Concrete Shell Structures Research Articles

Experimental and numerical study of wind effect on an ultra‐thin concrete triangular plan shell structure

AbstractSelf‐supporting concrete shell structures are highly efficient in distributing loads, which can result in very reduced thicknesses (ultra‐thin), giving them remarkable slenderness. Due to their geometric complexity, it is difficult to predict how they interact with wind action. The main aim of the present study is to assess the mean surface pressure coefficient distribution in a shell with a triangular plan shape and three supports for different angles of wind incidence. To determine the distribution of surface pressure coefficients and lift and drag force coefficients, an experimental study was carried out in a wind tunnel, and a numerical simulation study was performed through computational fluid dynamics. The experimental and numerical results were analyzed and compared, and making it possible to identify the most critical surface zones and wind incidences when the shell is under the wind action.

AI optimization and mathematical simulation validated by nondestructive testing for resonance frequency in advanced composite structures for bridge applications

This paper presents a novel approach integrating artificial intelligence (AI) optimization and mathematical simulation to predict the resonance frequency of nanoclay-reinforced concrete cylindrical shell structures intended for bridge applications. These composite structures, known for their enhanced mechanical properties, require precise evaluation of their vibrational behavior to ensure structural stability and longevity. Traditional methods for predicting resonance frequencies are often time-consuming and prone to inaccuracies, especially in complex materials like nanoclay composites. To address this, an AI-based optimization algorithm was developed, incorporating Particle Swarm Optimization (PSO) and a mathematical modeling to simulate resonance characteristics under varying material and geometric parameters. The mathematical modeling is validated using nondestructive testing (NDT) techniques, such as modal analysis, which provided real-world resonance data without damaging the structure. The nondestructive testing results is compared against the mathematical model to ensure accuracy and reliability. The integration of nanoclay into the concrete matrix significantly altered the vibrational properties, enhancing the stiffness and reducing damping losses, which is crucial for bridge applications where dynamic loads are prevalent. The optimized model not only predicted resonance frequencies with high accuracy but also demonstrated its potential for large-scale bridge infrastructure. This methodology offers a streamlined and robust tool for engineers, reducing the need for physical prototyping and providing enhanced design capabilities. Future research will focus on expanding the model to incorporate additional material behaviors and load conditions, furthering its application in civil engineering.

Computational Morphogenesis of Lightweight Continous Concrete Shell Structures by Utilizing Metaheuristic Algorithms

While the hanging model and physical prototyping are reliable methods for form-finding continuous lightweight shell structures, they cannot explore various design possibilities and consider multiple criteria in the design. This research aims to employ metaheuristic algorithms as a search tool for simultaneous form-finding (form exploration) and optimization, known as computational morphogenesis. This workflow consists of a parametric model and metaheuristic algorithms, which were implemented through costume Python codes. To evaluate the workflow, a double-curvature footbridge was defined, and the forms that GA found were in line with the anticipation. The GA found a better solution (0.04022) than the SA (0.064) by considering elastic energy change. In case study II, the optimal form of a continuous lightweight shell was explored by utilizing GA, PSO, SA, and the hybrid algorithm of GAPSO. The GA improved the fitness solution by 35% in the second run, while PSO showed similar results, and the hybrid GAPSO algorithm did not yield better results. The results show that the optimum result based on different algorithms was not significantly different. Nevertheless, hyperparameters considerably affected finding the global minimum. Moreover, NSGA-II was utilized, which let the designer trade-off between alternatives while considering other criteria.

Simulation and analysis of Automated Generalised Interleaved Layered Execution (AGILE) process for concrete shell structures

There has been increased research and interest in new methods of automated construction. This study presents a novel computational model for an augmented and generalised version of an automated construction process that was previously tested experimentally only for vertical concrete walls. The Automated Generalised Interleaved Layer Execution (AGILE) utilises a robotic arm for the alternating deposition of formwork and concrete, aiming to facilitate the creation of free-form concrete shell structures with enhanced design and construction versatility, overcoming the constraints of previous methods. The paper proposes an FEA analysis framework for this construction methodology, evaluating its implications, limitations, and challenges via a detailed case study that includes calculating lateral pressures and displacements throughout the construction process. Moreover, it introduces new failure criteria specific to this construction method, enabling the optimisation of the design and geometry of the shell and formwork, as well as the construction process details and parameters. The proposed computational analysis method allows designers to improve the performance of a broader range of shell structures while reducing construction costs, time, complexity, and environmental impact by replacing early-stage experimental methods with finite-element analysis. In conclusion, apart from generalising the limited process and identifying its design options and parameters, this study proposes a new and straightforward computational method for analysis of the AGILE construction method in its general form in the absence of any other analysis method and where only the experimental method in one particular case was used before, identifies four different construction failure modes, and paves the way for experimental verification and calibration of this analysis method for different specific setups and applications of this general construction process.

