Steel Fiber Reinforced Concrete Slabs Research Articles

Low-velocity impact behavior of two-way SFRC slabs strengthened with steel plate

Structural systems and structural elements can often suffer severe damage or even completely collapse under the effect of sudden dynamic impact loading, which is a different type of loading that is not considered during their design. Research on how structures behave under impact loading and how they can be strengthened to perform better against this type of loading has increased to avoid such undesirable severe damage. Within the scope of this study, it is aimed to improve the behavior and increase the performance of two-way steel fiber-reinforced concrete (SFRC) slabs, one of the leading structural elements that can be affected by impact loading, using steel fiber concrete (SFC) and placing steel plates on the surface of the RC slab. Within the scope of the study, the effects of placing FRC as layers in different positions within the slab and placing the steel plate on different surfaces of the slabs were examined. Impact loading was applied using a drop weight test setup designed by the authors, and the acceleration–time, displacement–time, and impact loading–time behaviors of the RC slabs were measured and interpreted. The use of fiber concrete in RC slabs and strengthened with steel plates increased the maximum acceleration values by an average of 3% and 113%, respectively. The use of fiber concrete in RC slabs reduced the maximum displacement and residual displacement values by an average of 2% and 25%, respectively. Placing steel plates on the slabs reduced the maximum displacement and residual displacement values by an average of 270% and 199%, respectively. In addition, the energy absorption capacities of RC slabs were calculated, and how they were affected by experimental variables was examined. Numerical analyses of the RC slabs tested in the study were also conducted using ABAQUS finite element software, and the results obtained were compared with the experimental ones.

Accurate Prediction of Punching Shear Strength of Steel Fiber-Reinforced Concrete Slabs: A Machine Learning Approach with Data Augmentation and Explainability

Reinforced concrete slabs are widely used in building structures due to their economic, durable, and aesthetic advantages. The determination of their ultimate strength often hinges on punching shear strength. Presently, methods such as closed hoops, steel bending, and fiber reinforcement are employed to enhance punching shear strength, with fiber reinforcement gaining popularity due to its ease of implementation and efficacy in improving concrete durability. This study introduces a novel approach employing six machine learning algorithms rooted in decision trees and decision tree-based ensemble learning to predict punching shear strength in steel fiber-reinforced concrete slabs. To overcome experimental data limitations, a data augmentation approach based on the Gaussian mixture model is employed. The validation of the data augmentation is conducted through “synthetic training—real testing” and “real training—real testing”. Additionally, the best machine learning model is analyzed for explainability using Shapley Additive exPlanation (SHAP). Results demonstrate that the proposed data augmentation method effectively captures the original data distribution, enhancing the robustness and accuracy of the machine learning model. Moreover, SHAP provides better insights into the features influencing punching shear strength. Thus, the proposed data enhancement model offers a reliable approach for modeling small experimental datasets in structural engineering.

Design and economic implications of using steel fibers in elevated slabs of multi‐story buildings

AbstractThis paper presents a comprehensive comparison between conventional reinforced concrete (RC) and steel fiber‐reinforced concrete (SFRC) slabs. Twenty‐two‐way rectangular RC and SFRC slabs are designed with varying dimensions, aspect ratios, and boundary conditions, following verified international standards to compare the steel quantities in a unique study. SFRC slabs with larger aspect ratios and discontinuous edges required significantly higher steel percentages than square slabs, as the random three‐dimensional distribution of steel fibers suited the load distribution pattern of square slabs. To further conduct a detailed design and economic feasibility case study on a realistic building model, two 12‐story buildings are computationally designed with RC and SFRC alternatives. The results indicate that SFRC slabs required approximately 25% more steel than RC slabs due to the uniform distribution of steel fibers throughout the section. Project cost and time estimates were conducted based on standard productivity manuals and cost databases in two distinct economies, India and the USA. Despite the higher steel requirements, the 12‐story SFRC building showed time savings of 34.1 days (5.44%) and cost savings of 4.88% and 1.27% when constructed in the USA and India, respectively. The results are compared with limited available data in literature. In conclusion, the study suggests that SFRC slabs in multi‐story buildings could be more economically favorable in countries with higher labor costs.

