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This study is focused on the punching strength of fiber-reinforced polymer (FRP) concrete slabs. The mechanical properties of reinforced concrete slabs are often constrained by their punching shear strength at the column connection regions. Researchers have explored the use of fiber-reinforced polymer reinforcement as an alternative to traditional steel reinforcement to address this limitation. However, current codes poorly calculate the punching shear strength of FRP-reinforced concrete slabs. The aim of this study was to create a robust model that can accurately predict its punching shear strength, thus improving the analysis and design of composite structures with FRP-reinforced concrete slabs. In this study, 189 sets of experimental data were collected, and six machine learning models, including linear regression, support vector machine, BP neural network, decision tree, random forest, and eXtreme Gradient Boosting, were constructed and evaluated based on goodness of fit, standard deviation, and root-mean-square error in order to select the most suitable model for this study. The optimal model obtained was compared with the models proposed by codes and the researchers. Finally, a model explainability study was conducted using SHapley Additive exPlanations (SHAP). The results showed that random forests performed best among all machine learning models and outperformed existing models suggested by codes and researchers. The effective depth of the FRP-reinforced concrete slabs was the most important and proportional to the punching shear strength. This study not only provides guidance on the design of FRP-reinforced concrete slabs but also informs future engineering practice. [ABSTRACT FROM AUTHOR]

This paper describes the 3rd Blind Simulation Competition (BSC) organized by the fib WP 2.4.1 which aims to assess the predictive performance of models based on the finite element method (FEM) for analysis and design of fiber reinforced concrete (FRC) structures submitted to loading and support conditions that promote punching failure mode. Fiber reinforcement is used in an attempt to eliminate conventional punching reinforcement and provide technical and economic advantages. The two tested real‐size prototypes represent a column‐slab interior region of an elevated steel‐fiber reinforced concrete (E‐SFRC) slab where anti‐progressive collapse reinforcement is disposed in the alignment of columns/piles. Despite a punching failure surface being formed in both experimentally tested prototypes at the rupture stage, fiber reinforcement was able to mobilize the yield capacity of the conventional flexural reinforcement, providing high deformation capacity, and ductility to the prototypes. The average post‐peak load‐carrying capacity of the tested prototypes at a deflection seven times higher than the deflection at yield initiation of the conventional reinforcement was still 90% of the average peak load. Regarding the BSC, a total of 26 proposals were received and involved 94 participants from 29 institutions and 17 countries, with 53.9% using smeared crack models (SCMs), 30.8% a concrete damage plasticity (CDP) model, 3.8% discrete crack models (DCMs) and 11.5% considered as “other models.” From these simulations it was verified, in average terms, that SCM assured the best predictive performance apart from the average strain in the SFRC and the maximum crack width which were better predicted by DCM. More accurate predictions were obtained by using in‐house software than by adopting commercial software. [ABSTRACT FROM AUTHOR]

In today's world, concrete structures are exposed to various influences, including explosive actions. With the increasing use of fiber-reinforced concrete (FRC), it is essential to investigate its response to blast effects. As there are few studies on this topic worldwide, this research is dedicated to the question of how blast effects affect the damage and properties of six different types of reinforced concrete (RC) slabs. These samples differ in concrete classes (C30/37 and C50/60) and in the type of fibers added (steel and polypropylene). Visual inspections and non-destructive measurements are carried out before and after blasting. The damaged area of the concrete surface is determined by visual inspection, while non-destructive measurements evaluate parameters such as the rebound value of the Schmidt hammer, the electrical resistivity of the concrete, the velocity of the ultrasonic wave, and the dynamic modulus of elasticity. Equal amounts of explosives are applied to five of the RC slabs to enable a comparative analysis of the resulting damage. Based on the comparison of the measured data from these five RC slabs, conclusions are drawn regarding the effects of the explosive impacts on conventionally reinforced concrete slabs compared to those with added fibers. In addition, one of the RC slabs with steel fibers is exposed to approximately three times the amount of explosives to assess the extent of increased damage and to evaluate the suitability of military standards in the calculation of explosive charges for blasting RC elements with fibers. [ABSTRACT FROM AUTHOR]

Steel Reinforced Concrete (RC) frequently faces durability problems. In certain areas, Glass Fiber-Reinforced Polymer (GFRP) rebars are considered a non-corrodible substitute for steel reinforcement. Elevated temperatures have a significant impact on the mechanical characteristics and the adhesiveness of GFRP rebars to concrete, particularly when the polymeric matrix's glass transition temperature is approached or surpassed. Three simply supported reinforced concrete slabs were considered in the experimental program. Each specimen had identical dimensions of 1500×540×120 mm. For the fire resistance requirements, a 45 mm clear concrete cover and an exception of a 200 mm unexposed (cool) anchor zone at the ends were considered. The GFRP replacement ratio was 0, 20, and 40%. The burning procedure involved fire exposure for an hour with a steady-state temperature of 500 °C in accordance with ASTM E-119 regarding the temperature time elevation and a sudden cooling condition. The optimal concrete cover was detected by testing a fire-exposed small model reinforced by GFRP bars of varying concrete cover. The specimen was tested under static intense loads. The reference slab and the slab with a replacement percentage of 20% failed due to flexural failure, whereas the slab with a replacement percentage of 40% failed due to shear failure. The influence of the GFRP replacement ratio was extended to include toughness and ultimate load. A replacement percent of 20% increased them by 18.30, and 2.62%, respectively, while a replacement percent of 40% decreased them by 28.16, and 3.13%, accordingly. It was also shown that the location of replacing the GFRP and 200 mm of unexposed (cold) installation area at the ends with a 45 mm concrete cover has a significant impact. The more the GFRP is located in the middle, away from the ends, the better the fire resistance is. [ABSTRACT FROM AUTHOR]

