Seismic Performance Of Reinforced Concrete Columns Research Articles

Seismic retrofit of intact and damaged RC columns using prefabricated steel cage-reinforced UHPC jackets and NSM GFRP bars

The use of high-performance materials, such as ultra-high-performance concrete (UHPC) and fiber-reinforced polymer (FRP), in the seismic retrofitting and strengthening of reinforced concrete (RC) columns has attracted wide attention. In this study, a novel prefabricated steel cage-reinforced UHPC jacket (PSRUJ) was proposed to improve the retrofitting efficiency of conventional cast-in-place UHPC jackets and combine the advantages of UHPC and steel jackets. PSRUJ was further combined with the near surface-mounted (NSM) technique to develop a new method for retrofitting the seismic performance of RC columns in buildings. To investigate the effectiveness of the proposed retrofitting method, cyclic loading tests were performed on one intact RC column retrofitted with PSRUJ and two damaged RC columns retrofitted with PSRUJ and the combination of PSRUJ and NSM glass FRP (GFRP) bars. After PSRUJ retrofitting, the load-carrying capacity, deformation capacity, and stiffness of the intact and damaged RC columns increased by (30∼46)%, (54∼74)%, and (24∼40)%, respectively. The inclusion of NSM GFRP bars further increased the load-carrying capacity but reduced the residual drift ratio while having little effect on the ultimate drift ratio of the retrofitted columns. Further, a damage index was proposed to assess the damage degree of core normal concrete and develop the peak strength and strain models for PSRUJ-confined damaged concrete. Finally, a flexural strength model was proposed for damaged RC columns retrofitted with PSRUJ and NSM bars.

Sensitivity analysis of parameters affecting the seismic performance of RC columns strengthened by fabric-reinforced cementitious mortar

In recent years, fabric-reinforced cementitious mortar (FRCM) has emerged as a popular choice for strengthening reinforced concrete and masonry structures due to several advantages over conventional fiber-reinforced polymer (FRP) composites. Particularly, the enhancement of Reinforced Concrete (RC) columns using FRCM composites has garnered significant attention. While experimental investigations are crucial for assessing the effectiveness of FRCM, physical experiments are often resource-intensive and time-consuming. Therefore, this study seeks to investigate the impact of various design parameters on the performance of RC columns strengthened with FRCM under low-amplitude cyclic loads simulating earthquakes through Finite Element (FE) analysis. The FE model, incorporating columns and FRCM strengthening materials, was developed using the DIANA 10.5 program. To assess the reliability of the model, analytical results were compared with experimental findings from a previous study, focusing on lateral strength, hysteresis behavior, and failure modes. The validation outcomes demonstrated a reasonable correlation between the test and numerical results. Subsequently, a sensitivity analysis was conducted to explore the influence of input parameters, such as concrete compressive strength, fabric reinforcement quantity, longitudinal reinforcement ratio of the columns, and pre-axial loading levels, on the seismic performance of RC columns reinforced with FRCM. The findings of the sensitivity analysis were discussed in detail.

Dynamic cyclic loading tests for investigating the influence of loading rate and axial force on the lateral response of RC columns

AbstractThe material properties of steel and concrete vary depending on the loading rate to which they are subjected. To realistically evaluate the seismic performance of reinforced concrete (RC) columns, it is necessary to simulate the loading rate that structures will experience during seismic events as accurately as possible. Real‐time dynamic testing is preferred over quasi‐static testing for this purpose. On the other hand, the seismic performance of RC columns also depends on the axial force applied to the column. However, due to the large axial stiffness of RC columns, accurately controlling the axial force during the test, particularly in real‐time testing, is challenging. Consequently, only a few component‐level dynamic tests have been conducted for RC columns. This study aims to explore the influence of axial force and loading rate on the seismic performance of RC columns. To this end, both slow and fast cyclic loading tests were conducted on square cross‐section RC columns subjected to four different axial forces. By utilizing a robust actuator control method along with a specially designed load transfer element, the axial force was successfully controlled, while the lateral displacements were imposed on the columns in real‐time. The results include lateral strengths, postyield responses, damage patterns, rebar strains, and their rates, all of which constitute unique experimental data that can contribute to a deeper understanding of the actual seismic response of RC columns.

