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In the building industry, it is a frequent cause of damage to elements at different stages: during transportation, operation, installation, etc. Since replacing an element is not always possible due to various circumstances, it entails significant financial losses, logistics, and others. For this reason, the expediency of studying the effect of damage on the bearing capacity of reinforced concrete elements is growing. This effect is dependent on its type and has significant variability. In the case of the combination of the defect and damage in reinforced concrete elements, the complexity of the research of this element increases significantly. In this article is discussed: a review of damaged reinforced concrete elements; researching the influence of the damage and additional factors on the element; developed testing methodology for bending reinforced concrete elements with damage to concrete in a compressed zone with insufficient reinforcement, when performing damage to the action of the load and during the action of the load, is presented; the influence on the deformability and bearing capacity of the variability of damage on the sample with insufficient reinforcement is reflected, taking into account the factor of change in the load at which the damage is performed; a comparison is made of the dependence of the change in the actual height of the compressed zone on the change in the load on the elements; implementation of conclusions on the result of the study.

Each structure is exposed to different influences during operation. As a result, there are various defects and damages of these elements that affect their safe operation. The article presents the results of experimental studies of reinforced concrete beams with damages to stretched reinforcement made with and without initial load application. As the damages were accepted one or five Ø5.6 mm holes. In one case, the damage was made until the beam destruction (up to the 8.4 mm opening) Control samples of both series were destroyed due to crushing of the compressed zone of concrete. Samples that were damaged without initial loading collapsed due to rupture of the stretched reinforcement. The same type of failure was identified for damages at the operational load level.

This article is devoted to experimental researches of the reinforced concrete beams strengthened by a RC jacketing under load. The program of experimental researches of reinforced concrete beams was envisaged to test four series with a total number of 16 beams 2,100 mm long, of which 14 reinforced beams were additionally pre-loaded. In all experimental samples the longitudinal working reinforcement were steel bars of 2 ∅14 mm А500С. The beams were reinforced by jacketing with the use of two unstressed reinforcement rods of 2 ∅10 A500C mm. To simulate the real life conditions, the loading levels of 30%, 50%, 70% and 90% of the non-strengthened beam bearing capacity were maintained during jacketing. The strengthening effect decreased from 92 to 76% depending on the actual load level (30–90% of the load-bearing capacity of non-strengthened beams). The results of the study could be taken into account in designing reinforced concrete beams strengthened by a RC jacketing under previous loading.

This paper presents the experimental testing of eccentrically compressed reinforced concrete columns. There are experimental results of crack resistance of non-strengthened (control) and strengthened RC columns in the tension zone. The columns were strengthened by carbon fiber reinforced polymers (CFRP). As a result of experimental studies with the columns strengthened by CFRP, we obtain that the width of their crack decreased by an average of 33%. The eccentric compression load of the crack’s appearance increased from 40 kN to 60 kN for strengthened columns.

In this work, the nanostructural changes in a Ni/NiO cermet material, during its reduction and oxidation at 600 °C have been studied. A series of the NiO ceramic specimens (mode 1) were undergone to the next three treatment modes at 600 °C, namely: (2) one-time reduction in hydrogen of 99.99 vol% H2 purity; (3) one-time reduction in Ar–5 vol% H2 mixture; (4) redox cycling (5 cycles), each redox cycle comprises the stages of isothermal holding in Ar–5 vol% H2 mixture and in air, with intermediate stages of degassing. Increased porosity, along with an increased amount of reduced Ni, has been revealed in specimens after mode 2 test. In contrast to treatment in pure hydrogen, no substantial volume changes in the material after mode 3 test were found, and single micropores were detected only at the sites of contact of nickel phase particles. In contrast to modes 2 and 3, the following structural peculiarities in the course of redox cycling of as-sintered NiO ceramics (mode 4) were detected: (1) formation of a network of nanopores in the outer layer of a Ni-phase particle; (2) reduction of Ni-phase particle size by separating thin pieces of reduced Ni subgrains; (3) coagulation of fine Ni pieces that allows the porosity to be partially decreased and “bridges” to be formed; (4) clustering of the initial Ni-phase particles with the formation of nanopores at the sites of former boundaries; (5) formation of a network of reduced Ni that consists of Ni fringes and “bridges” and improves electrical conductivity and structural strength of the cermet.

