Compressed Elements Research Articles

Load-bearing capacity and failure mechanism of integrated fluted-core composite sandwich cylinders

Fluted-core sandwich composites have a promising prospect in lightweight engineering applications due to their superior strength-to-weight ratio. Herein, trapezoidal fluted-core sandwich composite cylinders made of carbon fiber-reinforced plastics were designed and integrally fabricated to improve the deformation stability. The effects of circumferential cell number and wall thickness on the bearing characteristics and failure mechanism were assessed by quasi-static uniaxial compression and finite element analysis (FEA). The results revealed that local buckling was likely to appear in sandwich cylinders with small number of cells, leading to undesirable bearing capacity and inferior material utilization. Increasing the cell number and wall thickness could effectively improve the critical local buckling load. Considering the lightweight design requirements, the specific buckling load could be enhanced by increasing the core-rib to facesheet thickness ratio. Nevertheless, with the increase of the thickness ratio, the specific peak force increased rapidly first and then was almost saturated. Furthermore, an analytical approach with high computational efficiency was employed to predict the critical local buckling load. The theoretical predictions agreed well with the FEA results for the cylinders with large number of cells. Compared to other published composite cylindrical shells, the typical specimen fabricated in this study exhibited the highest specific peak force (563.4 kN/kg) and superior specific compressive strength (37.98 MPa/kg), demonstrating great application potential for large-size and lightweight launch-vehicle shell structures.

Hybrid Column Designs for Industrial Buildings

The article analyzes the possible application of hybrid steel-concrete structures for industrial buildings, presents new developments in the structural forms of columns, supports, as well as ways to interface steel-concrete elements. The calculation of the steel-concrete step column is performed, the analysis of the reduction in steel consumption and other advantages of hybrid steel-concrete structures in comparison with traditional solutions of steel and reinforced concrete columns is made. The use of hybrid steel-concrete structures is effective mainly in compressed elements: columns, posts, supports, compressed parts of beams and trusses, crane beams, frame and arched structures.

Einsatz einer Knautschzone bei der Sanierung des Gotschnatunnels, Klosters (CH)

AbstractDuring the renovation of the Gotschna Tunnel from 2019 to 2020, prefabricated elements made of Compex were used for the first time as a deformable yielding zone in the invert zone. The client, construction management, construction company and supplier of the compressible elements worked closely together to implement the design specifications. Consequently, the expectations of the special building material in terms of the production quality of the prefabricated elements and handling on the construction site were more than met. The parties involved in the construction thus see potential for further applications and further developments of Compex.

Learning to compress videos without computing motion

Video has become an increasingly important part of our daily digital communication. With the development of higher resolution contents and displays, its significant volume poses significant challenges to the goals of acquiring, transmitting, compressing and displaying high quality video content. In this paper, we propose a new deep learning video compression architecture that does not require motion estimation, which is the most expensive element of modern hybrid video compression codecs like H.264 and HEVC. Our framework exploits the regularities inherent to video motion, which we capture by using displaced frame differences as video representations to train the neural network. In addition, we propose a new space–time reconstruction network based on both an LSTM model and a UNet model, which we call LSTM-UNet. The combined network is able to efficiently capture both temporal and spatial video information, making it highly amenable for our purposes. The new video compression framework has three components: a Displacement Calculation Unit (DCU), a Displacement Compression Network (DCN), and a Frame Reconstruction Network (FRN), all of which are jointly optimized against a single perceptual loss function. The DCU removes the need for motion estimation found in hybrid codecs, and is less expensive. In the DCN, an RNN-based network is utilized to compress displaced frame differences as well as retain temporal information between frames. The LSTM-UNet is used in the FRN to learn space time differential representations of videos. Our experimental results show that our compression model, which we call the MOtionless VIdeo Codec (MOVI-Codec), learns how to efficiently compress videos without computing motion. Our experiments show that MOVI-Codec outperforms the Low-Delay P (LDP) veryfast setting of the video coding standard H.264 and exceeds the performance of the modern global standard HEVC codec, using the same setting, as measured by MS-SSIM, especially on higher resolution videos. In addition, our network outperforms the latest H.266 (VVC) codec at higher bitrates, when assessed using MS-SSIM, on high resolution videos. The MOVI-Codec project page can be found at https://github.com/Meixu-Chen/MOVI-Codec.

