Thin Concrete Shells Research Articles

Numerical investigation on the behavior of thin concrete shells subjected to nonuniform and asymmetrical loads

AbstractConcrete shells, designed with near optimal shapes for uniform gravity loads, can be subjected to nonmembrane effects caused by nonuniform and asymmetrical loads. In this paper, a numerical study on the effect of normative loads on a thin triangular concrete shell with three supports is presented. Two actions were considered, wind and snow, which present high spatial variability in both intensity and direction, assuming the values established in Eurocode 1 for the worst possible location, in Portugal. Linear, nonlinear and stability analyses were performed using the ABAQUS software. Results suggest that the wind action, but especially the exceptional snow load in drifted arrangement, produce significant bending moments, leading to decompression, and eventually to the development of stresses above the tensile strength of current concrete classes. Therefore, the production of these shells by assembling prefabricated un‐reinforced modules, requires the use of ultrahigh‐performance fiber reinforced concrete, combined with prestressing.

VISION SYSTEM FOR MONITORING SEISMIC TESTS IN CONCRETE SHELLS

Abstract. Structural monitoring plays a crucial role in assessing damage and detecting potential faults. Vision systems provide real-time information about the behaviour and state of conservation of structures, enabling precise and efficient analysis. Computer vision algorithms are employed to analyse images and extract relevant structural information. This information may encompass key points' displacement and deformation within the structure.This paper introduces a methodology for monitoring dynamic tests using computer vision. The approach employs a camera to track artificial targets placed on the structure. The camera captures multiple images during the tests and detects the coordinates of the target centres. Subsequently, displacements are calculated based on the differences in coordinates among the aforementioned targets.To validate the methodology, an experimental study was conducted using dynamic tests on a reduced-scale model of a thin concrete shell tested on a seismic table. Five dynamic tests were carried out, involving varied amplitude and frequency values to test the proposed approach. The results substantiate the efficacy of computer vision in monitoring dynamic tests. In conclusion, the developed methodology facilitates dynamic test monitoring through computer vision by continuously tracking artificial targets throughout the tests and computing their displacements.

Exploring the three-dimensional space with modular concrete shells: Form-finding, design and structural analysis

Thin concrete shells can span large distances thanks to their structural efficiency, following the optimum force flow. Despite the efficient use of material of well-designed shells, their construction suffers from labor-intensive and time-consuming fabrication techniques. This research therefore proposes a design method for the facilitated manufacturing of freeform shell structures. The manufacturing process has been considered from the design phase on, by generating an extensive range of different shell configurations based on a limited set of form-found modules and thus formworks. The challenge was to define which curved module geometries, after assembly, lead to the largest variety of freeform surfaces. More than sixty configurations resulted from a set of four modules only. This paper will discuss the form-finding process as well as the geometrical arrangement using tessellation patterns for the achievement of those modular configurations, going from domed to undulating shell shapes. In order to evaluate the structural efficiency of the shapes, twenty modular configurations were selected and analyzed under self-weight, using finite element simulations. To conclude, a prototype of one modular base element has been built, using a reusable casting wax in combination with a grid shell box, as the main parts of the formwork. The results demonstrate the structural feasibility and limitations of the modular shell design strategy. The modular approach contributes to circularity by encouraging reuse and allowing various combinations with a repeating set of modules, striving as such towards resource-effective innovative shell structures.

