Fiber-reinforced Concrete Slabs Research Articles

Yield line-based design of fibre reinforced concrete: assessment of suitability of material models

The present research is intended to address the adequacy of flexural toughness-based material models such as equivalent and residual flexural strength, and the deflection limits at which these parameters are estimated for design of fibre reinforced concrete (FRC), for various applications such as slabs-on-grade/pavements. The work is an experimental study using FRC concrete mixes with individual and hybrid combinations of hooked-end steel (SF) and macro polypropylene fibres (PF). The experimental investigation consisted of toughness testing unnotched and notched prisms and square slabs, prepared with a typical grade of concrete used for FRC pavement applications. To validate the material models, a comparison was made between the theoretical moment/load calculated based on material flexural toughness parameters and the actual moment obtained from slabs using actual yield line formed during testing. From the study it is observed that overall, both equivalent (from unnotched prism test) and residual (from notched prism test) flexural strength, are suitable for designing FRC slabs, however the equivalent strength parameter shows better correlation to the slab response. The results also indicate that the hybrid mixes of PF and SF, with a higher volume fraction of 0.6% Vf, shows a marginal increase in flexural performance, in comparison to the mixes with lower volume fraction but no or minimal synergy due to hybridisation.

Punching shear strength of fiber-reinforced polymer concrete slabs: Database-driven assessment of parameters and prediction models

This study examines the punching shear capacity of Fiber-Reinforced Polymer Concrete Slabs (FRPCS). Utilizing a database of 272 experimental interior and edge column-supported FRPCS samples, the research evaluates the influence of various design parameters on the punching shear capacity. This study stands out for its comprehensive database-driven approach and critically evaluates three code models (ACI 440.1R, JSCE, CAN/CSA-S06) and ten theoretical models from the literature. The findings reveal significant variability in model predictions, prompting the proposal to modify the ACI equation for enhanced prediction accuracy. The analyses indicate that the JSCE and CAN/CSA-S06 models provide reasonable estimations for punching shear capacity, while the ACI 440.1R model is over-conservative. The proposed modification provides a comparable prediction accuracy to the JSCE and CAN/CSA-S06 models.

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.

Investigation on the response of steel fiber reinforced lightweight aggregate concrete slab under sequential impact loading

The current study investigates the response of steel fiber-reinforced lightweight concrete slabs under sequential impact loading. The potential damages caused by impact loads which are a threat to many structures and the use of fiber to mitigate them was evaluated experimentally. Moreover, a comprehensive parametric study was conducted using the finite element method to evaluate the effect of influential factors such as fiber content, slab geometry, and energy of impact. The results show that impact loads can cause significant damage to lightweight aggregate concrete slabs, including cracking and spalling. The use of steel fibers in lightweight aggregate concrete can improve its stiffness, energy absorption, overall stability, and prevent crack propagation resulting in the reduction of the damage risk under impact loads, compared to specimen without fiber. The incorporation of fibers resulted in a significant rise in the number of impacts required for failure. In contrast to the control slab, which failed completely after three impacts, lightweight concrete slabs containing steel fibers at volume fraction of 0.5%, 1%, and 1.5% endured 87, 710, and 1213 impacts before failure, respectively. In addition, adding steel fibers causes a more consistent response in terms of stiffness as the frequencies of lightweight concrete slabs containing steel fibers at volume fraction of 0.5%, 1%, and 1.5% remained unchanged until 34%, 17%, and 40% of the total number of impacts resulting in failure. Moreover, the utilization of fibers preserves structural integrity and localizes crack formation. Overall, the current study provides valuable insights into the response of light weight aggregate concrete structures under impact loading and the potential benefits of using steel fiber and lightweight aggregate in concrete.