Simplified Numerical Model Development for Advanced Design of Lightweight‐Concrete Encased Cold‐Formed Steel Compressed Elements

The utilization of cold‐formed steel (CFS) elements has become more popular recently, due to their cost efficiency and feasibility in construction work. Nevertheless, since such elements are subjected to a variety of complex stability issues, numerous approaches to strengthening have been examined. Namely, CFS members were braced by using lightweight concrete through a previous experimental program. A simplified finite element model was performed consistently with the previous experimental work, to estimate the ultimate load of encased CFS members subjected to compression. The main aim of this research was to overcome the difficulties of modeling the concrete block by substituting the volume element with springs. In addition, a practical equation was proposed to predict the stiffness of springs, and an imperfection amplitude was set to obtain the design capacity of braced CFS compressed elements.

ФИЗИЧЕСКАЯ СУТЬ СОПРОТИВЛЕНИЯ БЕТОНА И ЖЕЛЕЗОБЕТОНА ОТ ДИСЛОКАЦИЙ ДО ТРЕЩИН

The physical essence of resistance of concrete and reinforced concrete from dislocations, micro-cracks to macro-cracks and its experimental justification is investigated. For the "eight" structure of crystals of different materials (concrete and steel) a general model in the form of a sphere was developed. For it the summation of volume sectors, levels - radii from the matrix of sliding planes (including octahedral and pure shear) is written down. This uses an alternative to the theory of plasticity in the form of energy interpretation on the surface of the sphere and determining the integral of the mean square of the tangential stresses. It is important to obtain dislocations in the microcrack, angular and linear deformations, and displacements in a representative volume of the concrete cube. As the intensity increases, the deformation process proceeds already to the mainline cracks, where the double-concole elements of tension, compression, transverse shear and torsion (its internal parameters) are refined. Significant issues are the dilatation modulus and transverse coefficient, for which functions have been developed at the stages of the stress-strain state of concrete during the evolution of the transition from crack formation to main cracks. Concrete compression and tension diagrams for strain intensity or minimum pure shear use shear stresses. The fundamental difference of the stress diagram in the downward section is the use of the ultimate resistance of the concrete. Stress reduction in a material whose failure has a "tear-off" character is an unnatural phenomenon, and the limiting resistance of concrete at and reduction of prism strength at the i-th step is . The deformation pattern of concrete during the formation of earlier microcracks and then later main cracks is oriented along for compression or across the loading line for tensile force.

ДЕФОРМИРОВАНИЕ ФИБРОБЕТОНА ПРИ ОДНОКРАТНОМ ДИНАМИЧЕСКОМ ВОЗДЕЙСТВИИ С УЧЕТОМ ВЛИЯНИЯ НАЧАЛЬНЫХ НАПРЯЖЕНИЙ ОТ СТАТИЧЕСКОЙ НАГРУЗКИ

An analysis of the experimental studies presented in the scientific literature indicates that the strength and deformability of fiber-reinforced concrete under dynamic additional loading may depend on the initial level of stresses caused by a preliminarily applied static load. In this regard, the purpose of this study was to build improved models of fiber-reinforced concrete deformation of operated fiber-reinforced concrete structures of bearing systems of buildings and structures during their dynamic additional loading, taking into account the nonlinearly elastic law of material deformation at the stage of loading with a static load, as well as changes in the parameters of viscous resistance during loading. As a model of the force resistance of fiber-reinforced concrete of loaded fiber-reinforced concrete structures during their dynamic additional loading caused by an emergency situation, the Kelvin-Voigt model for an elastic-viscous body was adopted. On the basis of the adopted model, an analytical solution of the differential equation of uniaxial compression of fiber-reinforced concrete was obtained under its single dynamic additional loading from an arbitrary level of initial stresses acting in it from a previously applied static load. A step-iterative approach to determining the parameters of state diagrams of fiber-reinforced concrete under static-dynamic loading conditions is proposed. An analysis of the obtained dependences between stresses and strains shows that an increase in the level of initial stresses acting in a compressed concrete element at the moment a dynamic load is applied to it leads to a decrease in the dynamic strength of concrete with the same impact parameters.

