Concrete Short Columns Research Articles

Strengthening of Fire-Damaged Reinforced Concrete Short Columns Using GFPPECC Composites

The study investigated the strengthening effect of glass fiber and polypropylene fiber-based engineered cementitious composites (GFPPECC) on fire-damaged reinforced concrete short exterior columns. Both moderate (500 °C) and high (900 °C) intensities of fire load corresponding to the ISO834 fire curve were adopted. A total of 15 columns (150 mm × 150 mm × 1000 mm) were cast. The columns were grouped as control column (CC), unstrengthened column-(C2, C3), and strengthened column-(C1, C4) with three columns in each group. The columns in group CC were subjected to axial compression up to failure and kept as the standard reference. The columns in the group (C2, C4) and (C1, C3) were fired up to 900 °C and 500 °C, respectively. Compressive loading on C2 and C3 was applied without any strengthening technique. C1 and C4 were repaired and strengthened using GFPPECC. A similar group of columns, namely unstrengthened-(A-C2, A-C3) and strengthened-(A-C1, A-C4) columns, were analyzed numerically using ANSYS. The parametric analysis was carried out from experimental and numerical results. Variations between experimental and numerical results were negligible. The strengthening has restored to about 68% of the stiffness of columns damaged due to moderate fire intensity. The energy absorption, ductility, and modulus of elasticity were also good, with only about less than 10% reduction compared to the control column. The performance of columns shows that the GFPPECC composite was utilized effectively without any debonding. Whereas for high fire intensity, the GFPPECC composite was not fully used, and premature failure has occurred due to the softening of concrete at high temperatures.

Axial Load-carrying Capacity of Steel Tubed Concrete Short Columns Confined with Advanced FRP Composites

Fiber Reinforced Polymers (FRPs) have wide applications in the field of concrete construction due to their superior performance over conventional materials. This research focuses on the structural behavior of steel tube FRP jacket–confined concrete (STFC) columns under axial concentric loading and proposes a new empirical equation for predicting the axial load-carrying capacity of STFC columns having thickness of FRP-fabric ranging from 0.09 mm to 5.9 mm. A large database of 700 FRP-confined concrete specimens is developed with the detailed information of critical parameters, i.e. elastic modulus of FRPs (Ef), compressive strength of unconfined concrete (fc’o), diameter of specimen (D), height of specimen (H), total thickness of FRPs (N.tf), and the ultimate strength of confined concrete (fc’c). After the preliminary evaluation of constructed database, a new empirical model is proposed for the prediction of axial compressive strength of FRP-confined specimens using general regression analysis by minimizing the error functions such as root mean squared error (RMSE) and coefficient of determination (R2). The proposed FRP-confinement strength model presented higher accuracy as compared with previously proposed models. Finally, an equation is proposed for the predictions of axial load carrying capacity of STFC columns. For the validation of proposed equation, an extensive parametric study is performed using the proposed nonlinear finite element model (FEM). The FEM is calibrated using the load-deflection results of STFC columns from literature. A close agreement was observed between the predictions of proposed finite element model and proposed capacity equation.

Finite element simulation of recycled large aggregate self-compacting concrete short columns with steel tubes

In order to study the mechanical properties of recycled large aggregate self-compacting concrete filled steel tube(RLA-SCCFST) and promote the research and application of the structure, the mechanical properties of nine groups of RLA-SCCFST short columns under axial compression were studied by ABAQUS simulation. Comparing the results of finite element simulation with the test results, it is found that: 1. The simulation results of the load-vertical strain curve are in good agreement with the test results, and the maximum error of the ultimate bearing capacity measured by the simulation and the test is within 3%; 2. The ultimate bearing capacity and ductility of RLA-SCCFST specimen increase with the increase of steel pipe wall thickness, recycled large aggregate strength and self-compacting concrete strength, and the ultimate bearing capacity of specimen decreases with the increase of recycled large aggregate content.

Axial Strength of Eccentrically Loaded FRP-Confined Short Concrete Columns.