Topology and Thickness Optimization of Concrete Thin Shell Structures Based on Weight, Deflection, and Strain Energy

Topology and Thickness Optimization of Concrete Thin Shell Structures Based on Weight, Deflection, and Strain Energy

Form-finding for free-curved reinforced concrete shell structure considering structural performance and construction formwork

A computational approach for free-curved reinforced concrete (RC) shells that simultaneously considers structural performance and associated construction strategy is proposed. First, for the rapid design and construction process, a unit–formwork construction system (UFS), which uses multiple construction methods dependent on curvature, is developed, and a mock-up test is conducted to validate its effectiveness of UFS. Although the construction time was reduced, the construction costs were confirmed to be approximately twice those of conventional methods. Furthermore, the error between the measured surface coordinates of the plywood form board (PFB) and corresponding three-dimensional (3D) data is computed, and the study confirmed that the error in construction was within half of the required level. Second, a multi-objective optimization problem is formulated to obtain a shell configuration and a suitable distribution of curvatures on the PFB by minimizing the squared normal curvatures of a PFB surface and the strain energy of the completed shell structure under distributed loads. To assess the manufacturability of PFB, the normal curvatures on the surface of the PFB, which are represented as quadrilateral meshes, are calculated. Finally, numerical examples demonstrate the efficiency of the proposed method for designing a free-curved RC shell from the perspectives of structural design and constructability.

Robotic knitcrete: computational design and fabrication of a pedestrian bridge using robotic shotcrete on a 3D-Knitted formwork

The research project presented here aims to develop a design-informed manufacturing process for complex concrete shell structures in additive manufacturing and thus overcome limitations of traditional construction methods such as formwork- and labor intensity. To achieve this, an effort was made to merge the two technologies of CNC knitted stay-in-place formwork, known as KnitCrete, and robotically applied shotcrete, known as Shotcrete 3D Printing (SC3DP), and thereby reduce their respective limitations. The proposed workflow unites both digital fabrication methods into a seamless process that additionally integrates computational form finding, robotically applied fiber reinforcement, CNC post processing and geometric quality verification to ensure precision and efficiency. As part of a cross-university, research-based teaching format, this concept was implemented in the construction of a full-scale pedestrian bridge, which served as a demonstrator to evaluate the capabilities and limitations of the process. While overcoming some challenges during the process, the successful prove of concept shows a significant leap in digital fabrication of complex concrete geometry, reducing reliance on labor-intensive methods. The results shown in this paper make this fabrication approach a promising starting point for further developments in additive manufacturing in the construction sector.

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.

A layer-wise plasticity-based approach for the analysis of reinforced concrete shell structures using a mixed finite element

The analysis of reinforced concrete shell structures accounting for material nonlinearity is addressed. The structural response is numerically evaluated using a mixed shell finite element and a plasticity-based material behaviour. The finite element is a quadrilateral with four nodes and is based on self-equilibrated assumed stresses. The kinematic fields are interpolated only along the element boundary by polynomials up to the third order. The generalised shell stresses are evaluated through layer-wise integration of the Cauchy pointwise stresses. This allows appropriated three-dimensional elastoplastic constitutive equation to be employed and to include multiple reinforcing layers. The integration of the constitutive laws is performed using a dual decomposition method which preserves the assumed stress interpolation. Results, including civil engineering applications, show that the proposed approach is reliable and accurate in evaluating the static nonlinear equilibrium path. Additionally, the mixed finite element shows a quadratic rate of convergence in the collapse load and low error even for coarse meshes.

