Efficiently including reclaimed steel elements in a truss bridge design by performing a stock-constrained shape and topology optimization

Abstract

To climb up the circular economy hierarchy and meet the goals of the European Green policy in the construction sector, steel profiles may be reused instead of recycled, which is currently the most common practice. An overarching digital database to efficiently match supply and demand of reclaimed structural elements will stimulate their application. To efficiently use the limited availability of reclaimed steel elements in a new structural system, the design process requires a different approach: form following availability. This thesis presents an algorithm to generate truss bridge designs using only reclaimed steel, optimising the material usage in relation to the function and avoiding cut-off waste. The algorithm is inspired by the growth method, a truss topology optimisation method in which truss designs are grown without the need to fit elements into an initial design or grid of possible positions, like the commonly used ground structure method. The growth method is a more intuitive starting point for stock-constrained design, as by attaching available reclaimed elements to each other, a geometry can be generated which effectively follows from availability. The algorithm has been scripted in Python within Grasshopper, resulting in a user-friendly parametric design process. By defining the required width and span of a truss bridge and providing a stock of reclaimed elements, a solution cloud is generated of locally optimal truss bridge designs in terms of capacity utilisation and which comply to Eurocode provisions and constraints regarding the manufacturability of connections. From this solution cloud, an optimal design can be selected with given objectives, e.g. the design with the lowest environmental impact. A comparison shows that the developed growth method, using reclaimed steel elements, can lead to a steel truss with 17% less embodied carbon than a truss design whereby reclaimed elements are fit in afterwards, and 63% less embodied carbon than a traditionally designed new steel truss.