Confinement Reinforcement Research Articles

Compressive behavior of FRP-confined reinforced concrete columns

The evolution of earthquake-resistance standards has led to introduction of new design equations for the amount of transverse steel reinforcement (TSR) to ensure ductile behavior of reinforced-concrete columns. In order to comply with the new codes’ TSR requirements there is a need to strengthen existing columns. One of the methods to strengthen reinforced-concrete columns is by using fibre-reinforced polymer (FRP) composites as confinement reinforcement. Critical reviews of existing studies pertaining to the fundamental behavior and analytical modelling of FRP-confined concrete columns have indicated that there are several aspects on which more research is required. These include, amongst others, the interaction between the internal transverse reinforcement confinement and the external FRP confinement, and non-uniform confinement as found in FRP-confined square/rectangular sections. This paper presents the development of a unified stress-strain model suitable to represent the axial behavior of circular and square/rectangular reinforced-concrete columns confined internally with TSR, externally with FRP, or both internally and externally with TSR and FRP, respectively. Moreover, experimental study of six FRP-/TSR-confined square reinforced-concrete columns under compressive axial loading was conducted. It is shown that stress-strain curves predicted by the proposed model are in good agreement with the presented as well as published experimental results.

Behavior of Ultrahigh-Performance Concrete Confined by Steel

AbstractUltrahigh-performance concrete (UHPC) offers a superior alternative to normal-strength concrete (NSC) due to its significantly higher compressive and tensile strengths, improved ductility, and enhanced durability. This paper presents an experimental study of the stress-strain behavior of UHPC confined by conventional transverse steel reinforcement. Test results are compared with two confinement models, as well as a large amount of available data on steel-confined NSC and high-strength concrete (HSC), and limited data available for UHPC confined by fiber-reinforced polymers (FRP). The study shows a potential threshold of confinement ratio beyond which the confinement effectiveness of UHPC exceeds that of HSC and nears that of NSC. This may have implications on the minimum level of confinement reinforcement for UHPC. For the most part, steel reinforcement is more effective than FRP as the confining device for UHPC, except for the very high end of confinement ratios, where FRP may become more effecti...

EXPERIMENTAL PROGRAM FOR REINFORCED CONCRETE RECTANGULAR COLUMNS CONFINED BY RECTANGULAR TIES

This paper presents an experimental study of the behavior of reinforced concrete rectangular columns confined by rectangular ties under concentric loading. The study incorporates all the relevant parameters of confinement that have been observed to play important roles in column tests. These parameters include the concrete compressive strength, amount of confinement reinforcement, the tie spacing, the tie yield strength, longitudinal reinforcement distribution, the transverse reinforcement configuration and section geometry. Nineteen normal strength concrete rectangular columns with different concrete dimensions, different concrete compressive strength and confinement characteristics were designed, constructed and tested in this research. Significant gains in strength and ductility are recorded for the concrete core of well confined columns.

Minimum confinement reinforcement for prestressed concrete piles and a rational seismic design framework

Minimum confinement reinforcement for prestressed concrete piles and a rational seismic design framework

Role of concrete confinement of wide-flange structural steel shape in steel reinforced concrete columns under cyclic loading

In this study, effects of wide-flange structural steel shapes on concrete confinement of steel reinforced concrete (SRC) columns were examined by conducting structural testing on six large-scale SRC columns under cyclic loading. Specifically, effects of the major- and minor-axis bending relative to the steel shape on the ductility and confinement effectiveness of SRC columns were investigated. Experimental results showed that concrete confinement of SRC columns were highly influenced by the bending direction. Details of the underlying confining mechanisms of SRC columns were uncovered. Findings from this study indicated that the required confinement reinforcement for the SRC columns subjected to major-axis bending could be significantly reduced, compared to that of the SRC columns subjected to minor-axis bending.

Performance of RC columns with debonded bars subjected to cyclic lateral loading

SummaryConcrete columns with light confinement reinforcement subjected to cyclic lateral load exhibit brittle shear failure along with flexural yielding of longitudinal steel reinforcement bars. The present study investigates the effect of debonding of longitudinal bars on the performance of columns under lateral loading. Column specimens were tested under quasi‐static reverse cyclic lateral loading. A comparative study has been carried out on the performance of columns with and without debonding using circular steel tubes of varying lengths. Steel tubes were provided to the longitudinal reinforcement in the potential plastic hinge zone. It is observed that the specimens with debonded reinforcement have significant enhancement in deformation capacity, ductility and energy dissipation capacity than the specimens without it. The congestion of reinforcement at the joints can also be eliminated by reducing the confining reinforcement for these debonded specimens. Copyright © 2015 John Wiley & Sons, Ltd.