Experimental and mesoscopic modeling numerical researches on steel fiber reinforced concrete slabs under contact explosion

This paper presents experimental research on the damage characteristics of steel fiber reinforced concrete slabs (SCS), steel fiber reinforced concrete slabs mixed with fly ash (CFS), and steel fiber reinforced concrete slabs mixed with fly ash and slag (CFSS) under contact explosion loads. The findings reveal that SCS and CFS exhibit crater damage on the top surface, spalling failure on the bottom surface, and certain damage cracks under the same contact explosion load. Additionally, the CFSS displays crater and spalling damage along with a through-hole at the center. Comparative analysis demonstrates that CFS offers the best explosion resistance properties. A reliable three-dimensional mesoscopic modeling using PYTHON and ABAQUS is established to analyze the dynamic response of the CFS, emphasizing its dependence on fiber volume. Furthermore, the study evaluates energy changes in the matrix and steel fiber to understand their impact on the slab's damage dimensions under contact explosion. Results indicate that the mesoscopic modeling effectively reflects structure damage and failure behavior under explosive super dynamic loads. Specifically, for CFS, with a steel fiber volume of 1.3%, the internal energy and stress generated by steel fiber are maximized, resulting in the smallest damage dimension under contact explosion and the best explosion-resistant effect. This research provides valuable insights for guiding the design of explosion-resistant structures and their deployment in concrete engineering applications.

Fibre orientation in SFRC slabs and consequences for punching shear and flexural resistance

The use of steel fibre reinforced concrete (SFRC) is a well-known method for enhancing the punching and flexural resistances of flat slabs. The structural performance of SFRC elements depends significantly on the fibre distribution and orientation, which are typically unknown. One of the largest uncertainties regarding the performance and reliability of SFRC concerns the determination of its post-cracking mechanical properties in the real structural element, normally performed via standardised tests. However, due to differences in element sizes and casting procedures, and to the presence of rebars, the fibre spatial distribution and orientation in the standard specimens differ in general from those of the structural member. Several researchers have studied the correlation between the orientation of fibres and the mechanical performance of SFRC, yet tests were rarely carried out under representative conditions of the actual behaviour of the target structural member. The present paper analyses the spatial distribution and orientation of steel fibres in six SFRC flat slabs that were previously tested in concentric punching at the University of Brescia. The aim of this work is to analyse the fibre orientation and spatial distribution in structural elements. Cores were extracted from the specimens after the punching tests and scanned using micro-computed tomography (μ-CT) to reconstruct the fibre skeleton. The fibre arrangement was analysed focusing on the variation of the fibre spatial distribution and orientation through the slab thickness. A formulation to express the actual fibre dispersion in concrete is proposed, and effectiveness factors are defined to reflect the efficacy of fibres in punching shear and flexure, based on their location in the slab thickness. Pseudo-horizontal fibre orientations are found to be governing, with closer distributions to a 2D scenario for thicker slabs and higher fibre contents. Furthermore, the influence of flexural reinforcement on the fibre orientation has been observed to be significant. The observed fibre orientations are detrimental for the direct transfer of shear forces across cracks, but are favourable for enhancing the flexural capacity of the slab.

Investigation on the influence of fiber fraction and orientation on the mechanical properties of fiber‐reinforced concrete slabs

AbstractThe current work examines an experimental and numerical investigation into how steel fiber reinforced concrete (SFRC) slab failure behavior is influenced by fiber orientation by pouring concrete in slab elements. Double‐ended hooked steel fibers with an aspect ratio of 50 were used in varying percentages by volume. Fresh and hardened properties of SFRC were determined based on slump flow, V‐funnel, L‐box, J‐ring test, compression, and flexure tests. The effects of different pouring/casting locations (center and corner), fiber orientation, and fiber content (0, 0.5%, and 1.0%) on the crack pattern of the SFRC slab were observed. While casting, the concrete was allowed to flow through a 30° chute angle to enhance the flowability of concrete. The SFRC slabs without fiber reinforcement undergo brittle failure without forming any prior micro cracks. Slabs with fibers experience ductile failure and show significant post‐cracking strength. The concrete's pouring position only affects the failure crack's inclination for the given workability. In the case of the corner cast slab, the crack was propagated from one edge to the opposite edge of the slab in a straight line and split into two halves. This crack pattern suggested that the fiber distribution was concentrated in half of the slab part in which the pouring corner was located. Adding 0.5% and 1.0% fiber content increased the load‐carrying capacity of slabs by 1.31 and 2.15 times, respectively. In addition to fiber content, the pouring position of concrete also made a difference in the load‐carrying capacity of slabs. The concrete pouring in the slab from the center position with 0.5% and 1.0% fiber content has 17.2% and 40% more load‐carrying capacity compared to the concrete poured in the slab from the corner position with the same fiber content. The deflection and load‐carrying capacity obtained through finite element modeling (FEM) fit the experimental results well.

