6th RILEM Symposium on Fibre-Reinforced Concretes (FRC) - BEFIB 2004
20-22 September 2004, Varenna, Italy
CONSTRUCTION OF JCHYPAR, A STEEL FIBER
REINFORCED CONCRETE THIN SHELL STRUCTURE
A. Domingo1, C. Lázaro2, P. Serna1
1
Department of Construction Engineering
2
Department of Continuum Mechanics
Universidad Politécnica de Valencia, Spain
CM Arquitectura, Ingeniería, Urbanismo y Medio Ambiente, S.L.
Abstract
The following document describes the construction of a thin shell structure using steel
fiber reinforced concrete. The roof called JChypar is a groined vault composed of four
hyperbolic paraboloids. Shell thickness equals 6 cm and distance between opposite
supports is 35,50 m. This paper describes the whole construction process of the
aforementioned structure. Previous characterization tests, materials selection, structural
design, shoring process, rebar placement, shotcreting process, curing process and
striking, are analyzed.
1. Introduction
The Oceanographic Park in Valencia (L’Oceanografic) is a leisure and educational
centre, promoted by the Valencian Goverment (Spain). The project forms part of the City
of Arts and Sciences, a the large complex currently under construction in Valencia
(Spain), we exposed it in the Fourth International Colloquium on Computation of Shell
and Spacial Structures IASS-IACM 2000 [1]. The Park occupies a plot of approximately
80,000 m2. L’Oceanografic is made up of a set of buildings and landscaped gardens
distributed around a large lake. The Park’s two emblematic features are the roofing
structures, “JChypar” and “AChypar”, in hyperbolic-paraboloids, based on Felix
Candela’s blueprints and ideas, and designed and technically assisted by the authors. The
following lecture presents the construction of one of them, the JChypar roof
2. JChypar´s Geometry
JChypar is directly modelled on the roof of the restaurant Los Manantiales in
Xochimilco, Mexico, constructed by the architect Candela in 1957. The shape of
JChypar is a groined vault system composed of eight radially symmetrical lobes (Fig. 1).
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6th RILEM Symposium on Fibre-Reinforced Concretes (FRC) - BEFIB 2004
20-22 September 2004, Varenna, Italy
Fig. 1.- Shell Geometry
Each lobe, along with the opposite, forms part of a hyperbolic paraboloid, which axes X
and Y lie on a horizontal plane forming an angle of 22,5º, and emerging from the centre
of the roof. The Z-axis is vertical. The intersection of each lobe with the adjacent one
forms the parabolic rib. The free edge of each lobe is created by the intersection of the
surface with a plane that forms an angle of 60º with the horizontal plane and starts from
the line that joins the bases of the consecutive ribs. These bases are situated on the
vertexes of an octagon with 13,58 m long sides. The distance between two opposite
supports is 35,50 m. The top of a free edges projects out 6,83 m, and reaches a height of
12,27 m. The free edges of the shell do not have a border beam. The shell is made up of
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6th RILEM Symposium on Fibre-Reinforced Concretes (FRC) - BEFIB 2004
20-22 September 2004, Varenna, Italy
steel fiber reinforcement concrete (SFRC) with a thickness of 6 cm giving it an absolute
light and slim appearance, and reaching a minimum slenderness of 1/600.
3. Structural design and materials selection
Design and structural analysis process was presented in [2]. For this an Elastic and
linear analysis using the finite elements program SAP2000 v7.10 by Computers and
Structures Inc., and a model of shell type finite elements. The use of shell type finite
elements makes possible the evaluation of the bending, twisting and shearing forces in
addition to membrane forces. The degree of bending stress results in the appearance of
tensile stress that could reach a level greater than the resistance of concrete’s
capabilities. This led to the use of steel fibres, capable of resisting tensile stresses, in the
composition of the concrete, and also to the use of central reinforcement in order to resist
membrane forces. After previous test, concrete composition and characteristics were
fixed as show in table 1
Table 1. Concrete Composition and characteristics
Cement – CEM II BM 42,5 (ASLAND)
300 kg/m3
W/C
0,5
Maximum aggregate size
10 mm
Fibres DRAMIX ZP 305
50 kg/m3
fck,28d
30 MPa
The addition of fibres has several effects: (a) a reduction in the with of the cracks as well
as their being distributed more uniformly, (b) a better adjusted behaviour to the used
model, (c) the gaining of a sufficient reserve of resistance that allows for ultimate design,
avoiding the risk of fragile fracture and (d) the provision of greater ductility to the
material.
Base reinforcement has been designed using the maximum values of factored axial
forces on the elements. A reinforcement mesh with bars of Ievery 15 cm along
parallel and perpendicular directions to axis of each lobe was designed.
The interaction diagram N-M has been calculated for the 6 cm thick base section. Fibre
manufacturer guarantees a characteristic value of the equivalent flexural tensile strength
of steel reinforced concrete equal to 2,4 N/mm2. This value has been verified in previous
test. The principal characteristics of the simplified used stress – strain diagram were:
Ultimate tensile stress for steel fibre reinforced concrete equals 0,37 fctd,eq,150 (0,6
N/mm2) acting on the entire cracker depth of the section, and compression block of a
value of 0,85 fcd (17 N/mm2) acting on 80% of the depth of the neutral fibre. Maximum
ultimate strain of concrete in compression is limited to 0,0035, and maximum ultimate
strain of steel fibre reinforced concrete is limited to 0,01.
