Slab Width Research Articles

Negative bending capacity of web-embedded U-shaped steel-concrete composite beams

This paper discusses the negative bending behavior of a new type of web-embedded U-shaped steel-concrete composite beams (WUSCBs). Considering the effective width of the concrete slab, a negative bending moment test was performed on eight WUSCB specimens. The web-embedded shear connector in the WUSCB has been shown to have good shear connection performance and maintain the overall function of the WUSCB. The failure process of the specimen was categorized by the cracking, yielding, and buckling loads which correspond to 0.29 Pu, 0.79 Pu, and 0.90 Pu, respectively. Negative bending failure was observed in the WUSCB, evidenced by the steel plate yielding and concrete slab cracking. The WUSCB was found to have good ductility and deformability under negative bending. A finite element model was established to verify with the experimental results. The calculation method for negative bending capacity is proposed; and the calculation results are in good agreement with the test results.

Evaluation of base sliding response and effective slab width in ten-storey tests

Evaluation of base sliding response and effective slab width in ten-storey tests

Shear lag effect of composite girders in cable-stayed bridges under dead loads

The shear lag effect is a common phenomenon among civil infrastructures, which is also a critical issue for composite girders. For composite girders in large-span cable-stayed bridges, there is a large proportion of internal forces caused by dead loads, and the shear lag effect of the concrete slab under dead loads is significant. To investigate the normal stress distribution at the construction and service stages, systematic in-situ stress monitoring of composite girders was performed on a cable-stayed bridge under dead loads. Then, the finite element models were built for numerical modeling. The theoretical analysis model was proposed to evaluate the shear lag effect of composite cable-stayed bridges under dead load. Then the law of the stress ratio and the shear lag effect was analyzed by contrasting the test data and simulation results. Meanwhile, the calibrated FE models were used to do the full-scale parametric analysis of the factors including span length, slab width, and cable spacing. The results show that the main girder segment near the bridge tower and the mid-span are critical sections at the construction and service stages for analyzing the shear lag effect. The cable spacing and slab width are the main factors affecting the shear lag effect under dead loads. The effective width coefficients are positively correlated with the stress ratio.

Experimental tests of FRP-HSC hybrid beams under four-point bending

This paper provides an experimental study of a new fiber-reinforced polymer (FRP)-high strength concrete (HSC) hybrid beam, which consists of a glass FRP (GFRP) I-shaped profile beam strengthened with a layer of HSC on top and carbon FRP (CFRP) sheets on the web. In this study, a total of two GFRP I-shaped profile beams, two GFRP I-shaped profile beams strengthened with CFRP sheets on the web and nine FRP-HSC hybrid beams were tested under four-point bending loading. The test parameters varied for the existence of CFRP sheets, the flange width of the GFRP profile, the width of the HSC slab, the type of shear connectors and the interfacial connection method. The test results indicated that bonding CFRP sheets, increasing the flange width and HSC slab width all showed positive effect on the ultimate bearing capacity and initial rigidity. Compared with U-shaped GFRP shear keys and inverted T-shaped GFRP shear keys, the hybrid beams using steel bolts had the highest ultimate load capacity and initial rigidity. The hybrid beams using the composite-bond interface (CB) performed better than the hybrid beams using wet-bond (WB) and dry-bond (DB) interfaces.

CYCLIC BEHAVIOR OF COMPOSITE CONNECTIONS IN COMPOSITE FLOOR DIAPHRAGMS

AbstractThis research explores the cyclic behavior and strength of the composite concrete‐filled steel deck diaphragm system through experimental pushout and cantilever diaphragm tests. This work is part of the Steel Diaphragm Innovation Initiative (SDII), a multi‐institutional project that is investigating the behavior of composite steel deck diaphragms in steel buildings structures in high seismic zones. Sixteen unique pushout tests were conducted at Northeastern University as part of SDII. These specimens had variations in the orientation of the steel deck, concrete density, effective slab width, shear stud position and grouping. Additionally, seven of these tests were cyclic. Eight cantilever diaphragm tests were conducted at Virginia Tech as part of SDII. The parameters included deck height, slab thickness, concrete density, layout of shear studs, and reinforcement. These experimental tests provide valuable knowledge that aids in the characterization of the behavior and strength prediction of this structural system.

