Reinforced Concrete Shells Research Articles

Laser Scanner-Based Hyperboloid Cooling Tower Geometry Inspection: Thickness and Deformation Mapping.

Hyperboloid cooling towers are counted among the largest cast-in-place industrial structures. They are an essential element of cooling systems used in many power plants in service today. Their main structural component, a reinforced-concrete shell in the form of a one-sheet hyperboloid with bidirectional curvature continuity, makes them stand out against other towers and poses very high construction and service requirements. The safe service and adequate durability of the hyperboloid structure are guaranteed by the proper geometric parameters of the reinforced-concrete shell and monitoring of their condition over time. This article presents an original concept for employing terrestrial laser scanning to conduct an end-to-end assessment of the geometric condition of a hyperboloid cooling tower as required by industry standards. The novelty of the proposed solution lies in the use of measurements of the interior of the structure to determine the actual thickness of the hyperboloid shell, which is generally disregarded in geometric measurements of such objects. The proposal involves several strategies and procedures for a reliable verification of the structure's verticality, the detection of signs of ovalisation of the shell, the estimation of the parameters of the structure's theoretical model, and the analysis of the distribution of the thickness and geometric imperfections of the reinforced-concrete shell. The idea behind the method for determining the actual thickness of the shell (including its variation due to repairs and reinforcement operations), which is generally disregarded when measuring the geometry of such structures, is to estimate the distance between point clouds of the internal and external surfaces of the structure using the M3C2 algorithm principle. As a particularly dangerous geometric anomaly of hyperboloid cooling towers, shell ovalisation is detected with an innovative analysis of the bimodality of the frequency distribution of radial deviations in horizontal cross-sections. The concept of a complete assessment of the geometry of a hyperboloid cooling tower was devised and validated using three measurement series of a structure that has been continuously in service for fifty years. The results are consistent with data found in design and service documents. We identified a permanent tilt of the structure's axis to the northeast and geometric imperfections of the hyperboloid shell from -0.125 m to +0.136 m. The results also demonstrated no advancing deformation of the hyperboloid shell over a two-year research period, which is vital for its further use.

Numerical Analysis of Textile Reinforced Concrete Shells: Force Interaction and Failure Types

In the case of solid slabs made of reinforced concrete that are usually subjected to bending, large areas of the structure are stressed well below their load-bearing capacity. Contrary to this are shell structures, which can bridge large spans with little material if designed according to the force flow. To improve the efficiency of ceiling slabs, we want to utilize the shell load-bearing behavior on a smaller scale by resolving the solid interior accordingly. In order to study a wide range of such constructions virtually, a parametric multi-objective simulation environment is being developed in an ongoing research project. The basic analysis approaches that were implemented are presented in this paper. The basic workflow, the used programs and material models, and their calibration on the tests on textile-reinforced concrete (TRC) samples are described.

Response of Reinforced Concrete Shell Elements Subjected to In-Plane and Out-of-Plane Shear

Response of Reinforced Concrete Shell Elements Subjected to In-Plane and Out-of-Plane Shear

Damage Characteristics and Dynamic Response of RC Shells Subjected to Underwater Shock Wave

Underwater bottom-sitting shell structures face threats from underwater explosion shock waves. To investigate the damage characteristics and dynamic response of bottom-sitting shell structures under underwater explosion shock waves, three-dimensional numerical models of semi-spherical and semi-cylindrical bottom-sitting reinforced concrete (RC) shells under underwater shock waves were established based on the Arbitrary Lagrangian–Eulerian (ALE) algorithm using LS-DYNA software. The influences of the shock wave transmission medium, explosive equivalent, explosive distance, hydrostatic pressure, and reinforcement on the damage characteristics and dynamic response of semi-spherical and semi-cylindrical bottom-sitting RC shell structures were studied. The results indicated that the damage and center vertical deformation of RC shells under underwater shock waves are significantly greater than those under air shock waves. With an increase in explosive equivalent or decrease in explosive distance, the damage and center vertical deformation of RC shells are increased. The damage to the inner surface of RC shells is more severe than the outer surface. The damage and center vertical deformation of RC shells can be reduced by bottom reinforcement and an increase in the diameter of the steel bar. The ‘hoop effect’ caused by hydrostatic pressure restrains the horizontal convex deformation and slightly decreases the macroscopic damage and vertical center deformation of the semi-spherical RC shell with an increase in hydrostatic pressure within the range of 0–2.0092 MPa. The hydrostatic pressure restrains the horizontal convex deformation of the semi-cylindrical RC shell. However, inward concave deformation of the shell center is increased by hydrostatic pressure, inducing an increase in the damage to and center vertical deformation of the semi-cylindrical RC shell. These findings may offer a reference for the construction and design of protective measures for underwater bottom-sitting shell structures.

