Analysis of 3D Plastic Deformation in Vertical Rolling Based on Global Weighted Velocity Field

Energy method is an essential theoretical approach to analyze plastic forming, which is widely used in rolling. An analysis model for vertical rolling process is established according to energy theory. By using global weighted method firstly, the 3D continuous velocity field, strain rate field and the corresponding power functional are proposed. The unknown variables are solved numerically based on the principle of minimum energy. Then, deformation parameters and rolling force are determined. The analysis on specific examples with the width reduction rate of 0.03~0.05 shows that the theoretical prediction value of weighted model is in good agreement with experimental results. Moreover, the effects of several shape and rolling parameters on rolling force, rolling power and edge deformation are studied. Both the width reduction rate and initial slab thickness have significant influences on dog-bone size and rolling force. A wider slab slightly increases the nonuniformity of dog-bone deformation. An increase of vertical roller radius can weaken the edge deformation.

Dielectric Slabs-Based Lens for Millimeter-Wave Beamforming

This paper proposes a dielectric slabs-based lens for millimeter-wave beamforming systems. The proposed lens is based on the graded steps of the effective refractive index of the semi-spherical lens. It consists of multiple dielectric slabs that match the selected gradient effective refractive index. These slabs have the same thicknesses and different radii. The slab thickness in this lens should not exceed a quarter of the operating wavelength to keep on a similar effective refractive index of the original semi-spherical lens. A horn antenna is used to examine the performance of the designed lens at 28 GHz frequency in terms of the maximum gain, sidelobe level, and 3 dB beamwidth. Sixteen switchable horn antennas are used to demonstrate lens capability for millimeter-wave beamforming. Every single antenna element is selected individually, thus the dielectric lens steers and enhances the corresponding radiation of the selected element in the desired direction.

Analytical Model Formulation of Steel Plate Reinforced Concrete Walls against Hard Projectile Impact

Steel plate reinforced concrete (SC) walls can effectively resist projectile impact by preventing the rear concrete fragments flying away, thus attracting much attention in defence technology. This work numerically and analytically investigated the hard projectile perforation of steel plate reinforced concrete walls. Impact resistance theories, including cavity expansion analysis as well as the petaling theory of thin steel plates were used to describe the cratering, tunneling and plugging phases of SC walls perforation. Numerical modeling of SC walls perforation was performed to estimate projectile residual velocity and target destructive form, which were validated against the test results. An analytical model for SC wall perforation was established to describe the penetration resistance featuring five stages, i.e., cratering, tunneling and plugging, petaling with plugging and solely petaling. Analytical model predictions matched numerical results well with respect to projectile deceleration evolution as well as residual velocity. From a structural absorbed energy perspective, the effect of front concrete panel and rear steel plate thickness combinations was also studied and analyzed. Finally, equivalent concrete slab thickness was derived with respect to the ballistic limit of SC walls, which may be helpful in the design of a protective strategy.

Study on MnS Inclusion Aggregation along Continuous Casting Slab Thickness of Medium Carbon Structural Steel

Precipitation of MnS inclusions in steel affects the mechanical properties of the material significantly. The evolution of MnS inclusions along the continuous casting slab thickness and its influencing factors has not been clearly established and comprehensively studied. In this paper, solidification macrostructure, sulfur segregation and MnS inclusions in the continuous casting slab of medium carbon structural steel 45# were studied by various methods, including the metallographic observations, elemental analysis, scanning electron microscope (SEM) with Energy Dispersive Spectrometer (EDS) observation, automatic particle analysis, and thermodynamic calculations. The 2D/3D morphologies of MnS inclusions suggest that the sulfides turn from globular to rodlike, and further to dendritic shape along the slab thickness progressively. Furthermore, it was found that MnS inclusions are remarkably aggregated in the columnar crystals and the equiaxed crystals mixed zone, where the sulfides have the largest average diameter of 6.35 μm and the second maximum area fraction of 0.025% along the slab thickness. In order to reveal the mechanism of this phenomenon, the precipitation temperature of MnS inclusion in the 45# steel was clarified by thermodynamic calculation and experimental observation, and the quantitative relationships among the distribution of sulfur content, secondary dendrite arm spacing (SDAS), and precipitation area fraction of MnS inclusions were discussed. Moreover, the inclusion size was numerically predicted to compare with the measured value. The results indicate that the large SDAS, high sulfur content and low cooling rate accounting for the large-size aggregated MnS inclusions in the mixed zone. Unfortunately, the dendritic MnS inclusions, even if the average diameter exceeds 52 μm, can act as the nucleation sites for ferrites, and the distribution of the sulfides promotes uneven microstructure in the steel.