A prototype low-carbon segmented concrete shell building floor system

Concrete shell structures offer a mechanically efficient solution as a building floor system to reduce the environmental impact of our buildings. Although the curved geometry of shells can be an obstacle to their fabrication and implementation, digital fabrication and affordable robotics provide a means for the automation of their construction in a sustainable manner at an industrial scale. The applicability of such structures is demonstrated in this paper with the realisation of a large-scale concrete shell floor system, completed by columns, tie rods, and a levelled floor. The shell was prefabricated off-site in segments that can be transported and assembled on-site, and which can be disassembled to enable a circular economy of construction. This paper presents the conceptual and structural design; the automation of fabrication, thanks to an actuated, reconfigurable, reusable mould and a robotic concrete spraying process; the strategy and sequence of assembly and disassembly on-site using standard scaffold elements; and the sustainability assessment using life-cycle analysis. This prototype offers a reduction of about 50% of cradle-to-gate embodied carbon benchmarked against regular flat slabs before further improvement and optimisation.

3D printing and assembling of frame modules using printable strain-hardening cement-based composites (SHCC)

Despite all their advantages, load-bearing concrete shell structures with double curvatures are not frequently in use. The main reason is the complexity of their construction. In such a context, this article starts with a brief, critical review of existing technologies while their pros and cons are highlighted. Against that background, the authors propose a new approach for the highly automated fabrication of gridshell structures from variable modules reinforced with textile meshes. To demonstrate the feasibility of such a new technology, a demonstrator called ConDIT 1.0, a sphere-like shell structure composed of several frames, was designed and built. The frame modules were fabricated automatically using extrusion-based 3D printing and a printable, strain-hardening cement-based composite (SHCC). This article presents the design of ConDIT 1.0, the mechanical material characterization of printed SHCC, the technology of module production, the results of geometry verification for print modules using 3D scanning, and the procedure for the demonstrator’s assembly.

Textile Reinforced Concrete for free-form concrete elements: Influence of the binding type of textile reinforcements on the drapability for manufacturing double-curved concrete elements

Textile reinforced concrete (TRC) is a sustainable composite material consisting of a cementitious based matrix in combination with an open meshed technical textile reinforcement made of carbon or glass fibres. In the future, TRC could be increasingly used in the form of double-curved concrete elements with the aim of producing filigree yet load-bearing concrete shell structures. To assess whether a textile is suitable as a reinforcement structure in double-curved textile concrete elements, numerous properties need to be investigated and evaluated. The most important of these include good handling properties, bending stiffness tailored to the application, sufficiently pronounced mesh openings, and defect-free drapability. In the course of this work, biaxially reinforced knitted fabrics with five different stitch types (pillar open, pillar closed, tricot counterlaid, tricot closed and plain) were investigated to evaluate the above properties. The draping tests were conducted on a robot-controlled draping test apparatus and evaluated with the aid of an optical measuring system. In addition, the geometric relationship between surface curvature of the double curved elements and the shear angle of different textiles was used to classify the influence of the stitch type on the drapability. Finally, for a given double curved geometry, based on the results the selection of an appropriate textile reinforcement which fulfil the component requirements is carried out and a double curved TRC demonstrator element is prefabricated.

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.

Structural assessment of St. Charles hyperbolic paraboloid roof

Abstract At the time of completion in 1961, the roof of St. Charles Church became the largest unbalanced hyperbolic paraboloid structure in the United States and the only shell structure in Spokane, WA. Situated on an 8-acre site on the north side of the city, St. Charles is a modernist structure designed through partnership of Funk, Molander & Johnson engineers, architect William C. James and in consultation with Professor T.Y. Lin of the Structural Engineering Laboratory at the University of California, Berkeley. This asymmetric structure spans over 33.5 m (110 ft) and utilizes folded edge beams that taper from 1067 mm (42 in) at the base to a 76.2 mm (3 in) thickness at the topmost edge using regular strength reinforcing steel and concrete load carrying components. The novelty of the pre-stressed shell structure serves both architectural and structural design criteria by delivering a large, uninterrupted interior sanctuary space in materially and economically efficient manner. This structural assessment summarizes the roof’s historic design and construction according to the original construction documents, newspaper reports and historic photographs. The FEA is completed using UBC 1955 design loads and ACI 334 Concrete Shell Structures provisions.