Seismic performance of RC columns strengthened with HSSSWR meshes reinforced ECC under high axial compression ratio

The cyclic loading tests under high axial compression ratio were performed to investigate the seismic performance of full-scale reinforced concrete (RC) columns strengthened with high-strength stainless steel wire rope (HSSSWR) meshes reinforced engineering cementitious composite (ECC), considering different axial compression ratios and strengthening schemes. The test results show that the seismic performance of RC columns was greatly improved after being strengthened. Specifically, the failure modes of the columns were changed from flexure-shear failure to compression-flexure failure, and the ductility and energy dissipation capability were significantly improved by 69.6% and 474.6%, respectively. Besides, the HSSSWR meshes reinforced ECC jacket was confirmed to be a more efficient strengthening scheme, compared with strengthening with only ECC or lateral HSSSWRs reinforced ECC. The RC columns still showed good ductility and energy dissipation capacity after being strengthened with HSSSWR meshes reinforced ECC under high axial compression ratios of 0.5 and 0.7. Finally, taking into account the confinement effects of ECC, lateral HSSSWRs, and stirrups, an analytical model used for predicting the envelope curve of strengthened columns with HSSSWR meshes reinforced ECC jackets under cyclic loading was proposed, which was in good agreement with the test results.

Seismic performance of RC columns under combined cyclic flexural and constant axial loadings

In this study, an experimental test procedure is conducted to investigate seismic performance of reinforced concrete columns under earthquake loading. Earthquake loading is simulated by combination of constant axial load and reversing cyclic load. The main variables of the experimental program are selected to be dimensionless axial load level and the ratio of shear span to effective column depth. Test results are compared with the current suggestions and approximations used for performance-based design and/or evaluation of reinforced concrete (RC) columns under seismic loads. It is observed that section curvature plays an important role to express failure damage limit state under cyclic loading as well as to sudden decrease in load carrying capacity. Besides, two new simple suggestions are made for performance-based design and/or evaluation process of RC columns. As a first step of this suggestions, a relation between damage limit states and curvature ductility ratios of RC columns is defined. This relation is validated with the experimental results of test columns through damage index model based on section curvature. The proposed damage limit states vary according to damage level definition and based on buckling parameter in terms of diameter, buckling length and yield strength of longitudinal reinforcement. The second suggestion is made to relate damage limit state to decrease in shear resistance of columns. To this purpose, a model to express concrete contribution to shear strength due to the proposed damage limits is used. With these two new proposed equations, it is both aimed to obtain a damage limit state in terms of curvature ductility ratio and to control ductile failure mode in a simple yet effective way.

Experimental Investigations of Reinforced Concrete Columns with Lap-Spliced Crossties Under Cyclic Axial and Lateral Load

The lap-spliced crosstie is formed by lapping two J-shaped reinforcing bars with a 180° hook at one end and a straight line at the other end, which can address the difficulty and poor construction quality of conventional crossties. This study conducted cyclic lateral load testing of four large reinforced concrete (RC) columns to explore the seismic performance of RC columns with lap-spliced crossties under cyclic axial force. The results are as follows: (1) Under the action of cyclic axial force, all the specimens basically fulfilled the requirements of earthquake-resistant structures under axial compression. The flexural ductility of the specimen with crossties of 180-deg hooks was the best, followed by the specimens using lap-spliced crossties. The specimen with conventional crossties performed the worst. (2) The seismic performance for all the specimens in enduring axial tension was more satisfactory than that for axial compression. (3) When an inner column endures only axial compression during an earthquake with a column axial force ratio of greater than 30%, the use of lap-spliced crossties both meets specification requirements and can facilitate the construction process. (4) When an outer column is subjected to cyclic axial compression and tension during earthquakes, the column axial force ratio is generally less than 30%. Therefore, lap-spliced crossties can be used to replace conventional crossties. (5) For columns that withstand only axial compression, when the column axial force ratio is less than 30%, lap-spliced crossties can be used instead of conventional crossties. (6) RC columns with lap-spliced crossties enclosing lapped longitudinal reinforcements as well as the rectangular column section and intermediate longitudinal reinforcements merit further research and clarification.

