Beam Specimens Research Articles

Flexural behavior of cold‐formed U‐shaped steel members encasing concrete composite beam using continues stud bolts

AbstractThe current paper presents an innovative form of the cold‐formed U‐shape steel encasing concrete composite beam (CUCB). The suggested CUCB consists of a cold‐formed U‐shaped steel encasing plain concrete beam which are connected to each other using continuous transversal threaded stud bolts. The experimental program consisted of eight beam specimens tested in the four‐point bending set‐up. One of them was a normal reinforced concrete beam and considered as a reference specimen while the remaining specimens were CUCB specimens without ordinary flexural and shear reinforcement. Four parameters were studied in this paper: (i) the thickness of the U‐shaped steel, (ii) the spacing between the stud bolts, (iii) the arrangement of the bolts, and (iv) the number of the bolt's rows. Results indicated an overall improvement in the load‐carrying capacity and stiffness of most CUCB specimens in comparison with the reference specimen. It was found that the using of three rows of bolts can significantly improve the ductility and toughness of the CUCB specimen in comparison with two rows of bolts. On the contrary, an increase in the bolt spacing entails a decrease in the CUCB specimens' toughness.

Effects of carbon/glass nonwoven interleaving veils and their areal density on opening and shearing mode interlaminar fracture toughness of glass epoxy composites

The study explores the impact of Carbon and Glass nonwoven interleaving veils with varying areal density on delamination resistance in unidirectional (UD) Glass epoxy composites under Opening (Mode-I) and Shearing (Mode-II) mode loadings. Commercially available non-woven Carbon and Glass interleaves with areal densities of 15, 20, 25, and 30 g/m2 were used to manufacture the interleaved Glass epoxy laminates. Double Cantilever Beam (DCB) and End Notch Flexural (ENF) specimens were used to determine the mode-I and mode-II fracture energies. The results reveal that, during mode-I initiation, interleaved laminates exhibit a lower interlaminar fracture toughness (IFT) except for the Carbon fiber interleaved laminates of areal density 30 g/m2. However, during propagation, all veils interleaved laminates presented significant improvement in IFT ranging from 5 to 25 % accompanied by substantial fiber bridging. In case of mode-II test, the laminates with Carbon and Glass veils exhibit enhanced IFT (60–182 %) with increasing areal density compared with the non-interleaved Glass laminates. Optical and scanning electron micrographs (SEM) provide evidence of fracture mechanisms involved in the interleaved and non-interleaved composite laminates.

Characterization of crack-bridging and size effect on ultra-high performance fibre reinforced concrete under fatigue loading

The use of ultra-high performance fibre-reinforced concrete (UHPFRC) has become popular owing to its high strength, durability and toughness characteristics compared to conventional concrete. In this work, experimental investigations have been carried out to examine the fracture behaviour of UHPFRC beam specimens under static and fatigue loading with an emphasis on understanding the size effect. Experimental results of both monotonic and fatigue have been utilized to develop a mathematical formulation for predicting crack bridging degradation considering the fatigue loading history. Subsequently, the size effect behaviour on the crack-bridging strength of UHPFRC beams under fatigue loading conditions has been explored. An algorithm has been developed to predict crack propagation as a function of load cycles and to estimate the fatigue life corresponding to any load amplitude, accounting for the size effect. The crack-bridging strength has been observed to decrease with an increase in specimen size, lowering the fatigue life.

Physio-chemical, mechanical and fracture analysis of ultra-high-performance cementitious composite

The aim of this research was to develop cost-effective and environmentally friendly ultra-high-performance concrete (UHPC) using fly ash (FA) and quartz powder (QP) as sustainable cement replacements. The performance of the various constituents was examined and their influence on fresh and hardened properties was investigated in order to determine the optimum trial mix design. A cube compressive strength of 144 MPa was achieved with 20% FA and 10% QP and other ingredients without any special heat treatment. Advanced characterisation studies, such as the heat of hydration and X-ray diffraction analysis, were performed to gain understanding of the performance of FA-blended UHPC. Various fracture properties (fracture toughness, fracture energy, brittleness etc.) were investigated considering geometrically similar notched beam specimens for UHPC mixes with steel fibre contents of 1.5% and 2.5%. The optimum UHPC mix achieved good scores in terms of the strength index and the embodied carbon dioxide emissions index, indicating that the concrete is eco-friendly and sustainable.

