Continuous Slab Research Articles

Failure analysis of collapsed parking garage building due to punching

The article deals with failure analysis of collapsed parking garage building due to punching shear failure of the roof slab. Overloading of the roof slab-column connections led to the progressive collapse of the five-story building. The reason of the failure is known however, answer how the structure could withstand such a high level of overloading for 8 months when the ratio of design values of shear force vs. punching capacity βVEd/VRd reached a value of 3.9 provides the article. The design equations for prediction punching capacity, e.g. the EC2 or ACI 318–19 model, are empirical models calibrated using results of the tests carried out on isolated slab specimens. Therefore, they do not allow take into account the favourable effect of membrane forces and redistribution of bending moments in continuous flat slabs. Application of the Critical Shear Crack Theory (CSCT) in combination with non-linear finite element analysis has shown actual punching shear capacity of the system.

Determination of the interfacial properties of longitudinal continuous slab track via a field test and ANN-based approaches

Due to the common existence of interlayer debonding and separation of longitudinal continuous slab track (LCST), accurately estimating the interfacial normal cohesive parameters between the concrete track slab and the cement emulsified asphalt (CA) mortar layer is an important task. This study first carried out a full-scale vertical pull test (VPT) to study the interfacial normal bond capacity of LCST. As a result, a series of load–displacement curves were measured. Then, an artificial neural network (ANN)-based approach was developed to map the relationship between the structural response and the interfacial properties under a machine learning (ML) framework. In addition, a refined macroscale finite element (FE) model that employed the exponential cohesive zone model (CZM) was established to simulate the interfacial debonding process. Two datasets of the global load–displacement and the local stress-slip responses obtained from the FE analysis were separately used to train and verify the ANN. Our results showed that the predictions given by the ANNs and the ground truth values were in close agreement. Furthermore, by feeding the well-trained ANN with the experimental load–displacement curves of the VPT, the realistic interfacial normal cohesive parameters of LCST were identified. Afterward, a comparative analysis of the experimental results and the recovered results according to the identified parameters was carried out. The results showed that the proposed parameter determination method is accurate and reliable. The developed hybrid approach that combines experimental and FE analysis with ML methods can be a promising alternative for identifying material properties in structural engineering.

Experimental and numerical study of continuous span concrete composite slabs

Vertical static loading tests were carried out on two kinds of continuous span concrete composite slabs with beam and slab connected by studs and open-hole folding plate connectors. Combined with the test results, on the basis of the analysis of load–deflection curves and load-reinforcement strain curves, the finite element software ABAQUS was used for the numerical study of the continuous span concrete composite slabs. The plate thickness, concrete strength, thickness of the shear key and slab span has carried on the finite element analysis. The results show that the strength of the concrete and the thickness of the shear bond have little effect on the flexural performance of the continuous span concrete composite slab, but the shear bond can strengthen the connection between the slab and the steel beam and reduce the sliding and lifting of the composite slab on the steel beam. The slab thickness and slab span have a great influence on the flexural performance of continuous span concrete composite slabs. The peak load of the specimen increases with the increase of slab thickness and decreases with the increase of slab span. This study will provide a theoretical basis for future design and engineering application of composite slabs.

Effect of Membrane Forces on Punching Shear Capacity of Flat Slabs

The paper presents the analysis of the membrane forces and moment redistribution effect on punching shear capacity of flat slabs on the area of the inner column. The previous experimental tests performed on the isolated slab specimens representing the slab-column connections are assessed by the method that uses the levels-of-approximation (LoA) approach, introduced in the fib Model Code 2010. LoA I to III are intended for design and the highest LoA IV, which uses non-linear finite element analysis (NLFEA) combined with the Critical Shear Crack Theory (CSCT) model is used for assessment and a better understanding of the punching shear phenomenon. Both, multi-layered (2D) shell and three-dimensional (3D) continuum elements were used to model the slab-column connection specimen and were found to accurately predict the structural response. The numerical model was then used to conduct a parametric study on the influence of slab continuity on punching shear resistance. The results from a non-linear analysis of continuous slab models are then compared with the punching shear resistance obtained from the code provisions. The paper will present the obtained results by the LoA method and recommendations concerning of NLFEA modelling of RC flat slabs.

