Ordinary Steel Bars Research Articles

An Experimental Study of the Impact Mechanical Properties of RC Beams following Replacements of Stainless Steel Reinforcements of Equal Strength

The reinforced concrete structure of a port wharf is affected by steel corrosion and ship docking impact. Replacing an ordinary steel bar with a stainless steel bar can solve the corrosion problem of the steel bar while ensuring the bearing capacity of the structure. However, the research on impact resistance of stainless steel-reinforced concrete structure is not perfect. In this paper, impact mechanical properties of reinforced concrete beams before and after equal strength replacement of stainless steel bars are analyzed by theoretical analysis and drop hammer impact test, and the possibility and applicable scope of equal strength replacement of stainless steel bars are put forward. The results indicated the following: (1) when the reinforcement ratios were small (0.21% to 1.32%), the stainless steel-reinforced concrete beams with equal strength were able to effectively reduce the stiffness losses of the beams undergoing impact loads, as well as improve the elastic resilience abilities, and reduce the structural damages. Therefore, the corrosion and impact problems of reinforcements could be solved by replacing ordinary reinforcements with stainless steel reinforcements and (2) when the reinforcement ratios were large (1.32% to 2.57%), the shear failures of the stainless steel-reinforced concrete beams were observed to be relatively serious, and the impact resistance performances had worsened. The research results provide technical support for the engineering application of stainless steel-reinforced concrete structure design.

Experimental study of the mechanical properties of reinforced concrete compression members under the combined action of sustained load and corrosion

Steel corrosion is an important factor in the durability of reinforced concrete members. There are numerous studies of reinforced concrete compression members in corrosive environments, but most studies involve corrosion under no load. To investigate the comprehensive effects of sustained load and corrosion on the mechanical properties of reinforced concrete members, this study simultaneously subjects 20 axial compression members to both sustained load and corrosion. The stirrups of 10 members are ordinary steel bars (A-type members), and the stirrups of the other 10 members are epoxy-coated steel bars (B-type members). The results show that the ultimate bearing capacity of corroded members can be significantly improved by using epoxy-coated stirrups, especially when the corrosion degree is high. A sustained load can reduce the actual corrosion degree of A-type members and increase the actual corrosion degree of B-type members. Under the same corrosion degree, the ultimate bearing capacity of the columns with stirrups made of ordinary steel bars increases as the sustained load increases, whereas for the columns with stirrups made of epoxy-coated steel bars, the ultimate bearing capacity decreases slightly as the sustained load increases.

Experimental Research on Prestressed Carbon Fiber Reinforced Plastic Reinforced Concrete Decks

A new type of bridge deck structure with prestressed Carbon Fiber Reinforced Plastic Reinforced (CFRP) tendons was designed. Flexural performance tests on the prestressed concrete bridge deck with CFRP tendons were conducted. The cracking and ultimate loads of such bridge deck and the stress states and failure modes of the CFRP tendons were systematically analyzed. Results showed that the bending force process of unbonded prestressed CFRP tendon bridge deck with ordinary steel bars in the tension zone can be divided into three stages, namely, initial elastic loading state, elastic-plastic stage from the appearance of cracks to ordinary steel yielding in the tensile area, and rapid deformation development and destruction stage during tension bearing of the CFRP tendons. The failure modes of unbonded prestressed CFRP tendon bridge deck were caused by the rapid deformation development due to the low modulus of CFRP tendons, and the extension of cracks and crushing failure of concrete were due to the decreased area of effective compressive concrete. The fractures were mostly equidistant parallel cracks. The cracks slowly developed in the early stage, whereas they rapidly developed after ordinary steel yielding.

Experimental investigations on corrosion resistance of innovative steel-FRP composite bars using X-ray microcomputed tomography

A steel-fiber reinforced polymer (FRP) composite bar (SFCB) is a new type of hybrid bar consisting of a steel core and an FRP shell coating. The advantages of the two materials are complementary. For example, the steel bar's good ductile properties and the FRP coating's corrosion resistance work together under tensile stress. This complementary combination provides better mechanical properties and durability than ordinary steel bars. This paper features the production of two different surface types of SFCBs, and these SFCBs' response to corrosion was accelerated by an electrochemical method encompassing three designed levels of corrosion at 5%, 15%, and 25%. The corrosion condition, including the thickness of the rust layer and the rust product distribution, was observed and qualitatively analyzed by environmental scanning electron microscopy (ESEM) and energy dispersive spectroscopy (EDS) techniques. Moreover, an X-ray microcomputed tomography (μCT) was used to investigate SFCBs corrosion, and the amount of corrosion product was quantitatively analyzed. The test results indicate that the fiber types, the micropore structure of the fiber coating layer, and the manufacturing process of the SFCBs are the main factors affecting SFCBs' corrosion resistance. The SFCBs show excellent corrosion resistance. The amount of corrosion product on the FRP coated-steel interface was much less than that of ordinary steel bars that experienced the same corrosion process. The actual corrosion rate of a carbon-type SFCB is less than 1/10 that of an ordinary steel bar, and the actual corrosion rate of a glass-type SFCB is less than 1/100 of an ordinary steel bar.