Global performance indicator (GPI) approach to predict the steel fiber reinforced concrete strength with error analysis

ABSTRACT The main aim and objective of the present research is to forecast the strength of steel fiber reinforced concrete (SFRC) using four mathematical models developed with five independent variables viz. control strength, aspect ratio, percentage of steel fiber, water to cement ratio and aggregate to cement ratio. These models provide the best model with the best performance to be determined by error analysis. For obtaining the experimental data, concrete cubes of size 150 mm x 150 mm x 150 mm are tested under compression. For flexure strength, beam specimens of size 150 mm × 150 mm x 700 mm are casted with steel fiber reinforced concrete. Thus error analysis is performed for exponential mathematical models, log-linear models, analytical models and Artificial Neural Network (ANN) models to compute response variables considered in the study. The calibrated model was analyzed, compared, and ranked using the Global Performance Indicator (GPI). Difference between standard deviation of predicted and experimental data is found to be -0.082 for exponential model and for ANN model it is computed as 2.771. The exponential mathematical model shows a higher GPI value as 0.67, whereas ANN model exhibits lower GPI value as -6.94. The novelty of the work is that, this research compares the models based on the mean value, mean error, % error, mean square error (MSE) and root means square error (RMSE) of the model when compared with field data. Experimental results are also provided for steel fiber reinforced concrete (SFRC). The effectiveness of GPI approach to predict the fiber reinforced concrete (FRC) strength is discussed.

A four-point bending technique for characterizing the interface fracture toughness between soft thin films and stiff substrates

Interface fracture toughness, also called work of adhesion or adhesion energy, is a quantity characterizing the resistance of an interface between two adhered solids against interfacial delamination. Determining the interface fracture toughness should be of great value to the studies on the related adhesion and delamination problems. Four-point bending test is an experimental approach that was originally used to measure the flexural stiffness and fracture toughness of monolithic materials. It was also used to characterize the fracture toughness of the interface when a bi-layered notched composite beam specimen is adopted (Int. J. Frac. 1989; 40: 235). However, this method does not work very well when a thin and soft material is encountered because the interface delamination cannot be triggered easily. To address this problem, in this paper, we revise the configuration of the four-point bending specimen from bi-layer to tri-layer by imposing an additional stiffer layer on the top of the thin and soft layer. The analytical solution to the energy release rate of the preexisting interfacial crack is revisited. Finite element analysis is carried out to assess the applicability and limitations of the analytical solution. With the modified four-point bending specimen, the interface fracture toughness between an epoxy coating and a steel substrate is successfully measured from the critical load that leads to the delamination of the preexisting interfacial crack.

Combined deterioration effects of freeze–thaw and corrosion on the cyclic flexural behavior of RC beams

Reinforced concrete (RC) stands as the predominant construction material, and with the growing prevalence of aging infrastructure, the safety assessment of deteriorating structures has emerged as a pressing and critical concern. This study presents an experimental investigation into the combined effects of freeze–thaw cycles (100, 200, and 300 cycles) and corrosion (corrosion ratio: 3% and 10%) on the cyclic behavior of RC beams. Seven RC beam specimens with varying types and levels of deterioration were fabricated, and static tests were conducted using a four-point bending method to assess the behavior of RC beams under each degradation factor. The experimental results revealed that increasing freeze–thaw cycles significantly impact RC beam behavior, leading to intensified crack formation due to cyclical frost-heaving pressure. This ultimately results in reduced yield loads ranging from 3% to 11% and peak loads reduced by 1–2% compared to the reference specimen A-0-0. Corrosion of steel bars in RC beams alters failure modes, with corroded specimens (C-0-3 and C-0-10) experiencing substantial decreases in yield load, a 15% reduction in C-0-3, and a 26% decrease in C-0-10, compared to A-0-0. Displacement at yield load and peak load also decreased, highlighting the detrimental impact of corrosion on beam mechanical properties. The combined deterioration from freeze–thaw cycles and corrosion further exacerbates these reductions, resulting in a substantial decrease in yield load (32%) and peak load (24%) in D-3-10 compared to the reference specimen A-0-0. Additionally, energy dissipation capacity and cumulative energy dissipation capacity exhibit dynamic changes influenced by the progression of freeze–thaw cycles, corrosion, and their combined effects.