Behaviour of prefabricated steel-concrete composite slabs with a novel interlocking system–Numerical analysis

Steel-concrete composite structures have been widely used in the on-site constructions due to the benefit of composite actions provided by the steel and concrete. However, prefabricated steel–concrete composite constructions for building structures are not very popular in practice due to insufficient research studies and the lack of information on the connection systems, especially for the connection of prefabricated composite slabs. Prefabricated slabs are usually designed and constructed as simply supported and discontinuous elements. However, on-site composite slabs are continuous and connected to steel beams using shear connectors. Hence, the capacity of the composite slab constructed on-site is higher than that of conventional prefabricated slabs. Therefore, there is a significant need to develop a prefabricated continuous composite slab system to utilise the full benefit of the composite action. This study proposes interlocking connection systems for prefabricated steel–concrete composite slabs. The proposed prefabricated composite slabs with an interlocking system are analysed using finite element (FE) modelling and compared the results with the conventional slabs such as simply supported non-composite slabs, non-composite continuous slab and composite continuous slab. The ultimate load capacity of the proposed prefabricated composite slabs with the interlocking connection system has been found to be 40% higher than that of simply supported non-composite slabs and 10% lower than that of the continuous composite slab.

Wheel Flats in the Dynamic Behavior of Ballasted and Slab Railway Tracks

Wheel flats induce high-impact loads with relevance for the safety of the vehicle in operation as they can contribute to broken axles, hot axle boxes, and damaged rolling bearings and wheels. The high loads also induce damage in the track components such as rails and sleepers. Although this subject has been studied numerically and experimentally over the last few years, the wheel flat problem has focused on ballasted tracks, and there is a need to understand the phenomena also for slab tracks. In this research, a numerical approach was used to show the effects of the wheel flats with different geometric configurations on the dynamic behavior of a classical ballasted track and a continuous slab track. Several wheel flat geometries and different vehicle speeds were considered. The nonlinear Hertzian contact model was used because of the high dynamic variation of the interaction of the load between the vehicle and the rail. The results evidenced that, for the same traffic conditions, the dynamic force was higher on the slab track than on the ballasted one, contrary to the maximum vertical displacement, which was higher on the ballasted track due to the track differences regarding the stiffness and frequency response. The results are useful for railway managers who wish to monitor track deterioration under the regulatory limits.

Effect of different strengthening techniques on the behavior of one-way continuous slab with insufficient length of development

The purpose of this paper is to investigate the effect of the different strengthening techniques on the behavior of continuous one-way slab with insufficient length of development of rebars at the internal joint. The insufficient length of development of rebars in the zone of negative steel reinforcement leads to a reduction in force which has dangerous consequences that affect the structure and its serviceability. This study proposed three strengthening techniques to compensate the insufficient development length which including: internal strengthening by confining the lap zone by spiral bar, externally strengthened by CFRP sheet and steel plates. Six one-way concrete slabs with dimensions of 2200 mm length, 500 mm width, and 125 mm thickness were casted and tested under static load. The main variables adopted in this study are: the length of development, type of strengthening, and presence of construction joint. All slabs were loaded to failure. Form results, it’s found that the presence of construction joint and insufficient length of development of rebars at internal support of the continuous one-way slab had a tangible influence on the structural behavior, also, the insufficient length of development resulted in a deterioration of the structure, decrease in stiffness, and change in the mode failure. It was observed that the strengthening techniques used in this study able to compensate the reduction in stiffness and enhancing mode of failure. All the proposed strengthening techniques was efficient especially steel plates which gave a high increasing in ultimate load by about 16.14 % and by about 8.7-3.73% for the other.

