Steel Fiber Reinforced High Strength Concrete Research Articles

Effects of amount and geometrical properties of steel fiber on shear behavior of high-strength concrete beams without shear reinforcement

This study aims to investigate the effects of the geometrical properties and volume content of steel fibers on the shear resistance of reinforced high-strength concrete (HSC) beams without stirrups. Hooked-end and twisted steel fibers with different aspect ratios ranging from 60 to 100 were used at volume fractions of 0.5%–1.0%. The shear strength of HSC beams without stirrups significantly increased due to the addition of steel fibers and by increasing their volume fraction by up to 1.0%, resulting in approximately 1.7 times higher shear resistance. A higher fiber aspect ratio was effective in improving the resistance to shear failure of HSC beams without stirrups and in enhancing beam deformability relative to the increase in shear strength. Using twisted steel fibers led to better shear resistance than hooked-end steel fibers, resulting in 1.11- and 3.34-times higher shear strength and ductility at the same fiber volume fraction on average. The shear strength of steel fiber-reinforced concrete (SFRC) beams was also predicted using eight different models. Narayanan's model most precisely predicted the shear strengths of reinforced SFRC beams without shear reinforcement, with an average vu,exp/vu,pred ratio of 1.16. The shear strength increased with the decrease in shear span-to-depth (a/d) ratio and the increase in the fiber factor. The contribution of steel fibers to shear strength was greater for deep beams than slender beams. The predicted shear strengths of deep beams and high-strength SFRC showed a significant deviation from the actual value and required careful consideration.

Shear Bearing Capacity of Steel-Fiber-Reinforced Concrete Shear Wall under Low-Cycle Repeated Loading Based on the Softened Strut-and-Tie Model

In this paper, the loading mechanism of steel-fiber-reinforced concrete (SFRC) shear wall (SW) under low-cycle repeated loading is analyzed, and the softened strut-and-tie model (SSTM) of SFRC SW composed of horizontal and vertical resistant members and diagonal strut is proposed, in which the contributions of distributed web reinforcement, concrete, and steel fiber (SF) to the shear bearing capacity (SBC) of SFRC SW is identified. Furthermore, a new algorithm to obtain the SBC of SFRC SW is established, and then it is validated by using the test results of steel-fiber-reinforced high-strength concrete (SFHSC) SW and SFRC SW under low-cycle repeated loading. The results show that the calculated values are in good agreement with the experimental values for the 11 SFRC SWs, and the average strength ratio between calculated and experimental values (Vjh,t/Vjh,c) is 0.958. Therefore, the proposed calculation method is scientific and accurate for analyzing and predicting the SBC of SFRC SW. In addition, the proposed calculation method can scientifically and accurately analyze and predict the SBC of SFRC SW.

Sustainable design framework for enhancing shear capacity in beams using recycled steel fiber-reinforced high-strength concrete

According to a recent estimate, over 1.5 billion wasted tyres which containing over 40% of vulcanised rubber and 15% of steel fibre are discarded yearly, which posing a serious threat to circular economy implementation and transition to net zero. To minimise the greenhouse gas(GHG) emission and the environmental side effect caused by burning and burying these waste tyres, recycling and reusing these materials for sustainable structural designs has become the centre of attention. This paper focuses on applying recycled bead steel fibre to improve the shear capacity of fibre-reinforced concrete beams. Moreover, the existing national standard known as Eurocode 2 and TR63 can hardly illustrate the relationship between fibre and high-strength concrete. This study is the first to investigate shear behaviours of high-strength industrial and recycled steel fibre reinforced concrete beams with consideration of different shear span ratios. Therefore, twenty real-scale beams are constructed to examine the shear capacity of high-strength industrial and recycled steel-fibre reinforced concrete beams, which aims to compare the improvement of shear strength through experiments and identify different shear strength improvements of the two categories of steel fibre. Besides, comprehensive data of 164 beams from previous studies have been collected to benchmark with the experimental results for the formula design. This study proves the feasibility of replacing industrial steel with recycled steel fibre to improve the shear capacity of fibre-reintroduced concrete beams. Moreover, there are six novel equations designed developed using Eurocode 2 and TR63 as a basis in this study. Based on the findings of the paper, the proposed formulas demonstrate remarkable accuracy, with an average value of 0.982 and standard deviation of 0.213, respectively. Following an exhaustive comparison of RSF and ISF reinforced concrete beams, with a focus on economic expenditure and GHG emissions, it can be concluded that RSF offers superior economic and environmental benefits, which reduce the emissions up to 25.39% and price up to 28.04% when replacing ISF 0.8% RSF, respectively.