Residual mechanical behavior of (SD 500) hot rolled TMT reinforcing steel bars after elevated temperatures

This paper intends to present an experimental investigation carried out to study the influence of elevated temperatures on residual mechanical properties of super ductile (SD 500) hot rolled deformed TMT bars in comparison with conventional hot rolled and ordinary TMT steel bars. The study also presents a detailed analysis of effect of heating on residual ductility characteristics of SD 500 rebars after exposure to various temperatures using various prevalent methods in the available literature. The experimental study involved heated residual tensile tests carried out on rebar specimens after being exposed to elevated temperatures and subsequently cooling down to ambient conditions covering a wide range of available sizes (8 mm, 10 mm, 12 mm, 16 mm and 20 mm). A detailed description of the test results, observations and discussion on results obtained from the testing, including comparisons with the available information in the existing relevant literature have been presented with particular emphasis on the influence of high temperature on ductility of super ductile (SD 500) hot rolled TMT bars. The results so obtained suggest better performance of SD TMT over ordinary TMT and conventional hot rolled rebars in terms of key aspects of mechanical behavior after exposure to elevated temperatures. The outcomes of this study have direct implications on procedures used for predicting the ultimate behavior of structural elements during and following exposure to elevated temperatures.

Three-dimensional reinforcement design method and program realization for prestressed concrete box-girder bridges based on a specific spatial lattice grid model

Reinforcement with prestressed steel tendons to prevent cracking is a major design procedure for most concrete box-girder bridges. They provide acceptable performance even though they do not cover all of the principal stress directions of the structural members because ordinary steel bars also play an important role in resisting external loads. However, with the limitations of current design methods, a plane model is always used as a standard for designers for manual performance of the procedure, but it does not provide sufficient information for the reinforcement of easily overlooked parts from the view of integral three-dimensional effects. Design experiences and detailing requirements must therefore be used extensively, leading to either a waste of materials or a greater likelihood of unexpected damage to members. To address this issue, this study proposes a solution for the reinforcement of prestressed concrete box-girder bridges with a new reinforcement method combined with a specific spatial lattice grid model. The model, which finely differentiates the stress sources of the members and especially emphasizes the in-plane stresses of the top and bottom plates, facilitates the establishment of a stress-based reinforcement method to completely consider the three-dimensional effects of prestressed concrete box-girders and provide the necessary information associated with current bridge codes. The method was implemented as the module of a bridge software with an automatic design function. The effectiveness of the method is demonstrated and discussed via numerical examples.

Corrosion characteristics of S23043 duplex stainless steel bars

Reinforcement corrosion is a main cause of durability deterioration of reinforced concrete structures. In recent years, stainless steel bars have been gradually applied to engineering practice because of its good corrosion resistance. However, under harsh environments such as chloride ion exposure, stainless steel bars will rust. Therefore, scholars began to study the corrosion characteristics of stainless steel bars. Previous studies mainly focused on the corrosion of steel bars in the zero-strain state, but steel bars in actual structures usually bear a sustained load resulting in initial strains. In this study, the corrosion characteristics of S23043 duplex stainless steel bars (S23043) under different strain levels were investigated by using acceleration corrosion tests and tensile tests under constant strain conditions in a chloride environment. The results showed that corrosion degree of S23043 increased by about 20% as the strain levels increased from 0 to 1 × 10−3. As the corrosion degree increased, the strength of stainless steel bars decreased, and the ductility decreased significantly. Finally, the mechanical properties of the stainless steel bars after corrosion were compared with those of ordinary steel bars.