Statistical Study of Ionospheric Equivalent Slab Thickness at Guam Magnetic Equatorial Location

The ionospheric equivalent slab thickness (τ) is defined as the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), and it is a significant parameter representative of the ionosphere. In this paper, a comprehensive statistical analysis of the diurnal, seasonal, solar, and magnetic activity variations in the τ at Guam (144.86°E, 13.62°N, 5.54°N dip lat), which is located near the magnetic equator, is presented using the GPS-TEC and ionosonde NmF2 data during the years 2012–2017. It is found that, for geomagnetically quiet days, the τ reaches its maximum value in the noontime, and the peak value in winter and at the equinox are larger than that in summer. Moreover, there is a post-sunset peak observed in the winter and equinox, and the τ during the post-midnight period is smallest in equinox. The mainly diurnal and seasonal variation of τ can be explained within the framework of relative variation of TEC and NmF2 during different seasonal local time. The dependence of τ on the solar activity shows positive correlation during the daytime, and the opposite situation applies for the nighttime. Specifically, the disturbance index (DI), which can visually assess the relationship between instantaneous τ values and the median, is introduced in the paper to quantitatively describe the overall pattern of the geomagnetic storm effect on the τ variation. The results show that the geomagnetic storm seems to have positive effect on the τ during most of the storm-time period at Guam. An example, on the 1 June 2013, is also presented to analyze the physical mechanism. During the positive storms, the penetration electric field, along with storm time equator-ward neutral wind, tends to increase upward drift and uplift F region, causing the large increase in TEC, accompanied by a relatively small increase in NmF2. On the other hand, an enhanced equatorward wind tends to push more plasma, at low latitudes, into the topside ionosphere in the equatorial region, resulting in the TEC not undergoing severe depletion, as with NmF2, during the negative storms. The results would complement the analysis of τ behavior during quiet and disturbed conditions at equatorial latitudes in East Asia.

Experiment and Simulation Study on the Dynamic Response of RC Slab under Impact Loading

Reinforced concrete (RC) slab is an important component in civil construction and protection engineering, and its dynamic response under impact loading is a complex mechanical problem, especially for two or multiple continuous impact loads. In this paper, a series of drop hammer impact tests were carried out to investigate the dynamic response of RC slabs with two successive impacts. The time history of impact force and the failure characteristic of the slab surface were recorded. Moreover, four influence factors, including slab thickness, reinforcement ratio, impact location, and drop hammer height have been discussed. Besides, a 3D numerical model based on the finite element method (FEM) was established to expand the research of constrained force, deflection, and vertical stress of an RC slab. The results show that increasing the slab thickness and reinforcement ratio can improve the impact resistance of an RC slab. The impact point location and drop hammer height have a great influence on the dynamic response of the RC slab. In addition, the RC slab will have more obvious damage under the second impact, but the dynamic response becomes weaker. It may be because of the local damage in the concrete caused by the first impact that would weaken the propagation of vibration.

