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Experimental study of reinforced concrete beams without stirrups under impact: performance evaluation and structural response Experiments on reinforced concrete beams without stirrups are often utilized as a simplified basis to calibrate numerical models of reinforced concrete slabs. This paper details an experimental study on the behavior of reinforced concrete beams without stirrups subjected to impact loading. For this study, the 11‐meter‐high drop tower at the Otto Mohr Laboratory of TU Dresden was used to accelerate a cylindrical impactor with a diameter of 100 mm. Compressed air accelerated the impactor to velocities between 2.7 m/s and 25.8 m/s. The impactor masses were 14.22 kg and 21.66 kg, respectively. Data on impactor and support forces, displacements, and accelerations were collected. Digital image correlation supplemented the measurements. The study revealed that the behavior of the beams exhibited different failure modes depending on the impactor velocity and mass. The shear cracks started to form at impactor velocities of approximately 11 m/s, corresponding to the lighter impactor's kinetic energy of 860 J. Furthermore, the formation of a punching cone near the loading point at impactor velocities of around 22 m/s was observed. These findings provide valuable insights for designing and thoroughly assessing the performance of shear‐deficient reinforced concrete beams under impact loading. The results serve as a foundation for enhancing the precision and reliability of numerical models, facilitating further investigations into complex structural systems. [ABSTRACT FROM AUTHOR]

Copyright of Materials & Technologies / Materiali in Tehnologije is the property of Institute of Metals & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The governing failure mode for flat slabs is punching shear, which occurs when the punching forces exceed the slab resistances in the critical area around the column surface. Recently, considerable knowledge has been obtained on understanding steel fiber reinforced concrete (SFRC) suspended slabs as a sustainable and reliable technique to enhance post‐cracking behavior and resist loading effects, including punching shear. The properties of the materials, loading, and dimension vary inevitably and may be represented in the form of statistical distributions. In this study, all parameters affecting the punching shear of the SFRC suspended slabs were treated as random variables. Monte Carlo simulations (MCS) and punching shear model developed previously using Artificial Neural Network (ANN) were combined (ANN‐MCS) to conduct a reliability analysis, cost optimization, and model calibration. Reliability results have shown that the inclusion of fibers increased the safety level (20% in terms of the reliability index β) of the slabs against punching shear. Furthermore, a reliability‐based cost optimization was performed on the ANN‐MCS model. The optimization outcomes demonstrated steel ratio has a significant impact on SFRC slab cost, and thus it should be minimized/reduced when the steel fibers are included in the mix. Moreover, the ANN model was calibrated following a code calibration procedure to account for the model, material, and fabrication uncertainties. The calibration results have shown that a reduction factor of 0.6 should be applied to the ANN‐based model to achieve the target reliability level, β ≥ 2.5. [ABSTRACT FROM AUTHOR]

Punching shear-reinforced flat slabs can fail in three modes: (1) inside the shear-reinforced zone, (2) outside the shear-reinforced zone, or (3) at the maximum punching shear capacity. By using the theory of structural systems reliability, this study investigates how these failure modes combined affect the safety level of reinforced concrete flat slabs with punching shear reinforcement, and ultimately, the variation of partial factors. Based on DIN EN 1992-1-1 together with the German National Annex DIN EN 1992-1-1+NA(D), and by using distinct reliability-based methods (i.e., levels II and III), the variation in the system failure probabilities and, consequently, partial factors were analysed. The results indicated that partial factors can fluctuate significantly depending on the governing ultimate limit state function and the scatter of basic variables. Furthermore, they indicated that the chosen reliability-based method had a significant influence on the resulting safety level. The sensitivity analysis confirmed the premise that partial factors can be reduced without compromising socially accepted safety levels (e.g., recommended in DIN EN 1990). Ultimate benefits include material and cost savings and CO2 emission reductions. Finally, the approach addressed in this paper offers a new perspective on the derivation of partial factors that can be considered by engineering practitioners. [ABSTRACT FROM AUTHOR]

A simulation-based probabilistic method is proposed for assessing the reliability of steel-lined and prestressed fiber-reinforced concrete (PFRC) slabs against the impact loads. The impact testing of several prestressed and non-prestressed FRC slabs of 800 × 800 × 100 mm in size was carried out. The experimental program involved projectile impact testing of prestressed and non-prestressed FRC slabs using a gas gun. Three parameters were varied for testing of slabs under the projectile impact, viz., a quantity of steel fibers in the concrete, steel lining on the backside of the slab, and the prestressing level. The probability-based reliability analysis of all the tested specimens was then performed to highlight the influence of steel lining, steel fibers, and prestress in enhancing the safety of RC (reinforced concrete) slabs against projectile impacts. Projectile impact velocity exceeding the slab's ballistic limit was assumed to lead to the failure of the PFRC slab, i.e., the perforation failure of the slab. Study results indicate that when no steel fiber was present, slab reliability was low. Adding fibers to slabs increases slabs' reliability significantly. Specimens with the highest steel fiber content (1.2%) showed the greatest increase in reliability. The steel lining on the back face makes the slab's reliability almost doubled in comparison with those without lining. Additionally, steel lining makes the PFRC slabs as reliable as desired. It was further noticed that the prestressing helps in enhancing the slab safety against projectile impacts. Even a minimal amount of prestressing makes a noticeable improvement in the reliability of PFRC slabs. [ABSTRACT FROM AUTHOR]

