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Enhancing the torsional capacity of reinforced concrete (RC) beams while maintaining reasonably economic and efficient cross-sections poses a practical challenge in the design of such elements. Thus, developing and testing economically viable reinforcing techniques for enhancing the torsional capacity of RC beams is a significant aspect. Among these techniques is the continuous spiral reinforcement system that has shown promising results in enhancing the torsional capacity of rectangular RC elements. In this study, the role of continuous rectangular spiral stirrups, as a transverse reinforcement with a controllable pitch (P) and inclination angle (θ), in enhancing the torsional behavior of rectangular solid and hollow RC beams has been investigated experimentally. The applied torque was directed to lock the spirals for all specimens. The experimental program of this investigation included testing of ten specimens of normal strength RC beams; two of which were solid with closed and spiral rectangular stirrups. While the rest of specimens were hollow specimens included one beam reinforced by closed stirrups and seven beams reinforced by rectangular spiral stirrups with different reinforcing ratios. Different variables were considered to develop a wide range of the beams’ reinforcing scenarios. This includes stirrups type (conventional closed stirrups and rectangular spiral stirrups), inclined stirrups ratio, pitch, inclination angle and finally the longitudinal reinforcement ratio. In addition, a three-dimensional finite element model using ANSYS-15.0 was developed to examine the capability of the model to capture the observed torsional behavior of the experimentally tested beams. The obtained results showed that using inclined spiral rectangular stirrups in reinforcing RC solid and hollow beams greatly enhanced the torsional capacity by about 16% and 18%, respectively compared to using the conventional closed stirrups. Moreover, the results showed that using that technique leads to higher twist- angles, more ductile failure and increased strain energy by about 27% and 16% for solid and hollow beams, respectively. Lastly, the comparison between the results obtained from numerical model and experimental results showed good agreement and thus the numerical model can be used to extend the experimental work for investigating different reinforcing schemes.

Bu araştırmada, yarı gevrek malzemelerdeki boyut etkisinin hasar-plastisite modeli kullanılarak çözümlemesi sunulmuştur. Çentikli ve çentiksiz üç noktalı eğilme deneyleri üç boyutlu (3D) sonlu eleman modeli ile analiz edilmiştir. Bu amaçla, Abaqus yazılımı kullanılmıştır. Beton elemanların gerçekçi bir şekilde analizinde, özellikle boyut etkisinin dikkate alınmasında, çatlak bant genişliği yaklaşımı uygulanmış, hasar-plastisite modelinin etkinliği araştırılmıştır. Kırılma mekaniği parametrelerinin bulunması amacıyla, açıklık-yükseklik oranı, L/D=2.176, olan üç noktalı eğilme deneyine ait 2D sonlu eleman modeli, her bir çentik derinliği için oluşturulmuştur. Bu modelde, kiriş 8-düğüm noktalı dörtgen düzlem gerilme elemanları ile modellenmiş ve çatlak uç noktasındaki tekillik “quarter point” tekniği kullanılarak oluşturulmuştur. Bu analizler sonucunda, J-integral bulunmuş ve enerji salınım oranı hesaplanmıştır. Elde edilen sonuçlar literatürde verilmiş olan deney sonuçları ve ayrıca Bazant’ ın boyut etkisi eğrisi ile karşılaştırılmıştır. Bu çalışma, çatlak bant genişliği yaklaşımı uygulanmış hasar-plastisite modelinin, beton gibi malzemelerde, boyut etkisini yakalamak için uygun olduğunu göstermiştir., Analysis of size effect phenomenon in quasi-brittle materials is presented in this research using damage plasticity model. Notched and unnotched specimens under three-point bending fracture test are analyzed by setting a 3D finite element model. For this purpose, Abaqus software is utilized. Concrete damage-plasticity model (CDPM) enhanced with crack band approach is used to conduct simulations of concrete specimens. The efficiency of this model is investigated especially for size effect phenomenon. 2D finite element model is setup for three-point bending beams in order to estimate fracture parameters for specific span to depth ratio, L/D=2.176. The simulations are conducted for each different notch depths. 8-node quadratic plane stress elements are used to define 2D domain and singularity field at the notch tip is modeled using quarter point technique. Energy release rate is calculated using J-integral approach. Obtained results are compared to experimental ones reported in literature and are also compared to the Bazant’s size effect law. This study shows that concrete damage-plasticity model enhanced with crack band approach can capture size effect observed in concrete-like materials’ fracture.

A series of experimental tests on reinforced concrete specimens with normal uncoated and epoxy-coated reinforcing bars (ECRBs) was carried out. A comprehensive report of the specimens, from material level to overall performance, is presented in this paper. At the material level, evaluation of the epoxy coating thickness showed that the production quality was not good. Some mechanical properties of bars with a thinner coating were better than those of their uncoated counterparts, while an increase in coating thickness offset the better mechanical properties and decreased the bond strength. Regarding durability, a comparison of the corrosion behaviour of the reinforcing bars and chloride penetration of the concrete cover in unloaded, statically-loaded and fatigue-loaded test specimens showed that higher fatigue loads and longer fatigue loading cycles decreased the corrosion resistance of the bars and increased the chloride penetration. The ultimate loads of the specimens were reduced and comparatively lower values were obtained for beams with bars with thicker coatings. The results of this work highlight the interrelationships among materials performance, durability and ultimate performance to achieve sustainable design for concrete elements with ECRBs in chloride-containing environments.