Tensile performance of cast-in headed studs in thin concrete panels with void formers

In recent times, voided concrete slab or wall system has been increasingly popular due to material and cost savings benefits offered by such system. Fastenings are required to be attached to such systems either to connect to other concrete elements or fixtures. There has been limited published literature on the performance of fastenings in thin concrete shell elements due to presence of voids. The Concrete Capacity (CC) method is the state-of the-art prediction model for capacity of anchors in concrete widely adopted in design standards worldwide. The CC-method has been proven to be a robust model for predicting concrete cone capacity of cast-in and post-installed anchors with effective embedment depths, hef between 4 and 20 times diameter of anchors with a minimum hef of 40 mm in mature age concrete. In this study, over 200 headed studs are investigated experimentally in early age concrete whereby the hef for over half of the specimens is lesser than 40 mm. Further, the failure mode for the headed studs in the presence of plastic void former is expected to be a plug failure which prohibits the development of the full concrete cone. The purpose of this study is to examine the applicability of the CC-method for pull out performance of headed studs in the presence of void formers. A total of 228 headed anchors with varying effective embedment depths ranging from 19 mm to 61 mm were tested in thin concrete panels with varying thicknesses. Based on structural reliability analysis, a modification factor was proposed to the CC-method to safely predict the pull-out design capacity of headed studs in thin concrete panels with plastic void formers to maintain the same degree of safety as for typical headed stud applications within the scope of the CC-method.

Thin corrugated-edge shells inspired by Nervi’s dome: Numerical insight about their mechanical behaviour

During the last decades, the constant evolution of the construction systems has led to the possibility of carrying out increasingly complex architectural project. Among the wide range of construction systems, thin concrete shells with corrugated-edge stand out for their relevance.In this paper, the mechanical behaviour of thin concrete corrugated-edge shell inspired by Nervi’s Flaminio dome has been analysed in detail, considering different load configurations (self-weight, uniform normal pressure and antisymmetric vertical load) and constraints (pure membrane vs. displacements restrained boundary conditions).Non-linear static analysis has been performed to assess the vertical load-bearing capacity of the corrugated-edge shell considering a Concrete Damaged Plasticity (CDP) constitutive model and linear and non-linear buckling analyses have been carried out to evaluate the effects of the corrugation on buckling behaviour.The results obtained from linear and non-linear analyses have been compared with those obtained for a concrete thin smooth-edge shell having the same geometric global characteristics. The comparison highlighted improvements provided by corrugated-edge in terms of structural behaviour.

Seismic evaluation cylindrical concrete shells

Abstract The reasons for concrete roof shells’ apparent seismic resistance have been subject to limited research but they have been shown to be inherently resilient to earthquakes. Shells constructed of concrete exhibit high structural efficiency and can therefore be made very thin. As a result of their relatively lightweight nature, thin shell structures are implicitly resistant to earthquake forces. The shell structure is typically designed so that it performs optimally under gravity loads, which are carried mainly by membrane action over the shell surface. As earthquakes induce unexpected horizontal forces, concrete shell structures can be damaged by bending stresses. By studying 8 cm-thick concrete roof shells using parametric analysis, this research shows that small and midsized (span <30 m) thin concrete roof shells can indeed be intrinsically earthquake resistant. These structures have high geometric stiffness and low mass, which results in fundamental frequencies far higher than those of realistic seismic events. Under earthquake excitation, these characteristics result in elastic shell behavior, without exceeding the maximum concrete strength. A shallow shell exhibits greater stress in response to earthquake vibrations caused by the vertical components than by horizontal components. Further, by increasing the rise and curvature of large shells, the fundamental frequency increases and the damaging effect of vertical earthquake vibration is reduced. The aim of this study in general is to show the analysis and the effect of earthquakes on cylindrical concrete shells.

The Invisible Beauty of the Zeiss-Dywidag Domes: Topology Optimization of the Triangulated Rebar Grids

ABSTRACT The Zeiss-Dywidag system was a pioneer in the history of thin concrete shells, which impacted and advanced theory and praxis worldwide. This study explains its relevance for the history of gridshells: the first ever built Zeiss-Dywidag dome started out as a geodesic gridshell, sprayed over by concrete. Walther Bauersfeld abandoned his own ingenious design for the first Planetarium in Jena in favour of a lamella-type topology for the equally self-bearing reinforcing grid of the later Zeiss-Dywidag domes. We reconstruct the optimization of the geometry and tessellation of the first built example of the latter, the Schott dome, and suggest possible motivations for the change. Bauersfeld’s strikingly advanced theory of equivalent membrane shells, which played an essential role in the process, is published here for the first time. The significance of a unique benchmarking parameter, the so-called bar density (D-value), introduced by Bauersfeld is investigated. Its applicability to assess geometric fitness is assessed by a comparative study of selected grid topologies and geometries.