Considering the continuous threat of terrorist attacks on vital structures, it is imperative to enhance their resilience to blast impacts. Current analytical approaches are costly and complex, necessitating a more streamlined method to evaluate structures under such threats. This research addresses this by introducing a machine learning (ML) model that predicts the highly nonlinear behaviour of reinforced concrete (RC) slabs under blast loadings. A database with 936 samples, including both experimental and numerical data, was carefully created for this study. The investigation scrutinized eight ML algorithms, refined them to four based on their performance, and optimized them using grid search, genetic algorithm, and particle swarm optimization (PSO). The gradient boosting-PSO hybrid model emerged to be superior, with a remarkable 91% accuracy in predicting maximum deflection. Further, a comprehensive influence analysis was conducted using the SHapley Additive exPlanations (SHAP) method to understand the contributions of various input parameters, pinpointing scaled distance and panel thickness as critical factors. This study, besides offering a rich database, also serves as an educational tool, shedding light on hyperparameter optimization techniques and SHAP analysis. The research promises a robust and interpretable ML model poised to significantly influence the practical engineering domain in improving the structural design of RC slabs facing blast impacts.

Improvement of the bonding and interaction between concrete and steel is crucial to achieving an optimal reinforced concrete member. The proposed technique in this paper is using perforated steel plates (PSPs) to reinforce two‐way concrete slabs. In this method, ordinary steel bar reinforcements in the tension region of the concrete slabs were replaced by PSPs. Concrete slabs reinforced with PSPs enhance structural characteristics with respect to concrete slabs reinforced with ordinary reinforcement (OR) due to the higher lateral stiffness of PSPs, the better confinement of concrete within the holes of PSPs, the biaxial performance of the steel in the tension region, and the efficient load transmission mechanism between the steel and concrete. In this paper, a comprehensive experimental investigation was conducted on two‐way concrete slabs reinforced with PSPs and ordinary steel bars. The behavior of PSPs slabs was evaluated in comparison with OR slabs in terms of failure types, ductility, energy absorption, stiffness, ultimate load, cracking load, and force transmission mechanism. Findings revealed that the PSPs slabs have higher ductility, energy absorption, and ultimate strength compared to the OR slabs. [ABSTRACT FROM AUTHOR]

This study is focused on the punching strength of fiber-reinforced polymer (FRP) concrete slabs. The mechanical properties of reinforced concrete slabs are often constrained by their punching shear strength at the column connection regions. Researchers have explored the use of fiber-reinforced polymer reinforcement as an alternative to traditional steel reinforcement to address this limitation. However, current codes poorly calculate the punching shear strength of FRP-reinforced concrete slabs. The aim of this study was to create a robust model that can accurately predict its punching shear strength, thus improving the analysis and design of composite structures with FRP-reinforced concrete slabs. In this study, 189 sets of experimental data were collected, and six machine learning models, including linear regression, support vector machine, BP neural network, decision tree, random forest, and eXtreme Gradient Boosting, were constructed and evaluated based on goodness of fit, standard deviation, and root-mean-square error in order to select the most suitable model for this study. The optimal model obtained was compared with the models proposed by codes and the researchers. Finally, a model explainability study was conducted using SHapley Additive exPlanations (SHAP). The results showed that random forests performed best among all machine learning models and outperformed existing models suggested by codes and researchers. The effective depth of the FRP-reinforced concrete slabs was the most important and proportional to the punching shear strength. This study not only provides guidance on the design of FRP-reinforced concrete slabs but also informs future engineering practice.

This study investigates the effect of continuous rectangular spiral shear reinforcement on reinforced concrete slabs under low-velocity conditions, crucial for scenarios such as landslides or vehicular collisions. By combining experimental and finite element analyses using ABAQUS, this research assesses the effectiveness of this reinforcement method. The experimental setup involves subjecting slabs to impact loading with consistent energy levels using a drop weight system. Various parameters, including acceleration time, strain-time in steel and concrete, and failure mode, are carefully monitored throughout the study. Results demonstrate a notable 216.13% improvement in energy absorption and a 43.70% increase in impact ductility compared to control specimens, reflecting higher rigidity and stiffness in spiral-reinforced specimens, as evidenced by elevated maximum acceleration values. Specimens with continuously rectangular spirals exhibit less severe surface damage upon complete failure, emphasizing their enhanced impact resistance. Diagonally arranged spiral reinforcements notably reduce damage, displacement, and stress. These findings highlight the significant potential of continuously rectangular spirals in improving the low-velocity behavior of reinforced concrete slabs, offering valuable insights for structural design and reinforcing systems. Additionally, using ABAQUS finite element analysis validates experimental findings, providing efficient insights into structural behavior under dynamic conditions.

When an explosion occurs close to or partially within the face of a concrete structure, fragments are rapidly launched from the opposite face of the structure owing to concrete spalling, posing a significant risk to nearby personnel and equipment. To study the lead fragment velocity of ultra-high-performance concrete (UHPC), partially embedded explosion experiments were performed on UHPC slabs of limited thickness using a cylindrical trinitrotoluene charge. The launch angles and velocities of the resulting fragments were the determined using images collected by high-speed camera to document the concrete spalling and fragment launching process. The results showed that UHPC slabs without fiber reinforcement had a fragment velocity distribution of 0–118.3 m/s, which are largely identical to that for a normal-strength concrete (NSC) slab. In addition, the fragment velocity was negatively correlated to the angle between the velocity vector and vertical direction. An empirical Eq. for the lead spall velocity of UHPC and NSC slabs was then proposed based on a large volume of existing experimental data.