An analytical exploration of the effects of shear span-to-depth ratio on the shear strength of reinforced concrete beams was carried out using a meso-scale finite-element method. Prior to the numerical analysis, a method of defining concrete as meso-scale composites of multi-phases was described. The concrete was assumed to be a composite with three phases (aggregates, cement matrix and interfacial transition zone), and the material properties of each phase were applied for the numerical analysis. The shear failure behaviour of reinforced concrete beams was examined by the numerical model that was constructed, and the effect of span-to-depth ratio on shear strength was confirmed through these analyses. An investigation of cases where span-to-depth was less than 1.0 was also carried out. Moreover, the performance of the numerical model was evaluated by comparing the numerical results with the experimental results obtained from the model code and other researchers. It was confirmed that the application of a meso-scale finite-element method was appropriate for the study on the effect of span-to-depth ratio on shear strength and the occurrence and progress of bending and shear cracks.

Web openings in reinforced concrete (RC) beams are provided to pass utility pipes and ducts through them. This causes high stresses (with local cracking) around the transverse web openings, which may lead to reduction in ultimate strength and stiffness of RC beams. Internal strengthening with shear reinforcement can increase ultimate strength of the beam with web openings. This paper presents an experimental study which was conducted to investigate load carrying capacity, mid-span deflection and failure modes of beams with web openings. A total of eighteen RC beams were included in the testing programme, which were tested under two-point loading. The beams contained both pre-planned and post-planned web openings. Experimental results showed that ultimate load of the beams decreased from forty-two to sixty-seven percent due to the presence of web openings in the shear zones. Shear strength of the beams with pre-planned web openings increased by thirty-six percent and one-hundred two percent as compared to the reference beam due to the increase of shear reinforcement by one-hundred twenty-two percent and three-hundred three percent, respectively. Similarly, increase in shear capacity up to six percent and fourteen percent was found for the beams with post-planned web openings due to the aforementioned increase in the area of shear reinforcement, respectively. The ultimate load carrying capacity was also compared with the theoretical models. Internal strengthening and pre planned opening were found effective for providing web openings in the beams.

Twelve concrete beams (1200 × 200 × 120 mm) were cast and cured before ten beams of there were subjected to pre-loading at different levels (45%, 60%, 70%, 80%, 100%) from the control beam failure load. The beams subjected to preload were repaired with two different techniques using CFRP sheet (U-warp and W-warp) and then tested to fail under a four-point loading system. The results showed that pre-loading at high levels had a detrimental effect on the shear-deficient concrete beams, on the other hand, CFRP sheets helped to restore as well as increase the ultimate load-carrying capacity of most of the beams. Experimental results prove that Repairing previously damaged beams not only helps them to recover but also greatly increases their ability to resist premature shear failure.

There are many researches has been done to replace the constituent materials in the concrete to meet out the scarcity of the available raw materials and also, they have proven a successful one up to a certain level. But in this study, we are focused on to improve the structural behaviour by adding steel fibres in concrete without replacing any constituent materials. The scope of this project is to study experimentally the strength properties of the beam on inclusion of steel fibres. It also aims to investigate the structural behaviour of conventional concrete beams and steel fibre reinforced beam when steel fibre is used as a secondary reinforcement in beams. To overcome the deficiency of the conventional concrete, fibres have been added as secondary reinforcement. Steel fibres are added below the neutral axis of the RC beam in order to overcome the development of micro cracks under applied stress in the RC beam. The addition of steel fibres to the concrete has many advantages and the most notable among them is the improvement in the mechanical characteristics of the concrete. In our project steel fibres and modified steel fibres (adding fibres below the neutral axis) are added in the proportion of 1 % to the concrete. The tests for the fresh concrete and hardened concrete are carried out and their results are compared. The project is further extended to check the performance of the steel fibres in the reinforced concrete beams when they are added below the neutral axis. Two-point loading is applied to the structural members and the corresponding deflections are noted down. The performance of the SFRC beam and the modified steel fibre reinforced concrete (MFRC) beam is compared with the conventional RC beam. The discussions and conclusion are arrived based on the test results.

The subject of the research deals with the study of the effect of recycling and addition of some cheap and locally available materials on the properties of the adhesive material (Epoxy) used to strengthen concrete beams. Where the study included the addition of glass powder, brick powder and porcelain powder to the adhesive material and with different ratios of the weight of the adhesive material (0, 0.25, 0.5, 0.75, 1 and 1.25). After conducting laboratory tests proved the results of the study that the best types of additions are porcelain powder and the best ratio of adding was about ( 0.25). This addition to the adhesive material in this ratio led to improve the reaction temperature at mixing the parts of the adhesive material where decreased by 15.56%, as well as improved workability through lower flow of the consistency of adhesive material about 7.89%, as increased compressive strength by 13.33% and improved the modulus of elasticity by11% only, but The modulus of rupture decreased by 7.04% and the strength to high temperatures (limit to 250C°) decreased by 29.17%. The new bonding material was tested to strengthen the CFRP concrete beams. The results showed that the compressive strength of these beams increased by 70.97% compared to the normal non-reinforced beams and the strength of the Toughness beams increased by 61.87%. © 2018 JASET, International Scholars and Researchers Association

