Shear Failure Mechanism Research Articles

Force transfer mechanism in RC beams strengthened in shear by means of steel plated concrete

Experimental and numerical studies were conducted to investigate the shear failure and force transfer mechanism of seven reinforced concrete (RC) beams that were shear-strengthened with a composite material based on steel-plated concrete (called also Steel-Plated Concrete Composite-SPCC). The SPCC method was proposed to overcome the disadvantages of the traditional, externally bonded, steel plate method. In the tests, the stress and shear contribution of the steel web were calculated based on strain values measured with rosette sensors, and in accordance to the theories of elasticity and plasticity. The shear contribution of new and old concrete was calculated by subtracting the shear force of the steel web from the total shear force. The experimental results demonstrated that the shear force of the steel web ranged from 50% to 77% of the designed shear strength, contrary to the typical assumption of 100%. The shear-span-to-depth ratio was an important factor influencing the force transfer mechanism of the steel-plated shear strengthened (SPSS) beam. In the numerical simulation analysis, an elaborate finite element (FE) model was developed based on the fixed angle crack model (FACM). Comparisons with the experimental results showed that the developed model predicts the overall structural behaviour, the individual contribution of the steel web, and the concrete and the failure modes, with a reasonable level of accuracy. Additionally, the influence of key factors on shear capacity is discussed in detail. Finally, a simplified prediction formula for the shear capacity of the SPSS technique was proposed with sufficient accuracy based on 1152 nonlinear FE models.

Full Height Rectangular Opening Castellated Steel Beam with Diagonal Stiffener

The full height rectangular opening castellated steel beam failed in Vierendeel mechanism. This makes the flexural capacity of castellated steel beam is lower than the original IWF section. This paper discusses analysis and test result of a full height rectangular opening castellated steel beam with diagonal stiffener. The diagonal stiffener used in this research has a purpose of preventing Vierendeel mechanism. This research used two specimens, a short span specimen to study shear behavior, and a long span specimen to study flexural behavior. Test results show that the long span specimen can avoid Vierendeel mechanism and increase the yield moment capacity by 1.6 times of the original IWF section. The failure of the short span specimen is a combination of shear failure and Vierendeel mechanism as in elastic condition, the diagonal stiffener, flange, and web post were worked and failed together. Based on the test result, truss analysis method can be used to calculate the flexural capacity of full height rectangular opening castellated steel beam with diagonal stiffener. Theoretical calculation of yield moment capacity of the long span specimen has 8.25% difference from the real yield moment capacity.

Mechanism of shear failure near fracture face during drainage process of CBM well

In this paper, whether the coal fines can be induced by shear failure during drainage process has been discussed in detail. By coupling with the percolation theory, the elasticity mechanics were used to construe the extra stresses in the formation surrounding with the hydraulic fracture. The safe window of the bottom hole pressure was also calculated from the failure envelope. The research shows that the formation pressure on the fracture surface of the coal seam is negatively related with the bottom hole pressure, and the induced stress is positively related with the bottom hole pressure during the drainage process of fractured CBM wells. The pore pressure around the fracture changed due to pore-elastic effects, which also caused a significant change of the in situ stresses. In order to avoid the breakout of the coal seam around hydraulic fracture during drainage process, the model of the reasonable bottom hole pressure is also built.

Numerical simulation and shear resistance of reinforced concrete beams under impact

High-fidelity finite element models of drop weight tests on reinforced concrete (RC) beams conducted previously by the authors are developed and validated by comparing the numerically simulated results with measured experimental data. The validated models are then utilized to examine the influence of beam span on the impact responses of typical beams. It is shown that the beam response is characterized by localization at an early stage during the impact process. By employing a modified span to characterize this response localization, the characteristics of local shear failure mechanisms under impact are investigated. Finally, a simplified three-degree-of-freedom model considering response characteristics of both local shear and overall flexural deformation modes is proposed and shown to perform comparably to the finite element simulations. The concept of a mass-velocity interaction diagram is proposed for shear damage evaluation of RC beams under impact.

