ORICRETE SYSTEM

STANDARD PROCESS FOR BUILDING CONCRETE SHELLS

Alexandrino José Basto Diogo

Assistant Professor, Faculty of Architecture, Lisbon University – FAUL, Portugal

This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract—this article aims to explore new construction processes capable of facilitating and optimizing the production cycle of structural forms based on the double curvature. We intend to explore the potential of an adaptable rigid formwork system capable of producing synclastic and anticlastic surfaces. This is an integrated approach that takes into account the generation of form, structural mechanics and its construction process, in order to generate architectural artefacts of great structural and constructive efficiency, with a strong artistic expression. This system combines cable net with cut linear pieces in a way that makes the material bend. The system is based on a cable network supported by a frame, covered with an adaptive formwork and then with shotcrete.

Keywords: Double curvature, Concrete shells, Construction logistics, Cable net, Formwork, Structural shapes.

Introduction

The concrete shells when well-designed have a structural efficiency resulting from the membrane effect that can allow large spans and savings on material usage. However, the production cycle proves to be very demanding in terms of infrastructure and labour work. Rigid formwork normally used in the construction of these surfaces proves to be difficult to produce and requires specialized and intensive labour. Moreover, it is not possible to reuse falsework. The amount of labour and production costs involved in this process makes the use of these shapes difficult, in spite of all the plastic, spatial and structural potential, these structural types are excluded from architecture today. It is however possible to adopt a production process that minimizes the costs of traditional processes for shell production. To solve the limitations of the traditional production process, we adopt an adaptive mass-produced formwork, which doesn’t require falsework. The system does not require such intensive labour or skilled labour, the production is faster and particularly suited to producing synclastic and anticlastic surfaces.

Objectives

His field of research is part of the technology department of the Faculty of Architecture of Lisbon which aims to develop technological solutions that give a solid response and the implementation of architectural ideas. The solutions are developed according to the principles of efficiency, ease of production, cost and robustness. It aims to establish partnerships with industry to leverage the economic impact and technological solutions, as well as the exponential spread of solutions.

Context

The earlier reflection suggests that one of the decisive factors in the production of Shell concrete is the formwork system used. A study of these processes allows us to split these methods into various categories. We have three main categories of rigid formwork made from wood boards, flexible resorting to the use of fabric membranes and a hybrid system utilizing small rigid parts articulated to a cable network.

HISTORICAL OVERVIEW

Flexible formwork

The British engineer James Hardress of Warenne Waller (1884-1968) was the first to apply fabrics in the construction of concrete shells. He developed a building system based on light parabolic arcs that could be transported and were made of wood or steel. The arches were placed in parallel, lined with sackcloth and then were subjected to slight tension. The weight of coating mortar generates a ripple that characterizes this process and acts as a lost formwork. The system was competitive for their low production costs and its implementation did not require intensive labour. Waller patented the system Ctesiphon in 1955 and in the late 70s the system had been used in over 500 structures throughout the world. One of the examples is the Chivas distillery warehouse which has a height of about 30m and a span of 150m.The thickness of the shell is impressively slender at only 6.4cm and the tissue between the spans measures 2,54m [1]. In 2006, the Eindhoven University of Technology developed a set of experiments based on the screen concrete projection method, whereby they made a prototype measuring 7m high by 2.5m wide and a thickness of 7cm. The analysis of the implementation process revealed that the projection of concrete might change the shape of the surface [2]. The University of Brussels built 10 prototypes with a span of 2m and 5cm thick, made from shotcrete tensioned on the screen. After applying the concrete, the original surface varied between 5% and 58%.This variation was due to the sliding of the attachment points as well as the dynamic effect induced on the surface by the concrete projection.[3].