Background: Creep in concrete is a long-term deformation under sustained loading. It is influenced by many factors, including constituent materials, environmental conditions, among others. Whenever there is an alteration in the convectional concrete preparation process, the creep characteristics need to be realistically assessed. In the present construction, rice husk ash has been used for partial replacement of cement in concrete production. This is because its properties of both tensile and compressive strength in concrete have been tested and found comparable with plain concrete. However, durability characteristics such as creep, which take place in the long run, have not been realistically assessed. Therefore, it is important to study the creep of rice husk ash concrete, which will further help in the development of a creep prediction model for such concrete for use by design engineers. Objectives: Rice husk ash was used as supplementary cementitious material in concrete, and the creep behavior was studied with the aim of producing a creep prediction model for this concrete. Methods: The cement was replaced with 10% of rice husk ash in concrete with a design strength of 30MPA. Reinforced concrete beams were cast and loaded for flexural creep 35 days after casting. The loading level was 25% of the beam’s strength at the time of loading. The creep observation was done for 60 days. The rice husk used was obtained locally from Mwea irrigation scheme in Kenya. The experiments were carried out in our school laboratory at Jomo Kenyatta university of Agriculture and Technology. Results: The creep strain data of rice husk ash concrete beams was obtained with the highest value of 620 micro strain for 60 days. The results were used to develop a creep prediction model for this concrete. Conclusion: A creep prediction model for rice husk ash concrete has been developed, which can be adopted by engineers for class 30 of concrete containing rice husk ash at a 10% replacement level.

Geotextile is made of permeable geosynthetic. Geotextile s are formed from synthetic fibers based on polymers that have high mechanical properties in tensile strength, trapezoidal tearing strength, and puncture resistance. Therefore, researchers want to increase the use of Geotextile as an added material in the tensile area of concrete blocks. The test objects used are 9 pieces of 150mm×150mm×600mm beams. The results of the research were that the addition of woven Geotextile s and non-woven Geotextile s on concrete blocks increased, for woven Geotextile s by 21.593% of beams without using Geotextile s and non-woven Geotextile s of 17.058% of beams without using Geotextile s. So the use of Geotextile s on concrete blocks can improve quality because the value of the flexural strength of beams using Geotextile s is greater than beams without using Geotextiles.

In this study, the long-term flexural behavior of beams reinforced by basalt fiber-reinforced polymer (BFRP) and steel in a simulated marine environment was investigated. Nine beams were designed based on the principle of equal-rigidity, and they were reinforced with steel rebars, BFRP bars and grids. Four-point flexural experiments were carried out after accelerated corrosion treatment for 0, 3 and 6 months respectively. The experimental results indicated that the flexural capacity, stiffness after yielding and crack control of the beams with hybrid reinforcements were effectively improved compared to the reinforced concrete (RC) beams. Compared with the beams without soak, the flexural behavior of the RC beams decreased after 6 months, on the contrary, the beams reinforced with steel and BFRP bars did not show any degradation. For steel bars-BFRP bars and grids hybrid reinforced beams, the additional grids led to a more outstanding flexural behavior before steel yielding compared to the RC beam, however, a sustained decline in flexural behavior was observed after steel yielding owing to the thinner cover and higher sustained loads in the simulated ocean environment. The secondary stiffness and ductility of the hybrid reinforced concrete beams changed slightly after conditioning. Further, the hybrid reinforced concrete beams exhibited narrower crack width compared to RC beams during the entire experimental period.

There is a limited design guidance for practitioners regarding the shear design equations of circular-concrete members with fiber reinforced polymer (FRP) reinforcements, especially the case of incorporating FRP bars and spirals. The objective of this study is to enhance the methods used for estimating the shear capacity of reinforced concrete (RC) beams with FRP bars and spirals. A database of 44 circular concrete beams reinforced with FRP bars tested under shear were compiled from different experimental studies. Two proposed models based on approaches developed for rectangular sections, to predict the shear capacity of beams without and with stirrups, were compared with the selected available shear design equations. The shear strength estimated using the proposed models are slightly more accurate. The comparison indicates that the shear capacity of FRP-reinforced concrete members with circular cross sections may be determined with the V cf and Vsf approaches developed for rectangular sections provided that certain modifications are made to take into account the effective shear depth, equivalent breadth, the mechanical properties and geometry of GFRP spirals.

3-point bending tests were carried out on notched low, normal and high strength concrete beams containing single or novel multiple hooked-end steel fibres, ranging 0 ~ 110 kg/m3 in dosage, 35 ~ 60 mm in length, and 0.55 ~ 0.90 mm in diameter. The experimental results suggest that the Limit of Proportionality (LOP), which is related to initial concrete cracking, largely depends on concrete strength rather than fibre properties. Increasing fibre dosage, length, aspect ratio and number of hooked-end are beneficial for enhancing residual flexural tensile strength of steel fibre reinforced concrete (SFRC). New empirical equations, which can explicitly characterise the effects of concrete strength and fibre properties, were proposed to predict the LOP and residual flexural tensile strength of SFRC. By using the proposed equations, the effects of concrete strength and fibre properties on LOP and residual flexural tensile strength were discussed in depth. It was concluded that the LOP is mainly governed by concrete strength, while the residual flexural tensile strength is mainly dictated by fibre properties.