The perforation of concrete‐like material targets against impact by nondeforming projectiles is always the research focus in engineering protective domain. In the present paper, a new punching plug model is proposed based on the similar features with punching shear in concrete slabs, utilizing the failure criterion of modified Mohr‐Coulomb. Semi‐empirical equations corresponding to ballistic limit, residual velocity, punching plug thickness are derived, where residual velocity is renewedly identified considering the effect of punching plug resistance. Eventually, the proposed punching plug model is validated and discussed by comparisons with perforation experiments. [ABSTRACT FROM AUTHOR]

In this paper, an automatic and quick evaluating method for the micro-hole size and form accuracy with a computer-aided technique was proposed. A special ultrasonic microforming method, that is, micro-ultrasonic thin-sheet-metal forming using molten plastic as flexible punch (short as Micro-USF), was used to punch out micro-holes with diameters of 500, 600, and 700 μm on a copper sheet with a thickness of 30 μm. Using the evaluation method proposed in this paper, the forming accuracy of micro-holes was discussed. The experimental results showed that the ratios of the maximum size error and the maximum roundness error of micro-holes to the corresponding punching die diameter were 1.40 and 1.47%, respectively. The ratios of the maximum size error range and the maximum roundness error range of micro-holes to the corresponding punching die diameter were 0.70 and 0.72%, respectively. This indicated that the accuracy and precision in the Micro-USF method were high for punching micro-holes. Moreover, it was found that there is no significant direct correlation between micro-holes sample errors and these forming parameters when the forming parameters such as ultrasonic power, ultrasonic time, and cylinder pressure were varied, which indicated that the sample errors were random to some extent. [ABSTRACT FROM AUTHOR]

Sheet-tube connection structures are widely applied in chemical, petroleum, medicine, and other industries. Its reliable connection and manufacturing are of great significance for the function of the corresponding equipment. To avoid the occurrence of too deep pits and easy warpage during the single-sided annular sheet squeezing process, an improved method to join sheets to tubes by double-sided annular sheet squeezing is proposed in this paper. The joining process is to squeeze the sheet through the top and bottom dies simultaneously, resulting in radial metal plastic flow, forming the interlock between the sheet and the tube. By experimental and numerical simulation, the joining process of Al6061-T6 sheet and tube under different process parameters using double- and single-sided annular sheet squeezing was conducted and compared. The pull-out test is used to evaluate the quality of sheet-tube joints. Results showed that using the double-sided annular sheet squeezing method can obtain a symmetrical interlocking structure rather than an asymmetric structure by single-sided squeezing, effectively reducing the pit depth on the sheet surface. In addition, the improved method can effectively reduce about 25% of the joining force, but the pull-out strength is about 1.5kN lower than that obtained by the single-sided squeezing method. The joining strength is comprehensively affected by the thickness of the die annulus, punch stroke, and squeezing type. The influence mechanism of process parameters on pull-out strength is discussed. This study provides a new and efficient joining way for the manufacture of sheet-tube connection structures. [ABSTRACT FROM AUTHOR]

A stiffened deep cement mixing (SDCM) pile is a type of composite pile that has a rigid pile at the core that reinforces the deep cement mixing (DCM) pile. An SDCM pile combines the advantages of both a DCM pile (i.e., high lateral friction resistance) and a rigid pile (i.e., high stiffness and strength). This work presents four sets of laboratory model tests that were aimed at investigating the vertical bearing capacity of SDCM piles with different cement contents by monitoring the pile top load, the axial force, the pile settlement, and the pile end resistance. Two failure modes of the SDCM piles were observed during the tests––pile failure (the pile ruptured at the section below the core pile) and punching failure (the pile penetrated into the underlying soil). It was found that the vertical bearing capacity of the SDCM piles increased with cement content, up to the point of punching failure. The pile end resistance increased with the pile top load. When the ultimate bearing capacities of the SDCM piles were reached in the model tests, the ratio between pile end resistance and pile top load ranged from 19.4% to 54.2%, indicating that pile end resistance cannot be ignored. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Beijing University of Technology is the property of Journal of Beijing University of Technology, Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Due to the low lateral stiffness of slabs supported on columns alone, reinforced concrete flat plates are typically combined with other structural elements, such as shear walls. In these structures, the slab–column connections are designed to carry gravity loads only, and the shear walls are required to resist both gravity and lateral forces. Therefore, the slab–wall connections are essential for the performance of both the gravity and lateral force resisting systems. However, most punching shear research and design provisions are focused on slab–column connections, even though punching failures around slab–wall connections have occurred experimentally. Empirical testing of slab–wall connections is difficult due to the specimen size. This paper investigates the punching shear behavior of interior slab–wall connections subjected to concentric vertical loading, and combined concentric vertical loading and uniaxial unbalanced moment using a plasticity‐based nonlinear finite element model (FEM) in ABAQUS. The analysis of isolated slab–wall connections demonstrates that punching failures can occur before one‐way shear failures. Since the overall connection capacity is much higher than the expected loads in most structures, if these punching failures happen they would be localized to the region around the wall end and are not expected to lead to structural collapse. [ABSTRACT FROM AUTHOR]

