Tension Reinforcement Research Articles

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.

Experimental shear tests of reinforced concrete beams with corroded longitudinal reinforcement

AbstractIn this study, shear tests were conducted to investigate the effect of corrosion damage induced in longitudinal reinforcement on the shear resistance mechanisms of reinforced concrete (RC) members without transverse reinforcement. A total of eight RC beam specimens were carefully designed and fabricated, and accelerated corrosion and typical shear tests were conducted considering various anchorage conditions and corrosion rates that were introduced in the longitudinal tension reinforcement as the key test variables. Test results showed that when the tensile reinforcement was not sufficiently anchored at the end regions of the RC members, the shear strengths of the test specimens decreased as the corrosion rate increased. In contrast, when the longitudinal reinforcement was properly anchored using the hook detail, the shear strengths showed a clear trend of increase, even when the longitudinal reinforcement was severely corroded.

Performance of hybrid bars in corrosion and flexure in concrete beams

Corrosion of reinforcing steel is a serious problem worldwide; the problem of steel rebar corrosion leads to a reduction in the lifespan of the structure and adds to the maintenance costs. Many techniques have been developed in recent past to reduce corrosion but none of these solutions seem to be applicable as an adequate solution to the corrosion problem. Besides the use of Fiber Reinforced Polymer (FRP) rebar, hybrid rebar consisting of both FRP and steel are also being tried to control the problem of steel corrosion. This research evaluates the performance of hybrid rebar in corrosion resistance by inducing natural corrosion in a number of concrete cylinders with a hybrid rebar embedded symmetrically. The research also studies the performance of hybrid rebar as a tension reinforcement in concrete beams.

Investigation on machining performance of boron carbide reinforced aluminium matrix composite during WEDM taper cutting process

Miniaturized devices and complicated three dimensional profiles with advanced metal matrix composites have been in demand in recent years. Taper cutting in wire electrical discharge machining (WEDM) is a deep routed not contact spark eroding technique which is a viable solution for machining complex three dimensional geometry using advanced metals, alloys, super alloys and composites. Hence, in the present work, machining performance of boron carbide reinforced aluminium matrix composite (AlB4C) during WEDM taper cutting has been investigated. Experiments have been conducted using Taguchi’s L27 orthogonal array. The effect of seven input parameters such as percentage of reinforcement (B4C), part thickness, taper angel, pulse duration, discharge current, wire feed and wire tension has been studied on performance measures such as angular error and surface roughness. Finally an optimal combination of process parameters has been proposed which give the minimum angular error and minimum surface roughness during machining of boron carbide reinforced aluminium matrix composite using WEDM taper cutting process. ANOVA analysis has also been carried out to obtain the most influential parameters during the process.

ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ПРЕДВАРИТЕЛЬНО НАПРЯЖЕННЫХ БЕЗ СЦЕПЛЕНИЯ ЖЕЛЕЗОБЕТОННЫХ ПЛИТ ПРИ ПРОДАВЛИВАНИИ

In this paper there are results of a punching shear test of slab samples, which were modeling post-tensioned reinforced concrete floor slabs when they are punched by columns. Geometrical dimensions of slab samples and properties of used materials are listed as well. There were 4 series of samples which differed to each other by level of prestress. Load have been applied through stamps of several types, which have allowed to research different positions of tensioned reinforcement relatively to the punching pyramid. Obtained results are discussed. Recommendations, which compliance may allow to obtain positive effect in ultimate punching shear loads for unbonded post-tensioned slabs are given.

Comparison of Moments for Pile-Cap Design

This paper discusses the comparative study of design moments for pile cap with conventional methods and finite element analysis. If a detailed finite element analysis is adopted, flexibility of the pile cap is considered. When a pile cap is designed by truss analogy, 80% of the tension reinforcement is concentrated in the region where the cap is supported on piles and at the column, which depends on design moments. It is observed that the difference in the design moments was considerable and should be taken into account for calculation and placing of reinforcement.