Six lightweight aggregate concrete (LWC) beams reinforced with carbon fiber–reinforced polymer (CFRP) bars were tested under a four-point bending load with different steel fiber contents, reinforcement ratios, and clear span lengths to investigate their flexural behavior and serviceability performance. The test results showed that using steel fiber–reinforced lightweight aggregate concrete (SFLWC) and increasing the reinforcement ratio enhanced the serviceability performance of the beams. The incorporation of 0.6% by volume of steel fibers reduced the midspan deflection by 22.70%–36.87% at the same load level in service stage. At service load, all the CFRP-reinforced beams exhibited conservative deflections when compared to the deflection limits recommended by ACI 440.1 R and GB 50608, and satisfied the crack width limit of 0.7 mm. Comparing the measured maximum crack widths with the corresponding predictions revealed that the bond-dependent coefficient value of 1.4 specified in ACI 440.1 R was reasonable yet conservative. Moreover, an energy-based method was adopted to quantify the influence of the fibers on the beam stiffness. On this basis, a rational deflection model for SFLWC beams reinforced with CFRP bars was suggested.

In this paper, the probabilistic behavior of plain concrete beams subjected to flexure is studied using a continuous mesoscale model. The model is two-dimensional where aggregate and mortar are treated as separate constituents having their own characteristic properties. The aggregate is represented as ellipses and generated under prescribed grading curves. Ellipses are randomly placed so it requires probabilistic analysis for model using the Monte Carlo simulation with 20 realizations to represent geometry uncertainty. The nonlinear behavior is simulated with an isotropic damage model for the mortar, while the aggregate is assumed to be elastic. The isotropic damage model softening behavior is defined in terms of fracture mechanics parameters. This damage model is compared with the fixed crack model in macroscale study before using it in the mesoscale model. Then, it is used in the mesoscale model to simulate flexure test and compared to experimental data and shows a good agreement. The probabilistic behavior of the model response is presented through the standard deviation, moment parameters and cumulative probability density functions in different loading stages. It shows variation of the probabilistic characteristics between pre-peak and post-peak behaviour of load-CMOD curves.

Although, international codes such as (CSA-S806-12) and (ACI-440-15) proposed shear design provisions for concrete beams reinforced with (FRP), many researchers are still investigating this case. Most of the available research investigated either beam without stirrups or beam with stirrups. The purpose of this study is to propose a unified formula for the prediction of the shear strength of FRP reinforced beams with and without stirrups. A collected experimental database of 553 shear tests on FRP reinforced concrete beams was used to develop a new formula to predict the shear strength using genetic programming technique. The accuracy of the proposed formula was compared with that measured during testing and calculated using the models available from literature. The new proposed formula showed more accurate predictions than the models from the literature, besides that, it is much simpler than them.

Externally bonded fiber-reinforced polymer (FRP) composites are commonly used to retrofit concrete beams in shear. However, debonding failure limits the effectiveness of such a system. Mechanically anchored systems eliminate the debonding mode of failure, which maximizes the effectiveness of the retrofit system. This study investigates the effectiveness of using a modified mechanical anchor to strengthen concrete T-beams in shear. The fabrication and design details of this system are discussed. Three reinforced concrete (RC) T-beams were tested up to failure under a four-point bending test to assess the effectiveness of the proposed retrofit system. One beam was tested as a control beam, while two beams were strengthened in shear using mechanically anchored dry carbon fiber (CF) sheets. The tested beams were instrumented with conventional instruments to monitor the load, strain, displacement, and acoustic sensors to monitor the damage initiation, progression, and location. The modified mechanical anchor retrofit system increased the shear capacity by up to 22 %. The acoustic emissions (AE) monitoring of the tested T-beams was able to detect the locations of the cracks that caused the failure of the beams.

The torsional behaviour of high-strength concrete beams that are transversely reinforced with continuous spiral reinforcement is experimentally investigated in this research. Seventeen specimens ar...

This study examines the flexural behaviour of hollow reinforced concrete (RC) beams experimentally, numerically, and analytically. The experimental work was accompanied to study the influence of internal concrete hollow core size on the flexural response of RC beams. A control beam with a solid section and three other specimens having a hollow core area of 3%, 7%, and 10% of the beam cross-section area were tested. During loading, the crack patterns for all the specimens were recorded. The results indicated that using less than 10% of the beam cross-section as the hollow part didn’t considerably affect the failure load of the RC beams. In conclusion, the concrete core didn’t contribute to the capacity of the RC beams; however, it affected the cracking pattern, i.e. size and height. A numerical model was implemented using ABAQUS to simulate the behaviour of the hollow RC beams. The numerical model accurately expected the response of the tested RC beams. Using the validated model, a parametric study was complemented to study the influence of the hollow size and location on the RC beam response.

PurposeBuilding elements that are damaged by fire are often strengthened by fiber wrapping techniques. Self-compacting concrete (SCC) is an advanced building material that is widely used in construction due to its ability to flow and pass through congested reinforcement and fill the required areas easily without compaction. The aim of the research work is to examine the flexural behavior of SCC subjected to elevated temperature. This research work examines the effect of natural air cooling (AC) and water cooling (WC) on flexural behavior of M20, M30, M40 and M50 grade fire-affected retro-fitted SCC. The results of the investigation will enable the designers to choose the appropriate repair technique for improving the service life of structures.Design/methodology/approachIn this study, an attempt has been made to evaluate the flexural behavior of fire exposed reinforced SCC beams retrofitted with laminates of carbon fiber reinforced polymer (CFRP), basalt fiber reinforced polymer (BFRP) and glass fiber reinforced polymer (GFRP). Beam specimens were cast with M20, M30, M40 and M50 grades of SCC and heated to 925ºC using an electrical furnace for 60 min duration following ISO 834 standard fire curve. The heated SCC beams were cooled by either natural air or water spraying.FindingsThe reduction in the ultimate load carrying capacity of heated beams was about 42% and 55% for M50 grade specimens that were cooled by air and water, respectively, in comparison with the reference specimens. The increase in the ultimate load was 54%, 38% and 27% for the specimens retrofitted with CFRP, BFRP and GFRP, respectively, compared with the fire-affected specimens cooled by natural air. Water-cooled specimens had shown higher level of damage than the air-cooled specimens. The specimens wrapped with carbon fiber could able to improve the flexural strength than basalt and glass fiber wrapping.Originality/valueSCC, being a high performance concrete, is essential to evaluate the performance under fire conditions. This research work provides the flexural behavior and physical characteristics of SCC subjected to elevated temperature as per ISO rate of heating. In addition attempt has been made to enhance the flexural strength of fire-exposed SCC with wrapping using different fibers. The experimental data will enable the engineers to choose the appropriate material for retrofitting.