Bearing capacity and failure mechanism of ground improved by deep mixed columns

Extensive research has investigated the bearing capacity of footings placed on leveled ground improved by deep mixed (DM) columns. However, few studies have focused on the effects of the embedment on the bearing capacity of footings on ground reinforced with DM columns. In geotechnical engineering practice underestimation of the limit load has occurred in China because of the increased use of conventional design methods for reinforced ground with embedment. In this investigation, a numerical model using a rigorous limit analysis tool, known as discontinuity layout optimization (DLO), is established. An equivalent area model is employed with an appropriate stress concentration ratio. Subsequently, a set of design charts of bearing capacity coefficients is produced with a special focus on the bearing capacity coefficient Nq and the failure mechanism. The results show that three failure patterns exist in the composite ground reinforced by DM columns. For cases without embedment, the bearing capacity coefficient Nc increases with the area replacement ratio to a certain value due to the occurrence of general shear failure mechanism. The bearing capacity coefficient Nγ decreases with the area replacement ratio, as the equivalent frictional strength of the reinforced region is reduced. When the embedment is considered, the failure mechanism of composite foundation has a significant influence on the coefficient Nq. Specifically, increase of column length leads to a larger value of Nq when block failure is observed. When a general shear failure pattern occurs, the effect of additional column lengths on the coefficient Nq can be neglected.

Visualization of Shear Cracks in a Reinforced Concrete Beam using the Digital Image Correlation

A low-cost digital image correlation system is used to visualize the formation and propagation of concrete cracking in a reinforced concrete beam. The system employed comprises an ordinary digital camera, a remote image recording controller (a smartphone) and a freely-available, open-source image correlation software package Ncorr. In this paper, the application of this system is demonstrated to obtain a comprehensive time-lapse of longitudinal strain fields developing before and after the onset of shear cracking, thus allowing one to fully appreciate the mechanisms of shear failure in the beam. It is shown that the longitudinal strain fields obtained from the DIC system are in a good agreement with hand-drawn crack maps and that obtained from nonlinear finite element analysis.

Dynamic breakage of glass sphere subjected to impact loading

The dynamic compression responses of four glass spheres with diameters 7.71 mm, 11.90 mm, 17.88 mm, and 24.87 mm are investigated by the modified split Hopkinson pressure bar device (SHPB). Based on the high speed images, the dynamic compression of the spheres can be divided into three stages, e.g. the quasi-elastic deformation stage, the non-linear deformation stage, and the brittle failure stage. The formation and growth of the shadow areas observed at the impact end and the support end in the spheres are the main causes of the catastrophic failure. The movement of the plane-like fronts of the shadow areas is activated and driven by local velocity gradients. Dynamic breakage of the spheres is then analyzed by the particle size distribution, the fractal properties, etc. The results show that there are two main failure mechanisms in the process of sphere breakage, e.g. the tensile failure mechanism and the shear failure mechanism. In order to investigate the transition of these two failure modes, a bimodal Weibull distribution model is preliminarily established on the Weibull statistical strength. The model shows both good simulations to the experimental data and obvious the transition process of two failure mechanisms. The scaling laws and the strain rate effects of breakage strength are then discussed. The results are helpful for the controlling of pulverization for brittle particles.

