Influence Of Stirrups Research Articles

Investigation of CFRP strengthening efficiency experimentally and analytically on reinforced concrete beams

The influence of stirrups, shear span to effective depth ratio, FRP strengthening configuration, and strip width to spacing ratio over the experimental performance of the CFRP-strengthened beams and the estimation accuracy of a total of eleven analytical expressions were evaluated in this study. The main findings obtained in the experimental investigation were as follows. CFRP Strengthening enhanced the load-carrying capacities in all series by an average of 44% with regard to the reference specimens. The use of CFRP for strengthening beams enhanced the maximum deflection and ductility of RC beams across all series. The reduction in stiffness owing to the shear cracks occurring diagonally was more apparent in the reference beams without strengthening. There was no significant difference in the failure loads and CFRP contribution to the strength of both side-bonded and U-wrapped beams when CFRP debonding controlled the failure of the specimens. The failure loads of the strengthened beams and CFRP contribution to strength occur lower as a/d increased. The shear contribution of CFRP was found to be lower in beams with stirrups compared to those without. The investigated equations had more reliable and consistent predictions in beams without stirrups in comparison to the beams with stirrups in both side-bonded and U-wrapped beams. The predictions of the ACI 440.2R, Fib-TG 9.3, CNR-DT200, and CSA-S806 yielded highly inconsistent and unconservative results when the stirrups ratio (ρw) is greater than 0.003.

Bond properties of GFRP bar embedded in marine concrete subjected to sustained loads

In this work, a total of 20 beam type concrete specimens were prepared to investigate bond behavior of glass fiber reinforced polymer (GFRP) bar embedded in marine concrete. The influence of sustained loads (load level: 0.25, 0.45 and 0.65 ultimate load (Pu)) and stirrup on bond properties was investigated. After sustained load period, flexural bond test was conducted to determine bond stress and slip. Test results indicate that bond strength of GFRP bars shows decreased trend with increasing sustained loading. Compared with specimen not subjected to sustained load, bond strength significantly decreased under 0.25, 0.45 and 0.65 Pu. Also, sustained load deteriorates the bond stiffness and bond toughness. What’ s more, differences in failure modes and bond strength of steel bar and GFRP bars in flexural bonding tests were analyzed and compared. All GFRP bar specimens subjected to sustained load exhibit bars pull-out failure. In contrast to steel bar, the influence of stirrups on GFRP bar-marine concrete bond strength is relatively limited (specimens with stirrups exhibited only 1.8 % increase over specimens without stirrups), due to GFRP bars lower rib heights and weaker mechanical interlocking with concrete. Characterization of different stages of bond-slip curves of GFRP bar beam specimen subjected to sustained loads was carried out and bond-slip curves of GFRP shows two peaks. According bond strength and slip test data, bond stress-slip mathematical relationship model between GFRP bar and marine concrete under sustained load has been fitted.

Study on restraint coefficient of the stirrups-stiffened square concrete filled double-skin steel tube axial compression stub columns

This paper proposes a novel structural design for stirrups-stiffened square concrete-filled double-skin steel tubular stub columns (SCFDST) that offers high capacity and superior advantages in terms of low consumption of concrete and steel, as well as economic efficiency. The study includes an axial pressure test on two sets of 8 SCFDST columns with varying hollow ratios and stirrup ratios, with a specific focus on the influence of stirrups on mechanical properties. Experimental results demonstrate that stirrups significantly enhance the mechanical properties of SCFDST columns with large hollow ratios, including stiffness, bearing capacity, and ductility, with a more pronounced effect observed as the stirrup ratio increases. A three-dimensional solid finite element (FE) model of the SCFDST columns is developed and validated using ABAQUS software and appropriate constitutive models. Parameter analysis is then conducted based on the FE model, revealing that the stirrups not only restrain the concrete itself but also provide additional restraint by limiting the deformation of the steel tube. This improvement effect was more significant in the middle of steel tubes section. When stirrup ratio was 0.015, the steel tube had the highest constraint efficiency on the concrete. The study introduces a constraint enhancement factor to represent the enhanced restraining effect of stirrups on the steel tube, which is incorporated into a fresh equation for determining the maximum bearing capacity (Nu) of SCFDST columns. The derived formula offers clear physical meaning and high accuracy, building upon the existing formula for CFDST columns.

Modelling of Stirrup Confinement Effects in RC Layered Beam Finite Elements Using a 3D Yield Criterion and Transversal Equilibrium Constraints

Apart from its recognized strengthening effect for shear loading, the presence of stirrups in reinforced concrete results in an increase of the ductility of structural members and in the capacity of reaching higher longitudinal compressive stress levels provided by transversal confinement. These effects are usually represented phenomenologically in fibre beam models by artificially increasing the compressive strength and the ultimate compressive strain of concrete. Two numerical formulations for layered beam descriptions accounting explicitly for transversal confinement are implemented and assessed in this contribution. The influence of stirrups is incorporated by means of a multi-dimensional yield surface for concrete, combined with equilibrium constraints for the transversal direction involving concrete and steel stirrups, and with a concrete ultimate strain dependent on the hydrostatic stress. This contribution focuses on the numerical formulations of both frameworks, and on their assessment against experimental results available in the literature.