The failure mode limitations presented in the International Society for Rock Mechanics (ISRM) were recognised as an obvious issue by invalidating most of the failure modes along the bedding plane. In this study, the anisotropic behaviour of index strength and failure mode of weathered shale are evaluated by utilising the point load test (PLT) and the block punch index (BPI). The outcomes elaborate that the degree of anisotropy of PLT is four times the BPI degree of anisotropy. The failure mode of weathered shale is observed to be controlled by the bedding plane orientation (β). Particularly, when the point loading is not perpendicular to the bedding plane orientation, it is necessary to consider the inclined failure mode along bedding since eliminating these results may cause a significant over-prediction of index strength. Meanwhile, the presence of secondary failures along a bedding in weathered shale under BPI is because of the normal stress distribution. Consequently, the very low bonding between the bedding planes is not able to resist the tensile stresses developed at the specimen faces during punching. The study also highlighted the effect of the horizontal angle of bedding orientation (θ) with respect to the puncher. [ABSTRACT FROM AUTHOR]

There are many factors influencing the punching effect of open air water holes, and it is of great significance to study each factor to control the sensitivity of the punching effect Based on the principle of orthogonal design, 9 on site blasting tests were carried out in Manjiazhai stope. Punching rate, average punching height of packing body and average punching acceleration of packing body were used as test indicators, and SPSS statistical software was used to introduce range analysis. With analysis of variance, four factors, including explosive unit consumption, packing length, packing particle size and hole spacing, which may affect the test index, are studied to control the sensitivity of the test index. The results show that only the packing particle size and packing length have a significant influence on the punching rate, and the most significant factor is the packing particle size. The packing length has a significant influence on the average punching height of the packing body, and the packing particle size and the unit consumption of explosive have a significant effect on the packing. The average punching acceleration of the volume has a significant impact, and the packing particle size is the most critical influencing factor. The optimal blasting parameter combination during mining in Manjiazhai stope is obtained. The unit explosive consumption is 0.35 kg/m$, the packing length is 5 m, the packing particle size is 5 -- 10 mm, and the hole spacing is 7 m. The parameters are substituted into the on site production blasting. The post punching rate dropped by 79. 75%, which is of guiding significance for subsequent production blasting and similar engineering practices in the stope. [ABSTRACT FROM AUTHOR]

This paper deals with an evaluation of the generalised partial safety factor for resistance properties by using a statistical determination of a resistance model for predicting the punching capacity. The factor takes the material, model and geometric uncertainties into account. The Eurocode 2 design model for the assessment of the punching resistance without shear reinforcement was statistically analysed using an extensive database of experimental tests. The correction factor b of the model and the coefficient of variation of the model errors were evaluated according to Annex D of EN 1990. The statistical parameters of the basic variables in the resistance functions were assumed according to the recommendations of the Joint Committee on Structural Safety Probabilistic Model Code. The comparison of the safety factors obtained with the material safety factor currently used reveals that the current factor 1.50 underestimates the values obtained for the design model analysed. [ABSTRACT FROM AUTHOR]

In flat-slab frames, which are typically designed as secondary seismic structures, the shear failure of the slab around the column (punching failure) is typically the governing failure mode which limits the deformation capacity and can potentially lead to a progressive collapse of the structure. Existing rules to predict the capacity of flat slab frames to resist imposed lateral displacements without losing the capability to bear gravity loads have been derived empirically from the results of cyclic tests on thin members. These rules account explicitly only for the ratio between acting gravity loads and resistance against concentric punching shear (so-called Gravity Shear Ratio). Recent rational models to estimate the deformation capacity of flat slabs show that other parameters can play a major role and predict a significant size effect (reduced deformation for thick slabs). In this paper, a closed-form expression to predict the deformation capacity of internal slab-column connections as a function of the main parameters is derived from the same model that has been used to develop the punching shear formulae for the second generation of Eurocode 2 for concrete structures. This expression is compared to an existing database of isolated internal slab-column connections showing fine accuracy and allowing to resolve the shortcomings of existing rules. In addition, the results of a testing programme on a full-scale flat-slab frame with two stories and 12 columns are described. The differences between measured interstorey drifts and local slab rotations influencing their capacity to resist shear forces are presented and discussed. With respect to the observed deformation capacities, similar values are obtained as in the isolated specimens and the predictions are confirmed for the internal columns, but significant differences are observed between internal, edge and corner slab-column connections. The effects of punching shear reinforcement and of integrity reinforcement (required according to Eurocode 2 to prevent progressive collapse after punching) are also discussed. [ABSTRACT FROM AUTHOR]

The high stiffness and great strength of three-dimensional (3D) braided composites mean they are widely used in the aerospace, marine and automotive industries. Three-dimensional braided composites exhibit very different mechanical responses under various strain-rate loadings (such as tensile, compression, punch and shearing) due to their complex structural characteristics. Studies under quasi-static and low strain-rate loadings predict the elasto-plastic properties of 3D braided composites, and research under high strain-rate loading has explored the conditions of industrial composites used in special environments. The investigation of the strain-rate effect can provide a sound database reference for engineering design. Through experiments and simulation analysis methods, this work reviews the braided structural effect, mechanical response and failure mechanism of 3D braided composites under various strain rates. Mechanical properties under different theoretical and structural models are reviewed and summarized. In particular, the damage evolution and stress propagation of 3D braided composites were revealed from both macroscopic and microscopic perspectives through finite element modeling. [ABSTRACT FROM AUTHOR]