Structural behaviour of steel fibre-reinforced concrete floor system for modular construction

Steel fibre-reinforced concrete (SFRC) slabs are ideal for modular construction owing to the shorter span of slab in standardised modules. To investigate the structural behaviours of SFRC floor system designed for modular construction, nine full-scale slab specimens were tested both at ambient temperature and under fire conditions. The crack pattern, failure mode, concrete spalling phenomenon, deformation capacity, load-carrying capacity and fire resistance time of the SFRC slabs are reported and compared with those of conventional steel rebar-reinforced concrete slabs. The experimental results showed that SFRC slabs achieved sufficient load carrying-capacity and fire resistance time for the application in modular buildings. A fibre-element model is proposed for computing the temperature distribution and cross-sectional moment resistance of SFRC slabs under fire conditions. Based on the experimental findings, design recommendations are provided to determine the fire resistance of SFRC floor system in modular construction.

Data‐driven reliability and cost‐based design optimization of steel fiber reinforced concrete suspended slabs

AbstractThe 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.

Application of steel fiber concrete in small box girder under vehicle explosion load

In recent years, the exceptional performance of steel fiber-reinforced concrete in blast and impact resistance has garnered widespread recognition, sparking considerable interest in its practical application in small box girders. To this end, nine groups of Trinitrotoluene (TNT) explosion simulation experiments were designed with the equivalent magnitudes matching those of actual automobile explosions to evaluate the anti-explosion and anti-penetration capabilities of steel fiber-reinforced concrete and ordinary concrete using the Arbitrary Lagrangian-Eulerian (ALE) method and the Smoothed Particle Hydrodynamics-ALE method. The aim was to explore the application prospects of steel fiber-reinforced concrete in small box girders. The research results demonstrate that with increasing TNT equivalent, the leading cause of breach to concrete slabs changes from spalling to cratering. The penetration resistance of steel fiber-reinforced concrete slabs is superior to its blast resistance. However, when the explosive force is larger than the sedan, the anti-explosion effect of steel fiber-reinforced concrete slabs becomes negligible. Moreover, under typical automobile explosion loads, the addition of 2% steel fibers can reduce spalling by up to 23% and cratering by up to 13% and can decrease the area of penetration damage by up to 47%. In designing blast-resistant structures, steel fiber-reinforced concrete is not recommended to enhance the blast resistance of bridges when the TNT equivalent exceeds 500 kg.

Improvement of flexural and cyclic performance of bridge deck slabs by utilizing steel fiber reinforced concrete (SFRC)

This paper aims at investigating how the utilization of steel fiber reinforced concrete (SFRC) improves the flexural and cyclic responses of reinforced concrete bridge deck slabs. Firstly, one plain concrete slab and two SFRC slabs reinforced by mill-cut steel fibers and corrugated steel fibers, respectively, were tested under cyclic loads. The load–deflection responses, cyclic deformation behaviors, strain and crack evolutions are discussed. Subsequently, a theoretical analysis method of SFRC slab is introduced and validated. Using this method, the effects of key strength parameters of SFRC, i.e. fL, fR1, fR4, on load–deflection responses and deck slab design indices (i.e. slab height, areas of steel rebars, slab span) are clarified through parametric analysis. Results demonstrate that using SFRC in deck slabs significantly enhances the cyclic deformation performance, decreases the residual strain in the slab section, and improves the crack behavior by reducing residual crack width and increasing cracking stiffness. An increase in fL and fR1 can enhance service capacity Ps and flexural stiffness ks, as well as improve design indices under the service requirement, whilst the influences of fR4 are minor. Increasing fR1 and fR4 can enhance ultimate capacity Pu and improve design indices under the ultimate requirement, whereas the effects of fL are rather limited. Since the use of mill-cut steel fibers produces higher fL and fR1 than corrugated steel fibers, the former has better advantages to enhance Ps and ks. These results may provide references for the application of SFRC in bridge deck slabs.