Seismic behaviour of regular reinforced concrete plane frames with fiber reinforced concrete in joints

According to most of current design standards, the need for high strength and ductility of reinforced concrete frame structures is accomplished utilizing a high amount of transverse reinforcement in beam–column joints. Reinforcement congestion can be overcome by means of Fiber Reinforced Concrete and High Performance Fiber Reinforced Concrete, which are known to improve the structural performance of single structural members or beam–column joints. Through an extended numerical simulation, this paper elaborates the overall benefits of using fiber reinforced concrete materials in critical regions to the seismic behaviour of regular reinforced concrete frame structures. An extensive number of non-linear static and dynamic analyses with distributed plasticity and fibre sections are performed to compare the behaviour of simple reinforced concrete and mixed reinforced concrete/fiber reinforced concrete frames in terms of total base shear and fragility curves and failure mechanisms. Even if execution and technological aspects are beyond the scope of the present work, the use of fiber reinforced concretes in critical regions of mixed frames seems to improve the structural performance of reinforced concrete frames at a global level.

Grain Boundaries Softening Thermoelectric Oxide BiCuSeO.

Engineering grain boundaries (GBs) are effective in tuning the thermoelectric (TE) properties of TE materials, but the role of GB on mechanical properties, which is important for their commercial applications, remains unexplored. In this paper, we apply ab initio method to examine the ideal shear strength and failure mechanism of GBs in TE oxide BiCuSeO. We find that the ideal shear strength of the GB is much lower than that of the ideal single crystal. The atomic rearrangements accommodating the lattice and neighbor structure mismatch between different grains leads to the much weaker GB stiffness compared with grains. Failure of the GBs arises from either the distortion of the Cu-Se layers or the relative slip between Bi-O and Cu-Se layers. This work is crucial to illustrate the deformation of GBs, laying the basis for the development and design of mechanically robust polycrystalline TE materials.

Shear behavior of concrete beams reinforced exclusively with longitudinal glass fiber reinforced polymer bars: Experimental research

This paper aims to investigate the shear failure mechanisms in beams exclusively reinforced with longitudinal glass fiber reinforced polymer bars and to propose a design‐based approach to predict the shear capacity of this type of beams. An experimental program composed of seven T cross section shaped concrete beams was executed to analyze the influence of the flexural reinforcement configuration on the shear capacity and deformability of the beams. Three values of the flexural reinforcement ratio ( ρ l), 1%, 1.4%, and 1.80% were adopted. Digital image correlation technique was used to better capture and analyze the cracking process up to the formation of the shear failure crack. Test results indicated that the shear capacity was not dependent of ρ l up to a limit of around 1.4%, but a tendency of the shear capacity to increase with ρ l was registered above this limit due to a more pronounced favorable contribution of aggregate interlock and dowel effect.

Numerical simulation of the effect of bedding layer geometrical properties on the punch shear test using PFC3D

In this research the effect of bedding layer angle and bedding layer thickness on the shear failure mechanism of concrete has been investigated using PFC3D. For this purpose, firstly calibration of PFC3d was performed using Brazilian tensile strength. Secondly punch shear test was performed on the bedding layer. Thickness of layers were 5 mm, 10 mm and 20 mm. in each thickness layer, layer angles changes from 0o to 90o with increment of 25o. Totally 15 model were simulated and tested by loading rate of 0.016 mm/s. The results show that when layer angle is less than 50o, tensile cracks initiates between the layers and propagate till coalesce with model boundary. Its trace is too high. With increasing the layer angle, less layer mobilizes in failure process. Also, the failure trace is very short. It\'s to be note that number of cracks decrease with increasing the layer thickness. The minimum shear punch test strength was occurred when layer angle is more than 50o. The maximum value occurred in 0o. Also, the shear punch test tensile strength was increased by increasing the layer thickness.

