Establishing the Optimal Solution for Obstacle Crossings. Application for Bridge Km.14+162 Placed on the Bypass of Bistrita City

The Bistrita city bypass crosses obliquely at km 14+162 the Bistrita river and a local road. In the area where the bridge is situated the river has a width of about 50.00m and the local road has 5.00m, being located at 12.00m from the bank of Bistrita. The bridge should provide a roadway that is 7.80m wide and two sidewalks of 1.50m.

The challenge is to design a bridge that allows the crossing of the two barriers (the river and the local road) in the most efficient way possible from an economical point of view, but in such a way that both the geometrical constraints and the design requirements contained in the family of the European standards Eurocodes are respected.

In order to achieve this goal, the author has investigated the design situation by comparing different possible technical solutions, by conducting a series of parametric studies and by utilizing mathematical optimization techniques.

Following these investigations a 100.00m long bridge resulted. The superstructure is a continuous beam with three spans: 20.00m + 60.00m + 20.00m and consists of a composite steel - concrete deck. The deck cross section is composed of two steel beams with variable height and a reinforced concrete slab disposed on top. This configuration of the superstructure leads to the development of negative reaction forces in the bearings located at the end points of the deck.

The study has covered 8 key steps as follows:

- Establishing the technical solution.

- Establishing the number and the length of the spans.

- Setting the static scheme.

- Determining the optimal cross section of the steel beams.

- Setting longitudinal beam geometry.

- Establishing the number of beams in the cross section.

- Determining the optimal mounting order of the concrete slabs.

- Establishing the optimal type and distribution of the bearing devices.