CRACK EFFECT ON THE NATURAL FREQUENCY OF COMPOSITE BEAM: FINITE ELEMENT ANALYSIS WITH EXPERIMENTAL STUDY

Cracks in structural elements can significantly affect their dynamic behaviour and lead to detrimental consequences. This study investigates the influence of cracks on the natural frequency of a laminated beam under free vibration, employing a combination of finite element method (FEM) analysis and experimental work. The numerical computation is done using ABAQUS simulation software by developing a comprehensive FEM model that accurately represents the laminated beam's mechanical behaviour, considering material anisotropy, geometry and crack propagation. The finite element model is validated through experimental tests conducted on both intact and cracked laminated beam specimens. The experimental setup utilizes Fast Fourier Transform (FFT) analyzer high-precision measurement tool to obtain accurate natural frequency values. The parametric study is conducted to analyze the impact of crack location, size, and orientation on the laminated beam's natural frequency. The FEM simulations reveal that the presence of cracks leads to a reduction in natural frequency, indicating a decrease in structural stiffness. The extent of frequency reduction is found to be influenced by crack characteristics and their proximity to critical locations within the beam. The experimental investigations corroborate the FEM findings, highlighting the consistency between numerical predictions and actual measurements.

Structural Behavior of a Fixed-End Arched Cellular Steel Beam without Lateral Support

The arched cellular beam has the advantages of both the solid-web arch and the straight beam with web opening, and has become increasingly admired by architects in recent years. In this paper, four arched cellular beam specimens are designed using an orthogonal test method (OTM) with a three-factor and two-level approach. Firstly, the static loading test is carried out to analyze the mechanical response of the arched cellular beam under concentrated load. Then, a numerical analysis based on ABAQUS finite element (FE) software is carried out. The results show that the simulation results agree well with the test results, which indicates the accuracy of the simulation analysis method. Finally, the buckling load of the arched cellular beam under three different loads is calculated using the variable parameter FE analysis. Combined with the range analysis in the OTM, the influence of the target factor on the buckling load of the arched cellular beam is determined. The results show that the order of the factors affecting the out-of-plane elastic buckling is rise–span ratio > web height–thickness ratio > diameter–depth ratio.

Demountable composite beams for a circular economy: Large‐scale beam tests

AbstractThe circular economy approach has been introduced to the construction sector to design out waste, reduce carbon emissions and energy use in production of primary materials and achieve resource efficiency. ‘Design for deconstruction’ is increasingly important for a sustainable economy, especially for composite structure that is deemed as resource‐efficient in the first cycle of use. With this background, research has been conducted to facilitate the use of demountable composite beams in steel‐framed structures. This article presents the results of two 6 m full‐scale composite beam tests with prefabricated composite slabs. Demountable shear connectors were used, which have been newly developed within the frame of an EU project. The nominal degree of shear connection of the composite beam specimens was 0.37, which was slightly below the required 0.4 specified in EN1994‐1‐1 for welded shear studs. Based on the experimental observations, it can be demonstrated that (1) the tested demountable composite beam produced higher resistance but lower stiffness values than a comparable reference composite beam with welded shear studs; (2) the beam specimens showed a good plastic behaviour with high ductility despite the non‐ductile nature of the applied demountable shear connectors. Remarks on the demountability of the developed demountable composite beams are provided.

Experimental investigations on tensile strength and fracture toughness of a polyoxymethylene fiber reinforced concrete

The crack resistance performance of concrete materials, characterized by tensile strength and fracture toughness, is vital for the durability and structural functionality of concrete components. In this study, polyoxymethylene (POM) fibers were added into concrete to enhance the crack resistance. Firstly, three-point-bending (3-p-b) tests and splitting tension tests were performed on notched beam and cubic specimens of plain concrete and POM fiber reinforced concrete. Then, considering the heterogeneity of concrete, the 3-p-b and splitting tension test results were analyzed to reveal the failure behaviors of plain concrete and POM fiber reinforced concrete materials. It was found that the addition of POM fibers was beneficial for improving the fracture resistance of concrete. The Boundary Effect Model (BEM) was used to estimate the tensile strength and fracture toughness of plain concrete and POM fiber reinforced concrete materials from the 3-p-b test results, which correlated well with those obtained from the splitting tension tests and the conventional method. Moreover, the influence of POM fiber length and volume fraction on fracture resistance was evaluated. Findings revealed that increasing fiber length and volume fraction effectively enhanced the tensile strength and fracture toughness of concrete material.

