Compression Zone Research Articles

Experimental investigations: Reinforced Concrete Beams Bending Strength with Brine Wastewater in Short Age

The scarcity of waste in some regions has led to the contemplation of other approaches to providing potable water for human use. In the present research, it is proposed that a portion of the brine wastewater be recycled for potable water purposes through its incorporation into concrete and reinforced concrete compositions. The researchers performed an extensive empirical investigation to examine the impact of incorporating brine wastewater into the concrete mixture on the shear strength, bending stress, and compressive strength of the material. A total of seventy-two beams, each measuring 500 mm in length, 100 mm in width, and 100 mm in depth, were observed. A total of twelve beams were designated as control specimens, while an additional sixty beams were subjected to immersion in brine wastewater at varying concentrations of 2.5, 5, 7.5, 10, and 15%. The beams were reinforced using two longitudinal steel bars with a diameter of 8 millimeters in the tension zone and 6 millimeters in the compression zone. The stirrups included in the study were also measured to have a diameter of 4 mm. The samples were examined at intervals of seven, fourteen, twenty-one, and twenty-eight days. Based on the findings of this study and other relevant studies, it was determined that the use of 10% fresh water as a substitute for brine wastewater yielded the most optimal outcomes. The results obtained after a duration of 28 days indicate a notable increase in both the compressive and bending strengths of the concrete samples, with improvements of around 22% and 2.6% seen in comparison to the reference specimens. The impact of brine wastewater on the corrosion of reinforcing steel in reinforced concrete was investigated. The empirical findings indicated that the introduction of brine wastewater at a concentration of 10% to the concrete constituents did not provide any discernible repercussions over a period of 65 days. Doi: 10.28991/CEJ-2024-010-01-010 Full Text: PDF

Dynamic and instability analysis of single walled carbon nanotubes with geometrical imperfections resting on elastic medium in a magneto-thermally-electrostatic environment with impact of Casimir force using homotropy perturbation method

The discovery of carbon nanotubes (CNTs) has renewed a major chapter in the field of physics, chemistry, mechanics and materials science owing to their high-quality possession of: excellent tensile strength, high conductivity, high aspect ratio, thermally stable and high chemical stability. In this work, dynamic and instability analysis of single walled carbon nanotube with geometrical imperfection resting on elastic medium in a magneto-thermally-electrostatic environments with impact of Casimir force. However, Eringen nonlocal theory and Hamilton principles are used to develop the nonlinear governing partial differential equations of motions and the governing equations of motion is converted into a duffing equation using Galerkin decomposition method and subsequently, the duffing equation is solve using Homotropic Perturbation Method (HPM), where dynamic responses are obtained. The results obtain depicted that, the effects of magnetic term, thermal term and Pasternak type foundation on dimensionless amplitude-frequency ratio for fixed-fixed and fixed-simple supports make the investigation novelty as it can be used as reference in future study. Finally, the deflection curves show how the compression zone is augmented using Casimir and electrostatic forces and the results obtained shows reasonable accurate.

Dimenzioniranje armiranobetonskih pravokutnih presjeka prema drugoj generaciji Eurokoda

This paper describes the design procedure for reinforced concrete rectangular cross-sections according to the standard FprEN 1992-1-1 (second generation of Eurocode 2). Design was carried out in two ways: using design tables for reinforced concrete rectangular sections and using a direct analytical procedure. The stress-strain diagram in the form of a parabola-rectangle was used for concrete, while for the reinforcing steel a bilinear stress-strain diagram with a horizontal post-elastic branch without strain limit was applied. For this reason, when designing the reinforced concrete cross-section, it is necessary to limit the strain in the compression zone of the concrete. Tables for the design of reinforced concrete rectangular sections were obtained using a new procedure in which the mechanical reinforcement ratio is varied. A direct analytical procedure was used for comparison, which can be used for the design of reinforced concrete rectangular sections without the need to use tables. The limit values of the coefficient of the height of the compression zone for pure bending were calculated according to the standard FprEN 1992-1-1.