Buildings of the John Paul II Center – a challenge for civil engineering and architecture

The buildings of the John Paul II Centre (CJPII) are located in Cracow-Łagiewniki on a heap of limestone sediments from the former "Solvay" Sodium Plant in Cracow. The area is called "White Seas" (Białe Morze) and is located in the natural depression of the Wilga river valley, between Św. Józefa hill in the north and Borkowska Hill (Góra Borkowska) in the south-west. The limestone sediments as a building substrate for CJPII buildings is unprecedented ground in the world and thus a challenge for civil engineering. The height of the heap reaches about 15 m and has retained the consistency of a white pulp until today. CJPII buildings are objects of the third geotechnical category, founded on a foundation slab of 0.8-m thickness, and in the central part of 0.45-m thickness. The slab is based on 200 reinforced concrete CFA-type drilled piles with a diameter of 1000 mm and 650 mm and length up to 26 m. The load-bearing structure of the CJPII buildings is a reinforced concrete frame and shell structure. The symbolism of the urban complex (e.g. the scale of the market square in Wadowice), located on a system of 200 piles above the post-industrial landfill/heaps of sediments, is ensured with architectural solutions referring to places connected with the life of John Paul II – during the occupation in 1940-1944 he was a student of Jagiellonian University in Cracow and the worker of the Solvay factory in the Podgórze district, in 1958 he became a bishop of Cracow, in 1967 – the cardinal (architectural details from the St. Mary Church and the Wawel Cathedral), 1978-2005 – the pilgrim-pope from Rome, who confirmed the mission of the Church continuing the tradition depicted in the early-christian churches on the wall mosaics (the Basilica of San Vitale and the Basilica of Sant’ Apollinare Nuovo in Ravenna).

Strengthening the 1960s UK Commonwealth Institute hyperbolic paraboloid roof

The Grade II*-listed 1960s roof to the former Commonwealth Institute consists of a central post-tensioned concrete hyperbolic paraboloid shell, typically only 75 mm thick, and is one of the few examples of large-scale concrete shell structures in the UK. After being unoccupied for a decade, in 2012, the Design Museum announced its plans to move into and redevelop the building. In order to make the space functional, the interior and foundations needed to be demolished and the entire 3100 m2, 2000 t roof held up 20 m above ground temporarily while the new structure was constructed underneath. This paper explores in detail the steps taken to assess the relatively delicate existing roof structure for the change in loading and future movements in both the temporary and permanent conditions and the resulting innovative strengthening, repair and temporary works required. Limited historical drawings and papers were available, and therefore, non-destructive testing and careful intrusive investigations were used to obtain more information on the as-built details. In order to determine the structural behaviour, hand calculations were conducted to back-calculate the original design intent, and computer modelling was used to conduct sensitivity analyses of the load paths.

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

Structural, daylighting, and energy performance of perforated concrete shell structures

In this work, a computational interdisciplinary design approach is used to integrate assessment of the structural and environmental performance of perforated concrete shell structures. Design parameters that co-exist in these disciplines and relevant performance criteria are identified. Questions result: how do these design parameters affect performance? What is the tradeoff between performance in each? Computer-aided design tools are used for form generation and performance assessment. Statistical analyses are used to study the sensitivity of performance to each parameter. Finally, the perforation ratio is found to be the most significant parameter affecting both disciplines; a value ≤ 10% to 20% is recommended for shell structures when translucent glazing is installed without shades in a Boston-type climate.

Shell-supported footbridges

Abstract Architects and engineers have been always attracted by concrete shell structures due to their high efficiency and plastic shapes. In this paper the possibility to use concrete shells to support footbridges is explored. Starting from Musmeci’s fundamental research and work in shell bridge design, the use of numerical form-finding methods is analysed. The form-finding of a shell-supported footbridge shaped following Musmeci’s work is first introduced. Coupling Musmeci’s and Nervi’s experiences, an easy construction method using a stay-in-place ferrocement formwork is proposed. Moreover, the advantage of inserting holes in the shell through topology optimization to remove less exploited concrete has been considered. Curved shell-supported footbridges have been also studied, and the possibility of supporting the deck with the shell top edge, that is along a single curve only, has been investigated. The form-finding of curved shell-supported footbridges has been performed using a Particle-Spring System and Thrust Network Analysis. Finally, the form-finding of curved shell-supported footbridges subjected to both vertical and horizontal forces (i.e. earthquake action) has been implemented.

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.