Effect of partial replacement of aggregate with oil palm shell on compressive and flexural strength of fiber concrete

Considerable innovation has been applied to concrete material to achieve specific properties such as density, strength, environmental sustainability, cost-effectiveness, among others. This study focused on the replacement of a portion of the aggregate with oil palm shell (OPS) to utilize previously underutilized waste. Concrete containing OPS typically exhibits reduced compressive strength compared to standard concrete. To enhance the compressive and flexural strength of OPS-infused concrete, the introduction of fibers was explored as an innovative measure. A particular focus was placed on using fibers from discarded masks due to the Covid-19 outbreak in Indonesia and globally. The non-biodegradable nature of polypropylene fibers in these masks necessitates further measures to minimize waste. Different proportions of OPS were incorporated into the concrete mix: 0%, 25%, 50%, 75%, and 100%, with each mix incorporating 0.20% mask fiber and 0.25% superplasticizer. Compressive strength testing employed cylindrical specimens with a diameter of 75 mm and a height of 150 mm, while flexural strength was assessed using beam specimens measuring 100 x 100 x 500 mm. The baseline compressive strength for concrete without OPS measured 17.76 MPa. The results of flexural strength testing revealed the highest value of 1.67 MPa for the 0% OPS mix and the lowest, 0.49 MPa, for the 100% OPS mix. Statistical analysis via analysis of variance (ANOVA) highlighted a notably significant correlation between the treatment combinations involving compressive strength and the replacement of OPS as coarse aggregate.

The effect of abrading treatment method on the bonding surface characteristics and fracture behavior of glass fiber-epoxy composite adhesive joints

The effect of the mechanical abrading method on the bonding surface characteristics and fracture response of glass fiber-reinforced polymer (GFRP) composite adhesively bonded joints was investigated. Double cantilever beam specimens were manufactured by bonding GFRP substrates with an epoxy adhesive to evaluate the mode-I adhesive joint fracture response. The bonding surfaces were treated with degreasing and abrading methods utilizing sandpapers with various grit sizes ranging from P60 to P800. The results showed that the sandpaper grit size can considerably change the bonding surface properties comprising the surface energy, roughness, morphology, and water drop contact angle and consequently, it can affect the joint fracture behavior. Reducing the sandpaper grit size continuously increased the surface roughness but there were optimum values for the surface energy and water drop contact angle. The fracture resistance of adhesive joints followed the trend of bonding surface energy as the higher the bonding surface energy, the higher the joint fracture resistance. The fracture energy and load-bearing capacity of adhesive joints were improved by 62 and 34%, respectively, when the joint bonding surfaces were abraded with P240. However, further reducing the sandpaper grit size to P60 caused a decrease in the fracture energy and load-bearing capacity of adhesive joints by 18 and 44%, respectively, compared to the joint with degreased and non-abraded bonding surfaces. Moreover, the abrading method considerably changed the microscopic and macroscopic failure modes of adhesive joints.

Fatigue Crack Propagation in 5754 Aluminum Alloy under Four-Point Bending

The aluminum 5754 alloy is one of the widely used engineering materials in shipping, rivet making, tread plates and automotive industries. These engineering structures envisage variable loading conditions during their service. In addition to it, it is also experiencing seismic vibrations. Hence, the engineering components made from such aluminum alloy are susceptible to fatigue fracture. In the current study, the prediction of fatigue crack growth (FCG) in 5754 aluminum alloy was made using the exponential function. The beam specimen comes up with a cross-section of 25X25 mm2, a span length of 300 mm with a mechanical notch length of 2.70 mm at the centre was subjected to four-point bending (FPB) employing hydraulic INSTRON 8800 tensile testing apparatus. The periodic loading condition deformed the material up to large plastic deformation. The applied load was further down the elasticity of the material. The experimental data provided the relation between crack length (a) to the number of cycles (N) to failure. The response surface methodology (RSM) and modified exponential equation were used to predict the FCG. In RSM, when “stress intensity factor (K)” and “number of the cycle (N)" were considered independent variables, the response (a) was optimum (maximum) as compared to when “stress intensity factor range (del K)” and “fatigue crack growth rate (da/dN)” were considered independent variables. Hence, for designing the aluminum 5754 alloys as engineering structures, it was the number of cycles which provides a safe design as compared to da/dN. The modified exponential equation using an exponential function predicted the FCG for aluminum 5754 alloy in the form of a beam specimen. The anticipated results agreed with experimental data as the prediction ratio was 1.20 and the % deviation was 3.7.