This paper presents an experimental program that includes 78 fiber reinforced polymer (FRP)-confined square concrete columns subjected to eccentric loading. The degradation of the axial strength of FRP-confined short concrete columns due to the load eccentricity is investigated in this work. A larger load eccentricity leads to a greater decrease in the axial strength. From the test results, it is found that FRP confinement can cause less strength degradation compared with that of unconfined concrete specimens. For FRP-confined square concrete specimens, the strength enhancement due to FRP confinement increases with increasing load eccentricity. However, the increasing load eccentricity decreases the confinement efficiency for FRP-confined circular concrete specimens. The relationship between the strength of eccentrically loaded FRP-confined square columns and their corner radii is evaluated.

Compression behavior of FRP-strengthened RC square columns of varying slenderness ratios under eccentric loading

FRP sheets have been extensively used for the strengthening of reinforced concrete (RC) short columns. However, their application in the strengthening of slender RC columns, especially under eccentric loading, has been very limited. In this paper, the compression response of FRP-strengthened RC square columns of varying slenderness ratios under eccentric loading is studied. The columns were strengthened using both longitudinal and hoop carbon FRP (CFRP) sheets. Three groups of 150 mm square columns of 600, 900, and 1200 mm height were prepared. The RC columns of 600 and 900 mm height belong to the short column category, whereas the column of 1200 mm falls into the category of a slender column. In each group, there were four RC columns. Out of these four columns, one was kept unstrengthened, whereas the other three were strengthened using externally bonded CFRP sheets. The unstrengthened column in each group was considered as a control specimen. The three strengthened columns were prepared by: (i) wrapping one layer of hoop CFRP sheet, (ii) bonding two layers of longitudinal CFRP sheets over the entire surface of the column and wrapping a single layer of hoop CFRP laminate over them, and (iii) bonding four layers of longitudinal CFRP sheets with the other details same as (ii). All the column specimens were tested under compressive load acting at an eccentricity of 25 mm. The test results indicate that the longitudinal CFRP sheets, in the presence of hoop CFRP sheets, control the lateral deflection and substantially improve the load-carrying capacity of the slender columns . The P-M diagrams of FRP-strengthened columns were analytically derived, which were reasonably close to the experimentally observed P-M diagrams.

Investigation of Residual Bearing Capacity of Corroded Reinforced Concrete Short Columns under Impact Load Based on Nondestructive Testing

This paper investigates the damage and residual bearing capacity of corroded reinforced concrete (RC) short columns after impact and presents a method for evaluating the residual bearing capacity of RC short columns by nondestructive testing. Firstly, accelerated corrosion test and drop hammer impact test were carried out to obtain specimens under different impact loads and corrosion rates. Then, the damage caused by corrosion and impact loads was evaluated by supersonic wave aided nondestructive test. Through the damage factor, the influence of corrosion rate and impact loads on the specimen was revealed, and the calculation method of corrosion rate and impact velocity was proposed. Finally, according to the bearing capacity test results, the influence factors of reinforcement, concrete, and impact were introduced into the bearing capacity calculation equation. Considering the relationship between the residual bearing capacity of RC short columns and the damage factor, an improved formula for calculating the residual bearing capacity of corroded RC short columns under impact loads was proposed. This work lays the foundation for further research on mechanical properties of corroded RC structures under impact loads.

Numerical analysis of axial compressive behavior of reinforced concrete short columns after exposure to fire

Numerical analysis of axial compressive behavior of reinforced concrete short columns after exposure to fire

Cyclic performance of corroded reinforced concrete short columns strengthened using carbon fiber-reinforced polymer

Steel corrosion in reinforced concrete (RC) members significantly degrades their structural performance, and such corroded members are typically strengthened using fiber-reinforced polymer (FRP). In this study, the cyclic performance of short corroded columns of RC strengthened with carbon FRP (CFRP) is investigated. Seven short RC columns were fabricated and tested under cyclic loading. Of them, six specimens were corroded and one was uncorroded. The parameters considered included the number of CFRP strengthening layers (zero, one, 1.5, and two) and the type of fine aggregate (river sand and sea sand). The hysteretic curves, failure modes, and load–strain relationships of the specimens were compared and are discussed in detail. Furthermore, the equation for calculating the shear resistance of FRP-strengthened short RC columns in Chinese code has been modified to predict the shear resistance of the corroded RC columns strengthened with CFRP. The results show the following: (1) The deformability and energy dissipation of the corroded specimens without CFRP strengthening were significantly lower than those of the uncorroded counterpart. (2) Through CFRP strengthening, these values were improved and were even higher than those of the uncorroded specimen. (3) The modified equation can predict the shear resistance of CFRP-strengthened specimens.