Rapid-Hardening and High-Strength Steel-Fiber-Reinforced Concrete: Effects of Curing Ages and Strain Rates on Compressive Performance.

High-strength steel-fiber-reinforced concrete (HSFRC) has become increasingly popular as a cast-in-place jointing material in precast concrete bridges and buildings due to its excellent tensile strength and crack resistance. However, working conditions such as emergency repairs and low-temperature constructions require higher demands on the workability and mechanical properties of HSFRC. To this end, a novel rapid-hardening HSFRC has been proposed, which is produced using sulphoaluminate cement (SC) instead of ordinary Portland cement. In this study, quasi-static and dynamic tests were carried out to compare the compressive behavior of conventional and rapid-hardening HSFRCs. The key test variables included SC replacement ratios, concrete curing ages, and strain rates. Test results showed: (1) Rapid-hardening HSFRC exhibited high early strengths of up to 33.14 and 44.9 MPa at the curing age of 4 h, respectively, but its compressive strength and elastic modulus were generally inferior to those of conventional HSFRC. (2) The strain rate sensitivity of rapid-hardening HSFRC was more significant compared to its conventional counterpart and increased with increasing curing ages and strain rates. This study highlights the great potential of rapid-hardening HSFRC in rapid bridge construction.

Experimental Investigation on Shear Capacity of Steel-Fiber-Reinforced High-Strength Concrete Corbels.

As short cantilever members, corbels are mainly used to transfer eccentric loads to columns. Because of the discontinuity of load and geometric structure, corbels cannot be analyzed and designed using the method based on beam theory. Nine steel-fiber-reinforced high-strength concrete (SFRHSC) corbels were tested. The width of the corbels was 200 mm, the cross-section height of the corbel column was 450 mm, and the cantilever end height was 200 mm. The shear span/depth ratios considered were 0.2, 0.3, and 0.4; the longitudinal reinforcement ratios were 0.55%, 0.75%, and 0.98%; the stirrup reinforcement ratios were 0.39%, 0.52%, and 0.785%; and the steel fiber volume ratios were 0, 0.75%, and 1.5%. According to the test results, this paper discusses the failure process and failure mode of corbel specimens with a small shear span/depth ratio and analyzes the effects of variables such as shear span/depth ratio, longitudinal reinforcement ratio, stirrup reinforcement ratio, and steel fiber volume content on the shear capacity of corbels. The shear capacity of corbels is significantly affected by the shear span/depth ratio, followed by the longitudinal reinforcement ratio and the stirrup reinforcement ratio. Moreover, it is shown that steel fibers have little impact on the failure mode and ultimate load of corbels, but can enhance the crack resistance of corbels. In addition, the bearing capacities of these corbels were calculated by Chinese code GB 50010-2010 and further compared with ACI 318-19 code, EN 1992-1-1:2004 code, and CSA A23.3-19 code, which adopt the strut-and-tie model. The results indicate that the calculation results by the empirical formula in the Chinese code are close to the corresponding test results, while the calculation method based on the strut-and-tie model of a clear mechanical concept yields conservative results, and hence the related parameter values must be further modified.

Axial compressive behavior of square concrete-filled steel tube columns with high-strength steel fiber-reinforced concrete

Adding fibers in the concrete is a practical approach to improving the deformation capacity of square concrete-filled steel tube (CFST) columns with high-strength concrete (HSC). To investigate the axial compressive behavior of square CFST columns with high-strength steel fiber-reinforced concrete (HSSFRC), 23 specimens were tested under monotonic axial compression, among which five specimens used an innovative testing method to directly obtain the load components of the steel tube and concrete infill. The test variables included the concrete compressive strength, the fiber volume fraction, and the yield strength and width-to-thickness ratio of the steel tube. The test results demonstrated that adding steel fiber basically did not change the failure modes of the specimens. In general, better postpeak behavior was observed as the fiber volume fraction increased; however, for the specimens with 130 MPa matrix concrete, adding steel fibers of a volume fraction of 0.75% basically did not bring any improvement. When the confinement index was between 0.29 and 1.43, the compressive strengths of the HSC or HSSFRC in square CFST columns were close to the corresponding unconfined concrete strengths. Based on the test results, an average stress–strain model was developed for the HSC or HSSFRC in square CFST columns.