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6th RILEM Symposium on Fibre-Reinforced Concretes (FRC) - BEFIB 2004
20-22 September 2004, Varenna, Italy
The pairs of values Nd and Md obtained as the result of the analysis were verified with
the said interaction diagram.
4. Construction process
4.1. Previous characterization tests
SFRC was chosen in order to meet the requirements of resistance, durability and
ligthness. The analysis and construction of the JChypar roof was preceded by several
tests developed in the Laboratory of the Department of Civil Engineering of the
Technical University of Valencia (UPV). The objetives of lab tests were a) To select the
concrete dosage b)To calibrate the analytical model and b) To check and propose a
suitable constructive method, feasible and economical according to the present
technology standards. Thanks to collaboration of PREVALESA and HORMIGONES
PROYECTADOS, SL (Fig. 2), CM S.L., ASLAND and BEKAERT, it was possible a
set of shell test specimen of 2x3 m and 6 cm thick for these tests. Two types of specimen
were tested: cast in place and shotcreted. Specimen were tested up to flexural failure. It
was stated that shotcreting gave a better execution and behavior. Results of these tests
are quoled in [5].
4.2. Construction
4.2.1. Shoring
The wooden formwork was supported by shoring towers (Fig. 3). These are formed by
1,5 x 1,5 x 1,5 m tubular structure modulus placed and braced one on another. Each
tower had for screwed clamps on the top to support the formwork. The elevation of each
clamp was set considering its position coordinates and the geometry of the shell. Shoring
towers were disposed in two groups. The first one shores the radial ribs and consists of
towers disposed on concentrical circles under the ribs; the second one shores the shell
lobes, consists of lines of towers placed along hypar’s X (or Y) axis on alternate lobes.
Fig. 2.- Previous test
Fig. 3.- Shoring towers
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6th RILEM Symposium on Fibre-Reinforced Concretes (FRC) - BEFIB 2004
20-22 September 2004, Varenna, Italy
4.2.2. Wooden formwork
The formwork consists of a surface or wooden tables fixed on two families of wooden
beams. The main family is fixed on the clamps of the shores towers; beams are parallel
to the X (or Y in alternate lobes) axis of every hyper lobe. The secondary family is fixed
on the main one following the Y (or X in alternate lobes) axis. The final surface was
made up of tables fixed on the secondary beam family. Tables are set parallel to the main
wooden beams (Fig.4). Nevertheless slight variations in the direction were necessary due
to the width of the tables. One month and a half was necessary to places all the beams of
the covering formwork.
The pine framing lumber boards used are 2 m in length and 8.5 cm in width. Its laying
started in 19/06/00, starting from the upper axis of the paraboloid towards the rib. Two
contiguous semilobes were started at the same time. The meeting point of the formwork
with the supports was solved in the construction site itself, since the resulting surface
comes from the intersection of the paraboloids with a cylinder. The complete cylinder
was executed on the construction site during the first stage of the formwork, lowering it
to the position where it had to be built, while at the same time, the framing lumber of the
cylinder and formwork was trimmed. After finishing one of them, a template was created
to carry out the rest of the joints between the covering formwork and its ending with the
support.
To carry out two complete lobes took 15 days. Later, this performance was improved
and the complete covering was sided with the framing lumber in one month and a half.
The protection of the wood was performed using mats which were moistened with water
sprinklers. While the formwork was performed, the liquid to remove the formwork,
Rheofinix 211 by Bettor, was being poured.
4.2.3. Roof reinforcement
On August 2000 started the reinforcement placement. Rib reinforcement was
prefabricated on site set on place, achiving a rate of one week for each rib.
The installation process of placing the
ribs concentrated on one complete rib,
that is, as suppor from one extreme to
the other. When part of the first rib
was placed, its frame was lowered
again and reinforced with mounting
frame, because this was not enough
stiff to be placed perfectly (Fig. 5).
Fig. 4.- Wooden formwork
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6th RILEM Symposium on Fibre-Reinforced Concretes (FRC) - BEFIB 2004
20-22 September 2004, Varenna, Italy
Shell’s rebar mesh is made up of I8 electrowelded bars of #15x15 cm. Due to an
interpretation mistake of the plans by the contractor company, the rebar mesh had to be
removed because it did not follow the direction specified in the plans. As a consequence,
it took approximately one month to mount rabar for all the lobes of the covering.
Increase 15 days used for the incorrect placing of the mesh, which means that the
workers performance doubled, mainly due to the acquired skill.