In today’s world, concrete structures are exposed to various influences, including explosive actions. With the increasing use of fiber-reinforced concrete (FRC), it is essential to investigate its response to blast effects. As there are few studies on this topic worldwide, this research is dedicated to the question of how blast effects affect the damage and properties of six different types of reinforced concrete (RC) slabs. These samples differ in concrete classes (C30/37 and C50/60) and in the type of fibers added (steel and polypropylene). Visual inspections and non-destructive measurements are carried out before and after blasting. The damaged area of the concrete surface is determined by visual inspection, while non-destructive measurements evaluate parameters such as the rebound value of the Schmidt hammer, the electrical resistivity of the concrete, the velocity of the ultrasonic wave, and the dynamic modulus of elasticity. Equal amounts of explosives are applied to five of the RC slabs to enable a comparative analysis of the resulting damage. Based on the comparison of the measured data from these five RC slabs, conclusions are drawn regarding the effects of the explosive impacts on conventionally reinforced concrete slabs compared to those with added fibers. In addition, one of the RC slabs with steel fibers is exposed to approximately three times the amount of explosives to assess the extent of increased damage and to evaluate the suitability of military standards in the calculation of explosive charges for blasting RC elements with fibers.

In the present study, a new type of slightly curved arc HRB400 steel bars (SCAHSs) was proposed to solve the problem of temperature-induced stress loss in mass concrete structures without cutting off steel bars. The flexural performance of SCAHSs and straight HRB400 steel bars reinforced one-way concrete slabs were first experimentally investigated. Then, the effects of the shape and dimension of SCAHSs on the distribution and width of concrete cracks were analyzed and discussed. Subsequently, the synergistic tensile work characteristics between SCAHSs and concrete were presented. Finally, equations for the bearing capacity and allowable crack widths for SCAHSs in hydraulic massive structures were proposed. The test results indicated that after replacing the straight steel bars in the concrete slab with SCAHSs, the crack width of the concrete slabs increased, with the maximum crack width at the bottom of the concrete slabs increasing by a factor of 1.2–1.4. As the rise-span ratio of SCAHSs increased, the flexural stiffness of SCAHSs reinforced concrete slab decreased slightly, but the deflection increased. The allowable crack widths of SCAHSs reinforced concrete slabs under environment categories I, II, and III were 0.20, 0.17, and 0.12 mm, respectively.

Blast simulators are capable of applying blast-like loading to components in a safe and controlled laboratory environment, overcoming the inherent shortcomings of blast testing in terms of data acquisition, test cycle time, and cost. In this paper, reasonable assumptions and refinements are made to the components and shape of the impact module, a key component of the blast simulator, to achieve diversity in simulated blast loading. By designing four rubber shapes, the importance of ellipsoid rubber as an elastic cushion for simulating blast loading was determined. In order to assess the effectiveness of this optimization, numerical calculations based on a calibrated finite element model were performed around four factors: flat rubber thickness, ellipsoid rubber thickness, impact velocity, and impact modulus mass. Additionally, a grey correlation sensitivity analysis was carried out to evaluate the effect of these factors on the impact loading on the reinforced concrete (RC) slab. The results indicate that peak pressure and impulse had opposite sensitivities to velocity and mass. Changes in ellipsoid rubber thickness had a more positive effect on the impact loading than flat rubber thickness. An in-depth study of the role of these influencing factors is important for the design and improvement of impact modules. [ABSTRACT FROM AUTHOR]

To study the blast resistance of reinforced concrete slabs under fire, the finite element software ABAQUS is used to simulate the static loading test of RC slabs under fire and the blast test of RC slabs at ambient temperature. After being validated, the FE model is employed to investigate the failure mechanism of RC slabs under the combined action of fire and blast using thermo-mechanical coupling technique. Moreover, the effects of fire exposure duration, scaled distance, and charge weight on the blast resistance of the RC slabs after fire are studied. The results show that blast results in the local shear failure in the center of the RC slab subjected to fire. Then, the whole floor slab undergoes flexural failure. With the increase of fire duration, the damage of RC slabs becomes more severe, and the plastic deformation gradually enables energy dissipation. The scaled distance and charge weight have the most significant influence on the failure mode and dynamic response of the RC slabs. The smaller the scaled distance, the more serious damage to the RC slabs. When the scaled distance is greater than 3 m/kg1/3, no damage occurs. The larger the charge weight, the more serious damage to the RC slabs. [ABSTRACT FROM AUTHOR]

This study presents a non-explosive method for simulating blast loading on reinforced concrete (RC) slabs. The method involves using a newly developed blast simulator to apply a speedy impact load on the slab, which generates a pressure wave similar to that of an actual blast. Both experimental and numerical simulations were carried out to evaluate the effectiveness of the method. The experimental results showed that the non-explosive method can produce a pressure wave with a peak pressure and duration analogous to those of an actual blast. The numerical simulations also showed good agreement with the experimental results. Additionally, parameter studies were conducted to evaluate the effects of the rubber shape, the impact velocity, the bottom thickness, and the upper thickness on the impact loading. The results indicate that pyramidal rubber is more suitable as an impact cushion for simulating blast loading than planar rubber. The impact velocity has the widest range of regulation for peak pressure and impulse. As the velocity increases from 12.76 to 23.41 m/s, the corresponding range of values for peak pressure is 6.457 to 17.108 MPa, and for impulse, it is 8.573 to 14.151 MPa∙ms. The variation in the upper thickness of the pyramidal rubber has a more positive effect on the impact load than the bottom thickness. With the upper thickness increasing from 30 mm to 130 mm, the peak pressure decreased by 59.01%, and the impulse increased by 16.64%. Meanwhile, when the bottom part's thickness increased from 30 mm to 130 mm, the peak pressure decreased by 44.59%, and the impulse increased by 11.01%. The proposed method provides a safe and cost-effective alternative to traditional explosive methods for simulating blast loading on RC slabs. [ABSTRACT FROM AUTHOR]