ЭКСПЕРИМЕНТАЛЬНЫЕ ИССЛЕДОВАНИЯ ДИНАМИЧЕСКИХ СВОЙСТВ КОРРОЗИОННО-ПОВРЕЖДЕННЫХ СЖАТЫХ ЖЕЛЕЗОБЕТОННЫХ ЭЛЕМЕНТОВ

There are practically no results of experimental studies of elements made of compressed reinforced concrete damaged by corrosion in the scientific literature. As a result, it is almost impossible to reliably assess the state of deformation-deformation of these structures, especially under dynamic loads. For experimental studies, 37 samples of reinforced concrete were made-columns of square cross-section with dimensions of 100x100 mm, height of 700 mm. Local corrosion damages of concrete and reinforcement were created in reinforced concrete samples, while a concentrated (37%) hydrochloric acid (HCL) solution was used as an aggressor to accelerate the corrosion of elements. The article describes experimental studies on changing the dynamic properties of reinforced concrete elements that undergo corrosion during eccentrically compression. Based on strain gauge data, it was found that corrosion damage leads to a decrease in the height of the compressed concrete section by reducing the cross-section of the stretched reinforcing bars, as well as to the lack of joint work of reinforcing bars with concrete. According to strain measurement data, deformations of uncompressed and undamaged sections were obtained, which showed that the deformation diagrams fundamentally differ in their contour. The results obtained as a result of the study of the nature of deformation of reinforcement and concrete allowed us to assess the state of deformation stress of damaged and non-corroded structures according to the parameter ne-1 / r (curvature). The effect of corrosion damage on the nature of destruction of eccentrically compressed elements has been established.

Evaluation on story-based stability in multistory frame under various restraining conditions

To estimate the critical buckling load, the effective length approach isolates a critical column inside a frame and analyses the rotational and translational stiffness of its end restraints. Although designers proportion leaning columns with K = 1, which is the correct K-value based on the column failure mode, buckling analysis fails to predict these values due to the influence of nearby columns and beams. In current design practise, beam-to-column and column-base connections in steel frames are typically idealised as wholly pinned or totally stiff connections. Various studies have demonstrated, however, that the semi-rigid behaviour of the systems beam-column connections affects the internal efforts in the structural parts, therefore the buckling critical loads and corresponding effective lengths of the compressed elements were also taken into account. In this study, a numerical analysis of the Effective length of column in multi-storey frames with single bay and dual storey (G + 2) is tried with variation in storey heights using rigid and semi-rigid jointed frames with rigid and semi-rigid jointed frames is undertaken. Webber's empirical equations are efficient in rigid frame systems for calculating the effects of adjoining columns and their critical buckling loading of the isolated column. The effective length K factor with the variance in critical length with different storey heights acquired a greater value when compared to other models. Moment rotations in semi-rigid jointed frames were influenced by differences in fixity factors in semi-rigid frames. The rigidity coefficient dropped as the stiffness coefficient increased, leading in an increase in the effective length factor.

