Reinforced Concrete Column Specimens Research Articles

The Influence of e-glass epoxy composite laminate material application on the crack pattern of cylinder concrete column cross-section

In order to better understand the phenomenon of applying GEC reinforcement to RCC based on the percentage of surface crack pattern (PCP), this research will use e-glass epoxy composite laminate (GEC) to obtain the damage pattern of reinforced concrete column specimens (RCC) utilizing GEC. Additionally, it will compare the splitting tensile strength (STS) and SCP. In accordance with ASTM C496 guidelines, the RCC specimens used in this investigation had a cylindrical shape and measured 150 mm in length and 50 mm in diameter. GEC material, consisting of 0–4 layers of woven e-glass fiber sheets, was applied as an extra layer on top of the RCC. In compliance with ASTM C496 guidelines, a Universal Testing Machine (UTM) was used to perform the split tensile test. With the aid of Adobe Photoshop software, the Histogram approach was used to calculate the crack pattern's proportion. The study's findings demonstrated that the specimens reinforced with four layers of GEC exhibited the highest damage pattern. This suggests that the reinforced specimens must be subjected to a sizable load in order to be damaged. Hence, the damage that occurs in the specimens can be lessened by applying GEC layers on RCC. Further information about the performance of RCC reinforced with GEC is also provided by a comparison of the splitting tensile strength and the percentage of fracture pattern

Reinforced concrete columns strengthened with near-surface mounted and hybrid FRP under compression with or without eccentricity: Experimental study and finite element modeling

The utilization of FRP in strengthening of reinforced concrete (RC) columns has garnered significant attention in the past two decades. Researchers have proposed the use of near-surface mounted (NSM) FRP bars with (hybrid) or without FRP jackets alongside the conventional approach of column strengthening through jacketing particularly in the presence of load eccentricity. In the realm of static loading scenarios, a significant focus has been directed toward the evaluation of the NSM, jacketing, and hybrid methodologies, while comparatively less attention has been given to the impact of various parameters on the capacity. In this article, a total of 22 RC column specimens with medium slenderness were tested under axial compressive loads with or without eccentricity to study the effect of the parameters the number and type of NSM FRP bar, the number of layers and type of FRP jacket, and the groove size for FRP bar mounting. The experimental results reveal the beneficial effects of using FRP jackets, increasing their layers and groove dimensions, and augmenting the number of NSM FRP bars on column capacity and ductility up to 36% and 197% respectively. Additionally, an accurate Finite element model has been developed and role of corbel in eccentricity application is investigated. The results showed that the corbel is not capable of transmitting the desired eccentricity.

Machine vision‐based automated earthquake‐induced drift ratio quantification for reinforced concrete columns

SummaryThis paper presents a novel method for estimating the seismic peak interstory drift ratio (IDR) in reinforced concrete (RC) columns after an earthquake using surface crack image analysis. The quantitative representation of the complexity and irregularity of crack images in damaged RC columns is obtained through the consideration of the generalized fractal dimensions. The authors have compiled a comprehensive database consisting of 445 crack maps obtained from cyclic experiments conducted on 110 rectangular RC column specimens exhibiting double‐curvature deformation mode. This database is utilized by the authors to develop and validate the proposed procedure. The research database contains a wide range of structural and geometric features. Five closed‐form equations are developed with the objective of estimating the peak IDR experienced by the RC columns during a seismic event. The predictive equations are derived through the utilization of symbolic regression technique, with the input parameters varying according to the availability of columns characteristic parameters. Results reveal that generalized fractal dimensions, especially D−1, are strong vision‐based indicator of damage in RC columns having correlation coefficients with IDR ranging from 0.82 to 0.92 across the considered plans. The seismic peak IDR obtained through the empirical equations can serve as the input engineering demand parameter (EDP) in the seismic loss estimation frameworks. This allows for the determination of the probability of exceeding damage states for structural and nonstructural components of concrete buildings. Finally, the practical implementation of the methodology is examined by its application to an actual case of a damaged column during the Kermanshah earthquake of magnitude 7.3 that occurred in 2017.