H-Polarised EM-Wave Transport in Polymeric-Chalcogenide Columnar Photonic Materials

The propagation of H-polarized electromagnetic (EM) waves in polymeric (PEI)-chalcogenide (As2Se3) photonic materials (PCCPM) has been theoretically optimized and investigated in the current work. We used the Transfer Matrix Technique (TMT) and Hankel Realism (HR) in columnar coordinates to show numerical findings for the unit columnar junction and columnar slab for both polymeric (low refractive index) and chalcogenide (high refractive index) materials composed at least loss wavelength window (632.8 nm). The optical transmittance with wavelength for both materials for the cylindrical unitary slab displays oscillating and non-oscillating signatures, indicating that the starting radius has a significant impact on the transmittance at a constant slab width. The oscillatory transmittance becomes squizzing when the starting radius is increased. Furthermore, for smaller modal numbers, optical transmittance is an oscillatory function of slab thickness, and for (m=4), it becomes minimum and flat. These scientific breakthroughs pave the door for a variety of photonic devices and sensor applications.

Experimental and Numerical Assessments of Slab-Column Connections Strengthened Using Bonded Hemp Fiber Fabric Sheets

The replacement of synthetic fibers with natural fibers in concrete has been recently investigated to counter the growing environmental and sustainable issues. Hemp fibers are environmentally friendly and are used in the manufacturing of composite materials. This paper reports on the experimental assessment of using hemp fiber reinforced polymer (HFRP) fabric sheets as an alternative to carbon fiber reinforced polymer (CFRP) sheets to strengthen interior slab-column connections. Small-scale interior slab-column connections were loaded centrally through the column stub up to failure. The main test variables were slab thickness, HFRP sheet width, number of HFRP layers, type of strengthening material (HFRP or CFRP sheets), and HFRP sheet's location relative to the column’s face. Assessment of the strengthening material was based on a comparison of load capacity, mode of failure, load–displacement history, and cracking patterns. The experimental results demonstrated that HFRP strengthening sheets led to improvement in the structural behavior of the slab-column connections depending on the slab thickness, width and configuration for HFRP sheets. Although the HFRP sheets led to lower improvement as compared to the synthetic CFRP sheets, however, the same improvement could be reached by the HFRP sheets if they are applied in larger width or different configurations. A finite-element model was developed using ABAQUS software to predict the behavior of simulated specimens. The numerical findings showed that the models predicted the connection behavior in good agreement with the experimental test results. In addition, an analytical model was calibrated to simulate the behavior of the tested specimens.

Vertical shear resistance of noncompact steel–concrete composite girders under combined positive moment and shear

For noncompact composite girders widely employed in bridge structures, the design can be more reasonable and economical if the shear contribution of concrete slabs is considered. In this study, the ultimate shear resistance of composite girders with noncompact sections under positive moments was investigated using the finite element method (FEM). The validity of the FEM was verified using existing test data. Subsequently, parametric studies were performed using the validated FEM. It was shown that the concrete slab thickness and web height-to-thickness ratio had notable effects on the shear resistance of the slab; the concrete slab width had a negligible effect on the shear resistance if its value exceeded twice the web height; the web aspect ratio mainly affected the shear resistance of the web. The numerical results indicated that the shear resistance of the composite girder was 1.02–1.63 times of that calculated using the ASSHTO code, and 1.12–1.55 times of that calculated using the EC4 code. After comprehensively considering the effects of these parameters, a design equation for predicting the shear resistance of noncompact composite girders under positive moments was suggested and verified using numerical and test data.

