Eccentric Junctions

reciprocal frameworks and interwoven structures

Synopsis

My bachelor thesis at the OTH Regensburg focuses on mechanical junctions furthermore called “eccentric” (in a technical meaning).

 

The explanation for that name: Most of industrially manufactured mechanical junctions nowadays feature a centric joint, which means there is one element in the center joining all other elements onto itself. For example, the Mero knot or the USM Haller modular system use that way of joinery, but also quite classical junctions like a tie plate. All of them have one thing in common: They are placed at the intersection point of the elements’ axes.

The advantage of this kind of junction relies on the fact that the knot absorbs a major part of the other elements’ torsional moments. But on the other hand this center element is exposed to considerable loads that present exacting challenges for this kind of junction.

 

But there is another way we’d like to call eccentric as opposed to centric. No additional knot will be necessary because the elements are connected to each other.

This kind of junction is actually not quite as exceptional as one would expect by considering the more common meaning of the word “eccentric”. Indeed, mankind has used the technique of eccentric joinery since primeval times.

 

Naturally, the most obvious way to join two or more branches together for a shelter is, to lean them onto each other and – if necessary – wrap them with bast, leather strips or whatever fiber else accessible. There you have an eccentric junction!

Here, occurring forces are transformed into bending stress in every connected element. But the failure of one single element will make the whole system collapse. Because of that eccentric junctions are mostly used in combination with centric ones in architecture and design.

 

Eccentric joinery is closely related to textile work, regarding the creation of stable structures made of single interwoven elements. So, there’s no surprise in the fact that many applications of eccentric joinery resemble braided or woven patterns, like the ancient chinese construction of the “woven bridge”.


Kinetic grid model

Starting from the knowledge examined in the theoretical paper, a kinetic grid cube was created. Its eccentric intersections allow it to be folded along the space diagonal.

 

Exceptionally, the construction does not need to rely on shearing mechanisms which provide functionality to structures like the Hoberman-Sphere. Instead, the single elements’ movements resemble the inversion kinematics of Paul Schatz’ “inversible cube”.