Model behaviour - BIM in use for Alessandria bridge


The growing acceptance of building information modelling, or BIM, is an acknowledgement that the building industry has fundamentally changed.

Project documentation is no longer simply a set of paper-based two-dimensional orthographic projection drawings, it is live views from a three-dimensional virtual model.

The building information model is a three-dimensional geometric model that is data-rich and the information contained within it can be used for many other purposes such as predicting energy consumption, structural performance, cost, scheduling, and identifying clashes between systems ahead of construction. It can even be leveraged for facility management uses.

However, this is more than a set of software programs; it is a process which is inclusive and may involve a wide group of stakeholders from design and construction, to operation and maintenance. It is an integrated database of construction information, including building components.

So a BIM solid model is an integrated, digital database, informed by the architectural, engineering, construction and operation industries, that consists of 3D parametric objects and allows interoperability. It is also possible to add parameters to the 3D model; in this way the model can be said to be programmable.

The model organisation can be classified into dimensions which range from 2D to 7D. Clearly 2D refers to flat drawings such as plans, sections and elevations, while 3D means the 3D digital model. Going into 4D includes the integration of time in the form of 3D phasing and construction sequences; 5D adds the aspect of cost, 6D deals with lifecycle, facility and energy management and finally 7D introduces safety issues.

Architects, engineers and consultants are heavily involved in the design/build process, and BIM has a major role in each of these phases: planning, schematic design, design development, construction documentation, bidding, construction phase and lifecycle.

Each phase of design can be managed by building information modelling, from planning through schematic design to construction documents and project completion. For analytical modelling, the use of BIM has several advantages; for example the major effort on the project can be aimed towards schematic design because of the time needed to create the parametric 3D model. Changes made during this phase can be cheaper to implement than if they are made subsequently, and they can have more impact on the project.

Finally the 3D model can also be used for simulation studies. One important advantage of a building information model is the coordination between the 2D and 3D information. As the project components are updated and increased in complexity, those changes will show on the update sheets. Analysis is a part of every phase of the design process, so as the level of information in themodel increases, greater accuracy in the analysis results becomes possible.

During the process of creating construction documents, professional firms find that building information modelling is incredibly powerful in comparison to other CAD documentation methods. The output from this phase is a set of integrated documents that are used in the bidding process and for the construction of the project.

Finally, the building information model is a fundamental component of the bidding and contract administration, making it easier for contractors to understand the complexities of the project for which they are bidding. Detailed cost estimation is easier and questions about the complexity of materials and construction methods can be answered more quickly.

However with such complex models being used by so many parties, the question of compatibility between software arises. The need to automatically exchange models and other data between different software platforms remains one of the biggest barriers to fully integrated and collaborative project delivery.

Rendering of the New Cittadella Bridge (Comune di Alessandria)

During the development of the design for the New Cittadella Bridge in Alessandria in Italy, the stakeholders involved in the final design and construction process assumed BIM procedures and software interoperability to permit the management of the complex geometry created by the conceptual design. The bridge, a 200m-long suspended arch bridge is being built for owner Città di Alessandria to a design by architect Richard Meier & Partners. Mantoan Progettazioni is BIM designer for the project.

Powerful parametric and generative modelling of projects was enabled by using plug-ins for Grasshopper and Rhinoceros. Generative BIM model exchange is provided by using a combination of open BIM formats, primarily industry foundation class, and direct application programming interface interaction to software packages including Revit, Archicad, Digital Project and Tekla.

Structural analysis models can be exchanged with many widely-used analysis software packages. Three-dimensional computer-aided design processes primarily use geometric elements such as solids, surfaces or other entities; the geometric models can be used to verify and to solve geometric problems. The BIM designers have used Rhinoceros and Grasshopper to manage the complex shape of the deck and the cladding of the bridge in order to clarify geometric conditions of individual parts, or of the bridge as a whole, to visualise the result from a purely geometric point of view and for collision detection in order to implement different construction solutions. Furthermore, the building information model includes information about mass, element specification, economy and programme and by using industry foundation class the designers are able to share this model with all the stakeholders involved in the design and construction process.

Since project presentation takes a significant role in the different design process phases, this case study aims to demonstrate that, by using a building information model from the outset, a 3D model is available for the following functions: for technical information verification, including geometry, (size and shape), position and relation between the parts and the whole; also for project navigation allowing the bridge to be presented three-dimensionally in real time in order to enable a higher quality exploration of the project.


The process of using building information modelling for the New Cittadella Bridge began with a commitment to coordination between all the stakeholders in the project. It is vital to establish the goals that all parties want to obtain right at the start. Conversations with the main contractor Itinera, the steel contractor Cimolai, the architect and the structural engineer were necessary to gain a clear understanding of what they expected from the building information modelling process. The BIM designers were asked to produce a building information model that would be appropriate to use for geometry investigation and rationalisation, construction documents, software interoperability, construction and erection simulation and cost estimation.

From the outset, all the necessary information was collected that was required to set up guidelines for modelling the bridge as preliminary d

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