Calculation of nodes of monolithic frames with reinforcement stressed on concrete in the settlement complex "LIRA-CAD"

The stress-strain state of sloping cross-sections remains poorly understood (in comparison with normal cross-sections), which is confirmed by the absence of a single method of calculation that would take into account all factors affecting the operation of reinforced concrete elements with simultaneous bending moment, action and longitudinal force. Pre-tensioning can be carried out both with and without adhesion of a stressed reinforcement with concrete. The difference between the post-tension technology and the widely known pre-stress (carried out in the conditions of the WB plant) is that the stressed reinforcement is tensioned after concreting and concrete with sufficient transfer strength (approximately 70-80% of brand strength). To ensure that the tension of the reinforcement is possible, after the concrete has hardened, it must be able to move freely in the concrete. For this purpose, on-elastic fittings are placed in channels (made of metal or plastic pipes). Efforts on concrete are made by means of the anchor devices installed at the ends. Typically, pre-stresses use arm-tour ropes arranged in structures between the upper and lower meshes of the arm-tour according to the shape of the plot of bending moments (line of the main tensile forces). When tensioning the ropes, the tension of the compression of the concrete (from the force of tension P) and the unloading force (reactive pressure) arise, which changes its direction on the supports in non-different structures. The calculation of the support units with curvilinear tension reinforcement is very important when designing these structures. One of the important issues is the proper modeling of such nodes in computational complexes to obtain reliable results (stresses and displacements).

Determination of Coefficients for Defining the Deformations when Calculating Reinforced Concrete Structures on Deformation and Cracking Disclosure

The problem of determining the coefficient of averaging the deformations in tensioned reinforcement when calculating reinforced concrete structures according to the limiting states of the second group is considered. An assessment is made of the effect on it of the adhesion stresses distribution type between the reinforcement and the concrete.

Pengaruh Kekuatan Balok Induk Terhadap Dimensi Balok Anak Pada Beton Bertulang

Generally, concrete can be categorized into normal quality concrete and high-quality concrete, both are commonly used in construction. Normal quality concrete has approximately 20 MPa to 58 MPa quality, while the high-quality concrete has higher than 58 MPa. One of the applications of these concrete in structure is the dimension and joist position toward the beam�s strength in a story structure. To analyze the effect of joist toward beam, Finite Element Analysis (FEA)is applied with the following: Utilizing ANSYS with SOLID65, SOLID45, LINK8 with varying size of joist and beam such as type A beam by the size of 30/40 and joist by the size of 20/40, 25/40, 30/40, type B beam by the size of 30/50 and joist size of 25/50, 25/40, 25/35 and type C beam by the size of 40/60 and the joist size of 35/60, 35/50, 35/40. Steel material is used each has 400 MPa for the main reinforcement tension, 200 MPa for the stirrup reinforcement, normal quality concrete tension of 25 MPa, placement tension of 400 MPa, steel modulus elasticity of 200,000 MPa. Based on the FEA it is obtained that the comparison of joist influence toward the beam is centered from the comparison result of

Influence of Fiber Content on Shear Capacity of Steel Fiber-Reinforced Concrete Beams

For shear-critical structural elements where the use of stirrups is not desirable, such as slabs or beams with reinforcement congestion, steel fibers can be used as shear reinforcement. The contribution of the steel fibers to the shear capacity lies in the action of the steel fibers bridging the shear crack, which increases the shear capacity and prevents a brittle failure mode. This study evaluates the effect of the amount of fibers in a concrete mix on the shear capacity of steel fiber-reinforced concrete beams with mild steel tension reinforcement and without stirrups. For this purpose, 10 beams were tested. Five different fiber volume fractions were studied: 0.0%, 0.3%, 0.6%, 0.9%, and 1.2%. For each different steel fiber concrete mix, the concrete compressive strength was determined on cylinders and the tensile strength was determined in a flexural test on beam specimens. Additionally, the influence of fibers on the shear capacity was analyzed based on results reported in the literature, as well as based on the expressions derived for estimating the shear capacity of steel fiber-reinforced concrete beams. The outcome of these experiments is that a fiber percentage of 1.2% or fiber factor of 0.96 can be used to replace minimum stirrups according to ACI 318-14 and a 0.6% fiber volume fraction or fiber factor of 0.48 to replace minimum stirrups according to Eurocode 2. A fiber percentage of 1.2% or fiber factor of 0.96 was observed to change the failure mode from shear failure to flexural failure. The results of this study support the inclusion of provisions for steel fiber-reinforced concrete in building codes and provides recommendations for inclusion in ACI 318-14 and Eurocode 2, so that a wider adoption of steel fiber reinforced concrete can be achieved in the construction industry.

