Main Steel Bars Research Articles

Ultra-high performance steel fibers concrete corbels: Experimental investigation

In the present paper, results of testing eleven ultra-high performance steel fibers concrete (UHPSFC) corbels with concrete compressive strength 150MPa and under vertical loading are reported. The main test variables were shear span-to depth ratio, main tension reinforcement ratio and the provision of secondary reinforcement (closed stirrups). In all corbels, except one, the main steel bars yielded before failure and corbels failed in a consistent manner. Whereas the validity from provision the secondary reinforcement in the UHPSFC corbels represents by a significant increase in the corbels stiffness with taking into consideration the corbels failure modes. The test results in terms of load versus deflection curves, stiffness, ductility and crack patterns show the effectiveness of using ultra high performance steel fibers concrete to ensure a superior strength and deformation capacity in reinforced concrete corbels. Experimental results have been compared with diverse prediction methods. The truss model can provide accurate strength predictions in comparison with the ACI 318-14 cod’s procedure.

Force- and Displacement-Controlled Non-linear FE Analyses of RC Beam with Partial Steel Bonded Length

The current work deals with the comparison between two different computer formulations, namely, force- and displacement-controlled approaches for non-linear FE analyses of an RC beam in flexure with partially developed and asymmetric steel reinforcement. Instead of inputting load–slip data of direct tension pullout test to ANSYS code for defining the bond property, a different approach is adopted. In the study, load slip data are extracted from bond stress model of Yousaf (Performance of self-compacting concrete in bond at beams intersection. PhD dissertation, 2015) where the model was developed using data of digital strain gauge mounted on main steel bar in flexural beam testing. The load slip data are fed to computer as a set of real contestants choosing large-deformation non-linear plastic analysis scheme, discrete modeling approach for material modeling and program-chosen incremental scheme following the Newton–Raphson method. Complete harmony is found in computer and experimental results advocating the correctness and validation of the approach adopted for computer analysis. Among both formulations adopted for ANSYS analysis, the results reveal that the displacement-controlled approach is easy and efficient in terms of time-saving and less disk space requirement along with the ability to give falling branch of load–deflection response, if element displacement capacity still exists. Furthermore, it gives an early estimate of the load carrying capacity of the structural element along with suitable values of convergence and non-linear solution parameters. On the other hand, force-based analysis for a beam with unsymmetrical reinforcement detailing seems to yield more realistic and practical results in terms of mid-span deflection and beam cracking behavior compared with assumed symmetric displacement-controlled technique. From the study, the superiority of the force-controlled approach in comparable conditions is established through observed performance simulation with that of practical beam results along with the applicability of the approach adopted in the study. A comparison of ANSYS and experimental stress of partially developed rebar shows that the used bond model performs extremely well.

Effects of spiral confinement to the bond behavior of deformed reinforcement bars subjected to axial tension

When grouted pipe splice connections are employed, the structural performance of the connected precast concrete components is significantly influenced by the bond behavior between the main reinforcing bars and the surrounding grout. Owing to this important characteristic, the bond behavior, in particular the local bond-stress slip relationship and the bond strength, of the main steel reinforcement bars embedded in grout needs to be investigated accordingly. This paper presents the bond behavior of main deformed steel reinforcement bars confined by a grouted spiral connection. A total of 36 pullout specimens were tested under increasing axial tensile load to investigate the effects of spiral confinement to the connected main steel bars. Parameters covered in this study were spiral diameter and spiral pitch distance. The experimental results showed that the spiral configurations influence the bond performance due to the effect of confinement generated by the spiral diameter and pitch distance. As compared to spiral pitch distance, the spiral diameter provides more dominant confinement effect which subsequently increases the bond strength significantly.

Grouted Pipe with Double Spirals for Precast Concrete Connections

This paper presents the pullout performance of grouted splice connections made with steel pipes and double spirals in connecting high tensile steel deformed bars. The parameters studied were the steel bar embedded lengths, grout strength and diameter of the pipe in influencing the tensile performance of the splice connections. A total of nine proposed grouted spiral connections with double spirals were tested under increasing axial tension until failure. The results indicated that the use of double spiral combined with grout strength of at least 60 N/mm2 and main steel bar embedded length of 10 times bar diameter could provide adequate bond strength to form a satisfactory precast connection system.

