Gridshells are defined as structures that have the shape and rigidity of a double curvature shell but consist of a grid not a continuous surface. This study concerns those obtained by elastic deformation of an initially flat two-way grid. This paper presents a method to generate gridshells on an imposed shape under imposed boundary conditions. A numerical tool based on a geometrical method, the compass method, is developed. It is coupled with genetic algorithms to optimize the orientation of gridshell bars in order to minimize bar breakage during the construction phase. Examples of application are shown.Keywords: Gridshell, Formfinding, Compass method, Genetic algorithms. IntroductionGridshells are often defined as structures that have the shape and rigidity of a double curvature shell but consist of a grid rather than a continuous surface. In this work, they are obtained by elastic deformation of an initially flat two-way grid. This reduces the grid's shear stiffness allowing large deformations. The deformed grid is then rigidified using a third direction of bars or panels. A gridshell thus has interesting structural potential and can respond to complex architectural requirements. A dozen gridshells have been constructed Two methods have been used in gridshell formfinding, one experimental, the inversion method [5]; and one numerical, principally the dynamic relaxation method [6-7-8-9]. The inversion method is based on the assumption that the flexural stiffness of the grid elements is negligible. This method was used in the design of the Mannheim Bundesgartenschau gridshell in Germany, the first and largest timber gridshell ever built.The second method, the dynamic relaxation method, is a numerical tool that uses dynamic calculation to find the static equilibrium state of a mechanical system. The Downland museum gridshell in the United Kingdom and the two prototypes of gridshell in composite materials at the Ecole des Ponts ParisTech were designed using this method. Both techniques, the inversion method and the dynamic relaxation method, lead to a deformed grid through calculation. The shape obtained is close to the one proposed by the architect but is difficult to control. These methods are described in the first part of the paper.In this paper, the first aim is to focus on the generation of gridshells on an imposed form and under imposed boundary conditions. By definition, mapping a gridshell on a form is equivalent to drawing two-way parallel and equidistant curved axes, i.e. parallelograms, on the surface. Mathematically speaking, those nets are called Tchebychev nets [10][11]. The problem is very similar to that encountered with fabric draping. Among the methods used for composite forming, a geometrical method, the fishnet algorithm, was introduced by Van Der Waëen [12]. Other mechanical approaches are described by Boisse in [13][14]. A method for mapping a two-way elastic grid using finite element simulations was inspired from those approaches and was introduced previously in [15].A geometrical me...

The aim of this paper is to present a simplified life cycle assessment on an innovative bridge structure, made of wood and ultra high performance concrete, which combines mechanical performance with minimum environmental impact. The environmental analysis was conducted from cradle to grave using the Life Cycle Assessment method. It was restricted to energy release and greenhouse gas emissions. Assumptions are detailed for each step of the analysis. For the wood end-of-life, three scenarios were proposed: dumping, burning, and recycling. Results show that the most energy needed is in the production phase, which represents 73.4% of the total amount. Analysis shows that the renewable energy is about 70% of the production energy. Wood, through its biomass CO2, contributes positively to the environmental impact. It was concluded that no scenario can be the winner on both impacts. Indeed, the end-of-life wood recycling gives the best impact on CO2 release, whereas burning wood, despite its remarkable energy impact is the worst. According to the emphasis given to each impact, designers will be able to choose one or the other.

Purpose: the objective of the study is to progress towards a comprehensive component-based Life Cycle Assessment model with clear and reusable Life Cycle Inventories (LCIs) for High Speed Rail (HSR) infrastructure components, to assess the main environmental impacts of HSR infrastructure over its lifespan, to finally determine environmental hotpots and good practices. Method: a process-based LCA compliant with ISO 14040 and 14044 is performed. Construction stage LCIs rely on data collection conducted with the concessionaire of the HSR line combined with EcoInvent 3.1 inventories. Use and End-of-Life stages LCIs rest on expert feedback scenarios and field data. A set of 13 midpoint indicators is proposed to capture the diversity of the environmental damage: climate change, consumptions of primary energy and non-renewable resources, human toxicity and ecotoxicities, eutrophication, acidification, radioactive and bulk wastes, stratospheric ozone depletion and summer smog. Results: The study shows major contributions to environmental impact from rails (10-71%), roadbed (3-48%), and civil engineering structures (4-28%). More limited impact is noted from ballast (1-22%), building machines (0-17%), sleepers (4-11%), and power supply system (2-12%). The two last components, chairs and fasteners, have negligible impact (max. 1% and 3% of total contributions, respectively). Direct transportation can contribute up to 18% of total impact. The production and maintenance stages contribute roughly equally to environmental