Impact sound pressure values - Field measurements for different configurations of concrete slabs on the ground

The presentation will summarize and discuss values of field measured normalized impact sound pressure level L'n,w measured sideways with different configurations of concrete slabs on ground within buildings. All results are adjusted to receiving room volume of 100 m3 and with thickness of concrete slab 80-100 mm. Measurement on continuous concrete slab on expanded polystyrene gives L'n,w between adjoining rooms of 74 dB. Different principles of splitting have been investigated to evaluate the effect on L'n,w. The configuration where only the concrete slab is split (and with a plastic film between the concrete base and the upper layer of expanded polystyrene), gives L'n,w of approximately 66 dB which is 8 dB lower than for a continuous bare concrete slab. When both the concrete slab and the upper layer of expanded polystyrene are split, measurements show L'n,w of 58-61 dB for the case of no flooring, which is 13-16 dB lower than for a continuous concrete slab (no split). When both concrete slab and all layers of polystyrene are split down to continuous foundation measurements show L'n,w of 55 dB. The situation with concrete slab and all layers of polystyrene split and with no foundation beneath gives L'n,w of 46 dB. Consequences for airborne sound and R'w will be discussed as well for the above mentioned configurations.

Longitudinal Crack Detection Approach Based on Principal Component Analysis and Support Vector Machine for Slab Continuous Casting

Longitudinal cracks are the typical surface defects of continuous casting slabs, resulting in additional processing or even casting interruption. Monitoring longitudinal crack defects is of great significance in stabilizing and improving the slab quality. Herein, a monitoring model is developed to recognize the longitudinal crack defect of continuous casting slabs using principal component analysis (PCA) and support vector machine (SVM). First, the typical characteristics of the temperature patterns corresponding to the longitudinal crack defect are extracted, including the normal casting temperature with small and large fluctuations, as well as the longitudinal crack temperature. Then, PCA is used to reduce the dimension of these characteristics for removing the redundancy and reducing the computational burden. Subsequently, an SVM is applied to identify normal and longitudinal crack temperature patterns for training the monitoring model PCA–SVM. The monitoring performance is verified by the test data, in which the training accuracy and test accuracy are 100% and 96%, respectively. It is worth mentioning that the model can successfully predict all the real longitudinal crack defects, showing excellent detection performance. The established model is expected to provide a theoretical basis and a reliable way for online monitoring of slab surface cracks.

Generation of Reverse Meniscus Flow by Applying An Electromagnetic Brake

A numerical study is presented that deals with the flow in the mold of a continuous slab caster under the influence of a DC magnetic field (electromagnetic brakes (EMBrs)). The arrangement and geometry investigated here is based on a series of previous experimental studies carried out at the mini-LIMMCAST facility at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The magnetic field models a ruler-type EMBr and is installed in the region of the ports of the submerged entry nozzle (SEN). The current article considers magnet field strengths up to 441 mT, corresponding to a Hartmann number of about 600, and takes the electrical conductivity of the solidified shell into account. The numerical model of the turbulent flow under the applied magnetic field is implemented using the open-source CFD package OpenFOAM®. Our numerical results reveal that a growing magnitude of the applied magnetic field may cause a reversal of the flow direction at the meniscus surface, which is related the formation of a “multiroll” flow pattern in the mold. This phenomenon can be explained as a classical magnetohydrodynamics (MHD) effect: (1) the closure of the induced electric current results not primarily in a braking Lorentz force inside the jet but in an acceleration in regions of previously weak velocities, which initiates the formation of an opposite vortex (OV) close to the mean jet; (2) this vortex develops in size at the expense of the main vortex until it reaches the meniscus surface, where it becomes clearly visible. We also show that an acceleration of the meniscus flow must be expected when the applied magnetic field is smaller than a critical value. This acceleration is due to the transfer of kinetic energy from smaller turbulent structures into the mean flow. A further increase in the EMBr intensity leads to the expected damping of the mean flow and, consequently, to a reduction in the size of the upper roll. These investigations show that the Lorentz force cannot be reduced to a simple damping effect; depending on the field strength, its action is found to be topologically complex.