Repair of reinforced concrete beam by adding external reinforcement

The negligence in construction are usually due to error in replace or calculation of required reinforcement. The mistake known after construction and must be corrected as soon as possible. Some actions should be taken namely, add some pretension, augmented the beam size, use the FRP, and add some external reinforcement. Studies on rehabilitation and retrofitting are gaining importance due to the need for restoration of partially damaged structures due to wind load and earthquake. To prevent any disaster during the future earthquakes, the existing deficient buildings need to be retrofitted. The external tension reinforcement added when the flexural beam capacity inadequate, and the stirrups added when the shear beam capacity inadequate. The adding with external reinforcement also done after some tensile failure or cracks in the beam. In this case some damage of concrete must being consider in reducing stiffness and strength. The objective of this research is studied about the adding of external tensile reinforcement and stirrups after tensile failure and explore the influence of those action to the beam and then compared the strength, stiffness, ductility and crack pattern of beams before and after retrofit. The specimens were 12 original beam, and 12 retrofitted beam. The original beams have dimensions of 15 cm x 15 cm x 100cm, the tensile reinforcement were 4ф6 and compression reinforcement 2ф6. The stirrups were ф6-200 along the beam. Retrofit strategies were adding bottom tensile reinforcement 2ф6 and 3ф6, and adding stirrups ф6-60 in the shear span. The experiment shown the increase of beam ultimate load after retrofitting, but decrease the ductility and stiffness of the beam. The pattern of cracks also changed between original and retrofitted beam.

A More Realistic Estimation of Ductility in Reinforced Concrete Beams Through Three-Dimensional Finite Elements

Ductility in reinforced concrete (RC) beams subjected to bending is generally assessed on the basis of the one-dimensional (1D) beam theory through the moment–curvature relationship of its cross-section. The inhomogeneity of concrete, however, inevitably imposes a three-dimensional (3D) stress state in any RC structural member. The importance of this work is its different approach to assessing the ductility in RC beams, taking into account this triaxial stress state. A concrete model which has been well documented experimentally in the literature is used, in conjunction with an in-house 3D smeared fixed-crack finite element code. Simply supported beams under three-point monotonic loading are used as numerical examples. After validating the results with experiments, three important parameters which affect the ductility and strength of RC beams are investigated. These are the tension reinforcement ratio, the yield strength of tension reinforcement steel and the compression reinforcement ratio. It appears that, for the first two, the general trend remains the same as with the 1D approach of the Codes, whereas the third does not affect the ductility of the under-reinforced beams, contrary to the Codes.

Performance of hybrid fibres on mechanical properties of self-compacting concrete at elevated temperature

Purpose The present experimental investigation attempts to study the behaviour of hybrid fibre-reinforced self-compacting concrete (HFSCC) subjected to elevated temperature. The purpose of this study is to find out the performance of hybrid fibres of 0.5 per cent by volume of concrete (out of which 75 per cent are steel fibres and 25 per cent, polypropylene fibres). Reinforced beams were casted and tested for the flexural load-carrying capacity, and comparisons were made with the load-carrying capacity of reinforced beams without the inclusion of fibres. Design/methodology/approach The study includes 60 concrete cubes of 150 mm and 60 beams of 150 × 150 × 1,100 mm reinforced with minimum tension reinforcement according to IS 456-2000. The specimens were subjected to elevated temperature from 100°C to 500°C with an interval of 100°C for 2 h. The residual compressive strength and the load-carrying capacity of beams for 5-mm deflection were measured. Parameters such as load at first crack, width and length of cracks developed on the beam during the application of load were also studied. Findings The result shows that for self-compacting concrete without fibres (SCCWOF), there is a gain in compressive strength between 200°C and 300°C, beyond which the strength decreases. For HFSCC, the gain in strength is between 300°C and 400°C, and thereafter the strength gets reduced. The load-carrying capacity of beams reduces with an increase in temperature. An increase in load-carrying capacity (up to 40.7 per cent) for HFSCC beams is observed when compared to SCCWOF beams at 500°C. Originality/value Better performance was observed with the usage of fibres when the specimens were subjected to elevated temperatures.