Axial compressive behaviour of concrete confined with polymer grid

This study presents results of an experimental investigation on the axial compressive behaviour of concrete confined with polymer grid. A total of 14 concrete specimens with 150 mm diameter and 300 mm height were prepared and tested under axial compression. Two types (Type A and Type B) of polymer grid with different mechanical properties were selected. Type A polymer grid (36 mm × 36 mm) was manufactured from polypropylene fibres, while Type B polymer grid (36 mm × 24 mm) was manufactured from high modulus polyester fibres. For each type of polymer grid, one layer, two layers, and three layers were used to investigate the influence of the amount of polymer grid confinement on the axial compressive behaviour of concrete specimens. The test results show that concrete specimens confined with polymer grid obtained much higher deformation capacity than unconfined concrete specimens, although the improvement in the strength was not highly significant. Type A polymer grid performed better in improving the strength and deformation capacity of concrete specimens than Type B polymer grid. The test results indicate that polymer grid can be used as a secondary confinement reinforcement for concrete specimens. Based on the analysis of test results in this study as well as test results from previous studies, an empirical model for the polymer grid confined concrete was developed. The developed empirical model predicts the peak strength, axial strain at peak strength, strength at ultimate strain, and ultimate strain of polymer grid confined concrete with good accuracy.

Prediction of stress–strain behavior of spirally confined concrete considering lateral expansion

This paper proposes a new analytical model for the relationship between the axial and transverse strains of confined concrete in uniaxial compression. The proposed model was developed based on empirical data for a circular section confined by spirals. A column with a circular section and subjected to uniaxial compression was considered. The proposed model predicts the stress in the transverse confinement reinforcement to estimate the relationship between the axial strain of the column and tensile strain of the transverse confinement reinforcement. The model can also produce the axial stress–strain relationship of the confined concrete of the column. The predicted axial and transverse strains of the confined concrete section corresponded to the observed axial peak stress of a column evaluated in previous research with good accuracy. This model will be an effective tool for investigating the effect of circular spirals on the structural behavior of confined concrete and enhancing the accuracy of structural behavior analysis for a column under uniaxial compression.

Limit state design criteria for FRP strengthening of RC bridge components

Fiber-reinforced polymer (FRP) composite materials provide novel, effective and potentially economical solutions for rehabilitating and strengthening existing reinforced and pre-stressed concrete bridges, buildings and other structures where deterioration has occurred or performance requirements have changed. FRP composites may be designed to act as external flexural, shear or confinement reinforcement to increase the load capacity of the strengthened structural components. This paper summarizes research to develop technical support for practical limit state (strength) design criteria for repair and strengthening of reinforced and pre-stressed concrete bridge elements for compression and/or flexure using externally bonded FRP composite systems. The limit state design criteria take uncertainties in structural strength and stiffness into account using structural reliability methods, and will support and enhance the use of FRP materials in civil construction by providing engineers with rational guidelines for repair and strengthening.

Compressive behavior of concrete confined by CFRP and transverse spiral reinforcement. Part A: experimental study

This study presents the results of an experimental investigation of 18 short concrete columns confined by carbon fiber-reinforced polymer (CFRP) and transverse spiral reinforcement (TSR) under uniaxial compression. Longitudinal rebars are not installed in the specimens in order to eliminate their confinement effect to concrete which affects the analysis of 3-D compression of concrete. The paper only consider for FRP and spiral reinforcement confinement in transverse direction. Two key experimental parameters were investigated: the thickness of the CFRP tube (0.167, 0.334, and 0.501 mm) and the spacing of the TSR (25 and 50 mm). The failure mode, axial and transverse stress–strain relationship, confinement effectiveness, Poisson’s ratio and dilatation performance of the specimens were discussed. Test results show that the ultimate strength of concrete has a linear proportional enhancement with an increase in the FRP layer in each TSR category and a decrease in the TSR spacing in each FRP layer category. The ultimate load carrying capacity of the confined concrete depends on the confinement pressure during failure in terms of ultimate strength and axial strain.