Punching shear capacity of fiber-reinforced concrete suspended slabs: Database analysis and models assessments

The punching shear capacity is critical in the design of suspended slabs. Fiber reinforcement has been introduced to improve the punching shear capacity of these slabs. Several models have been used to predict the punching shear capacity of fiber-reinforced concrete slabs (FRCS). Some of these models accounted only for the contribution of concrete (e.g., ACI 318–19 and CSA-19), while others also accounted for the contribution of reinforcing steel (e.g., JSCE-07 and Eurocode-2 and/or fibers (e.g., fib MC-10). In the present study, experimental results from 240 FRCS and 78 control slabs (without fibers) were collected and analyzed to assess the effect of various parameters and the extent to which these parameters affect the predicted punching shear capacities by various models. Four main parameters, concrete compressive strength, steel reinforcement ratio, fiber reinforcement, and punching shear perimeter, were considered in the assessment of various design and theoretical models. The study revealed that most design-based models underestimate, to varying degrees, the punching shear capacities with large variability. To better capture the dependence of the punching shear capacity on the four main parameters, a new model was proposed for FRCS. The proposed model considers the critical shear perimeter at a distance d from the face of the column and accounts for the fiber contribution as a function of the residual strength parameter obtained from standard beam tests (ASTM C1609). Predictions of the proposed model were characterized by high accuracy and low coefficient of variation (CV).

Explainable machine learning model for predicting punching shear strength of FRC flat slabs

Reinforced concrete slabs are vulnerable to punching shear failure at the slab-column joint, which can initiate catastrophic progressive collapse. The addition of steel fibers in the concrete matrix has emerged as an effective strategy to mitigate such progressive failure. However, the effects of the diverse mixture proportions of the concrete matrix with different types and dosages of fibers have made the accurate prediction of the punching shear strength (PSS) of the fiber-reinforced concrete (FRC) flat slabs a complex task, where the existing mechanical models have several limitations. Therefore, this study proposes an explainable XGBoost model for predicting PSS of flat slabs made with different types of FRC based on a newly established comprehensive database of 251 flat slabs including normal strength FRC slabs, high-performance FRC slabs, and ultra-high-performance FRC slabs. A customized procedure was proposed to establish the XGBoost model considering data preparation, feature selection, hyperparameter tuning and model validation. The performance of the XGBoost model was then compared with that of existing mechanical models. Finally, sensitivity analysis and SHapley Additive exPlanations (SHAP) analysis were applied to identify the most influential parameters on the prediction of PSS. Results show that the proposed feature selection method is effective in identifying six influential parameters from the eleven parameters related to the PSS of FRC flat slabs. The developed XGBoost model yielded highest prediction accuracy and lowest variation, which outperformed the other mechanical models. Sensitivity analysis also indicated similar trends of parameters in both the XGBoost model and the mechanical models. The PSS of FRC flat slabs can be improved by increasing the concrete compressive strength, reinforcement ratio, and fiber volume, and by decreasing the column width-to-depth ratio, water-to-binder ratio, and aggregate size ratio. The proposed XGBoost model could enhance the understanding of PSS of FRC flat slabs and guide future pertinent design code provisions.

Projectile impact response of prestressed fiber-reinforced concrete slabs having perforated steel lining

Projectile impact response of prestressed fiber-reinforced concrete slabs having perforated steel lining

Numerical investigation of projectile impact behavior of hybrid fiber-reinforced concrete slabs

In our earlier study, the impact resistance of slabs made up of concrete containing hybrid fibers (i.e., steel and synthetic fibers in various proportions) was evaluated through an experimental program. The test specimens, measuring 600 × 600 × 90 mm, were cast with varying amounts of fibers, while some were kept as control samples without any fibers. The high-velocity impact tests were conducted using a gas-gun system, where hemispherical steel projectiles were fired at the slabs. The craters’ sizes and penetration depths were measured. The hybrid fibers in the concrete reduced spalling and scabbing damage and reduced the size of craters. In the current study, the impact response of the hybrid fiber-reinforced concrete (HFRC) slabs was investigated numerically. LS-DYNA software was employed for this investigation, and crack sizes, areas of spalling and scabbing damages, and penetration depths were estimated. The numerical simulations provided an efficient and practical tool for analyzing the HFRC slabs’ response against impact load. The use of hybrid fibers decreased front surface damage and prevented concrete particles from flying out of the back face. The inclusion of fibers in concrete increased the perforation energy by 49%–203%. The numerical predictions of penetration depth were reasonably close, with absolute errors varying from 3.6%− 32.6%, and the error in the prediction of maximum rebar strain varied from 2.5% to 12.7%. The presented model thus has the capability to predict the local damages of various types of RC and HFRC slabs with acceptable accuracy.