Numerical investigation of two-dimensional Mode-II delamination in composite laminates

Existing standards for delamination tests on composite materials typically employ one-dimensional (1D) beam specimens. However, such specimens may not represent real delamination scenarios in composite structures, where cracks tend to propagate in two dimensions. To address this limitation and compare the delamination behavior under both 1D and two-dimensional (2D) Mode-II fracture conditions, a numerical investigation was carried out based on previous experiments. A novel cohesive zone model, considering both microcracking and fiber bridging within the fracture process zone, was developed using a semi-experimental approach and incorporated in three-dimensional finite element simulations. According to the numerical results, the investigated laminates exhibited similar maximum strain energy release rates in both 1D and 2D delamination; however, different traction-separation responses were obtained. Practical methods of locating the tip of an embedded crack were proposed based on curvature and strain measurements on the laminate surface, demonstrating potential for application in structures with irregular crack shapes.

Cohesive Properties of Bimaterial Interfaces in Semiconductors: Experimental Study and Numerical Simulation Using an Inverse Cohesive Contact Approach.

Examining crack propagation at the interface of bimaterial components under various conditions is essential for improving the reliability of semiconductor designs. However, the fracture behavior of bimaterial interfaces has been relatively underexplored in the literature, particularly in terms of numerical predictions. Numerical simulations offer vital insights into the evolution of interfacial damage and stress distribution in wafers, showcasing their dependence on material properties. The lack of knowledge about specific interfaces poses a significant obstacle to the development of new products and necessitates active remediation for further progress. The objective of this paper is twofold: firstly, to experimentally investigate the behavior of bimaterial interfaces commonly found in semiconductors under quasi-static loading conditions, and secondly, to determine their respective interfacial cohesive properties using an inverse cohesive zone modeling approach. For this purpose, double cantilever beam specimens were manufactured that allow Mode I static fracture analysis of the interfaces. A compliance-based method was used to obtain the crack size during the tests and the Mode I energy release rate (GIc). Experimental results were utilized to simulate the behavior of different interfaces under specific test conditions in Abaqus. The simulation aimed to extract the interfacial cohesive contact properties of the studied bimaterial interfaces. These properties enable designers to predict the strength of the interfaces, particularly under Mode I loading conditions. To this extent, the cohesive zone modeling (CZM) assisted in defining the behavior of the damage propagation through the bimaterial interfaces. As a result, for the silicon-epoxy molding compound (EMC) interface, the results for maximum strength and GIc are, respectively, 26 MPa and 0.05 N/mm. The second interface tested consisted of polyimide and silicon oxide between the silicon and EMC layers, and the results obtained are 21.5 MPa for the maximum tensile strength and 0.02 N/mm for GIc. This study's findings aid in predicting and mitigating failure modes in the studied chip packaging. The insights offer directions for future research, focusing on enhancing material properties and exploring the impact of manufacturing parameters and temperature conditions on delamination in multilayer semiconductors.

Study on Crack Resistance and Calculation Model of RAC Beams Strengthened with Prestressed CFRP

With the development of recycled aggregate concrete (RAC), the recovery rate of construction waste is improved, and the pollution problem is alleviated. In particular, RAC beams strengthened with prestressed carbon fiber reinforced plastics (CFRP) can exhibit improved mechanical properties, expanding RAC application. Four groups of reinforced RAC beam specimens contained 0%, 40%, 70%, and 100% recycled coarse aggregate, respectively. Each group of beams was first pre-cracked and then strengthened by prestressed CFRP with one layer and two layers respectively. Finally, the bearing capacity tests were performed for these beams. The test results show that as the recycled coarse aggregate content increases, the cracking moment and ultimate load capacity of the beam decrease, while its crack width increases. As the CFRP layer increases, the deformation and crack width of the beam decreases, while the number of cracks increases. The prestressed CFRP also exhibited tensile and peeling failure. A beam deflection calculation model was established by introducing a coefficient k representing the interaction between recycled aggregate and CFRP. The influence coefficient of concrete elongation on the crack width and average crack spacing of the beam was modified, and the crack width analysis model of the beam was established. The calculated results are in good agreement with the experimental observations. It can provide reference for the application and design of recycled concrete beams strengthened with prestressed CFRP.