The level of maximum punching strength is of major importance to design highly stressed slab‐column connections and to choose the type of punching shear reinforcement. Since a couple of years, there is consensus that the maximum punching strength of shear‐reinforced concrete slabs can be defined as a multiple of the reference punching strength without shear reinforcement. The upper bound of this load‐increasing effect depends mainly on the anchorage and arrangement of shear reinforcement elements. Despite numerous research studies and database evaluations, there are ongoing discussions regarding the final effectiveness of stirrups and double headed studs installed in flat slabs and column bases. In this paper, a strictly filtered punching database is used to highlight the significant impact of underlying reference strength comparing the maximum load increase according to current Eurocode 2 and the draft for the next generation of Eurocode 2 (prEC2). Based on this unifying database, the origin of current discrepancies is discussed and a combination of constant lower bound coefficients with a refined formula as specified in prEC2 is proposed. Additionally, the effect of adapting current European Technical Approvals for double‐headed studs and punching shear optimized lattice girders to prEC2 is shortly analyzed. A further database evaluation also allows for setting the basis for optimized detailing provisions regarding the maximum permissible diameter of shear reinforcement. [ABSTRACT FROM AUTHOR]

We developed a hot stamping method for panel parts with a step-shaped wall. The die-set for the developed method divides the punch at a step-shaped wall into an outer punch and an inner punch. The outer punch is placed first. In addition, an opening is added to the blank of the developed method. The developed method makes it possible to change the main forming type from draw forming to cylindrical stretch flange forming in the middle of a forming stroke. The stretch flange forming can prevent a fall in temperature at a hole edge, because the hole edge does not come into contact with the die-set during forming and because the high ductility of high-temperature materials can be used, making it advantageous for hot stamping. If the preceding amount of the outer punch is large with the developed method, the effect of suppressing wrinkles is large but the sheet thickness reduction that can cause cracking rises. If the preceding amount of the outer punch is small, the rate of sheet thickness reduction ratio is greatly restrained, but the wrinkles become larger. By setting an appropriate preceding amount of the outer punch with the developed method, forming without cracks or wrinkles is possible. [ABSTRACT FROM AUTHOR]

The punching and post-punching shear behaviours of reinforced concrete (RC) flat plate structures are often studied by using a representative slab–column connection isolated from the parent structure. In this study, a set of numerical modelling techniques is established to create a competent three-dimensional non-linear model to simulate punching and post-punching shear behaviours of RC slab–column connections without shear reinforcement, through the use of which the punching shear failure featuring a critical punching shear surface and an abrupt drop of the applied force in the load–displacement response is able to be accurately reproduced. The post-punching shear behaviour, taking the form of an increased load-carrying capacity which is ceased by rebar fracture in the suspension stage, is also well captured. Using the proposed numerical model, typical punching and post-punching shear failure mechanisms are studied in some detail. [ABSTRACT FROM AUTHOR]

In this study, punchless punching by the compression ignition of octane and the effect of varying the amount of fuel on punchability were investigated. In the experiment, the compression in compression ignition was applied using a drop hammer. As the amount of fuel increased, the variation in the initial height of the hammer required for completing the piercing could be divided into the following four parts of the basis on the amount of fuel. In the first part, corresponding to the smallest amount of fuel, the height exhibited a large decrease. In the second part, the height decreased by a small amount. In the third part, the height increased. Finally, in the fourth part, corresponding to the largest amount of fuel, the height remained constant. The four parts were believed to be caused by differences in the chemical reactions. Moreover, the optimum amount of fuel for punching was the largest amount of fuel under the conditions of the first part. [ABSTRACT FROM AUTHOR]

The determination of uniaxial compressive strength (UCS) is central to most mining and geotechnical engineering analyses and designs in rock engineering. Direct measurement of UCS through uniaxial compression tests are costly and time-consuming. This is a challenge in mining engineering practice. However, there is a possibility to have results of other tests (e.g. punch tests) which are simple to conduct, particularly at the early stage of many mining engineering projects. The information contained in the results of multiple punch tests can be combined under a Bayesian approach to characterise UCS. This study proposes a Bayesian approach for probabilistic characterisation of UCS based on information from multiple sources, including the results of multiple punch tests available at a specific rock site. The proposed Bayesian approach is formulated to sequentially incorporate data from the parameters of three punch tests, namely Schmidt rebound hardness (SRH), block punch index (BPI) and point load strength ( I s (50) ) to update statistics and probability distribution of UCS. The approach is illustrated using real SRH, BPI and data at a sandstone site. The proposed Bayesian approach is shown to perform satisfactorily for the probabilistic characterisation of UCS as results of additional type of punch tests are incorporated. [ABSTRACT FROM AUTHOR]

A major part of central European infrastructure buildings was designed decades ago and has different needs of strengthening. Increasing traffic volume, increasing axle loads, and a growth in transport volume as well as more restrictive design rules are the reasons why the support regions of existing bridges and flat slabs often show a lack of punching resistance today. At the University of Innsbruck, a system for subsequent strengthening by the use of concrete screws was developed. Various laboratory tests showed that the system leads to a significant increase of punching resistance with minimal efforts for its installation. This article deals with the development of a numerical model that can predict the punching loads of unstrengthened and screw‐strengthened punching plates. Further the punching loads from the laboratory tests and the simulations are compared to the predictions of a design approach. The presented novel design approach is an advancement of the existing Eurocode 2 provisions and allows the influence of the screws on the punching resistance to be taken into account. The comparison shows that the numerical model predicts the punching resistances in an appropriate way and the design approach predicts them on the safe side. The presented design approach was included into the technical assessment for the concrete screws of the system reLAST as post‐installed punching reinforcement system [Z‐15.1‐340 (2019)] in order to be applicable in practice. [ABSTRACT FROM AUTHOR]

