Feasibility project for the new Ponte della Becca

NET Engineering has always offered a system approach to engineering topics arising from the awareness that a ‘holistic’ approach, integrated with the many aspects involved in design is necessary to obtain excellent results.

One example of integrated design is that developed by NET Engineering, grouped with the engineering firm CFC – Carlos Fernandez Casado, and F. Torta, in the context of the feasibility study for the Ponte della Becca (Becca Bridge), put out to tender by Infrastrutture Lombarde S.p.A. (now ARIA S.p.A.) on behalf of Lombardy Region.

Context

Becca Bridge lies in the province of Pavia at the confluence of the Rivers Po and Ticino and was constructed in 1912 to make the connection between the Oltrepò and the rest of Lombardy more stable and no longer subject to the conditions of the two rivers. It is now an essential element in the landscape and the identity of the place, collective memory and the feeling of belonging of the people who live there.

After more than 100 years since its construction, however, the existing bridge is no longer able to fully perform its connection function. It was designed for traffic different from current traffic, for both volume and types of vehicles – speed and axle loads, and now severe limitations on transit are impose – there is a ban on heavy vehicles, except for Public Transport and emergency vehicles, and a speed limit of 50 kph with accesses for light vehicles.

As a result of this situation and the solicitation of the area, Lombardy Region started the procedure for the creation of a new bridge with a tender for the drafting of the Feasibility Document, divided into two stages – defining and comparing the alternatives and the design analysis of the preferable solution.

The environmental context: “ante operam” status with the existing “Ponte della Becca” (Becca Bridge).

The design approach

The context was complex because of the hydraulic and geologic features, environmentally sensitive, the bridge is in the Parco del Ticino (Ticino Park), and delicate in terms of landscape because of the scale of the spaces, the extraordinary size and the impossibility of escaping a visual comparison with the existing bridge. There was also the imperative of efficiency for a work that would be justified above all by the usefulness it could generate for the community and the need for discussions with the stakeholders to reach a solution as far as possible shared.

All this led to the indication of integrated design as the only way of working to reach a solution representing utility, efficiency, sustainability and iconicity. NET had already declared that it was aiming for a ‘holistic’, multi-disciplinary approach during the partner selection stage and the formulation of the tender proposal.

NET’s experience and inter-disciplinary skills in the design of transport infrastructure was integrated with that of one of the leading international specialists in the design and construction of large bridges – the Spanish firm CFC – Carlos Fernandez Casado, and Fabio Torta’s expertise in the assessment of the economic impact of transport infrastructure and deep knowledge of the Lombard context.

The project team was formed by grouping specialists with specific skills in the analysis of mobility hydraulics, geotechnics, environmental assessment and design, transport infrastructure design, BIM management, structural calculations, design and construction of large bridges in sensitive contexts, visual design, life cycle assessment, resilience of infrastructure systems, smart infrastructure, and the economic assessment of the effects of the construction of transport infrastructure.

The New “Ponte della Becca” (Becca Bridge) in the project context – 3D modelling and rendering by NET Engineering

The project

The project was developed so that a 360° view of both the work and its context was allowed and maintained, conceived individually and together as interdependent systems and not simply the result of the sum of separate elements.

Thus, the definition of the aims of technical and economic efficiency, hydraulic safety, environmental protection (for both the natural habitat and human habitat) and the common property (including the landscape and memory) were intersected with the opportunities and recognised restrictions through the analysis of the various subsystems involved (mobility, hydraulic context, natural environment and that affected by human activity, geology, and construction techniques, to name the main ones) understood to be components of a single complex system. This originated a series of alternative designs, mainly differing in the localisation and architectural-structural solution proposed for the new bridge.

The alternative designs, like the proposal of converting the existing bridge to a different use, were presented to the main institutional stakeholders. The feedback stimulated a further widening of the overall view of the project and contributed to the refinement of the design proposals that were then subjected to a rigorous evaluation and comparison stage.

The desire to guarantee extensive assessment which considered both the aspects more easy to quantify economically and the sustainability, environmental and social aspects as well as the economic one and with reference to the whole useful life cycle led to the development of a comparison method based on Cost-Benefit Analysis, carried out for each alternative, combined with a Multi-Criteria Analysis set up on the  Envision^TM and Life Cycle Assessment rating systems.

The result was a clear, comparable indication of the features, not only in terms of economic efficiency but also the overall performance of the individual alternatives which enabled a rapid evaluation of the preferable solution to subject to design analysis.

Photosimulation of the New “Ponte della Becca” (Becca Bridge): front view – 3D modelling and rendering by NET Engineering

Detailed studies

The design analysis was also developed with the awareness of the need to always maintain a broader view and ensure efficient integration between all the subsystems and their related requirements, also through a correct set-up of the design process and adequate sharing of the work among the different specialists.

Thus, the in-depth analysis of the environmental impact suggested appropriate improvements to the planimetric layout with the new bridge.

The needs linked to the disposal of the surface water from the work (more than 2,500 metres long overall), the restrictions imposed by the hydraulic and environmental context to the localisation of suitable areas for the treatment and final delivery, and the aims of minimising the height of the road level to reduce the visual impact of the work were systematised in a final solution satisfying all the requirements identified.

The transport analyses already conducted were further analysed to give more detailed indications useful for guiding the correct sizing of the planned intersections and evaluating the possible effects and the relative countermeasures on those not involved in work.

The development of a hydraulic simulation model enabled the design to be checked and improved in terms of the safety features of the whole Pavia-Broni section. Integration with the data on the geometric features of the piles and foundations produced the data on the scouring necessary to improve the sizing and check of the structural element.

A structural calculation model enabled the precise sizing of the structural elements on which the design of the bridge and approach viaducts, including the completion works, could then be refined and the overall architectural outcomes checked. The data collected through the geotechnical surveys, specially conducted although not strictly required at this level of project, provided the elements necessary for the in-depth analysis of the geotechnical checks (including those on the liquefaction of the sand).

Visual design techniques were used to give stakeholders an immediate understanding of the work and its visual and landscape impact.

Considerations linked to the management and maintenance of the works for the whole life cycle led to, amongst other items, the adoption of solutions developed for smart infrastructure for the monitoring structural of new works. The traffic simulation model already developed in the first stage was used to study the resilience of the work based on an increase of traffic, linked to possible future changes in the settlement pattern and a possible loss of functionality of the other bridges on the Po in the province of Pavia.

Photosimulation of the New “Ponte della Becca” (Becca Bridge): view from the road deck – 3D modelling and rendering by NET Engineering

The result

The result of the design process was a work that fully responds to the reasons for its construction, is economically efficient, and integrates into its context, enriching it. The environmental impact is contained and, in any case, offset in the same setting that generates it.

It is a work that is appreciated by the customer and stakeholders for the completeness and study of the topics dealt with, able to provide a valid base for the subsequent design stages.

A result reached as a result of the integrated approach, despite the limitations imposed by the lockdown for the Covid-19 emergency and the necessity to develop the whole design analysis stage through smart working.