ВЛИЯНИЕ ПОЛЗУЧЕСТИ НА НАПРЯЖЕННО-ДЕФОРМИРОВАННОЕ СОСТОЯНИЕ ЖЕЛЕЗОБЕТОННЫХ МНОГОЭТАЖНЫХ ЗДАНИЙ

With long-term action of the load in concrete and reinforced concrete, an increase in inelastic deformations occurs, which is associated with the creep of concrete. The viscous properties of any concrete are determined by its measure of creep and creep coefficient. Modern software systems make it possible to calculate structures taking into account the rheological properties of concrete. To analyze the stress-strain state of a multi-storey building, taking into account the long-term deformation of concrete, a 45-storey model of a frame building was calculated. The creep characteristics of concrete were set according to Eurocode 2. The results of the calculation showed that the creep of concrete during its long-term deformation leads to a redistribution of forces in the building elements, an increase in floor slab deflections and an increase in the buckling of eccentrically compressed elements. A comparative analysis of the creep coefficients of high-strength concretes according to Eurocode 2 and SP 63.13330.2018 was carried out, which showed the need for an experimental study of the values specified in SP 63.13330.2018 due to a single coefficient for concretes of class B60-B100.

Влияние циклов замораживания и оттаивания на несущую способность внецентренно сжатых элементов железобетонных конструкций

As a result of calculations in a probabilistic formulation, the initial data for which were formed in accordance with the results of the experiment, the following is shown. The impact degree of freezing and thawing cycles on the bearing capacity of eccentrically compressed elements of reinforced concrete structures depends on such structural factors as longitudinal force eccentricity, flexibility and percentage of longitudinal reinforcement. The identified features must be taken into account when calculating and designing elements of reinforced concrete structures subjected to eccentric compression under conditions of freezing and thawing cycles.

ПРОЧНОСТЬ СЖАТЫХ И ВНЕЦЕНТРЕННО СЖАТЫХ ЖЕЛЕЗОБЕТОННЫХ ЭЛЕМЕНТОВ С ЗОННЫМ АРМИРОВАНИЕМ ИЗ СТАЛЬНОЙ ФИБРЫ

The real nonlinear diagrams of concrete, reinforcement and steel-fiber concrete under dynamic loading are formulated and analytically described. Theoretical and experimental studies of the operation of compressed and non-centrally compressed elements with different levels of load application eccentricity under static and short-term dynamic loads are carried out. 3 reinforced concrete and 9 steel-fiber concrete elements were manufactured and tested for short-term dynamic load under central and off-center compression. New experimental data characterizing the process of deformation and destruction of steel-reinforced concrete models of columns have been obtained. Also, the schemes of destruction and cracking, the dependence of changes in the dynamic load over time, the movement of concrete, reinforcement and steel-fiber concrete over time are obtained. A method has been developed for calculating the strength and stability of such elements, taking into account the reinforcement of the section with steel fiber concrete. The influence of the use of zone reinforcement with steel fiber of compressed and non-centrally compressed reinforced concrete elements is numerically analyzed. The results of the calculation according to the developed methodology are compared with the results of experimental data. The optimal variant of the application of zone reinforcement made of steel fiber for compressed and non-centrally compressed elements operating under static and short-term dynamic loads is proposed. The analysis of the calculation results based on the developed method for calculating the strength of normal sections of non-centrally compressed reinforced concrete and steel-fiber concrete, based on the deformation model, and their comparison with the data of experimental studies under short-term dynamic loading show that the deviations are on average 10-18 %, which indicates that the developed method has sufficient accuracy to solve practical problems.

Taking into account the operation of compressed composite polymer reinforcement when calculating the strength of compressed elements according to the deformation model

Taking into account the operation of compressed composite polymer reinforcement when calculating the strength of compressed elements according to the deformation model

