Steel Ratio Research Articles

Probabilistic evaluation of chloride-induced corrosion effects on design parameters of RC beams

The chloride-induced corrosion in reinforced concrete (RC) structures could decrease their service life. In this regard, studying the effects of corrosion on the designing parameters could prevent these costly expenses. The presence of uncertainties in the corrosion process requires probabilistic models to be applied. Therefore, in this study, Monte Carlo simulations have been used to investigate the effects of corrosion in RC elements. To do so, the remained area of reinforcements, changes in yield stress, ductility and flexural capacity of RC beam sections under propagating corrosion were studied. These changes were applied to a singly reinforced beam model and its behavior in the flexural limit state was investigated. Results have indicated that statistical dispersion in remained area of rebars and their yield stress increases over time. As a result of a decrease in yield stress, the balanced steel ratio in cross-section increases. Moreover, the ductility of the beam decreases as corrosion propagates. Reliability analysis of the beam in different conditions emphasized the deteriorating effect of reducing concrete cover, increasing the w/c ratio and using reinforcements with smaller diameters or lower yield stress. Furthermore, reliability analysis of corroded RC beams can effectively be used in planning inspections of existing structures.

Behavior and design of steel-tubed-reinforced-concrete columns reinforced with non-through section steel

This paper presents an experimental and analytical study on the seismic behavior and load-carrying capacity of the steel-tubed-reinforced-concrete (STRC) column reinforced with non-through section steel. A total of 8 columns with different built-in section steel lengths and varying axial compression ratios were tested under low-period cyclic load. The damage features, hysteresis curves, and steel tube strain of the specimens were analyzed, respectively. The effects of built-in length of section steel and axial compression ratio on seismic performance were discussed. The results indicated that: the STRC columns are mainly subjected to compression-bending failure mode. Within a critical built-in length range of section steel, the section steel-concrete transition section is damaged, and the seismic performance and bearing capacity increase significantly with the increase in section steel length. When the critical value is exceeded, the column root section is damaged, and the performance of the specimens is no longer improved. The damage position and lateral load capacity of the STRC column with non-through section steel are determined by the critical length and the bearing capacity of the two typical sections. Based on experimental and finite element analysis, the calculation methods for the compression and bending capacity of two typical sections are given, and the calculation formula for the critical length of section steel is provided.

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

AbstractThe governing failure mode for flat slabs is punching shear, which occurs when the punching forces exceed the slab resistances in the critical area around the column surface. Recently, considerable knowledge has been obtained on understanding steel fiber reinforced concrete (SFRC) suspended slabs as a sustainable and reliable technique to enhance post‐cracking behavior and resist loading effects, including punching shear. The properties of the materials, loading, and dimension vary inevitably and may be represented in the form of statistical distributions. In this study, all parameters affecting the punching shear of the SFRC suspended slabs were treated as random variables. Monte Carlo simulations (MCS) and punching shear model developed previously using Artificial Neural Network (ANN) were combined (ANN‐MCS) to conduct a reliability analysis, cost optimization, and model calibration. Reliability results have shown that the inclusion of fibers increased the safety level (20% in terms of the reliability index β) of the slabs against punching shear. Furthermore, a reliability‐based cost optimization was performed on the ANN‐MCS model. The optimization outcomes demonstrated steel ratio has a significant impact on SFRC slab cost, and thus it should be minimized/reduced when the steel fibers are included in the mix. Moreover, the ANN model was calibrated following a code calibration procedure to account for the model, material, and fabrication uncertainties. The calibration results have shown that a reduction factor of 0.6 should be applied to the ANN‐based model to achieve the target reliability level, β ≥ 2.5.