Reinforcement is one of the important factors affecting the anti-blast performance of reinforced concrete (RC) slabs. In order to study the impact of different reinforcement distribution and different blast distances on the anti-blast performance of RC slabs, 16 model tests were carried out for RC slab members with the same reinforcement ratio but different reinforcement distribution and the same proportional blast distance but different blast distances. By comparing the failure patterns of RC slabs and the sensor test data, the impact of reinforcement distribution and blast distance on the dynamic response of RC slabs was analyzed. The results show that, under contact explosion and non-contact explosion, the damage degree of single-layer reinforced slabs is more serious than that of double-layer reinforced slabs. When the scale distance is the same, with the increase of distance, the damage degree of single-layer reinforced slabs and double-layer reinforced slabs increases first and then decreases, and the peak displacement, rebound displacement and residual deformation near the center of the bottom of RC slabs gradually increase. When the blast distance is small, the peak displacement of single-layer reinforced slabs is smaller than that of double-layer reinforced slabs. When the blast distance is large, the peak displacement of double-layer reinforced slabs is smaller than that of single-layer reinforced slabs. No matter how large the blast distance, the rebound peak displacement of the double-layer reinforced slabs is smaller, and the residual displacement is larger. The research in this paper provides a reference for the anti-explosion design, construction and protection of RC slabs. [ABSTRACT FROM AUTHOR]

Reactive powder concrete (RPC) is one of the most recent and significant advancements in the world of building. Due to its higher concrete characteristics, it has a common excessive benevolence happening in the globe at the moment, excessive ductility, shrinkage resistance, and corrosion and abrasion resistance. Investigated is the method for amending the RPC experimentally in punching shear slab action and the properties of construction material to investigate properties of volumetric ratios of steel fiber, and silicas fume, tensile steel ratio, the most important component for construction is reinforced concrete, which works well with other materials to create structures in any shape that is needed. In the present research, investigational work of RC slab with (1,000 × 1,000 × 60) mm dimensions was tested. This study aims to see how the relative volume of steel fibers (Vf) and silica fume content (Sf) affect the actions of RC slabs after being exposed to fire. It originated that a concrete mix containing 2% steel fibers improved the RPC slab's cracking and final punching shear. The existence of reactive powder increases fire resistance. This study's experiment aimed to see how reactive powder and Slab's ultimate punching shear strength were affected by replacement ratio. Whenever a fire is present. After fire exposure, the initial and subsequent stiffness of reinforced concrete slabs reduced considerably the temperature grew from 25 to 750°C.

Recent reinforced concrete Flat slabs (RC) failures under two-way shear have raised a question mark on the reliability of the current understanding of the two-way shear design. Moreover, the two-way shear strength of Flat slabs subjected to membrane tensile forces is a dilemma, where design codes provision varies significantly for this case. In this study, the full behavior of flat RC slabs subjected to combined two-way shear and axial tension is investigated. The behavior in terms of load versus deformation, ultimate strength, and deformation. Firstly, an extensive review of the existing literature on the experimental testing and design models for Flat slabs under combined two-way shear and axial tensile forces was conducted. Secondly, an experimental test setup designed to apply combined two-way shear and tensile forces simultaneously on flat slabs was presented. Four flat slabs (1500 × 1500 × 150 mm) were tested under two-way shear up to failure, while subjected to different levels of membrane tensile forces. Thirdly, experimentally measured strength from current and previous studies were compared with that calculated using selected design codes and mechanical models. For flat slabs under two-way shear combined with membrane tensile forces, the following was concluded: (1) a disagreement between selected design codes, while the European design code is the closer to the experimental results; (2) The stiffness and the strength were reduced by 57% and 29% respectively which is highly dependent on the level of tension.

From the perspective of optimizing the construction process, the steel-PVA hybrid fiber reinforced cementitious composite (HFRCC) permanent formwork, which can take full advantage of the mechanical properties of HFRCC and factory prefabrication, was presented. Firstly, the fiber hybrid ratio of HFRCC was determined based on the slump flow tests and four-point bending tests. It was found that the HFRCC containing 0.25 % PVA fiber and 1.5 % steel fiber exhibited excellent workability and flexural behavior, and was adopted to manufacture the permanent formwork. Subsequently, the mechanical properties of prefabricated HFRCC formwork subjected to the construction load were studied. The results showed that the ratio of the maximum elastic load to the design load was 1.38–1.66 and the prefabricated HFRCC formwork with a thickness of 10 mm can ensure the safety of construction. Then, seven reinforced concrete (RC) slabs with 10 mm thick HFRCC permanent formwork (composite slabs) and one RC slab were tested under four-point loading to explore the impact of span length, depth of cast-in-place concrete, reinforcement ratio, and HFRCC-RC interface treatments. The results showed that the addition of HFRCC formwork can improve the flexural behavior of RC slabs. The cracking load of such composite slabs was increased by 20.1–31.7 % compared with the reference RC slab. Due to the favorable bonding properties between HFRCC and concrete, the flexural behavior of composite slabs with different interface treatments (manual smoothing, isometric grooves, and surface scratching) was similar, and negligible interfacial slip occurred. Moreover, a theoretical method was put forward for estimating the flexural strength and deflection of composite slabs. The feasibility of the developed model was verified by the comparisons between the estimated value and test data.

