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PERSONALISED FORMWORK – scientific approach for new solution variants

Application of personalised formwork is of most interest for architects and engineers now-a-days. Although a required demand when designing special constructions, there is little data and material solutions for this case. The cost and domain of application are of most importance in determining new solutions for concrete formworks. To contribute to these requests (a wider usage domain, productive material cost and maintenance), a personalised formwork concept is presented. The idea of reusing the formwork led to an elastic material – membrane (thermoset elastomers, synthetic rubber) with a punching tie-rod solution in order to obtain any architectural shape desired. This first solution was evaluated taking into account different membrane thicknesses. Several experimental tests denoted that the named chosen membrane variants are of low resistance for pouring a concrete architectural slab, so new solutions were discussed. Hence, a re-analysis of the PLM steps was achieved in order to find an answer for the encountered problem. By using creative methods, we obtained a second solution and put it to test. The attained results are used in order to establish the area of workability, to enlarge the tested domain and to assess the sustainability of a new type of personalised formwork


Introduction
The now-a-days architectural demands require new formwork solutions for concrete free shape structural elements. The need for special shapes was put to test in the early '40s ( Fig.  1), but still, the current technical solutions for creating such concrete elements are limited and expensive. Hence, a solution is required for these types of structures.
The article discusses different equipment variants that can be reused as formwork and can satisfy different architectural shape. The first tested equipment is composed of pistons that act upon a membrane. Tests showed that this solution is limited: the membrane does not resist to concrete unless the piston density is increased, making this solution inconsistent for large dimensions. A thorough investigation on this formwork variant problem was carried out.
The article focuses on the PLM approach in order to obtain a new second solution for the demands.
We will establish the functions that such equipment must satisfy, followed by technical solutions specification and finally certify through tests the attained new solution.
We conclude the article by evaluating the results in order establish the area of workability, to enlarge the tested domain and to assess the sustainability of the new equipment solution for a personalised formwork.

State of the art
After a reminder of the free architectural shapes, an analysis regarding the multitude of shapes encountered in those 3D structural elements was detailed (Fig. 2).
Knowing all these possible patterns, one can see the necessity of a personalised formwork type that can satisfy all of the above described shell types and the possible variants that each shape can led to. During the years, the idea of creating a formwork for such shapes has fallen, in the last few decades, into place. Besides the step by step assembly of traditional timber or steel formwork (Poggeler [16]), CNC milling solutions were used (Kolarevic [17]), fabric formwork or even 3D printing solutions.
From these appeared researches in order to simplify or to re-use the formwork: Troian [22] or vacuumatics solutions -Hulijben [23].
But when large scale elements such as roofs/ slabs are involved, the usage of such solution is not optimum neither from the material consumption point of view, assembly or cost. In our research (including this article) we try to find an answer for this situation by using a scientific approach.
Hence, multiple solutions for a personalised formwork were analysed. Previous experimental research [15] resulted in various equipment solutions.
Among them is the one represented bellow (Fig. 3): a personalised formwork composed of an elastic material -membrane (thermoset elastomers and synthetic rubber) and a series of punching tie-rods for curvature definition and support.
After several experimental tests, the solution proved to be invalid. At difference levels bigger than 230 mm, after the complex surface is attained, at concrete loading, excess deformations appear that chances the surface characteristics (note: a SBR rubber of 2 mm thickness was used and a single support rod - Fig. 4). Although the shape preserves, when changing the piston density on the membrane (Fig.  5), this first solution equipment is ranged as inconsistent for large dimensions. As a consequence, a thorough analysis, by using the PLM approach is necessary because it allows even in the solution design stage to satisfy the new functions obtained from the invalid tested variant (e.g. maintaining the deformed surface unchanged after concrete pouring) (Fig. 6).

Function analysis
As noted, in the figure above, one of the PLM steps in obtaining an optimum solution for a personalised product is the demands and their analysis.
Because the experimental tests done on the equipment were invalid, the next step was to establish the reason for the test failure, finding a solution for the encountered problem and then determining the resulting requirements.
Step two was defining their corresponding functions by using creative methods. Because most of them were complex ones, other focus sessions were made in order to obtain the basic (primary) ones (Table 1).
Another statement referring to the equipment's functions is that, because on the previous tests no other problems were encountered, the elaborate explored demands were the ones concerning shape moulding and fixing: formwork material types, obtaining methods for deformation, blockage and fall-back.
For the other ones, named also annex functions, intuitive or experimental based solutions were adopted. Also, for this case study no reinforcement for the concrete element was considered. Future analysis will show the steel mounting approach and concrete depth assurance solutions.

USAGE & MAINTENANCE
After the market launch, the product must be permanently observed and monitored. Also the periodically evaluations can be made in order to see the efficiency and line up to the constant evolution of the technology.

RECYCLING & END OF LIFE
Before the retirement phase, the product (or some parts) can be recycled and reintroduced in the loop.

PRODUCTION
The fabrication process includes an economically pre-analysis to see the costs involved in the production.

DEMANDS
The market analysis is one of the most important aspects because from here one can determine the requirements for a new solution.
, 0 For these functions, in order to obtain new ideas, brainstorming sessions were formed. Building on the ideas of others or on previous solutions was a plus.
As previously mentioned, for the annex functions, the solutions assigned were based on intuition and test results (Fig. 7). The table below (Table 2) is a representation of the found solutions for each primary function regarding shape assurance. The next step in the PLM analysis is the evaluation of the solutions. Hence, each technical solution was analysed to determine the best one taking into account different criteria. For this case, the QFD matrix was used (Fig.8a,b).

Possible solution
After a thorough analysis of all the possible solutions regarding the optimisation aspect, efficiency and costs, the possible was adopted solution and will be put up to tests. The morphological matrix shows in a suggestive manner the chosen variant (Fig. 8). Each solution was named as Solution 1-7 for each of the functions F1-6. As shown above, the personalised formwork is composed of an elastomeric material with cable pulling solution for shape formation and a spacer rod for thickness assurance. The wires assure the fixing of the membrane. Also, in the spacer, two perpendicular pipes are envisioned in order to strengthen the material. A section through the personalised formwork may clarify the resulting solution (Fig. 9).

Experimental testing
Because the solution needs to be validated, an experimental test must be conducted. For this step, the working stages were kept in mind in order to cover all the aspects within a pouring process (Fig. 10).

Fig. 10. Working stages for executing a structural element
Taking these steps into account, a virtual testing line for free architectural shape elements was featured (Fig. 11). The new solution for the personalised formwork is then put to test. Note: The given shape is considered to be a free architectural shape for a roof. The final desired shape (Fig. 12) designed also in a CAD programme is of help in defining the points for the formwork. The control and fixing points of the nurb lines mark the spacer positioning.  The same rubber types and thicknesses are used as previous tests [15]:

Conclusions
After a thorough research regarding demands, functions and multiple solution variants, the obtained constructive solution is an option to be put to test. By using the PLM approach, we could reanalyse the problem, find new resources and establish a new constructive variant that serves all the new requirements for the personalised formwork.
By validating a new solution we can establish the area of workability, enlarge it and assess the sustainability of a new type of personalised formwork.