A study on the punching shear behavior of 8 slabs with recycled aggregate concrete (RAC) was carried out. The two main factors considered were the recycled coarse aggregate (RCA) replacement ...percentage and the steel fibre volumetric ratio. The failure pattern, load-displacement curves, energy consumption, and the punching shear capacity of the slabs were intensively investigated. It was concluded that the punching shear capacity, ductility and energy consumption decreased with the increase of RCA replacement percentage. Research findings indicated that the incorporation of steel fibres could not only improve the energy dissipation capacity and the punching shear capacity of the slab, but also effectively improve the integrity of the slab tension surface and thereby changing the trend from typical punching failure pattern to bending-punching failure pattern. On the basis of the test, the punching shear capacity formula of RAC slabs with and without steel fibres was proposed and discussed.
One-way slabs under concentrated loads may fail by one-way shear, two-way shear, flexure, or a combination of these modes. This paper reviews shear and punching shear-failure mechanisms of one-way ...slabs under concentrated loads tested from the literature and investigates the accuracy of different approaches to predict the ultimate capacity for such slabs using the ACI code expressions. A database with 160 test results was evaluated. Shear and concentrated loads measured at failure were reviewed according to parameters such as the load position, slab width, and reinforcement ratios. The load position and slab width play a marked influence on the failure mechanism and tested loads. The analyses improved the understanding of the main parameters influencing the behavior of one-way slabs under concentrated loads. Finally, the proposed effective shear width expression enables accurate shear capacity predictions using the ACI code expressions.
The study of punching shear resistance and failure mode for reinforced concrete (RC) slab-column structures has been constantly highlighted, due to a number of catastrophic punching shear failures in ...engineering applications. However, mechanics-based punching shear resistance models and failure mode identification models have problems of prediction accuracy and influential factors quantification. In this paper, the prediction models based on machine learning (ML) are proposed to predict the punching shear resistance and failure mode. Compared with other seven ML models, extreme gradient boosting (XGBoost) is selected as the best model, which performance is examined by several performance measures. The prediction process of XGBoost is explained by shapley additive explanation (SHAP) and partial dependence plot (PDP). A comparative SHAP and PDP analysis reveals the relationships between punching shear resistance/failure and influential factors, which cannot be quantified through traditional experimental and theoretical analysis. Furthermore, suggestions for choosing the influential factors are provided to avert the brittle punching shear failure and improve the punching shear resistance of RC slab-column joints.
•Our numerical analysis results agreed well with test results.•The effects of longitudinal rebar and shear bar were enumerated.•The appropriate number of layer of longitudinal rebar was ...recommended.•The appropriate shear bar spacing was recommended.•Two efficient designs of reinforced concrete walls was recommended.
In this paper, the punching resistance of a reinforced concrete (RC) wall under missile impact loading is evaluated using the finite element approach. The model is analyzed using LS-DYNA, a commercially available software program. The structural components of the RC wall, missile, and their contacts are fully modeled. Included in the analysis is material nonlinearity, which considers damage and failure. Damping effect is also taken into account. The analysis results are then verified with the test results. Parametric studies with a varying number of layers of longitudinal rebar and shear bar spacing are carried out to investigate the punching behavior of RC walls under missile impact. The distance travelled, scabbing area, and failure mode of various RC walls are examined, and efficient designs are recommended thereafter.
The effect of stress and temperature coupling on gradient alloyed surfaces induced by punching severe deformation has been investigated by scanning electron microscopy, energy dispersive ...spectroscopy, X-ray diffraction and microhardness tests. The stress field and temperature field were simulated using the Abaqus finite element method. The results show that surfaces experiencing the stress and temperature coupling effect have a greater depth of the alloying layer and a finer grain. In particular, the level of alloying, as determined by parameters such as the solid solubility of Cr atoms in a Fe crystal lattice and the quantity of the compound (Fe, Cr)7C3, is significantly increased. These differences are attributed to the coupling effect of stress and temperature, which can increase the number of crystal defects and the metallic Cr diffusion coefficient. Punching deformation without cooling treatment produces a higher hardness when compared to punching deformation with cooling treatment; without cooling treatment the hardness gradually decreases from 295 Hv at the top surface to 185 Hv in the matrix.
•During punching deformation, the high stress can also increase the sample temperature to 226.7 °C due to collisions between atoms and friction, in addition to creating numerous defects in the material.•The coupling effect of stress and temperature increases the level of alloying by increasing the solid solubility of Cr atoms in the Fe crystal lattice and the quantity of (Fe, Cr)7C3.•The defects produced by the coupling of stress and temperature result in greater mechanical properties.
