High-strength Reinforcement Research Articles

Influence of steel fibers on the static and blast response of beams built with high-strength concrete and high-strength reinforcement

This paper presents the results of a study examining the influence of steel fibers on the static and blast performance of beams built with high-strength concrete (HSC) and high-strength steel reinforcement. As part of the study, a series of fiber-reinforced HSC beams designed with Grade 690 MPa ASTM A1035 reinforcement are tested under static and blast load conditions using a shock-tube. The performance of the beams is compared to that of a control set of specimens built with plain HSC and high-strength bars. In addition to the effects of the steel fibers, the effects of reinforcement type (Grade 690 MPa vs. 400 MPa) and high-strength steel ratio (ρ = 1–2.2%) are also investigated. Under static loads the provision of fibers is found to significantly enhance the ductility of the high-strength reinforced concrete beams. Under dynamic conditions, the use of fiber-reinforced HSC leads to important enhancements in blast behavior, including better control of displacements, increased blast capacity and improved damage resistance. As part of the numerical study the blast response of the beams is predicted using 2D finite element (FE) modelling.

Impact of High Strength Rebars on Seismic Behavior of Lightly Reinforced Boundary Elements

Considering economic reasons and attempting to reduce the carbon footprint of concrete structures, there is an increasing tendency toward the use of high strength reinforcement in seismically active regions. ACI 318-19, Iranian steel rebars standard INSO 3132 and next edition of Iranian national building allow the use of high strength rebars in elements of ductile force-resisting systems. Therefore it is important to verify that if S520 rebars are capable of providing adequate, a) strain capacity, b) out of plane buckling deformation capacity, which are the two common sources of failures observed in recent earthquakes in boundary elements of lightly reinforced shear walls. An experimental program is designed to compare strain capacity of boundary elements reinforced with S400 and S520 rebars, which include monotonic and cyclic loading considering probable loading on lightly reinforced boundary elements. Considering test results for specimens under monotonic and cyclic loading it is shown that, a) gauge length suggested by INSO for rebar test could be misleading in the evaluation of rebar axial strain capacity, b) S520 rebars have limited ductility compared to S400, but considering strain demand, this limited strain capacity is adequate to avoid rebar fracture, c) local strain (crack width) has a better correlation with out of plane buckling compared to average strain as suggested by some researchers, d) it seems that out of plane buckling for S520 rebars occurs at smaller deformation, which means there is the need for larger minimum dimension for sections reinforced with S520 compared to S400.

3D non-linear finite element analysis of concentrically loaded high strength reinforced concrete column with GFRP bar

The use of High Strength Concrete (HSC) material in Reinforced Concrete (RC) column has become widely used. HSC was found to be durable, strong in compression, but it has low ductility. This low ductility of HSC can be improved by providing confinement. However, for HSC with concrete strength higher than 70 MPa, additional clause for confinement in ACI 318-19 generates denser arrangement of transverse bars and eventually creates weak planes between the concrete core and the cover. These weak planes can trigger early cover spalling. To reduce the utilization of confining bars, high-strength Glass Fiber Reinforce Polymer (GFRP) bar can be used. However, the performance of GFRP bar varies significantly from their uniaxial behavior in tension or compression to the real performance when it is used as the main reinforcement. For that reason, this paper tries to investigate the behavior of HSC RC column with bars made of conventional steel rebar and with GFRP bars. Due to limited data on the strain gauge reading on the GFRP bars from the available test result, an inverse analysis is carried out to determine the best stress-strain curve for GFRP bars used as the main reinforcement. For that purpose, an inhouse finite element package called 3D-NLFEA is used. From the comparisons, it was found out that the peak load, softening behavior, and the concrete core enhancement prediction agrees well with the test result. From the inverse analysis, only 25% and 45% of the GFRP bar yield strength can be deployed when loaded under compression and tension, respectively.

Experimental Study on Shear Capacity of High Strength Reinforcement Concrete Deep Beams with Small Shear Span-Depth Ratio.