EXPERIMENTAL RESPONSES OF HIGH-STRENGTH KC COLUMN WITH LARGE AXIAL LOAD

A kernel-confined (KC) column, which a reinforced-concrete (RC) column moves partial longitudinal reinforcements from conventionally placed on outer periphery of section to inner kernel-confined region (KC bar), was concerned in this paper. This paper mainly intended to investigate seismic behaviors of the KC column with large axial loads. There are six sets of high-strength RC column specimens with 600 mm × 600 mm in section to be conducted. Their design strength of concrete was 70 MPa, and steel grades of SD550W and SD790 were designed as the longitudinal and transverse reinforcements, respectively. The number and location of the KC bar and the number and strength of transverse reinforcement are key study parameters. Test results indicated that for all specimens, including KC columns, the testing maximum moments were larger than the computed moment from ACI model and their average value of overstrength ratio of the testing to the computed was 1.25. In addition, the strength obtained from the XTRACT software had a better prediction with an average error of 0.99. Based on test deformation results for all specimens, the amount of the confined reinforcement per ACI 318-19 with an axial load of 0.5fc’Ag, can provide 3% radian of inter-story drift angle capacity for the high-strength RC column.

Rehabilitation of overload-damaged reinforced concrete columns using ultra-high-performance fiber-reinforced concrete

Abstract One of the problems experienced by reinforced concrete (RC) structures, whether a mistake at the design phase or a change in building use, is an overload. The goal of this study is to determine whether ultra-high-performance fiber-reinforced concrete (UHPFRC) is effective in repairing damaged concrete columns utilizing 30 mm thin concrete jacketing made of different steel fibers at various contents with varied aspect ratios (28, 37, and 45). Nine pieces of 500 mm long RC column specimens with a cross-sectional size of 150 mm × 150 mm were cast as part of the experimental program. By loading these columns with roughly 90% of their actual ultimate axial load capacities, damage was caused, and the columns were subsequently strengthened and rebuilt using UHPFRC jacketing materials. The results demonstrated that when steel fiber content increased, so did the mechanical qualities, such as compressive and tensile strengths. Rehab materials that contained 0.5% steel fiber recovered 138% of their maximum load-bearing capacities, while materials that contained 1.5% steel fiber recovered 164% of their original capacities, which were roughly 1.38–1.64 times that of the unjacketed reference column. Additionally, it was observed that employing steel fiber in UHPFRC contents in these approaches resulted in the ultimate displacement being improved from 2.91 to 5.53 mm at 1.5% of steel fiber content, which is an increase of almost double that of control specimens.

Cracking Mechanism of Corroded Reinforced Concrete Column Based on Acoustic Emission Technique

The Acoustic Emission (AE) technique is applied to study the failure mode, damage evolution process, and cracking mechanism of reinforced concrete (RC) columns under the coupling effect of exterior compression load and interior reinforcement corrosion. AE signals are collected from different loading stages for corroded and uncorroded RC column specimens. Parameter analyses are conducted to analyze the peak frequency, energy distribution, and phase parameters used to achieve the general changing conditions of AE signals. Fast Fourier Transform is applied to reveal the time-variant rules of signal frequency and energy in different damage stages. Discrete Wavelet Transform is used for a better understanding of the local time-frequency properties of the non-stationary AE signals and optimally interprets the damage evolution process of the RC structure. Results show that the peak frequency has a 3-layered distribution; an obvious “double-peak” trend of the energy distribution indicates two cracking mechanisms: steel/concrete interface damage and aggregate/cement damage. The damage process consists of four stages: micro-crack formation, micro-crack development, crack expansion, and cracking failure. The corrosion behavior remarkably influences the energy distributions of the two cracking mechanisms, the characteristics of the spectra in different stages, and the damage evolution process inside the RC columns.

Post‐earthquake stiffness loss estimation for reinforced concrete columns using fractal analysis of crack patterns

AbstractThe seismic damage to reinforced concrete (RC) components is conventionally quantified through various damage indices. In this paper, an image‐based procedure is developed for post‐earthquake residual stiffness quantification of RC columns. The proposed scenario‐based methodology is built upon the multifractal indices of the surface crack maps of the seismically damaged RC columns as the complexity measure for the images. An extensive databank from experiments on RC column specimens with a broad range of structural characteristics are collected and employed for generation and validation of the proposed procedure. Based on the availability of the structural information, five closed‐form regression‐aided equations are offered for estimating the stiffness loss in seismically damaged RC columns using predicting parameters among fractal indices, concrete strength, and the aspect ratio of the column. Results reveal that multifractal dimensions of crack maps are largely correlated with the stiffness degradation in RC columns. A sample specimen at various stiffness‐based damage indices is also presented as a case study to evaluate the predicted versus measured damage indices. The updated stiffness values acquired by the proposed equations can be utilized for stability evaluation, system identification, or further analysis of the seismically damaged RC buildings following an earthquake.