Computational design exploration of a segmented concrete shell building floor system

The construction industry is responsible for nearly half of the UK's carbon dioxide emissions and the use of an extremely large volume of concrete – the world's most widely used man-made material – accounts for more than 7% of global carbon dioxide emissions. The scale of this problem spawned research to explore the potential for structurally efficient non-prismatic geometries to reduce the amount of concrete used in building elements substantially, thus also reducing their embodied carbon dioxide footprint. In particular, the research focused on segmented thin concrete shells as floor slabs, leveraging computational design and digital fabrication methodologies to automate their production off site. An important part of this research was the development of a computational framework for the design of thin concrete shells in order to make such a construction methodology accessible to building designers in practice. The framework combines solutions for parametric modelling, finite-element analysis, isogeometric analysis, form-finding and optimisation, along with embedded fabrication constraints specific to the project's automated manufacturing system. The application of the developed computational framework in the design of a 4.5 m × 4.5 m prototype is documented in this paper, illustrating how automating concrete construction can transform the industry towards net-zero.

Reconstructing Pérez Piñero’s Anoeta Velodrome

The 1972 dome to cover the Anoeta Velodrome is the product of the experiences up to that date of the architects Emilio Pérez Piñero and Félix Candela, specialists, respectively, in the design of deployable reticular structures and thin concrete shells using hyperbolic paraboloids. It is a very relevant project in the careers of both architects, as the Anoeta dome was Pérez Piñero’s last project, and also the last of the domes in which Candela participated since 1965. Pérez Piñero’s death in 1972 marked the end of a phase in Candela’s life. This paper describes the virtual reconstruction of a variation of the project and analyses its geometry, based on the subdivision of the sphere into polygons onto which hyperbolic paraboloids were then inserted. New documentation is provided which offers context for the evolution of Candela’s work, linking this project to his previous major work: the Palacio de los Deportes built for the 1968 Mexico Olympics.

Stress and buckling resistance of dual-purpose concrete shells

In this contribution, and as an extension of previous work, the simultaneous use of thin concrete shells for roofing and liquid containment is explored, with a particular focus on the bending and buckling behaviour of the shell. The concept of dual-purpose concrete shells is a novel one, and has the potential to revive the widespread use of elegant thin concrete shells once again. It is shown how excessive stresses due to water loading can be controlled through gradual thickening of the shell over the submerged region. Not only are membrane stresses lowered, but the bending stresses in the vicinity of the shell edge are also significantly moderated. Through a linear eigenvalue buckling analysis followed by a nonlinear Riks-type buckling analysis accounting for geometric imperfections, such thickening is also shown to be effective in enhancing the buckling resistance of the shell. The overall conclusion is that the concept of dual-purpose concrete shells is structurally viable, and deserves more attention.

Prefabrication of a Thin Concrete Shell: The Case of St Kevin's Church in Dee Why, Australia

Location of Project: Dee Why, NSW, Australia<br/> Structural Type: Prefabricated thin concrete shell <br/> Project Scale: Length 30 m, width 15.5 m, height 12 m <br/> Owner/Client: Warringah Catholic Parish <br/> Architect: Gibbons & Gibbons Architects <br/> Structural Engineer: Concrete Industries Australia (Monier) Engineers Pty. Ltd.<br/> Construction: Concrete Industries Australia (Monier) Pty. Ltd. <br/> Construction year: 1961<br/>

A calculation approach for sandwich panels with facings made of UHPFRC and pre-tensioned CFRP reinforcement

