THE FLEXIBLE JUMP-FORM
I have sought to investigate the possibilities of creating to a double-sided vertical casting system that incorporates some sort of flexibility. I have throughout my experiments worked with deformation and addition as the means of manipulation. At this point I’m working with a system that combines the semi-flexible surface with a jumping formwork system. There are of course endless ways of incorporating flexibility to a vertical casting system. My physical experiments have only touched a small corner of the field. An investigation of the proposed flexible jumping formwork has uncovered both potentials and some limitations. These are the parameters that define my architectural design conditions.
A limitation of the casting technique is that it is next to impossible to cast anything besides than vertical. The cast has to be between 60 – 120 degrees on the foundation otherwise it becomes too difficult to fill the mould. This limits the casted structure to be a wall-like, horizontal oriented structure.
PLAN AND SECTION DEPENDENCE
The formwork is quite flexible, especially in the longitudinal direction one has almost unlimited shaping possibilities. The vertical deformation raises a geometrical specified issue. When the formwork is curved in a vertical direction, the structure is not able to hold a straight bottom edge. This issue arises because of the difference in curvature two surface areas. As this is a rule of geometry, I see no way of ‘solving’ this problem without taking a change of direction of my investigation. Instead I would like to work with this issue as a designing factor: For instance the foundation and plan design of the structure determine how much the structure is allowed to deflect in the sections. This would create a sort of essential cross-reference between the horizontal plan design and the vertical sections of the structure. The proposal of using the substrate or foundation as a designing factor generates a whole new and more site-specific perspective to the forthcoming experiments.
When casting a double-sided structure, the sides can be held parallel to secure an even thickness of the structure. This however consequence a problem when trying too obtain a steep curvature. By allowing nonparallel sides, you are able to cast a more kinked geometry. This ability to create different thicknesses within the same structure can be exploited to generate an optimized construction or achieve a specific architectural design intent.
MANIPULATION OF THE FORM
The manipulation of the form is quite a complex matter as the triangles and thereby the geometry all is interdependent. Once a bend is employed the rest of the geometry are forced to follow. E.g. If the corners of two triangles a pinched together, the in between edge will kink out. Actually the same form can be achieved in various ways. In my identification of the forces in play, it is understood that most form-scenarios are attained by employing a combination of the forces.
As the formwork is an insitu-system, it is possible to use the surroundings and terrain to obtain the desired shape. As mentioned the terrain can employ an upward force by lifting the bottom edge, forcing the sides to curve or kink. However it is also possible to use the clamps of the formwork as anchor-points. By tying together two anchor-points, you are able to control the in-between geometry.
CONTROLLING THE THICKNESS
The length of the wire controls the thickness of the structure.
The wire is also used to hold the formwork together and clamping the jump-form to the existing cast.
I have been able to develop a grasshopper script that allows me to predict and evaluate different curves. This script can be used in both plan and section to envisage the faceted surface. The script subdivides a curve into a facets defined by a variable geometry. This allows me plan out the composition and choose the ideal geometry for the structure.
EXPERIMENT V JUMPING FORMWORK
In this experiment I sought to incorporate the semi-flexible surface to the jumping formwork system
– Investigate the possibility of incorporating a semi-flexible surface to a jumping formwork system
– Casting in a larger scale
– Exploring different formwork materials
– Achieving a higher quality of formwork that allows the mould to be reused
– Investigate the detailing of the formwork
EXECUTION AND PRELIMINARY CONSIDERATIONS
SIZE OF FORMWORK
Not being set on a fixed geometry yet, I choose to work with what in the previous experiment is referred to as pattern II. Mainly because the formwork of this design is easy to produce and the geometry fitted the materials at hand. Each triangle had a height and width of 210 mm. This translates into a scale of roughly 1:5 of the actual final formwork. I envisage that each triangle of a full-scale formwork would have dimensions from 1000 – 1500 mm. It’s a balance of choosing a scale where the design produce panels that is able to generate a spacious quality (and not merely is perceived as a pattern) and having a formwork that is physically manageably by a human.
I decided to produce a mould where the base-geometry was repeated 6 times (12 triangles on each panel). As it is a jumping formwork system I need to always use 1 row of geometry to clamp the formwork to the structure. This requires that the base-geometry always is repeated minimum 2 times in each panel. By using an extended version of the essential formwork, it is possible to build larger structure in fewer castings.
I conctructed my formwork as a double layered surface: A flexible surface to incorporate the bends and a reinforced backside to hold the rigid geometry. The rigid geometry was made up by 0,5 mm MDF. The edges of the triangles where all cut in a 45 degree angle, allowing the geometry to bend both ways. Each triangle had 0,7 mm hole drilled in the middle, which were to be treaded with a 0,6 mm cable. The cable where to act as a clamp, replacing what in the previous experiments where screws. I used cable glands to fix the length of the cable. The glands were tightened to maintain the desired distance between the formwork panels.