RETRACTED: Behaviour of RC flat slabs with openings strengthened with CFRP

Nine half-scale reinforced concrete continuous slabs with and without openings have been tested up to failure. The main objectives of this paper is to investigate the effect of the openings on the behavior of the flat slabs and study the effect of using Carbon Fiber Reinforced Polymer (CFRP) as a strengthening method to restore the load capacity of flat slabs after the introduction of the openings. The limit of the opening size according to two different international codes such as American Concrete Institute ACI 318-19 and Egyptian Code ECP 203-2007 have been examined. The Finite Element Method (FEM) is utilized via the software ANSYS12 to extend this study and the finite element results were compared with those experimentally obtained. The results show that strengthening flat slabs with openings by using CFRP could not restore behaviour to the slab without openings. The use of CFRP improves the ductility of the slab with openings by about 28 %. The opening located just at the column face makes the strains in the steel reinforcement larger; especially with the low deflections for this slab this ensures that this location is not preferable without strengthening. Although the ACI 318-19, limits the opening size to one-eighth of the column strip it has been noted that an opening size of one-fourth the width of the column strip is still safe in some cases. The numerical results obtained from the computer program ANSYS12 showed that, this software can be used successfully to simulate the behaviour of slabs with openings strengthened with CFRP.

Feeding Steel Strip Technology in Continuous Casting Process: A Review

Feeding strip into continuous casting mold is a technique that can reduce the central segregation and increase the equiaxed zone ratio of continuous casting slab. Over the past decades, some steel mills have gradually applied this technique, but it still lacks a comprehensive understanding of the control theory of process parameters. Many parameters joint the influence of the steel strip melting process and strip feeding ratio, deciding the inner quality of the slab eventually. Herein, the mechanism and heat transfer of feeding strip technology are analyzed. Parameter sensitivity studies and feeding strip experiments are summarized and some new conclusions are proposed. Finally, some suggestions for industrial production will give an outlook for future work.

Irreversible loss of hot ductility following simulated primary cooling of a C–Mn steel to temperatures above the ferrite transformation temperature

A hot ductility study has been performed on a low carbon peritectic steel grade with the view to simulate the effect of a temperature drop in the region just below the mould on the reduction of area during simulated unbending of a continuous cast thick broad slab. A Gleeble 1500D thermomechanical simulator was used to subject cylindrical specimens to various thermal histories, which included a fast primary cooling cycle to various minimum temperatures, Tmin, followed by a temperature rebound cycle and a slow secondary cooling step up to the unbending temperature prior to straining at a constant strain rate. Poor ductility was found when primary cooling was terminated at 70 °C above the ferrite start transformation temperature for primary cooling. This loss of ductility was not recovered during the rebound heating or secondary cooling steps. Dilatometry was performed to investigate this observation and it was shown that a small amount of ferrite formed at low temperatures, during the rebound heating. The deterioration in ductility was determined to be due to the formation of these thin ferrite films on the prior austenite grain boundaries. Dilatometry was used to show that the ferrite films later transformed back to austenite and the irreversible loss of the hot ductility was attributed to finely dispersed second phase particles remaining in position where the ferrite films had initially formed on the austenite grain boundaries.

Experimental and numerical studies of six small-scale continuous concrete slabs subjected to travelling fires

This paper presents the experimental results of six small-scale continuous reinforced concrete slabs with three compartments subjected to various compartment fire scenarios. The study investigates the influence of several key factors, including concrete age, thickness (span-thickness ratio), applied loads, and fire scenarios, on the fire behaviour of the continuous slabs. A nonlinear finite element program, Vulcan, was used to predict the fire behaviour of three tested slabs where spalling did not appear. The results indicated that increasing the slab thickness is one of the most effective methods for enhancing the fire resistance performance of continuous slabs subjected to any fire scenario. As the span-thickness ratio increased, the applied load had an increasingly significant effect on the deflection trend and maximum deflection of each span in the continuous slab. The conventional temperature failure criteria should be modified to consider the detrimental effects of fire-spreading scenarios, particularly the effects of a time delay and the direction of fire spreading. The numerical results revealed that, for any fire scenario, larger thermal straining leads to a larger mid-span deflection in continuous slabs subjected to various travelling fires.