Determination of the Probabilistic Properties of the Critical Fracture Energy of Concrete Integrating Scale Effect Aspects

This paper presents an extension of the validation domain of a previously validated three-dimensional probabilistic semi-explicit cracking numerical model, which was initially validated for a specific concrete mix design. This model is implemented in a finite element code. The primary objective of this study is to propose a function that enables the estimation of the critical fracture energy parameter utilized in the model and validate its effectiveness for various concrete mix designs. The model focuses on macrocrack propagation and introduces significant aspects such as employing volume elements for simulating macrocrack propagation and incorporating two key factors in governing its behavior. Firstly, macrocrack initiation is linked to the uniaxial tensile strength (ft). Secondly, macrocrack propagation is influenced by a post-cracking dissipation energy in tension. This energy is taken equal to the mode I critical fracture energy (GIC) based on the linear elastic fracture mechanics theory. Importantly, both ft and GIC are probabilistic properties influenced by the volume of concrete under consideration. Consequently, in the numerical model, they are dependent on the volume of the finite elements employed. To achieve this objective, numerical simulations of fracture mechanical tests are conducted on a large double cantilever beam specimen. Through these simulations, we validate the proposed function, which is a crucial step towards expanding the model’s applicability to all concrete mix designs.

Comparison of stiffness degradation in fatigue-loaded concrete cylinders and large-scale beams

Wind and wave loads subject the tower structures of wind turbines to bending stress. The resulting initial linear strain gradients in the tower cross-section cause fatigue-induced degradation of the concrete at the outer edge of the structures. As the number of load cycles increases, stresses are gradually redistributed to the inner cross-section of the structure consequently. Most of the test results documented in the literature were obtained from small-scale concrete specimens or small-scale components. In those cases, the stiffness and stress redistributions occurring in the real component can only be insufficiently derived, and possible scale effects cannot be taken into account. Besides, available test results for individual component tests are mostly only for load cycles up to 2⋅106. However, significantly lower load levels and thus higher number of load cycles are expected to occur in wind turbines compared to usual fatigue tests. To deal with this issue, extensive fatigue tests on small cylindrical specimens as well as large-scale beams in the very-high-cycle fatigue range are carried out in this work. The test results of both cylindrical and beam specimens show the typical three-phase stiffness curves known from the literature. These curves exhibit a disproportionate decrease at the beginning of the loading, followed by a constant decrease in stiffness, and finally, a greater decrease in stiffness shortly before failure. Moreover, the stiffness curves from the tests on both specimen types show good agreement. It can be concluded that the results from small cylindrical specimen tests can be transferred to large-scale structural components.

Influences of nano-clay amount on flexure behavior of concrete identified by acoustic emission

Nano-modification is an effective method currently used to improve mechanical properties of concrete by adding various nanomaterials. The results obtained from previous studies demonstrate that presence of these particles has positive effects on both mechanical and durability performances of concrete. However, while the existing studies investigate the state of resistance, revealing progressive failure mechanism of nano-particle added concrete under loading is a significant subject. In this regard, Acoustic Emission (AE) method is useful for identification of invisible damage progress by means of basic phenomenon defined as release of energy due to a fracture and propagation of it as elastic waves in a stressed medium. Apart from the existing studies in the literature, this paper is focused on investigation of the influences of nano-clay on mechanical and failure behaviors of concrete by AE. For this purpose, a plain and three different concrete mixtures including 1%, 3% and 5% nano-clay (NC) of cement weight were prepared. 100x100x600 mm beam specimens were produced from these mixtures and were tested under three-point-bending. Furthermore, to reveal invisible failure mechanisms of the specimens, all tests were simultaneously monitored with AE method. The results reveal that presence of nano-clay increases the load capacity and ductility of the concrete specimens which is also confirmed by AE results, as more amount of micro-scale events are obtained.Nano-modification is an effective method currently used to improve mechanical properties of concrete by adding various nanomaterials. The results obtained from previous studies demonstrate that presence of these particles has positive effects on both mechanical and durability performances of concrete. However, while the existing studies investigate the state of resistance, revealing progressive failure mechanism of nano-particle added concrete under loading is a significant subject. In this regard, Acoustic Emission (AE) method is useful for identification of invisible damage progress by means of basic phenomenon defined as release of energy due to a fracture and propagation of it as elastic waves in a stressed medium. Apart from the existing studies in the literature, this paper is focused on investigation of the influences of nano-clay on mechanical and failure behaviors of concrete by AE. For this purpose, a plain and three different concrete mixtures including 1%, 3% and 5% nano-clay (NC) of cement weight were prepared. 100x100x600 mm beam specimens were produced from these mixtures and were tested under three-point-bending. Furthermore, to reveal invisible failure mechanisms of the specimens, all tests were simultaneously monitored with AE method. The results reveal that presence of nano-clay increases the load capacity and ductility of the concrete specimens which is also confirmed by AE results, as more amount of micro-scale events are obtained.