Effectiveness of Various Techniques Using FRP for the Strengthening of R. C. Beams with Tension Lap Splices

This paper presents an experimental program conducted to investigate the flexural performance of RC beams with tension reinforcement lap splice strengthened using externally bonded FRP different techniques in splice region. The specimens were reinforced on the tension side with four deformed bars spliced at mid span. The tested beams are of 3200 mm total length and 250*120 mm cross section, tested in positive bending. The considered parameters were splice length, type of FRP (glass or carbon), strengthening techniques in splice region (externally confine strips around cross section, Near Surface Mounted technique "NSM" stirrups, externally bonded sheets or bars on the tension face, number of GFRP strips layers (one layer, two layers, and three layers), and shape of NSM stirrups (Box or U shape). No additional anchorage mechanism or bonding methodology was applied for the FRP strips on the concrete except the epoxy adhesive. The effect of these factors on the failure of modes, the ultimate load, the bond strength and that the ductility were investigated. The results indicated that all applied strengthening techniques were efficient in improving the bond strength of the lap splices, the ductility, and the load-deflection behavior of the tested beams, especially when strips were installed over the splice region. This study approved that NSM technique gave more prominent simplicity of employ.

Ductility of Concrete Members Reinforced with Welded Wire Reinforcement (WWR)

Past research studies have been conducted on the ductility of concrete members reinforced with welded wire reinforcement (WWR) and determined a new phenomenon called strain localization reduces member ductility due to superior bond between WWR and concrete. Such studies have concluded that strain localization adversely affects the ductility of members reinforced with WWR and it is unsafe to use WWR as tension reinforcement. In this study, 50 simply-supported, concrete slabs with a representative slab width of 2 ft (610 mm), thickness of 7 in. (180 mm), and total length of 21 ft (6.4 m) were tested to further examine the strain localization phenomenon on global deformations. Two major parameters were investigated, cross-weld spacing and wire diameter. The impact of these two parameters on strength, ductility, and mode of failure of concrete members reinforced with WWR was also studied. Moment curvature analysis was used to estimate inelastic deflections and ductility to investigate the effect of the reinforcement total elongation at failure of the wire material on the overall member ductility. It was observed that members reinforced with WWR with cross-weld spacing of 14 in. (355 mm) or more had similar ductility as members reinforced with loose wires (without cross-weld). Members reinforced with WWR with closely spaced cross-weld (i.e., 3 or 7 in. (75 or 180 mm)) showed erratic and often less ductility, however, the wire itself was shown to have low ductility. Failure of members reinforced with WWR provided sufficient warning prior to failure as evidenced by the ductility ratios in excess of 2.5. Additionally, a moment-curvature analysis based parametric study showed that an acceptable level of ductility can be achieved with a minimum total elongation of wire reinforcement of 3% at failure.

Detection and Measurements of Cracks in Axially Loaded Tension RC Members by Image Processing Technique

Concrete cracking is very common and appeared in all types of concrete structures. Detection of concrete crack initiation and measurement of their characteristics has been a part of structural monitoring and maintenance program. Though manual inspection of cracks in the concrete structure is the oldest and still an accepted method of crack measurements, a more accurate technique for crack detection and measurement, applicable for all kind of concrete structures, is required. Automatic crack identification and crack width measurement by the image analysis method has been gaining popularity due to its versatile applicability, more accuracy and safety standard in difficult situations. In this context, the image analysis method is adopted in laboratory testing of the concrete prism with reinforcement under axial tension to identify and measure cracks in concrete prism samples. In this research work, a crack quantification method based on 2D image analysis is utilized. Raw colour images (RGB images) were obtained by means of a camera for cracks formed due to axial tension in reinforcement. Processing of RGB images with sufficient information will provide the dimension of crack. For all the image post-processing, an open source ImageJ software was utilized and characteristics of cracks were automatically determined by Ridge Detection Plugin. The results of image processing were also verified with the results from microscopic measurement of cracks in reinforced concrete prism samples.

FLEXURAL DUCTILITY OF STRUCTURAL CONCRETE MEMBERS SUBJECTED TO LIMITED CYCLES OF REPEATED LOADING

For structural concrete members that may expose to serious earthquake, overload or accident impact, the design of ductility must be given the same importance as the flexural strength. The aim of this investigation is to study the change in ductility of structural concrete flexural members during their exposure to limited cycles of repeated loading. Twenty full-scale beam specimens have been fabricated in to two identical groups; each group consisted of ten specimens. The first group was tested under monotonic static loading to failure and regarded as control beams, while the specimens of the second group were subjected to ten cycles of repeated loading with constant load interval, which ranged between 40% and 60% of ultimate load. Specimens in each group were categorized as follows: two traditional reinforced concrete specimens with different intensity of tension reinforcement; three partially prestressed specimens with bonded strands; three partially prestressed specimens with unbonded strands; and two fully prestressed concrete specimens. The main variable, which was considered for all specimens was the partial prestressing ratio (PPR). It was observed that, the ductility of reinforced concrete beams was insignificantly increased during subjecting to limited repeated loading. For fully prestressed and partially prestressed concrete beams with high level of PPR, the ductility was significantly enhanced, while, it was decreased for specimens with small level of PPR.