Effect of Different Strengthening Techniques on the Structural Behaviour of Continuous Two-Way Slabs with Partially Corroded Reinforcement at Internal Support

This research studies the combined effects of partial corrosion of the negative reinforcement in two-way continuous slabs (two spans) with a construction joint at the internal support and investigates the efficiency of the proposed strengthening methods to overcome these effects. The partial corrosion in reinforcement comes from exposure to the corrosive outdoor environment due to an unplanned stoppage in concrete pouring for a long-time which left part of the negative reinforcement without protection. The construction joint formed at the internal support after resume the concrete pouring later. Three types of strengthening are proposed to overcome those effects. The study adopted an accelerated corrosion technique which is running an electrical current in the steel bars partially immersed in a 5% salt solution (elect-chemical cell). The proposed strengthening was: NSM CFRP bars, CFRP strips, and steel plates. All applied to the top face in the tension zone at the internal support. Six two-way continuous (two spans) concrete slabs were cast (2200, 1000, and 100 mm). The strengthening was: four strips of CFRP had 50 mm width, four of 6 mm CFRP bars applied using the NSM technique, and four steel plate 50 mm width and 5 mm thickness. All the strengthening extended to the third of span length and was aligned with the slab continuity axis. The specimens were tested and the deflection, first positive and negative crack width, and failure mode were recorded. Numerical analysis and comparison with the experimental results were conducted to verify the numerical model. The study found that the construction joint and corrosion had a clear influence on the structural behavior of the slab. Those effects were on the ultimate load, deflection, and the negative cracks. The proposed treatments were highly effective and efficient in increasing the ultimate load, delay the appearance of cracks, and reduction of deflection under the load points.

The Deep Structure of the Alps Based on the CIFALPS Seismic Experiment: A Synthesis

AbstractThe European Alps are the site where classic geologic concepts such as nappe theory, continental subduction and slab breakoff have been first proposed. However, the deep tectonic structure of the Alps has long been poorly constrained by independent geophysical evidence. This review paper summarizes the main results of the CIFALPS passive seismic experiment, that was launched by Chinese, French and Italian scientists in the 2010s to provide new insights on the deep tectonic structure of the Alpine region. The application of a wide range of tomographic methods to the analysis of a single fossil subduction zone makes the CIFALPS experiment a potential reference case for the analysis of other orogenic belts. Major results include: (i) the first seismic evidence of European continental crust subducted into the Adriatic upper mantle, beneath the place where coesite was first recognized in continental (U)HP rocks in the Alps; (ii) evidence of a major involvement of the mantle wedge during (U)HP rock exhumation; (iii) evidence of a serpentinized plate interface favoring continental subduction; (iv) evidence of a continuous slab beneath the Western and Central Alps, ruling out the classic model of slab breakoff magmatism; (v) evidence of a polyphase development of anisotropic fabrics in the Alpine mantle, either representing active mantle flows or fossil fabrics inherited from previous rifting stages. Detection of these major tectonic features allows to propose interpretive geologic cross‐sections at the scale of the lithosphere and upper mantle, providing a baseline for future analyses of active continental margins.