Rehabilitation of Fire-damaged Reinforced-concrete Slabs Using Ferro-cement

his study was conducted to investigate the effect of strengthening with ferro-cement on the flexural behavior of two-way RC slabs after exposure to direct fire. Twelve reinforced-concrete slabs were exposed to direct fire for one hour and cooled with air and water. They were then rehabilitated with a layer of ferro-cement using different bonding patterns (surface roughening, SBR material and screws). The effect of these variables was studied on the load-deflection relationship, ultimate load capacity, stiffness, energy absorption, ductility factor and strains of the compressed zone. The results showed a significant improvement in all the investigated parameters, demonstrating the efficiency of ferro-cement strengthening in improving the behavior of the slabs. It contributed to increasing the ultimate load capacity and initial stiffness of the slabs and to preventing and arresting crack propagation after cracking and even after reaching collapse. The effectiveness of SBR material in ensuring the bonding between the surface of the damaged slabs and the reinforcement layer was also revealed. KEYWORDS: Solid slab, Direct fire flame, Ferro-cement, Rehabilitation, SBR (styrene-butadiene rubber), Roughing.

ELASTIC-PLASTIC DEFORMATION OF STEEL-CONCRETE BEAMS WITH LOCAL CRUMPLING DURING THREE-POINT BENDING

The study presents the results of experimental modeling of elastoplastic deformation of bent massive concrete filled steel tube beams under three-point bending. It has been shown that local deformations and local crushing in such structures have a significant impact on their behavior. The applicability of the theory of bending of a hollow steel beam according to the Bernoulli model is analyzed. A comparison has been made of the bearing capacity and stress-strain state of hollow steel tubes (according to the Bernoulli model and the results of experiments) and concrete filled steel tube beams, and the contribution of the concrete core to the bending resistance during elastoplastic deformation has been quantitatively assessed. The actual load-bearing capacity of a hollow pipe during three-point bending does not exceed 50% of the calculated theoretically determined one, which indicates the impossibility of using the classical bending model when designing systems of this kind. In this case, the concrete filled steel tube beam not only ensures the full functioning of the metal during the deformation process, preventing its disruption, but also provides some increase in load-bearing capacity due to the inclusion of a compressed zone in the concrete work. The increase in the load-bearing capacity of a beam due to the introduction of a concrete core can reach 70%. Despite their significant weight, bendable tube-concrete rods can be recommended in conditions of a complex stress-strain state, in which, in addition to transverse bending loads, significant longitudinal forces arise, as well as local force factors that contribute to the occurrence of local crushing deformations, since, unlike a thin-walled hollow tube, concrete the core significantly prevents these effects. Based on the results of the study, the potential effectiveness of flexible tube-concrete elements for a number of structures was proven.

Study on modeling of contact interaction in roll modules

The main problem of the mechanics of contact interaction in roll modules is to determine the stress-strain state in the technological zone. The article presents mathematical models of the laws of distribution of contact stresses and analytical dependencies of their main indices, which make it possible to calculate the power parameters of roll modules of technological machines. When developing mathematical models, empirical formulas for the laws of distribution of normal stresses along roll contact curves and a friction stress model were used, considering the effect of external forces, roll drive, and compliance of the roll coating on the distribution of shear stresses. It is shown that normal stresses in the compression zone increase from zero to the maximum value by the harmonic law, and in the recovery zone, they decrease from the maximum value to zero by the parabolic law. It was revealed that in the driven roll, the neutral point is located on the left side of the point of maximum normal stress, and the points that determine the maximum normal stress and compression of the interacting bodies coincide and are shifted from the line of centers towards the supply of the processed material into the contact zone.

Evaluation of flexural failure for concrete beams partially reinforced by geogrid sheets

ABSTRACT The behavior of reinforced concrete beams with biaxial and uniaxial geogrids as a partial reinforcement with traditional steel bars under flexural loads has been experimentally studied. The effect of geogrid layers with traditional steel reinforcement in concrete beam specimens in compression and tension zones has also been investigated. Geogrid is one of the geosynthetic materials that exhibits both tensile and flexural behavior similar to traditional steel. To examine the effect of geogrids on traditional steel as a composite reinforcement system, strain gauges were fixed to the concrete beams and bottom reinforcement (steel bars). The studied parameters in this investigation are the number of geogrid layers, types of geogrids, and their position in concrete beams. First cracking load, failure load, initial and post-cracking, deflection, and ductility of beam specimen were investigated. The experimental results indicated that using geogrid sheet layers as partial reinforcement greatly contributed to resisting flexural stresses of concrete beams. An increase in the ductility and the capacity load of the concrete beam specimen was also observed. Based on this experimental investigation, the geogrids can be applied as additional or alternative reinforcement with/without traditional steel bars in concrete beams.