Bond Behavior between High-Strength Rebar and Steel-Fiber-Reinforced Concrete under the Influence of the Fraction of Steel Fiber by Volume and High Temperature

Steel-fiber-reinforced concrete (SFRC) is a composite material made by randomly distributing short steel fibers in normal concrete (NC). In this study, central pull-out tests of 32 specimens were performed to investigate the bond behavior between high-strength rebar and SFRC under the influence of the fraction of steel fiber by volume (Vf = 0%, 0.5%, 1.0% and 1.5%) and temperature (T = 20, 200, 400 and 600 °C). The results show that in NC specimens, splitting failure occurs below 400 °C, while split-pullout failure occurs above 600 °C. Split-pullout failure occurs in all SFRC specimens at each tested temperature. The bond strength between rebar and SFRC was found to decay significantly between 400 and 600 °C. The effect of Vf on the improvement in bond strength was more obvious between 400 and 600 °C than between 20 and 400 °C. The positive contribution of steel fibers to bond behavior is the construction of a rigid skeleton with coarse aggregates that can play a bridging role and effectively retard the expansion of concrete cracks. This improves the bond strength between rebar and SFRC at high temperatures. The bond–slip curve can be divided into five stages, namely the initial micro-slide phase, slip phase, splitting failure phase, stress drop phase and residual pull-out phase. A model of the bond–slip relationship between rebar and SFRC considering temperature and Vf was developed by modifying the existing model of the bond–slip relationship between rebar and NC. The model calculation results agree well with those of testing.

Fatigue behavior and calculation methods of high strength steel fiber reinforced concrete beam

Adding steel fibers into concrete was considered as one of the most effective ways to restrain the crack development and improve the stiffness for reinforced concrete (RC) structures. To explore the reinforcement mechanism of steel fibers on the fatigue behavior of high-strength RC beam, eight high-strength steel fiber reinforced concrete (HSSFRC) beams subjected to fatigue loading were tested in this study. The main design parameters considered in this work were stress level and steel fiber content. The failure mode, crack patterns, fatigue life, crack width, and stiffness degradation of HSSFRC beams under fatigue loading were discussed. The results showed that steel fibers could significantly increase the fatigue life, restrain crack development, and improve crack patterns of HSSFRC beams under fatigue loading compared to ordinary RC beams. Both the crack width and stiffness degradation rate of beams decrease with increasing steel fiber content. Besides, the empirical formulas for calculating the maximum crack width and midspan deflection of HSSFRC beam under fatigue loading were proposed and validated using experimental results.

Using Machine Learning Algorithms to Estimate the Compressive Property of High Strength Fiber Reinforced Concrete.

The low tensile strain capacity and brittle nature of high-strength concrete (HSC) can be improved by incorporating steel fibers into it. Steel fibers’ addition in HSC results in bridging behavior which improves its post-cracking behavior, provides cracks arresting and stresses transfer in concrete. Using machine learning (ML) techniques, concrete properties prediction is an effective solution to conserve construction time and cost. Therefore, sophisticated ML approaches are applied in this study to predict the compressive strength of steel fiber reinforced HSC (SFRHSC). To fulfil this purpose, a standalone ML model called Multiple-Layer Perceptron Neural Network (MLPNN) and ensembled ML algorithms named Bagging and Adaptive Boosting (AdaBoost) were employed in this study. The considered parameters were cement content, fly ash content, slag content, silica fume content, nano-silica content, limestone powder content, sand content, coarse aggregate content, maximum aggregate size, water content, super-plasticizer content, steel fiber content, steel fiber diameter, steel fiber length, and curing time. The application of statistical checks, i.e., root mean square error (RMSE), determination coefficient (R2), and mean absolute error (MAE), was also performed for the assessment of algorithms’ performance. The study demonstrated the suitability of the Bagging technique in the prediction of SFRHSC compressive strength. Compared to other models, the Bagging approach was more accurate as it produced higher, i.e., 0.94, R2, and lower error values. It was revealed from the SHAP analysis that curing time and super-plasticizer content have the most significant influence on the compressive strength of SFRHSC. The outcomes of this study will be beneficial for researchers in civil engineering for the timely and effective evaluation of SFRHSC compressive strength.