Numerical analysis of one-way continuous slab with partial corrosion strengthened with deferent material

This paper investigates numerically the combined effects of a construction joint and reduction in the cross-section area of negative reinforcement in one-way continuous slab on the structural behavior and the efficiency of three types of strengthens techniques. In this paper, the modles were greated by ABAQUS (software) is used to numericaly represent the specimens and simulate the applied loading. This numerical study's models represent six one-way continuous slabs, as a part of a expermentail study. The specimen's dimensions were (2200 mm in length, 500 mm width ,and 100 mm thickness). Five of the six models had a vertical construction joint and reduced the negative reinforcement steel bars' cross-sectional area. The sixth specimen used as refreance. The proposed strengthening technique were: Carbon fiber Reinforced Polymers strips, 6 mm Carbon fiber Reinforced Polymers bars Near Surface Moutain technique and steel plates. All the proposed strengthening's applied to the tension side on the top face at the internal support. The program outcomes are represented visually as stresses distribution diagrams,load-deflection curves, and cracks pattern. The results from the numerical analysis compared to the experiment results. In the experiment, the reduction in the cross-section area resulting from partial corrosion happened in one span due to the outdoor atmosphere's exposure because of the stoppage in the concrete pouring, which also resulted in forming the construction joint. The results highlighted the construction joint's effect and the steel cross-sectional area reduction on the ultimate load and the deflection. The proposed strengthening methods improved the member's overall responses, and There was a good convergence between the numerical and experimental works that verify the specimens' observed behavior.

Effect of electropulsing on austenite to ferrite transformation in low-carbon steel

We explore the application of electropulsing for the control of phase transformation in a low-carbon steel. The effect of electropulsing on the transformation from austenite to ferrite in continuous casting low-carbon steel slab has been studied through experimental and thermodynamic investigations. The results reveal that electropulsing promotes the precipitation of ferrite within austenite grain in the low-carbon steel. When the electropulsing intensity increases, the precipitation of ferrite increases within austenite grains, and ferrite omentum precipitates become thinner along the austenite grain boundary. The results provide a basis for controlling the austenite to ferrite transformation in low-carbon steel.

Experimental study on evolution of oxidation behavior on high-temperature continuous casting slab surface

The oxidation kinetics, oxide layers composition and thicknesses of X70 steel, Y55 steel and 304 stainless steel are investigated. The results show that the oxidation rate of X70 steel increases rapidly at 1000 °C, while that of Y55 steel and 304 stainless steel increases rapidly at 1100 °C. The oxidation kinetic coefficients of X70 steel, Y55 steel and 304 stainless steel are exp (10.7), exp (11.58) and exp (30.15), respectively, and the apparent activation energy of oxide layer are 196879.7 J/mol, 207608.1 J/mol and 469284.3 J/mol, respectively. The cross-sectional morphology and element distribution of oxide layer are obtained. With the oxidation time increases from 30min to 80 min at 1100 °C, the oxide layer thickness of X70 steel and Y55 steel increases by 1242.33 μm and 965.59 μm respectively when the weight of steels increases by 1 mg/mm2, and the oxide layer of Y55 steel is denser than that of X70 steel. A variable temperature oxidation mathematical model of the slab surface is established to predict the oxide layer thickness of slab surface.

Formation and Control of Transverse Corner Cracks in the Continuous Casting Slab of a Microalloyed Steel

To investigate transverse corner cracks for a microalloyed steel continuous casting slab, the metallography, microtopography, and three‐dimensional (3D) morphology of cracks are studied, respectively. High‐temperature mechanical properties are investigated and compared from two positions where samples are extracted from both the slab corner and surface of the slab center. The thermal history of the slab is simulated and optimized experiments are conducted. Transverse corner cracks are generated on the valley of oscillation marks. Mold powder and wear elements of the mold are not detected. Microstructures are refined near the cracks. Cracks are generated in secondary cooling zones and the cracking temperature is higher than Ar3 temperature. The extension path of cracks is not linear and cracks extend along the grain boundary. The third brittle temperature ranges (TBTR) are 764–832 °C and 793–808 °C in the two positions, respectively. The temperature at the slab corner in the bending and straightening zone falls into the brittle zone during the original water cooling condition, leading to the formation of cracks. The secondary cooling scheme is optimized to prevent the temperature at the slab corner in the bending and straightening zone from entering the TBTR, significantly reducing the occurrence of transverse corner cracks.