This study aims to investigate the local failure mechanism of reinforced concrete slabs subjected to hard and deformable projectile impacts. This is done by conducting impact tests and numerical simulations. In a series of impact tests, a hard/deformable steel projectile (8.3–8.4 kg) collided with a reinforced concrete slab with a thickness of 10–30 cm at an impact velocity of 64–90 m/s, and the impact and reaction forces were measured. The numerical simulation demonstrated that the failure of the reinforced concrete slab was affected by the rigidity of the projectile in terms of the maximum impact force and impulse. [ABSTRACT FROM AUTHOR]

Due to the low lateral stiffness of slabs supported on columns alone, reinforced concrete flat plates are typically combined with other structural elements, such as shear walls. In these structures, the slab–column connections are designed to carry gravity loads only, and the shear walls are required to resist both gravity and lateral forces. Therefore, the slab–wall connections are essential for the performance of both the gravity and lateral force resisting systems. However, most punching shear research and design provisions are focused on slab–column connections, even though punching failures around slab–wall connections have occurred experimentally. Empirical testing of slab–wall connections is difficult due to the specimen size. This paper investigates the punching shear behavior of interior slab–wall connections subjected to concentric vertical loading, and combined concentric vertical loading and uniaxial unbalanced moment using a plasticity‐based nonlinear finite element model (FEM) in ABAQUS. The analysis of isolated slab–wall connections demonstrates that punching failures can occur before one‐way shear failures. Since the overall connection capacity is much higher than the expected loads in most structures, if these punching failures happen they would be localized to the region around the wall end and are not expected to lead to structural collapse. [ABSTRACT FROM AUTHOR]

In the search for adopting methods that provide more comfort in the housing system, they require better structural performances in current buildings. Construction practices in the region have been discredited over time, conceiving vulnerable buildings whose inhabitants are subject to risk. The objective of this research is to comprehensively analyze the technical, construction, and design characteristics of reinforced concrete slabs regarding their implementation as a reinforcing structure for green roofs in the city of Tuxtla Gutiérrez, Chiapas, Mexico. To carry out the structural analysis, the intrinsic properties of the supporting members (slabs) were considered, as well as their current condition, and design based on durability standards. The research results revealed that the slab depth and the amount of steel were lower for average spans, as stipulated by the corresponding technical standards. Corrosion damages in steel bars are expected and they were found under an inadequate design standard, combined with deficiencies throughout the construction process. The constructions analyzed and developed with formal construction or self-build processes show similar pathologies. The city of Tuxtla Gutiérrez lacks training centers for homeowners and workers to be able to adopt self-build methods. Moreover, the authority is not rigorous regarding the compliance with building codes. These members have become a key knowledge gap. Finally, the implementation of green roofs in these structures is unlikely without prior significant changes in the entire construction. [ABSTRACT FROM AUTHOR]

According to modern seismic codes, in certain cases, the vertical component of the ground motion has to be taken into account. However, no specific instructions concerning the structural modelling—and especially the modelling of vertical masses—are provided. The objective of the present paper is the evaluation of alternative structural models of reinforced concrete slabs under vertical seismic excitation. For this purpose, a series of single-storey buildings were analysed by means of linear and nonlinear time-history analysis and the values of representative response quantities were calculated. The influence of several parameters such as the dimensions and the shape of the slabs, the existence of openings, the distribution of the vertical load, the type of the seismic excitations and the analysis method was investigated. The whole evaluation study led to the derivation of useful conclusions. [ABSTRACT FROM AUTHOR]

Damaged tires or ended-life tires represent a difficult problem due to their ability to sustain for a long time which are not able to be dissolved easily. Present study focuses on the ability of using the damaged tires strips (DTS) in the field of structural engineering as an innovative reinforcing material used additionally with the main reinforcement. The adopted technique in the present work represents a clean solution to reuse and recycle DTS to increase the ultimate flexural capacity of the reinforced concrete one-way and two-way slabs used in structural systems satisfying clean environment and economic considerations. The tests were conducted upon eight specimens of reinforced concrete one-way slabs (RCOWS) and two specimens of reinforced concrete two-way slabs (RCTWS) reinforced by the DTS as an additional reinforcement. Experimentally obtained results exhibited enhancement for the ultimate flexural load capacity of the RCOWS and RCTWS models reinforced by the DTS in the range of 16-80 and 14.28% respectively, compared to the original reference specimens. [ABSTRACT FROM AUTHOR]

This paper presents a study on the behavior of fiber reinforced concrete slabs using finite element analysis. A previously published finite element program is used for the nonlinear analysis by including the steel fiber concrete properties. Concrete is represented by degenerated quadratic thick shell element, which is the general shear deformable eight node serendipity element, and the thickness is divided into layers. An elastic perfectly plastic and strain hardening plasticity approach are used to model the compression behavior of concrete. The reinforcing bars were smeared within the concrete layers and assumed as either an elastic perfectly plastic material or as an elastic-plastic material with linear strain hardening. Cracks initiation is predicted using a tensile strength criterion. The tension stiffening effect of the steel fibers is simulated using a descending parabolic stress degradation function, which is based on the fracture energy concept. The effect of cracking in reducing the shear modulus and the compressive strength of concrete parallel to the crack direction is considered. The numerical results showed good agreement with published experimental results for two fibrous reinforced concrete slabs.

Punching shear behavior is experimentally investigated through testing a total of thirteen reinforced concrete flat slabs. Four different types of punching shear reinforcement configurations are examined, namely, ordinary closed rectangular stirrups (ST group), rectangular spiral stirrups (RSP group), advanced rectangular spiral stirrups (ARSP group), and circular spiral stirrups (SP group). Each configuration included three different spacings of 100, 150 and 200 mm. In addition, a reference slab specimen is cast without any punching shear reinforcement. The test results indicated that the circular spiral reinforcement scheme has the highest enhancement with regard to the punching shear capacity compared to the other reinforcement schemes. The percentage of enhancement of the SP group compared to the reference specimen ranges between 23% and 30%. For the other three different rectangular schemes, the enhancement of the punching shear strength for the RSP group and the ARSP group is in the range of 15–23% and 16–25%, respectively. Finally, the punching shear capacity of the ST group increased by 9–13% compared to the reference specimen. The shear carrying capacity of the specimens is also calculated using the ACI 318-19 code and Eurocode 2 equations. The results showed that both codes are capable of predicting the shear carrying capacity for all the schemes. Also, although both codes are conservative, the Eurocode 2 gives a better estimate of the shear carrying capacity than the ACI 318-19 code.