Corrosion behaviour of stainless steel reinforcement in concrete

AbstractIn Europe, stainless steel rebars have been used since the mid-80s, whilst in North America, their use has been progressively growing only since the mid-90s. Due to their higher resistance to corrosion in comparison to ordinary black steel bars, they have been employed in a wide number of applications worldwide to achieve the durability performance of reinforced concrete structures, especially in extremely corrosive marine environments or when long service lives are required. In this paper, a state of the art on the corrosion resistance of stainless steel bars is reported. In particular, the contribution of Professor Luca Bertolini in this research field is considered. Initially, different testing methods are presented to point out their advantages and limitations and then the results on corrosion behaviour of different grades of stainless steel bars (i.e. austenitic, ferritic and duplex), obtained especially with tests in concrete, are analysed. Afterwards, some of the recent applications of stainless steel bars are illustrated.

Experimental Study on Basic Mechanical Properties of BFRP Bars

Basalt Fiber Reinforced Polymer (BFRP) bars have the advantages of corrosion resistance, high strength, light weight, good dielectric properties, and they are new type of green reinforced alternative material. In order to determine the mechanical properties of BFRP bars, the tensile strength of basalt fiber bars was necessary to be studied. The diameters of the basalt fiber bars were compared by means of uniaxial tensile test in this article. Then the stress-strain curve can be drawn out. The results show that the stress - strain curve of BFRP bars present straight line relation, and there is no sign before failure; there is no yield platform on the stress-strain curve of BFRP bars, which are typical brittle material;the tensile strength of BFRP bars is about 3 times higher than that of ordinary steel bars. and the elastic modulus is about 1/5 of that of ordinary steel; the ultimate tensile strength of BFRP bars varies little with the increase of diameter, but there exist some differences in modulus values.

Behavior of stainless steel–reinforced concrete piers under lateral impact loading

In this study, stainless steel bars with the same diameter were used to replace ordinary stressed steel bars in reinforced concrete bridge piers. An ultra-high drop hammer impact test system was ad...

Enhancement of impact performance of reinforced concrete beams without stirrups by adding steel fibers

The impact strength of reinforced concrete beams without shear reinforcement is studied in this paper, with emphasis on the improvement of the impact performance achieved by using steel fiber-reinforced concrete (SFRC). Drop-weight and companion quasi-static tests have been completed on 2000×125×250mm beams containing ordinary longitudinal steel bars. Seven SFRC mixes have been studied, including three fiber types (smooth, hooked and prismatic) and three volumetric fractions (0% i.e. plain concrete, 0.5% and 1.0%). The study has confirmed the brittle impact behavior of beams without fibers, which failed by shear. With the addition of 0.5% steel fibers, shear failures were obtained with hooked and prismatic fibers but not with smooth fibers. Finally, all beams with 1.0% steel fibers developed a flexural failure mode. The improvement of the impact behavior of beams with SFRC is also confirmed by the fact that most of the specimens which developed a flexural failure had thin diagonal cracks in the webs of the shear spans, but such cracks did not progress due to the fiber-bridging capacity. In the paper, the study is completed with an analysis of the rate sensitivity of the shear strength and the capacity for energy absorption of tested beams.

Mechanical Properties of Steel-FRP Composite Bars under Tensile and Compressive Loading

The factory-produced steel-fiber reinforced polymer composite bar (SFCB) is a new kind of reinforcement for concrete structures. The manufacturing technology of SFCB is presented based on a large number of handmade specimens. The calculated stress-strain curves of ordinary steel bar and SFCB under repeated tensile loading agree well with the corresponding experimental results. The energy-dissipation capacity and residual strain of both steel bar and SFCB were analyzed. Based on the good simulation results of ordinary steel bar and FRP bar under compressive loading, the compressive behavior of SFCB under monotonic loading was studied using the principle of equivalent flexural rigidity. There are three failure modes of SFCB under compressive loading: elastic buckling, postyield buckling, and no buckling (ultimate compressive strength is reached). The increase in the postyield stiffness of SFCB rsf can delay the postyield buckling of SFCB with a large length-to-diameter ratio, and an empirical equation for the relationship between the postbuckling stress and rsf is suggested, which can be used for the design of concrete structures reinforced by SFCB to consider the effect of reinforcement buckling.