Recomendações para avaliação da resistência à força cortante e punção de lajes unidirecionais sob cargas concentradas de acordo com a ABNT NBR 6118:2014

Abstract This study describes a set of recommendations to improve the precision of shear and punching shear capacity predictions for one-way slabs under concentrated loads, regardless of the governing failure mechanism, using the ABNT NBR 6118:2014 code provisions. For this purpose, a database of 143 test results was developed, including one-way slabs with different support conditions and loading layouts and that failed by different shear failure mechanisms: one-way shear, punching shear or a mixed mode. The key parameters influencing the load capacity and failure mechanism of these slabs were considered for the proposed recommendations: load position and slab width. Adjustments to the effective shear width definition and shear resisting control perimeter were described. Arching action for loads close to the support was also considered in both one-way shear and punching shear predictions. Considering the whole database and without separation by the failure mechanism, the ratio between tested and predicted resistances with the one-way shear expressions shows an average value of 1.22 and a coefficient of variation of 18.3%. The respective ratio between tested and predicted resistances with the punching shear expressions reached an average ratio of 1.23 with a coefficient of variation of 21.3%. Therefore, the proposed recommendations allow for reaching enhanced levels of precision in assessing the shear and punching shear capacity of one-way slabs under concentrated loads, regardless of the governing failure mechanism of the slabs.

Resolving old problems with layered polytungstates related to hexagonal tungsten bronze: phase formation, structures, crystal chemistry and some properties.

A 60-year-old problem with the atomic arrangements and exact compositions of alkali polytungstates related to hexagonal tungsten bronze (HTB) was solved. The systems A2WO4-WO3 (A = K, Rb) were restudied and the average monoclinic layered structures of stoichiometric polytungstates A4W11O35 (A = K, Rb, Cs, Tl) and A2W7O22 (A = K, Rb, Cs) were first successfully determined. The structures resemble those of "MoW11O36" and "MoW14O45" (J. Graham and A. D. Wadsley, Acta Crystallogr., 1961, 14, 379-383) and are derived from HTB by breaking into slabs parallel to (100) due to the ordered omission of some [WO]∞ chains along the hexagonal tunnels. The slabs in A4W11O35 (A = Cs, Tl) and A2W7O22 (A = Rb, Cs) are mutually shifted by the a/2 HTB unit cell axis. These data mainly confirmed our preliminary structural models of HTB-like alkali polytungstates (S. F. Solodovnikov, N. V. Ivannikova, Z. A. Solodovnikova and E. S. Zolotova, Inorg. Mater., 1998, 34, 845-853) and revealed a new similar thallium polytungstate. The structures of the HTB-like polytungstates and related compounds form a homologous series of layered complex oxides or fluorides An+2-xM3n+2X9n+8 where n = 2, 3 and 4 are equal to the numbers of HTB hexagonal tunnels across the polytungstate slab width for Tl2W4O13, A4W11O35 and A2W7O22 (A = K, Rb, Cs or Tl), respectively. The structures of the HTB-like polytungstates seem to intergrow with HTB-type AxWO3 to form, in particular, higher homologues of the series. Our group-supergroup analysis, measurements of nonlinear optical activity and electrical conductivity, and calculations of the bond-valence site energy barriers indicate possible ferroelectric/ferroelastic properties and moderate 2D oxide-ion mobility within the HTB-type slabs of the studied polytungstates.

Numerical and theoretical research on flexural behaviour of steel-precast UHPC composite beams

In order to promote the utilization of high strength materials and application of prefabricated structures, flexural behaviour of section steel-precast UHPC (Ultra-High performance concrete) slab composite beams prefabricated with bolt shear connectors are numerically simulated by the finite element (FE) software ABAQUS. The model is verified by three prefabricated steel-concrete composite beams tested. Numerical analysis results are in good accordance with experimental results. Furthermore, parametric studies are conducted to investigate the effects of strength of section steel and concrete of precast slab, thickness of section steel, width and height of precast concrete slab, diameters of steel bars and bolt shear connectors. The flexural behaviour of composite beams, in terms of bearing capacity, deflection, ductility and energy dissipation, are compared. The numerical results indicate that the improvement of strength of section steel results in a decrease of ductility, but a significant increase of the ultimate load and energy dissipation. Compared with composite beam made of section steel with thickness of 10 mm, the ultimate load of beams made of section steel with thickness of 14 and 18 mm improve by 29.0% and 58.8%, respectively, the ductility enhance by 2.8% and 8.3%, respectively, and the energy dissipation improve by 8.0% and 12.3%, respectively. With the increase of concrete strength, the ultimate load, deflection and energy dissipation gradually increase. The ductility of steel-UHPC composite beam is the highest, that of steel-HSC composite beam is the lowest. The effect of reinforcement ratio of concrete slab and diameter of shear bolts on the ultimate load of composite beam is limited. Simplified formulae for two different sectional types of proper-reinforced section steel-precast UHPC slab composite beams occurred bending failure are proposed, and the predicted results fit well with the simulated results. The results can be taken as a reference for the design and construction of section steel-precast UHPC slab composite beams.

