Yuri Ribakov

Ariel University · Department of Civil Engineering

The present study summarizes a long-term 14 - year research program, focused on investigation of reinforced concrete (RC) two - layer beams (TLB). In the frame of this program the TLB idea was proposed in 2007. The idea was based on using high strength steel fibered concrete (SFHSC) in the compressed zone of RC bending elements and normal strength...

This study aims to select an eco-friendly earthquake-resistant design using life-cycle assessments (LCAs). The study compares LCAs of three retrofitting cases: concrete shear-wall strengthening (Case 1); reinforced concrete column jacketing with shear-wall strengthening (Case 2); and high-damping rubber bearing base isolation with viscous fluid dam...

The theoretical stress-strain model for compressed composite cement materials’ behavior without empirical coefficients was proposed by Iskhakov in 2018. This model includes the following main parameters describing concrete behavior: stresses and strains corresponding to the border between the elastic and non-elastic behavior stages of a concrete sp...

Many critical concreting activities require the determination of the in-place concrete strength. It can be costly to wait too long to execute these activities, but acting too early can have a negative impact on structural performance. Conventional moulded concrete cylinders and alternative strength assessment methods such as the maturity method are...

The paper deals with composition design of self-compacting concrete containing blast furnace granulated slag and polycarboxylate type superplasticizer in a wide range of concrete strength classes. Optimal superplasticizer content, cement, and blast furnace slag consumptions are obtained from the viewpoint of minimum water demand and water-cement ra...

Ground blast-furnace slag is one of the waste products available in Ukraine and other countries. It is obtained at metallurgical enterprises in huge quantities and can be efficiently used for concrete production. The article is devoted to obtaining experimental-statistical models of the influence of technological factors that determine the composit...

This study suggests an intensive green roof as part of a sustainable and hazard-resistant conceptual design for the retrofitting of old buildings in Israel. The roof is suggested to be built with waste-based materials. A five-story reinforced concrete residential building was retrofitted with: Case 1: concrete wall strengthening (CWS)-conventional...

In this work, a new method for solving an optimal semi-active control problem is formulated. It extends previously published results by addressing a continuous-time bilinear quadratic regulator control problem, defined for a structure that is controlled by multiple controlled hydraulic dampers and subjected to external, a priori known deterministic...

Combining different fiber types may improve the mechanical properties of fiber reinforced concrete. The present study is focused on investigating hybrid fiber reinforced concrete (HFRC) with steel and basalt fiber. Mechanical properties of fiber reinforced fine-grained concrete are investigated. The results demonstrate that using optimal steel and...

Loading rates affect the behavior of concrete specimens from the beginning of the loading process until failure. At rather high loading rates, longitudinal deformations in concrete specimens under a compressive load are practically elastic up until the ultimate limit state. It has been previously demonstrated that transverse deformations effectivel...

This study evaluated Life-Cycle Assessment (LCA) of two different designs of high-performance concrete beam: (1) a single-layer beam (SLB) that consisted of steel fibered high-strength concrete in both the compression and tensile zones and (2) a two-layer beam (TLB) that consisted of steel fibered high-strength concrete and normal-strength concrete...

Investigation of buckling under tension is highly important from theoretical and practical viewpoints to ensure safety and the proper performance of mechanical systems. In the present work, tensile buckling is investigated experimentally, and the critical force is measured in systems where one end of an elastic tensile rod slides along a straight g...

This study continues a series of investigation of two‐layer beams (TLB), performed by the authors. This series includes developing an idea of a TLB, testing steel fibered high strength concrete (SFHSC) as material, testing simple supported and continuous two‐span TLBs. The present research is focused on testing full‐scale prestressed simple support...

This study aimed to determine the difference between two alternatives for pre-stressed normal-strength concrete beams according to life-cycle assessments (LCAs): strengthening the PNSC (pre-stressed normal-strength concrete) beam on one side with a 70 mm width, steel-fibered, high-strength concrete layer (Case 1) and strengthening the PNSC beams by...

This study continues a series of theoretical and experimental investigation of two‐layer beams (TLBs), performed by the authors. Such beams consist of normal strength concrete (NSC) layer in the tensile zone and steel fibered high strength concrete (SFHSC) in the compressed one. The present research is focused on comparison of prestressed single la...

