Fiber-reinforced Concrete Slabs Research Articles

Flexural behaviour of light-weight steel fibre reinforced concrete slabs: Testing and prediction model

This study investigated the flexural performance of eight lightweight fibre-reinforced concrete (LW-FRC) slabs, categorised into two groups with varying longitudinal reinforcement ratios (0.3 % and 0.6 %) and varying steel fibre content (0, 20, 40, and 60 kg/m3). In addition, a modified formula was proposed to calculate the deflection of LW-FRC slabs, which considers the influence of fibre content and the interaction between fibre content and longitudinal tensile reinforcement. The experimental results revealed that the effectiveness of dispersed steel fibres in LW-FRC slabs was significantly influenced by the interaction between the longitudinal reinforcement ratio and the fibre volume fraction. Consequently, the effectiveness of steel fibres in improving the flexural behaviour and deflection of LW-FRC slabs, e.g., crack resistance, flexural strength, energy absorption, ductility, as well as deflection and crack width, not only increased with the fibre volume fraction but also exhibited a clear correlation with the increasing longitudinal reinforcement ratio. Furthermore, it was evident from the experimental results that the longitudinal reinforcement of LW-FRC slabs started to yield during the serviceability limit state (SLS). This noteworthy finding requires further investigation as it significantly compromises the safety margin when designing such LW-FRC components, particularly concerning SLS requirements such as deflection and cracking. The proposed formula for predicting deflection of LW-FRC slabs considered the nonlinear behaviour of the slabs in the post-cracking stage. The predicted deflection from the proposed formula closely aligns with the experimental results.

Effective Moment of Inertia of Reinforced Concrete and Reinforced Steel Fiber-Reinforced Concrete One-Way Slabs

Effective Moment of Inertia of Reinforced Concrete and Reinforced Steel Fiber-Reinforced Concrete One-Way Slabs

Finite Element Analysis of Fiber Reinforced Concrete Slabs under Torsion

Finite Element Analysis of Fiber Reinforced Concrete Slabs under Torsion

Key effects on the structural behavior of fiber-reinforced lightweight concrete-ribbed slabs: A review

Abstract A concrete slab is one of the chief structural members in buildings, considered the most prominent member consuming concrete. Structural engineers are challenged to work on the new trend introduced using different slabs. One-way ribbed slabs are commonly used in construction due to their efficiency in spanning long distances while maintaining a low overall depth and giving the least possible number of columns. The main limitation of slab design in the construction of a reinforced concrete structure is the span between columns; a greater span between columns necessitates more supported beams or increased slab thickness; these requirements lead to an increase in the structure weight due to other concrete and steel which make the structure more costly. On the other hand, any increase in the structure’s self-weight limits the horizontal slab’s span, increases the structure’s stress, and raises the inertia forces that must be resisted. Lightweight aggregate concrete has been effectively utilized for structural applications for a long time. The density of lightweight concrete (LWC) is sometimes more essential than its strength in structural applications. The dead load is reduced for structural design and foundations when the density is lower for the same strength level. Reinforced concrete ribbed slabs have become increasingly popular in industry construction as an alternative to solid slabs in building structures. The incorporation of steel fibers facilitates flexural softening, which takes longer than sudden brittle failure, indicating its ability to increase energy absorption and improve crack behavior. Designing structures requires materials with higher strength-to-weight ratios. Ribs and LWCs are two leading sustainable assets. The world is moving toward sustainability by reducing the amount of concrete used and the overall weight of the unit. Studies have shown that the drop in compressive strength was about 4.85–65.55%. The structural performance of lightweight fiber-reinforced concrete slabs is influenced by the concrete mix ratio, fiber type and content, reinforcement detail, and rib geometry. The study provides valuable insights into the properties and performance of key effects on the structural behavior of fiber-reinforced LWC-ribbed slabs. It provides recommendations for future research and advancement of sustainable building methods.

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

The aim of this research was to assess the adequacy of material models based on flexural toughness (such as equivalent and residual flexural strength) and the deflection limits at which these parameters are estimated for the design of fibre-reinforced concrete (FRC) for various applications such as slabs-on-grade and pavements. The experimental work was conducted using FRC mixes with hooked-end steel fibres (SF) or macro polypropylene fibres (PF) and hybrid combinations of SF and PF. Toughness testing was carried out on unnotched and notched prisms and square slabs, prepared with a typical grade of concrete used for FRC pavement applications. To validate the material models, comparisons were made between the theoretical moment/load calculated based on material flexural toughness parameters and the actual moment obtained from slabs using the yield line formed during testing. It was found that, overall, both equivalent flexural strength (from unnotched prism tests) and residual flexural strength (from notched prism tests) are suitable for designing FRC slabs. However, the equivalent strength showed better correlation to the slab response. Hybrid PF–SF mixes with a higher volume fraction of 0.6% showed a marginal increase in flexural performance compared with mixes with a 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.

Crack Width Behaviour of High-Performance Fiber Reinforced Concrete Slabs Affected by Steel Fiber Composition

Crack Width Behaviour of High-Performance Fiber Reinforced Concrete Slabs Affected by Steel Fiber Composition

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).

Ultra-high-performance fiber-reinforced concrete flat slabs' punching shear resistance as a function of drop panel thickness

Ultra-high-performance concrete including fibers (UHPFRC) is used to build skyscrapers, towers, and bridges.This type of concrete may have smaller skeletal components than normal concrete. However, flat slabs are thicker than reinforced concrete slabs. Brittle punching shear failure may happen rapidly and abruptly in flat slabs. The punching load was applied to four two-way internal UHPFRC-supported flat slabs: three reinforced concrete flat slabs with 10mm, 14mm, and 18mm drop panels and one control reinforced concrete slab without drop panels. The drop panel thickness enhanced punching shear resistance by 40% at fracture load and 48% at ultimate stress. In addition, deflection, shear strain at the concrete surface, strain in reinforcement, rotation at supports, and fracture inclination angles between top and bottom fibers improved by 30%, 316 percent, 74%, 385 percent, and 1.01 percent at peak load, respectively.

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