Seismic performance of lap-spliced pre-damaged and intact concrete columns strengthened or retrofitted with UHPC and NSM

Reinforced concrete (RC) columns with deficient lap splice details such as short lap splice length and widely spaced stirrups were vulnerable to earthquakes. In the present study, to evaluate the effectiveness of an innovative retrofitting technique using the combination of ultra-high performance concrete (UHPC) and near surface mounted (NSM) technique on the seismic performance of RC columns with deficient lap splices details, cyclic loading tests were performed on four large-sized RC column specimens. Two RC columns were strengthened with UHPC or the combination of UHPC and NSM, and the other two were retrofitted with the combination of UHPC and NSM after the lateral strength decreased to 85% peak strength during the pre-damage cyclic tests. The load–displacement relationship, stiffness degradation, energy dissipation, and residual displacement of RC columns are evaluated. The test results showed that the peak strength and ductility of RC columns with deficient lap splice are significantly improved after strengthening or retrofitting with the combination of UHPC and NSM. The seismic performance of severely damaged RC columns due to deficient lap splice details can still be effectively restored after retrofitting with the combination of UHPC and NSM. Considering the adverse effect of pre-damage, a design method is proposed to predict the flexural capacity of RC columns retrofitting with UHPC or the combination of UHPC and NSM. The proposed method is also applied to predict the flexural capacity of RC beams strengthened with UHPC. The proposed method predicted well the test results of this study and existing tests.

Experimental study on the prestress loss of double‐end prestressing of carbon‐fiber reinforced polymer fabric for strengthening large‐diameter reinforced concrete circular columns

AbstractWhen using single‐end tensioned carbon‐fiber reinforced polymer (CFRP) fabric to strengthen reinforced concrete (RC) columns, the contact length between CFRP fabric and column increases with the increase in column diameter, and the prestress losses are often very large at the distance farthest from the anchorage. To address the problem, a method for double‐end transverse prestressing of CFRP fabric for strengthening large diameter RC columns is proposed in this paper. Tests were carried out on 20 RC column specimens strengthened with prestressed CFRP fabric in constant temperature and humidity. The prestress losses due to friction during the tensioning process and the prestress losses in CFRP fabric during load holding were analyzed. A theoretical formula for the CFRP fabric prestress losses was established. The test results revealed that compared to single‐end tensioning, double‐end tensioning of CFRP fabric can effectively reduce the average friction loss ratio. The friction loss ratio in large‐diameter columns is more significant than that in small‐diameter ones. Applying epoxy coating to the column surface can reduce the prestress loss ratios due to friction and CFRP fabric retraction. The latter can also be effectively reduced by repeated tensioning. The prestress losses calculated using the formula proposed in this paper were in good agreement with the measured data.

A new Distinct Element meso‐model for simulating the rocking‐dominated seismic response of RC columns

AbstractThe rocking‐dominated seismic response of reinforced concrete (RC) columns is a complex mechanism that entails P‐Δ effects, concrete crushing and spalling, rupture and dislocation of steel bars and stirrups, as well as combined localized failures causing splitting and shear‐flexure cracking. In this paper, we present a new meso‐scale numerical modeling strategy for the detailed simulation of the rocking response of slender RC columns under seismic actions. This work advances the current state‐of‐the‐art by exploring the unprecedented use of the Distinct Element Method (DEM), originally conceived for geotechnical studies and whose applicability in earthquake engineering has been primarily limited to the assessment of unreinforced masonry sub‐structures. To decrease analysis time and enable the use of DEM for RC problems, concrete is herein idealized as an assembly of solid macro‐block layers of size directly proportional to their distance from expected plastic hinges. These layers are connected by nonlinear interface springs to simulate tensile and shear cracking via a simplified Mohr‐Coulomb criterion. Crushing of concrete in deformable blocks is modeled using the Feenstra and De Borst strain‐softening linearized compression law, while confinement and combined failures are accounted for numerically through the explicit representation of longitudinal and transversal reinforcement bars, idealized as link elements. Previous experimental static and dynamic tests on full‐scale RC column specimens and results from fiber‐based Finite Element and sectional analysis models are used to evaluate DEM results and quantify the influence of key modeling parameters, including block number and deformability, as well as the amount of damping. The agreement between simulated failure modes and force and displacement capacities and their experimental counterparts demonstrate the applicability of the proposed approach, while demonstrating the pros and cons of simplified numerical methods.