A Study on Evaluation of Temperature Stresses in Fiber Reinforced Concrete Slab

Temperature is an important parameter which affects the design and performance of both flexible and rigid pavements. Temperature variations within the rigid pavement structure induces many distresses. Knowledge of temperature effects is essential for the design and maintenance requirement. The temperature differential depends mainly on the thickness of slab and the grade of concrete.

Practical flexural design approach for one-way hybrid fiber-reinforced concrete slabs based on a parametric study on slenderness limits

Fiber-reinforced concrete (FRC) is increasingly used for structural applications. Slabs are a particularly attractive use for FRC due to a potentially increased redistribution capacity, as well as the efficient cracking control that fibers provide. However, methods for reliably establishing slenderness limits of such elements are missing. Therefore, in this study, a previously developed closed-form solution for slenderness limits of hybrid FRC (HFRC) slabs (steel reinforcement bars and steel fibers) is presented and updated. Subsequently, a comprehensive parametric study on one-way solid slabs is performed, drawing clear conclusions on which parameters are the most influencing and offering a practical flexural design approach in the form of graphs and tables for determining minimum thicknesses of HFRC slabs that may be used as design aids for practitioners.

Thickness of Glass Fiber-Reinforced Polymer-Reinforced Concrete Slabs

Thickness of Glass Fiber-Reinforced Polymer-Reinforced Concrete Slabs

Effect of coarse aggregate and carbon fiber content on ohmic heating curing of concrete slab in realistic severely cold weather

In this work, carbon fiber-reinforced high-performance concrete (CF-HPC) slabs with coarse aggregate content of 25 vol%/35 vol%/45 vol% and carbon fiber content of 0.6 vol%/0.8 vol%/1.0 vol% were cured by ohmic heating (OH) curing under realistic severely cold condition for practical on-site construction. Results indicated that the coarse aggregate content has a substantial influence on the electrical resistance and curing time of concrete slab. Higher and lower content of coarse aggregate will lead to insufficient ohmic heats and curing time. On the contrary, carbon fiber content only has a limited influence on OH curing feature, such as slight value difference of electrical resistance and curing temperature. Besides, the correlation between the curing temperature of concrete slab and the associated factors (OH curing power, ambient temperature) was quantitatively analyzed. It is found that the OH curing power had a strong correlation with the concrete temperature during the most time of curing period, while the snowfall weather enhanced the correlation between ambient temperature and concrete temperature. At last, a criterion of feasible resistance range based on the experimental results and theorical analysis was proposed to evaluate the feasibility of OH curing and assist the concrete mix design.

Behavior of prestressed fiber-reinforced steel-lined concrete slabs under projectile impact

Behavior of prestressed fiber-reinforced steel-lined concrete slabs under projectile impact

Shear Strength of Extruded, Prestressed Steel Fiber-Reinforced Concrete Hollow-Core Slabs

Shear Strength of Extruded, Prestressed Steel Fiber-Reinforced Concrete Hollow-Core Slabs

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.

Reliability Assessment of Steel-Lined and Prestressed FRC Slabs against Projectile Impact