Flexural Tensile Behavior of Single and Novel Multiple Hooked-End Steel Fiber–Reinforced Notched Concrete Beams

Novel multiple hooked-end steel fibers possessing high anchorage with the concrete matrix have been invented and are desired to achieve significant improvement in the performance of steel fiber–reinforced concrete (SFRC). In this study, C50/C70/C80 notched concrete beams containing 4D steel fibers with 1.5 hooked ends at a dosage of 0–110 kg/m3, 5D fibers with double hook-ends at a dosage of 0–110 kg/m3, and 3D steel fibers with a single hooked end at a dosage of 0–70 kg/m3 were tested under three-point bending. The experimental results indicated that increasing fiber dosage and the number of hooked ends were generally effective in improving the flexural tensile behavior of concrete beams, especially high-strength concrete beams. The two linear relationships of the equivalent flexural tensile strength feq,2 and feq,3, evaluated by RILEM TC 162-TDF, as well as the residual flexural tensile strength fr,1 and fr,4, evaluated by BS EN 14651, were confirmed to be appropriate for concrete beams reinforced by 3D, 4D, and 5D steel fibers. Based on the experimental results from this study and more in the literature, the analytical equation, proposed by Naaman et al. and simplified by Pajak et al., was verified to be reliable for predicting the maximum flexural tensile strength for concrete beams reinforced by 3D, 4D, and 5D steel fibers. Furthermore, the analytical equation, proposed by Venkateshwaran et al., that can explicitly take into account the effects of concrete compressive strength, fiber volume fraction, fiber aspect ratio, fiber length, and number of fiber hook ends, was modified for predicting the residual flexural tensile strength (fr,i) of novel multiple hooked-end SFRC. It was found that the modified Venkateshwaran et al. equation was approved as valid for high-strength SFRCs in this study, whereas the original one only applies for low-strength and normal-strength SFRCs. All these represent a step forward in advancement on the knowledge and understanding of SFRC with novel multiple hooked-end steel fibers.

Centrifuge modelling of ultra-thin high strength steel fibre reinforced concrete pavements

Ultra-thin continuously reinforced concrete pavement (UTCRCP) is an innovative pavement type that consists of a 50 mm high strength steel fibre reinforced concrete (HS-SFRC) layer overlain on a pavement substructure. The thickness results in a flexural stiffness significantly smaller than for conventional concrete pavements. In this paper, the conceptual understanding of the response of UTCRCP to traffic loading was investigated using centrifuge modelling. Simplified pavement models were subjected to a bidirectional moving axle load. The results indicated that axle loading, and not single wheel loading, should be used to investigate the response of UTCRCP as there is significant interaction in substructure deformation caused by the wheels on the ends of an axle. Due to the flexural toughness of the highly reinforced concrete layer, a gap forms between the ultra-thin HS-SFRC overlay and its substructure. Brittle, cemented bases between the HS-SFRC overlay and subgrade should be used with caution, as the flexible nature of the layers above and below the stabilised layer may result in rapid degeneration of the brittle layer.

Load spreading in ultra-thin high-strength steel-fibre-reinforced concrete pavements

Ultra-Thin Continuously Reinforced Concrete Pavement (UTCRCP) consists of a 50 mm thin High-Strength Steel-Fibre-Reinforced Concrete (HS-SFRC) overlay placed on existing pavements as rehabilitation or used as part of new pavements. Difficulties have been experienced with the construction of UTCRCP. Additionally, the thin HS-SFRC has superior fatigue properties, but poor load-spreading ability compared to conventional concrete pavements due to its reduced thickness. This results in high deflections when the pavement is loaded. The substructure of UTCRCP plays an important role in its performance. Cement-stabilised granular materials can be used to ensure gradual load spreading with depth, but its behaviour under flexible concrete layers is not yet well understood. In this study the effect of increasing the HS-SFRC layer thickness and the effect of incorporating cement-stabilised base layers were investigated using linear elastic finite element modelling. From stress levels calculated, it was found that C1 and C2 materials perform well underneath a 50 mm HS-SFRC layer subjected to standard axle loads of 80 kN, while C3 and C4 would deteriorate faster. Stabilised layers placed below a thin, flexible concrete layer may however crack, resulting in increased damage to supporting layers. It is recommended that the response of UTCRCP should be investigated using advanced material models for the cement-stabilised base and other substructure layers.

Research on the Fracture Behavior of Steel-Fiber-Reinforced High-Strength Concrete.