Deep learning‐based evaluation for mechanical property degradation of seismically damaged RC columns

AbstractThe evaluation of mechanical property degradation (i.e., stiffness and strength degradation) for seismically damaged reinforced concrete (RC) components is a critical step in the post‐earthquake assessment of the residual seismic capacity of buildings. In this study, a novel approach based on deep learning (DL) was proposed to evaluate the stiffness and strength degradation of RC columns according to visible seismic damage. A database was constructed by linking the test photos of RC column specimens with the loading points on the hysteretic curves, from which the stiffness and strength reduction factors (λK and λQ, respectively) were analyzed. Two novel convolutional network (CNN) modules were designed to enable feature extraction and integration of seismic damage with a reduced number of parameters, and multitask learning was introduced to enable adaptive feature fusion for stiffness and strength degradation individually. A deep convolutional network (DCNN) was therefore proposed to model the correlation between visible seismic damage and mechanical property degradation of flexural‐dominated RC columns, which can integrate visual characteristics and spatial topologies of visible damage to estimate λK and λQ. The application to two test specimens validated the preferable accuracy and robustness of the proposed DL‐based approach, and demonstrated its high potential for use in post‐earthquake performance assessment of buildings.

GFRP bar RC columns under lateral low-velocity impact: an experimental investigation

The performance of GFRP (Glass Fiber polymer) bar RC (Reinforced Concrete) circular columns subjected to lateral impact was experimentally investigated. Sixteen GFRP bar RC column specimens representing offshore bridges were constructed and tested. Laboratory tests were performed considering two types of loading conditions (static monotonic and lateral impact) and two different boundary conditions (cantilever and propped cantilever). For the static tests, the displacement and loading performances were estimated by applying lateral monotonic static load through a hydraulic actuator. For the dynamic impact tests, a steel-made truck with a rigid nose was used to simulate the typical vehicle or vessel collision scenarios. The dynamic lateral impact and displacement responses were detailed evaluated under three different impact velocities (2.25, 3.00, and 4.50 m/s). Moreover, a semi-empirical model based on experimental results was proposed for a performance displacement-based structural assessment and maximum displacement prediction. It is found that GFRP bar RC columns have similar performance compared to traditional steel RC columns under lateral impact loads given the same static capacity.

A lumped plasticity model for corrosion-damaged reinforced concrete columns

Chloride-induced corrosion is one of the most important causes of the strength degradation of reinforced concrete (RC) bridges. As the piers of RC bridges are important elements for sustaining lateral loads, corrosion of pier columns may lead to significant degradation of the structure. It is thus necessary to have an appropriate evaluation technique to assess the effect of corrosion on the behaviour of RC columns. Numerical modelling approaches based on a concentrated plastic hinge can predict structural behaviour rapidly and with acceptable accuracy, and are highly regarded by engineers. In this study, a numerical approach was conducted to develop an empirical lumped plasticity model (LPM) for corroded RC column elements. In this study, 13 440 RC column specimens, including corroded and uncorroded columns of both rectangular and circular cross-section, were analysed under monotonic and cyclic loading. The LPM was extracted based on regression of the results of cyclic and monotonic analyses. The calibrated model, valid for corroded and uncorroded columns, was assessed using experimental results and numerical models with data out of the range of those used in the parametric study and was found to have high accuracy. The newly developed plastic hinge model can be used to model and analyse corroded bridge columns rapidly. The results are appropriate for use in further assessments such as fragility or rehabilitation analyses.