This study aimed to investigate the shear capacity performance for eight deep beams with HTRB600 reinforced high strength concrete under concentrated load to enable a better understanding of the effects of shear span–depth ratio, longitudinal reinforcement ratio, vertical stirrup ratio and in order to improve design procedures. The dimension of eight test specimens is 1600 mm × 200 mm × 600 mm. The effective span to height ratio l0/h is 2.0, the shear span–depth ratio λ is 0.3, 0.6 and 0.9, respectively. In addition, the longitudinal reinforcement ratio ρs is set to 0.67%, 1.05%, 1.27%, and the vertical stirrup ratio is taken to be 0%, 0.25%, 0.33%, 0.5%. Through measuring the strain of steel bar, the strain of concrete and the deflection of mid-span, the characteristics of the full process of shear capacity, the failure mode and the load deflection deformation curve were examined. The test results showed that the failure mode of deep beams with small shear span–depth ratio is diagonal compression failure, which is influenced by the layout and quantity of web reinforcement. The diagonal compression failure could be classified into two forms: crushing-strut and diagonal splitting. With decreasing of shear span–depth ratio and increasing longitudinal reinforcement ratio, the shear capacity of deep beams increases obviously, while the influence of vertical web reinforcement ratio on shear capacity is negligible. Finally, the shear capacity of eight deep beams based on GB 50010-2010 is calculated and compared with the calculation results of ACI 318-14, EN 1992-1-1:2004 and CSA A23.3-04, which are based on strut-and-tie model. The obtained results in this paper show a very good agreement with GB50010-2010 and ACI 318-14, while the results of EN 1992-1-1:2004 and CSA A23.3-04 are approved to be conservative.

Special Moment Frames with High-Strength Reinforcement�Part 2: Columns

Special Moment Frames with High-Strength Reinforcement�Part 2: Columns

Special Moment Frames with High-Strength Reinforcement� Part 1: Beams

Special Moment Frames with High-Strength Reinforcement� Part 1: Beams

Determination of the Optimum Percentage of High Strength Bars in RC Beams with Combined Reinforcement Using Fem

Abstract In this work on the basis of the developed and tested mathematical model, the numerical experiment is conducted in order to study in more detail the specifics of performance of concrete beams` with combined reinforcement. For this purpose nine series of reinforced concrete beams with different combination of steel bars (A400C, At800, A1000) and ribbon reinforcement (C275) were modeled. In the developed series two classes of concrete were used: C50/60, C35/45. The functions derived on the basis of mathematical modeling allow us to determine the recommended percentage of high-strength reinforcement of common reinforced concrete structures with single reinforcement. Therefore, the possibility is obtained to reduce the total structures` reinforcement percentage, increasing their deformability by the specified value without affecting the bearing capacity.

Structural behaviour of prestressed concrete beams with high-strength stirrups

Many studies related to high-strength concrete material have been conducted, but relatively few studies have considered high-strength steel reinforcement. Four current design codes – ACI 318-14, Eurocode 2, CSA A23.3-04, and JSCE-07 – limit the yield strength of transverse reinforcement to control diagonal crack width, and to ensure yielding of transverse reinforcement prior to brittle failure mode. ACI, Eurocode 2 and CSA A23.3-04 limit the yield strength of transverse reinforcement to 420, 600, and 500 MPa, respectively; while JSCE-07 limits the yield strength to 800 MPa, when the compressive strength of concrete is higher than 60 MPa. The implementation of high-strength transverse reinforcement in prestressed concrete (PSC) and reinforced concrete (RC) beams has been determined in this study. A total of 16 beams were strengthened using higher yield strength stirrups than the code limitations, and were monotonically loaded to failure. All the beams were designed to experience shear failure prior to flexural failure. Most of the test results showed yielding of the stirrups, and narrower crack width than the code limitations even though the specimens were strengthened with higher than 420 MPa stirrups. The test results imply the feasibility of using high-strength stirrups for PSC beams with regard to serviceability.