This study presents a macro-modeling method for analysis of reinforced and prestressed concrete slabs under soft and hard missile impact loads. The analysis method is based on the Modified Compression Field Theory, incorporating a rational approach based on fundamental principles of solid mechanics and eliminating the need for extensive material characterizations. An iterative self-calibrating procedure was developed and implemented into a finite element analysis framework to systematically determine element erosion limits and damping coefficients, expanding the applicability range of the analysis method. Two different implementation methods for incorporating damping into the analysis formulation are investigated. Special considerations are given to modeling strain rate effects and advanced material mechanisms. The performance of the analysis method is evaluated through modeling 12 missile impact tests from the literature as well as conducting a series of analytical parametric studies. The analysis results show that the proposed modeling method is an efficient and reliable approach for analysis of concrete slabs under impact loading capable of capturing localized damages and shear failures. [ABSTRACT FROM AUTHOR]

Damaged tires or ended-life tires represent a difficult problem due to their ability to sustain for a long time which are not able to be dissolved easily. Present study focuses on the ability of using the damaged tires strips (DTS) in the field of structural engineering as an innovative reinforcing material used additionally with the main reinforcement. The adopted technique in the present work represents a clean solution to reuse and recycle DTS to increase the ultimate flexural capacity of the reinforced concrete one-way and two-way slabs used in structural systems satisfying clean environment and economic considerations. The tests were conducted upon eight specimens of reinforced concrete one-way slabs (RCOWS) and two specimens of reinforced concrete two-way slabs (RCTWS) reinforced by the DTS as an additional reinforcement. Experimentally obtained results exhibited enhancement for the ultimate flexural load capacity of the RCOWS and RCTWS models reinforced by the DTS in the range of 16–80 and 14.28% respectively, compared to the original reference specimens.

The present paper proposes a new finite element formulation for the analysis of RC slabs, accounting for concrete cracking and reinforcement yielding. The proposed formulation, developed within the framework of Lumped Damage Mechanics, considers that all inelastic effects are localized in lines and relates all numerical parameters to the mechanical properties of the slab. The proposed variational approach is presented as a Nash noncooperative equilibrium point. It is verified, numerically, that the proposed FE leads to mesh-independent results. Numerical simulations of some experimental tests are also presented. The results in terms of collapse mechanism, cracking network, and force-deflection curves showed that the model has significant accuracy, even for non-symmetric free clamped and simple supported boundary conditions. It is also shown, through the confrontation with experimental results, that the model correctly characterizes the initiation and development of complex networks of cracks. • A new lumped damage model is proposed for reinforced concrete slabs. • The proposed approach is presented as a Nash noncooperative equilibrium point. • The numerical results are quite close to experimental ones. • The numerical cracking pattern is in agreement with the experiments. [ABSTRACT FROM AUTHOR]

We consider the problem of finding the optimal location of point supports under a monolithic reinforced concrete floor slab, which provides the minimum of the objective function. The maximum deflection, potential strain energy, and reinforcement consumption are selected as the objective function. The load and plate configuration can be arbitrary. A restriction on the number of supports is introduced. The solution is performed using stochastic and deterministic optimization methods in combination with the finite element method to determine the objective functions An assessment of the proposed methods for a different number of supports n is made. Particular solutions are presented for n = 3,4,5.The optimal relations between the marginal and middle spans are established for buildings with a rectangular grid of columns with large n. It is shown that only the pitch of the columns of the marginal rows can act as a variable parameter, and the steps of the middle rows at the optimal arrangement are equal to each other. The developed methods were tested for the real object. It is established that of the three criteria used, the criterion of the minimum potential strain energy is preferable. It was also revealed that in most of the considered problems, the selected criteria give very close results. The plate thickness and material characteristics do not affect the optimal arrangement of columns.

This paper proposes a novel simplified analytical approach, named the slab strip model, to assess the ultimate bearing capacity of reinforced concrete (RC) two-way slabs when large deflections are reached and tensile membrane action plays a key role. The motivation for the work derives from the fact that in recent years, investigations into the behaviour and modelling of laterally restrained and unrestrained RC slabs have been intensified owing to the reserve of bearing capacity provided by the tensile membrane action. The approach has been developed in the framework of the strip method and analyses the tensile membrane effect. Two failure criteria are accounted for: the maximum ultimate slab strip elongation and the maximum ultimate rotation of the structure at the supports. The rationality of the proposed approach is validated for laterally restrained slab strips and two-way laterally unrestrained simply supported slabs by comparing the analytical results with experimental data from the literature. The results show that despite its simplicity the method is accurate in estimating the load-carrying capacity of RC two-way slabs able to develop significant tensile membrane action. For its characteristics, the proposed method can be considered a useful initial design tool in a robustness context for conducting alternative load path analysis of RC structures characterised by two-way slabs. [ABSTRACT FROM AUTHOR]

In the present study, new models are proposed for tension stiffening and cracked shear modulus to study their effect on the response of the slab. These models are used in the nonlinear analysis of High Strength Steel Fiber Reinforced Concrete (HSSFRC) slabs. The suggested models have multiple shapes depending on the curvature factor, these models are compared with the wellknown formulas used in previous studies and great agreements are achieved. The Serendipity “eight-node” element type has been adopted for representing the concrete and layered approach is used to simulate the concrete elements and a smeared layer approach is used to represent the steel reinforcement. The concrete compression behavior is modeled using strain hardening plasticity method, the first two stress invariants of the yield condition is used. For finite element analysis, a computer program coded in Fortran 90 is developed and used for performing nonlinear analysis on the slabs. In order to check the validity of the current models, many actual results for testing slabs “in the laboratory” are compared with the results from the present study and a great agreement is achieved. All studied slabs were simply supported from four sides and loaded with concentrated load at the middle of the slab, but slab S5 is simply supported by two opposite parallel sides with line load parallel to the supports at the middle of the span of the slab. For the curvature factors (Bt, Bg) it is found that the values (Bt =0.005-0.5, Bg =0.001-0.05) give the best simulation for the slab. The effect of tension stiffening model is more than the effect of cracked shear modulus model and there is an interaction between tension stiffening and cracked shear modulus models. [ABSTRACT FROM AUTHOR]