Influence of confinement reinforcement on the compression stress–strain of grouted reinforced concrete block masonry boundary elements

Reinforced masonry (RM) shear walls are widely used in medium- to high-rise masonry buildings as part of the lateral force resisting system to provide the lateral strength, stiffness and energy dissipation capacity required to resist lateral loads arising from earthquakes or wind. In the past few decades, there has been considerable advancement in the design of RM shear walls for new construction with variable types of confinement of the compressed boundaries of the wall for increasing ductility level. Recent codes and standards for design of masonry structures are introducing the use of Ductile Reinforced Masonry (DRM) Shear Walls with column-like boundary elements for the improvement of the ductility capacity of the walls. A key component in the evaluation of the ductility capacity of shear walls is evaluating the compressive response of their boundary elements. This paper presents an experimental and analytical investigation on the compression stress–strain behavior of fully grouted unconfined and confined reinforced concrete block masonry boundary elements. Full scale boundary elements were constructed and tested under concentric axial compression. An analytical stress–strain model was proposed that can be used in the design and assessment of DRM walls with boundary elements.

The Strength and Strain of High-strength Concrete Elements with Confinement and Steel Fiber Reinforcement Including the Conditions of the Effect of Elevated Temperatures

The article introduces the results of the experimental research of the effect of confinement and steel fiber reinforcement on the strength and strain of the compressed elements of high-modified as well as high-strength SFRC. Analytical expressions to describe the strength and strain of elements with confinement reinforcement under axial compression have been proposed. The results of the research of the effect of concrete age and temperatures elevated up to 150°C on the strength and strain of high-strength SFRC have been introduced.

Correlation between Asphalt Concrete Strength, Amount of Bitumen and Asphalt Mix Batching Modes

The article introduces the results of the experimental research of the effect of confinement and steel fiber reinforcement on the strength and strain of the compressed elements of high-modified as well as high-strength SFRC. Analytical expressions to describe the strength and strain of elements with confinement reinforcement under axial compression have been proposed. The results of the research of the effect of concrete age and temperatures elevated up to 150°C on the strength and strain of high-strength SFRC have been introduced.

Stress–strain behaviour of confined Geopolymer concrete

Fly ash based Geopolymer concrete (GPC) is an environment friendly alternative to conventional concrete made from alkali activated aluminosilicate and aggregate. This study intends to examine the effects of confinement on the behaviour of GPC and conventional Portland Cement Concrete (PCC). Out of the 36 cylinders tested under monotonic loading 24 cylinders were made with GPC and the remaining with PCC. The variable considered in this study is the volumetric ratio of confinement. An analytical model is proposed for the stress–strain behaviour of confined GPC. The results showed that confinement reinforcement greatly improved the strength and ductility of GPC than PCC.

Effects of confinement reinforcement and concrete strength on nonlinear behaviour of RC buildings

This paper investigates the effects of confinement reinforcement and concrete strength on nonlinear behaviour of reinforced concrete buildings (RC). For numerical application, an eleven-storey and four bays reinforced concrete frame building is selected. Nonlinear incremental static (pushover) analyses of the building are performed according to various concrete strengths and whether appropriate confinement reinforcement, which defined in Turkish seismic code, exists or not at structural elements. In nonlinear analysis, distributed plastic hinge model is used. As a result of analyses, capacity curves of the frame building and moment-rotation curves at lower end sections of ground floor columns are determined. These results are compared with each other according to concrete strength and whether appropriate confinement reinforcement exists or not, respectively. According to results, it is seen that confinement reinforcement is important factor for increasing of building capacity and decreasing of rotations at structural elements.

Experimental Study of End Region Detailing and Shear Behavior of Concrete I-Girders

This paper presents the results of an experimental program conducted to evaluate the effects of end region detailing on the capacity and behavior of pretensioned concrete I-girders. The program was conducted using six Florida I-Beam specimens, 1,372 mm (54 in.) in depth, which were load-tested in three-point bending at a shear span/depth of 2.0. Variables in the program included confinement reinforcement configuration, presence/lack of steel bearing plate, strand shielding pattern, and strand layout. Specimen behavior and capacity were found to be significantly affected by end region detailing, especially placement of fully bonded strands. Experimental results were compared with theoretical models for web-shear, bond-shear, and lateral-splitting capacity. By considering multiple models, calculations were able to accurately identify the failure mode of each test specimen.