On the Application of High-Strength Reinforcement in Beamless Slab

The paper considers the peculiarities of the stress-strain state in the zone of junction of the slab of slabs with the joint using conventional and high-strength reinforcement. The maximum stresses in the stretched concrete before cracking correspond to the tensile strength of the concrete, and the stresses in the reinforcement before cracking depend on the reduction factor and were calculated for various classes of concrete. After the formation of cracks, the increase in stresses in the tensioned reinforcement depends on the width of the crack opening and the deformation of the reinforcement between the cracks. The paper shows that with a sufficient width of crack opening and a certain distance between the cracks, high-strength reinforcement can be used to increase the bearing capacity of the support sections of the plate. The total stresses in the reinforcement were calculated for different crack opening widths and different distances between the cracks, the results of which were used to plot the graphs. The graphs of the dependence of the content of high-strength reinforcement on the strength of the normal section, as well as the graphs of the growth of strength with different ratios of the number of rods, are plotted. According to the results of the work, it can be seen that, depending on the class of high-strength reinforcement and its quantity, the strength of normal sections can be increased up to two times.

Development of Mechanized Arc Welding Technology for High-strength Reinforcing Steel in a Reductive Carbon Monoxide Atmosphere

Modern methods of welding high-strength reinforcing steels were analyzed. Comparative studies of welded joints obtained using manual arc welding and welding in a reducing atmosphere of carbon monoxide were carried out. A chemical and metallographic analysis of welded joints was performed. It has been established that welded joints of microalloyed steels made at low temperatures may have reduced strength and viscous properties. The possibility of making welded steel joints using highly-efficient arc welding in a reducing medium of carbon monoxide was investigated. Welding modes have been selected to ensure the formation of a quality welded joint. Studies showed that the use of the proposed welding method in a reducing medium of carbon monoxide ensures full strength of the welded joint and the base metal.

Seismic Behavior of Ultra-High Performance Concrete Short Columns Confined with High-Strength Reinforcement

In order to further study the performance of ultra-high performance concrete (UHPC) structures under seismic conditions, three UHPC short columns confined with high-strength reinforcement were tested alongside one UHPC short column confined with normal-strength reinforcement and one reinforced UHPC short column confined with carbon fiber reinforced polymer (CFRP). The results show that high-strength reinforcement improved the ductility and energy-absorbing ability of the UHPC columns. In addition, high-strength reinforcement only made a marginal difference to stiffness degeneration but did contribute to the specimen's initial stiffness; both high axial loads and small shear span ratios accelerated stiffness degeneration.

Study on Anti-Explosion Behavior of High-Strength Reinforced Concrete Beam Under Blast Loading

To investigate the anti-explosion behavior of high-strength reinforced concrete (RC) beam subjected to blast load, the ANSYS/LS-DYNA finite element analysis software was applied. Based on anti-explosion test results, the effects of reinforcement strength grade, reinforcement ratio and stirrup ratio on dynamic response, failure mode, resistance curve and ductility of RC beams under uniform blast load were studied. The anti-explosion performance of RC beam can be effectively improved by increasing the strength grade of the high-strength reinforcement. When the shear capacity is high enough, the ultimate capacity of high-strength RC beam can be significantly enhanced by increasing its reinforcement ratio. Anti-explosion performance may deteriorate due to the change of failure modes when the reinforcement ratio is increased to a certain extent. Increasing stirrup ratio can improve the shear capacity of high-strength RC beam to guarantee the full utilization of the advantage of high flexural capacity. For high-strength RC beam with sufficiently shear capacity, the further increase of stirrup ratio has a slight effect on the anti-explosion ability.

Stress-deformation state of compound reinforced concrete bars with high-strength reinforcement prone to long-term compression

Introduction. Considering that reinforced concrete is the most common material in construction and reconstruction of buildings and facilities, research of work of high-strength reinforcement in reinforced concrete elements, including compressed columns, are still relevant at present. Analysis of compound-section columns with high-strength longitudinal reinforcement is of particular interest since the method of sectional build-up is widespread enough in the reconstruction of buildings and facilities. However, no information on the work of this kind of reinforced concrete structures under long-term compression was found either in foreign or domestic literature; this fact provides relevance and academic novelty of the study.
 Materials and methods. The article provides the research of parameters of the strain-stress state of compound reinforced concrete bars with high-tensile reinforcement under long time compression employing the modern methods of mathematical simulation.
 Results. The developed calculation method allows determining additional parameters of the strain-stress state of the compressed compound-section reinforced concrete bars considering the concrete creep deformations forming in time of the long-term compression. When comparing the analytical study results with authors’ experimental data and previous results of other researchers, an adequate degree of reliability of the developed calculation method was confirmed.
 Conclusions. When applying the developed calculation method of stress-deformation state parameters for the compressed compound-section columns with high-strength longitudinal reinforcement, the study discovered that significant effort redistribution from concrete to high-strength reinforcement occurs under long-term compression. This fact was confirmed with the results of an experimental investigation on the resistance of the compound reinforced concrete bars with high-tensile reinforcement to the longtime compression.