Determination of uni-axial bending resistance of reinforced fly ash concrete columns

As a by-product from coal burning of thermal power plants, fly ash has appropriate physical properties and chemical composition that can be utilised for the concrete industry, in a form of a fine-mineral additive to reduce cement up to 25% by mass and to enhance the workability of concrete. However, the negative effect of fly ash on the strength of reinforced concrete (RC) members has not been considered in current design provisions. Hence, the determination of uni-axial bending resistance of a basic member - RC column - having 20% cement weight replaced by fly ash is presented in this paper in the following research steps: (i) Experimental investigation on a number of 8 RC column specimens; (ii) Validation of test results with a number of code provisions including Eurocode 2, ACI 318-19, and TCVN 5574:2018; and (iii) Proposal of a simplified justification approach for TCVN 5574:2018 to be capable of modelling the reduction and predicting the uni-axial bending resistance of reinforced fly ash concrete columns.

Artificial intelligence-enhanced seismic response prediction of reinforced concrete frames

Existing physics-based modeling approaches do not have a good compromise between performance and computational efficiency in predicting the seismic response of reinforced concrete (RC) frames, where high-fidelity models (e.g., fiber-based modeling method) have reasonable predictive performance but are computationally demanding, while more simplified models (e.g., shear building model) are the opposite. This paper proposes a novel artificial intelligence (AI)-enhanced computational method for seismic response prediction of RC frames which can remedy these problems. The proposed AI-enhanced method incorporates an AI technique with a shear building model, where the AI technique can directly utilize the real-world experimental data of RC columns to determine the lateral stiffness of each column in the target RC frame while the structural stiffness matrix is efficiently formulated via the shear building model. Therefore, this scheme can enhance prediction accuracy due to the use of real-world data while maintaining high computational efficiency due to the incorporation of the shear building model. Two data-driven seismic response solvers are developed to implement the proposed approach based on a database including 272 RC column specimens. Numerical results demonstrate that compared to the experimental data, the proposed method outperforms the fiber-based modeling approach in both prediction capability and computational efficiency and is a promising tool for accurate and efficient seismic response prediction of structural systems.

Seismic behavior and damage evolution of corroded RC columns designed for bending failure in an artificial climate

Several past studies have shown that artificial climate simulation techniques can address obstacles in electrochemical corrosion methods. However, few experimental studies have investigated the seismic behavior of corroded reinforced concrete (RC) columns in an artificial climate. Therefore, in this study, seven corroded RC column specimens that experienced bending failure were subjected to pseudostatic tests after artificial climate accelerated corrosion tests. The variable parameters of the specimens were the corrosion degree of the reinforcement and axial compression ratio. The seismic behavior of the columns corresponding to corrosion-induced cracks, corrosion morphology of the steel bars, failure process, hysteretic behavior, skeleton curve, ductility, stiffness, energy dissipation capacity and flexural performance were investigated. Based on the test results, a two-parameter damage model was established to evaluate the damage evolution of the corroded RC columns. The results of the test and analysis revealed that the surface characteristics of corroded steel bars under the artificial climate were similar to those in the natural environment. The corrosion ratio of the reinforcement at the RC column edge was higher than that at the middle region of the specimen. As the corrosion degree increased, the seismic behavior of the specimen deteriorated continuously. As the axial compression ratio increased, the bearing capacity and bending bearing capacity initially increased and then decreased since the failure pattern of the columns changed from large eccentric compression failure to small eccentric compression failure. The corrosion and axial compression ratio accelerated the damage development of the RC columns. The proposed damage model accorded with the experimental phenomena before yielding and under the ultimate state, but underestimated the damage between the yield state and the peak state.

Evaluation of square slender RC columns subjected to eccentric loading strengthened with longitudinal FRP sheets based on PIV analysis

In this study, the behavior of square slender reinforced concrete (RC) columns strengthened with carbon fiber-reinforced polymer (CFRP) sheets was investigated. The externally bonded reinforcement on grooves (EBROG) method as a new technique was employed to strengthen the specimens compared to the externally bonded reinforcement (EBR) method as the conventional strengthening technique. Twelve small-scale slender square RC columns (i.e., 125 × 125 × 900 mm) with a slenderness ratio of 25 were loaded under eccentricity-to-cross-section ratios (e/h) of 0, 0.24, 0.48, and 0.72. The results showed the EBROG's superiority over EBR in load-carrying capacity enhancement of the strengthened RC column specimens in various eccentricities; i.e., the loading enhancements were 10.6 to 99.3% for the EBROG specimens and 1.2 to 41.7% for the EBR specimens at varying eccentricities of 0 to 90 mm, compared to those of un-strengthened specimens. Furthermore, the moment capacity enhancement of the EBROG specimens was higher than that of the EBR columns; i.e., it was 100.0% for the EBROG specimens and 42.2% for EBR specimens in the eccentricity of 90 mm, compared with the un-strengthened specimen. Using particle image velocimetry (PIV) analyses, the results of flexural stiffness, strain distribution, ductility, and energy absorption were presented and discussed. Results revealed that by increasing the eccentricity, flexural stiffness decreases; this reduction was more intense for EBR specimens (42%) than the EBROG specimen (36%). An analytical procedure was conducted to compare the experimental and theoretical results. The analysis demonstrated good agreement between the results and the superiority of the EBROG method over the EBR.