The main issue of the article is the corrosion of the reinforced concrete elements by the co-influence of the aggressive and power factors. The problem of corrosion is ex-tremely actual one. Therefore the tests were carried out upon the specimens considering the corrosion in the acid environment, namely 10 % H2SO4. The acid environment H2SO4 was taken as a model of the aggressive environment. Conclusions concerning the corrosion model of the cross section and investigation of stress-strain state have been made. That material concerns the problem of the reinforced concrete corrosion as a whole construction. Reinforced concrete beams were tested with and without the co-action of the aggressive environment and power factor.

Determination of shear-load-bearing capacity of reinforced concrete beams (according to the current normative documents), comprises particular recommended values, which do not depend on the parameters of the sample or load. This article describes the methodology for determination the shear strength with suggestions for calculation the coefficient C Rd,c and compressed element tilt angle Ѳ while reinforced concrete elements` calculation with the use of “truss model”. In order to confirm the methodology 4 reinforced concrete beams were tested. Tests were performed in order to investigate each particular inclined section separately. Variable parameter was the relative shear span a/d, with its values a/d=2, a/d=1,5 and a/d=1. Another parameter was the usage of composite strengthening system, made for relative shear span a\d=2. Samples were tested as single-span beams subjected to short-term loading. The calculation with the use only the values, given in norms showed significant divergence of results. Using the refined parameter values provided the convergence of results within 16-29% toward overestimation of the experimental data. The composite reinforcement system calculation showed the overestimation of 23%, which is within the same limits as for the control samples.

This article presented results of impact corrosion on reinforce concrete beams during time with previous loading. Before testing the RC beams were loaded by 37% and 75% from bearing-capacity load of undamaged corrosion beams. There were tested two types of beams. First type beams were tested under force loading action and second type beams were tested under force loading and corrosion action. As an aggressive environment were used the 10% solution of sulfuric acid H2SO4. Such environment takes place in separate chemical manufactures, galvanic workshops, flue pipes of thermal power plants. The results of experimental studies have established that the effect of the aggressive environment with simultaneous loading significantly impairs the stress-strain state of reinforced concrete beams. Bearing capacity due to the yielding of reinforcement bars for specimens with the simultaneous action of aggressive environment and previous loading of 37% and 75% takes place on 51…53 and 58…60 days. The destruction of these specimens, by crushing compressive concrete, at previous loading 37% occurred after 75…79 and at previous loading 75% - after 79…88 days. The history loading does not impact significantly on beams failure, on finite deflections and timing exhaustion bearing capacity since the start of the simultaneous action of aggressive environment and loading.

In this article presented results of researching corrosion of steel bars in aggressive environment in time under loading. For researching were used special equipment. The experience and research works shown that steel bars in the crack cross-section area can be corrode. With increasing width of crack in re-bars and power of aggressive of environment increased the level of corrosion and decreased time of progress. The level of danger of corrosion in the crack in depend of specialty of steel bars. It is geometry parameters of steel bars and characteristic of corrosive behaviour. The general tendency of the influence of various defects on the strength of steels is widely studied experimentally and theoretically only for geometrically correct stress concentrators. For damages that are irregular in shape, such as corrosion ulcers, significantly less researching in each case must experiment to find their effect on the mechanical properties of steels. In this work the influence of simultaneous action of the aggressive environment and loading on strength of steel re-bars has been described.