НЕСУЧА ЗДАТНІСТЬ ПОШКОДЖЕНИХ ЗАЛІЗОБЕТОННИХ ДВОТАВРОВИХ КОЛОН

Abstract. The article presents the results of experimental and theoretical studies of the work, the parameters of the stress-strain state and the methodology for calculating the residual bearing capacity of reinforced concrete I-section columns damaged during operation and combat operations. The analysis of the literature on this subject made it possible to study the main factors affecting the residual bearing capacity, namely: the depth of damage; the angle of inclination of the damage front; relative eccentricity of application of external compressive force. A three-factor three-level experimental design has been developed. The conducted field tests of prototypes of damaged reinforced concrete columns made it possible to determine the parameters of the stress-strain state of damaged elements and their actual residual bearing capacity. On the basis of the performed experimental-statistical modeling, the main factors influencing the residual bearing capacity of damaged elements have been established. The prerequisites for calculating damaged reinforced concrete I-beams are proposed and equilibrium equations are drawn up. The proposals set out in the article are based on the main provisions of the current norms and expand the effect of their use. The analysis of influence of various factors on bearing capacity of the damaged I-beam reinforced concrete columns is carried out. It was found that the columns can withstand a maximum destructive load of 1738 kN at an angle of inclination of the damage front of 60о and in the absence of relative eccentricity. And the least destructive load columns can withstand in the absence of the angle of the damage front, and the relative eccentricity will be 1/8 of the applied load. On the basis of the conducted researches the technique of definition of reliably substantiated residual bearing capacity of reinforced concrete compressed elements of a T-profile profile damaged in the course of operation is developed. This makes it possible to determine the possibility of further trouble-free operation of structures or the need for their reinforcement or reconstruction.

REGULATION OF STRESS-DEFORMED STATE IN COMPRESSED ELEMENTS OF STEEL FRAMES

The article is devoted to the regulation of the stress-strain state in the compressed elements of steel frames under full operating load. It is proposed to perform reinforcement of such elements with different end eccentricities of load application by rational regulation of the stress-strain state in the reinforcement elements. It is shown that the use of SDS adjustment for frame racks increases their bearing capacity and reduces deformability and welds. The new proposed technology of SDS regulation and possible constructive decisions are offered. Numerical experiment revealed high efficiency of application of the proposed solutions during the reconstruction and reinforcement of the metal frame system. The implementation of the proposed method of SDS regulation confirmed its effectiveness.

Enchainment of the Coefficient of Structural Quality of Elements in Compression and Bending by Combined Reinforcement of Concrete with Polymer Composite Bars and Dispersed Fiber.

Polymer composite reinforcement (PCR) and its use to produce high-quality concrete with the right design and technological and formulation solutions can demonstrate the results obtained with the steel rebars. This article discusses the synergistic effect from the combined reinforcement of concrete with traditional polymer rods and dispersed fiber, which, as a result, lead to an increase in strength and deformation characteristics and an improvement in the performance of compressed and bent structural elements. The synergistic effect of the joint work of polymer rods and dispersed reinforcement is considered in the context of relative indicators (structural quality factor CSQ), showing the relationship between strength characteristics and concrete density. The behavior of glass fiber in a cement matrix and the nature of its deformation during fracture were studied by scanning electron microscopy. It is shown that the use of PCR and dispersed reinforcement makes it possible to increase the strength characteristics of concrete in bending. In quantitative terms, the achieved results demonstrated that the CSQ values of a beam reinforced with a PCR frame with the addition of glass fiber were 3.4 times higher compared to the CSQ of a beam reinforced with steel reinforcement frames. In addition, for a beam reinforced with a PCR frame with no fiber addition, the CSQ values were three times higher.

Nonlinear seismic evaluation of confined masonry structures using equivalent truss model

Modern Performance-Based Design (PBD) approach for seismic analysis of building structures is based on the evaluation of nonlinear response to earthquake-induced demand and assessment of performance based on the lateral displacements/drifts. One of the key challenges associated with the application of PBD for seismic evaluation of confined masonry (CM) structures is the development of an adequate numerical model for simulating nonlinear response at different seismic demands. In this paper, an Equivalent Truss Model (ETM) has been proposed for nonlinear analysis of CM structures. The model is based on a truss analogy concept, where a CM wall is idealized as a truss consisting of pin-ended elements. A masonry panel is modelled as a compression element (strut), while horizontal and vertical reinforced concrete (RC) confining elements are modelled either as struts or tension elements (ties). ETM is essentially a macro-model that simulates nonlinear behaviour of a CM wall through lumped nonlinearity of masonry struts, while RC confining elements show linear elastic behaviour. The proposed model has been validated using the results of experimental studies on CM walls subjected to in-plane reversed cyclic loading. The paper also presents a case study, in which ETM was applied for seismic evaluation of an existing three-storey CM apartment building located in an area of moderate seismic hazard in India using nonlinear static analysis. The damage states for PBD were established based on past research studies on CM structures. A comparison of the results of conventional force-based design and PBD analyses showed that ETM can be used in conjunction with the PBD approach to evaluate existing CM buildings and also optimize design solutions for new buildings, which were developed using a conventional, force-based seismic design approach.

