Ductility Of High Strength Concrete Research Articles

Behaviors of FRP confined rectangular concrete-filled thin-walled steel tubular stub columns using high-strength materials under axial load

Rectangular concrete-filled thin-walled steel tube (CFT) columns using high-strength steel and concrete are susceptible to local buckling, which will weaken the constraint effect and reduce the advantages of high-strength materials. Fiber reinforced polymer (FRP) has favorable mechanical properties, which can be used to delay or even prevent the outward buckling of steel tube. This paper presents the experimental and theoretical study on axial compressive behavior of FRP confined concrete-filled thin-walled steel tube (FRP-CFT) stub columns with high-strength materials. The test variables included the aspect ratio of section, concrete strength and the layers of FRP, etc. Results show that the confinement of FRP delays the local buckling of steel tubes and increases the restraint strength of core concrete. The ductility of high-strength concrete is also improved. Based on the superposition theory and the effective width theory, this paper proposed the design approach to calculate the ultimate compressive resistance, considering the effect of local buckling of thin-walled steel tube and the confinement of the FRP. The design approach was verified with experimental results and can be used in practice.

Flexural Capacity Prediction Model For Steel Fibre-Reinforced Concrete Beams

Steel fibre (SF) reinforcement has been shown to improve the ductility of high strength concrete (HSC), which is known to be brittle. Research conducted to date on steel fibre reinforced concrete and its effects have emphasised post-failure performance and cracking mechanism. The difficulty in predicting the behaviour of fibres is due to the randomly distributed nature of the material within the matrix leading to a probability distribution of results. Published literature has shown a benefit of adding steel fibres in terms of the ductility performance of structures. Clearly, there is a potential for such material as replacement of conventional steel reinforcement. This study proposes a theoretical model of evaluating the potential of using steel fibres as a replacement material to conventional steel reinforcement bars based on the case study, laboratory and theoretical methodologies. The compressive strength of the concrete at key dates, the effective fibre cross-sectional were measured, and a prediction model was created based on the measurement parameters. The use of four-point flexural testing, standard compressive testing and software image modelling provided the study with relevant data used to analyse and compare to the prediction. Greater ductility performance and toughness were observed with increased fibre volumes, confirming proposed predictions and conclusion drawn from published literature. No consistent or conclusive correlations between fibre volumes and the compressive strength of concrete were found. A relationship between fibre volumes and predicted moment capacities of steel fibre reinforced concrete beams was found based on the proposed theoretical flexural analysis method.

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.

Load-deformation Behaviour of Eccentrically Loaded SSTT-confined High Strength Concrete Columns

The application of steel-straps confinement or better known as steel-strapping tensioning technique (SSTT) has been proven to be effective in increasing the strength and ductility of High-Strength Concrete (HSC) column comparable to Fiber-Reinforced Polymer (FRP). However, most of the research of confined HSC column has mainly concentrated on concentric loading. In actual practical condition, most of the columns are subjected to eccentric loading. The scarcity of the experimental data for eccentric loaded confined HSC column has prevented the potential use of this type of structure element. In this paper, five HSC columns were tested. The specimens were SSTT-confined and tested with 25mm and 50 mm eccentric loading. The results show that SSTT confinement can increase the strength and deformability of high-strength concrete column, although the strain gradient reduces the confining efficiency. Therefore, smaller capacity enhancement factor should be used in eccentrically loaded SSTT-confined HSC columns compared to concentrically loaded columns. Furthermore, the non-linear theoretical model established in this study can be used for templates for future work on SSTT-confined HSC columns.