In current economic trends, changes in construction using are required. It usually leads to changes in value and type of the working load on building structures, with the requirement to rate the technical state and replace or strengthen the elements. An important aspect of determining the residual bearing capacity of damaged bending reinforced concrete elements is the research concerning the influence of difference defects and damages on the change of strength and deformability. In the article main types of damages and defects, methods of studies of damaged reinforced concrete elements and the expediency of usage of this elements are described. However, most methods are suitable only for certain defects and damages due to the large complexity of calculations and the consideration of multifactoriality. Significant complexity of a single method for calculating damaged elements depends on the possible changing stress strain state of an element in combination with certain defects and damages, the presence of a non-complete separation where during loading or alteration of the damaged element the fractions become included in the work, reinforced concrete is the composite material which carrying complexity in calculating the joint work of its components.

In this work, the nanostructural changes in a Ni/NiO cermet occurred due to its high-temperature (600 °C) reduction and reoxidation have been studied. A series of the NiO ceramic specimens (mode 1) were undergone to the next treatment: one-time reduction at 600 °C in hydrogen of 99.99 vol% H2 purity (mode 2); one-time reduction at 600 °C in Ar–5 vol% H2 mixture (mode 3); redox treatment (5 cycles) at 600 °C consisting of the stages of exposition in Ar–5 vol% H2 mixture and air, with intermediate stages of degassing (mode 4). After mode 2, a high percentage of reduced Ni has been found in material along with high porosity. In contrast to treatment in pure hydrogen, no substantial volume changes in the material treated according to mode 3 were found, and single micropores were detected only at the sites of contact of nickel phase particles. Contrary to modes 2 and 3, some distinguished nano- and microstructural peculiarities in the course of redox cycling of as-sintered NiO ceramics (mode 4) were detected, namely, a network of nanopores was formed in the external layer of particles of the nickel phase; thin pieces of reduced Ni subgrains were separated causing a reduction in the size of particles of Ni-phase; tiny Ni pieces were coagulated causing partial reduction of the porosity and formation of “bridges”; the initial particles of the nickel phase were united in clusters with the formation of nanopores at the sites of former boundaries; a nickel network was formed that consisted of Ni fringes and “bridges.” Finally, the specific electrical conductivity of the material increased along with its strength.

The paper present the results of reinforce concrete beams damaged at compressed fiber. Study of damaged reinforced concrete elements is associated with certain complexity in both theoretical and practical issues. In such cases the number of factors take place which influence on elements’ performance, which is caused by composite features of reinforced concrete elements. In addition certain factors occur due to damages. In the article experimental data is analyzed concerning concrete damages’ influence in the compressed zone on the bearing capacity of the reinforced concrete elements. Results of 4 reinforced concrete beams’ testing are proposed one of which was the control one (tested without damages) and three,- typically damaged in compressed zone at different load levels. As the result the effect of damage and load influence on bearing capacity of beams was indicated, as well as effect of neutral axis position change. Research results demonstrate increase of 3.8% in reinforced concrete beams bearing capacity, if they are damaged under the load, comparing with the unloaded damaged reinforced concrete beams.

This article describes the strengthening of normal sections of reinforced concrete beams by pre-stressed reinforcement under load. Experimental samples had the length of 2100 mm, the width of 100 mm and the height of 200 mm. Strengthening of experimental beams is designed from flat frames and isolated rods, which were combined into a spatial frame by transverse rods. In all the be the longitudinal working reinforcement were steel bars of 2 2 O 12 A500C, constructive and transverse reinforcement was represented by– O 8 A240C bars with spacing of 50…100 mm. The load was applied by means of a hydraulic jack in thirds of the span. The beams were tested for bending. The beams were reinforced with the use of two unstressed or pre-stressed reinforcement rods of O12 A500C mm.