Application of Engineered Cementitious Composites (ECC) in interior beam–column connections for enhanced seismic resistance

This study aims to evaluate the feasibility of using ultra-ductile Engineered Cementitous Composites (ECC) as a means to enhance the performance of beam–column connections. Nine one-third scale specimens, consisting of type 2 (ACI352R-02) interior connections at a zone of high seismicity (UBC-zone 3), were tested under reverse cyclic loading, simulating seismic excitation. The joints of these specimens were typical in geometry and main reinforcement detailing to specimens of a prototype building frame designed according to ACI318-08. The primary variables were the amount and arrangement of transverse reinforcements, and the materials within the plastic zone of the connection.The performances of a series of ECC-enhanced beam–column interior connections were compared to that of a control concrete counterpart to evaluate the benefits of using ECC in this type of application. The column load–displacement response (including the ultimate load and ultimate displacement), the (hysteresis) energy absorption capacity, and the cracking response were used as criteria in the comparison.The test results indicated that the use of ECC material in the connection plastic zone as a replacement of concrete and partial replacement of transverse (confinement) reinforcement can significantly enhance the joint shear resistance, energy absorption capacity, and cracking response, thereby, enhancing the joint seismic resistance and reducing reinforcement congestion and construction complexity.

Performance Evaluation of Concrete Columns Reinforced Longitudinally with FRP Bars and Confined with FRP Hoops and Spirals under Axial Load

AbstractNowadays, AASHTO LRFD Bridge Design Specifications and the Canadian Highway Bridge Design Code contain flexural and shear provisions for the design of concrete bridge members reinforced with fiber-reinforced polymer (FRP) bars. Because of a lack of research, these standards do not recommend using FRP bars to resist compressive stresses in compression members. This paper reports on 14 full-scale circular RC columns tested under concentric axial load. The columns were reinforced with longitudinal FRP bars and confined with circular FRP spirals or hoops. Sand-coated glass-FRP (GFRP) and carbon-FRP (CFRP) reinforcement was used. The test parameters included configuration of the confinement reinforcement (spirals versus hoops), hoop lap length, volumetric ratio, and FRP reinforcement type (glass versus carbon). The test results indicate that the GFRP and CFRP RC columns behaved similarly to columns reinforced with steel. Using GFRP and CFRP spirals or hoops according to the provisions of the Canadian S...

Fire Resistance Performance of High-Strength Concrete Columns Reinforced with Pre-Stressed Wire Ropes

In this study, the fire resistance performance of high-strength concrete columns was evaluated to see the influence of lateral confinement reinforcement with wire ropes for improving ductility, fire resistance reinforcement with fiber cocktail and load ratio. For this, loaded fire test was conducted under ISO834 standard fire condition. The axial ductility of the 60MPa high-strength concrete column reinforced with pre-stressed wire ropes was improved and its fire resistance performance was also improved by 23% compared with its counterpart without wire ropes. The appropriate load for the 60MPa concrete column reinforced with wire ropes was found to be 70% of design load. The fire resistance performance of the 100MPa high-strength concrete column reinforced with pre-stressed wire ropes and fiber-cocktail was improved as much as 4 times compared with that reinforced with tie bars only. The appropriate load for the 100MPa columns was found to be less than 70% of design load in order for the columns to secure required fire resistance performance.

A Semi-Analytical Model of Cyclic Behavior of Reinforced Concrete Joints Rehabilitated with FRP

This paper presents a semi-analytical model for damaged reinforced concrete (RC) beam-column joints that are restored with fiber reinforced polymers (FRP). Constituent materials are characterized by their stress-strain curves. Confinement to concrete offered by the FRP is discussed. Stress-strain behavior of control and yielded steel bars and FRP laminate are presented. Material properties are utilized to develop the cross-sectional model in the form of moment-curvature ( M-φ) relationships. Effect of confinement and longitudinal FRP reinforcement on moment-curvature relationships is discussed. Cross sectional properties are extended to obtain the load-displacement relationships of the beam-column joints. A softening model is developed to incorporate the progressive damage of the joint. Variations of softening coefficient with displacement cycles, displacement history and confinement are reported. Models presented are validated using experimental results.