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.

Seismic Fragility Analysis of the Aging RC Columns under the Combined Action of Freeze–Thaw Cycles and Chloride-Induced Corrosion

The combined action of freeze–thaw cycles and chloride-induced corrosion are generally recognized as one of the main causes of the degradation of the mechanical properties and seismic performance of reinforced concrete (RC) structures in the northern frozen coastal regions. To investigate the degradation mechanisms of the seismic performance of RC columns subjected to the combined action of freeze–thaw cycles and chloride-induced corrosion, the impact of freeze–thaw cycles on the chloride diffusion coefficient of concrete was studied through concrete deterioration tests and theoretical analysis. This paper proposed a time-dependent deterioration model for RC columns, which is suitable to consider the combined action of freeze–thaw cycles and chloride-induced deterioration. The proposed deterioration model could be applied to the investigations of time-dependent seismic performance and the seismic fragility of RC columns. Based on the established deterioration model, this paper proposed a time-dependent seismic fragility analysis framework for the aging RC columns, considering the combined action of freeze–thaw cycles and chloride-induced corrosion. In addition, a representative three-span RC continuous T-shaped girder bridge that is located in the high-latitude northern frozen coastal regions of China was taken as the case study, and the time-dependent seismic fragility analysis of RC columns was conducted considering the involved uncertainties in geometric parameters, the deterioration mechanisms of the materials, and ground motions. The time-dependent seismic fragility curves of RC columns were obtained at different service time points. The results indicated that the combined action of freeze–thaw cycles and chloride-induced deterioration had a significant influence on the time-dependent seismic responses of the deteriorating RC columns. Under the combined action of freeze–thaw cycles and chloride-induced corrosion, when the RC bridge was in service for 75 years, the stirrup strength decreased by 3.88% and the cross-sectional area decreased by 30.03%. The peak stress of the confined concrete decreased by 52.1% and its peak strain increased by 12.2 times, respectively. Moreover, the time-dependent seismic fragilities of the aging RC columns under different damage states exhibited a nonlinear increase as the service life increased.

Experimental research on seismic behaviors of RC columns considering buckling of HRB600 longitudinal steel bars

The inelastic buckling of longitudinal bars and premature fracture that followed can always be observed in laboratory research and earthquake damage of reinforced concrete (RC) columns. The buckling deformation and accompanied fracture of HRB600 high-strength steel bars are more significant than those of conventional reinforcing bars, but the buckling properties of HRB600 reinforcement and the influence of premature fracture on the seismic performance of RC columns are far from clear. In this paper, low cyclic loading tests were conducted on six full-scale RC columns reinforced with HRB600 reinforcement by changing the slenderness ratios of longitudinal bars and the axial compression ratios of columns, and the lateral buckling displacements of longitudinal bars were measured by an identified method. Based on the lateral buckling displacements, the buckling behaviors of longitudinal bars were analyzed. It shows that cover concrete has a significant constraint effect on preventing buckling of HRB600 reinforcement. The inelastic buckling behaviors and premature fracture of HRB600 bars on the ultimate deformation capacity and ductility of RC columns were investigated according to the lateral buckling displacements and ductility coefficient. It is found that the increase of the slenderness ratio would cause larger buckling displacements making the local plastic deformation concentration and low-cycle fatigue damage of HRB600 reinforcement more serious, resulting in the premature fracture of longitudinal bars and decrease of ductility of RC columns. Furthermore, a series of individual bars accompanied by the RC columns were tested. Based on the average stress–strain curves, the effects of yield strength and slenderness ratio were discussed. Former researches of conventional longitudinal bars were involved to form a comparison group with HRB600 bars. The results indicate that the deformation capacity reserves of HRB600 reinforcement after 85% peak load were significantly lower compared with conventional bars. It is suggested to limit the application of RC columns reinforced with HRB600 longitudinal bars in high seismic intensity areas and improve the limitation on the slenderness ratio of high-strength steel bars.