Performance of square concrete-filled steel tubular columns under repeated lateral impact

In this paper, a series of simulations are conducted to study the dynamic performances of square concrete-filled steel tubular (CFST) columns under repeated lateral impact by considering the effects of common design parameters. The results show that the impact force response of square CFST columns with proper design under five lateral impacts is similar to that under single lateral impact. The failure mode of the specimen mainly presents the overall bending failure. The energy absorption ratio decreases gradually with the increase of impact times. The plastic deformation of the tube works as the main energy dissipation mechanism of CFST, therefore the impact resistance of square CFST columns can be effectively increased with the increase in steel yield strength, sectional steel ratio and dimension. The axial compression ratio less than 0.6 is beneficial for the impact resistance of the model. The prediction formulas of the dynamic flexural capacity and the residual axial-compression resistance of square CFST columns under repeated lateral loads considering the influence of impact times and various parameters are proposed and in good agreement with the numerical results.

Multi-scale mechanism of steel tube restraint effect on concrete of CFST

A multi-scale numerical model was used to study the mechanism of steel tube restraint effect on the concrete of concrete-filled steel tube (CFST) columns under compression. In the developed model, aggregates, mortar, and interfacial transition zones (ITZ) of concrete core were fabricated in meso-scale; however, steel tube was considered to be in macro-scale to investigate the interactions of all phases. Parametric analyses with different diameters and steel ratios were conducted to evaluate multi-scale model. The developed multi-scale numerical simulation could be employed to provide a better understanding on cracking processes of concrete and stress paths of steel tubes in CFST.

Dry rolling-sliding wear behavior of ER9 wheel and R260 rail couple under different operating conditions

This work aimed to evaluate the effects of contact stress and slip ratio on wear and rolling contact fatigue of ER9 wheel steel and R260 rail steel couple under unlubricated conditions using a dual disk test. It was demonstrated that as either contact stress or slip ratio increased, so did the wear rate and surface damage of both ER9 wheels and R260 rail rollers. The wear rate of the ER9 wheel steel containing proeutectoid ferrite and the smaller structure size of pearlite increased significantly when compared to the rail steel containing fully pearlite in each pair. After testing according to the conditions used in this work, the surface hardness of the pearlitic rail steel was higher than that of the ferrite-pearlite wheel steel. The average hardening ratio of ER9 wheel steel and R260 rail steel was 0.7 and 1.28, respectively. This was consistent with the subsurface deformation angle. With full pearlite in the microstructure of rail steel, the main wear mechanism was predominantly caused by fatigue cracking and peeling, with some adhesive wear. Whereas the most prominent mechanism of the ferrite-pearlite wheel steel was adhesive wear, which was followed by spalling and small fatigue cracks.

Behavior of steel reinforced UHPC-filled stainless steel tubular columns under eccentric loads

This study was conducted to examine the behavior of steel-reinforced ultra-high performance concrete-filled stainless steel tubular (SRUHPCFSST) intermediate columns under eccentric loads. There were nine columns tested in the test program, all of which were subjected to static eccentric loading with consideration given to the effects of the eccentricity, diameter-to-thickness ratio, steel ratio, and eccentric direction. The columns were evaluated to determine their performance characteristics such as ductility, load-displacement relationships, load-strain relationships, and failure modes. The intermediate SRUHPCFSST columns demonstrated good load-carrying and deformation capacity as well as a clear instability failure under eccentric compression after reaching their maximum load. The ultimate bearing strength of the columns decreased significantly with the increase of the diameter-to-thickness ratio and eccentricity, and the increase of the steel ratio or loading in the major axis of the steel skeletons effectively improved the ultimate bearing strength and ductility of the columns. The numerical simulation of the eccentric compression on the SRUHPCFSST was carried out with the finite element software ABAQUS, and the effects of the L/D ratio, concrete strength, steel skeleton strength, and large eccentricities on its eccentric bearing strength were expanded and analyzed. The eccentric bearing strength of the SRUHPCFSST intermediate columns was calculated using a formula derived from the test data and the numerical analyses. The results of the equation correlated well with the experimental data and can serve as a reference for future research in this area.