Experimental and numerical investigations on the size effect of moderate high-strength reinforced concrete columns under small-eccentric compression

The paper deals with an experimental investigation and numerical simulation of moderate high-strength reinforced concrete (RC) columns subjected to a small-eccentric compressive loading ( e0 = 0.25 h0). A series of tests on the behavior of 12 geometrically similar moderate high-strength reinforced concrete columns with two different stirrups ratios (i.e., 0% and 0.66%) were conducted. The maximum structural size of the square reinforced concrete columns was 800 mm. A 2D mesoscale method for the simulation of the behavior of reinforced concrete columns was established. The numerical tests on the reinforced concrete columns with larger stirrup ratios (1.2% and 2.4%) were carried out complementarily, based on the fact that the simulation results were consistent with the available test observations. The failure patterns, the nominal compressive stress–strain relationships, the nominal compressive strength, and the post-peak softening behavior of the reinforced concrete columns were studied. Furthermore, the influence of stirrups on failure behavior and size effect of the reinforced concrete columns was revealed. One can conclude that (1) the size effect exists in the nominal compressive strength of the eccentrically loaded high-strength reinforced concrete columns with the four different stirrup ratios; (2) comparison of the present test results and the “size effect law” proposed by Bažant shows good agreement; (3) the presence of stirrups improves the nominal strengths, makes the failure of columns less brittle, and weakens the size effect; and (4) the proposed mesoscale numerical method is capable of describing the mechanical behavior of eccentrically loaded reinforced concrete columns.

Influence of Stirrups on Overlap Splice Strength of Epoxy Coated Deformed Bars

Influence of Stirrups on Overlap Splice Strength of Epoxy Coated Deformed Bars

Numerical Test Research on High-Strength Concrete Square Columns with High-Strength Aseismic Transverse Reinforcement under Concentric Compression

This paper focuses on the the relationship between strength and ductility of high-strength concrete (HSC) columns with high-strength aseismic transverse reinforcement under concentric compression and its influencing factors. Some confining models for HSC with high-strength aseismic transverse reinforcement are introduced. Based on 10 groups of high-strength aseismic stirrup confined high-strength concrete square columns are tested under concentric compression, the influence of stirrup in binding strength and the ductility of concrete columns on different stirrup strength, different volume ratio of reinforcement, different stirrups type and different stirrup spacing form is studied by using finite element software ABAQUS. The results indicate that a good agreement is obtained between calculated results and experimental ones. The high-strength stirrup confined concrete columns can improve the bearing capacity and deformation performance of components effectively, laying the foundation of the applications of high-strength stirrups in concrete structures.

Influence of Stirrups and Concrete Strength on Behavior of RC Beams Strengthened in Shear with CFRP–Strips

This paper presents the results of an experimental investigation conducted on rectangular RC beams strengthened externally in shear with CFRP-U strips. The main objective of this research was to evaluate experimentally and analytically the influence of the following parameters on the shear performance of such beams; amount of internal shear reinforcement with and without (stirrups), amount of longitudinal steel, and concrete compressive strength (normal and high strength). Test results indicated that the contribution of CFRP strips to the shear capacity of beams is strongly influenced by the studied parameters. CFRP strips are less effective when beams are heavily reinforced with stirrups. The gain in shear capacity increases as amount of longitudinal steel and/or concrete compressive strength increases. After analyzing the experimental results, the empirical model previously proposed by the author, to predict the contribution of CFRP-U strips, was modified to take the effect of the studied parameters into consideration. The modified model can predict the experimental results with acceptable accuracy, while ACI code guidelines fail to capture the influence of the studied parameters. At the end, recommendations for further work have been given.

A new design equation for predicting the joint shear strength of monotonically loaded exterior beam-column joints

In this study a new design equation for predicting the shear strength of monotonically loaded exterior beam column joints is proposed. For this purpose, the influence of several key variables on the behaviour of beam-column joints are inspected using results of parametric studies on an experimental database compiled from a large number of exterior joint tests. The design equation suggested has three differences from the previously proposed equations. First, the equation proposed considers the influence of beam longitudinal reinforcement ratio, which was not taken into account in previously suggested design equations. Second, as the influence of this parameter is taken into account, a more realistic estimate of the influence of joint aspect ratio is obtained. Third, the influence of stirrups is considered differently for joints with low, medium and high amount of stirrup ratios, in a way, which was not considered in previously suggested equations. The results showed that the proposed design equation predicts the joint shear strength of exterior beam column connections accurately with minimal standard deviation and is more reliable than the previously suggested equations.

Corrosion of Steel Bars with Respect to Orientation in Concrete

Corrosion of steel bars (main steel and stirrup) with respect to the orientation in concrete is presented. A detailed study on macrocell and microcell corrosion of steel bars in concrete was conducted on horizontal and vertical steels, depending on the casting direction. The horizontal steel was divided into top and bottom halves. The study was conducted with chloride ions in concrete. Water-cement ratios were 0.5 and 0.7. The electrochemical investigations, microscopic, and physical observations of steel bars were performed. The laboratory investigations were verified with the long-term (23 year) exposure investigations on reinforced concrete beams. The study also focused on the influence of stirrup on macrocell formation of main steel, and corrosion of plain and deformed steel bars. It was concluded that orientation of steel bars has a significant influence on macrocell and microcell corrosion of steel bars in concrete. Formation of gaps under the horizontal steels cause significant corrosion. Stirrups play an important role in increasing macrocell corrosion of main steel. The deformed bar corroded more than the plain bar.

Anchorage of deformed bars in lightweight concrete. influence of concrete cover and spacing of stirrups

Anchorage of deformed reinforcing bars at a beam end of simply supported beams of extremely lightweight concrete (called 3L-concrete and with a density about 1100 kg/m3) has been studied. Comparison between test results and the design recommendations given in the Swedish concrete code BBK 79 is made. A macro model concerning the splitting failure and the influence of stirrups on splitting failure in beams is discussed and design rules for this type of concrete are proposed, based on the splitting failure theory.