Theoretical Calculation of Flexural Load Capacity of RC Beams Reinforced with Aluminum Alloy -ECC Composites

In order to study the flexural performance of RC beams reinforced with aluminum alloy-ECC composites under different damage modes and to improve the theoretical method of calculating their flexural ultimate bearing capacity, the formula for the ultimate flexural bearing capacity of concrete beams reinforced with aluminum alloy tendons under two different damage modes of aluminum alloy tendons pulling off and concrete crushing in the compression zone was derived based on the intrinsic relationship of concrete in the compression zone, and the formula for the ultimate bending bearing capacity of concrete beams reinforced with aluminum alloy tendons and ECC composites under different reinforcing modes was calculated. The ultimate bearing capacity of concrete beams under different reinforcement modes was calculated, and the finite element analysis of the flexural performance of the reinforced beams was carried out at the same time, and the theoretical values were compared with the results of finite element simulation and the existing test values to verify the correctness of the formulae. The results show that the theoretical calculated values of RC beams reinforced with aluminum alloy -ECC composites are in good agreement with the results of finite element analysis and test values, and the accuracy of the theoretical calculations is high, and the formulae derived can effectively avoid the problems that are unfavorable to the practical application of engineering due to the excessive complexity of theoretical calculations, and the relevant calculation methods are of certain reference value for guiding the design of RC beams reinforced in actual projects.

FLUID MIGRATION IS THE MAIN CRITERION OF THE GAS-BEARING CAPACITY OF THE CLOSED AREA OF MINES OF THE COAL-BEARING FIELDS OF THE DONBAS

Fluid migration is determined, first of all, by different in shape and rank types of dislocations that control compression and rarefaction zones as the main regulators of the distribution of matter and energy in the Earth's crust, represented mainly by Phanerozoic formations, and in our studies by carbon deposits. Gas migration through the newly formed fractures in the massif, due to the impact of mine workings on the upper layers of the lithosphere, allows for the formation of gas accumulations in the near-surface and surface areas. As a result, a significant amount of gas is concentrated in relatively small areas, which will contribute to gas-dynamic phenomena on the surface and can cause significant damage to buildings and human life. Mass transfer of deep fluids is associated with the formation of mineral deposits, including the most explored ones, ore and oil and gas. At the same time, the distribution of gas in coal-bearing massifs is related to their tectonic structure, especially to faulting, which is a way for hydrocarbon-hydrogen mixtures to migrate from deeper horizons. The study of the signs of uneven distribution of fluids under the influence of tectonic and anthropogenic factors was based on observations of new formations in the post-sedimentary geological environment: textural and structural characteristics based on the study of samples, grinds and laboratory observations, which determine the sequence of changes in the material composition of consedimentary and post-sedimentary formations and their relationship in space and time. Unsaturated hydrocarbons, such as ethylene, propylene and acetylene, can be characterised as adventitious gases of hydrocarbon massifs that have taken their current position in the gas component of the hydrocarbon gas mixture by being transported by fractures from deep horizons to the surface.