Concrete additive latex

Latex Polymer when added to mortars in the coating process provides sealing and elasticity to the surface. Suitable for creating bonding layers, repairing mortars, screeds for wear-resistant floors, waterproof  mortar for concrete, mortar resistant to chemical effects, plasters with high strength and impermeability. The "Roof Nez" how it is affectionately called, owes its name to its designer George Nez. This coverage is characterized by low production costs and a remarkable resistance and waterproofness. It is constructed by applying concrete added with latex on a screen support. Despite its simplicity, this process is highly effective. Tests conducted by the bureau of parks in the United States, in Knott Laboratory in Denver, show that this coverage has a high performance compared with normal covers, resisting four times more to cold and heat. Although the cover is 1 cm thick, it is sufficiently strong to support the weight of a truck on it. The process consists of fixing a screen on the support elements of which the core consists of fibreglass and then poured concrete composed of sand, cement, water and latex[4]. In Ethiopia, the Architecture Institute in collaboration with ETH Zurich Institute made a prototype with a concrete additive covered with latex and this project was coordinated by the associate professor at ETH Dirk Hebel.[5].

Rigid formwork

Félix Candela adopted double curvature as his elected universal form. The vast work attributed to his professional practice comes from unifying the design and construction phases, resulting in the development of a set of construction techniques.

His vast knowledge of the hyperbolic parabolic geometry allowed him to design a formwork system based on conjugated linear elements with part wedges. To optimize the constructive process, he conceived a constructive strategy that used formwork boards with a ½- inch (1.27cm) thickness, by placing wedges between them to get the desired curvature [6].

Pre-stressed masonry

Eladio Dieste developed a set of technical and structural morphologies thanks to an interdisciplinary approach that embraces the structures, materials and architecture. His work is based on the relationship of structure and form and his architecture is a synthesis between form finding, structural behaviour and spatial qualities. He believes in shape as a medium to obtain structural resistance, so by geometry manipulation he moulds the structure so as to obtain structural efficiency, and gives significance to the architectural space. For David Billington the work of Eladio Dieste is "structural art" combining efficiency and structural expressivity [7]. Diest has a strong link to the construction process, which in many cases is the origin of his innovations. His constructive concept was largely due to a systematic refusal to incorporate technology coming from the "developed world". He tried to solve problems bearing in mind the circumstances and their environment [8]. To contrast with European designers, he avoids the use of concrete, choosing brick as his construction method. This option was based on an indigenous and ancestral tradition in Uruguay. He used the curved surface of vaults to resist buckling and to improve the structural efficiency and focused his research on pre-stressed masonry. His construction technique was based on low-tech solutions, to pre-stress his structural shapes he overlapped steel loops firmly anchored to the vaults, and then with a car jack introduced stress to the surface.

Discrete flexible formwork

This process has several variations, but basically this system replaces the membrane of flexible formwork for insulating material tiles, which are linked with cables. At Purdue University, Indiana, USA Waling and Greszczuk also developed a two-layer sandwich of cables with EPS tiles cast in concrete. Geometry of buildings was resold to a panel of four hypermarkets. This method was used in both the Refining Gas Station and Carwash in Midland, Michigan, and the club-house at the Purdue Golf Course in West Lafayette, Indiana which was demolished in the mid-1990s. This shell had two layers of 3.4 mm wires with 1.8 m offset from the straight-line generators. The bottom wires were spaced 30 cm apart and the top layer 60 cm apart. The shell used a 3-inch thick EPS foam, a 0.5-inch stiffening mortar, a 3-inch concrete cover and traditional rebar measuring 16.5 cm in total [9].

Flexible formwork

NEST is an Empa and Eawag project in collaboration with ETH Zurich. The work developed tries to prove that it is possible to reduce the amount of material used in the construction process, especially in the falsework, by introducing a flexible formwork. To do that, the shuttering is replaced by a fabric and the falsework by a cable net, supported by an external frame at its boundaries [10]. The challenge is then to design the flexible formwork so that the resulting shape matches the designed geometry. This approach proves to be very innovative, able to solve the main production problems of the doubly curvature geometry. However, the flexible formwork made of brick proves to be inaccurate, causing deformations on the surface that could be aesthetically displeasing to the appearance of some surfaces. 