Sandwich panels are widely applied in construction industry, e.g. for modern building envelopes. They show low self-weight and high load-bearing capacity as well as sufficient physical properties, but are usually limited to relatively short spans. In contrast, thin concrete shell structures show high stiffness as well as load-bearing capacity even for long spans. Combining both construction methods and applying non-corrosive high-strength materials enables multifunctional, light elements with long spans, high load-carrying capacities and additional physical properties.In this paper, sandwich panels with flat and folded plate facings made of ultra-high performance fibre reinforced concrete (UHPFRC) and carbon fibre reinforced polymer (CFRP) prestressing strands are investigated. For a reliable bond strength and to account for spatial facings, a special production method was developed. For the prediction of the flexural behaviour, a new calculation approach is derived step-by-step which accounts for non-linear behaviour. Theoretical bending moment–curvature relationships are derived for UHPFRC cross-sections with CFRP prestressing strands and incorporated in differential equations of sandwich theory to account for cracking and residual stresses in facings. As additional merit of this approach, the tensile strength of UHPFRC is derived from material samples. Spring models to consider stiffness of shear connectors and core material are applied. The non-linear calculation approach covers typical failure mechanisms. Non-linear load-deformation relationships are calculated and compared to experimental test data of prestressed sandwich panels.

Dual-purpose concrete domes: A strategy for the revival of thin concrete shell roofs

The use of thin concrete shells as long-span roofing solutions has declined over the past 60 years, largely as a result of the expensive nature of the formwork for curved surfaces, and the stiff competition from other more economical options such as steel space grids. The purpose of this contribution is to explore the simultaneous use of thin concrete shells for roofing and liquid-containment purposes. It is hoped the concept of dual-purpose concrete shells will provide enhanced justification for the higher costs associated with the construction of curved surfaces, thereby helping to revive the widespread use of elegant thin concrete shells once again. Specifically, the state of stress in various dual-purpose configurations is evaluated, and the effect of varying shell thickness in critical zones is investigated, allowing some preliminary insights to be gained. With appropriate thickness enhancement in the critical zones, the concept appears feasible, but before firm conclusions can be made, detailed buckling studies need to be undertaken.

Gridshell as Formwork: Proof of Concept for a New Technique for Constructing Thin Concrete Shells Supported by Gridshell as Formwork

Abstract This paper documents an empirical experiment conducted in August 2014 as proof of concept for a new method of constructing concrete shells. An idea initially presented by the first author ...

Finite Element Analysis of Cylindrical and Spherical Concrete Vaults

Concrete shell structures, often cast as a monolithic dome or stressed ribbon bridge or saddle roof. The thin concrete shell structures are a lightweight construction composed of a relatively thin shell made of reinforced concrete, usually without the useof internal supports giving an open unobstructed interior. This project aims to investigate the displacement and to find the maximum shear stress of cylindrical and spherical concrete vaults subjected to pressure load and it’s self-weight. Boundary condition is given for the concrete vaults as simply supported. Concrete vaults of 3m, 6m and 9m span and of length 8m with same loading conditions were applied. If the shear stress is more it is easy to resist the more load on it. ANSYS results shows that the displacement values when compared with cylindrical and spherical shells, Spherical shells can resist more load

A design methodology to reduce the embodied carbon of concrete buildings using thin-shell floors

This paper explores the potential of thin concrete shells as low-carbon alternatives to floor slabs and beams, which typically make up the majority of structural material in multi-storey buildings. A simple and practical system is proposed, featuring pre-cast textile reinforced concrete shells with a network of prestressed steel tension ties. A non-structural fill is included to provide a level top surface. Building on previous experimental and theoretical work, a complete design methodology is presented. This is then used to explore the structural behaviour of the proposed system, refine its design, and evaluate potential carbon savings.Compared to flat slabs of equivalent structural performance, significant embodied carbon reductions (53–58%) are demonstrated across spans of 6–18 m. Self-weight reductions of 43–53% are also achieved, which would save additional material in columns and foundations. The simplicity of the proposed structure, and conservatism of the design methodology, indicate that further savings could be made with future refinements.These results show that considerable embodied carbon reductions are possible through innovative structural design, and that thin-shell floors are a practical means of achieving this.