Effects of material disorder on impact fragmentation of brittle spheres

Brittle materials have many excellent properties for structural applications, whereas the brittleness and disorder due to defects and micro-cracks cause failure. Fragmentation may occur and often lead to a catastrophic damage, bring dangers to the users especially when brittle materials suffer dynamic loads like impact and explosion. The impact fragmentation of brittle material belongs to the continuum/discretization domain. The combined finite and discrete element method (FDEM) is used to investigate the impact fragmentation of disordered material in detail. In this work, structural disorder in the brittle material is not considered, and the disorder is only reflected in the strength heterogeneity. Assuming that the mesoscopic fracture parameters of brittle materials obey the Weibull distribution, the degree of disorder can be quantified by the Weibull modulus k. The impact of a brittle sphere against a rigid plate is simulated using the FDEM. The dynamic response can be classified into damage and fragmentation zones. In sphere with low material disorder, cracking pattern is mainly dominated by single or more penetrating cracks. Increasing the disorder degree by smaller k, branch cracks emerge. Finally, it changes into a global branch crack in highly disordered sphere. Besides, mass index analysis indicates that higher disordered sphere has a higher critical velocity in impact events, in which the critical impact velocities equal 10, 15, 40 and 80 m/s when the values of m are 10, 5, 2 and 1, respectively. Furthermore, the principal component analysis is adopted for digging the crack features from fragments morphology description. The statistics of two fragment shape indexes shows that fragments coming from the highly disordered spheres have greater variability with a rougher surface and higher flatness overall, corresponding to the fracture pattern. Finally, we conclude that the effects of disorder on impact fragmentation can be ascribed to the dominant cracking mechanism-specifically, the proportion of shear failure mechanism grows with the disorder degree, implying more non-penetrating branch cracks existing in the fragments. We demonstrate that the effect of disorder on impact fragmentation is probably a consequence of a continuous phase nucleation-avalanche-percolation transition as well.

Experimental study of shear strength and failure mechanisms in RC beams scaled along height or length

The paper presents results of laboratory experiments carried out on longitudinally reinforced concrete beams subjected to four-point bending. Beams of separately varying height and length were analyzed to investigate the size effect on nominal strength and post-critical brittleness. Beams were scaled in the height direction in the first test series and in the length direction in the second series. Due to lack of geometrical similarity, different failure mechanisms were exhibited. Load-deflection diagrams and crack paths were registered during experiments. The digital image correlation technique was applied to visualize strain localization on the concrete surface. The crack opening and crack slip displacements were also measured. The beam response was characterized by two non-dimensional parameters ηa = a/D and ηb = b/D defined as the ratios of shear and bending spans to the beam depth D assumed as the size parameter and the reinforcement position parameter ηc = c′/D. Two major failure mechanisms were observed: flexural failure in the central beam zone combined with plastic yielding of the reinforcement and the diagonal shear crack failure in external shear zones. Two distinct modes of shear failure can be specified depending on the dominance of crack opening or crack closure contact zones. Two different effective stresses associated with failure mechanisms were defined to specify the beam strength’s dependence on ηa, ηb, ηc and D. Some analytical formulae specifying the critical shear stress dependence on ηa, ηc and strengths ratio of reinforcement and concrete were presented at the end of paper and compared with experimental data.

Failure mechanism analysis of asphalt\u2013aggregate systems subjected to direct shear loading

In order to investigate the mechanical behavior of asphalt–aggregate systems subjected to direct shear loading and reveal the shear failure mechanism, four groups of direct shear tests were conducted on composite specimens under different experimental conditions with a self-manufactured direct shear test apparatus at 25 °C. Comparative studies were conducted to evaluate the effects of stone surface treatment, asphalt film thickness and loading rate on the shear mechanical behavior of asphalt–aggregate specimens. Results showed that two kinds of the complete stress–displacement curves, including the general single-peak curve and the first-known double-peak curve, were clearly observed for each condition. In addition, the internal failure mechanisms were analyzed based on qualitative and quantitative methods. It can be concluded that the potential failure modes of the direct shear test include adhesive failure at the asphalt–aggregate interface and cohesive failure within the asphalt film. The research results enhance understanding of the shear mechanical behavior and failure mechanism of asphalt mixture, and also provide a reference for the interfacial failure.