This book gathers the latest advances, innovations, and applications in the field of effective methods of calculation, resource-saving technologies and advanced materials in civil and environmental engineering, as presented by leading international researchers and engineers at the XVII International Scientific Conference Current Issues of Civil and Environmental Engineering “Lviv- Kosice – Rzeszow”, held in Lviv, Ukraine on September 11-13, 2019. It covers highly diverse topics, including structural shaping and optimization; aspects of structural behavior and modeling; advanced analysis methods; experimental tests and numerical simulations; design codes, in particular Eurocodes and other national and regional limit state codes; and highway and bridges engineering. It also discusses modern architectural and structural solutions; innovative materials and products; durability and maintenance; fabrication and erection; sustainability in construction; renewable energy sources; heat, gas and water supply; ventilation and air-conditioning; ecological and energy-saving technologies, modern water-purification and treatment technologies; and the protection of water ecosystems. The contributions, which were selected by means of a rigorous international peer-review process, highlight numerous exciting ideas that will spur novel research directions and foster multidisciplinary collaborations.

In this article, results of experimental testing of reinforced concrete beams without transverse shear reinforcement are given. Three prototypes for improved testing methods were tested. The testing variable parameter was the shear span to the effective depth ratio. In the result of the tests we noticed that bearing capacity of RC beams is increased with the decreasing shear span to the effective depth ratio. The design method according to current codes was applied to test samples and it showed a significant discrepancy results. Than we proposed the improved design method using the adjusted value of shear strength of concrete CRd,c. The results obtained by the improved design method showed satisfactory reproducibility.

In the article, theoretical researching of the influence of damage in the compressed area in bending reinforced concrete elements is presented. The main attention is paid to the comparison of the impacting two factors on the bearing capacity: level of loading and the loss of the cover in the compressed area. In the first step, carried the formation of a matrix of the dependence impact of each factor on the bearing capacity with the subsequent determination of coefficient of influence and the formation of the regression equation. Analyzing the regression equation, obtained results of the impact of each factors, and their interaction, on the bearing capacity of the element. Second step is modeling of the experiment research using software “Femap with NX Nastran”. Thereafter, there was created a table of the distribution factors and their combinations with the indications of their impact on the carrying capacity of the model. It is possible to concluding, that the main factor is the initial level of loading, when the bending reinforced concrete beams received damages. The obtained results show the relevance and expediency of conducting experiments with the aim of determination of the residual bearing capacity in damaged reinforced concrete elements.

Most important parameter of serviceability limit state (SLS) for reinforced concrete (RC) beams is crack resistance. These include width of crack opening, cracking distribution, load at which is achieved limit and maximum width of crack opening. This is especially important for shear resistance. In this article, new data of crack resistance of rectangular RC beams are described. Changing parameters were shear span (acquiring values 1, 1.5, 2) and strengthening with FRCM (Fiber Reinforced Concrete Matrix) system in the supporting area. Eight samples for experimental researches were carried out: six once from them without strengthening but with different shear span and two once with composite system. Using the limit width of the crack opening as criteria of exhaustion of the bearing capacity can conclude that remains about 19–26% of load caring capacity before the danger of shear failure of the beam. When the shear span decreases on the 25% the maximum width of the crack opening decreases only on the 7% and on the 40$ when shear span decreased by 50%. External strengthening system reduced maximum crack opening on the 43%: from 0.75 to 0.43 mm and values exceed limit insignificant.

In this paper the results of calculation of eccentrically compressed reinforced real scale concrete columns strengthened with carbon fiber reinforced polymers (CFRP) laminates is presented. In order to check the calculation results, four real scale experimental reinforced concrete columns 2200 mm long and with sectional dimensions 180 × 140 mm were manufactured. Reinforced samples were strengthened with a 25 mm CFRP laminates. The calculation was made according to Eurocode 2. The usage of carbon laminates limit strain introduced into the calculation, is proposed. On the basis of normative documents the block diagram of calculation algorithm for such structures is created. As a result of the calculation it was established that according to the presented calculation algorithm the divergence between calculated and experimental values reaches 5 … 10%, while the experimental data exceeds the theoretical ones. It makes it possible to reliably calculate and design strengthening of eccentrically compressed RC structures with CFRP laminates according to the algorithm presented in the work.