Moment-Curvature Behaviors of Concrete Beams Singly Reinforced by Steel-FRP Composite Bars

A steel-fiber-reinforced polymer (FRP) composite bar (SFCB) is a kind of rebar with inner steel bar wrapped by FRP, which can achieve a better anticorrosion performance than that of ordinary steel bar. The high ultimate strength of FRP can also provide a significant increase in load bearing capacity. Based on the adequate simulation of the load-displacement behaviors of concrete beams reinforced by SFCBs, a parametric analysis of the moment-curvature behaviors of concrete beams that are singly reinforced by SFCB was conducted. The critical reinforcement ratio for differentiating the beam’s failure mode was presented, and the concept of the maximum possible peak curvature (MPPC) was proposed. After the ultimate curvature reached MPPC, it decreased with an increase in the postyield stiffness ratio (rsf), and the theoretical calculation method about the curvatures before and after the MPPC was derived. The influence of the reinforcement ratio, effective depth, and FRP ultimate strain on the ultimate point was studied by the dimensionless moment and curvature. By calculating the envelope area under the moment-curvature curve, the energy ductility index can obtain a balance between the bearing capacity and the deformation ability. This paper can provide a reference for the design of concrete beams that are reinforced by SFCB or hybrid steel bar/FRP bar.

Mechanical properties of concrete beams reinforced with CFRP prestressed prisms under reverse cyclic loading

This paper presents the results of cyclic loading tests on concrete beams reinforced with various reinforcement, including ordinary steel bars, CFRP bars and CFRP prestressed concrete prisms(PCP). The main variable in the test program was the level of prestress and the cross section of PCP. The seismic performance indexes including hysteretic loops, skeleton curve, ductility, energy dissipation capacity and stiffness degradation were analyzed. The results show that the CFRP prestressed concrete prisms as flexural reinforcement of concrete beams has good seismic performance. And the ductility and the energy dissipation capacity were good, the hysteresis loops were full and had large area.

Structural performance of continuous RC slabs strengthened in negative moment regions with a mineral‐based composite

AbstractAn experimental programme was proposed and carried out to assess the effectiveness of the mineral‐based composite (MBC) technique for the flexural strengthening of negative moment regions in continuous reinforced concrete slabs. In addition to the testing of the two reference specimens, the experimental programme included the testing of nine continuous RC slab specimens with different strengthening techniques, namely, using ordinary steel bars and MBC material. This experimental programme was conducted to study the failure modes, the load‐deflection behaviour and the failure loads.Furthermore, we present and describe a comparative study between the two strengthening techniques, namely, steel reinforcing bars with MBC or steel bars with epoxy mortar. Based on the experimental results presented, both strengthening techniques for continuous slabs are evidently efficient. In this study the measured results for the average crack spacing were compared with the limits stipulated in CEB‐FIP code 1990 and the failure load calculations were extended with an analytical approach based on the ultimate theory for the failure load calculation. In conclusion, the results obtained from the analytical model are in agreement with the experimental results.

Flexural behavior of concrete beams reinforced with CFRP prestressed prisms

An experimental investigation on the behaviour of concrete beams reinforced with various reinforcement, including ordinary steel bars, CFRP bars and CFRP prestressed concrete prisms(PCP). The main variable in the test program was the level of prestress and the cross section of PCP.The modes of failure and the crack width were observed. The results of load-deflection and load-crack width characteristics were discussed. The results showed that the CFRP prestressed concrete prisms as flexural reinforcement of concrete beams could limit deflection and crack width under service load and PCP can overcome the serviceability problems associated with the low elastic modulus/strength ratio of CFRP.

Shear behavior of light weight ferrocement concrete slabs

The objective of the work presented in this research was to develop light weight composite slab subjected to punching load by using column slab connection at the center of the slab which comprises polystyrene block of thickness 80 mm reinforced with welded galvanized steel mesh or expanded steel mesh. The use of expanded metal mesh and welded steel mesh was proposed as a viable alternative to ordinary steel bars in reinforcing ferrocement plates, also it was proposed to use it with ordinary steel bars to enhance the mechanical behavior of the composite slab. For light weight sandwich elements, light weight polystyrene of density 12Kg/m3 is used as a core material and welded wire meshes or expanded steel meshes are to be used as steel reinforcement at the two thin skin layers. Twelve squares composite light weight slabs were developed having the dimensions of 1200mm x 1200mm and overall thickness of 140mm were tested simply supported along all four sides under central column slab connection until failure. This research presents the behavior of ferrocement lightweight slabs under punching shear. The effects of various types of reinforcing materials were investigated. Using such lightweight materials will contribute to decreasing the weight of the elements and consequently decreasing the overall dead load of the building. Moreover, the study aimed at improving some other characteristics like flexural strength, crack pattern, first crack load, crack width, and deflection.