The main purpose of fiber reinforcement in concrete is to increase the post-cracking resistance of the composite, which reflects on toughness gain, being steel fibers traditionally used for this purpose. In recent years, an alternative to the steel fibers has emerged in the market for concrete reinforcement: the macro-polymeric fiber. However, there is few research on its performance as a reinforcement element in concrete, particularly when it is a high strength concrete. Given this, the behavior of high strength concrete, without fiber and with macro-polymeric fiber, both in fresh and hardened state, is analyzed in this paper. The workability was evaluated by the slump test and the mechanical properties were evaluated by the tests of compressive strength, Barcelona, flexure of prisms and punching of plates. It was found that, depending on the property to be analyzed, the increase of the macro-polymeric fiber content may be unfeasible. In the flexural test in prisms, for example, most parameters evaluated showed no significant changes when increasing the fiber content. In addition, it was observed that the same concrete mixture may present different behavior depending on the test performed. [ABSTRACT FROM AUTHOR]

This paper is concerned with the development and application of a small punch creep testing method for assessment of the effects of thermal aging and associated precipitate coarsening on the high temperature creep life and deformation behavior of a 9Cr ferritic–martensitic steel. The tests are conducted on P91 steel, for both aged (up to 1 year) and unaged specimens, at temperatures of 600°C. The unaged test results are shown to be consistent with previously published creep tensile test rupture life data in terms of Chakrabarty membrane stress. Aging is shown to have a significant, detrimental effect on creep life and deformation rate. The steady‐state displacement rate, time to failure, and displacement at failure data, for both aged and unaged, were successfully correlated via the modified Monkman–Grant relationship. [ABSTRACT FROM AUTHOR]

This paper investigates the axisymmetric thermoelastic contact of a functionally graded material (FGM) coated half-space. A rigid insulated punch rotates on the surface of the FGM coating with a constant angular velocity. The frictional heating is generated within the contact region. The thermoelastic properties of the coating vary exponentially along the thickness direction. By using the Hankel integral transform, the problem is reduced to Cauchy singular integral equations, which are solved numerically to obtain the normal contact stress, radial stress and surface temperature. The effects of the friction coefficient, angular velocity, gradient index, coating thickness and punch geometry on the surface thermoelastic contact characteristics are investigated and discussed in detail. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of minor additions of carbon nanotubes (CNTs) and boron on the structure and mechanical properties of nanocrystalline TiAl intermetallic compound. Nanocrystalline TiAl-xB(0.0 < x < 1.5 at.%) composites containing 1 wt.% CNT were synthesized by mechanical alloying and spark plasma sintering. Microstructure and mechanical properties of samples were evaluated using a scanning electron microscopy, energy-dispersive x-ray spectroscopy, elemental mapping, differential scanning calorimetry, Vickers hardness measurement, and shear–punch test. The findings of the current study show that milling up to 40 h results in the formation of Ti(Al) solid solution. Further milling up to 60 h is associated with a complete amorphization of the structure. Results also show that spark plasma sintering leads to the transformation of Ti(Al) solid solution into a mixture of Ti3Al, Ti2Al, and TiAl intermetallic compounds. Minor additions of boron and CNTs cause a significant grain refinement. The addition of the latter significantly improves the elongation as well. The implications of boron/CNT additions for the microstructure of TiAl and how it correlates with the mechanical properties are thoroughly discussed in this paper. [ABSTRACT FROM AUTHOR]

Punching shear behaviour of steel fibre reinforced flat slabs with punching shear reinforcement The guideline "Steel Fibre Reinforced Concrete" published by the German Committee for Reinforced Concrete (DAfStb) contains the current normative regulations for the punching shear design of steel fibre reinforced flat slabs. Due to a lack of sufficient experience and knowledge, a consideration of the combined action of steel fibres and shear reinforcement was explicitly excluded. While numerous punching shear tests on steel fibre reinforced flat slabs without shear reinforcement are available in literature, only eight tests in combination with shear reinforcement are known to the authors. These few tests used types of shear reinforcement which are not common for engineering practice in Germany, or showed bending failure, which limits the reliability of statements about the behaviour of such a combination. In this context and the expected favourable behaviour, seven tests were carried out to systematically investigate the punching shear behaviour of steel fibre reinforced flat slabs with stirrups and shear studs as shear reinforcement. The test program included one fibre reinforced test without punching shear reinforcement, two fibre‐free and four fibre reinforced tests with punching shear reinforcement. This paper describes the experimental investigations carried out and discusses the results obtained. [ABSTRACT FROM AUTHOR]

Copyright of Slobozhanskyi Herald of Science & Sport is the property of Kharkiv State Academy of Physical Culture and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The strengthening of concrete structures is becoming more and more important. To achieve this need for strengthening measures, technically innovative, simple and economical systems for subsequent strengthening are required. At the University of Innsbruck, a system for subsequent strengthening of the punching shear zone through the installation of concrete screws has been developed. These screws are installed from the soffit side of the slab in vertically predrilled holes and are arranged concentrically around the support. This paper discusses the results of four test series, with a total of 21 specimens used to develop the system. The system, which can be very easily installed, demonstrates a significant increase of the shear punching capacity and a reduction in brittle failure modes. In addition, cyclic loading with typical levels of service load has no negative effect on the effectiveness of the system. Finally, the influence of the flexural reinforcement ratio on the effectiveness of the strengthening system was investigated. [ABSTRACT FROM AUTHOR]