Characteristics of Restrained Drying Shrinkage on Arched Steel Fiber-Reinforced Concrete

The volumetric changes of concrete, including drying shrinkage, are effectively controlled in steel fiber-reinforced concrete (SFRC) mixtures due to the action of the included steel fiber. The current code provision in ANSI/SDI C-2017 allows a minimum steel fiber content of 0.2% of the volume fraction of concrete to control drying shrinkage and to manage cracking in the slab. Limited research has addressed replacing the shear reinforcement in concrete beams with steel fiber. In this study, we used newly developed arched steel fiber to evaluate shrinkage characteristics, including free-drying shrinkage and restrained drying shrinkage, of SFRC and scaled-down deck slab elements. We compared the measured drying shrinkage test results to predicted results obtained from models found in the literature. We confirmed that, overall, the number, width, and length of cracks were reduced significantly at the surface of SFRC slabs when arched steel fiber at 0.2% volume fraction was included in the mixture.

Fatigue behavior of steel fiber reinforced concrete composite girder under high cycle negative bending action

Tensile concrete crack is a critical factor in the negative flexural region of a steel–concrete composite girder, which could influence the entire structural safety and durability dramatically. The steel fiber reinforced concrete (SFRC) has been utilized for constraining these cracks because of its good tensile performance and low cost in practice. But the practical application of SFRC is still hindered by the unclear fatigue performance of SFRC composite girder. To this end, four 3.3 m-long composite girder tests were executed for investigating the static and cyclic effects of SFRC and connector arrangement. About 3 million load cycles with a monolithic ultimate loading process were applied on each specimen. Generally, the fatigue load cycles in tests resulted in about 10–30% reduction of girders’ global bending stiffness without interlay bonding, and the effect of SFRC on it was not obvious. Even though there were more fatigue load induced cracks found on SFRC slabs than on the normal concrete slabs during loading, the SFRC crack width was smaller. Moreover, the steel–concrete interlayer slip development was found to be slower in SFRC composite girders, while arranging stud connectors in groups resulted in faster slip development. In addition, the test simulation and parametric analysis with material damage plasticity models were carried out, which showed a higher longitudinal reinforcement ratio in SFRC could further reduce fatigue damage on concrete.

An improved calibration method of the K&C model for modeling steel-fiber reinforced concrete

The K&C material model, one of the widely used concrete models implemented in LS-DYNA for blast or impact analysis, is modified to improve its numerical accuracy for steel-fiber reinforced concrete (SFRC). Many input parameters are required in this model to describe the material properties of SFRC. To address this, an improved calibration method that can easily predict the stress–strain relationships of SFRC by modifying the three strength surfaces and the damage function η(λ) based on uniaxial and triaxial compression data from previous studies is proposed in this paper. The calibration method is verified by single element tests for unconfined uniaxial and triaxial compressive data. In addition, with the introduction of the dynamic increase factor (DIF), a finite element model is produced to demonstrate the validity and applicability of the proposed method through comparison with the experimental results of SFRC slabs subjected to projectile impact.

Numerical simulations of blast responses for SFRC slabs using an orthotropic model

This paper proposes a material model of steel fiber reinforced concrete (SFRC) subjected to dynamic loadings on the basis of an orthotropic concrete model. The effects of strain rate and fiber reinforcement are taken into account in the material model of SFRC from the uniaxial stress-strain relation to the triaxial strength envelope. The compressive and tensile strains as failure criteria are developed by reflecting the dynamic material properties, respectively. In particular, the post-cracking response according to steel fiber addition is investigated to improve the accuracy of the blast analysis for SFRC structures, and the proposed model is implemented as a user defined material model in LS-DYNA. The numerical results are compared with the experimental data in terms of damage pattern and average diameter of the damaged area for RC and SFRC slabs under explosions. The plastic based concrete models of K&C and CSCM are additionally compared to predict the behavior of SFRC structures. Furthermore, parametric studies are conducted with the proposed model to investigate the effects of reinforcement spacing and steel fiber on improving the structural resistance of SFRC slabs.