Bond stress-slip behaviour of steel reinforcing bar embedded in hybrid fiber-reinforced concrete

Experimental study was carried out to evaluate the application of metallic fibers to confine the concrete in column-beam joint. Pullout tests on cubic specimens of size 200 × 200 × 200 mm with deformed steel bar embedded for a fixed length of 5 times the diameter of tested deformed bar were performed under monotonic applied displacement at the tip of the bar (displacement controlled tests). The key variable of the experimental study was the different confining conditions; by ordinary reinforcing steel bars, and by metallic fibers. To confine the concrete by the fibers, two different types of metallic fibers were used; amorphous metallic fibers and carbon steel hooked-end fibers. The fibers were investigated both in mono and hybrid forms. The dosage of fibers in mono fiber-reinforced concrete was kept 40 kg/m3. In case of hybrid fiber-reinforced concrete, two concrete compositions were investigated: one containing 20 kg/m3 of each fiber and second containing 40 kg/m3 of each type of fiber. The pullout tests results revealed that both types of fibers contribute to ameliorate the peak bond stress and also to improve the ascending branch of the bond stress versus slip curve in terms of stiffness. Comparison of the bond stress-slip response of anchored bar in concrete confined by the ordinary reinforcing steel bars and by the metallic fibers demonstrated that the concrete confined by the fibers in hybrid form showed better performance than the concrete confined by the ordinary steel bars in terms of peak bond stress and toughness. Since the hybrid form of investigated metallic fibers realize same effect as that by ordinary steel, the congestion of steel in seismic resistant column-beam joint can be avoided by replacing some percentage of steel ratio to confine the concrete by the metallic fibers.

Experimental study on flexural behavior of concrete beams reinforced by steel-fiber reinforced polymer composite bars

Experimental studies investigating the flexural behavior of six concrete beams were conducted with various reinforcements, including ordinary steel bars, steel-fiber reinforced polymer composite bars, pure fiber-reinforced polymer bars (either carbon fiber reinforced polymer bars or basalt fiber reinforced polymer bars), and hybrid bars (steel bars and basalt fiber reinforced polymer bars). The test results show the following: (a) steel-fiber reinforced polymer composite bar beams exhibit stable post-yield stiffness after the yielding of the inner steel bar of the steel-fiber reinforced polymer composite bar and concrete crushed after the rupture of the outer fiber-reinforced polymer of the steel-fiber reinforced polymer composite bar; (b) the ordinary reinforced concrete beam has the largest ductility coefficient, but the ultimate load was just approximately 31% of that of the corresponding steel-fiber reinforced polymer composite bar beams; (c) brittle shear failure was observed for both fiber reinforced polymer bar reinforced beams because of the high ultimate tensile strength of fiber-reinforced polymer bar; (d) although the steel-fiber-reinforced polymer ratio of the hybrid beam (reinforced by steel and basalt fiber reinforced polymer bars) is the same as that of the steel-fiber reinforced polymer composite bar beams, the ultimate load of hybrid beam is approximately 72% of that of the corresponding steel-fiber reinforced polymer composite bar, which is caused by the premature slip of basalt fiber reinforced polymer bar in hybrid beam where the bond stress is large; (e) by comparing coefficients of displacement ductility and energy ductility, it is demonstrated that energy ductility coefficient is more reasonable for evaluating the performance of steel-fiber reinforced polymer composite bar beams take into account of the post-yield stiffness of steel-fiber reinforced polymer composite bar beams; and (f) high initial stiffness and good ductility for steel-fiber reinforced polymer composite bar reinforced concrete beams can be obtained by adjusting the steel-fiber-reinforced polymer ratio and fiber-reinforced polymer type. Furthermore, because of the steel-fiber reinforced polymer composite bar’s outer fiber-reinforced polymer, steel-fiber reinforced polymer composite bar reinforced concrete beams have a high durability.

A Nonlinear Study on the Prestressed Structure of High Strength Concrete - Steel Fiber Concrete

In the construction of high-rise buildings, large span structures and tall structures, the combinatorial design structure of high strength concrete, steel fiber concrete, prestressed tendon and ordinary steel bar is a main measure to bring the advantages of high strength concrete into full play. This paper studies the nonlinear constitutive relations of high strength concrete, steel fiber concrete and steel bar. By using finite element method, this paper carries out a numerical simulation of the whole monotonic loading process of box prestressed continuous beam of high strength concrete - steel fiber concrete and gets comparatively detailedc calculating results, which provide a theoretical reference for the reasonable combinatorial design of high strength concrete,steel fiber concrete, prestressed tendon and ordinary steel bar.