Analysis of deformation characteristics of high-strength reinforced concrete beams under explosion load

The dynamic response and failure characteristics of reinforced concrete beams under explosion loads are affected by various factors. To study the effect of reinforcement strength on the deformation properties of RC beams and to analyze the deformation differences of high-strength RC beams under different explosion loads, comparative explosion tests on two kinds of simply supported RC beams with longitudinal reinforcement yield strength of 400 MPa and 700 MPa were carried out respectively in this paper. The test results show that the deformation of the mid-span section concrete of the high-strength RC beam is basically the same as that of the ordinary RC beam when the peak overpressure value is small, and the strength advantage of the high-strength reinforcement has not been fully exerted. With the increase of explosion load, the maximum tensile strain and compressive strain of concrete at the mid-span section of high-strength RC beams are 46.6% and 43.5% of ordinary RC beams respectively. Under the action of high overpressure explosion load, the deformation of RC beams can be significantly reduced by high-strength reinforcement, which limits the development of cracks.

An investigation into the behavior of special moment frames with high-strength reinforcement subjected to cyclic loading

High-strength reinforcement (HSR) application has many advantages, such as decreasing expenditures and construction time, and improving construction quality. However, its application has been limited in special moment frames by several building codes. This limitation is due to some challenges related to a possible reduction in overall ductility and serviceability of reinforced concrete (RC) structures. In this research, the effects of HSR application on the stiffness, drifts, energy dissipation, ductility, cracking patterns, and damage indices of four special moment frames are experimentally investigated. These special moment frames have the same geometry and equivalent amounts of reinforcement (with yield strengths of 500 and 580 MPa). The frames are tested under cyclic loading. Results indicate that all the frames achieved drift ratios exceeding 4% before they showed a critical decline in their lateral strength. Moreover, replacing the grade 500 MPa reinforcement with reduced amounts of the grade 580 MPa reinforcement led to a comparable deformation capacity. Experimental observations also showed that by using higher-strength reinforcement, the cracking patterns changed: the higher the yield strength, the wider and deeper the cracks.

Study on explosion resistance performance experiment and damage assessment model of high-strength reinforcement concrete beams

To investigate the explosion resistance performance of high-strength reinforced concrete (RC) beams and analyze the effect of high strength reinforcement on the dynamic response and damage characteristics of RC beams, comparative experimental research of three groups of high-strength RC beams and ordinary RC beams under different uniformly distributed blast loads are conducted in this paper. The P–I damage curves of two kinds of RC beams are established with the maximum tensile reinforcement strain as the damage criterion. The damage assessment of RC beams under various test conditions is carried out, and the assessment results are compared with the test results. The results show that high strength reinforcement can effectively improve the explosion resistance performance of RC beams under blast loads by reducing the deformation of components as well as the length and width of cracks. The damage evaluation results of RC beams according to P–I curves agree well with the experimental results, which indicates that the P–I curves established by using the steel strain of mid-span section as the damage criterion of RC beams can accurately evaluate the failure of the high-strength RC beams under the explosion loading. The research results provide references for the application of HTB700 high strength reinforced concrete beams in the explosion resistant field of civil engineering and the damage assessment of components.

Effect of Casing and High-Strength Reinforcement on the Lateral Load Transfer Characteristics of Drilled Shaft Foundations

AbstractIncreased seismic flexural demands on drilled shaft foundations have led to significant increases in the amount of steel reinforcement, leading to a greater number and/or larger sized steel...