A strain rate dependent nonlinear elastic orthotropic model for SFRC structures

A strain rate dependent orthotropic model for steel fiber reinforced concrete (SFRC) structures subjected to impact or blast loads is proposed in this paper. Based on the previously introduced orthotropic model for plain concrete, an improved strain rate dependent material model for SFRC is developed to account for the effect derived from the addition of steel fibers in the concrete matrix and to cope with the multiaxial strain rate dependent behavior of SFRC. In addition to verification of the constructed multiaxial strength envelope of SFRC through correlations with experimental data, improved failure strains in the uniaxial stress-strain relation are also introduced to minimize the mesh size dependency in the numerical results. Finally, the proposed orthotropic model is incorporated into LS-DYNA as a user defined material model. Numerical analyses were performed for experiments of RC and SFRC slabs under projectile impact and blast loading, and the obtained results show that the addition of the steel fibers provides a considerable improvement in the structural resistance and the proposed model effectively simulates the structural responses of SFRC structures while minimizing the mesh size dependency in the numerical results.

Dynamic attainment of mixed aspect ratio for concrete members reinforced with steel fiber under impact loading

Steel fiber reinforced concrete (SFRC) (an impact resistant material) has a good energy dissipation capacity and ductility through the developing of impact toughness and tensile strength. Due to lack of adequate data over the dynamic performance of SFRC in previous studies, the design procedures and analyzing of SFRC are under investigation. The current study has focused on the empirical test and the finite element analysis (FE) of dynamic response for SFRC slabs and beams containing mixed aspect ratio of steel fibers (SFs) subjected to impact loading. Adding SFs increased the slab capacity and reduced the crack spacings.

Experimental and numerical study of shear connection in composite beams of steel and steel-fibre reinforced concrete

To explore the shear behaviour of high strength bolted connectors in steel-SFRC composite beams, push-out tests were carried out on 18 steel-fibre reinforced concrete (SFRC) specimens and 4 normal concrete (NC) specimens. The failure modes, ultimate shear strength, load-slip response as well as the shear stiffness of the tested specimens were determined accordingly. During the experiment, two failure modes that involved bolt shear failure and concrete splitting failure were observed in both NC and SFRC specimens. As the bolt-to-hole clearances of specimens were infilled, the slip plateau at the early loading stage therefor were avoided and the corresponding shear stiffness of bolted connectors increased as well. Compared to NC specimens, the extension of cracks on SFRC slabs were limited and the width of cracks efficiently decreased because of the addition of steel fibre in concrete. The ultimate shear strength of the bolted connectors in steel-SFRC composite beams was about 21.2% higher than that of the bolted connectors in steel-NC composite beams, with the volume percentage of steel fibre in concrete being approximate 1.0%. The applied pretension on bolted connectors had a significant effect on the shear stiffness of bolted connectors, but almost had no effect on the ultimate shear strength. The ultimate shear strength of bolted connectors increased with the increase of concrete compressive strength, bolt shank area and bolt tensile strength. Finite element models, which confirmed by the tested results, were also employed to perform the parametrical analysis involved in concrete compressive strength, as well as bolt pretension, and diameter and tensile strength. Upon the experimental and independent FE results, practical calculation formulas were further proposed, which can properly estimate the ultimate shear strength as well as the load-slip curves of high strength bolted connectors in steel-SFRC composite beams.

Computational Analysis of Punching Shear Models of Steel Fiber Reinforced Concrete Slabs

A computational analysis is presented to predict the ultimate and cracking shear strength of steel fiber reinforced concrete slabs. Different models are suggested considering the effect of concrete compressive and tensile strength, amount of flexural reinforcements, yield strength of the reinforcement bars and steel fiber properties (volume percent, aspect ratio, and type of steel fibers). The predicted results are compared with the experimental data found in literature and found good agreement.

Evaluation of Organizational and Technological Aspects of Construction of Elevated Steel Fibre Reinforced Concrete Slabs

Evaluation of Organizational and Technological Aspects of Construction of Elevated Steel Fibre Reinforced Concrete Slabs

강섬유보강 콘크리트를 이용한 콘크리트궤도 패널의 휨성능 평가

강섬유보강 콘크리트를 이용한 콘크리트궤도 패널의 휨성능 평가