Structural design of the Orosházi út flyover in Békéscsaba

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Technical data

Building trades

bridge and structural design

Principal

Békéscsaba Megyei Jogú Város Önkormányzata

Design value

0.00 millió Ft

Years of completion

2010 to 2015

Years of construction

2014 to 2015

During the upgrading of the Békéscsaba railway station, it was required to raise the roadway elevation of Orosházi út by more than 1 m in order to provide for railway clearance, and the required road traffic capacity of Orosházi út increased to two lanes per direction. Due to this, the reconstruction of the existing bridge became unavoidable for geometric, functional and structural reasons alike.

The flyover carries traffic in Orosházi út over the tracks of the Békéscsaba railway station. The section above the tracks is a 2 × 59.2 m span single-pylon stayed girder steel bridge, to which monolithic reinforced concrete access ramps are connected, which in turn continue in retaining wall-supported sections.

The required clearance above the tracks and the elevation of the crossing roadway determined the (rather low) structural height of the bridge, and the improvement of the conditions of railway transport required the minimisation of the number of piers between the tracks. The idea of a stayed girder steel bridge was born in such a way, which also won the approval of the Chief Architect of the town, because this bridge type can be aesthetically much more favourable than a ‘customary’ girder bridge.

In the detailed design phase, the Bridge and Structural Design Office of Főmterv was responsible for preparing the designs of bridges and retaining walls (except for the pylon), and in the supplementary detailed and technological design phase, for checking the reaction of the technology on the bridge superstructure and the preparation of the steel structure product designs.

Since at the level of construction, this was the first time that Főmterv designed a stayed girder bridge, we faced a number of novelties during the design process. Determining the cable-tensioning forces, designing anchoring structures in cooperation with the manufacturer, and calculating the aeroelastic instability and fatigue of cables were all new challenges.

The detailed design envisaged construction on auxiliary supports, but the Contractor required that the superstructure is constructed in an assembly area behind the bridge abutments, followed by the longitudinal pushing in of the superstructure using intermediate supports, then the supports are removed before tensioning starts, and the double-span superstructure is pulled up into its final position with cables.

The two construction phases that are the most critical from a structural point of view were the longitudinal pushing in of the bridge and its lowering to its final elevation, and the tensioning of the cables.

During longitudinal pushing in and lowering, the superstructure also receives loads that are not applied or applied not with such intensity when it is used, therefore, the structure had to be reinforced at several points, such as many stiffening ribs had to be included in the design on the ridges of the main girders and the hoisting cross beams.

The issue of tensioning the cables was already raised when the steel structure product designs were prepared, because the anchoring tubes of the cables had to be set in the appropriate direction and caused to be manufactured in such a way. Finally, the Contractor did not permanently weld the tubes into the receiving structures, thus the possibility of adjusting them depending on the results of on-site measurements remained. For the adjustment of the tubes, the sagging of the cables resulting from their own weight, deformations developing during the individual tensioning phases, the tolerances of anchoring and the unfavourable behaviour of the cable relative to cross directional mechanical impact had to be taken into account. We also had to cooperate with the French specialists of Freyssinet in devising the tensioning phases. In addition, we also had to pay attention to the load-bearing capacity of the cable shoes manufactured by the German company Maurer.

Crane operation was a very interesting element of the technology. Formwork boards, a concrete casting container and cable anchoring structures had to be conveyed up to the pylon located in the middle of the bridge. To start with, hoisting by crane from below was excluded by the need to maintain railway transport, therefore, it was only possible to use a crane standing on the deck. Somewhat unexpectedly, the Contractor chose not a crane truck but a tower crane for this purpose, thus, we faced the uncommon task to set conditions for the operation of a tower crane on a bridge.

The reinforced concrete bridges and retaining walls were constructed with monolithic structures.