High-strain-rate plastic deformation and fracture behaviour of Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy at room temperature

To study the plastic deformation and fracture behaviour of Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy under high strain rate loading conditions, a series of dynamic compression tests on Ti-55511 alloy have been performed at constant strain rates ranging from 350 s−1 to 2900 s−1 by means of split Hopkinson pressure bar technique at room temperature. The different strain and strain rate loading conditions are realized by changing the length and velocity of the striker bar, and high intensive localized shear region is induced in Ti-55511 alloy. The dynamic compression stress-strain response, strain rate hardening effect and strain rate sensitivity, and the fracture behaviour are discussed. The experimental results demonstrate that: The strain rate hardening effect and strain rate sensitivity of Ti-55511 alloy are apparent; Brittle shear bands form at high strain rate loading conditions, and the formation of a shear band does not mean the occurrence of phase transformation; Collapse of the specimens occurs along a plane inclined at an angle of about 45° to the compression axis at room temperature for both quasi-static and dynamic compression loading; The shear-compression zone and tension-shear-compression zone coexist in the fracture surface, and collapse of the specimens is attributed to shear failure mechanism for Ti-55511 alloy under compression loading at room temperature.

Modeling of Entrainment in Debris Flow Analysis for Dry Granular Material

Debris flow entrainment refers to the increase in mass by way of erosion of the channel beds or undermining the channel banks. Entrainment makes the calculation of travel distance and velocities of debris flow much more complex and difficult. Shear failure of the material in the channel bed is usually considered to be the dominant mechanism in entrainment analysis. However in granular flow, material at the surface of the channel bed can be eroded by progressive scouring under the base of the debris. This may result in more material being eroded and entrained than just considering the shear failure mechanism. A new analytical model is proposed to calculate entrainment in debris flow analysis by considering both rolling and shearing motion. Newton’s Law of Motion is used to calculate accelerations, velocities, and displacements of granular particles. To study the entrainment process inside granular flow and to verify the new entrainment model, numerical experiments have been carried out using the Discrete Element Method (DEM). Velocities, including translational velocity, rotational velocity and average velocity, total volume, shear stresses are monitored using measurement circles in the numerical experiment. Variations of the depth of erosion at specific locations along the debris flow channel are monitored and the average entrainment rates are calculated. By comparing the numerical experimental results with the analytical solutions, it is found that results from the analytical model agree well with that from the numerical experiments. In order to use the new entrainment model into debris flow runout calculation, the new entrainment model has been incorporated in a runout model based on an energy approach. Entrainment calculation governed by a second order partial differential equation is solved using the finite difference method. The total mass and profile of the channel bed are adjusted during the entrainment calculation. Sensitivity analyses have been carried out on the new model by varying the model parameters including internal friction angle, basal friction angle, turbulent coefficient and mean of Probability Density Function (PDF) etc. Back analysis of historical cases is carried out using the new model. Several case histories have been studied which include the Tsingshan debris flow, Niumian Rock Avalanche, Fjaerland debris flow, Faucon debris flow and Zymoetz River rock avalanche. An extremely large rock avalanche occurred on April 9, 2000 at Yigong is also studied in the thesis. Measurements obtained from site investigation, including flow velocity, flow height, entrainment depth at specific locations, run-out distance and total volume at deposition fan, have been used to evaluate the model. The results are encouraging based on comparisons of the run-out distance, front velocity and total volume of the debris. Improvements are required on the entrainment depth and total volume in some cases when lateral spreading of the debris is significant.

Experimental study on shear performance of plain construction joints integrated with ultra-high performance concrete (UHPC)

As a part of an ongoing research to develop construction joints using ultra-high performance concrete (UHPC) and reinforcements, shear performance of plain concrete construction joints is experimentally examined with push-off tests. Two different sets, namely, a combined set of UHPC (180MPa) and a set of UHPC (180MPa) and NSC (normal strength concrete, 30MPa) were considered, each of which had five cases of interface treatment including use of water jet, vertical joint, and three cases of a grooved joint. In addition, cases without any construction joint were also considered as a reference. Key factors affecting shear performance of individual construction joint were investigated in terms of shear strength, failure mechanism, and displacement responses. Experimental results show that steel fibers and grooved geometry greatly affect shear performance for the combined set of UHPC, while interlocking mechanism of coarse aggregates is crucial for the set of UHPC and NSC.