Influence of Operating Modes of High-Temperature Thermomechanical Processing on Mechanical Properties of Reinforcing Bars

The strenghening thermomechanical treatment represens the combined processing treatment – a combination of plastic deformation and hardening in one technological process. Year after year, it is more widely applied in industry.Purpose of research. The study of strenghening thermomechanical treatment operating modes influence on the formation of mechanical properties of steel, which is a very important scientific problem associated with obtaining materials with a given set of mechanical features.Methods. High-temperature thermomechanical treatment was conducted under the conditions in which the processes of recrystallization of deformed austenite were partially or completely supressed, and the process of polygonization got the most development, with the goal of forming a developed substructure of austenite inherited by martensite during subsequent quenching.The paper investigated the change in the properties of high-strength reinforcement under heating (tempering) with different intensity. High-temperature thermomechanical treatment was carried out by including a hardening device in the technological line of the mill No. 280 LLC “Tulachermet-steel”. The studies were carried out on two modes of mill No. 280 operation. Low-carbon reinforcing steels St3 and ST5 were accepted as the studied steels.Results. It has been experimentally established that the maximum cooling capacity of the existing hardening device is manifested when three working sections with a water pressure of about 13 in each section are turned on. In this case, high-temperature thermomechanical treatment should be carried out at the maximum cooling rate in the strengthning device in accordance with the specified strength class, i.e., include the least number of working sections. Intensive cooling mode contributes to the formation of a homogeneous structure in the reinforcement with a high mechanical complex. It was found that during high-temperature thermomechanical treatment it is advisable to withstand the deformation temperature in the range of 1000...1050 ℃ to guarantee the production of reinforcement of a given class. It has been shown that the inclusion of a strengthening device in the mill line directly behind the flying shears, and not behind the finishing stand of the mill leads not only to the trouble-free operation of shears, but also to an increase in the post-deformation aging between the end of deformation and the beginning of bar hardening to a value close to the optimal, responsible for the formation of a polygonal substructure in austenite, the inheritance of which by martensite provides high mechanical properties of steel after high-temperature thermomechanical treatment.Conclusion. These results can be applied to create resource-saving material treatment processes.

Experimental investigation of strengthening of RC short columns using high strength reinforcement

The design and construction of structures with fewer amounts of materials such as concrete and steel led the researchers to move towards the production and usage of optimum materials with higher resistance. High strength reinforcement (HSR) shares a higher ultimate resistance in addition to being economical which distinguishes them from the ordinary ones. Short columns, due to possessing a brittle behavior against cyclic loads, have caused serious damage in the past earthquakes, which can be considered as a major cause of building failure and collapse. In this research, three reinforced concrete short columns specimens are tested under constant axial load and cyclic lateral displacement. Since in the past earthquakes, the failure in the short columns was in the form of diagonal cracks and shear failure, therefor, in this study two new techniques are used to strengthen the diameter of the short columns against seismic loads. These techniques include externally bonded reinforcement (EBR) and near surface mounted (NSM) with HSR. The experimental results show that the above-mentioned strengthening techniques lead to a change in the cracks pattern and column failure. Also, EBR and NSM techniques show successful increase in the ductility, loading capacity, and the amount of dissipated energy.

Seismic behavior of reinforced concrete squat walls with high strength reinforcements: An experimental study

A total of 15 squat reinforced concrete (RC) shear walls (12 of them were reinforced with high strength reinforcement of HRB600 [Grade 600 MPa] and the remaining 3 with normal grade reinforcement of HRB400 [Grade 400 MPa]) have been tested under the cyclic loading. The influencing parameters considered in the test specimens include the grade of reinforcement, axial load ratio, types of cross section, and reinforcement ratio. The seismic performances of the squat RC shear walls have been studied using the test results based on the failure mode, hysteretic behaviors, peak shear strength, deformation capacity, secant stiffness degradation, and inelastic energy dissipation capacity. The test results reveal that the failure modes of the walls with HRB600 steel bars are similar to those walls with HRB400 reinforcement. The walls with high strength reinforcement tend to achieve a larger ultimate deformation but slightly lower load carrying capacity. Both the initial stiffness and energy dissipation of the specimen hysteretic curves decrease as the reinforcement ratio increases and the parameters of cross section and reinforcement ratios have more significant effect on the seismic behavior of shear walls than that by the axial load ratio. Comparing with the walls reinforced with lower reinforcement ratio, the ones with higher reinforcement ratio exhibit larger and better peak load and deformation capacities. Shear walls with symmetrical cross section have better seismic performance than those having the asymmetric ones. When the specimens are subjected to the peak load, the stress in 90% horizontal reinforcement could reach 425 and 385 MPa for the 95% horizontal reinforcement.