Nexorade Hybrid

Shell nexorade hybrid 82

e. Nexorade Hybrid Again, the use of a reciprocal structure was favoured for its ability to operate on the basis of a multitude of short elements combined by a simple assembly. However, it turns out that the RFs lIn return, a low structural resistance appears. A new element thus appeared: panels stiffened the structure by bracing the torsional forces. But the use of plates induces a very complex geometry to be prepared. The dynamic aspect of reciprocal structures - i.e. all fragments work simultaneously, without hierarchy - implies limited effectiveness on a particular project scale. The loss of a single part greatly weakens the structure. That is why Mesnil, Douthe and Baverel propose a new variety of reciprocal frames called shell nexorade hybrid equipped with planar reinforcements bracing the assembly. The structure is composed according to the translation method - which we will see later -, which preserves the planarity of the original subdivision in the formed structure. The parts are connected to each other by means of screws and nuts in a kind of dowel system. A space is cut in the elements so that the panels can be placed without making them stand out. This pavilion was designed to have a lifespan of one year, to withstand the vagaries of the weather. It is estimated that the structure can tolerate up to 700 kg and the whole structure has been designed to comply with European building regulations. The objective is also to take the first steps in the use of dynamic and standardized structures. The non-hierarchy of the elements requires very complex and sometimes approximate calculations, which makes it difficult to certify their structural strength. Adding this reinforcement reduces internal efforts by tenfold. The interest of this device is in this case obvious, particularly because of the small increase in weight, of 30 % additional, for its realization.60

Shell nexorade hybrid - Original shape83

Shell nexorade hybrid - Adapted shape84

Shell nexorade hybrid - Detail85

Lifting of a structure Gridshell Ekilaya86

2.15. Nexorade, nexorade hybrid, ou gridshell

If nexorades are very suitable for forming double curved surfaces, this is also the case for gridshells, much more widespread and effective, but whose constructive details are much more complex. Both systems share a fundamental rule: the weight of the structure increases in proportion to the range covered. The reciprocal system works only by using the force of gravity, it cannot compete with the resistance of the gridshell, which is prestressed to maintain its shape. Gridshells are also lighter. The shell nexorade hybrid, although almost as structurally effective as a gridshell, will be much heavier, particularly due to the weight of the planar reinforcements.61 To come back to the gridshells :

« A “gridshell” is a structure that derives its strength from its double curvature, but composed of a mesh or lattice. It can be based on any material, but is often made from wood or steel. The large spans achieved in “gridshell” are often built by placing all elements flat in a regular frame and then deforming them to the desired shape. »62

Gridshells are structures that work rather with the elasticity of the material they are made of, while nexorades stabilize mostly with gravity by imposing their own pressure stress. The gridshells shave the current state of Otto’s research. It is possible to visualize both approaches in the chapter on the computational approach to wood. For example, of the two pavilions proposed by the ICD/ITKE seen in the first chapter, the first is built by addition and the second by transformation. I am particularly interested in this difference because it means that a gridshells requires the application of considerable physical force to deform and maintain its components. It is simpler, even necessary to do it mechanically. The gridshells are now more present in the architecture than reciprocal frames, because they are more efficient, but also, they have already been investigated using catenary models in the past. The renewed popularity of reciprocal structures in algorithmic research is rather due to its ease of implementation. It is for the same reason that we saw this system develop with Friedrich

Shell nexorade hybrid and nexorade, structural graphics87

Zollinger in post-war Germany. It was necessary to be able to build quickly with limited technological and material resources. The interest of reciprocal structures lies in this direction. The fact that they depend mainly on a position in space and not on a physical deformation makes their condition more static, without being rigid. They represent a more flexible and user-friendly constructive challenge. They can be easily adapted in a plan and its implementation is almost didactic, because it can be done by successive addition. Nexorades therefore have an advantage over gridshells not only because of the simplicity of the means to be used in their realizations (materials, technology...), but also in terms of flexibility and ease when it comes to realizing structures with more complex geometry, because they are not constrained in a physical deformation.

The nexorades are thus based on an elegant construction principle that makes their constructions almost educational, but suffer from a too low structural capacity. The Shell nexorade hybrid could be the missing step forward in propelling these structures into new applications.63

This concludes an overview of the nexorades and the structures associated with them. In order to be able to understand in greater depth the functioning of all these buildings, it is essential to understand more precisely the composition of the reciprocal structures and how these pavilions could be erected. It is undoubtedly interesting to make a few comebacks between the concepts that will be described later and their tangible results, which we have just discussed.

Nexorade, shell nexorade hybrid and gridshells structural graphic88

2.16. Composition of a nexorade

The term « nexorade » refers to a network of a reciprocal composition of executives. The term was proposed by Olivier Baverel to define these structures with multiple names. I also intend to use this term, because the French language does not really have a translation to describe a multitude of reciprocal frameworks. Each element constituting the nexorade is referenced as « nexor ». A nexor has four points of contact. Two at the ends and two along its length. The word nexor comes from Latin and means « link». A Nexorade is therefore a « nexor assembly ».

Nexors can be grouped by forming fans, they are arrangements of three or more nexors, with reference to the helical shape resulting from these arrangements. A fan is equivalent in this case to the central polygon formed by a reciprocal frame. The fans are studied according to the length of their nexors, their engagement lengths, their inclinations, their sections and finally their eccentricities. 64

In order to talk about the algorithmic aspect of this technique, I will set up a basic vocabulary. But this vocabulary will not include the mathematical formulas developed about them. The variables used for them depend on the analysis and the research problem and that is why we will adopt it from the point of view of an architect, with moderate mathematical knowledge and whose interest would be more in the process of integrating such a system than in its resolution. The objective is to see if it is possible to solve it in an algorithmic way, based on logics discovered by scientists without the implementation of a specialized computing device. I decided to classify the parameters related to nexorades into three categories: length and length of engagement, inclination and number of nexor, eccentricity and cross-section.

Fan

Nexor