The Effect of Steel Fiber as Additional Reinforcement in the Reinforced Concrete Beam

In the normal practice in the reinforced concrete design, the main reinforcement steel bar and links was used to fabricate the concrete structure. However new materials such as steel fiber has been introduced as the reinforcement to the reinforced concrete structure [1]. Nowadays, the application of fiber in concrete increase slightly as an engineering material demands. Fibers have distinctive of geometry, size and material. The characteristics and properties of fiber influence the properties concrete. Steel, glass and synthetic fibers were used in concrete in 1960s because of the difficulty to handle the asbestos fiber [2].

Investigation Strength Of One Way Slab Panel Using Steel Fibers And Wire Mesh (Ferro Cement)

This paper presents a study of the flexural behavior of the reinforced mortar slabs using both of steel fiber concept and ferrocement layer in tension zone cover as an additional reinforcement to the main steel bars .The concept of steel fibers mean that substitution the common types of steel fibers by alternative material exhibit the same action that produced by the tradition fibers. This material represented by short length of steel nails (SLSN) ,which is cheapest and more available than the first type in the local markets .The efficiency of this material have been checked using seven samples of beam prototypes tested under flexural behavior and reinforced with the nails. Results produced that the nails will improve ultimate flexural strength of mortar noticeably .The increasing ratio in flexural strength of mortar was in the range of (400-1200)% related with these seven beams .Therefore, and according to this advantage, eight one way reinforced slab panel have tested under flexural loading. They reinforced with the nails ,one layer of wire mesh to produce ferrocement cover, and the both material . After testing these eight panels ,the once reinforced with SLSN as an additional reinforcement exhibit the best performance in resisting flexural stresses by increasing flexural load capacity from 17.25kN to about 20kN. Furthermore, maximum central deflection was also reduced by this material from 24.75mm for non fiber reinforced panels to 4.9mm for reinforced once. Although the action of ferrocement was less than the results produced by the fibers ,ferrocement cover increases the ultimate flexural load capacity for panels reinforced with single layer of wire mesh as well as decreasing in the maximum central deflection for these panels in comparison with the control specimens .

Experimental and analytical study of corroded shear-critical reinforced concrete beams

This paper presents the experimental results of two highly corroded shear-critical deep beams subjected to a chloride environment to assess the shear behavior of long-term-corrosion damaged beams. A 26-year-old reinforced concrete beam corroded by exposure to a chloride environment was cut into two small short-shear-span beams, or deep beams, which were tested under three point bending until failure, along with a control beam of the same age, same length and same cross-section (115 × 28 × 15 cm). Cracking and corrosion maps were drawn for the corroded beams in order to assess the corrosion. Force displacement curves were drawn for the corroded and control beams. After testing the beams until failure, the main steel bars and the stirrups were extracted from the beams and loss of mass was measured and plotted for both longitudinal and transverse reinforcement. It was noted that the loss of mass of transverse and longitudinal reinforcements had not had an important influence on the failure mode and it had not affected the load-bearing capacity of the beam. It was found that the stirrups came into action after the failure of the compression strut and thus decreased the ductility of the corroded beams. Analytical investigations were made to compare the experimental shear capacity with the theoretical value. Strut and tie model predictions were more accurate than the conventional sectional methods provided for in ACI 318-08 and Eurocode 2.

Experimental and numerical investigation for the flexural strengthening of RC beams using near-surface mounted steel or GFRP bars

In this paper, the effectiveness of NSM bars as a means of restoring or upgrading the flexural capacity of RC beams is experimentally and numerically investigated. The studied parameters included type of NSM bars: steel versus GFRP, and NSM reinforcement ratio (number and diameter of inserted NSM bars). A total of eight groups of 16 beams were tested under four-point bending. The two beams of the first group were reinforced with three main steel bars and were used as control specimens. The two beams of the second group were reinforced with three main GFRP bars and were utilized for comparison with control specimens. Assuming that one of the three main steel bars in the control specimen had corroded, three groups of six beams were designed in which one NSM steel or GFRP bar was inserted in the tension side. Yet, with the assumption of the corrosion of two main steel bars in the control beam, the last three groups of six beams were planned in which two NSM steel or GFRP bars were planted in the tension side. For NSM-upgraded beams, special type of epoxy paste was used as bonding agent. Test results showed that by using NSM steel or GFRP bars to compensate the difference in the main reinforcement, the original load capacity of the control beam was successfully restored. The ultimate capacity of the beams was predicted using the ACI 318-11 code and ACI 440.1R-06 guidelines. A numerical investigation utilizing nonlinear finite element (FE) analysis was also carried out using LS-DYNA software. A comparison was made between the experimental and numerical results and good agreement was obtained. Based on the validation of FE results, the numerical analysis was extended to include additional cases to study the effect of FRP reinforcement ratio on the flexural performance of NSM-upgraded beams.