Research focused on concrete tensile strength is rather limited compared to that of compressive strength. In most cases concrete tensile strength is neglected in design, but in special cases (gas holders, tankers, nuclear plants, big diameter pipes, etc.) this strength is dominant. Although research related to concrete tensile strength has increase...

This paper introduces a new method for the computation of an optimal semi-active feedback of a plant, which is controlled by multiple semi-active control dampers and subjected to external, a priori known deterministic disturbance input. The control force is written in bilinear form in equivalent damping gains and a linear combination of the states....

This study addresses an optimal control problem that is defined for a type of bilinear excited plant, multiple control inputs, a biquadratic finite horizon performance index, and control trajectory constraints. A novel sequence of improving functions, which suits this problem, is derived, and the corresponding Krotov's algorithm is formulated. The...

As known, high-strength compressed concrete elements have brittle behavior, and elastic-plastic deformations do not appear practically up to their ultimate limit state (ULS). This problem is solved in modern practice by adding fibers that allow development of nonlinear deformations in such elements. As a rule, are applied steel fibers that proved h...

Optimal process control with control constraints is a challenging task related to many real-life problems. In this paper, a single input continuous time constrained linear quadratic regulator problem, is defined and fully solved. The constraints include both bilinear inequality constraints and customary control force bounds. As a first step, the pr...

The paper deals with experimental results on temperature and curing duration influence on strength properties of high strength concrete (HSC). Dependences for calculating strength of high strength concrete at 12 h, 1, 7 and 28 days are developed for normal hardening conditions. Equations, allowing considering curing temperature in diapason between...

This paper deals with positive Gaussian curvature reinforced concrete (RC) shallow shells and panel shells, including monolithic connection between the shell itself and its edge elements, such as columns, diaphragms, walls, etc. Connections of such shells with edge elements are subjected to additional bending moments and shear forces due to horizon...

This study focused on lifecycle assessment (LCA) and evaluation of the sustainable performance of structures retrofitted by adding stiff diaphragms or by using seismic isolation systems. To analyze the mitigation measures, methodological options addressing LCA uncertainties were used. For this purpose, a two-stage, nested, mixed, and balanced ANOVA...

Semi-active systems provide an attractive solution for the structural vibration problem. A useful approach, aimed to simplify the control design, is to divide the control system into two parts: an actuator and a controller. The actuator generates a force that tracks a command which is generated by the controller. Such approach reduces the complexit...

In this paper, an optimal feedback, for a free vibrating semi-active controlled plant, is derived. The problem is represented as a constrained optimal control problem of a single input, free vibrating bilinear system, and a quadratic performance index. It is solved by using Krotov’s method and to this end, a novel sequence of Krotov functions that...

The punching problem of reinforced concrete flat slabs and flat foundations has two main aspects, related to load carrying capacity of these structures under shear forces. The first is obtaining the shear force value, and the second–finding the control area (failure zone dimensions). Generally, the punching shear force is taken, based on experiment...

Using stone crushing waste products allows more rational and complex use of mineral resources and increases the ecological safety level of quarry works and production of stone materials. This paper focuses on an experimental investigation of the composition effect of vibro-pressed fine-grained concrete incorporating granite siftings on compression...

As known, fillers directly affect the properties of self-compacting concrete. Fly ash is one of the common fillers used in production of SCC. Using lightweight concrete is extremely important for reducing the self-weight of structures, especially in heavy ones, like high rise buildings. It enables to decrease additional loads in case of renovation...

Models and full-scale statically determinate two-layer beams (TLB), made of steel fibre high strength concrete (SFHSC) in the compression zone and normal strength concrete (NSC) in the tensile zone, have been tested by the authors. The present study is a further stage of these investigations, focused on testing a continuous two span TLB with optima...

The study deals with life cycle assessment evaluation of mitigation measures for sustainable structural performance under earthquakes. A case study building using four different mitigation measures was evaluated. To analyze the mitigation measures, CO2 emissions, and environmental damages, six methodological options of Eco-indicator 99 addressing l...

