With the making of the first 3D printed bridge by MX3D (work in progress), not only the scale and usefulness of 3D printing leaps forwards, it also opens up a new avenue for large design options. Design of urban structures has always been constrained by the available materials, technology and tools. This constraint goes all the way back to the Stone Age. There is a good chance that those early designers and builders could have conceived of more advanced structures and things than they produced but the implementation constraints limited them.
3D printing has its own constraints with respect to materials and the way in which they complement each other. At present, we couldn’t 3D print in one effort a fully functional screwdriver made of stainless steel with a hard plastic handle that is soft to the touch. This may seem like a fairly basic limitation but 3D printing complements existing production technology, so this isn’t a big constraint. What 3D printing does allow us to and is incredibly good at is to manufacture structures that cannot be built in any other way. For example, the “Shadow tree” we presented in the previous post, could not me manufactured in a single process other than through 3D printing. The outer branches get in the way of the inner branches, making moulding or even CNC routing impossible.
In the design of traditional bridges and other large structures, we are generally constrained to using straight rods and beams to built with. We can ofcourse bend rods and beams but are limits. One limit is that shaping rods and beams has to be done in a workshop and can’t be done on site.
If the MX3D 3D printed bridge shows us anything, it is that complex and large structures could be produced on site. This opens the door to locally adapted complex design forms such as those suggested by Genetic Fractals.
Genetic fractals are essentially an organic solution to dealing with complex structures. Given a point from which we need to “grow” a structure towards a given boundary, these fractals will adapt and morph to fill that space. But in general, such fractal structures in the real world can only be 3D printed or produced by CNC routers.
Putting all this together, the idea of a 3D printed bridge can benefit from a design based on genetic fractals. On the top of this page, and below are some alternative designs for such bridges.
These designs are only shown from a side view which serves to show the concept of constrained organic forms. When using this approach in a 3D design, the organic forms show natural elegance that can be achieved in no other way. In an upcoming post, we will look at such a design in 3D.
Although the constrained form of these bridge designs are the same, we can see the impact of chosing different root points along the bottom support beam.
One interesting feature of such genetic fractals is that we can let them evolve to any precision that we need. Below is a similar bridge design but with twice to number of “branches” at the upper beam.
Although this may not be immediately apparent, other than the points where these fractals attached to the the upper and lower beams, the curves are smooth and have no angles anywhere. At each point where branches split, the breaking apart is smooth and gradual. This gives these structures some interesting mechanical properties.
Also shown is the gradual reduction in diameter of the branches as they split and evolve. This is not only a natural and organic approach to such designs, it also ensures that the strains and stresses are equivalent throughout the structure.
Therein lies the power of fractal design: they fundamentally describe complexity and reveal the simple patterns that underpin them.