Numerical Simulation and Deformation Behavior of a Ti/Steel Clad Plate during the Rolling Process

The deformation mechanism is complex in the hot rolling process of clad plates, and head bending is a common defect. In this paper, an analytical computational mechanical model of a metal plate was established by the classical elastic mechanics method, and the relationship between uneven thickness extension and warpage was obtained. The hot rolling bonding process of dissimilar bimetallic plates of Ti/Steel was investigated. On this basis, the mechanical origins of the plate bending defects and the influence of various factors on the evolution of the plate bending defects of the metal plates were revealed. The results indicated that the rolling forces increased with the increase in reduction ratio and thickness ratio. As the total reduction ratios of the clad plates increased, the reduction ratio of each layer increased. Furthermore, it was found that the thickness reduction ratios of steel were larger than those of Ti at a certain total reduction ratio, which could reach up to 59.6%. When the reduction ratios were 0.4 and 0.45, the bending degree increased with the thickness ratio of the upper and lower plates increasing gradually. The maximum warpage could reach 0.349 m. The clad plate shape was better when the roll speed ratio was 1.02 and the reduction rate was 0.4. The present numerical results provide a valuable insight into the deformation behaviors and mechanisms involved in the hot rolling of clad plates.

Axial compressive behavior of built-in carbon-steel marine concrete-filled stainless steel tubular columns

To investigate the axial compressive behavior of marine concrete-filled stainless steel tubular (MCFST) columns with built- in carbon steel, a total of 10 specimens were tested under axial loads. The mechanical failure process and morphology of the specimens were observed, and the axial load-displacement curve and the strain curve of each steel were obtained. Based on the test data, the influence of various variation parameters on the ultimate bearing capacity, axial ductility, energy dissipation capacity and damage development of kinds of specimen was analyzed. The three-dimensional nonlinear finite-element (FE) models were established and verified with the experimental results. The test results indicated that the failure modes of specimens are local buckling and wrinkle of stainless steel tube and oblique shear failure of concrete. The built-in carbon steel can improve the ultimate bearing capacity, axial ductility and energy dissipation capacity of the specimen, and inhibit the damage development of the specimen. Under the condition of increasing the unit carbon steel ratio, MCFST column with built-in circular steel tube achieved the axial compression performance best. Considering the positive effect of the constraints of built-in carbon steel, the calculation methods of bearing capacity were proposed, and the calculated value reflected the measured data well.

Axial compression capacity of rectangular CFST columns under random pitting corrosion

To study the effect of random pitting corrosion, this paper presents the change law of the bearing capacity of the rectangular concrete-filled steel tube (CFST) column under the action of axial force with the mass loss ratio of the outer steel tube. Existing experimental data, including the axial ultimate bearing capacity and load displacement curves of the uncorroded and corroded rectangular CFST columns, are collected to verify the rationality of the finite element model. ANSYS software was used to establish a model that can simulate the pitting corrosion, and the results of the finite element analysis were compared with the experiment, which illustrates that the established model can accurately predict the actual load changes. For further research, the corroded thickness tc/t, which include constant tc/t and random tc/t, and other influencing factors such as corrosion pit diameter Dc, steel tube wall thickness t, material strength, shape and section size of specimens are discussed, the results reveal the effect of these parameters on the decline of axial compressive load capacity. Meanwhile, to visually reflect this effect, this study introduces the concept of bearing capacity reduction coefficient Rcs and Rc to express the ratio of bearing capacity of specimens before and after corrosion. The extensive stochastic finite element analysis was carried out, and on this basis, a suitable calculation formula for the reduction factor is proposed to predict the axial compression bearing capacity of the corroded rectangular CFST column by measuring the value of local mass loss ratio of the outer steel.