Cement-based composite materials have minimum of two components, one of which has higher strength compared to the other. Such materials include concrete, reinforced concrete (RC), and ferrocement, applied in single- or two-layer RC elements. This paper discusses experimental and theoretical results, obtained by the authors in the recent three decad...

This book deals with the challenges of academic teaching in higher education with regard to quality, mobility, and globalization. The articles reflect a unique interdisciplinary effort at collaboration, generated by colleagues and partners who joined together to form a community that aimed to chart the course of academic teaching. The book is divid...

p>Dangerous defects in the concrete bases of wind turbines are known to be caused not only by external factors, such as temperature changes or fatigue of construction materials over the time, but often particularly by constructional defects or design failure. The valid standards and guidelines suggest specific measurement methods and descriptions a...

p>Steel fibered high strength concrete (SFHSC) is effective for repairing structures from normal strength concrete (NSC). Design of NSC structures that should be repaired is based on general concepts for design of two-layer beams, developed by the authors. Such beams are effective when their section carries large bending moments. Steel fibers incre...

One of the main goals of a good and effective structural design is to decrease, as far as possible, the self-weight of structures, because they must carry the service load. This is especially important for reinforced concrete (RC) structures, as the self-weight of the material is substantial. For RC structures it is furthermore important that the w...

In the present study a method for improving the reliability of measuring the elastic critical buckling load of sway frames is proposed. The critical load is obtained by extrapolating the dependence between the lateral stiffness and vertical load that acts on the frame up to zero value of the lateral stiffness. The reliability is improved by plannin...

In the present study a method for improving the reliability of measuring the elastic critical buckling load of sway frames is proposed. The critical load is obtained by extrapolating the dependence between the lateral stiffness and vertical load that acts on the frame up to zero value of the lateral stiffness. The reliability is improved by plannin...

Using Steel Fibered High Strength Concrete (SFHSC) for repairing normal strength concrete bending elements has been previously proved to be effective for statically determined beams. After repairing using this method a beam becomes a two-layer element that consists of SFHSC in the compressed zone and Normal Strength Concrete (NSC) without fibers in...

Passive control is a known method for vibrations damping in civil structures. The simplicity and reliability of passive damping devices makes them a worthy candidate in many practical applications. However, despite of its practical simplicity, the optimal design of passive controller is quite a hard computational problem. In this work, an enhanced...

During the last decades the general theory of pre-stressed concrete elements is well developed, but at the same time the ultimate limit state (ULS) of these elements is not enough investigated like their service limit state, which presently forms a basis for design concepts. The problem of pre-stressed concrete elements in ultimate limit state is r...

Passive control is a known method for vibrations damping in many mechanical systems, including civil structures. The simplicity and reliability of passive damping devices makes them a worthy candidate in many practical problems. However, despite of its practical simplicity, the optimal design of passive controller is quite hard computational proble...

Control is one of the methods used for reducing structural response to earthquakes. Optimal active control algorithms allow calculating the forces that should be applied by supplemental devices in order to yield desired structural behavior during an earthquake. However, active devices require large amounts of external power, which are not always av...

In spite of a wide experimental and theoretical data on shear that forms a basis for modern design approaches, exact solution of shear problem for inclined cracked bending reinforced concrete elements is still not found. It yields high dispersion in the bearing capacity of concrete according to the main compression stresses. A similar problem appea...

Two-layer beams (TLB), consisting of steel fibered high strength concrete (SFHSC) in the compression zone and normal strength concrete (NSC) in the tensile one, are studied experimentally. The current study is based on results of previous theoretical investigations and tests that showed high efficiency of such beams, carrying rather big bending mom...

Large‐span reinforced concrete (RC) shells collapses that occurred in the last decade caused many death toll as well as significant losses to national economies. The most famous cases were the collapse of the aqua park cover in Moscow on February 2004 and the 2E terminal roof destruction at Charles de Gaulle Airport near Paris on May 2004. Followin...

The paper deals with results of experimental research on cement glue mortars containing non-milled fly ash and organic-mineral modifiers are given. The organic-mineral modifiers (OMM) include finely dispersed additives like microsilica or milled fly ash and organic substances (naphthalene formaldehyde superplasticizers and redispersed polymers). Gl...