Essential stressing state features of spirally reinforced concrete short columns revealed by modeling experimental strain data

This study discovers the essential stressing state features of spirally reinforced concrete (SRC) short columns from the modeling of the experimental strain data. The structural stressing state method models the measured strains into generalized strain energy density (GSED) values to describe the stressing state mode and the corresponding characteristic parameter. Then, the Mann-Kendall criterion detects the leap feature of the column’s stressing state from the GSED sum-load curve. This reveals the starting point in the failure process of the column and updates its failure load definition. And it is verified that the stressing states of the components constituting the column also present the leap features around the updated failure load. Finally, the formula is fitted to calculate the failure loads with a verification. The essential leap feature of the column’s stressing state is the embodiment of the natural law from quantitative change to qualitative change, which explores a new way to analyze the working behavior of SRC short columns.

Experimental Study of AFRP-Confined Square and Circular Concrete Columns Using Fiber Bragg Grating Sensors

An experimental investigation on square and circular high-strength concrete short columns confined with aramid fiber-reinforced polymer (AFRP) sheets was conducted in this study. Fiber Bragg grating sensors have been applied successfully in monitoring of the strains of the AFRP-confined square and circular concrete columns. The experimental results demonstrate that two types of axial force-strain curves were observed depending on the form of the column. Results show fiber Bragg grating sensors have good repeatability and the ultimate load of the circular concrete column is larger than that of the square concrete column. The interlaminar strains of AFRP and high-strength concrete have also been attained. It helps to analyze the constraint effect of the concrete column and compute the ultimate load of the square and circular concrete column.

Nonlinear damping properties of recycled aggregate concrete short columns under cyclic uniaxial compression

Although recycled aggregate concrete (RAC) has been studied intensively over past two decades, its damping property is still not analyzed sufficiently. In this paper, a nonlinear damping model for RAC prisms subjected to cyclic uniaxial compression are presented. Then with the combination of the compressive strength and damping property of RAC, an optimum recycled concrete aggregates (RCA) content including particle size and replacement percentage are recommended. The cyclic uniaxial compression test was conducted to investigate the dynamic modulus and nonlinear damping property of RAC, meanwhile tests for the RAC’s static compressive strength and modulus of elasticity were also carried out. Then based on the nonlinear damping model and compressive strength, relationships among the compressive strength, damping property, load indicators and RCA content are analyzed to obtain the optimum RCA content. Test results indicate that RAC obtains a higher loss factor than NAC. The loss factor of RAC is an increasing power function of RCA particle size and a decreasing power function of RCA replacement percentage. However, the compressive strength and dynamic modulus of RAC decreases compare with that of natural aggregate concrete. The different choice of cyclic uniaxial compression load indicators (cyclic stress range, stress level or strain range) has significance impact on RAC damping property and optimum RCA content.

Experimental investigation of the contributions of CFRP and externally collar strengthening to the seismic performance of RC columns with different cross-sections

In this study, the performance of nine reinforced concrete (RC) short columns under cyclic lateral loading effect was investigated experimentally. The columns are divided into three series with cross-sectional dimensions of 300 × 400, 300 × 550 and 300 × 700 mm2. Each series includes three columns that are strengthened with one Reference column, two CFRP Wrap and Externally Collar columns. Aspect ratios (αs) of all columns in the series are 1.5. Therefore, the columns were tested under the same behavior demand according to the cross-section dimension. Reference columns in each series are perfect columns with sufficient stirrup spacing as required by regulations. The performance of RC columns was evaluated in terms of crack development, hysteretic character, stiffness, ductility, and energy consumption. The results showed that CFRP wrap and collar strengthening significantly improved the performance of the columns.

