The Ctesiphon System. British Origin
- A sheet of concrete with self-supporting textile sackcloth-based formwork, which avoids conventional shuttering and uncasting.
- Its form is an inverted catenary arch, where the forces generated by the weight of the concrete on the rest arches are purely compressive, thus avoiding the need for traction and flexion reinforcement. From both a structural and formal point of view, this system had already been used by Gaudí in his famous domes .
- The simplicity of the system, not only in design and calculation but in execution, requires only a small number of unskilled workers to complete the construction in a short space of time.
2. Materials and Methods
- Secondly, a collection of case studies has been preselected. From this initial group, two buildings constructed by De la Hoz and García Paredes with the Iberlar patent system adapted for housing purposes have been selected as case studies.
- Thirdly, for the analysis of this construction system used by De La Hoz and García Paredes, different material and performance tests have been carried out. For this purpose, in situ samples have been extracted from the case studies for subsequent laboratory characterization. Additionally, thermographic analysis of these constructions has also been conducted in order to analyze their structure and interior composition.
- Finally, a discussion was carried out based on the results obtained.
2.2. Waller and IBERLAR Patent
- Foundation framework: The framework of the concrete element on which the laminate is supported, which we could assimilate to the foundation of the building.
- Sag rods: Steel framework that forms the convex curvatures of the trough of the waves between the crests are moulded “in a catenary curve”.
- Crest rods. Frameworks similar to the sag rods, but with a concave form, and put in place after those used to form the normal curvature of the arch.
- Arch rods: Reinforcements that follow the shape of the main arch and will absorb the effects of the wind in the same plan of the arch.
- Flexible shuttering: As has been mentioned, the patent refers to the stretched mesh, low-thickness mesh, or natural fibre sackcloth as different possibilities.
- Fastening support elements: Hooks, wires, bolts, and other support materials.
- Arch height: 1/3 of the arch span
- Crest width: 1/10 of the main arch span
- Width of crest: 1/4 of the crest span
2.3. Case Studies in Spain: Rafael De la Hoz works
- Complex 1: Palma del Rio (Cordoba), Calle Huertas
- Complex 2: Villaviciosa de Cordoba (Cordoba), CO-3075
2.3.1. Complex 1: Palma del Rio Houses
2.3.2. Complex 2: Villaviciosa Houses
3.1. Samples Analysis
- Sample 1 was taken on the crest area. Formed by three layers of mortar (2 + 2 + 2 cm), corresponding to three concrete pouring carried out at different times, with chicken wire between two of them, the middle one and the exterior one. This chicken wire, with a hexagonal geometry and low thickness, appears in all three samples, thus we can therefore give it the function of flexible shuttering. On the inside there is a fourth layer of plaster with sackcloth reinforcement.
- Sample 2 was taken on the wave. The composition of the sample taken is the same as the previous one, but with lower thicknesses as a result of the execution and lower sectional requirement on the wave trough, since, at these points, they do not have to respond to the transmission of loads to the foundation to horizontal loads.
- Sample 3 was taken from a construction joint. There are construction joints every four arches, meaning every three waves. These joints are a matter of planning the execution and performance of the workers. To make these joints, a strip of bituminous material is used in contact with the two layers of concrete that joins the two arches and is reinforced outwardly with double chicken wiring. Within the concrete sheet, there are several strips of lead, approximately 6 cm wide, located on the axis of the constructive joint and deposed perpendicular to the joint.
3.2. Thermography Analysis
3.3. Thermal Tests, U-Values
- Laying the foundations: The system is based on top of a continuous foundation of unreinforced concrete ditch.
- Supports and trusses: The prefabricated trusses are simplified enormously in their design by the fact that the cage of reinforcements, and the flexible shuttering in this case, are self-supporting. This implies that they do not require external trusses that would simply add complexity for large spans.
- In terms of the strip of lead located on one of the crests appearing in the samples performed, we can see, thanks to the thermography images (Figure 10), that they are repeated every three waves, coinciding with the constructive joints. The choice of this material is very appropriate due to its malleability and ease of adaptation to the curvature of the catenary. Its main task if that of a sealing construction joint.
- Positioning of the sackcloth: The sackcloth is positioned by means of attaching it to the lead strips and to the trusses. Its function is to act as support from the first layer of fresh mortar. Subsequently, the metal reinforcement mesh is positioned between the successive layers of concrete. The function of the mesh is to control the forces provoked by the shrinkage of the concrete and to avoid cracking provoked by possible flexion in the laminate.
- Applying the mortar: The materials used are similar to any job using reinforced concrete, excluding steel and coarse aggregate. A controlled granulometry of no greater than 12mm is recommended, along with a ratio of gravel with a sand content between 40% and 80%. In countries without significant seismic risk, as is the case, these laminates can be applied without any metallic reinforcement. Although chicken wire is used in this case, it cannot be considered a metallic reinforcement, but simply as a woven support used when applying the mortar, and because it can “incur imperfections relatively easily in construction” .The positioning of the material is done in three successive layers with a thickness of approximately 2cm. There are two reasons for splitting the execution into three different moments. First, for the self-supporting limit of the woven shuttering. And secondly because the system, once the first layer has set, turns into a support for the next layers.For guidance on the performance of these constructions, we could build on the data published by J. Weller’s company in [15,21] which generate an “average of 0.278 m2 per workman and hour”. This advice could allow us to estimate the construction time of each dwelling in Palma del Rio in approximately four days, using a group of four people.
- Removal of formwork: Uncasing does not exist per se. The supports are simply taken away by dismounting them from the inside. The simplest way of removing the formwork involves taking away the central bar and loosening the spring at its highest point.
- Curing should involve avoiding moisture loss from the concrete since there is a large amount of surface in contact with the air in relation to the volume of material. This can be achieved on one hand by protecting the surface with plastic or by using traditional methods like sprinkling fine sand on the surface and often water to create a protective layer that will isolate the mortar mass from outdoor conditions .
- Finally, an inner layer of a material consisting of plaster and a sackcloth fabric made from hemp is applied to the structural system, once dried, to provide some thermal insulation (according to the authors in ).
- Form: Having a curved surface, the sun exposure is always minimal, so at no point is a direct incidence produced over a plane that heats up. This allows the majority of the surface to be in a position to dispel this heat in summer as it is exposed minimally or not at all; while just one part of the laminate is heated up by an incidence close to the normal surface or perpendicular surface.
- The use of traditional lime coating on the outside generates a reflection surface which improves the previous situation.
- The high thermal conductivity of the concrete, along with the large surface in contact with the outside, ensures that the dissipation of stored heat is as fast as possible, and in all cases, during the night, the building reverses the diurnal heating cycle due to this high dissipation capacity. Once again, in the thermographic images, we can observe the transition of temperatures from hot to cold produced on the laminate, depending on the sunny area.
- Elimination of the exterior truss complexes that support the woven shuttering during concreting;
- Elimination of all types of fastening reinforcements except from chicken wire during the process of creating the laminate;
- Elimination of foundation framework, sag rods, crest rods, and arch rods defined in the patent;
- Involvement in the structural system of an inner layer of material composed of plaster and a sacking fabric made from hemp or something similar to provide thermal insulation and hygroscopic regulation;
- Involvement of innovative lead rods in the construction joints every three arches, which simplifies the construction with a double purpose: to substitute the so called foundation framework or starter framework, performing the work and configuration of the construction joint itself, as well as to provide continuity to solve the problem related to water infiltration.
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|W/(m2∙K)||[°C] T int||[°C] T wall||[°C] T ext||T ext—T int|
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