This monograph analyses experimental and theoretical investigations in the field of reinforced concrete structures and elements from the viewpoint of a new mini-max principle and application of this principle for calculation of forces, strengths and critical buckling loads in RC shells, columns, plates, etc. The basis of the mini-max principle was...

Existing methods for design of reinforced concrete (RC) bending elements in the ultimate limit state are based on calculating the compressed zone depth of the section. At the same time, in isotropic materials the neutral axis of the bending section crosses its center of gravity (CG). It was proved that if a neutral axis of bending RC element crosse...

Two-layer high-performance RC beams can be used in the traffic (longitudinal) direction of long-span bridges. The beam section consists of two parts: a bottom part made of normal-strength concrete (NSC), which has a U-type section, and an upper one made of steel fibre-reinforced high-strength concrete (HSC), which has a rectangular section. Using t...

This study describes a useful contribution to the ultrasonic non-destructive evaluation of both micro and macro-scale defects or damages induced in concrete under initial and peak level load applications, respectively. The presented research findings are based on measuring linear and non-linear ultrasonics parameters. For this purpose 45 cubes of 1...

Shake tables are widely used for testing structural models subjected to earthquakes. Time histories of real ground motions are reproduced by a moving shake table platform, controlled using an appropriate algorithm, considering the limitations in the platform's maximum displacement. As the real peak ground displacement is usually higher, compared wi...

Seismic isolation and energy dissipation are used for improving the dynamic response of bridges. However, no general concept for selecting the most appropriate devices for each structure is available, therefore understanding the dynamic processes is important for the selection and design of proper energy dissipation system to improve bridges' dynam...

Steel fibered high strength concrete (SFHSC) is an effective material that can be used for repairing concrete elements. Design of normal strength concrete (NSC) elements that should be repaired using SFHSC can be based on general concepts for design of two-layer beams, consisting of SFHSC in the compressed zone and NSC without fibers in the tensile...

According to the seismic modal approach, optimal modal control design should derive a control signal affecting only the dominant modal coordinates. However, existence of an optimal state feedback, affecting only a selected set of modes, is questionable. This study proves the existence of optimal modal feedback for the case of infinite horizon LQR a...

General concepts for design of two-layer beams, consisting of fibered high strength concrete in compressed zone and normal strength concrete without fibers in the tensile one, were developed about two years ago. It was shown that such beams are effective when the RC section carries rather big bending moments. Steel fibers have little effect on beam...

Shaking tables are widely used for testing structural models under earthquake excitations. Real ground motions are reproduced by a moving shaking table platform, which is controlled according to appropriate algorithm that considers the limitations in the platform's maximum displacement. Usually the real ground motion record is scaled to allow repro...

Proper evaluation of the hydration process of concrete mixtures is essential and useful to assess the quality of concrete mixtures and cement mortars used for the repair of structures. Currently the penetration resistance test is widely used to evaluate the strength development of fresh mortar and concrete. Ultrasonic through transmission and wave...

In this paper concrete damage detection is experimentally studied investigating the effectiveness of applying ultrasonic wave atte-nuation. The study is focused on nonlinear ultrasonic evaluation of standard size concrete cubes subjected to compression at different loading levels inducing distributed damages. At each damage level ultrasonic attenua...

Improving structural seismic response using dampers became a widely used method in the recent decades. Various devices were developed for seismic protection of structures and appropriate methods were proposed for effective design of control systems. An actual problem is how many dampers should be used as is their optimal location for yielding the d...

Steel Fibred High Strength Concrete (SFHSC) is an effective material that can be used for repairing concrete elements. The design of Normal Strength Concrete (NSC) elements that should be repaired using SFHSC can be based on general concepts for design of two-layer beams, consisting of SFHSC in compressed zone and NSC without fibres in the tensile...

Mathematical planning presents methods of experiments for the decision of tasks of concrete compositions design with the set of given properties presented in this book. The procedures for obtaining different types of mathematical models and their technological analysis are presented. Examples of application of the mathematical planning methods of e...

Shaking tables with moving platforms are widely used in laboratory testing of structural models and full-sized devices. In most cases, the platform’s movement should reproduce real ground acceleration records. However, the stroke of the platform, required for reproduction of real records, is usually rather large. This limitation does not allow an a...