Liberty Bridge

Location and name of the bridge
Name of the bridge: "Szabadság" bridge
Distance: 1645+300 km
Country: Hungary
City/town: Budapest
Year of building - completion: 1894 - 1896.
Year of reconstruction: 1945 - 1946.
Span lengths: 79.3 + 175.0 + 79.3 m
Roadway widths: 2.9 + 1.4 + 11.5 + 1.4 + 2.9 m
Designer: MÁVAG, on the basis of original plans
Main contractor: MÁVAG, Gusztáv Fáber
Construction cost: 6.164 million HUF

Traffic function of the bridge
Highway bridge (2 lanes) carrying tramway line (2 tracks)

Antecedents; the history of the bridge
The construction of the Elisabeth and Liberty bridges was ordered by law No. XIV. in 1893 on the occasion of the forthcoming millennium of Hungary in 1896, and a common tender was held with great success. All together 74 designs were presented, among them 53 for the Elisabeth bridge, and 21 for the Liberty bridge. The members of the international jury were bridge engineers of the highest reputation of that time. The reporter of the jury was Antal Kherndl, the well-known professor of Technical University. 41 designs were solved with a single-span structure; 15 designs were Hungarian, 16 ones were American, several ones were Italian, Austrian, German and French.
The first prize was given to the cable-bridge of Julius Köbler from Germany for the later Elisabeth bridge; while the second prize winner plan of János Feketeházy and the third prize winner plan of Róbert Totth were prepared for the Liberty bridge.
The second prize winner plan of János Feketeházy was realized with small modifications. The details of the plan were worked out by István Gállik and József Beke, the portals, having an architectural importance, were designed by Virgil Nagy, professor of the Technical University, who was the architect specialist of the design team.
The construction started in 1894. The foundations are iron caissons, made by Gartner and Zsigmondy Company. The erection of the steel superstructure was carried out between July 1895 and August 1896.
The opening of the bridge took place on October 4th, 1896, during the millennium ceremony in the presence of Ferenc József, Hungarian King and Austrian Emperor. The bridge was called Ferenc József bridge for it for decades.
The simple supported midspan and the cantilevers were blown up in January 1945. During construction of a provisory bridge, the Buda side span fell down, as the ballast weights at the side support were not removed.
A provisory bridge was built in the midspan on five barges and on the wrecks of the Buda span, but it was drifted by an ice-flow in January 1946.
As this bridge was the relatively less damaged one in Budapest, its reconstruction was the most realistic. For this material of the other destroyed bridges also was used. The midspan had to completely rebuilt, its material was produced in the iron-works of Diósgyőr and Ózd.
Further reconstructions were made in 1980, when the roadway structure was changed to a composite one, and in 1985-86, when the pavements and their supporting structures were renewed. During this process, because of very heavy corrosion damages of some members of the main girder, a local collapse developed in a column of the main truss. After it the corroded parts of the main trusses were strengthened.

The technical data of the bridge

Structural system, span lengths, widths
The statical system of the main girder is a so called Gerber truss, having an appr. 50 m long simple supported part in the symmetry axis. Because of balancing the tension reaction forces from self weight, ballast weights of 609 t each were necessary at both bank supports.

Deck
The deck was reconstructed in the original form and changed later into a composite construction.

Method of construction/erection; joints
First the raising operations of the Buda span took place. Lifting of the structure was done with 16 hydraulic jack of 100 t capacity each resting on piled pedestals to a height of 9 m. It was accomplished in five days.
After reconstruction of the two cantilevers the lift-in operation of the midspan structure was realised with the floating crane of "József Attila" and "Ady Endre" having a lifting capacity of 100 t each. The total weight of the 46.9 m long piece of main was 240 t, so this operation needed a special care.

Test loading(s); periodical assessment of serviceability
After 33 years of service the complete floor system and the suspension system of the counterweights had to be reconstructed in 1979. The next step of rehabilitation became necessary in 1985, when the replacement of the side walks and the repair of main elements was decided.
Vertical and diagonal members of the main trusses are led through the slab of the side walks, practically without any gap, which is the "result" of a previous repair. Dust and salted sand, thrown in winter time, caused very heavy corrosion. Cross section reduction of the diagonals was around 10 %, while that of verticals exceeded 40 % in some cases.
During the rehabilitation process, the one of the mostly damaged columns in its complete cross section broke and moved 15 mm downward and 35 mm sideways. The traffic was closed immediately, provisional fixing elements were built in by HSFG bolts.
Reconstruction should be started with the determination of the remaining force in the damaged member. Applying the trepanation method, strain gages were bonded to the elements of the column. Drilling pairs of hole near the ends of strain gages, the remaining stresses could be measured and the total force was calculated. The active force in the column was found as 871 kN instead of 1930 kN, calculated from the dead loads.
Special devices and technology were designed to achieve the necessary position of the column ends, to replace the damaged part of them and to induce the required force into the column.
The complete process was continuously controlled and measured.
To examine the behaviour of the repaired part of the main trusses local loading tests were carried out. The live load intensity in the column achieved the maximum design value. The difference between the actual and calculated behaviour was realistic.
At the end of the reconstruction work the complete bridge was tested again using 30 trucks of 20 t each.

Literature
Haviár, Gy.: Reconstruction of the blown Szabadság-Bridge, Műegyetemi Közlemények, 1947. No. 2.
Széchy, K.: A Ferencz József-hid és a Szabadság-hid épitésének összehasonlitása, Általános Mérnök, 1947. No. 2.