The article presents the development of a method of experimental study of reinforced concrete beams with damaged steel reinforcement. In addition, the purpose is to conduct experimental tests of undamaged samples with steel reinforcement of 20- and 16-mm diameter. Also, the 20 mm steel bars were damaged to the area equal to 16 mm samples, experimental tests of such samples were performed and corresponding analysis and comparison of the results of both tests was conducted. According to the study program, 6 beam samples were tested. Two of them were undamaged control samples with single load bearing reinforcement of Ø20 mm diameter; 2 samples with Ø20 mm reinforcement had about 36% damages (which corresponds to area of the 16 mm diameter samples) and 2 samples with Ø16 mm single reinforcement, which corresponds to 36% load bearing reinforcement damage of control samples (the area of 36% damages of 20 mm samples corresponds to 16 mm diameter). The experimental study identified the strength and strain parameters of reinforced concrete beams with damages in the load bearing stretched reinforcement due to the action of the bending moment, which causes the exhaustion of the bearing capacity.

Theoretical method of crack width calculation in jacketed reinforced concrete columns is described and validated in this paper. The total number of tested columns was 12. The initial load applied to the column before strengthening was the main variable parameter in this test. Columns were strengthened by reinforced concrete jacketing after loading. Two RC columns were tested without strengthening to serve as reference samples. Two RC columns were strengthened with RC jacketing without any initial loading to determine maximum strengthening effect. Loading was applied in steps. This study is the calculation of the crack resistance parameters RC columns, strengthened by RC jacketing under the influence of various initial loads. Crack width and pattern were checked after each step. The maximum allowed crack width for test samples was adopted as wmax = 0.3 mm. The rest eight samples were preliminarily loaded to 0.3; 0.5; 0.7 and 0.9 of reference columns bearing capacity, strengthened and tested to failure. The results of theoretical calculation deviate from test results by 13.6…27.9%.

The need of structural retrofitting and strengthening of different buildings, engineering structures or their elements is always present. Among the main reasons are demages and material deterioration due to aging, improper maintenance or physical damages; planed repairs; reconstruction or extension of the building; technical modification or complete change of operations inside the building or the structure, etc. In some cases operation of the building during retrofitting or strengthening of its structures has to be partially or fully stopped. In other cases the strengthening process takes place while the building is still operational which means that structures are strengthened under service loads. The main goal of this research is to determine the strengthening effect of reinforced concrete jacketing applied to columns under service load level. For that the experimental study of six reinforced concrete columns were carried out: four reference columns, both strengthened by jacketing and unstrengthened and two strengthened under service load. The main results of the research are presented.

The article is devoted to an experimental research of the strength of reinforced concrete beams, and its dependence on a simultaneous influence of a corrosion environment and a loading factor. The tests have been carried out upon reinforced concrete specimens of 2100×200×100 mm size, with a regular reinforcement. The beams are of a span equaling to 1,9m with different reinforcing ratio of beams. The acid environment, namely 10 % H2SO4, was taken as a model of an aggressive environment. Reinforced concrete beams have been tested with and without the co-action of the aggressive environment and loading factor. Beams, which underwent a simultaneous action of the corrosive environment and loading, were loaded to a level 0.7 of its load-carrying capacity. The load-carrying capacity in aggressive environment in all the beams of all the series was achieved in 46-60 days. The influence of the simultaneous action of the aggressive environment and loading on the strength of reinforced-concrete beams has been described in the following work. It is necessary to note that the design code of Ukraine does not allow determining load carrying capacity of the beams affected by corrosion with simultaneous influence of loading with adequate accuracy. The analysis of experimental data has been done and the main directions of the design code’s correction have been formulated.

This article presents experimental study of sheer strength of reinforced concrete beams without transverse steel reinforcement, which strengthened by composite materials. The feature of tests is that the beams’ strengthening is made under simultaneous action of loading. The research program involves a series of test beams with size 2100 × 200 × 100 mm and which contains control sample and three reinforced samples by reinforcing FRCM system. FRCM system consisting of two components: mineral mortar based on modified cement Ruredil X Mesh M750 and reinforcing P.B.O. fiber mesh Ruredil X Mesh Gold (Italy). The strength research of test samples was carried out with the shear distance to effective depth ratio a/d = 2. The strengthening loading levels were selected at 0.0, 0.3, 0.5 from shear strength of non strengthened control sample. As a result of experimental studies we found that during strengthening design the inclined cross section of beams we should take into account the existing level of loading. Using the strengthening system Ruredil X Mesh Gold the strengthening effect is reduced at 2.8 to 2.9 times while the existing level of loading increase from 0 to 50%.