Behaviour of GGBS-dolomite geopolymer concrete short column under axial loading

Geopolymer concrete was developed from Ground Granulated Blast furnace Slag (GGBS) and dolomite which are obtained from steel and rock industries. Optimum proportions of GGBS and dolomite were found out based on the maximum compressive strength. GGBS-Dolomite geopolymer concrete can reduce construction time and cost due to high early age strength. Experimental investigations were conducted to evaluate the behavior of GGBS-dolomite geopolymer concrete short columns under axial loading. GGBS-dolomite geopolymer concrete column showed better stress-strain behavior compared to cement concrete specimens. Load carrying capacity of geopolymer concrete specimens were improved by adding steel fibres at 0.25, 0.5 and 0.75% by volume of concrete. Ductility of geopolymer concrete was enhanced by 18%, 30% and 45% with the addition of steel fibres in the range of 0.25-0.75% by the volume of concrete. Parameters such as ultimate load, deflection, ductility and crack pattern of axially loaded short columns were evaluated using finite element method. It was observed that geopolymer concrete has 28% reduction in cost/ultimate load compared to ordinary concrete. GGBS-dolomite geopolymer concrete short columns without ductile detailing behaves similar to that of cement with ductile detailing (as per IS 13920-2016) with reduced cost/strength ratio.

Experimental Investigation on Short Concrete Columns Reinforced by Bamboo Scrimber under Axial Compression Loads

The paper presents bamboo scrimber bars as a reinforcing material instead of steel reinforcement in low‐strength concrete columns. Twelve short concrete columns with different reinforcements are tested under axial compression load to study the axial compressive behavior of short concrete columns reinforced by bamboo scrimber. Three columns are reinforced concrete columns, and the other nine columns are bamboo scrimber reinforced concrete columns. The failure process, bearing capacity, axial deformation, and strain of the specimens are compared and analyzed. The results show that the bonding performance between the bamboo scrimber bars by surface treatment and low‐strength concrete is excellent. In low‐strength concrete columns, the material properties of bamboo bars play more thoroughly than those of steel bars. When the bamboo reinforcement ratio is increased, the concrete column ductility is significantly improved, but the bearing capacity of the concrete column is not increased. The bamboo scrimber bars with the size of 10 mm × 10 mm or 15 mm × 15 mm can be used as longitudinal bars of low‐strength concrete columns. The ductility of the short concrete column with 2.56% bamboo scrimber reinforcement is close to that of the short concrete column with 0.72% steel reinforcement.

Seismic Behavior and Finite Element Analysis of Reinforced Concrete Short Columns Impacted by Oblique Earthquakes

This study evaluates the seismic behavior of reinforced concrete (RC) short columns with a high axial compression ratio under oblique earthquake conditions. The studied parameters include the loading angle, axial compression ratio, the high‐strength stirrups with small spacing, and the carbon‐fiber‐reinforced polymer (CFRP) wrapped column end or outer steel plate mesh at the end of the column. Low‐cycle repeated loading tests were used to analyze the specimens’ seismic performance indices of hysteretic behavior, strength, stiffness, deformation capacity, and energy dissipation capacity. Results suggest that the OpenSees finite element program can sufficiently simulate the nonlinear response of the specimen. Oblique loading led to the increase of damage to the specimens and the deterioration of stiffness of the specimens, which was especially seen with the increase of the axial compression ratio. Accordingly, arranging high‐strength stirrups with small spacing and the column end outer steel plate mesh both transform the failure mode from shear failure to bending shear failure. Additionally, wrapping the CFRP at the end of columns improves their strength but does not improve their deformation capacity. The demonstrated success of these strategies in improving the seismic performance of RC short columns under diagonal loads with high axial compression ratios can inform practical engineering applications.

Load-Carrying Capacity of Short Concrete Columns Reinforced with Glass Fiber Reinforced Polymer Bars Under Concentric Axial Load

In this paper, 1 group of plain concrete square columns 150×150×600 mm and 11 groups of concrete columns reinforced with glass fiber reinforced polymer (GFRP) were cast and tested, each group contains of 3 specimens. These experiments investigated effect of the main reinforcement ratio, stirrup spacing and contribution of longitudinal GFRP bars on the load carrying capacity of GFRP reinforced concrete (RC) columns. Based on the experiment results, the relationship between load-capacity and reinforcement ratio and the plot of contribution of longitudinal GFRP bars to load-capacity versus the reinforcement ratio were built and analyzed. By increasing the reinforcement ratio from 0.36% to 3.24%, the average ultimate strain in columns at maximum load increases from 2.64% to 75.6% and the load-carrying capacity of GFRP RC columns increases from 3.4% to 25.7% in comparison with the average values of plain concrete columns. Within the investigated range of reinforcement ratio, the longitudinal GFRP bars contributed about 0.72%-6.71% of the ultimate load-carrying capacity of the GFRP RC columns. Meanwhile, with the same configuration of reinforcement, contribution of GFRP bars to load-carrying capacity of GFRP RC columns decreases when increasing the concrete strength. The influence of tie spacing on load-carrying capacity of reinforced columns was also taken into consideration. Additionally, experimental results allow us to propose some modifications on the existing formulas to determine the bearing capacity of the GFRP RC column according to the compressive strength of concrete and GFRP bars.