The behavior of steel fiber concrete, which is the most widely used building material, has been widely examined. However, methods for calculating Fracture parameters differ by fracture behavior of SFHSC with different strengths. In this study, the fracture behavior of steel-fiber-reinforced high-strength concrete (SFHSC) was -investigated using three-point bending tests. A total of 144 notched concrete beams with a size of 100 mm × 100 mm × 515 mm were tested for three-point bending in 26 groups. The effects of the steel fiber volume ratio, steel fiber type, and relative notch depth on the fracture toughness (KIC) and fracture energy (GF) of SFHSC specimens were studied. The results show that an increase in the volume fraction of steel fiber (ρf) added to high-strength concrete (HSC) significantly improves the fracture behavior of HSC. As compared to milled and sheared corrugated steel fibers, cut bow steel fibers significantly improve the fracture behavior of SFHSC. The effect of incision depth changes on the KIC and GF of SFHSC and HSC for the comparison group has no common characteristics. With an increase in incision depth, the values of KIC of the SFHSC specimens decrease slightly. The GF0.5/GF0.4 of the SFHSC specimens show a decreasing trend with an increase in ρf. According to the test results, we propose calculation models for the fracture behavior of SFHSC with different strengths. Thus, we present a convenient and accurate method to calculate fracture parameters, which lays a foundation for subsequent research.

Machine learning prediction of structural response of steel fiber-reinforced concrete beams subjected to far-field blast loading

Owing to its superior mechanical properties, enhanced energy absorption, and improved blast resistance, steel fiber-reinforced cementitious composites are a prime choice for the development of resilient structures. Sizable advancements have recently been made in assessing the blast performance of steel fiber-reinforced concrete (SFRC), high-strength steel fiber-reinforced concrete (HSFRC), and ultra-high-performance steel fiber-reinforced concrete (UHPFRC). However, there is still need for concerted research to explore the effects of fiber parameters under blast loading and to develop simple and robust predictive models. Thus, the present study develops a machine learning model to predict the maximum displacement of SFRC, HSFRC, and UHPFRC beams subjected to far field blast loading. Using Gaussian Process (GP) regression and Conditional Tabular Generative Adversarial Networks, a novel model was developed considering 117 experimental and 300 synthetic datasets. The proposed model was appraised through several statistical performance metrics and compared to existing analytical and numerical methods. The model imparts noteworthy reduction in modeling complexity in terms of static and dynamic material properties. A parametric analysis was conducted using the developed model to investigate the effects of fiber properties for diverse beam configurations. The proposed simplified model achieved highly favorable predictive performance with MAE of 2.75, R2 of 90.32%, and MAPE of 13.8%.

Seismic performance evaluation and experimental validation of steel-fiber-reinforced high-strength-concrete composite shear walls

The seismic performance evaluation method for the Steel-fiber-reinforced High-strength-concrete (SFRHSC) composite shear walls are studied in this paper. Currently, seismic design codes do not include such high-performance elements, due to the lack of reliable predictive equations for the lateral load bearing capacity and the deformation capacity, which are essential quantities in design. In this study, the capacity predictive equations for the wall element are proposed, corresponding to four different performance levels with “flexure-dominated failure” mode. Cross-sectional analysis on stress and strain with a series of parameters determined according to experimental results is used to attain the predictive equations. The constitutive models for unconfined and confined SFRHSC considering fiber-bridging action are developed and discussed. Additionally, the flexural and shear displacements are quantified separately to allow the estimation of the total deformation. The accuracy of such equations is validated against experimental results, from which it is ascertained that the proposed models are able to accurately predict both the material and the element behavior. The results of this study are relevant for the development of the next generation of seismic design codes.

Seismic Behavior of Steel-Fiber-Reinforced High-Strength Concrete Shear Wall with CFST Columns: Experimental Investigation

To improve the seismic behavior of shear walls, a new composite shear wall composed of a steel-fiber-reinforced high-strength concrete (SFRHC) web and two square concrete-filled steel tube (CFST) columns, namely a steel-fiber-reinforced concrete shear wall with CFST columns, is proposed in this paper. Therefore, the main purpose of this paper is to present an experimental investigation of the seismic behavior of the SFRHC shear wall with CFST columns. Pseudo-static tests were carried out on seven composite shear walls, and the seismic performance of the shear walls was studied and quantified in terms of the aspects of energy consumption, ductility and stiffness degradation. Furthermore, the experimental results indicated that adding steel fiber can effectively restrain the crack propagation of composite shear walls and further help to improve the ductility and energy dissipation capacity of composite shear walls and delay the degradation of their lateral stiffness and force. Moreover, the seismic behavior of the SFRHC shear wall with CFST columns was obviously superior to that of the conventionally reinforced shear wall, in terms of load-bearing capacity, ductility, stiffness and energy dissipation capacity, because of the confinement effect of the CFST columns on the web. Finally, the preliminary study demonstrated that the composite shear wall has good potential to be used in regions with high seismic risk.