Prospects For Application Of Non-Metal Composite Valves As Working Without Stress In Compressed Elements

An analysis is given of the possibility of using glass-composite non-metallic reinforcement in compressed concrete elements. The results of comparison of studies of strength and deformability with high-strength composite and steel (class A800) working reinforcement in our country and abroad are presented. Proposals are given for further research of composite reinforcement as longitudinal in compressed elements.

Post-fire behaviour and resistances of S690 high strength steel welded I-section stub columns

The cross-sectional behaviour and residual compression resistances of S690 high strength steel welded I-section stub columns after exposure to elevated temperatures up to 950 °C have been investigated, underpinned by testing and numerical modelling, and fully presented in this paper. The testing programme used three S690 high strength steel welded I-sections — I-80×60×5, I-100×100×5 and I-140×70×5, and for each aforementioned I-section, seven geometrically identical stub column specimens were prepared and tested after exposure to different levels of elevated temperature (including 30 °C, 300 °C, 600 °C, 700 °C, 800 °C, 900 °C and 950 °C). This was followed by a numerical modelling programme, where finite element models were developed and validated against the post-fire stub column test results and then adopted to conduct parametric studies to generate further numerical data over a wide range of cross-section dimensions. Given that there are currently no available design standards for high strength steel structures after exposure to elevated temperatures, the relevant ambient temperature design rules, as set out in the European code, American specification and Australian standard, were assessed, using post-fire material properties, for their applicability to S690 high strength steel welded I-section stub columns after exposure to elevated temperatures up to 950 °C. The results of the assessments revealed that (i) all three sets of codified ambient temperature slenderness limits for internal and outstand plate elements in compression are generally accurate when used for cross-section classification of S690 high strength steel welded I-section stub columns after exposure to elevated temperatures and (ii) the ambient temperature local buckling design rules (i.e. slenderness limits in combination with effective width methods), as set out in the three considered design standards, are capable of providing accurate and consistent post-fire compression resistance predictions for S690 high strength steel welded I-section stub columns.

Probabilistic Approach to Limit States of a Steel Dome.

In this paper, Numpress Explore software, developed at the Institute of Fundamental Technological Research of the Polish Academy of Sciences (IPPT PAN), was used to conduct reliability analyses. For static-strength calculations, the MES3D module, designed by the authors, was employed. Ultimate limit state was defined as condition of non-exceedance of the capacity value, resulting from the stability criterion of the bent and compressed element. The serviceability limit state was defined as the condition of non-exceedance of allowable vertical displacement. The above conditions constitute implicit forms of random variable functions; therefore, it was necessary to build an interface between the Numpress Explore and MES3D programs. In the study, a comparative analysis of two cases was carried out. As regards the first case, all adopted random variables had a normal distribution. The second case involved a more accurate description of the quantities mentioned. A normal distribution can be adopted for the description of, e.g., the randomness in the location of the structure nodes, and also the randomness of the multiplier of permanent loads. In actual systems, the distribution of certain loads deviates substantially from the Gaussian distribution. Consequently, adopting the assumption that the loads have a normal distribution can lead to gross errors in the assessment of structural safety. The distribution of loads resulting from atmospheric conditions is decidedly non-Gaussian in character. The Gumbel distribution was used in this study to describe snow and wind loads. The modulus of elasticity and cross-sectional area were described by means of a log-normal distribution. The adopted random variables were independent. Additionally, based on an analysis of the elasticity index, the random variables most affect the failure probability in the ultimate limit state and serviceability limit state were estimated.