A simulation-based probabilistic method is proposed for assessing the reliability of steel-lined and prestressed fiber-reinforced concrete (PFRC) slabs against the impact loads. The impact testing of several prestressed and non-prestressed FRC slabs of 800 × 800 × 100 mm in size was carried out. The experimental program involved projectile impact testing of prestressed and non-prestressed FRC slabs using a gas gun. Three parameters were varied for testing of slabs under the projectile impact, viz., a quantity of steel fibers in the concrete, steel lining on the backside of the slab, and the prestressing level. The probability-based reliability analysis of all the tested specimens was then performed to highlight the influence of steel lining, steel fibers, and prestress in enhancing the safety of RC (reinforced concrete) slabs against projectile impacts. Projectile impact velocity exceeding the slab’s ballistic limit was assumed to lead to the failure of the PFRC slab, i.e., the perforation failure of the slab. Study results indicate that when no steel fiber was present, slab reliability was low. Adding fibers to slabs increases slabs’ reliability significantly. Specimens with the highest steel fiber content (1.2%) showed the greatest increase in reliability. The steel lining on the back face makes the slab’s reliability almost doubled in comparison with those without lining. Additionally, steel lining makes the PFRC slabs as reliable as desired. It was further noticed that the prestressing helps in enhancing the slab safety against projectile impacts. Even a minimal amount of prestressing makes a noticeable improvement in the reliability of PFRC slabs.

Punching Shear Characterization of Steel Fiber-Reinforced Concrete Flat Slabs

Punching shear failure in thin slabs under concentrated loads can cause shear stresses near columns. The use of steel fiber is a practical way to improve a slab-column connection's punching strength and deformation capacity. In this study, the capacity and behavior of steel fiber-reinforced concrete flat slabs are examined under punching shear force. Ten small-scale flat slabs were tested, eight of which had steel fiber and two without. Two parameters are studied in this paper, which are the fiber volume ratio (from 0% to 2%) and the stub column load shape (circle and square). The test results include the concrete compressive strength, crack patterns, punching shear, and load-defection behavior of the slabs. Based on the experimental results, it was found that the punching shear capacity of slabs with steel fiber (S5) increased by 21.8% compared to slabs without steel fiber (S1), and the slabs with steel fiber had more ductility compared to the slabs without fiber. Doi: 10.28991/HIJ-2022-03-04-08 Full Text: PDF

Experimental and numerical investigation on the resistance of steel fiber-reinforced heavyweight concrete slabs against rigid projectile impact

This study presents an inclusive experimental and numerical investigation of the resistance of steel fiber-reinforced heavyweight concrete under the impact of a high-velocity rigid projectile. Thus, concrete specimens were made using hooked-end steel fibers at 0%, 0.5%, 1%, 1.5%, 2%, and 2.5% volume fractions to assess the physicomechanical specifications of heavyweight concrete containing iron ore as fine and coarse aggregates. Also, the compressive and splitting tensile strengths, modulus of elasticity, stress–strain relationship, bulk density, and water absorption capacity of heavyweight concrete specimens were compared to those of the equivalent normal-weight concrete. The penetration tests were conducted on concrete slabs fabricated with normal weight and heavyweight concrete mixes to examine the specimens’ failure mode, penetration depth, and spalling volume. The results revealed that normal-weight concrete's compressive and splitting tensile strengths were more susceptible to adding steel fibers. It was also shown that increasing the density and fiber content significantly affected the impact resistance and residual velocity of fiber-reinforced concrete elements. Heavyweight concrete provided better life safety measures against the impact load than normal weight specimens, while the repair and reuse of heavyweight concrete components were feasible. Moreover, numerical modeling was performed using LS-DYNA finite element software, and the predictions were compared to the proposed experimental results and the analytical relations in the literature. There was good agreement between the results.

The Ultimate Load of the Fiber-Reinforced Concrete Slab Foundations Subjected the Concentrated Load by ANSYS

In practice, the slab foundation is used widely in civil engineering. Besides the concrete material, fiber concrete is applied more popular in the slab foundations. Determining the ultimate load of the slab foundations is a complex problem due to the relation of the soil-structure interaction (SSI) problem, which depends on both the structures and the subsoil characteristics. ANSYS is a finite element software which is a reliable and effective technique to simulate the structure model. This paper aims to determine the ultimate load of the fiber-reinforced concrete slab on the ground subjected to the concentrated load by ANSYS software. The nonlinear material of the structure and the subsoil will be considered in this work. The validation test of the numerical model will be through the experiment data. This study has shown that the numerical model is reliable for the structure design.