Standard vaults

In 2012, Serguei Bagrianski, a student at Princeton University, developed a standard vault as part of his master's thesis. He believes in the potentiality of the double curvature. For him the answer to build this structural shape is standardization, so he built a prototype to a large scale, made with ultra-high-performance fibre reinforced with concrete. To produce its modular pieces, he divides the vault surface into 256 triangles. He also created an algorithm to manage the vaults’ divisions. The shape is only built with 16 adjustable 15x15 feet modules with a ½-inch thickness. With these modules he can replicate this shape easily, minimize the construction time and reduce labour costs. [11].

ORICRETESYSTEM

Support frame

The construction process is based on a reusable and prefabricated frame. This element is made up of two pairs of telescopic bars, stabilized by a telescopic truss. These articulated joints form the frame and allow to stabilize and manage the size and curvature of the surface. This support has a set of predefined attachment points for the cables, which form the cable net that defines the surface.

Oricrete formwork

The formwork and its requirements are decisive for the final cost of the construction, as well as the final expression of the built form. The present research takes advantage of the experiments previously made with flexible formwork associated with cable net. This process proves to be very effective because it does not need falsework; however it is very susceptible to deformations. In order to solve this problem, a folded metal plate is adopted using several origami patterns. The process basically uses origami which can transform a plate into a curved surface. To achieve economic sustainability, a mass-produced system is created. This standard origami is produced by carving origami patterns onto metal plates. The specific patterns allow the production of folded sheet plates and a curved surface is easily generated. The irregular surface produced by the folds make it easier for concrete adherence. The metal folded sheets work as the formwork. The folds of the surface work as shear studs. This multi-layered system is a simple process, which is very similar to normal composite decking.

Materials

To produce this system, metal plates are used because the material provides both lightness and rigidity. These materials prove to be more stable than fabrics used with flexible formwork, so the final form will be more steadfast to the project. Wood and cork also have a more favourable thermal behaviour than the screens used in flexible systems.

Origami patterns

There are several patterns able to produce a double curvature surfaces like the Ron Resch quadrangular origami pattern, the Diamond cross origami pattern or the Ron Resch triangular origami pattern. These patterns have different configurations, so one should be informed regarding the choice of pattern and of the difficulty in production and its implications in the final performance of the shell.

------------------------------FULL TEXT IN HOUSE DETAILS MAGAZINE NUMBER 2|3 (DOUBLE EDITION) NOVEMBER 2018------------------------------

References

Anon, Curved roofs of large span. Concr Constr Eng 1959;54(5):171–4.

Pronk A, Houtman R, Afink M, The reconstruction of the Philips Pavilion volume 1. In: Sources of architectural form, theory and practice. Kuwait City, Kuwait; 2007.

West M, Araya R, Fabric formwork for concrete structures and architecture. In: Krõplin B, Oñate E, editors. Proceedings of the international conference on textile composites and inflatable structures, structural membranes 2009. Barcelona; 2009.

Ned,Gorge,Latex Concrete Habitat, Trafford, 2005.

Ettlin, Anna, Architektur ist eine Lebensphilosophie [Online], Available: http://www.hebel.arch.ethz.ch/

Billington, D.P..Thin Shell concrete Structures, New York. McGraw-Hill, 1995.

Dieste: Innovation in Structural Art, New York, Princeton Architectural Press, 2004.

Pedreschi R., The Engineer’s Contribution to Contemporary Architecture, London, Thomas Telford Ltd. 2000

Waling J, Greszczuk L. Experiments with thin-shell structural models. In: Proceedings, annual meeting, American Concrete Institute, vol. 57; 1960. p. 413–31.

Veenendaal, Diederik; Block, Philippe. Design process for prototype concrete shells using a hybrid cable-net

and fabric [Online], Available: formwork(http://www.block.arch.ethz.ch/brg/files/2014-veendendaal-engstruct-design-process-for-prototype-concrete-shells-using-a-hybrid-cable-net-and-fabric-formwork_1402752074.pdf)

Sooho , Jane. 2012,  Princeton University [Online], Available: http://www.princeton.edu/cee/news/archive/?id=9047