This article presents an experimental study on hollow floor slab-column-reinforced connections, which are enhanced by installing locally solid zone of slab around the column and hidden beam in the ...floor. To investigate the punching-shear behavior of hollow floor slab-column-reinforced connections, six hollow floor slab-column-reinforced connections under vertical load were conducted on three types of connections with different thickness, namely, two hollow floor slab-column-reinforced connections without punching component, two hollow floor slab-column-reinforced connections with bent-up steel bars, and two hollow floor slab-column-reinforced connections with welding section steel cross bridging. Meanwhile, the strength, stiffness, failure mode, and ductility of hollow floor slab-column-reinforced connections with punching components were obtained and compared with the hollow floor slab-column-reinforced connections without punching component. The results showed that hollow floor slab-column-reinforced connections had the double failure characteristics including punching shear and flexural failure, and flexural failure was the main failure mode as a result of installing hidden beam. The hollow floor slab-column-reinforced connections with punching components exhibited higher initial stiffness and higher loading capacity than hollow floor slab-column-reinforced connections without punching components, but welding section steel cross bridging have a better on improving the connections’ punching-shear capacity than bent-up steel bars.
The stretch flangeability of a medium Mn steel prepared by quenching and partitioning was examined using a hole-expansion test. Samples were heat-treated at quenching temperatures 90 °C ≤ TQ ...≤ 170 °C, at which no secondary martensite is formed upon final quenching. The hole-expansion test used a 60° conical punch. The hole at the center of the specimens was prepared by punching or wire cutting. In both sample preparation conditions, hole expansion ratio (HER) increased as TQ decreased. The dependence of HER on TQ was more pronounced in the samples prepared by punching than in samples prepared by wire cutting. While there is no clear correlation between HER and tensile properties, the HER decreased as retained austenite increased. By punching, the retained austenite transformed to strain-induced martensite in the shear-affected zone near the hole edge. This martensite has a negative impact on the HER.
The aim of this study was to determine the advantages and limitations of two commonly used sampling techniques, i.e., punching tissue block (PTB) and laser capture microdissection (LCM) when ...investigating tumor cell-derived gene expression patterns at the invasive front of colorectal cancer (CRC). We obtained samples from 20 surgically removed CRCs at locations crucial for tumor progression, i.e., the central part, the expansive front and the infiltrative front exhibiting tumor budding (TB), using both sampling techniques. At each location, we separately analyzed the expressions of miR-200 family (miR-141, miR-200a, miR-200b, miR-200c and miR-429), known as reliable markers of epithelial-mesenchymal transition (EMT). We found significant downregulation of all members of miR-200 family at the infiltrative front in comparison to the central part regardless of the used sampling technique. However, when comparing miR-200 expression between the expansive and the infiltrative front, we found significant downregulation of all tested miR-200 at the infiltrative front only in samples obtained by LCM. Our results suggest that, PTB is an adequate technique for studying the differences in tumor gene expression between the central part and the invasive front of CRC, but is insufficient to analyze and compare morphologically distinct patterns along the invasive front including TB. For this purpose, the use of LCM is essential.
One of the attractiveness of flat slab structures and flat plate structures is that the structural types without beams have the advantage of a high degree of freedom to use of indoor spaces. The new ...construction method that we will describe in this study is a flat slab mixed structure with steel capitals in RC slab. The distinctive of this construction is that the columns are generally designed in RC but changed to small diameter steel round bars. In addition, by replacing the RC drop panel and the RC capital with a steel capital in RC slab, the structure will provide a space with a high degree of freedom as well as flexibility. The purpose of this research was to experimentally grasp the failure in RC slab by punching shear, the strength and the deformation capacity under lateral load. Furthermore, it is a characteristic of this structure that the decrease in the rigidity of RC slab due to cracking has a great effect on the properties of the structure. Therefore, we will also describe the serviceability and reparability limits by the observation of the residual crack width of the specimens. The following conclusions were obtained from this study. 1) If the circumference obtained by adding the effective depth of RC slab to the capital plate diameter is taken as the critical section for shear in RC slab, it is confirmed that the ultimate vertical force when only the vertical force is transmitted can be calculated with a safety factor of about 10% by using the AIJ standard for RC structure6). Here, we use the effective depth is calculated by subtracting the capital plate thickness from the effective depth of the AIJ standard. 2) By setting the long-term allowable load to about 1/3 of the ultimate vertical force when only the vertical force, it was confirmed from the observation of the crack width that there is no problem in the serviceability of RC slab under the long-term load. 3) Under the 1/3 (inner column) or 1/6 (outer column) of ultimate vertical force on RC slab, in the lateral loading test, regardless of the inner and outer columns in all the loading directions, it was confirmed that the resistance for lateral force did not decrease up to the story drift angle (“R”) become 20×10-3 rad, and it was confirmed the high deformation capacity. 4) The lateral initial stiffness of this method was almost equal when the inner column and outer column specimens were applied in the positive direction. Then the outer column was applied in the negative direction, it was about half that of the positive direction. Furthermore, as the story drift angle increased, the lateral stiffness further reduced due to the damage of RC slab. We also confirmed that the story drift angles of all the specimens were about 10 to 20% of the initial stiffness at R=40×10-3 rad. 5) At the story drift angles (R=10×10-3 rad) often used as the design criteria for large earthquakes, high reparability of this structure was confirmed from the observation of the residual crack width. 6) The shear failure strength around the column was verified that the correlation equation Vu/Vo+ Mu/Mo≧1.0 of the AIJ standard using RC column is established when punching failure occurs.
PDF