This study presents the performance of carbon textile reinforcement used as strengthening layers for reinforced concrete (RC) slabs under repeated impact loads. In order to reveal the contribution of carbon textile reinforcement to the behavior of RC slabs under impacts, five identical RC slabs with the dimensions of 1.5 m × 1.5 m × 0.20 m were manufactured and tested at the Technische Universität Dresden. To understand failure mechanisms of RC slabs under impact loadings, two specimens were kept unstrengthened and tested under different impact velocities. The rest of the specimens was strengthened with three different carbon textile reinforcements embedded in an additional 2 cm fine‐grained concrete layer and subjected to impact loads with the same striker velocity. The results observed from the tests revealed that the carbon textile reinforcement is very effective at increasing the impact capacities of the specimens. Additionally, displacement–time histories and crack profiles are highly affected due to the carbon textile reinforcement types and ratios during the impact loadings. [ABSTRACT FROM AUTHOR]

In this paper, the punching shear behavior of interior slab-rectangular column connections without shear reinforcement under static concentric loading is studied using a three-dimensional, nonlinear, finite element model (FEM) in ABAQUS version 6.12 based on the concrete damaged plasticity model. The FEM was calibrated based on seven experimental tests selected from literature. The predicted shear capacities were compared to punching and one-way shear predictions according to published standards and the critical shear crack theory (CSCT). The finite element analysis results show that the impact of column rectangularity on punching shear capacity is not only dependent on the column aspect ratio but becomes more severe as the ratio of the minimum column dimension to the effective depth of the slab increases. This behavior was found to be implicitly accounted for in some published European standards and the CSCT. [ABSTRACT FROM AUTHOR]

Tests on Shear Behaviour with Concurrent Normal Tensile Action Reinforced concrete (RC) slabs under shear loading can sometimes be subjected to additional normal tensile stresses. Examples are slabs under constraint stresses, RC bridge deck slabs of composite arch bridges or silo walls. The coefficient for normal stresses in the current design approach for shear without shear reinforcement according to Eurocode 2 (EC2) was calibrated using tests on prestressed simply supported beams. The influence of normal tensile forces is only approximately covered by the design approach. Therefore, tests were carried out at the Institute of Structural Concrete at RWTH Aachen University on slab strips under shear and simultaneous tensile normal force loading. In addition to single‐span slab segments, tests on continuous members were also carried out to investigate the influence of more realistic structural systems. The point of contraflexure in multi‐span systems results in an area without bending stresses, which divides the shear span into two regions (sagging and hogging moment area). Since the critical shear crack usually develops from a flexural crack for flexural shear failure, the load‐bearing behaviour is influenced by the loading conditions on the one hand and by the combined normal and flexural loading on the other hand. Contrary to the linear approach for the influence of the normal stress in the EC2, a degressive influence of the tensile normal stress on shear capacity was found in the own experimental investigations as well as in tests from literature review with increasing tensile stress. [ABSTRACT FROM AUTHOR]

This study examines the flexural behavior of reinforced concrete (RC) one-way slabs strengthened with near-surface mounted (NSM) basalt fiber-reinforced polymer (BFRP) bars. Ten RC slabs were subjected to four-point loading until failure. Various parameters including the steel reinforcement ratio (0.48and 0.95%), the NSM-BFRP reinforcement ratio (0.17, 0.25, and 0.35%), and two types of epoxy adhesives (Sikadur-30 and NSM-Gel) were investigated. The experimental results demonstrated the remarkable efficacy of the NSM-BFRP bars in enhancing the flexural performance of the strengthened slabs, especially those with lower steel reinforcement ratios. Compared to the control slabs, the ultimate loads were increased by 51‐123% and 21‐44% for slabs with 0.48 and 0.95% steel reinforcement ratios, respectively, while the ductility indices were increased by 10‐53% and 29‐79%. The type of the epoxy adhesive used had minimal impact on the flexural behavior of the strengthened slabs. Failure primarily occurred due to steel yielding followed by the rupture of the NSM-BFRP bars or by concrete crushing, depending on the reinforcement ratio provided. The cracking, yield, and ultimate loads of the strengthened slabs were predicted using the formulations of ACI 440.2R [3] guideline. Good agreement between the predicted and the experimental results were obtained, with ACI formulations being on the conservative side. • NSM-BFRP increased slab load capacity by up to 124%. • Effectiveness of NSM-BFRP varied based on steel reinforcement ratios. • Strengthened slabs exhibited improved ductility with ductility indices increasing up to 79%. • Failure modes differed based on both steel and NSM-BFRP reinforcement ratios. • Experimental results aligned well with ACI 440.2 R (2017) predictions. [ABSTRACT FROM AUTHOR]

This paper’s objective is to provide simple design relations for the reinforced concrete slabs by a hybrid reinforcing of uniaxial or triaxial geogrids in addition to steel rebars. We hope this can provide guidance for further researchers to estimate the flexural bending capacity of the concrete slabs, the necessary grade of uniaxial or triaxial geogrids, and the necessary count of uniaxial or triaxial geogrids’ layers by conducting first-principles analytical, quantitative analyses for a previously published concrete slabs’ experimental data of reinforced concrete slabs by hybrid reinforcing of steel rebars and uniaxial or triaxial geogrids. Throughout this paper, simple design relations were added to estimate the concrete slabs’ experimental moment at the post-peak load based on the assumption that the uniaxial or triaxial geogrids’ tensile force (as concrete slab’s reinforcement) is equal to its peak tensile strength (obtained by the experimental axial tensile test). This resulted in a variance that frequently has a range of ±10% when compared with the actual experimental data. For more accuracy, simple design relations were added to estimate the uniaxial or triaxial geogrids’ characteristic tensile force at the post-peak load, which resulted in an estimated concrete slab’s experimental moment at the post-peak load with a variance that frequently has a range of ±5% when compared with the actual experimental data.