Investigation of Deformation-Based Damage Limits of RC Columns for Different Seismic Codes

The seismic performance of reinforced-concrete columns is related to the expected damage limits under seismic loads and how this damage relates to safety of the structure. In order to assess the performance of reinforced-concrete columns under seismic loads, performance-based deformation and damage limits are proposed by the seismic codes. Adequacy of the deformation and damage limit levels given in the codes such as Seismic Evaluation and Retrofit of Existing Buildings Standard, ASCE/SEI-41 (2017) and Turkish Building Earthquake Code (2018) were evaluated by carrying out parametric studies for RC columns. Reinforced-concrete circular columns are designed in parametric studies to present the effects of various parameters such as concrete compressive strength, axial load levels and spiral reinforcement ratio on performance-based damage limits. Performance limits corresponding to each performance levels obtained by different seismic guidelines were compared. When the results obtained from the analyzes are examined, it has been observed that there are significantly different results in the cross-section damage limits values of ASCE/SEI-41 (2017) and TBEC (2018) regulation, which can change the performance level of the building. TBEC (2018) gives approximately 50% conservative limitations when they are compared with the ASCE/SEI-41 (2017) limitations. As a result, TBDY (2018) seems to offer safer and ductile solutions than ASCE ASCE/SEI-41 (2017).

Investigation of seismic performance of RC column with electrochemical chloride extraction-strengthening by MPC-CFRP

The electrochemical accelerated corrosion of reinforced concrete (RC) columns was carried out with the target corrosion rate of longitudinal rebar as 15%, then the magnesium phosphate cement (MPC)-carbon fiber reinforced plastics (CFRP) as strengthening approach and electrochemical chloride extraction (ECE) method were integrated to process the RC columns. Among them, when the dechlorination period was 35d, the current density of dechlorination was selected as 1 A/m2, 2 A/m2, and 3 A/m2; when the periods of dechlorination were 21d, 35d and 49d respectively, the dechlorination current density was set as 2 A/m2. Finally, the seismic performance and dechlorination efficiency of RC columns under different dechlorination current densities and dechlorination periods were mainly analyzed by failure mode, hysteresis performance, lateral strength, ductility performance, stiffness degradation, residual deformation plus energy dissipation. Compared with the corroded RC columns, the cumulative energy dissipation capacity of the RC columns enhanced by MPC-CFRP promoted by 101.33%−206.36%. When the dechlorination period was 35d, the seismic performance of the RC columns dechlorided by the current density of 1 A/m2 and 2 A/m2 did not decrease significantly, and the seismic performance of RC columns with the dechlorination current density of 3 A/m2 greatly reduced. When 2 A/m2 was regarded as the dechlorination current density, the seismic performance of concrete columns with the dechlorination periods of 21d and 35d did not decrease significantly, and the seismic performance of the concrete columns with the dechlorination periods of 49d greatly reduced. However, it was worth noting that the chloride ion content of the interface between rebar and concrete abated significantly with the growth of the current density and the dechlorination period.

Seismic performance assessment of RC columns with interlocking hoops

The aim of this study is to analytically assess the seismic performance of reinforced concrete (RC) columns with interlocking hoops using a novel damage index, and to provide data for developing next generation seismic design criteria. Interlocking hoops are used in rectangular or non-circular columns, the splices shall be located in the column interior. Seismic performance of RC columns is controlled by the level of confinement provided by transverse steel. Interlocking hoops are commonly used in RC columns because they can provide more effective confinement than rectangular hoops. Three RC interlocking columns were tested under a constant axial load and a cyclically reversed horizontal load. A computer program, Reinforced Concrete Analysis in Higher Evaluation System Technology (RCAHEST), is used to analyze RC structures. Novel damage indices aim to provide a means of numerically quantifying the performance level in RC columns with interlocking hoops sustained under earthquake loading. The proposed numerical method for the seismic performance assessment of interlocking columns is verified by comparison with the experimental results.