Fig. 5.- Roof reinforcement
4.2.4. Supports
The structure is supported on 8 points. Each support was considered into he FE model as
a hinge, with restricted lateral displacement and free rotations. Such hinge was
performed by using a confined elastomeric bearing “Stronghold H-150”, fixed to slope
trunk-conic concrete basements on the sub-structure. (Fig. 6)
Fig. 6.- Support hinge
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6th RILEM Symposium on Fibre-Reinforced Concretes (FRC) - BEFIB 2004
20-22 September 2004, Varenna, Italy
4.2.5. Shotcreting process
Shotcreting process started on September 2000. The process involved concrete
projecting in dry way. In order to do this, the appropriate machinery, tools and materials
(cement, fibers and aggretates) were prepared on site.
The process was as follows: First, the key of the covering was shotcreted, in order to
achieve a uniform concrete joint. Second, shotcreting of ribs and third, shotcreting of
lobes (Fig. 7), dividing each semilobe in six lanes. The process of shotcreting included
mastering and superficial finishing (Fig. 8) of the section being carried out.
After finishing one of the lanes, it is protected with a plastic sheet to prevent staining
during the next phase. 75 continuous hours were necessary for shotcreting of the first
lobe.
Among the most interesting data to point out are the refusal of the material during the
projection, which was 30 % in the most difficult situations. Later, the rib channels were
shaped, and thus the covering was completed on 19/11/00 - it was started on 20/09/00.
Fig. 7.- Shotcreting of lobes
4.2.6. Process of arch center disassembling
To disassemble and remove the formwork, a thorough process was followed to check
constantly the conditions of its deformations, in order to compare them to the results
obtained in the model used. In this way, the lobes were disassembled as it is shown in
the Fig. 9, thereby obtaining the immediate deformations at the points marked. Such
deformations were insignificant and the covering showed a virtually nil deformation.
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6th RILEM Symposium on Fibre-Reinforced Concretes (FRC) - BEFIB 2004
20-22 September 2004, Varenna, Italy
Fig. 8.- Superficial finishing
Fig. 9.- disassembling process
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6th RILEM Symposium on Fibre-Reinforced Concretes (FRC) - BEFIB 2004
20-22 September 2004, Varenna, Italy
When the arch center was completely released, while the ribs remained underpinned and
with the formwork, the next step was to disassemble the ribs. This process started by
progressively releasing from the center of the covering to the spiral supports, controlling
the deformations in the ribs, as shown in the Fig. 8. As it happened with the covering
lobes, the lowering of supports and ribs was virtually nil, which matches the results
obtained in the model used. (Fig. 9).
5. Analysis of the constructing process performance
The important peculiarity of this type of construction, leaving aside its planning, are the
constructing processes followed and the materials used. Within the different tasks related
to the construction of this type of coverings, we present those which due to their
singularity and relevance make this type of elements special structures. Without any
doubt, when we face the planning of the construction of a laminar element, as this is the
case, there are no data regarding the performance of tasks to carry out especially on
formwork, framing and concrete casting of the cover. If we define as typical
performance the theory for a horizontal flat surface carried out with the same means,
materials and workforce; and actual performance the one taken into account during the
production of this covering, I suggest the term difficulty ratio for the relationship
between the typical performance and the actual performance. (Table 2)
Fig. 10.- Final aspect of the JChypar roof
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6th RILEM Symposium on Fibre-Reinforced Concretes (FRC) - BEFIB 2004
20-22 September 2004, Varenna, Italy
Table 2.- Cost analysis
Typical
Performance
Formwork (h/m2) 1.55
Reinforcement
0.02
(h/kg)
Shotcrete (h/m3)
1.33
Actual
Performance
3.81
0.0787
Difficulty
Radio
2.46
3.93
2.09
1.57
6. Conclusion
The development of this project manifests the great expressive force of the structures.
The formal and no forced conjunction of the architectural design and its supporting
frame, a modern vision of the structural behavior of thin shell structures, to have itself
made a recovered element of the architecture. By means, a suitable construction method
and the use of new technologies using classical materials, decreases its costs and
providing, as E. Ramm said “the primadonna of structures”, an adequate element to be
reincorporated to our designs, projects and constructions. The authors want to greet Felix
Candela, one of the masters in design and construction of shell structures, helping to
come true his last dream.
References
1
2
3
4
5
ACI 544.1R-82, ‘State of the Art Report on Fiber Reinforced Concrete’, Concrete
International, (May. 1982)
A. Domingo, C. Lázaro, P. Serna, ‘Design of a thin shell steel fiber reinforced
concrete hypar roof’, in R. Astudillo, A.J. Madrid (eds.), Shell and Spatial
Structures: from recent past to the next millenium, CEDEX, (1999) A 169-A 179.
Dramix Guideline, ‘Steel fiber reinforced concrete structures with or without
ordinary reinforcement’, Infrastructuur in het Leefmilieu, 4, (1995), 227–239
ACI 506.1R-98, ACI Committee Report on Fiber Reinforced Shotcrete, (Apr.
1998)
A. Domingo, C. Lázaro, P. Serna, ‘Use of steel fiber reinforced concrete in thin
shell structures: Evaluation of fiber performance through testing of shell
speciments’, abstract Congress of Computation of Shell & Spatial Structures
IASS-IACM 2000, Chania-Crete, Greece, (2000) pp. 176-177
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