EXPERIMENTAL STUDIES OF A DAMAGED BEAM REINFORCED WITH FIBER CONCRETE

The paper presents the results of a study of the load-bearing capacity of a beam damaged during hostilities, which was reinforced with steel fiber concrete. A beam with 20% damage in the compressed zone is considered. Before concreting, a foam liner was installed in the area of the planned damage, the shape and dimensions of which corresponded to the planned damage. After the concrete gained 70% of the brand strength, the liner was removed, and the resulting cavity was filled with a 2% mixture of fiber-reinforced concrete. This is one of the options for strengthening a beam in a comprehensive testing program for damaged beams, which involves studying a series of beams with different types of damage, damage zone (tension and compression) and its size, geometry and method of strengthening. The authors have developed a special stand for testing. Plane transverse bending of the loading of the beam under test is created using a hydraulic jack and a metal I-beam with a traverse that transmits two equal concentrated forces to the beam. The created load is controlled by an exemplary dynamometer of the Tokar system and a ring dynamometer, which acts as a support. Experimental studies have shown that a beam, the cross-section of which is 20% damaged in the middle compressed zone, and the shape of the damage is close to rectangular, has a load-bearing capacity of 93.6 kN, which is 95.0% of the load-bearing capacity of an undamaged beam (98.5 kN). Crack formation began on the 5th stage of loading, when the load value was 32.5 kN, that is, 34.7% of the load-bearing capacity of the damaged beam. In this case, 4 cracks formed in the pure bending zone. At the sixth stage, three more cracks appeared. At stages 9, 10 and 14 of loading, 7 more cracks formed. The maximum final crack opening width was 0.8 mm. throughout the testing process, the fiber-reinforced concrete liner worked with the beam as a single unit. It can be argued that strengthening a beam with 20% damage in the compressed zone using the method considered in the work makes it possible to achieve its load-bearing capacity, which is 95% of the load-bearing capacity of an undamaged beam.

Innovative ways to improve machines for preliminary work given the needs of the modern construction industry

The bulldozer-ripper is the main machine during preliminary work. The creation of high-performance machines is carried out in two directions: the production of fundamentally new working elements and machines based on the use of fundamental scientific achievements and the improvement of existing working elements, and traditional type machines that are in operation.
 The creation of working elements for ripper-picks is a perspective development direction of machines designed for ripping frozen and hard soils. They would make it possible to significantly increase the productivity of ripping work through the rational use of the base machine traction force. We applied the superposition principle of the impact on the working medium of several factors concurrently for this, such as static and dynamic loads, through the energy accumulation and its subsequent use to create a high-speed power impulse on the cutting edge to ensure the preliminary formation of the compressed zone in the soil massif. This will lead to the power intensity reduction of the static load on the soil element separation.

Flexural behavior of GFRP-RC beams confined with CFRP in compression zone

In this study, the CFRP sheets and CFRP stirrups are employed to confine the compression zone in GFRP-reinforced concrete (GFRP-RC) beams to improve the ductility of the beams. Four-point bending tests are conducted on four CFRP sheets and six CFRP stirrups confined GFRP-RC beams. The cracking bending moment, crack width, mid-span deflection, bearing capacity, and ductility of all the beams are analyzed. Results show that the effect of the confinement in the compression zone on the cracking bending moment and crack width under service load can be ignored. The cracking bending moment can be accurately estimated using ACI 440.11–22, while the GB50608–2020 standard provides an accurate prediction for the crack width under service load. The GFRP-RC beams confined with CFRP stirrups exhibit mid-span deflections reaching up to 95 mm prior to failure. In addition, the CFRP stirrups confinement is more effective compared to CFRP sheets confinement due to the poor bond performance between the CFRP sheet and concrete. Furthermore, an accurate equation for the calculation of bearing capacities of GFRP-RC beams confined with CFRP sheets and stirrups has been proposed. It has also been demonstrated by this study that significant improvements in the ductility of GFRP-RC beams can be achieved by confining the compression zone. Deformation ductility factors of all the beams are analyzed to support this conclusion.

Flexural behaviour of optimised steel tubular beams partially filled with concrete

A partially concrete-filled steel tubular beam (PCFST) is proposed in this study to optimise the design and construction of the concrete-filled steel tubular beams (CFST). Concrete filling prevents the local buckling of the slender tubes. However, it is not needed in the beam’s tension zone. Therefore, in PCFST, concrete is filled in the compression zone while the tension zone is kept empty. In this paper, the flexural behaviour of the PCFST beam is studied experimentally and numerically. The ultimate moment resistance and flexural stiffness of PCFST are the same as CFST beams, while the weight reduction in PCFST is up to 60%. A finite element (FE) model is developed using ABAQUS software to investigate the effect of geometric and material properties of the PCFST beam on flexural behaviour. The FE model is validated by the present test results and the literature reports on CFST beams. Next, a parametric study is conducted to study the effect of concrete wall thickness in the web region, length-to-depth ratio, steel yield strength, concrete compressive strength, and beam shear span-to-depth ratio. The results show that the concrete filling is useful for slender steel tubular cross-sections rather than compact ones. A higher grade of concrete increases the beam ductility, while high-strength steel reduces the ductility. The results also show that the PCFST beam is more suitable for beam lengths where flexure is predominant than shear. Further, a flexural capacity equation is proposed for PCFST beams, and it agrees well with the test and numerical results. The reliability of the proposed equation is checked as per the recommendation in EN:1994–2004 and AISC 360–2016 code provisions.