Finding a material suited to the flexible surface proved to be quite the challenge. Unsure of how much plasticity to allow I decided to test a few different types before applying it to my rigid formwork. I found a ribbed rubber that seemed to have the desired amount of flexibility without the elasticity. Despite having conducted a glue test on the rubber, where everything seemed fine. The material once applied to the formwork, had some sort of chemical reaction with the glue. The conclusion being that I decided to change to a more firm plastic material. The new material was a polyethylene, estimated 0,2 mm.
The jumping formwork structure is casted in sections. Once the first casting has cured, the formwork can be removed and reattached to cast the next section. In addition to the original cast I was able only able to produce a recast in the longitudinal direction before the submission deadline of this rapport. Nevertheless I intend to cast my next extension of the structure in a vertical direction.
The 0,5 MDF was easy to work with (it was possible to cut it without using a saw), but had the disadvantage that it doesn’t respond well to moisture. The MDF would be acceptable as a disposable formwork. However I would like to use a more durable material, possibly plywood or a steel sheet, in my further experiments.
The flexible plastic membrane did the job. The structure had a beautiful surface and sharp edges. The only problem being that the plastic had fractured in a few of the cuts and allowed the glue to react with the concrete. When concrete cures alongside contract glue, the chemical reaction leaves sandy trails in the cast. In my further investigations I have been looking into using a 0,75 -1 mm PET plastic. It seems once it has been pre-cut, it has the ability to bend without shoving any signs of fracture.
The cables and cable glands held up perfectly. They were able to withstand the pressure of the concrete and where easily removed. I think even in a larger scale it will be necessary to use some sort of flexible cable or wire, as it has to be able to incorporate the slight difference of the entry/exit holes. I imagine that it is possible to obtain cables that are suitable and well proportioned in a 1:1 scale.
The formwork only had one hole positioned in each triangle. Surprisingly the single hole was enough to clamp the formwork with minimal leakage during the recast. Ideally I should have placed a series of clamping holes along each triangle edge. This would allow the formwork to have a tighter grasp with a smaller chance of the concrete leaking on the already cured cast.
REINFORCEMENT AND JOINTS OF THE CASTINGS
I had no problem joining the second cast to the original. Despite second cast had to join a smooth concrete surface, the bond between the two seems quite strong. In a larger scale one could imagine that reinforcement would be added to take the tension in the joint. I would like to do an experiment where the reinforcement is casted into either side of the cast to strengthen the joints.
AN ADHESIVE-FREE DOUBLESKIN FORMWORK
I imagine that my final formwork will be a glue-free mould. Instead of permanently attaching the two layers of the formwork I want to keep them separable. The rigid and heavy outer-formwork will be elements that can be assembled and dismantled on site. The flexible inner-formwork will be a lightweight membrane that likewise can be de/attached to the mould. I envisage that the two layers of formwork could be held together by the same bolts/cable glands that control the deformation.
SEMI-FLEXIBLE SURFACE AS A JUMPING FORMWORK
I succeeded to use the semi-flexible formwork as a jumping formwork. Casting additional sections in either direction is straightforward. There are however some limitations of the formwork: Same issue as noticed in experiment III. Forcing the formwork to obtain a too steep curvature will generate difficulties when having to fill the mould. Also when the formwork is curved in a vertical direction, the structure is not able to hold a straight top and bottom edge. This issue arises because of the difference between a straight and curved surface area. As this is a rule of geometry, I see no way of ‘solving’ this problem without taking a change of direction of my investigation. Instead I would like treat this issue as a designing factor: For instance the base and plandesign of the structure determine how much the structure are allowed to curvate in section. This would create a sort of essential cross-reference between the horizontal plan design and the vertical sections of the structure.
Origami is made up by a flexible surface with rigid geometry.
By studying different origami-patterns and distorted surfaces I hope to gain a better understanding of the concept of having a flexible surface.
I also really like the idea of the light, delicate origami pattern being interpreted in a concrete (which possess almost the opposite characteristics)
A combination of a hard and flexible surface
Taking back control of the deformation I decided to try making a semi-flexible surface from a double-layered plastic sheet with cuts allowing the surface to deform. With this formwork I kept the same front and back panels, and then changed the sides to change the form. I made 3 casts creating different elements but reusing the formwork.
Thus working in a rather small scale (30 x 20 cm) I discovered a greater need to control the deformation. In this experiment it is the obvious solution to use bolts to control the deformation. By either tightening the bolts (in this scale I used screws). In my first cast I only used 4 screws to hold the cast together. My later one I decided to add more screws to fully be able to control the deformation.
Using the bolts to control the deformation could be an ideal way to introduce the parametric and digital side of the design. By digitally controlling the deformation, you could produce an overall design made up by minor deformations in the individual elements.
I believe this experiment has some interesting potential. The formwork could be used as an in-situ system, or be produced as prefabricated elements. This experiment has opened up for more questions and further investigations.
– What is the scale of these elements?
– How does the scale of the elements affect the possibilities of the design?
– How can you control the deformation of a surface flexible?
– How can the elements/formwork be joined?
– Is it possible to adapt the interlocking formwork to a flexible surface?
– How many cuts and where should they be?
– What other materials would be suitable as formwork when working in a larger scale?