This paper is concerned with the finite element modeling of strengthened interior slab‐column connections in the existing continuous flat slab structural system by employing steel angle plates at the slab‐column junctions and fastened by shear bolts. This technique utilizes the advantage of combined action between the angle plates and bolts in resisting shear particularly at the slab‐column edges. Three‐dimensional analysis was carried out on such slabs employing concrete damaged plasticity model in ABAQUS to investigate their performance in terms of punching shear resistance, load–displacement response, and crack pattern at failure. The numerical models were first validated against the experimental results reported by other researchers. The proposed strengthening technique results in a substantial increase of load‐carrying capacity ranging from about 59 to 79% compared to the unstrengthened slab, and has also provided better stiffness, ductility and energy absorption in the slab system that change the mode of failure from a pure punching shear to flexural failure. The finite element results are compared with the calculated values according to provisions in the current design codes for evaluation purposes. A simple but reliable approach which is based on yield line theory to estimate the flexural capacity of the strengthened slabs is also outlined in this paper. [ABSTRACT FROM AUTHOR]

The present work investigates the load carrying capacity of vertically and horizontally reinforced floating stone column group through model testing. Two group arrangements using three and four stone columns for both unreinforced and reinforced conditions are testing under compressive loading. The geotextile reinforcement is provided throughout the stone column length (300 mm) in vertical direction and in form of circular discs at spacing of 30 mm along column length for reinforcing horizontally. The results of load-settlement behavior and failure mechanism of both unreinforced and reinforced group is studied. The testing results indicated reduced lateral bulging and higher stone column load capacity for horizontally reinforced columns in comparison to vertically reinforced. For validation of experimental results, numerical modeling using finite element (FE) code Plaxis 2D has also been conducted. The FE results depict lower load capacity as compared to model testing for settlement of 30 mm. However, the failure mode for both model tests and FE analysis was marked by bulging near the top of stone column and punching. Furthermore, load capacity is also check using empirical relations as given by IS code and previous literature. It is observed that experimental and analytical results are found in good agreement. [ABSTRACT FROM AUTHOR]

The general concept of blanking seems a simple one but governing parameters are many and have a complex relation-ship, which directly affect the quality of the produced parts. These parameters are assessed using three main criterions: the burr amount, the appearance of the cut edge and dimensional accuracy. However, the optimization of these parts produced depends on full understanding of the fine blanking process. The aim of our work is to develop the numerical computations in order to investigated the influence of selected parameter of the cutting process on the stress state of cold-rolled steel sheets being cut. The material testing and the characterization are carried out in order to fit the constitutive model parameters to the experimental data and to establish the sheet metal constitutive law. The identified model is, then, used for numerical simulations which are performed using LsDyna/Explicit software of various blanking tests. During of numerical simulations of the fine blanking process was observed elongation in shear surface and simultaneous reduction in fracture zone versus clearance punch/die and also that punch is be considered deformable or not. The numerical results of the validation simulations were in agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Precast segmental reinforced concrete (PSRC) bridge piers have been widely used in bridges. Many experimental and numerical studies have been conducted to investigate the seismic and impact behavior of PSRC piers, but very limited effort has been completed on the blast resistance of PSRC piers. In this paper, reduced-scale field tests were performed on PSRC piers to study their behavior and failure mode under close-in blast loading, including one monolithic pier and 12 PSRC piers. The influences of some typical variables on the PSRC pier were investigated. Compared with the different failure modes between monolithic piers and PSRC piers under the bottom explosion, the experimental results show that the monolithic piers exhibit a localized flexural failure in the near explosion zone and numerous transversal cracks due to stress wave propagation vertically, while the PSRC piers show signs of localized punching shear failure at the bottom segment and vertical cracks due to concrete squeeze resulting from the relative rotation in other segments. Meanwhile, the PSRC pier with crushed concrete at the bottom segment collapsed completely under a smaller scaled distance. Under the middle explosion, the middle segments of PSRC piers experienced a flexural failure by showing bending deformation and concrete spalling. Through variable analysis, seven segments can reduce the localized residual deformation of the PSRC pier and small slenderness ratio can decrease the overall residual deformation of the PSRC pier. Shear key, ED bar, and the axial compression ratio of 0.1 can decrease the concrete damage including the concrete spalling and vertical cracks. Circular cross sections can effectively weaken the prestressing force loss due to small damage. [ABSTRACT FROM AUTHOR]

This work aimed to study the automation of measuring the speed of punches of boxers during shadow boxing using inertial measurement units (IMUs) based on an artificial neural network (ANN). In boxing, for the effective development of an athlete, constant control of the punch speed is required. However, even when using modern means of measuring kinematic parameters, it is necessary to record the circumstances under which the punch was performed: The type of punch (jab, cross, hook, or uppercut) and the type of activity (shadow boxing, single punch, or series of punches). Therefore, to eliminate errors and accelerate the process, that is, automate measurements, the use of an ANN in the form of a multilayer perceptron (MLP) is proposed. During the experiments, IMUs were installed on the boxers' wrists. The input parameters of the ANN were the absolute acceleration and angular velocity. The experiment was conducted for three groups of boxers with different levels of training. The developed model showed a high level of punch recognition for all groups, and it can be concluded that the use of the ANN significantly accelerates the collection of data on the kinetic characteristics of boxers' punches and allows this process to be automated. [ABSTRACT FROM AUTHOR]