The effectiveness of a strengthening technique devised for the concrete beams subjected to bending is presented in this study, where recycled-steel fiber-reinforced mortar (RSFRM) panels are used as an eco-friendly replacement for ordinary steel fibers. Different mix designs for RSFRM are first investigated experimentally by testing 160 × 400 × 400 mm3 notched beam-like specimens in 3-point bending, while 100 × 100 × 100 mm3 cubes are tested in compression, to optimize the mix design. Finite element (FE) analyses are carried out on strengthened and non-strengthened beams to investigate the effectiveness of the proposed strengthening technique based on RSFRM panels. Starting from the tests on notched beams, an inverse FE analysis is used to optimize the RSFRM’s parameters to be implemented into the numerical model. The results show that applying RSFRM panels not only markedly increases the load-bearing capacity of the beams (up to 3.19 times with 3% of fibers by volume), but also changes their fracture mechanism from brittle to ductile fracture.

This study aims at experimentally and theoretically investigating the cracking moment (Mcrc) of hybrid Fiber Reinforced Polymer (FRP)/steel Reinforced Concrete (RC) beams. Six hybrid Glass FRP (GFRP)/steel and three GFRP RC beams with various GFRP and steel reinforcement ratios are tested in four-point bending scheme. Experimental results indicate that both GFRP and steel rebars affect Mcrc, but the effect of steel reinforcement is more significant. When the steel reinforcement ratio increases to 1.17%, Mcrc goes up to 15.9%, while the same value for GFRP is only 9.7%. An analytical method is proposed based on the plain section assumption and nonlinear behavior of materials for estimating Mcrc. The proposed model shows a good agreement with the experimental data conducted in this study and collected from the literature. The results of the parametric study give evidence of the positive effects of hybrid reinforcement ratios and elastic modulus of FRP on Mcrc of hybrid RC beams.

Three-point bending tests are performed on notched concrete beams under various cyclic loading regimes. Meanwhile, the digital image correlation (DIC) method is used to monitor the crack propagatio...

Owing to the good ductility of steel and high strength and excellent corrosion resistance of fibre-reinforced polymer (FRP), concrete beams reinforced with hybrid steel and FRP bars exhibit better ductility than FRP-reinforced concrete beams as well as higher load-carrying capacities and better corrosion resistance than steel-reinforced concrete beams. However, the inherent brittleness of concrete in tension results in steel corrosion because of wide cracks and accelerated fracture of FRP reinforcement because of crack-induced stress concentration. This study investigated the effects of ultra-high ductile engineered cementitious composites (ECCs) on the flexural behaviour of hybrid steel and FRP-reinforced beams. Six hybrid-reinforced beams with various reinforcement ratios, matrix types and ECC pouring positions were tested in four-point bending. The flexural behaviours of the beams in terms of failure modes, crack patterns and developments, load versus deformation relationships and ductility are discussed herein in detail. We observed that substituting ECC with concrete results in a higher load-carrying capacity and better ductility of the hybrid reinforced beams owing to the excellent characteristics of ECC materials. When a layer of ECC is poured in the tension zone, the average crack width and crack spacing along the beam decrease; therefore, the longitudinal reinforcements can be adequately protected.

Analytical, experimental and numerical results of determination of natural frequencies and forms of oscillations of reinforced concrete and fiber concrete beams are given. Modern analytical, numerical and experimental methods of studying the dynamics of reinforced concrete and fiber concrete beams are analyzed. The problem of determining the natural frequencies and forms of oscillations of reinforced concrete and fiber concrete beams at the initial modulus of elasticity and taking into account the nonlinear diagram of deformation of materials is solved analytically. Computer modeling of the considered constructions in four software complexes is done and the technique of their modal analysis on the basis of the finite element method is developed. Experimental researches of free oscillations of the considered designs and the comparative analysis of all received results are carried out. It is established that all involved complexes determine the imaginary frequency and imaginary form of oscillations. The frequency spectrum calculated by the finite element method is approximately 4% lower than that calculated analytically; the results of the calculation in SOFiSTiK differ by 2% from the results obtained in the PC LIRA; the discrepancy with the experimental data reaches 20%, and all frequencies calculated experimentally, greater than the frequencies calculated analytically or by the finite element method. This rather significant discrepancy is explained, according to the authors, by the incorrectness of the used dynamic model of the reinforced beam. The classical dynamics of structures is known to be based on the theory of linear differential equations, and the oscillations of structures are considered in relation to the unstressed initial state. It is obvious that in the study of free and forced oscillations of reinforced concrete building structures such an approach is unsuitable because they are physically nonlinear systems. The concept of determining the nonlinear terms of these equations is practically not studied. Numerous experimental researches and computer modeling for the purpose of qualitative and quantitative detection of all factors influencing a spectrum of natural frequencies of fluctuations are necessary here.