Parameter Identification for Digital Fabrication: A Gaussian Process Learning Approach

Tensioned cable nets can be used as supporting structures for the efficient construction of lightweight building elements, such as thin concrete shell structures. To guarantee important mechanical properties of the latter, the tolerances on deviations of the tensioned cable net geometry from the desired target form are very tight. Therefore, the form needs to be readjusted on the construction site. In order to employ model-based optimization techniques, the precise identification of important uncertain model parameters of the cable net system is required. This paper proposes the use of Gaussian process regression to learn the function that maps the cable net geometry to the uncertain parameters. In contrast to previously proposed methods, this approach requires only a single form measurement for the identification of the cable net model parameters. This is beneficial since measurements of the cable net form on the construction site are very expensive. For the training of the Gaussian processes, simulated data is efficiently computed via convex programming. The effectiveness of the proposed method and the impact of the precise identification of the parameters on the form of the cable net are demonstrated in numerical experiments on a quarter-scale prototype of a roof structure.

Design method for precise-forming of air-supported structures considering weld seams

Abstract Air-supported structures have been increasingly used as formwork for constructing thin concrete shell structures. However, shape deviation from design shape of air-supported structures as airform can result in varying radius of curvature and differing stress distribution. Precise-forming is an inevitable requirement for the design of air-supported structures. This paper presents a design method of air-supported structures considering weld seams for precise-forming. Simulation method of weld seams is integrated in the full design process. Cable elements are included into computation and fill moduli of membrane elements are modified for simulating the influence of seams in warp and fill directions respectively. Force-finding for real stress distribution is utilized to deal with the influence of seams on stress distribution. Residual Pressure Method for cutting forms is adopted to avoid solving zero stress state, in which displacement restriction is imposed on the boundary in deflation analysis for actual construction. Based on a Datun air-supported structure in the shape of hemisphere and cylinder, which is designed to be 71.3 m in diameter and 39.15 m tall, three models with different considerations of weld seams are compared to reveal the influence of seams on stress distribution and cutting form. Measurement results of actual structure demonstrate excellent forming precision of the proposed design method for precise-forming.

Efficient construction of concrete shells by Pneumatic Forming of Hardened Concrete: Construction of a concrete shell bridge in Austria by inflation

AbstractConcrete shells are very efficient structures, spanning wide areas with very little construction material. Unfortunately the formwork needed to erect concrete shells is still very labor and material intensive. An alternative construction method which is more time and resource friendly is Pneumatic Forming of Hardened Concrete. A simple air cushion in combination with additional post‐tensioning tendons are used to transform a flat concrete plate into a double curved shell. This paper describes the design and construction of the first practical large‐scale application of this building method for the construction of the deer pass “AM 2” over the newly built two‐track rail Koralmbahn in Carinthia in the south of Austria. The plan measurements of the bridge are 36.2 m by 38.7 m with the height of the shell from the top edge of the foundations to the vertex mounting to 7.6 m. Within the construction process a flat 100 mm thick hardened concrete plate with a weight of 546 t was lifted to the designed double curved shell. This thin concrete shell served as lost formwork for the final bridge.

Control of an Architectural Cable Net Geometry

Tensioned cable nets can be used as a lightweight supporting formwork in the construction of thin concrete architectural shells. Meeting the structural and mechanical specifications of such shells requires precise positioning of the nodes of the cable net. We develop and experimentally verify a control strategy that uses measurements of the nodal positions to identify model parameters and calculate adjustments to the boundary cable lengths to achieve the desired form. As cable net lengths adjustments on the construction site are time-consuming, the number of control adjustments is minimized via a sparsity-promoting optimization-based method.