Flexural behaviour and ductility of high strength concrete (HSC) beams with tension lap splice

An experimental program has been conducted in order to investigate the flexural behaviour of concrete beams with variable length of tension reinforcement lap splice. A test series of eighteen simple beams containing different lap splice length (0, 300, 500 and 700mm) had been conducted in this investigation. The tested beams are of 2200mm total length and 200×150mm cross-section, loaded at the middle third with two equal concentrated loads. The parameters included in the experimental program are the splice length, the bar diameter (12, 16mm), the amount of transverse reinforcement provided within the splice zone, the shape of the anchor at the splices end and the concrete cover (20, 35mm). The test program has been performed on two grades of high strength concretes (0%, 15% silica fume); 55, 65MPa. Two deformed bars of tension reinforcement were spliced in the constant moment zone. The effect of splicing tension reinforcement on the response, cracking load, crack propagation, deflection, ultimate capacity, mid-span reinforcement strain, failure mode and beam ductility, is examined. Results show that by introducing an appropriate amount and distribution of transverse reinforcement, a satisfactory ductility response can be obtained (91% of reference beam).

Study on the Dynamic Performance of Steel Fiber Reinforced Concrete in SHPB Experiment

It is important to enhance the ductility of high strength concrete (HSC), and one possible direction is to use steel fibers reinforced, named steel fiber reinforced high strength concrete (SFRHSC).In this paper, The crack characteristics of steel fiber reinforced concrete is investigated in the SHPB test. The incident wave and transmission wave varying with the time have been obtained by SHPB experiment. The relationship curve for stress and strain of material concrete has also been obtained.

FLEXURAL BEHAVIOR OF OVER REINFORCED HSC BEAMS CONFINED BY RECTANGULAR TIES

This paper presents an experimental and analytical investigation on the flexural behavior of over reinforced concrete beam confined by rectangular ties. The experimental investigation was conducted through testing four full-scale beams with normal strength concrete (NSC). Three out of these four beams were confined using rectangular ties located on the compression region of the beams. The variables studied in these specimens were the volumetric ratio of transverse reinforcement, and the volumetric ratio of the main rebars. A finite element model was established with both material and geometrical non-linearity by using ANSYS software package. Accuracy of the model was assessed by applying it to the three tested beams. Comparison of analytical results with the available experimental results for ultimate load values and load– deflection relationships show a good agreement between the finite element and experimental results. After validating the accuracy of the proposed model, parametric study was undertaken to gain additional insight into the overall behaviour, failure modes, and deformation capacity for the concrete beams using high class concrete strength. The parameters studied were, the concrete compressive strength, the number and diameter of longitudinal rebars, and diameter of rectangular ties. The obtained results show that, the strength and ductility of high strength concrete (HSC) beams are enhanced through the application of rectangular tie reinforcement located in the compression region of the beams. The concrete compressive strength, the longitudinal bars number and diameter, and the diameter of rectangular ties are important parameters controlling the level of strength and ductility enhancement of overreinforced HSC beams.

Investigation of stress-strain models for confined high strength concrete

The effects of confinement reinforcement on the behaviour of high strength concrete columns are investigated for which prismatic experimental specimens were prepared. In the experiment specimens, four longitude reinforcement and confinement reinforcement were used. For each experiment, stress-strain relationship of concrete was obtained and compared with models proposed earlier. The results show that confinement reinforcement improved the ductility of high strength concrete. The ascending branch of stress-strain curves depended on the ratio of confinement reinforcement was similar to the modified Kent-Park model and the descending branch similar to the Nagashima model.

External reinforcement of high strength concrete columns

With the technology development on the compressive strength of concrete over the years, the use of high strength concrete has proved most popular in terms of economy, superior strength, stiffness and durability due to many advantages it could offer. However, strength and ductility are inversely proportional [J. Mater. Civil Eng. 11 (1999) 21]. High strength concrete is a brittle material causing failure to be quite sudden and `explosive' under loads. It is also known that structural concrete columns axially compressed rarely occur in practice. The stress concentrations caused by the eccentric loading further reduce the strength and ductility of high strength concrete. Therefore, studies for high strength concrete columns under eccentric loading are essential for the practical use. This paper experimentally investigates a number of high strength concrete columns that are externally reinforced with galvanised steel straps and fibre-reinforced polymers subjected to concentric and eccentric loading. The experimental results show that external reinforcement can enhance the properties of high strength concrete columns.

Brittleness versus Ductility of High Strength Concrete

Due to the shape of the stress-strain curve and the typical fracture phenomenon, high strength concrete (HSC) is considered as a brittle material. However, structural members in reinforced high str...