An Intelligent Logic-Based Mold Breakout Prediction System Algorithm for the Continuous Casting Process of Steel: A Novel Study.

Mold breakout is one of the significant problems in a continuous casting machine (caster). It represents one of the key areas within the steel production facilities of a steel plant. A breakout event on a caster will always cause safety hazards, high repair costs, loss of production, and shutdown of the caster for a short while. In this paper, a logic-judgment-based mold breakout prediction system has been developed for a continuous casting machine. This system developed new algorithms to detect the different sticker behaviors. With more algorithms running, each algorithm is more specialized in the other behaviors of stickers. This new logic-based breakout prediction system (BOPS) not only detects sticker breakouts but also detects breakouts that takes place due to variations in casting speed, mold level fluctuation, and taper/mold problems. This system also finds the exact location of the breakout in the mold and reduces the number of false alarms. The task of the system is to recognize a sticker and prevent a breakout. Moreover, the breakout prediction system uses an online thermal map of the mold for process visualization and assisting breakout prediction. This is done by alerting the operating staff or automatically reducing the cast speed according to the location of alarmed thermocouples, the type of steel, the tundish temperature, and the size of the cold slab width. By applying the proposed model in an actual steel plant, field application results show that it could timely detect all 13 breakouts with a detection ratio of 100%, and the frequency of false alarms was less than 0.056% times/heat. It has the additional advantage of not needing a lot of learning data, as most neural networks do. Thus, this new logical BOPS system should not only detect the sticker breakouts but also detect breakouts taking place due to variations in casting speed and mold level fluctuation.

Shear behavior of web-embedded steel-concrete composite beam

To optimize conventional composite beam, this paper proposes a new steel-concrete composite beam without top flange, and discusses the shear behavior of this novel web-embedded steel-concrete composite beam (WSCB). Five patterns of embedded shear connectors are proposed, including the shapes of swallow tail, gear, modified gear, circular hole, and steel bar. A shear experiment on ten specimens with the shear span ratio λ = 1.5 were conducted, considering effects of the concrete slab width ( B) and the shear connector pattern. The experiments showed two typical shear failure modes depending on the shear connector type. All five kinds of shear connectors guaranteed good integral action in the specimens. The concrete slab width B shows an obvious positive effect on the shear capacity and ductility. Furthermore, a FE model was established and verified by the experimental results to investigate the shear mechanism of WSCB. According to the experimental and numerical analysis results, a specific calculation method for the shear capacity of the WSCB is proposed, which includes the contributions from the steel web and concrete slab.

Comparing the Dynamics of Free Subduction in Cartesian and Spherical Domains

AbstractThe effects of sphericity are regularly neglected in numerical and laboratory studies that examine the factors controlling subduction dynamics. Most existing studies have been executed in a Cartesian domain, with the small number of simulations undertaken in a spherical shell incorporating plates with an oversimplified rheology, limiting their applicability. Here, we simulate free‐subduction of composite visco‐plastic plates in 3‐D Cartesian and spherical shell domains, to examine the role of sphericity in dictating the dynamics of subduction, and highlight the limitations of Cartesian models. We identify two irreconcilable differences between Cartesian and spherical models, which limit the suitability of Cartesian‐based studies: (a) the presence of sidewall boundaries in Cartesian models, which modify the flow regime; and (b) the reduction of space with depth in spherical shells, alongside the radial gravity direction, which cannot be captured in Cartesian domains. Although Cartesian models generally predict comparable subduction regimes and slab morphologies to their spherical counterparts, there are significant quantitative discrepancies. We find that simulations in Cartesian domains that exceed Earth's dimensions overestimate trench retreat. Conversely, due to boundary effects, simulations in smaller Cartesian domains overestimate the variation of trench curvature driven by plate width. Importantly, spherical models consistently predict higher sinking velocities and a reduction in slab width with depth, particularly for wider subduction systems, enhancing along‐strike slab buckling and trench curvature. Results imply that sphericity must be considered for understanding the dynamics of Earth's wider subduction systems, and is already a significant factor for slabs of width 2,400 km.