Experimental study on the behavior of eccentrically compressed reinforced concrete columns strengthened with CFRP composite sheets

Strengthening of reinforced concrete (RC) columns is needed when the actual load-carrying capacity of the columns does not reach the required level due to either structural deterioration or increasing acting loads. This experimental study aims to evaluate the strengthening effect on the eccentrically-compressed RC columns using Carbon fiber reinforced polymer (CFRP) sheets, that confine around the column cross-section. Three RC column specimens with the same geometrical dimensions, reinforcement detailing, and concrete compressive strength were cast and tested in the current experimental investigation. One RC column without being strengthened is referred as the control specimen whereas two other RC columns were partially strengthened by CFRP sheets. All three RC columns were axially loaded with the same initial eccentricity e0 of 80 mm. Based on the test results such as the ultimate load-carrying capacity, the load-rotation relationship, and load-curvature at the middle of column height, the effectiveness of the strengthening technique is discussed.

Fire performance of earthquake-damaged reinforced concrete columns: an experimental study

PurposeEarthquake tremors not only increase the chances of fire ignition but also hinder the fire-fighting efforts due to the damage to the lifelines of a city. Most of the international codes have independent recommendations for structural safety against earthquake and fire. However, the possibility of a multi-hazard event, such as fire following an earthquake is seldom addressed.Design/methodology/approachThis paper presents an experimental study of Reinforced Concrete (RC) columns in post-earthquake fire (PEF) conditions. An experimental approach is proposed that allows the testing of a column instead of a full structural frame. This approach allows us to control the loading and boundary conditions individually and facilitates the testing under a variety of these conditions. Also, it allows the structure to be tested until failure. The role of parameters, such as earthquake intensity, axial load ratio and the ductile detailing of the column on the earthquake damage and subsequently the fire performance of the structure, is studied in this research. Six RC column specimens are tested under a sequence of quasi-static earthquake loading, followed by combined fire and axial compression loading conditions.FindingsThe experiment results indicate that ductile detailed columns subjected to 4% or less lateral drift did not lose significant load-carrying capacity in fire conditions. A lateral drift of 6% caused significant damage to the columns and reduced the load-carrying capacity in fire conditions. The level of the axial load acting on the column at the time of earthquake loading was found to have a very significant effect on the extent of damage and reduction in column load capacity in fire conditions. The columns that were not detailed for a ductile behavior observed a more significant reduction in axial load carrying capacity in fire conditions.Research limitations/implicationsThis study is limited to columns of 230 mm size due to the limitations of the test setup. The applicability of these findings to larger column sections needs to be verified by developing a numerical analysis methodology and simulating other post-earthquake-fire tests available in the literature.Originality/valueThe experimental procedure proposed in this paper offers an alternative to the testing of a complete structural frame system for PEF behavior. In addition to the ease of conducting the tests, the procedure also allows much better control over the heating, structural loading and boundary conditions.

Compression tests of C-FRCM jacket confined hollow section RC columns

This paper describes an experimental investigation on column tests of carbon fiber-reinforced cementitious matrix (C-FRCM) jacket confined hollow section reinforced concrete (RC) columns. The experimental program consists of twenty columns on two series of confined specimens and two series of unconfined specimens. Test specimens comprise of columns having solid section and hollow section with different hollow ratios. The material properties of C-FRCM were measured through tensile coupon tests. The load carrying capacities, load-end shortening responses, load–strain curves and failure modes of RC column specimens are presented and discussed in this paper. It is shown that the hoop strain of columns under compression decreases with the increase of the hollow ratio, which means the reduction of confinement effect. The effect of hollow ratio on the compressive strength of confined concrete was discussed and an equation was proposed. It is shown that the predictions from the proposed equation agree with the test results generally well.