This article presents the results of experimental investigation of reinforced concrete beams without transverse reinforcement on the shear. In researching, the variable parameter was relative span to effective depth ratio, which acquired the values a/d=2, 1.5, 1. The testing program involves testing of each beams samples twice. Beams were tested by the static loading of applied force at two points. Experimental results have shown the difference between the experiments of twin beams above 5 - 9%. The obtained results indicate an increase of the bearing capacity with a decrease of relative span to the effective depth ratio. The first inclined crack disclosed in mid-height cross section, at the load 50 kN at an angle equal to 45°. With increasing loading, the width of crack increased and the crack propagation occurred to the top surface of the testing sample. On occurrence of limit width of crack wmax=0.4 mm, another crack was opened in the direction from the loading point to the edge of beam support. The limit values of the crack opening width are fixed at 71 - 84% of the load carrying capacity of the samples. The effect of increasing the shear strength, according to the serviceability, is similar to the increasing of the bearing capacity and close by the value.

The usage of carbon fiber-reinforced polymers (FRP) are described as modern methods of strengthening for reinforced concrete constructions. The advantage of these materials are the great corrosion resistance to environmental factors, high stiffness and strength and weight in comparison with other materials. The disadvantage of relatively high cost is offset by the cost reduction and labor when performing work on strengthening, by decreasing of performance time, by lack of needs to use the expensive equipment, installed and used without unloading the structures. This paper presents experimental results of 6 reinforce concrete columns strengthened by CFRP strips Sika Carbodur S512 with 50 mm width. The comparative analysis was carried out and strengthened effectiveness was determined for 2 unstrengthen control specimens, 2 specimens strengthened without initial load and 2 specimens strengthened at 1/2 of experimentally determined destructive efforts of the unstrengthen column.

Bearing capacity of normal cross section of bending concrete elements reinforced with reinforced concrete ring under load was investigated. Experimental researches of 4 sets of beams with the total number of 16 units were carried out. The results of changes of stress-strain state settings depending on the load level, additional reinforcement, influence of limit level load were analyzed. The three characteristic stages of stress-strain state of reinforced concrete beams strengthened with reinforced concrete ring were defined. Results of experimental investigations of bearing capacity of normal cross section of strengthened beams with reinforced concrete ring under load were presented. Enhancing effect was calculated. According to the results of researches of strengthened beams plots of strain of working armature depending on current bending moment were constructed.

During the research, the main causes and consequences of damage to reinforced concrete eccentrically compressed structures of the H- shaped cross-section were established Three main factors that affect the value of the residual bearing capacity of the elements are identified. A three-level three-factor Boks-Benkin plan has been created, which will give statistically substantiated results (within the variation of variable factors) in the research of only 15 experimental columns. Samples of compressed elements were made and tested (according to the experimental plan). As a result of the experiments, data were obtained that allowed us to describe the stress-strain state of the damaged H- shaped reinforced concrete columns. The dependences of stresses in reinforcement and relative deformations in concrete on the parameters of damage and load level are obtained. Based on the analysis of scientific proposals and the stress-strain state obtained experimentally, the basic preconditions for calculating the residual bearing capacity of elements damaged during the operation of structures are adopted. A system of equations is developed, as a result of the solution of which the value of the residual capacity of the damaged columns is obtained. A system of equations is created and the ways of its solution are planned. Proposals for determining the residual bearing capacity of damaged reinforced concrete compressed columns are based on the main provisions of current regulations and extend their effect to damaged structures of the most common cross-section – H- shaped.