Accuracy of Seismic Response Evaluation of Two-Dimensional Analysis Model with Rigid Joints for RC Frame Buildings.

Three- or two-dimensional (2D) numerical models are used for the evaluation of the seismic performance of reinforced concrete (RC) buildings. This study examines a 2D numerical model for a specimen used in a full-scale four-story RC shaking-table test and evaluates the accuracy of the seismic response of the 2D numerical model, which is composed of a square fiber section model for the columns, a T-shape fiber section model for the beam and slab, and a rigid joint model for the beam-column joint. A parametric analysis of the effective slab width is performed to analyze its effects on the modal shape and natural period. The results suggest that the primary natural period of the considered model is almost identical to that associated with the experimental results. The applicability of the 2D numerical model for estimating the seismic response of the structure is established. By comparing the results of the seismic analysis and the experiment in the 50% amplitude of the JMA-Kobe wave, which corresponds to slightly exceeding VII on the modified Mercalli intensity scale, the root-mean-square percentage error of the 2D numerical model is 1.03% for the floor acceleration and 4.7% for the inter-story drift. Thus, the analytical model used in this study has sufficient accuracy in evaluating the seismic performance of buildings constructed in regions with a maximum seismic intensity of VII.

Predicting Crack Width in CFRP-Strengthened RC One-Way Slabs Using Hybrid Grey Wolf Optimizer Neural Network Model

This study deploys a hybrid Grey Wolf Optimizer Neural Network Model for predicting the crack width in reinforced concrete slabs strengthened with carbon fiber-reinforced polymers (CFRP). Reinforced concrete (RC) one-way slabs (1800 × 400 × 120 mm in size) were strengthened with CFRP with various lengths (1800, 1100, and 700 mm) and subjected to four-point bending. The experimental results were compared to corresponding values for conventional RC slabs. The observed crack width results were recorded, and subsequently examined against the expression recommended by Eurocode 2. To estimate the crack width of CFRP-reinforced slabs, ANN combined with the Grey Wolf Optimizer algorithm was employed whereby the applied load, CFRP width/length, X/Y crack positions, and stress in steel reinforcement and concrete were defined as the input parameters. Experimental results showed that the larger the length and width of the carbon fiber, the smaller the maximum crack width in the tensile area of the slab at the final load step. On average, the crack width in slabs retrofitted with CFRP laminates increased by around 80% compared to a slab without CFRP. The results confirm that the equation provided by Eurocode 2 provides an unconservative estimation of crack widths for RC slabs strengthened with CFRP laminates. On the other hand, the results also confirm that the proposed informational model could be used as a reliable tool for estimating the crack width in RC slabs. The findings provide valuable insight into the design approaches for RC slabs and rehabilitation strategies for existing deficient RC slabs using CFRP.

Assessing Premature Cracks in Urban Concrete Pavements

There are many urban jointed plain concrete pavements (JPCPs) constructed annually in the U.S. by counties, cities, and municipalities, which typically use state department of transportation standards but are not part of a systematic check to determine if design, construction, and performance are meeting expectations. A field evaluation survey with nondestructive testing was initiated on urban JPCPs throughout Illinois to assess performance and identify any deficiencies in design and construction. A total of 67 JPCPs were selected based on their design features and age. A significant number of sections (57%) were selected because they exhibited some level of premature cracking. Based on the field investigation, multiple mechanisms were proposed to explain the premature cracks. Many transverse and longitudinal cracks observed had excessive slab lengths or widths that were inconsistent with best slab geometry practices. There was no link established between observed cracking and the slab-base frictional restraint or the concrete mixture. For some sections, ultrasonic tests over the contraction joints determined certain joints had not activated and likely contributed to transverse cracks in adjacent slabs. Lack of dowel bar lubrication at the transverse contraction joints was also a plausible mechanism that restrained joint movements and produced excessive tensile stresses in the slab, which led to premature transverse cracks. The mechanisms leading to almost all observed premature cracks for these urban JPCPs were attributed to not adhering to existing state standards (slab geometry limits) and specifications (saw-cut timing/depth and dowel lubrication) during the pavement design and construction phases.