Surface texture of stamping tools affects the performance of the tool, tool life, and surface quality of the stamped product. In this work, punch samples were machined after heat treatment by milling and turning strategies in super finish processes and part of the punches were submitted either to plasma nitriding or nitrocarburizing treatment before the experiments using hot stamping of washers, which were made in two stages. Based on roughness results, for non-treated punches, most of the milled punches presented more intense surface damage than turned punches after hot stamping process, possibly due to the marks left by machining processes, affecting mechanical obstacles to wear evolution and lubricant retention on punch surface. For nitrided punches, surface damage was less intense than it was on non-treated punches. Parallel contours strategy and turning upward strategy presented less intense surface damage after the hot stamping process. For nitrocarburized punches, surface damage was less intense than it was to non-treated punches, mainly for milling strategies. SEM images of nitrided and nitrocarburized punches suggested alveolar corrosion occurrence during hot stamping process for circular upward strategy. [ABSTRACT FROM AUTHOR]

Industrial servo presses have been used to successfully demonstrate improved formability when deforming sheet metals. While the time dependent viscoplastic behavior of material is attributed to the observed formability improvement, much less effort has been devoted to understand and quantify the underlying mechanisms. In this context, the hole expansion test (HET) of a dual phase steel was interrupted at pre-defined punch travel heights to understand the time-dependent effects on stretch-flangeability. The effect of pre-strain, hold time and edge quality on hole expansion ratio (HER) improvement was studied. The present study shows that the HER improves significantly in interrupted HET. This improved HER is due to the combined effects of stress relaxation and friction on deformation behavior. The ductility improvement estimated from uniaxial stress relaxation tests was used to estimate the contribution of stress relaxation and friction, respectively, in HET. This study shows that friction plays a significant role in improving HER at high pre-strain. It was also demonstrated that frictional effects are largely influenced by edge quality. [ABSTRACT FROM AUTHOR]

This paper presents a new bending method of sheet metal for forming diversified shapes and enhancing operability. The method, "asymmetric bending", uses a punch and a pair of front and back dies. While the punch moves down for bending, the two dies move at different velocities so that the movement of the front side of the sheet metal can severely be restricted. The front side of the metal can be deformed with diversity in advance as it can escape from geometric interference with the bending tools. The method also improves operability and safety for operators due to the movement restriction. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental investigations and numerical analyses performed on reinforced concrete flat slabs. Two tests were carried out on two flat slab specimens designed without specific shear reinforcement. The present paper deals only with the experimental behaviour and numerical modelling of such slabs, this representing the initial part of a larger study which aims to evaluate the shear capacity of such deficient slabs resulted from faulty design or execution and to identify viable and efficient strengthening solutions. ATENA finite element software package was used to numerically model the behaviour of the specimens. A very good agreement was achieved between the results of experimental investigations and numerical modelling with deviations of 0.2% in terms of maximum load carrying capacity and of 7% in terms of corresponding displacement. The specimens were able to carry loads of more than 950kN, larger than those evaluated using designated Eurocodes, displaying a safety factor of 2.72. [ABSTRACT FROM AUTHOR]

The Netherlands has a large number of thin, transversely prestressed concrete bridge decks, cast in-situ between flanges of prestressed concrete girders dating back to the 1960s and 1970s. These bridges are critical in shear when analyzed using EN 1992-1-1:2005; however, in reality, they show no significant signs of distress, possibly because of residual bearing (punching shear) capacity arising from compressive membrane action. Since these bridges are old, it is an astute approach to check whether they can be used for a few more decades, provided they are safe and reliable against modern traffic loads. The results could then be applied to a wider range of structures, especially in developing countries facing economic constraints. A prototype bridge was selected and experimental, numerical and theoretical approaches were used to investigate its bearing capacity. Respective coefficients of variation of 11% and 9% were obtained when the experimental and the finite element analysis punching loads were compared with the theoretical results. This led to the conclusion that the existing transversely prestressed concrete bridge decks still have sufficient bearing capacity and considerable cost savings can be made if compressive membrane action is considered in the analysis. [ABSTRACT FROM AUTHOR]

Several empirical models have been introduced during the last two decades to estimate the punching capacity of two-way slabs reinforced with fiber-reinforced polymer (FRP) reinforcement. In this study, the applicability of these models on FRP-reinforced concrete (RC) slab-column interior and edge connections subjected to gravity loads is assessed. The models are also calibrated against experiments conducted previously by the authors on FRP-RC edge connections subjected to reversed-cyclic lateral loads. Test results of 68 interior and 25 edge specimens, 6 of which were tested under reversed-cyclic lateral loads, were used to evaluate the available models. Based on the analysis, a universal model capable of accurately predicting the capacity of both interior and edge specimens subjected to gravity or cyclic loads is proposed. The proposed model provided a mean test-to-predicted strength of 1.01 ± 0.14 and 1.01 ± 0.09 for interior and edge specimens, respectively. Furthermore, a design model is proposed to estimate gravity shear limits for FRP-RC connections without shear reinforcement and subjected to cyclic load. [ABSTRACT FROM AUTHOR]

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Reinforced concrete (RC) slabs are characterized by reduced construction time, versatility, and easier space partitioning. Their structural behavior is not straightforward and, specifically, punching shear strength is a current research topic. In this study an experimental database of 113 RC slabs without shear reinforcement under punching loads was compiled using data available in the literature. A sensitivity analysis of the parameters involved in the punching shear strength assessment was conducted, which highlighted the importance of the flexural reinforcement that are not typically considered for punching shear strength. After a discussion of the current international standards, a new proposed model for punching shear strength and rotation of RC slabs without shear reinforcement was discussed. It was based on a simplified load-rotation curve and new failure criteria that takes into account the flexural reinforcement effects. This experimental database was used to validate the approaches of the current international standards as well as the new proposed model. The latter proved to be a potentially useful design tool. [ABSTRACT FROM AUTHOR]