Six one-way reinforced concrete slabs, simply supported along the short sides by means of corbels (dapped ends), were recently tested for bending and shear behavior in Milan under two different crosswise load distributions and with three partially different reinforcement layouts in the supporting corbels and in the main body (size 2200 x 1300 mm [7.22 x 4.27 ft]; thickness/length ratio close to 1/14; corbel depth and overhang/length ratio close to 1/23). The tests in bending under the service loads and in shear up to and beyond the peak load show that load crosswise-distribution plays a minor role. In shear, the quite complex crack patterns in the D-regions close to the dapped ends clearly indicate the formation of very effective strut-and-tie systems if the bottom bars of the main body are bent up, and of shallow arch-and-tie systems if the same bars are straight. In the former case, a proper introduction of the bond along the tension bars of the corbels is a must to define the position of bond-related joints and to make strut-and-tie models more reliable in predicting the bearing capacity, while in the latter case, the design equations provided by the codes for constantsection shear-unreinforced beams (ACI 318, EC2, and fib Model Code 2010) prove to be adequate also in the case of corbels. [ABSTRACT FROM AUTHOR]

In this study, reinforced concrete slabs in two groups, having 0.004 (D1 series) and 0.002 (D2 series) longitudinal reinforcement ratios in two orthogonal directions, were cast with concrete mixes containing 0%, 0.5%, 1% and 1.5% steel fiber ratios in volume. Slabs were 2150x2150x150 mm in dimensions. Eight slabs were tested in total under static loads. For slabs without steel fibers, the slab with higher reinforcement ratio showed punching failure before the yielding of longitudinal bars, whereas the slab with lower reinforcement ratio displayed a significantly higher ductility before final punching failure. Addition of steel fibers increased the punching load capacity up to two times. However, although addition of steel fibers also increased the maximum displacements in D1 series slabs, it did not make any significant effect on the maximum displacements of D2 series slabs. Maximum displacements were still controlled by the yielding of longitudinal reinforcement. Increasing the steel fiber ratio increased both the punching capacity and the maximum displacements in D1 series slabs, but it did not make a significant difference in behavior of D2 series beyond 1% fiber ratio. An analytical study of the test specimens were also performed using Critical Shear Crack Theory and based on comparisons of experimental and analytical results some improvements in the model were proposed. [ABSTRACT FROM AUTHOR]

For reinforced concrete structures, as beams, slabs or walls, failure under bending is well known and its description and design is relatively internationally agreed. However for the shear failure phenomenon, there is not yet a common agreement at the international level, no consensus is reached on the subject at this time. Many parameters are involved in the shear resistance mechanism and many phenomena coexist. The shear force transfer mechanisms are sometimes complex and difficult to discern. By analyzing the different shear design codes, some shear parameters are taken into account and ignored by others, which makes that a shear effect may be omitted. In addition, different ways are adopted to take into account the different shear parameters. The main purpose of this study is to help the engineering by presenting a comparative study of all the main analytical models for the determination of shear capacity: The EN 1992-1-1:2005 standard (EC2) (CEN, 2005), French National Annex (FD P 18-717, 2013), ACI 318-14 (ACI Committee 318, 2014), fib Model Code 2010 (Fib Model Code 2010, 2012) using level of approximation LoA I and LoA II and (CSA Committee A23.3, 2004) both Modified Compression Field Theory (MCFT) based models, and finally the Critical Shear Crack Theory (CSCT) which is the basis of the Swiss standard SIA 262 (SIA 262, 2003) are all examined. The results obtained are discussed regarding their agreement with eighteen shear experimental results on thick slabs (30 cm, 35 cm, and 40 cm) and thin slabs (10 cm) without shear reinforcement. [ABSTRACT FROM AUTHOR]

In several areas worldwide, the high cost and shortage of natural resources have encouraged researchers and engineers to explore the serviceability and feasibility of using recycled aggregates in concrete mixtures, substituting a normal aggregate percentage. This technique has advantages for the environment by reducing the accumulation of waste materials, while it impacts the fresh and hardened concrete performances, reducing workability, flexural strength, compressive strength, and tensile strength. However, most studies have investigated the influence of replacing normal aggregates with waste aggregates on the concrete mechanical properties without examining the impact of using waste materials on concrete structural performance. The aim of this research is to investigate the effect of replacing 75% of sand volume with polyvinyl chloride (PVC) fine waste aggregates on the performance of reinforced concrete slabs. Different thicknesses of the concrete layer (0%, 25%, 50%, and 100% of slab thickness) containing PVC fine waste aggregates are investigated. Based on the reductions in the toughness and flexural strength capacity due to incorporating 75% PVC fine aggregate dosage, two approaches are used to strengthen the slabs with 75% PVC fine aggregates. The first approach is adding polyvinyl alcohol (PVA) to the PVC fine aggregate concrete mix to improve the mechanical properties of the concrete. The PVA increases the water viscosity in the concrete, which reduces the dry out phenomenon. With that said, the PVA modified fresh concrete does enable the use of the limits of the PVC fine aggregate dosage for high dosage plastic aggregate concrete. The second approach uses two fiber wire mesh layers as an additional reinforcement in the tested slab. Results show that the PVC-30 slab exhibits an 8% decrease in total area toughness compared to the control (Con) slab, while for PVC-60 slab toughness, the total area shows 26% less. Additionally, the inclusion of PVA in the concrete with 75% PVC plastic waste fine aggregate replacement greatly influences the pre-and post-cracking ductile performance among other slabs, representing that using PVA with higher contents might increase the flexural performance. Therefore, due to the substantial effect of PVA material on the concrete flexural performance, it is proposed to utilize PVA with an optimum PCV fine aggregate dosage in the concrete mix.