Olivier Baverel

On the Design and Construction of Elastic Gridshells with Irregular Meshes

Despite the time and cost advantages by the manufacture, transport and assembling of elastic gridshells, high material stresses are induced on the structures during their shaping process. An optimisation of the grid arrangement in order to reduce the curvature of the grid profiles and with it the initial bending stresses is therefore crucial when considering the stress reserves under subsequent external loading. To be able to deploy and bend the structure as a whole grid and thereby accelerate their construction process, elastic gridshells usually exhibit constant mesh size (regular gridshells). However, this condition makes the optimisation of regular gridshells only possible until a certain level. In this paper, several double-curved gridshells have been optimised allowing variation on the mesh size (irregular gridshells), so that a further reduction of the profiles curvature and lower concentration of stresses could be obtained. By the construction of irregular gridshells, the grid profiles are normally independently bent in an incremental process, generally more time-consuming than by regular gridshells. Nevertheless, if the bending stiffness of the grid profiles is low enough, large deformations can be induced on the irregular meshes and the structures can be built by bending the whole grid. The stresses generated during the construction process must be previously controlled, e.g. using numerical simulation. For this paper, the erection process of an elastic hemisphere with irregular mesh and 10m diameter has been analysed by means of finite element modelling and tested on a 1:1-prototype. The comparison of the resulting geometry and load-bearing behaviour between the modelled and real structures are presented.

Analytical Investigations on Elementary Nexorades

Nexorades or reciprocal frames can be seen as a practical way to reduce the complexity of connections in spatial structures by connecting reciprocally the members by pairs. This reduction of the technological complexity of the connections is however replaced by a geometrical complexity due to numerous compatibility constraints. The purpose of this article is to make explicit these constraints for elementary structures and to solve analytically the resulting system of equations. Applications to regular polyhedrons are presented and a practical realization (a 3 m high dodeca-icosahedron) is shown. In the brief conclusion, perspectives for complementary analytical developments for spatial structures are drawn forth.

Construction of a Large Composite Gridshell Structure: A Lightweight Structure Made with Pultruded Glass Fibre Reinforced Polymer Tubes

Abstract The Ephemeral Cathedral of Créteil at Paris, France, is a gridshell structure made of composite materials. Built in 2013, this 350 m2 religious edifice is a temporary church meant to gather the parishioners during the two year renovation of their permanent cathedral. This large-scale prototype represents a first in the building industry which still shows excessive apprehension for the use of non-traditional materials such as composites, especially when it comes to structural applications.

Morphological and Mechanical Investigation of Interconnected Elastic Gridshells

This paper describes the structural reinforcement of elastic gridshells by interconnecting several gridshells together. Reference for the present investigation is taken from the composite (GFRP) gridshell structure built for the Forum of the Solidays music festival in Paris in 2011. The principle of interconnection is illustrated with various structures which are generated using numerical toolbox developed by the laboratory for the automatic meshing of free-forms structures on Rhino. Then the effect of the interconnection on the structural behaviour is briefly discussed based on elementary loading cases. Finally, the feasibility of the concept as well as its architectural and morphological potential is show by the construction of a double gridshell prototype. The authors conclude on the possible future developments of such morphologies which could give interesting and unexpected architectures.

Gridshell in composite materials: Towards large span shelters

ABSTRACT In 1975, the gridshell of Mannheims Bundesgartenschau revealed the extraordinary aesthetic potential of a new type of lightweight structures with very interesting mechanical properties; it however did not become widespread. This article shows how composite materials can be an original and profitable solution for such constructions. In the first section, the authors recall the principal characteristics of gridshells. They explain then why glass fibres reinforced polymers provide a very attractive solution for this kind of application. The second section is dedicated to the numerical modelling of the structure. The basic principles of the dynamic relaxation method are presented. The third section shows the results of the measures taken on the prototype built at the Navier Institute and compares them with the results of the numerical simulations. A fourth section deals with the roofing solutions of such structures, and shows scale: 1 realisation. Finally the authors conclude on the potential of such structures for larger span constructions.

Kinetic of fibre ruptures in a UD composite material with a viscoelastic matrix subject to traction [Cinétique de ruptures de fibres dans un matériau composite UD soumis à la traction avec une matrice viscoélastique]

Structural applications of fiber reinforced polymers are strongly dependent on long-term durability studies. Subject to sustained loading, the material undergoes several phenomena reducing its mechanical performances and potentially leading to its failure. To understand the creep rupture mechanisms and identify relevant mechanical parameters that will need to be adjusted during the composition of the material, modeling at the fibers scale seems adequate. In this article a shear-lag model will be presented. This 2D model integrates a viscoelastic behavior of the matrix and a stochastic distribution of fibers strength. Results showing the main phenomena occurring in the stress redistribution in the composite material will also be presented.

The Potential of Shape Memory Alloys in Deployable Systems—A Design and Experimental Approach

This study focuses on deployable systems actuated by shape memory alloys in the perspective of designing adaptive sun shading devices for building facades. We first set the context of smart materials for adaptive facades and underline the remarkable characteristics of shape memory alloys for mechanical actuation purposes. After outlining the constraints on the integration of this material into deployable structures, we introduce three different prototypes actuated by shape memory alloy wires. They have been fabricated and tests have been carried out on two of them. Finally, we present some perspectives on the use of these actuators for solar shading systems in facade engineering.