This study is focused on punch shape design in tube hydro-piercing processes of SPFC590Y carbon steel tubes. The flow stresses of the carbon steel tubes obtained by tensile tests are used in the finite element simulations of tube hydro-piercing process with software "Deform 3D." The ductile fracture criterion of Normalized Cockcroft and Latham is used during the FE simulations. The critical damage value for NCL fracture criterion is obtained by comparing simulation results and tensile test results. The effects of various parameters such as punch strokes, internal pressures, etc. on tube deformation and fracture mechanism in hydro-piercing processes are investigated. Hydro-piercing experiments are conducted. The characteristics of the experimentally pierced hole sections are compared with the simulation results to validate the analytical models. The effects of various parameters on the characteristics of pierced hole sections after hydro-piercing processes are discussed numerically and experimentally. [ABSTRACT FROM AUTHOR]

Many bridge deck slabs in Europe are rated insufficient load-carrying capacity in shear and punching according to the Eurocodes. In the past, assessment models have mainly been developed from laboratory studies that simplified real-world conditions. Large-scale or full-scale field experiments are needed to validate more recent improved models. The goal of this study is to calibrate improved models using data obtained from a full-scale bridge deck slab shear test; the objective is to exploit and share our findings and to make recommendations for the planning, design, and implementation of such a complex experiment. Full-scale destructive tests of a 55-year-old reinforced concrete bridge deck slab on prestressed concrete girders were conducted to calibrate a model used to assess existing bridges. Concrete properties were also tested to evaluate the condition of the bridge. Results show that both the load-carrying capacity of the bridge deck slab and the strength of the concrete were much greater than were assumed in design. Finite-element analysis of the parameters governing loading positions and prestress in the girders showed that arch action and boundary condition simplification had important effects on shear distribution. [ABSTRACT FROM AUTHOR]

The problem related to the effect of the corner column load on the punching shear resistance of the slab was presented. Existing experimental studies on internal columns demonstrated that the column pressure could lead to an increase in the punching shear resistance. Because of different confinement conditions of corner column-slab connection joints, it is unclear if such an effect exists for corner columns. New experimental investigations were initiated to clarify this issue. They covered a total of three corner column-slab connection specimens - slabs with a thickness of 140 mm and a longitudinal reinforcement ratio -l = 1.09% connected with columns of a cross-section of 200×200 mm. The only variable parameter was the column load equal to 500, 1000 and 1500 kN. A reduction of the slab load-carrying capacity of about 9% due to a three-fold increase in the column load was noted. Therefore, the effect of the column load turned out to be opposite to that observed for most previous tests on internal column-slab connections, which could have a result of a limited capacity of the slab reinforcement due to additional tensile forces from the lateral expansion of joint concrete. Comparison in the light of test results demonstrated, that EN 1992-1-1 procedure allowed for safe, yet conservative estimation of the punching shear resistance. An average ratio of experimental to theoretical load of 1.82 was obtained. [ABSTRACT FROM AUTHOR]

A super lightweight deck can enhance load rating and functionality of a bridge, especially those identified as structurally deficient. This study was aimed to develop and experimentally validate a novel bridge deck as an ultra-lightweight low-profile waffle slab of ultra-high-performance concrete (UHPC) with either carbon fiber reinforced polymer (CFRP) or high strength steel (HSS) reinforcement. The proposed system lends itself to accelerated bridge construction, rapid deck replacement in bridges with load restrictions, and bridge widening applications without the need to replace girders. Performance and failure modes of the proposed deck were initially assessed through extensive lab experiments and finite element analysis, which together confirmed that the proposed deck panel meets the AASHTO LRFD requirements. The proposed deck system is not susceptible to punching shear of its thin slab and fails in a rather ductile manner. To evaluate its long-term performance, the system was further tested under the dynamic impact of wheel load at the Accelerated Pavement Testing (APT) facility of the Florida Department of Transportation using a Heavy Vehicle Simulator (HVS). [ABSTRACT FROM AUTHOR]

In this paper, the evolution of flow lines during the forging of bearing rings was investigated. The formation mechanisms of flow-line defects were revealed by a finite element method (FEM) simulation of the entire forging process. To avoid the flow-line disorder caused by the bearing ring manufacturing method, two hot forging processes were employed to optimize the flow-line distribution of an M50 steel bearing ring with a deviated groove. The simulation and experimental results show that the punching die and the location of the punching recess had a significant effect on the flow-line formation. The V-shaped punching pin and punching recess setting at the bottom of the billet resolved the flow-line disorder caused by the punching process. Finally, a bearing outer ring with a reasonable flow-line distribution was obtained. Furthermore, the improved hot forging process reduced the average grain size and improved the M2C carbide-aggregation phenomenon. Given the direction of the flow lines, the bearing ring exhibited mechanical anisotropy in the tensile direction. [ABSTRACT FROM AUTHOR]

The flow stress of wire material, the friction coefficient and the sticking capability of the lubrication coating on the wire surface are evaluated with a single test. In this test, the specimen cut off from the end of a wire coil is set on a V-groove die and then is compressed into the V-groove by a punch. Friction coefficient is determined by the ratio of the punch load and the die load. The flow stress curve is calculated using the punch load-punch stroke curve. The proposed method is suitable for the use in the wire manufacturing shops for cold forging. [ABSTRACT FROM AUTHOR]