Analytical Model for the Design of HSFC and UHSFC Jackets with Various Steel Fiber Volume Fraction Ratios for the Retrofitting of RC Beam-Column Joints

High-strength steel fiber-reinforced concrete (HSFC) and ultra-high strength steel fiber-reinforced concrete (UHSFC) jackets have been proved experimentally to be much more effective with respect to other strengthening schemes in improving the hysteresis performance of existing substandard reinforced concrete (RC) structural members. In this paper, an existing analytical model for the prediction of the shear capacity of RC beam-column joints strengthened with a HSFC or UHSFC jacket is extended to provide design formulation of these innovative HSFC and UHSFC jackets. An authoritative validation of the proposed formulation is also achieved by comparisons of experimental results of 50 beam-column joint specimens with the analytical predictions of the model. Test data used for verification have been collected from the literature based on experimental studies of the authors and other researchers. The merits of the HSFC and UHSFC jacketing technique are also highlighted in the state of practice. Design and application of the proposed fiber-reinforced concrete jackets in deficient existing RC beam-column joints provides a sustainable strengthening technique by contributing to the reduction in the cost and to labor-intensive procedures of common jackets by completely replacing the installation of reinforcement.

Experimental study of HSS-reinforced exterior beam–column joints with different enhancement details

High-strength steel (HSS) bars are used as beam and column longitudinal reinforcements to reduce the amount of bars and thereby, prevent reinforcement congestion and insufficient concrete compaction. However, the use of high-strength steel reinforcements may induce bond failure of beam steel bars. To improve joint performance, steel fiber-reinforced high strength concrete (SFRHSC) and X-shaped reinforcement are proposed. Six full-scale specimens reinforced with steel fiber-reinforced high strength concrete and X-shaped reinforcement were designed and tested under reverse cyclic loading. The main parameters included the enhancement details, shear compression ratio, and concrete patterns. The seismic performance of the tested exterior beam–column joints (BCJs) was evaluated based on the cracking patterns, load capacity, energy dissipation, and ductility. The test results revealed that the combination of steel fiber-reinforced high strength concrete and X-shaped reinforcement significantly improved the loading capacity and energy dissipation. This was attributed to the enhancement of the shear by the X-shaped reinforcement, regulation of crack propagation by the steel fibers, and confinement of the joint core concrete by stirrups. Although the specimens displayed shear failure in the joint core area, both X-shaped reinforcement and steel fiber-reinforced high strength concrete could improve the failure modes. Here, steel fiber-reinforced high strength concrete was more effective. The bond performance of the beam longitudinal reinforcements was investigated to study the strain of the reinforcements, degradation of the bond stress, and slippage of the beam reinforcements. Anchorage methods of national codes were compared, and an anchoring recommendation was put forward.

Influence of Tension Stiffening and Cracked Shear Modulus Models on Non-Linear Analysis of High Strength Fibrous Reinforced Concrete Slabs

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 well-known 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.

Analysis on the Seismic Performance of Steel Fiber-Reinforced High-Strength Concrete Beam-Column Joints.

The present research study aims to investigate numerically the behavior of steel fiber-reinforced high-strength concrete (SFRHC) beam–column joints (BCJs) under seismic action. Based on the plastic damage constitutive model of concrete and elastic–plastic mixed-strengthen constitutive model of steel material, the finite element software ABAQUS was utilized to establish the 3D finite element (FE) model of BCJs. Additionally, the feasibility and accuracy of the numerical simulation were verified by comparing the computed results and experimental observations in terms of the hysteresis curves, skeleton curves, and failure mode. Furthermore, based on the validated FE modeling approach, load vs. displacement hysteresis curves of SFRHC–BCJs during the loading process were analyzed in detail; the failure process was also investigated. Furthermore, the effect of various parameters on the seismic behavior of BCJs was analyzed comprehensively, including the concrete strength, the volume ratio of steel fiber, and the stirrup ratio in the core area. Finally, parametric studies illustrated that increasing the concrete strength helps in enhancing the ultimate load, while the ductility decreased noticeably. Both adding the steel fiber and increasing the stirrup ratio can significantly improve the seismic performance of BCJs.