Predicting Embodied Carbon and Cost Effectiveness of Post-Tensioned Slabs Using Novel Hybrid Firefly ANN

Post-tensioning has become a strong contender for manufacturing reinforced concrete (RC) members, especially for flat slabs in large-span structures. Post-tensioned (PT) slabs can lead to considerable material savings while reducing the embodied carbon (embodied CO2), construction time, and life cycle maintenance and repair costs. In this research, a novel hybrid Firefly–Artificial Neural Network (Firefly–ANN) computational intelligence model was developed to estimate the cost effectiveness and embodied CO2 of PT slabs with different design variables. To develop the dataset, several numerical models with various design variables, including the pattern of tendons, slab thickness, mechanical properties of materials, and span of slabs, were developed to investigate the sustainability and economic competitiveness of the derived designs compared to benchmark conventional RC flat slabs. Several performance measures, including punching shear and heel drop vibration induced by human activity, were used as design constraints to satisfy safety and serviceability criteria. The economic competitiveness of PT slabs was more evident in larger spans where the cost and embodied CO2 emissions decreased by 39% and 12%, respectively, in PT slabs with a 12-m span length compared to conventional RC slabs. Sensitivity analysis also confirmed that the cost and embodied CO2 emissions were very sensitive to the slab thickness by 86% and 62%, respectively.

Comparative Study Of Conventional Slab, Flat Slab And Grid Slab Using ETABS

In today’s construction, the traditional slab is mostly supported by a beam, with a small slab thickness and a large beam depth, and the weight is carried from beam to column. The flat slab allows architects to place partition walls wherever they are needed. It is widely used because it reduces weight, speeds up building, and is cost effective. Similarly, since its inception, the conventional slab has provided benefits such as increased stiffness, increased weight carrying ability, as well as being safe and cost effective. Grid slabs are necessary where the span is greater, and grid beams are provided to lessen the spanning. Grid slabs reduce dead load due to voids and are appropriate for longer spans with heavy loads. The Grid slab is less expensive and provides superior vibration resistance. The project’s goal is to find the most cost-effective slab among standard slab, flat slab with drop, and grid slab. A G+5 Commercial multi-story structure with flat slab, conventional slab, and gird slab was investigated for characteristics such as storey displacement, shear force, bending moment, and storey drift in this study. There are a total of 18 structures examined. The performance and behaviour of all structures in India’s seismic zone III have been investigated with the application of dead load, live load and seismic load. The results of shear force, Bending Moment, story shear, story displacement, story drift and quantity of concrete and steel shows that the overall result values makes flat slab a suitable structure as compared to the conventional and grid slab.

Limitations on ACI Code Minimum Thickness Requirements for Flat Slab

Reinforced concrete two-way flat slabs are considered one of the most used systems in the construction of commercial buildings due to the ease of construction and suitability for electrical and mechanical paths. Long-term deflection is an essential parameter in controlling the behavior of this slab system, especially with long spans. Therefore, this study is devoted to investigating the validation of the ACI 318-19 Code long-term deflection limitations of a wide range of span lengths of two-way flat slabs with and without drop panels. The first part of the study includes nonlinear finite element analysis of 63 flat slabs without drops and 63 flat slabs with drops using the SAFE commercial software. The investigated parameters consist of the span length (4, 5, 6, 7, 8, 9, and 10m), compressive strength of concrete (21, 35, and 49 MPa), the magnitude of live load (1.5, 3, and 4.5 kN/m2), and the drop thickness (0.25tslab, 0.5tslab, and 0.75tslab). In addition, the maximum crack width at the top and bottom are determined and compared with the limitations of the ACI 224R-08. The second part of this research proposes modifications to the minimum slab thickness that satisfy the permissible deflection. It was found, for flat slabs without drops, the increase in concrete compressive strength from 21MPa to 49MPa decreases the average long-term deflection by (56, 53, 50, 44, 39, 33 and 31%) for spans (4, 5, 6, 7, 8, 9, and 10 m) respectively. In flat slab with drop panel, it was found that varying drop panel thickness t2 from 0.25 to 0.75 decreases the average long-term deflection by (45, 41, 39, 35, 31, 28 and 25%) for span lengths (4, 5, 6, 7, 8, 9 and 10 m) respectively. Limitations of the minimum thickness of flat slab were proposed to vary from Ln/30 to Ln/19.9 for a flat slab without a drop panel and from Ln/33 to Ln/21.2 for a flat slab with drop panel. These limitations demonstrated high consistency with the results of Scanlon and Lee's unified equation for determining the minimum thickness of slab with and without drop panels. Doi: 10.28991/cej-2021-03091769 Full Text: PDF