Material synergy and parameter optimization of axially-loaded circular UHPC-filled steel tubes

This paper aims to investigate the material synergy and parameter optimization of circular ultra-high performance concrete (UHPC) filled steel tubes towards excellent axial bearing capacity and material utilization efficiency. 12 stub columns of UHPC-filled steel tubes (UCFST) were tested and analysed combined with 293 literature data sets under axial compression. The results show that increasing confinement index ξ and steel ratio α can enhance the ductility of the axial load-displacement curve and the failure mode of the column. Threshold values of ξ = 1.0 and α = 0.25 are proposed to distinguish the failure modes. Appropriately higher steel strength grade, lower D/t, larger α and ξ are recommended to ensure the good axial bearing capacity of the UCFST columns. To produce excellent material synergy and axial bearing capacity, the optimum steel and UHPC strength grades are recommended around C100 ∼ C160 and Q345 ∼ Q690 for the axially-loaded UCFST short columns, respectively. Furthermore, the optimum ranges of diameter-to-thickness ratio D/t, steel ratio α and confinement index ξ are <90·(235/fy), 0.10–0.30, 0.7–2.0, respectively. The current normal CFST design codes are inappropriate for the UCFST columns due to the parameter values exceeding limit values. Therefore, a reliable analytical model is proposed and well validated to predict the axial bearing capacities of circular UCFST short columns.

Numerical investigations on flexural behavior of I-shaped CFRP-encased high-strength square concrete filled steel tubes

To enhance the mechanical properties of high-strength concrete-filled high-strength steel tubular (HSCFHST) members, a new type of composite structure is proposed in which an I-shaped CFRP is encased inside the HSCFHST member. The objective of this research is to improve the theoretical foundation for HSCFHST members by analyzing the flexural behavior of inner I-shaped CFRP on HSCFHST members. HSCFHST members' nonlinear finite element models is created using ABAQUS and confirmed by comparing simulation and test data. It is subjected to pure bending stresses. The flexural behavior of the HSCFHST members are examined with respect to failure mode, complete curve, moment sharing ratio, longitudinal and contact stresses in steel tubes and concrete. Additionally, material interaction mechanisms among three components are investigated to explore the range of restraint between the components. To assess a substance's effect and structural parameters on the flexural behavior of the members, including different combinations of the three types of materials, steel's yield strength, concrete's compressive strength, and the ratio of steel. The findings demonstrate that the steel tube's restraint of the concrete is mostly concentrated at its corners on the tensile side. The HSCFHST member's deformation capacity and stiffness were both increased by the usage of the CFRP encased in the member, which also decreased the height of the central axis' upward movement. The flexural load capacity is largely affected by the steel ratio, which also has an impact on steel strength.

The Effect of Using Different Cross-Sectional Shapes of Steel on the Flexural Performance of Composite Reinforced Concrete Beams

Various types of structures can be constructed using reinforced concrete, including slabs, walls, beams, columns, foundations, frames, and more. The incorporation of structural steel and reinforcements in concrete enhances the strength and durability of structural elements while compensating for the tensile weaknesses in the concrete material. This study aimed to investigate the behavior of reinforced concrete beams utilizing structural steel of different shapes. Four types of concrete beams were prepared: a standard beam with normal reinforcement, and three composite beams, each featuring structural steel with different sectional shapes – T-section, I-section, and channel section. The consistent parameters included the cross-sectional area of the specimens, each measuring 100x150x450 mm, a steel reinforcement percentage of 2% of the total volume, and the compressive strength of the concrete. The conducted tests involved applying a concentrated load at the mid-span of each beam to examine the specimens’ behavior in terms of strength, flexural load capacity, deflection, crack patterns, and failure mode. The results of this study reveal that, given the same steel ratio, the load capacity of beams reinforced with structural steel of a channel shape has surpassed that of the other beams. Additionally, specimens with structural steel plates exhibited higher maximum deflections before failure compared to the beams with conventional reinforcement.

Comparative Study on Seismic Performance of Steel Building &amp; Composite Building with CFT &amp; CFST Column

In this paper a comparative study is done on Steel building &amp; Composite building with CFT, CFT with stiffeners, CFDST Hollow &amp; CFDST column. Seismic Analysis of (B+G+9) building is done in both Equivalent Static method &amp; Response Spectrum method using ETABS software &amp; Optimum Composite column is obtained from Parameter 1 (Steel Ratio, Buckling Load, Plastic Resistance, H/T Ratio), Parameter 2 (Displacement, Story Drift, Base Shear, Overturning Moment, Story Stiffness), Parameter3 (Moment of Inertia, C/S Area, Total Weight, Total Tonnage).