Reinforced concrete beams consisting of both steel and glass-fiber-reinforced polymer rebars exhibit excellent strength, serviceability, and durability. However, the fatigue shear performance of such beams is unclear. Therefore, beams with hybrid longitudinal bars and hybrid stirrups were designed, and fatigue shear tests were performed. For specimens that failed by fatigue shear, all the glass-fiber-reinforced polymer stirrups and some steel stirrups fractured at the critical diagonal crack. For the specimen that failed by the static test after 8 million fatigue cycles, the static capacity after fatigue did not significantly decrease compared with the calculated value. The initial fatigue level has a greater influence on the crack development and fatigue life than the fatigue level in the later phase. The fatigue strength of the glass-fiber-reinforced polymer stirrups in the specimens was considerably lower than that of the axial tension tests on the glass-fiber-reinforced polymer bar in air and beam-hinge tests on the glass-fiber-reinforced polymer bar, and the failure modes were different. Glass-fiber-reinforced polymer stirrups were subjected to fatigue tension and shear, and failed owing to shear.

This paper studies the flexural behaviour and ductility ratio of reinforced concrete beams made with steel fibres and coarse recycled aggregates (RAs) and strengthened after failure. Eight reinforced concrete beams (of 150 by 200 mm cross-section and 1500 mm span), with various transverse reinforcement spacings, were manufactured and tested. RAs from building demolition were used at 0% and 100% by mass to replace natural aggregates. Furthermore, steel fibres were added to improve the flexural behaviour of the beams at 0% and 2% (by volume). Both shear and flexural failures in a four-point bending test were analysed in specimens with various transverse reinforcement spacings. First, the specimens were tested to failure and then strengthened with a concrete jacket. In these tests, the flexural capacity, maximum displacement at mid-span and ductility before and after strengthening using the concrete jacket were measured. The effects of the steel fibres and of the transverse reinforcement spacing on the flexural behaviour of RA concrete beams, with and without a concrete jacket, were determined. Concrete jacketing is an efficient method for strengthening RA concrete beams, and when steel fibres, RA, and a combination of both were used, the ductility ratio increased by 160, 24 and 146%, respectively.

The work investigates changes in the beam structure under the action of local freezing, which leads to a change of the mechanical properties of the material and, consequently, of the beam structure. Two types of beam samples were used: from cement-sand mortar and from concrete. The work investigates the change in the development of deformations depending on the conditions of freezing of samples. The second accelerated method for assessing frost resistance was chosen according to DSTU B В.2.7-47-96. An accelerated method was chosen for assessing frost resistance at the temperature of -20 ±2 C°. After every five freeze-thaw cycles, the following changes were monitored: mass, water absorption, ultrasound transmission rate, damage coefficient, tensile bending strength, splitting strength, compressive strength, carbonization depth. The results showed that both in concrete and in mortar samples, the compressive strength after freezing was lower by 8% and 15% accordingly. The experimental results obtained confirm the assumptions made that the frost resistance of the material depends on the conditions of exposure of negative temperatures on products and structures and it can be used in a wider range of construction which will push regional development.

This paper offers a finite element method (FEM) to simulate the behavior of steel fiber reinforced concrete (SFRC) beams with corrosion of the longitudinal reinforcement using the ABAQUS package. This work was undertaken with the concrete damaged plasticity model (CDP). The expansion of corrosion product was utilized to represent the steel-concrete boundary to study the behavior of SFRC beams. Three beams with three volume fractions of steel fiber (0.8 %, 1.2 %, and 1.8 %) and three reinforced concrete (RC) beams with and without stirrups were created and tested under four-point loading to assess the shear capacity of beams. Corrosion of rebars at one of the RC beams that does not contain shear reinforcements will be studied. The crack patterns and load deflections of these beams were compared with experimental results found by the authors. The conclusions of this analysis will be valuable in considering the structural behavior of SFRC structures with uniform steel bar corrosion using FEM. Analytical results showed that the suggested model is qualified in better simulation and in accuracy of numerical and experimental results. The differences between analytical and experimental results were less than 8 % for load carrying capacity and 14 % for deflection; these differences are also satisfactory within the limits of the engineering conclusion.

The object of the experimental work carried out in this investigation is to study the behaviour of concrete beams reinforced externally with non-woven fabric: under impact loading. Crack initation and pattern, i.e. crack width, heights and spacing records at different stages of loading are reported and discussed. Plain and glass fibre reinforced concrete beams were cast and tested under the same conditions and cases of loading as non-woven fabric reinforced concrete beams for comparison.

As the use time of concrete structures increases, defects such as concrete cracks, corrosion and exposure of steel bars gradually appear, resulting in additional repair of concrete structures to increase their durability and life. In this article, the effects of nano-modified polymer cement-based materials as repair material on the bending behavior of repaired concrete beams were studied. Based on the moment, deflection, strain, surface quality and cracking development monitor of repaired concrete beams, the bending behavior of repaired beams with polymer, nano-modified polymer and fibers was compared and the failure mechanism of the beams was analyzed. The results showed that the nano-modified polymer cement-based materials are helpful in improving the performance of repaired beams, manifested by the increase in the ultimate bending moment and the significant improvement in the quality of the interface between repair and matrix concrete. Compared with polymer cement-based materials, nano-modified polymer cement-based materials result in a 27% increase in ultimate bending moment of the repaired beam and a 58% increase in cracking moment, while reducing the total number of cracks by 23% and the average width of cracks by 17% in the repaired beam. This article demonstrated the availability of nanomaterials for improving the loading behavior of structural components with polymer-modified cement-based materials.