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.

Fatigue Life Prediction for Reinforced-Concrete Low Domes

Abstract The study of fatigue of thin reinforced-concrete shells presents a complex modelling approach. This work is devoted to the numerical evaluation of the fatigue life of reinforced-concrete domes, with the concrete class of C25/30. For the formulation of a fatigue criterion under a symmetrically alternating load, with a very high number of cycles (106 ), the approach begins with the study of mechanical behavior under monotonic loading, related to the fatigue response. The numerical correlation results of the studied cases, based on a conservative fatigue limit of concrete in compression, enables to estimate the service life of these structures, knowing only the response under monotonic loading. The correlation formula proposed in this article can therefore directly estimate the service life of reinforced concrete domes, based on the maximum stress resulting from monotonic loading.

Modeling of Heat Transfer in Composite Bodies Reinforced with Tubes with Swirlers Through Which a Twisted Liquid Heat Carrier Moves in the Turbulent Mode. II. Model Problem

For a model problem, we compute the velocity form-parameters of the flows of heat carrier in tubes and the temperature fields in concrete cylindrical shells longitudinally and spirally reinforced with steel tubes filled with air pumped through these tubes. We compared the results obtained in the cases of reinforcement of these structures with smooth tubes and tubes with swirlers. It is shown that the application of tubes with swirlers significantly intensifies the process of heat removal from the structure as compared with the tubes with smooth inner surfaces if all other conditions are identical. It was discovered that, for some types of thermal boundary conditions, the efficiency of heat removal from the structure strongly depends on the direction of pumping of the heat carrier through the tubes. We also studied the influence of the parameters of reinforcement, the cross-sectional sizes of the tubes, and the velocity of motion of the heat carrier in the tubes on the temperature field formed in the shell. It was shown that the variations of these parameters make it possible to control, to a significant degree, the intensity of heat removal from the composite body. It is also demonstrated that some well-pronounced temperature edge effects may appear in the vicinities of edges of the reinforced-concrete shell.

An efficient elastoplastic model for the analysis of reinforced concrete shells

Shell structures made of Reinforced Concrete (RC) are used in many civil engineering applications. However, their analysis can frequently require a high computational cost, since fine mesh discretisations are needed for accurate solutions. In this work, a Finite Element (FE) for the analysis of RC shells is presented. It has four nodes and 24 degrees of freedom and both generalised stresses and displacements are interpolated. In particular, the assumed stress field a-priori satisfies equilibrium equations, thereby ensuring good accuracy and convergence properties. The heterogeneous material is described through a layer-wise approach in which a 3D stress yield function is used for concrete. Results confirm that the proposed FE is accurate on coarse meshes and shows good convergence properties if compared with state-of-art alternatives. The approach can be readily extended to model additional material layers, for example reinforcements applied for retrofitting purposes.

Investigating the Nonlinear Performance of Reinforced Concrete Shell Foundations

The present study involved a numerical investigation of two types of shell foundation having the same dimensions, these are the "Inverted" and "Upright" shell foundations. This type of foundation is considered as an alternative of the shallow foundations when the footing is subjected to a high load or used in a weak soil. The study includes a comparison between these two types of shell foundations. The results showed that the “Inverted” shell footing is superior to the “Upright” one in terms of Load carrying capacity, settlement and contact pressure. The study involved the effects of using different edge angles namely (10°, 20°, 30 and 40°). It was found that by increasing the angle the load-bearing capacity increased in case of “Inverted” shell footing, while it was decrease in the case of “Upright” shell footing. Different thickness of footing is considered, these are 160,200 and 240mm. it was found that by increasing the thickness of footing, the load-bearing capacity increased in both types of shell footing.

Müther’s shell structures in Germany – a solution to avoid demolition

This article is intended to give an overview of an almost forgotten construction form – a great innovation not only in the former German Democratic Republic (GDR) but for the whole world. This type of construction, made of reinforced-concrete shell structures, was brought to perfection, inter alia, by the outstanding civil engineer Ulrich Müther, who was one of the most important engineers in Germany. These structures stand out due to their appearance and their very slim design with large spans. The material shortage in the GDR catalysed the pioneering spirit of Ulrich Müther and resulted in the possibility of building those slender structures. This article should give an overview of the life and work of Ulrich Müther, highlighting his most important shell constructions. Furthermore, the current condition state and the possibilities for preserving these architectural artworks will be discussed. By taking the example of the Hyparshell in Magdeburg, it is shown that the use of the innovative and high-performance building material carbon-reinforced concrete as a strengthening or rehabilitation system allows to keep the slim and filigree nature of the concrete structures and prevent them from being demolished.