BEHAVIOUR OF HIGH-PERFORMANCE CONCRETE BEAMS AS AFFECTED BY BONDED PART AND RIB GEOMETRY OF MAIN STEEL REINFORCEMENT

The need of high-performance concrete is increased in the recent years. Also using steel of high grade and maximize the benefit of using these material become necessary .So, different ribs are used for enhancing the bond strength between steel reinforcement and high-performance concrete . There is little information in the available literature about the bond characteristics for the different forms of rib geometry of the deformed bars and its effect on behavior of high-performance concrete beams for different relative rib area( αsb ) and development length. The main objective of this research is to study the effect of bonded part and rib geometry of main steel bars on behavior of high-performance concrete beams, also Pattern of cracks, final mode of failure and deformation characteristics (deflection, slip, concrete strain and slope for beams) were investigated.

Numerical modelling of FRP strengthened RC beam-column joints

This paper reports part of a comprehensive research study conducted at the University of Queensland on the ability of CFRP web-bonded systems in strengthening an exterior beam-column joint subjected to monotonic loads. One 1/2.2 scaled plain and four CFRP repaired/retrofitted joints subjected to monotonic loads were analysed using the nonlinear finite-element program ANSYS and the results were calibrated against experiments. The ANSYS model was employed in order to account for tension stiffening in concrete after cracking and a modified version of the Hognestad's model was used to model the concrete compressive strength. The stress-strain properties of main steel bars were modelled using multilinear isotropic hardening model and the FRPs were modelled as anisotropic materials. A perfect bond was assumed as nodes were shared between adjacent elements irrespective of their type. Good agreement between the numerical predictions and the experimental observation of the failure mechanisms for all specimens were observed. Closeness of these results proved that the numerical analysis can be used by design engineers for the analysis of web-bonded FRP strengthened beam-column joints with confidence.

Performance of Steel Fibrous Reinforced Concrete Corbels Subjected to Vertical and Horizontal Loads

A softened strut-and-tie macromodel able to reproduce the flexural behavior of corbels in plain and fibrous concrete and with the presence of steel bars, including softening of compressed struts and yielding of main and secondary steel bars, is presented in this paper. The main focus of the proposed model is the determination of the load-deflection curves of corbels subjected to the coupled effects of vertical and horizontal forces bearing in mind the influence of the type of concrete (normal or high strength), of the fiber percentage and of the arrangement and percentage of the main and secondary (horizontal stirrup) steel bars. A validation of the proposed model is made therefore with reference to some of the experimental data available in the literature and also to numerical results obtained by using a nonlinear finite-element program (ATENA-2D) able to analyze the flexural behavior of deep members. Finally some design considerations on the use of fibrous reinforced concrete in RC corbels are given.

Flexural response of FRC corbels

Abstract A strut-and-tie macro-model is proposed to determine the flexural response of fiber reinforced concrete (FRC) corbels, reinforced with longitudinal bars and subjected to vertical load. The effects of the corbel geometry, the percentage of steel fibers, and grades of concrete and steel bars are also included. The model, which is specific for FRC corbels with hooked steel fibers, allows the determination of load levels, and corresponding displacements, associated with the first cracking, yielding of the main steel bars and crushing of the concrete strut. The sequential occurrence of these phenomena is established, depending on the amounts of steel fibers and reinforcing steel. The simplified flexural response of corbels, in terms of load–deflection curves, is in good agreements with experimental data collected from the literature. In addition, prevision of bearing capacity and failure modes (yielding of main steel or crushing of concrete strut) is obtained with reference to other experimental data collected from the literature. Finally, some recommendations on the design of FRC corbels are given.