– How many casts can be done in the same formwork?
Vertical vs. horizontal fabric casting
In both experiments we used a rigid frame formwork to hold the membrane in place. The fabric membranes were manipulated in various ways to test the material. These experiments where executed to gain a better understanding of how fabric acts as a formwork when used in a vertical or horizontal cast.
We discovered that it was very challenging to control the deformation. Especially in the vertical cast you really had to take gravity into consideration. When working with such a stretchy material it is important that you work with gravity as a design factor. This made it very had to make any accurate predictions how the final elements would be shaped.
Our trouble with controlling the deformation would probably have been less significant if we had used a more firm fabric or a thicker material (like a rubber).
On the positive side the elements had a beautiful surface structure resembling the surface of the fabric. Some of the casts had even been slightly dyed from the fabric.
My own mini-pise structure.
To put my knowledge to the test I decided to construct my own pise structure.
Because I was building a relatively small rammed earth wall/column, I decided that I would not go through the trouble of drilling holes and clamping the sides from the inside. As shown on the photos below clamping the sides of the formwork from the outside required a lot more effort than expected.
-Maybe the amounts of clamps used tell the story by it self.
In my further casting experiments I will take this lesson with me.
The structure is made of 1 bucket of dirt to 2 handfuls of concrete. A splash of water is added after the dry materials are mixed. Because I used grey (normal) concrete the colour of my mixture was a bit more dark/greyish than the one I saw on site. However after the structure was completely dry (3 days +) it dried up to be a beautiful light red colour.
The formwork was made of plywood components; a new layer of formwork was added for every layer of dirt.
The shiny surface of the plywood guarantees that formwork can be easily removed leaving a smooth surface.
Possibilities within the pise system
The pise system does satisfy some of the requirements stated by my research question:
– It’s a vertical casting system
– The formwork panels are reused
– The same formwork elements can put together in various ways to produce customized elements
Even though the pise system is somewhat flexible and you are able produce double-sided elements. The system is quite limited when it comes to exploring the design potential in amorphous shapes. The systems rigid nature is primarily designed to produce perpendicular elements. These restrictions can be traced back to the formwork and the technique used when tamping the dirt. Most amorphous and vertical variations become impossible when having to compress the earth from above.
When working with rammed earth the tamping is an essential part of the technique. Obviously when working with concrete casting a different technique is employed and the tamping becomes excessive. Changing material and therefore part of the technique generates new possibilities for incorporating a far more flexible mould system. My further investigation will revolve around the possibilities and potentials of working with a flexible surface. However I would like to take with me some of the lessons learnt from working with the pise formwork:
– The interlocking mould panels make it very easy to hold the formwork in place.
– By using bolts to clamp the formwork together from the inside, minimal support structure is needed.
Examples of vertical casting systems
In the initial stage of my research I would like start out by exploring already operating methods of vertical casting systems. By taking a closer look at casting systems that are already fully functional, I hope to gain a better understanding of problems and potentials related to the vertical casting technique.
Rammed earth, Pise systems
Having a close contact within the rammed earth industry, it seemed obvious to have a closer look at the pise system. Also when working with tectonic and architectural integrity the rammed earth can be a particular good example of technique, material and construction all working together. In a pise structure both material and technique contributes to the final appearance.
Understanding rammed earth production
To gain a better understanding of the pise formwork, I first went to visit a building site of a rammed earth house. My next step was to produce a smaller rammed earth wall myself. Building a rammed earth wall involves compressing a damp mixture of earth that has suitable proportions of sand, gravel and clay into an externally supported frame, creating a solid wall of earth. Often cement is mixed in with the soil mixture to increase the structure’s load bearing capacity. A temporary frame of prefabricated formwork is first built, usually out of varnished wood or plywood, to act as a mould for the desired shape and dimensions of each wall section. The frames must be sturdy and well braced, and the two opposing wall faces clamped together, to prevent bulging or deformation from the high compression forces involved. Damp material is poured in to a depth of 10 – 25 cm and compressed to around 50% of its original height. The compression of material is done iteratively in batches, to gradually build up the wall to the required height dictated by the top of the frame. Once the wall is complete, it is strong enough that the frames can be immediately removed. The walls are best constructed in warm weather so that they can dry and harden. Walls take some time to dry out completely, and may take up to two years to completely cure. Compression strength increases with increased curing time.
Rammed earth shares many of the same properties as concrete:
– Reinforcement: Like concrete, rammed earth can only take pressure forces and need reinforcement to withstand tension. Rammed earth uses re-bar, wood or bamboo reinforcement.
– Low cost material, but labor-intensive production: Soil is a widely available, low cost and sustainable resource. Like concrete the cost of material is low, but constructing rammed earth structures are a very labor-intensive process mainly because of the tamping.
– Formwork has to be able to hold in enormous forces: On site there was actually surprisingly minimal support structure to hold the formwork in place. Being a vertical casting system I was of the perception that it would take a lot more effort to withstand the forces from the tamping. Some of the key features were that the formwork was interlocking and bolted together from the inside