Enhanced strength-plasticity matching of lamellar 1 GPa-grade dual-phase steels via cyclic intercritical quenching

In this work, an innovative cyclic intercritical quenching process has been proposed for achieving excellent mechanical properties in terms of strength and plasticity, which results in a lamellar martensitic-ferritic dual-phase steel. The microstructural evolution under cyclic heat treatment was thoroughly investigated, and the mechanism that enables the lamellar structure to enhance its strength-plasticity matching was also explored. The experimental results revealed that the incomplete austenitization process inhibits the coarsening of the reversed austenite, and the cyclic intercritical quenching procedure finer and more evenly distributes the reversed austenite. The single intercritical quenching (C1) generated mostly massive martensite with traces of ferrite, whereas three-cyclic intercritical quenching (C3) yielded a fine and uniformly distributed lamellar structure. A comparison in terms of the mechanical properties between C3 and C1 steels indicates that uniform elongation, total elongation, and the product of strength and uniform elongation of the C3 steel increased by 85.4%, 47.3%, and 65.0%, respectively, while ultimate tensile strength was dropped by only 11.0%. In addition, the yield ratio of C3 steel is just 0.48. The slight decrease in strength is due to the fine lamellar microstructure. The high plasticity is attributed to the good deformation compatibility between lamellar ferrite and lamellar martensite with excellent plastic deformability. Therefore, cyclic mechanical heat treatment is very promising for the production of low-cost dual-phase steels.

Experimental tests of two span continuous concrete beams reinforced with hybrid GFRP-Steel bars

The current paper aimed at investigating the flexural performance of five large-scale continuous concrete beams reinforced by both steel bars and glass fibre reinforced polymer (GFRP). All the studied specimens had the same geometrical dimensions, with 200 mm width, 300 mm depth, and two identical spans of 2600 mm. The quantity of longitudinal steel reinforcement, GFRP reinforcement, and hybrid reinforcement ratio at the top and bottom layers of beams were the key parameters explored in this study. The experimental findings indicated that using the hybrid reinforcement of steel and GFRP in multi-span continuous concrete beams exhibited a ductile behaviour. However, the hybrid ratio of steel bars/GFRP is critical for restricting the extent of moment redistribution ratios. Moreover, using the same hybrid reinforcement ratios at sagging and hogging regions led to a limited moment redistribution. On the other hand, the hybrid beams strengthened by various hybrid ratios in the critical sections of the tested beams demonstrated a remarkable moment redistribution up to 43 %.The test results were compared with the available theoretical model and equations for predicting the beams’ moment capacity. It was found that the ACI.440.2R-08 reasonably predicted the flexural capacity of tested beams whereas the Yinghao and Yong equation underestimated the flexural capacity in the hogging sections. It was also shown that using the collapse mechanism with plastic hinges at sagging and hogging sections yielded good predictions for the loading capacity of hybrid reinforced concrete continuous beams.

Experimental and analytical investigation of square-shaped concrete-filled steel tube columns

Square-shaped concrete-filled steel tube (CFST) columns inherit the advantages of conventional steel and concrete columns, and have been used in several super high-rise buildings. This paper presents a calculation model for square-shaped CFST columns. Based on the experimental results of a square-shaped CFST column and the application of a super high-rise building, numerical models are established to simulate the force–displacement curves of the CFST column and the stress–strain curves of square steel tubes and stiffeners, which show consistency with the experimental data. Meanwhile, the load-bearing capacity and ductility of CFST columns can be effectively increased by incorporating tensile plates, diaphragms, shear studs, and stiffeners. Considering the steel ratio, axial compression ratio, and concrete strength, nine finite element models are developed to evaluate the ductility and load-bearing capacity of the columns under the reversed-cyclic lateral load. The seismic and wind resistance properties of the structures are analyzed using a CFST column application.

Correlation between Laboratory-Accelerated Corrosion and Field Exposure Test for High-Strength Stainless Steels.