Mechanical role of reinforcement in seismic behavior of steel-strip reinforced earth wall

In the current design practices of steel-strip reinforced earth walls (SSREWs), the length of the reinforcing material is determined based on the equilibrium between the reinforcement tension and the earth pressure acting on the wall. Here, the resistance of the reinforcing material laid in the active failure zone (AFZ) is not considered. Moreover, the mechanical role of the reinforcing material against the integrity of the SSREW has not been sufficiently verified. Regarding the seismic stability of SSREW, although it is investigated by treating the entire reinforced earth wall as a rigid body, this inspection method is for gravity-retaining walls, and the difference in the seismic behavior between the SSREW and the rigid body is not clear. In this study, therefore, dynamic centrifuge model tests on 6 types of SSREWs were conducted to clarify the following items: (1) the basic earthquake behavior of a SSREW, (2) the mechanical role of the reinforcing material laid in the AFZ and (3) the mechanical role of the reinforcing material against the integrity of the SSREW. The results indicated that the reinforcing material laid in the AFZ can restrain the amount of deformation of the wall during earthquakes. Furthermore, the more stable the AFZ is, the smaller the maximum wall displacement will be.

A new generation of soil-geosynthetic interaction experimentation

A new device was developed to comprehensively assess the interaction between soil and reinforcement as well as the interaction between neighboring reinforcement layers in a reinforced soil mass, under both working and ultimate interface shear stress conditions. An understanding of these two interactions is required to assess the mechanical behavior of a geosynthetic-reinforced soil mass considering varying vertical reinforcement spacings. Specifically, the new device allows direct visualization of the kinematic response of soil particles adjacent to the geosynthetic reinforcement layers, which facilitates evaluation of the soil displacement field via digital image analysis. Evaluation of the soil displacement field allows quantification of the extent of the shear influence zone around a tensioned reinforcement layer. Ultimately, the device facilitates investigating the load transfer mechanisms that occur not only at the soil-reinforcement interface, but also at distances farther from the interface, thereby providing additional insight into the effect of vertical reinforcement spacing on a reinforced soil mass. Finally, the device allows monitoring of dilatancy within the reinforced soil mass upon shear stress generation at the interface between soil and reinforcement. Overall, the device was found to provide the measurements needed to adequately predict the strains developing both in reinforcement layers tensioned by direct application of external loads as well as in reinforcement layers tensioned by the shear transfer induced by adjacent geosynthetic reinforcements. Ultimately, the proposed experimentation technique allows generation of data required to evaluate the load transfer mechanisms amongst soil and reinforcement layers in reinforced soil structures. The strain magnitude in the neighboring reinforcements was found to exceed a magnitude of 10% of the strain magnitude obtained in the active reinforcement. The zone of shear stress transfer from the soil-reinforcement interface was found to exceed 0.2 m on each side of the active reinforcement.

A NONLINEAR FINITE ELEMENT ANALYSIS OF PRECAST INDUSTRIALISED BUILDING SYSTEM BEAM UNDER FLEXURAL TEST

Software simulation enables design engineers to have a better picture of possible structural failure behaviour and determine the accuracy of a design before the actual structural component is fabricated. Finite element analysis is used to simulate the behaviour of the reinforced concrete beam under the flexural test. During the flexural test, results are recorded for both simulation and experimental tests. By comparing the results, beam displacement, crack patterns, and failure modes can be studied with better accuracy. The accuracy percentage for yield load and ultimate load between the two tests results were 94.12 % and 95.79 %, respectively, whereas the accuracy percentage for elastic gradient before the yielding stage was 81.08 %. The behaviour between simulation and laboratory models described is based on crack pattern and failure mode. The progression of von Mises (VM) stresses highlighted the critical areas of the reinforced concrete beam and correlation between the experimental specimen, in terms of flexural cracks, shear cracks, yielding of tension reinforcement, and the crushing of concrete due to compressive stress. This paper concludes that simulation can achieve a significant accuracy in terms of loads and failure behaviour compared to the experimental model.