Influence of Class of Concrete on Oscillations of Thin-Wall Cylindrical Reinforced Concrete Shells

Thin-walled cylindrical shell made of reinforced concrete, is widely used in the construction of buildings and structures as coatings and forms of architecture of buildings. Thin-walled shell its shape can give entertainment to the architectural design of buildings, and their rigidity helps to block large spans, creating more closure of the room without additional supports. Another advantage of using cloud forms of structures is the efficiency of this design, since for the manufacture of shell forms of structures less construction material is spent than any other design for coating. The purpose of theoretical calculations and the studied excrement over reinforced concrete shells with different elastic modules, is to ensure reliability in the operation of buildings and structures, and to exclude accidents arising resonance phenomena of free vibrations of the shells from the effects of external forces (loads). On the basis of the laboratories of Komsomolsk-on-Amur state University in the laboratory of building materials and structures, experimental studies were conducted to determine the spectra of forced and free vibrations of the reinforced concrete shell with different elastic modules. The purpose of research on reinforced concrete shells is to determine the oscillation frequencies at different locations of the combined masses. The article deals with the theoretical calculation based on the equation of the theory of flat thin-walled shells, using the Bubnov-Galerkin method, by which we determine how the parameters of the shell affect the process of free oscillation.

Nonlinear Deformations of Stiffened Reinforced Concrete Shells

The paper discusses the process of non-linear deformation of shell structures made of reinforced concrete. A mathematical model of deformation in the form of the functional of full potential deformation energy is provided. The model is based on the Kirchhoff–Love hypotheses, and allows accounting for structure reinforcement with stiffeners. An orthogonal network of stiffeners, located from the concave side, is considered as the structure support. Type of load — external, uniformly distributed. The Ritz method is applied to the functional to reduce the variational problem of the functional minimum to a system of nonlinear algebraic equations. Then, for each load value, the problem is solved using iterative methods. Analysis of strength and stability of shallow shells of double curvature and rectangular planform is performed. Values of critical loads, deflection and stress fields are obtained. Curves of deflection depending on load are provided. All results are given in dimensionless parameters. The Mohr–Coulomb criterion was used to analyze concrete strength, and the Lyapunov criterion was used for stability analysis. Influence of the number of stiffeners reinforcing the shell on the resulting stress values is shown. It has been revealed that with account for physical non-linearity of concrete, when the dependence of stresses and deformations is curvilinear, deformations (and deflections as well) of shells increase in comparison with the linear-elastic solution. It has been also found that when nonlinearity is taken into account, redistribution of stresses over the shell field occurs (the maximum stresses shift towards the shell contour).

The Influence of Concrete Class on Vibrations of Thin-Walled Cylindrical Reinforced Concrete Shells

The article deals with the theoretical calculation of the cylindrical thin-walled shell of concrete of different classes with different modules of elasticity. Constructions in the form of a cylindrical shell are widely used in the construction of hydraulic facilities, nuclear power plants, stadiums and other large-span structures. During the operation of such facilities, they are affected by wind and snow loads, including the operation of equipment from the action of which there are forced oscillations. The imposition of own fluctuations of thin shells and forced vibration from external loads, which have not been taken into account by the designer or improper work in the course of construction that result in emergency situations. In addition to the theoretical calculation of the cylindrical closed thin-walled reinforced concrete shell, the article considers the results of the study as a practical part where it is shown how the forced oscillation occurs in different concrete classes and how the concrete class affects the Frequency spectrum of forced oscillations.

An Analytical Failure Envelope for the Design of Textile Reinforced Concrete Shells

Shells have the potential to considerably reduce material consumption in buildings due to their high structural efficiency compared to equivalent structures acting in bending. Textile reinforced concrete (TRC) is a promising material for the construction of thin concrete shells due to its strength, geometric versatility, and durability. Existing design methods for TRC shells predicts the local capacity by linear interpolation between experimentally determined values of strength in pure tension, pure bending, and pure compression. This simplification leads to a significant underestimation of strength in combined bending and compression. Relying entirely on physical test results also effectively prohibits exploration and optimisation of the shell design. This paper proposes a new analytical design approach for TRC which is instead derived from the properties of the concrete and reinforcement, and for the first time captures the highly non-linear interaction between axial and bending forces.A series of pure tension, pure bending, and combined bending and compression tests were carried out on TRC specimens of 15 mm and 30 mm thickness. The predicted strengths were conservative under combined compression and bending but otherwise accurate. For the specimens tested, the proposed method increases the predicted strength by a factor of up to 3.7 compared to existing methods, whilst remaining conservative, and hence its use could lead to significant material savings and new applications for TRC shells.