Anchor serves to connect steel and concrete construction that can transfer steel pull-out load to concrete. Sanko hammer drive anchor usually has been available in the model of expansion that can be installed into concrete with cast in place and post installed methods. The experiment was aimed at comparing pull out failures of Sanko hammer drive expansion anchor using cast in place and post installed installation methods based on pull-out failure behavior. Experimental data were obtained from the pull-out strength test of Sanko hammer drive expansion anchor, compressive strength test and ready-mix concrete split tensile test, adhesion strength test and group anchor pull-out test which consists of four units of anchor with diameter of 10 mm planted 90 mm depth on T concrete beams with dimension of 300 mm x 300 mm x 150 mm as many as three beams for each of them using cast in place and post installed installation methods. The results of the experiment showed that concrete compressive tension value (f’c) is 25.69 MPa, anchor tension value (fu) is 383.25 MPa, anchor adhesion tension value (μ) with cast in place method is 2.25 MPa and post installed method is 1.56 MPa. Theoretically, the damage occurred in pull-out condition; while in the experiment, the test showed a difference in pull-out capacity using cast in place installation method of 38.38 kN with deformation of 13.81 mm, which is higher than theoretical value of 26,083 kN and using post installed method of 36.62 kN with deformation of 8.89 mm, which is higher than theoretical value of 18,084 kN and the experiment indicates that the anchor is perfectly pull-out.

Reactive powder concrete (RPC) is a special type of concrete with a microstructure optimised by precise gradation of all particles in the mix to yield the maximum density. Therefore, RPC exhibits ultrahigh strength and durability. High-strength reinforcement has both high strength and good plastic deformation properties, so a combination of RPC and high-strength reinforcement can fully exploit their respective advantages. At present, there is little research on the shear capacity of beams made from RPC reinforced with high-strength steel, neither are there design guidelines for this type of structure. This paper reports on 32 full-scale shear tests of RPC beams containing high-strength steel reinforcement. The parameters affecting the shear capacity of this type of structure were studied and the major failure modes due to shear were identified.

An analytical model is proposed to predict the transfer length in pre-tensioned concrete (PC) beams under corrosive cracking. The coupling effects of Hoyer effect and corrosion-induced cracking are incorporated in the proposed model. An experimental study is employed to assess the transfer length in PC beams under corrosive cracking. The influence of strand corrosion on the effective prestress and transfer length is investigated by the four-point bending test. Experimental results are employed to validate the accuracy of the analytical model. Results show that the transfer length depends on the corrosion degrees and corrosion positions. The transfer length increases by 24.3% once the corrosion loss of strand reaches 35%. The transfer length with the corrosion loss of 35% will extend 8.6% when the corrosion position moves from the mid-span to the beam end. The elastic modulus of concrete and the Poisson’s ratio of strand can affect the transfer length in PC beams under corrosive cracking. The transfer length under corrosive cracking will increase with the increase of elastic modulus of concrete and Poisson’s ratio of strand, and Poisson’s ratio of strand has a significant effect on the transfer length as compared to the elastic modulus of concrete.

Analytical models are proposed to predict the shear strength of steel-fibre-reinforced concrete beams from existing experimental results of 222 such beams without stirrups. The beams were sorted into six different types based on ultimate strength of concrete, span–depth ratio and shape of the steel fibres (plain, crimped and hooked). A genetic-algorithm-based approach was used to predict the most feasible equation to estimate the shear strength of each group of beams accurately. A variety of statistical analyses for each suggested model was performed and compared with the results of existing studies in predicting the beams’ shear capacity. The proposed empirical models were able to assess the shear strength of beams more accurately than previously developed models.

This paper describes experimental results that focus on impacts of elevated temperature on concrete with GGBFS. GGBFS from waste of steel factory PT Krakatau Steel Tbk. has been discovered to be appropriate for geopolymer cement as substitute for cement in concrete. Normal concrete and GGBFS concrete beams (150×150×750mm) and cylindrical (150×300mm) with 40% GGBFS content as substitute of cement weight were burned for two hours, which the first beam was burned at 600°C, second beam at 700°C and third beam at 800°C. After cooling to room temperature, cylindrical and beams were tested. Compressive strength, modulus of elasticity and flexural strength were examined and compared. The results show that GGBFS increased durability of concrete and might be utilized in applications including elevated temperatures. High temperature exposure causes compressive strength of normal concrete decreased extremely up to 69.08%, compared to GGBFS concrete only 46.21%. Flexural strength decreased to 30.37% when the temperature rises to 700°C. Furthermore, it decreased significantly to 50.82% when the temperature reached 800°C.