INJECTION OF CRACKS IN A RC BEAM WITH EPOXY RESIN USING THE GRAVITY FLOW METHOD

The restoration of the load-bearing capacity of RC beams through crack injection is one of the most efficient and practical methods for executing repairs in the field of civil engineering. In the article, following an analysis of crack injection methods in RC structures, an economically viable method for injecting RC beams is proposed. The core approach of the proposed crack injection method involves the process of introducing epoxy resin into the crack, which occurs by gravity flow (without specialized equipment and pressure). The paper outlines a systematic process for preparing the crack in the RC beam for epoxy resin injection. The crack injection method was conducted comprehensively, including the restoration of the compressed concrete zone within the RC beam. The test results demonstrated the effectiveness of the crack injection method, as there were no new crack formations at the injection sites, and the load-bearing capacity of the RC beam was restored to 115%.

Quantitative damage evaluation of tunnel subjected to a subsequent strong seismic after a quasi-static reverse faulting

An individual fault dislocation or seismic effect is often considered to investigate the deformation and failure of a fault-crossing tunnel, while emerged in high-intensity seismic zones, it will be likely to subject to a superimposed effect from fault dislocation and strong seismic excitation. In this study, a three-dimension numerical model to simulate fault dislocation and subsequently dynamic response characteristics of fault-crossing tunnel was established, in which fault dislocation and earthquake levels at the site of interest. The nonlinear damage feature of tunnel was considered to furtherly reveal damage states of tunnel under the superimposed effect. And then, a quasi-static large-scale model test was performed to verify the correctness of pre-order fault dislocation calculation results. The results showed that only when the tunnel was subjected to fault dislocation, a prominent relative deformation of tunnel exists in the fault fracture zone and tension and compression zone were noticeably identified at the convex and concave zones respectively. After superimposing the seismic loading, acceleration and equivalence plastic strain amplification of tunnel near the fault fracture zone is great of significance and the damage of the tunnel under the fault dislocation was concentrated at the fault core. More importantly, the fault-crossing tunnel is more of sensitivity to the initial fault dislocation from the obvious rising on the tension damage index, and when PGA is greater than 0.2 g, the tunnel emerged in the host rock mass should also be paid more attentions, not only the tunnel in the potential fault-affected zone.

Study on the Static-Bending Properties of Surface-Reinforced Wood with Asymmetric Fibers

In order to investigate the mechanism of the effect of asymmetric reinforcement on the static-bending properties of wood, this paper tests and analyzes the static-bending properties of SPF wood and seven different types of asymmetric fiber surface-reinforced wood (AFRWC) formed by SPF wood as the substrate and bamboo and carbon fibers as the reinforcement materials. The results of the study found that (1) the moduli of rupture of the seven types of AFRWC were increased to varying degrees, but the static-bending moduli of elasticity increased or decreased; (2) the asymmetric reinforcement changed the cross-section strain distribution and damage type of the wood in static bending; (3) the results of the cross-section strain-field tests and the ABAQUS finite element simulation showed that the asymmetric reinforcement method of bonding the bamboo material and the two layers of CFRP in the compression and tensile zones, respectively, can greatly enhance the static-bending performance of the wood. The error between the simulated and measured values of specimens MOR and MOE is only −0.7% and −7.3%, respectively. This type of asymmetric reinforcement makes it possible to obtain a more reasonable cross-section stress distribution.