Does the Carbon Fibre Coating Reinforcement Have an Influence on the Bearing Capacity of High-Performance Self-Compacting Fibre-Reinforced Concrete?

This study investigated the impact of the location of a carbon fibre coated reinforcement ring (CFCRr) inside the structure of high-performance self-compacting fibre-reinforced concrete (HPSCFRC). Nowadays, cement matrix is considered as an alternative binder when reinforcing concrete structures with composite materials. Due to the plastic behavior of composite structures at relatively low temperatures when carbon fibres are reinforced with epoxy resin, the author attempted to locate carbon fibres inside a concrete structure. Thanks to this, the reinforcement will be less vulnerable to high temperatures (during a fire) and more compatible with concrete. The fibres act as a perimeter reinforcement that is compatible with the concrete mixture. The position of the CFCRr in the structure of concrete has an influence on the load capacity, stiffness and stress-strain behavior of concrete elements. The research was conducted on circular shape short concrete columns and tested under axial compression. The results demonstrated that by including CFCRr inside a concrete specimen, the maximum compressive strength decreases with an increase in the number of composite rings and a greater distance from the vertical axis of symmetry to the edge of the element. It has been proven in these studies that carbon fibres do not have good adhesive properties between CFCRr and a concrete mixture. As a result of this phenomenon, a shear surface is created, which leads to crack propagation along the CFCRr. Therefore, the presented idea of an internal CFCRr should not be used when designing new concrete structures.

Seismic Shear Strengthening of Reinforced Concrete Short Columns Using Ferrocement with Expanded Metal

Seismic Shear Strengthening of Reinforced Concrete Short Columns Using Ferrocement with Expanded Metal

Investigation on seismic performance and shear strength of high‐strength concrete‐filled polyvinyl chloride tube short columns

SummaryThis paper innovatively designs polyvinyl chloride tube (PVCT) with high‐strength concrete (HC) and presents the results of cyclic loading tests on new reinforced high‐strength concrete short columns, including three high‐strength concrete‐filled PVCT (HC‐PVCT) short columns, one high‐strength concrete‐filled steel tube short column and one HC short column. The main objective of this research was to evaluate the seismic behaviors of HC short columns based on the quasistatic test of the columns. The design parameters of the columns in the experiments were axial compression ratio, reinforcement measures, concrete strength, stirrups configuration, and the height‐diameter ratio of tubes. The crack distribution, failure modes, hysteresis loops, skeleton curves, energy dissipation capacity, strength degradation, stiffness degradation, and cumulative damage of the columns were presented and analyzed. The results showed that the HC‐PVCT column had a fuller hysteretic loop and a higher peak load than the HC column. Compared with HC column, the strength degradation of HC‐PVCT columns was slower, and the ductility increased significantly. With a larger axial compression ratio, the ductility of HC‐PVCT columns was decreased. Based on the test and analysis results, a modified HC‐PVCT design method was proposed to calculate the nominal shear strength of HC‐PVCT short columns.

Seismic Behavior of Ultra-High Performance Concrete Short Columns Confined with High-Strength Reinforcement

In order to further study the performance of ultra-high performance concrete (UHPC) structures under seismic conditions, three UHPC short columns confined with high-strength reinforcement were tested alongside one UHPC short column confined with normal-strength reinforcement and one reinforced UHPC short column confined with carbon fiber reinforced polymer (CFRP). The results show that high-strength reinforcement improved the ductility and energy-absorbing ability of the UHPC columns. In addition, high-strength reinforcement only made a marginal difference to stiffness degeneration but did contribute to the specimen's initial stiffness; both high axial loads and small shear span ratios accelerated stiffness degeneration.