How Slab Age and Width Combine to Dictate the Dynamics and Evolution of Subduction Systems: A 3‐D Spherical Study

AbstractMany of the factors expected to control the dynamics and evolution of Earth's subduction zones are under‐explored in an Earth‐like spherical geometry. Here, we simulate multi‐material free‐subduction of a complex rheology slab in a 3‐D spherical shell domain, to investigate the effect of plate age (simulated by covarying plate thickness and density) and width on the evolution of subduction systems. We find that the first‐order predictions of our spherical cases are generally consistent with existing Cartesian studies: (a) as subducting plate age increases, slabs retreat more and subduct at a shallower dip angle, due to increased bending resistance and sinking rates; and (b) wider slabs can develop along‐strike variations in trench curvature due to toroidal flow at slab edges, trending toward a “W”‐shaped trench with increasing slab width. We find, however, that these along‐strike variations are restricted to older, stronger, retreating slabs: Younger slabs that drive minimal trench motion remain relatively straight along the length of the subduction zone. We summarize our results into a regime diagram, which highlights how slab age modulates the effect of slab width, and present examples of the evolutionary history of subduction zones that are consistent with our model predictions.

Prediction of Residential Slab Foundation Movement Through a Finite Element-Based Deep Learning Algorithm

Deep learning networks were employed to predict the maximum differential deflection of stiffened and waffle rafts due to reactive soil movements, Δmax. Four deep learning networks were used to predict Δmax, these are (1) stiffened rafts on shrinking soil, (2) stiffened rafts on swelling soil, (3) waffle rafts on shrinking soil, and (4) waffle rafts on swelling soil. The deep learning models were used to create design lines, which showed that both soil and structural features strongly influence the stiffened rafts. In contrast, waffle rafts showed a strong dependence on soil features in shrinking soils and beam depth in swelling soils. This demonstrates that the finite element-based deep learning networks captured the effect of the embedment of the beams. The results of the deep learning models led to non-linear design curves, which are disparate from the suggested standard Australian design. These results suggest that increasing the value of beam depth can have a positive or negative impact on the global residential slab depending on the type of substructure and whether the founding reactive soil is shrinking or swelling. Global sensitivity analyses of the deep learning models showed that for stiffened rafts on shrinking soil, the slab length, slab width and active depth zone of reactive soil had the most significant influence on Δmax, whilst for stiffened rafts on swelling soil, the primary drivers are ground movement, beam depth, and slab width. The prediction of Δmax for waffle rafts on shrinking soil was driven by the surface characteristic and mound movements, and the active depth zone, whilst waffle rafts on swelling soil was driven by the beam depth. Overall, the finite element-based deep learning showed the capacity to estimate Δmax in both shrinking and swelling design scenarios for different types of residential footing systems to further understand the characteristic behaviour of shallow residential slab foundations on reactive soils leading to improved designs.

Research on the Influence of Process Parameters on the Flow Field in Mold

The mold is one of the core components of steelmaking, and its flow field distribution will directly affect the quality of the casting slab. A three-dimensional nozzle model is built in this work, and fluid simulation is carried out to investigate the influence of the casting speed, immersion depth, slab thickness, and width on flow behavior in the mold. This model combined simulation with real conditions. The casting speed, immersion depth, slab width, and slab thickness are the actual process parameters used in the steel factory. The results show that when the casting speed increases from 0.6 to 1.0 m/min, the strike positions of the narrow surface are 0.439, 0.476, and 0.480 m below the liquid level, respectively. When the immersion depth increases from 180 to 220 mm, the impact depth of the stream at the exit of the nozzle side hole moves down, the lower recirculation zone moves to the centre and bottom of the slab, and the upper recirculation zone moves downward. When the slab thickness increases, the strike locations of the narrow face move down. Further, when the slab width increases, the distance of the strike location from the strike position increases first and then decreases. From the fluid results, the process parameters can be optimized by considering the strike location and the change of the surface turbulent kinetic energy. The model proposed in this work provides a theoretical guidance and optimization for the nozzle.