tarn in the south of France. The bridge is one of the wonders of engineering and design. The viaduct Millau was designed by the French engineer Michel Virlageau and the brilliant architect Norman Foster. The builders immediately set three most difficult tasks: to build the highest bridge piers in the world at the height of several hundred meters, to put the roadway on them weighing 36 thousand tons, to put seven steel pylons weighing 700 tons each. There are three world records in the construction: the highest pylon - 245 meters; the record height of one of the pylons together with the support - 343 meters, which is 19 meters higher than the Eiffel Tower, the maximum height of the roadway above the ground - 270 meters. It was extremely difficult to build such a unique structure.

The bridge is 2,460 meters long. It includes eight spans: the length of the six central ones is 342 meters each; the two outer ones are 204 meters long. The 32-meter wide bridge has a curve in the horizontal plane with a radius of curvature of about 20 kilometers and a slope of 3percent from south to north. There are two working lanes in each direction. In addition, there are two additional reserve lanes.

The huge supports, each one mounted on piles, are being constructed in four-meter sections, step by step. The concrete is poured into temporary sliding hydraulic formwork, where the reinforcement cage is tied in advance. These supports hold the cable-stayed spans weighing 36,000 tons (more than four Eiffel Towers). More than 16 tons of steel reinforcement was required to build the entire structure. Wells up to 15 meters deep and 5 meters in diameter were drilled and filled with reinforced concrete.  The longest column is 24.5 meters in diameter at the base and 11 meters at the roadway. It took 200,000 tons of concrete to build them, and a special concrete plant with a very precise composition was built near the construction site for these enormous numbers of material needed.

In order to assemble the bridge into an accurate single structure and to measure the vertical alignment of the pylons perfectly, a GPS method was used. It consisted of several satellites giving the exact coordinates of the builders' location to maximize the accuracy of the construction. This unique method had an accuracy of no more than four millimeters.

Then the construction of the roadway began. The framework of the roadway was made of steel box girders with a rectangular cross section profile. The installation of the spans was carried out from both sides by sliding the roadway longitudinally over the main and temporary supports that were built in the middle of each span in order to shorten it. During the advancement the engineers closely monitored the weather forecasts.

Wind speeds could reach up to 130 kilometers per hour, which could cause collapse, as this stage is the most dangerous in the construction of the bridge. It took 14 months to connect the roadbeds on the different sides of the bridge into a single piece.

The bridge deck was assembled from 22 meter sections, each manufactured in the factory with its own original geometry. On each support there was a highly complex system of hydraulic jacks with wedge-shaped guide rods that lifted and simultaneously moved the entire roadway in the longitudinal direction. This system was used for the first time in bridge construction.

When the roadway was extended, pylons and cables were used to increase the stiffness of the free hanging cantilevers, which moved with the roadway. The speed of this system was 600 millimeters in 4 minutes. Due to the GPS satellite positioning system also used when closing the roadway over the center span, the discrepancy between the contact surfaces was less than one centimeter after the pylons had been driven over a distance of 2,460 meters on both sides. Thanks to the tremendous efforts of the engineers and construction workers, the accuracy of the work was almost unimaginable – 100 percent.

According to the builders' ideas, the web cross-section has the shape of an inverted airplane wing. Because of this, in a strong wind, the air stream does not lift, but rather presses the roadway to the supports. The shape of the section was tested at the design stage during the wind tunnel test of the bridge model.

The last stage of the project was the installation of vertical pylons weighing 700 tons and the tensioning of cables. The technology used to erect the obelisks of the ancient Egyptians was used in their installation. To prevent the bridge from sagging and collapsing, 154 cables were used. Each cable consists of 91 steel strands and can hold up to 25 thousand tons. Unlike known cable-stayed structures, the Millau Viaduct is not supported by a double but a single row of steel wires, each of which has triple protection against corrosion: electroplating, a protective wax layer and a polyethylene extruded coating. The outer surface of the cables is braided, with spiral grooves running the entire length for directional water drainage. It was made to prevent the development of aeroelastic phenomena, connected with the hydraulic jets and whirlpool formation under rain and strong wind. At the same time, multitoned cables are strongly affected by the elements, which causes self-oscillation. To prevent the elastic vibrations of the cables from being transmitted to the stiffening beams of the roadway, dampers in the form of hydraulic cylinders with pistons are used. What is more, whereas on a standard wide-span bridge one end of the suspension cable is attached to the ground, on the Millau Viaduct the cables are spanned over pylons holding the two adjacent spans together.

After the builders did the final finishing work - about 10 thousand tons of asphalt were laid on the canvas. The researchers needed two years to find the optimal formula for a special type of asphalt concrete based on mineral resin. The material turned out to be soft enough to adapt to joint deformations with metal without creating cracks. It had characteristics such as resistance to wear, tire traction, density, absence of overlap and rutting, which meet all the requirements for the road pavement. After that, the bridge was tested with a 900-ton load, and the maximum deflection of the span under load was 26 centimeters.

The structure of the mega structure contains tens of kilometers of electric cables. About 30 kilometers of them are high-voltage cables, 20 kilometers are fiber optic cables and 10 kilometers are low-current cables. For operative communication of the service teams both with the control center and with each other there are 357 telephone exchange points, located on different parts of the bridge.

The viaduct is literally studded with various sensors and systems for monitoring the condition of the bridge: instruments measuring temperature, slope changes, wind speed and direction, and mass of other parameters. On the highest pylon, 12 strain gauges measure deformation and up to 100 measurements are taken per second. All data about the condition of the viaduct are streamed to the monitoring and control center located near the toll booth. The monitoring equipment is designed to monitor the oscillations and shifts of the whole structure as well as individual sections.

In 2004, on December 14, the President Jacques Chirac inaugurated the Millau Bridge, which has become a real pride of France. A total of 477 million dollars were spent on the construction. In just three years, the tallest road crossing in the world was built, with a service life of at least 120 years. Not a single accident occurred at the construction site during the entire time, which is extremely rare for construction of such tall bridges.

Conclusions:

1. The Millau Viaduct represents a series of ingenious design and technological solutions, from the design of a bridge of this size in the gorge to the composition and properties of the road surface.

2. Although counterparts to this bridge have surpassed it in length and height, the supports of the Vidauk Millau are deep in the gorge, making it the tallest transportation structure in terms of design.

References:

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