Experimental Study of the Shear Strength of Bonded Concrete–Rock Interfaces: Surface Morphology and Scale Effect

The shear strength of the concrete–rock interface is a key factor to justify the stability of a hydraulic structure foundation. The Mohr–Coulomb failure criterion is usually used as shear strength and evaluated by extrapolating shear tests results carried out in a laboratory on small-sized samples. This paper presents an experimental study on the concrete–rock interface shear behavior. The effect of rock surface morphology on shear behavior was studied by performing laboratory direct shear tests on prepared square samples with a previously characterized rock surface. The scale effect and the test conditions were also studied by comparing the results to those obtained by performing usual laboratory shear tests on cored samples at lower scale. The tested interfaces were composed of the same concrete and granite and have a natural rock surface. The results displayed that the peak shear strength is strongly dependent on the concrete–rock bonding, the rock surface morphology and the applied normal load. A new surface morphology description tool was developed in order to characterize the main waviness. Moreover, the concrete–rock shear behavior at medium scale was reproduced by a 2D finite elements model to study the stress distribution along the sheared interface. Under low normal load, the concrete–rock adhesion is thus progressively mobilized according to the waviness on the rock surface and the local shear failure mechanisms depend on the type of this main waviness. Consequently the shear strength of a concrete–rock interface must be analyzed with respect to the various morphology aspects on its rock surface.

Non-linear static behaviour of ancient free-standing stone columns

This work investigated the non-linear behaviour of ancient natural stone columns in the Mediterranean region made from multiple blocks or ‘drums’. A two-dimensional custom-made computational model based on the discrete-element method was employed. In the numerical model, the columns were represented as an assemblage of distinct blocks connected together by zero-thickness interfaces, which can open and/or close depending on the magnitude and direction of the stresses applied to them. Through non-linear static analysis, capacity curves and corresponding failure mechanisms of each of the studied models were obtained. The influence of different parameters (the number of drums, geometrical properties and imperfections at columns) was also assessed to observe their influence on the response of drum assemblies. The results of analyses revealed that rigid overturning is the main collapse mechanisms under uniform horizontal forces. A combination of rigid and shear failure mechanisms might also occur, depending on geometric characteristics and the choice of joint material properties. A higher displacement capacity was observed for columns constructed with a larger number of drums. It was also found that imperfections in the ancient free-standing columns have a significant influence on the lateral load resisting capacity. Therefore, structural analysis of undamaged columns may not represent the actual capacity of the columns due to their very sensitive and highly non-linear characteristics.

Incorporation of non-associative flow rules into rock slope stability analysis

The circular shear failure mechanism in rock slopes occurs in large-scale, heavily jointed or weak rock masses. Most rock slope stability analysis problems do not consider the effect of flow rules, i.e., the dilatancy angle. The failure criteria commonly applied are the linear Mohr-Coulomb or the non-linear Hoek and Brown. In general, all slope stability methods originate from the assumption of the associative flow rule, calculating equivalent values of the cohesive strength and friction angle. In this study, the non-linear Hoek and Brown failure criteria are applied in the parametric form, which permits the incorporation both the associative and non-associative flow rules. A theoretical approach of the limit equilibrium method is performed for circular slip surfaces under the assumption that there are only self-weight forces acting on the failure mass of the slope, taking the critical plane failure mode as the foundation. Both the analysis and results are performed in dimensionless form. The study emphasizes the importance of the value of dilatancy angle and “non-conservative” character of the hypothesis of the associative flow law, i.e., the overestimation of the value of the factor of safety. Specific examples are analysed and compared to the finite difference method and a real case is presented.