Pre-Design Assessment of Demountable Short Superstructures

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Rijkswaterstaat aims to build circularly from 2030 onward, with the purpose of having a fully circular economy by 2050. Therefore, the aim of this study is to design a reusable modular superstructure, with a small span, which can replace an existing so-called volstortligger superstructure. This is a structure that Dura Vermeer often uses and it regularly happens that these constructions are demolished after a lifespan of, for example, 10 years. This is a waste of materials and therefore an alternative will be investigated in this research. The following research question guides this study:

What is the optimal structure, in terms of shadow costs, mass and financial costs, for a modular superstructure?

In order to answer this question, a parametric study is performed using the software Grasshopper, using the Finite Element Model plug-in Karamba3D. In this way, quick structural analyses were performed, to explore multiple options. In total, more than 11.000 bridge design variants have been generated, divided over 12 different runs. The model allowed targeted optimization of shadow costs, weight and financial costs. Optimization is achieved by varying the following input parameters: number of steel girders, steel profile girders, outrigger deck, concrete deck thickness, concrete class, outrigger deck, FRP sandwich panel height, facing thickness, web thickness, and fibre volume.

In total, 6 different variants would be developed in this way, 3 with a concrete deck and 3 with an FRP deck. However, the optimization results in only 4 different variants, 3 with a concrete deck and just one with an FRP deck. The results show that the variant with the FRP deck is indicative for Shadow costs, Financial costs and weight.

After the four pre-designs had been developed, these variants were weighed against each other by means of a Trade-Off Matrix (TOM). Using this method, a distinction is made between the variants based on the pre-chosen performance indicators. All performance indicators have a weighting that adds up to a total of 100.

This study concludes that it can be advantageous to replace the traditional design with a demountable design, with the assumed boundary conditions of this study. All developed variants have an advantage with regard to environmental impact and financial costs compared to the traditional design, assuming a lifespan of 100 years in which it is moved 10 times.