Technical Condition Assessment of Double-Layer Reinforced Concrete Shells of NPP-2006 and NPP-WWER TOI* Project Reactor Compartment

The paper considers a theoretical solution of the technical state estimation of protective hermetic shells. It proposes a solution duplicating the regular system that is independent of the time factor and is intended to determine and assess the stress-strain state of the protective hermetic shells during the acceptance and delivery period. The proposed approach increases the knowledge reliability of the shell current state which increases the NPP operation safety.

МОДЕЛЮВАННЯ ПОВЗУЧОСТІ ЗАЛІЗОБЕТОННИХ ОБОЛОНКОВИХ КОНСТРУКЦІЙ З УРАХУВАННЯМ АНІЗОТРОПІЇ ВЛАСТИВОСТЕЙ

МОДЕЛЮВАННЯ ПОВЗУЧОСТІ ЗАЛІЗОБЕТОННИХ ОБОЛОНКОВИХ КОНСТРУКЦІЙ З УРАХУВАННЯМ АНІЗОТРОПІЇ ВЛАСТИВОСТЕЙ

The Influence of Temperature Change on Crack Openings in a Reinforced Concrete Shell of Pressure Piping at Kruonis Pumped Storage Power Plant

Cracks are classified according to their geometry (length, width and depth), statistical parameters (mean and variance of the number of cracks per unit area), crack riskiness for structures, etc. In this paper, crack openings in a reinforced concrete shell of the pressure piping at Kruonis Pumped Storage Power Plant, which appeared due to temperature change, are analysed. Detailed analysis of cracks and deformations due to temperature changes was performed after the evaluation of the technical state of the pipeline. Specific illustrations, calculations and guidance for repair of these deteriorations were offered.DOI: http://dx.doi.org/10.5755/j01.erem.72.3.14865

Development of CSMM-based shell element for reinforced concrete structures

Reinforced concrete shell structures have been widely used in a variety of modern engineering applications. It is found from earthquake reconnaissance that reinforced concrete (RC) shell structures, such as nuclear containments, cooling towers, roof domes, shear walls, etc., are the key elements in resisting earthquake disturbances. This paper presents the development of a finite element analysis (FEA) program, SCS-3D, to predict the inelastic behavior of RC shell structures. In the program, a Cyclic Softened Membrane Model (CSMM)-based shell element is developed based on the degenerated shell theory with a layered approach and taking into account the CSMM developed at the University of Houston. To form the FEA program, the constitutive relation modules and the analysis procedure were implemented into a finite element program development framework, OpenSees developed at UC Berkeley. Several large-scale structural tests were employed to validate the developed FEA program, including RC panels subjected to a combination of shear and bending, three-dimensional RC shear wall and cylindrical RC tanks subjected to reversed cyclic loading.

Conservation of Tallinn seaplane hangars

The roof of Tallinn seaplane hangars is among the first, remaining and still-preserved early large reinforced-concrete shells in the world. The hangars were constructed in 1916–1917 by the Danish company Christiani & Nielsen for Tsarist Russian military purposes. The roof consists of three 36·4 × 36·4 m spherical thin reinforced-concrete shells and seven 36·4 × 6·8 m short cylindrical shells attached to them. In 2010–2012, the seaplane hangars were completely renovated for the Estonian Maritime Museum. The high-quality conservation works received the Europa Nostra Grand Prix award in 2013. This study aims to give a comprehensive overview of the conservation process of the Tallinn seaplane hangars from a combined engineering and heritage protection perspective. The paper focuses on the conservation techniques and methods used and explains why and how such approaches were selected. The main findings of previous technical studies are presented to stress the critical technical condition of the hangars before the conservation process. A brief overview of the history of the building is also given, with an emphasis on the uniqueness of the Tallinn seaplane hangars in construction history.

Strain-stress State and Strength of Chimney Reinforced Concrete Shell

The load-bearing part of a chimney pipe is a reinforced concrete shell of revolution. Its design model is a free-standing bar of the circular cross-section. It is recommended to conduct the analysis of cross-section guided by the branch construction norms VSN 286-90 [1]. This document was developed for “hand” calculations. Therefore, it contains simplifications which can be avoided. A method based on stricter presuppositions is suggested. Its basis is deformation plasticity theory. Concrete and steel are considered as nonlinear materials. The problem is reduced to a sequence of nonlinear equations which are solved by the method of variable parameters of stiffness. The approach does not require to predetermine a diagram of a limit state of the section, as it is formed in the process of solution. The criteria of a load-bearing capacity of the section are concrete and steel strains. Their maximum values are specified by construction norms.