Equipment in a long-term marine atmosphere environment is prone to corrosion failure. Natural field exposure tests usually require a long time to obtain corrosion information. This study worked out a laboratory-accelerated corrosion test method that has a strong correlation with the natural environment test in Wanning, Hainan, and can be used as the basis for life assessment and the prediction of two high-strength stainless-steel materials. The mathematical model of corrosion weight loss of two high-strength stainless steels (3Cr13 and 00Cr12Ni10MoTi) was established by a field exposure test and a laboratory-accelerated corrosion test. Then, the correlation between the field exposure test and the laboratory-accelerated corrosion test was evaluated using qualitative and quantitative methods, and the acceleration ratio was calculated using the accelerated switching factor (ASF) method. The results show that: (1) The corrosion morphology of the two stainless steels after 15 days of laboratory-accelerated corrosion testing is similar to that obtained after two years of field exposure. (2) The value of gray correlation between the laboratory-accelerated corrosion test and the field exposure test is not less than 0.75. (3) The acceleration ratio of both stainless steels increases with the corrosion test time in the laboratory. The corrosion prediction models for the two stainless steels are T3Cr13 = 6.234 t1.634 and T00Cr12Ni10MoTi = 55.693 t1.322, respectively.

Influence of Structural Parameters on the Buckling of Longitudinal Steel Bar in RC Structural Wall

Reinforced Concrete (RC) structural wall is widely used in multistoried RC frame buildings to enhance lateral stiffness and lateral strength for earthquake resistance. One of the possible failure modes, observed during strong earthquake shaking, is the buckling of longitudinal steel reinforcement in the boundary elements of the wall. This also assumes importance in establishing damage states for seismic fragility analysis of RC wall. Although a few past studies have focussed on longitudinal bar buckling in RC members, detailed parametric study is absent particularly for such instability of bars in the boundary elements of the wall. In the present study, displacement-controlled nonlinear static analysis of several wall specimens is carried out using fibre-discretization of cross-section and distributed plasticity modelling in OpenSEES. Here, 27 different models of the isolated slender wall are created considering variations in six structural parameters, namely (a) length ratio of the boundary element to the wall, (b) axial force ratio, ratios of (c) longitudinal steel in web, and (d) transverse steel and (e) longitudinal steel in the boundary elements. The effect of wall thickness is accounted for through variation in axial force ratio. Using the analytical results from the nonlinear analysis of the wall models, the trends in drift ratio at the onset of longitudinal bar buckling damage states as functions of various key structural wall properties, has been investigated.

Axial compressive behavior of geopolymer recycled brick aggregate concrete-filled steel tubular slender columns

Geopolymer and recycled brick aggregates are applied into the concrete-filled steel tubular column to provide a promising solution to environmental sustainability. This paper investigates the mechanical behavior of geopolymer recycled brick aggregate concrete-filled steel tubular (GRBAC-FST) slender columns under axial compression. Apart from cross-section type, the replacement ratio of brick aggregates (BA) and slenderness ratio are also selected as the main variables. The analysis of the failure mode, bearing capacity, deformation behavior, and strain behavior is conducted. A modified stress–strain model for the GRBAC-FST slender column is proposed and validated, then the parametric analysis on φ-λ relation curves is performed to propose a simplified calculation method for the bearing capacity. Results demonstrate that GRBAC-FST slender columns exhibit obvious lateral deflection, and mid-span bulging of steel tube. Compared with square specimens, circular specimens exhibit plane fracture of concrete, and developed higher bearing capacity and better plastic deformation capacity. The ultimate strength of GRBAC-FST slender columns decreases with the increase of the replacement ratio of BA and slenderness ratio. The stability coefficient φ decreases with the increase of the slenderness ratio, the yield strength of the steel tube and the concrete strength, while it was little affected by the steel ratio. The modified stress–strain model could well reflect the full-range response of GRBAC-FST slender columns under axial loading. The proposed calculation method could be used for the compressive bearing capacity of GRBACFST slender columns, with satisfying accuracy and efficiency.