Different techniques were employed for the passage of different utilities through structural elements. The reduction of the overall building weight was the main concern that needs to be achieved, especially for a multistory building. It can be done with the eliminating of a suspended ceiling with a portion of the beam’s weight by taking the advantages of the hollow sections. In this study, an equivalent reinforcement to the traditional ribbed reinforcement was employed to fabricate a reinforced concrete (RC) beam with a hollow section along the length of the beam. A steel pipe was used based on the equivalent moment from section analysis. Two diameters were selected of steel pipes as an equivalent to the commercial reinforcement. A total of four RC beams were cast and tested, two of them with traditional reinforcement and the other with steel pipe reinforcement. The comparison showed a promising result in terms of ductility, cracking pattern, ultimate strength, and mode of failure compared to the reference beam. The peak loads for the specimens with steel pipe were 160.6 kN and 184 kN, while they were 192 kN and 203.5 kN for the beams with traditional reinforcement.

In this research, the long-term potential cracking of normal concrete internally cured with clay brick waste as a sustainable approach was investigated. 10% and 15% volume of sand was substituted with corresponding quantity of pre-saturated clay brick waste to enhance the hydration of cement and improve properties of concrete. Four beams internally cured were compared with two control beams. The use of clay brick waste can improve the compressive and splitting tensile strength and also a significant reduction in cracks were observed. Depending on the recorded results, it is demonstrated that the exemplary percentages of clay brick waste to natural fine aggregate was found to be 15%, which developed greatest compressive and splitting tensile strength, and reduce the crack by means of flexural test.

In this research, experiments and numerical simulations are employed to research the failure process of concrete. Fracture experiments on three-point bending (TPB) concrete beams with a prefabricated edge notch at the middle of the beam bottom are performed using a modified rigid testing instrument. The characteristics of the crack and section are analyzed, including the crack tensile opening displacement, crack length and width, and crack faces characteristics. Also, the full curves of the force-crack tensile opening displacement (CMOD) and force-deflection of the TPB beams with the prefabricated edge notch after breakage are obtained. The phase field (PF) damage model is applied to the mixed-mode and mode-I failure processes of concrete structures through the ABAQUS subroutine user defined element (UEL). The crack path and the full curves of force-CMOD and force-deflection obtained by numerical calculations are consistent with the experimental results and the calculated results of other researchers. The influences of the mesh sizes, initial lengths, and notched depths on the TPB beam of concrete are also analyzed.

When glass fibre-reinforced polymer (GFRP) bar splices are used in reinforced concrete sections, they affect the structural performance in two different ways: through the stress concentration in the section, and through the configuration of the GFRP–concrete bond. This study experimentally investigated a new method for increasing the bond strength of a GFRP lap (two GFRP bars connected together) using a carbon fibre-reinforced polymer (CFRP) sheet coated in epoxy resin. A new splicing method was investigated to quantify the effect of the bar surface bond on the development length, with reinforced concrete beams cast with laps in the concrete reinforcing bars at a known bending span length. Specimens were tested in four-point flexure tests to assess the strength capacity and failure mode. The results were summarised and compared within a standard lap made according to the ACI 318 specifications. The new method for splicing was more efficient for GFRP splice laps than the standard lap method. It could also be used for head-to-head reinforcement bar splices with the appropriate CFRP lapping sheets.

This paper presents an investigation of the performance of concrete beams reinforced with glass fiber-reinforced polymers (GFRP) under short-term loading. A total of six specimens with rectangular cross-sections (75 mm in height and 150 mm in width) were tested under a four-point bending test to failure. Each specimen was reinforced with two GFRP bars with diameters of 8 mm. The results of this study demonstrated the behavior of GFRP-reinforced concrete members and a validation of the available calculation methods for the deflection of these members and assumed possibilities of the use of a GFRP reinforcement over the long term. The results of the study presented show a very good agreement of an experimentally measured and theoretically calculated instantaneous deflection when using the approaches in the European and American standards. In calculations of long-term deflections, the results are highly inconsistent and seem to be quite overestimated in some cases. The study shows the necessity of real-time long-term measurements to demonstrate the real deformations to be assumed during design of structures reinforced with GFRP reinforcement.

This Lightweight concrete is one of the important types familiar of concrete, as the local stone Attapulgite was used as aggregate after treating it with a solution of minors, then it was used in pouring five -reinforced concrete beams by adding steel fiber and iron filing separately with two percentages of 0.5 and 1, these beams were examined to determine the shear capacity. The results showed that iron filing by 1% improve the mechanical properties of concrete and similar to that of using steel fibers, but with a minimum effect. The results also showed that adding 1% of steel filing improves the maximum shear resistance and the first cracking resistance of the concrete by 38%.

Lightweight concrete reduces the total dead load of structural elements and seismic loads significantly. This paper presents the production Attapulgite Lightweight aggregate concrete (ALWAC) and its effect on the flexural behavior of reinforced concrete beams. Attapulgite was treated with sodium hypochlorite of 6% concentration for 24 hours. The variable considered was the aluminum waste (AW), used as a fiber, of fraction (0, 0.5 and 1%) by concrete volume. Behavior was investigated in terms of cracking and ultimate load, load-deflection relationship, failure mode, crack patterns and flexural ductility. The mechanical properties of the ALWAC were studied. It was observed that, Attapulgite improves the mechanical properties of concrete when comparing the experimental value with theoretical ones for the reference mixture. AW has a disparate effect on the mechanical properties of ALWAC. The increase in the proportions of AW showed an increase in the cracking load and decrease in the ultimate load by 37.14% and 22.45 %, respectively, at AW of 1%. Experimental value of ultimate load in all beams was higher than the theoretical value (ACI simplified method). AW increases the deflection at the same magnitude of applied load, and reduces the number and propagation of the flexural cracks in beams. All beams exhibited a typical tension failure mode and failed in ductile manner.