Functionally Graded Concrete: Structural Design and Effect on Sustainability Parameters

Researchers have become interested in functionally graded concrete (FGC) in recent years due to its potential to enhance the desired performance. Functional gradation can be carried out in a continuous or stepped/layered manner. Most studies have been conducted on two layered FGC beams by substituting the richer mixes in either tension or compression zone. Previous studies have incorporated and presented the structural design approach of such two-layered beams. Moreover, the layer in the compression zone was assumed to bear entire compressive stresses. Previous studies exhibited savings in cement by up to 37% using a layer of the concrete class defined by exposure conditions around reinforcement and the concrete of minimal structural class. However, using structural concrete of minimal class in the remaining segments may result in a higher reinforcement requirement, reducing the benefits of savings in embodied CO2 offered by reduced cement consumption. This paper examines how designing the beam as a Functionally Graded Reinforced Concrete (FGRC) beam following Indian Standard 456:2016 affects the cost and embodied CO2 based on cement and steel consumption through the durability approach of design, wherein the substitution of the layer is considered in the tension zone. The study revealed that a 10% and 16% reduction in cost and embodied CO2 could be accomplished.

Reinforcement layout design for deep beams based on bi-objective topology optimization

Determining an effective and efficient reinforcement layout for reinforced concrete deep beams is still a challenging problem. This paper proposes a bi-objective evolutionary structural topology optimization method for the reinforcement layout design. Based on a discrete model for steel bars, the optimization aims to achieve a uniform stress distribution of steel rebars while promoting the peak rebar stress. A lexicographic method is used to solve the bi-objective optimization. Two numerical examples are presented to demonstrate the proposed algorithm's feasibility, stability and universal applicability. It is shown the reinforcement stresses in both tension and compression zones are more uniformly distributed and, on average, closer to the yield strength than those of the single-objective optimization. Compared with the design based on the conventional strut-and-tie method, the deep beams optimized by the proposed method use less reinforcement steel, provide a higher ultimate load capacity, and, more interestingly, fail in a ductile failure mode.

Flexural Behaviour of FRC Beams Wrapped With FRP

Structural elements such as beams, slabs and columns may require strengthening during their service life period. A concrete structure may need strengthening for many reasons such as to increase live load capacity, to add reinforcement to a member that has been unsigned or wrongly constructed. The FRPs have various advantages like, high strength to weight ratio, corrosion resistance and ease of installation and flexibility in its use. FRP material which are available in the form of sheet are being used to strengthen a variety of RC elements to enhance the flexural, shear and axial load carrying capacity of these elements. The objective of this experiment is to strengthen the RC beams using fibres and FRP sheets in flexure. In this experimental program CFRP and GFRP sheets were applied to the bottom surface and sides of the concrete beam with different configuration and their performance in flexure were studied. In this experimental program eight RC beams of size 1500 x 150 x 200mm were casted with two 10mm dia. bars as tension zone, two 8mm dia. bars as compression zone and 8mm dia. bars @ 200mm c/c spacing as shear reinforcement. The experimental result shows that the flexural strength of FRP wrapped beams were increased in the range of 23.49% to 67.9% in comparison with the flexural strength of the control beam (unwrapped). The flexural strength of the beam wrapped with the single layer CFRP at the soffit and around the sides (for full depth of the beam) and beam wrapped with the single layer GFRP at the soffit and around the sides (for full depth of the beam) exhibits better performance compared with other FRP beams and increase in flexure was 67.9% in comparison with the capacity of the control beam.

The Challenges and Advantages of Distributed Fiber Optic Strain Monitoring in and on the Cementitious Matrix of Concrete Beams

Distributed fiber optic strain measurement techniques have become increasingly important in recent years, especially in the field of structural health monitoring of reinforced concrete structures. Numerous publications show the various monitoring possibilities from bridges to special heavy structures. The present study is intended to demonstrate the possibilities, but also the challenges, of distributed fiber optic strain measurement in reinforced concrete structures. For this purpose, concrete beams for 3-point bending tests were equipped with optical fibers on the reinforcement and concrete surface as well as in the concrete matrix in order to record the strains in the compression and tension zone. In parallel, an analytical approach based on the maximum strains in the uncracked and cracked states was performed using the Eurocode 2 interpolation coefficient. In principle, the structural design correlates with the measured values, but the strains are underestimated, especially in the cracked zone. During load increase, structural distortions in the compression zone affected the strain signal, making reliable evaluation in this zone difficult. The information content of distributed fiber optic strain measurement in reinforced concrete structures can offer tremendous opportunities. Future research should consider all aspects of the bond, sensor selection and positioning. In addition, there is a lack of information on the long-term stability of the joint and the fiber coating, as well as the effects of dynamic loading.