Effects of tie detailing configurations on reinforcement buckling and seismic performance of high-strength RC columns

The premature buckling and subsequently low-cycle fatigue fracture of longitudinal bars is one of the main failure modes of reinforced concrete (RC) columns under earthquake loading. The use of high-strength steel bars (HSSB) in RC columns reduces rebar diameter or increases tie spacing, thus increases the vulnerability of bar buckling. In view of this, this paper studies the effects of transverse reinforcement detailing (referred hereafter also as ‘tie detailing’) configurations on reinforcement buckling and then on the seismic performance of high-strength RC columns. Five rectangular RC columns with different tie detailings and axial load ratios were tested under constant axial load and reversed horizontal load. All three tie detailings studied have the same large rectangle closed-hoop, while small hoops/ties are different: including two cross-ties (Type Ⅰ), a small rhombus closed-hoop (Type Ⅱ), or two small rectangle closed-hoops (Type Ⅲ). The axial load ratio includes 0.06 and 0.18. The anti-buckling constraint mechanisms of different tie detailings are proposed, and then the global buckling length of longitudinal bars in RC columns with different tie detailings are calculated. On this basis, the effects of tie detailing on bar buckling and on the seismic performance of RC columns are studied. The observed results of bar buckling verify the reliability of the proposed anti-buckling constraint mechanisms and reinforcement buckling length calculation model. Type Ⅲ tie detailing provide better anti-buckling constraint, and thus reduces buckling length of longitudinal bars of RC columns than that with Type Ⅰ & Type Ⅱ tie detailings. Meanwhile, the use of Type Ⅲ tie detailing enhances the seismic performance of RC columns (ultimate drift ratio and hysteretic dissipated energy) than that with Type Ⅰ & Type Ⅱ tie detailings. The effects of tie detailing on seismic performance of RC columns are more significant under high axial load ratio. As the longitudinal bars are more susceptible to buckle under high axial compression, thus Type Ⅲ tie detailing can more prominently play its advantages of delaying bar buckling and improving the seismic performance of RC columns.

Seismic behaviour of RC columns with lap-spliced crossties under various axial loads

Lap-spliced crossties are formed from the lap splicing of two J-shaped reinforcement bars (rebars) with a 180° hook on one end and a straight end on the other. In this study, cyclic lateral load testing of four large-scale reinforced-concrete (RC) column specimens was performed. Moreover, the integrity of lap-spliced crossties and the seismic performance of RC columns with lap-spliced crossties under various axial load ratios were examined. The results indicated the following. (i) Under various axial load ratios, column specimens with lap-spliced crossties were verified to possess favourable seismic performance and effectiveness in confining the concrete core. (ii) For all specimens with lap-spliced crossties, the straight ends of the J-shaped reinforcement bars did not slide toward the column interior. This indicated that the two J-shaped reinforcement bars were effectively combined into a crosstie with 180° hooks on both ends. (iii) Compared to conventional crossties, lap-spliced crossties are not only easier to install but also more effective in confining core concrete since lap-spliced crossties possess two effective seismic hooks while conventional crossties possess just one.

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.

Analytical modeling of corroded RC columns considering flexure-shear interaction for seismic performance assessment

Corrosion of transverse reinforcement can lead to significant shear capacity deterioration resulting in a ductile-designed reinforced concrete (RC) column to potentially fail in a shear manner. Increased risk of shear failure can be more significant for short shear-critical columns when corrosion occurs. Therefore, shear response can be a particularly important issue in seismic performance assessment of corroded RC columns. An efficient analytical model which can capture the shear capacity deterioration due to corrosion and the flexure-shear interaction behaviors of corroded columns is developed in this work. Corrosion effect on flexural behavior is accounted for through the appropriate modification of steel reinforcement, concrete and bond properties. Shear response is simulated by a new macro zero-length shear spring element, and its shear force-shear deformation relationship is modelled with the Ibarra-Medina-Krawinkler deterioration model that can capture strength and stiffness deterioration as well as pinching behavior. A calibration study is carried out based on a collection of experiments of corroded columns failed in shear. Subsequently empirical formulae for the determination of the modeling parameters of the shear spring are proposed. The proposed model is validated by simulating several corroded columns and compering the predictions obtained with the relevant test data. Results show that the proposed model is able to predict reasonably the overall hysteretic behavior. Corrosion effects on the seismic performance of RC columns are investigated with the proposed model. Results demonstrate that the flexure-shear interaction behaviors should be considered for seismic performance assessment of corroded columns.

Analysis of Bearing Capacity and Seismic Performance of Circular RC Columns Strengthened with Externally Wrapped Steel Plates

Based on a practical project, the construction method of circular reinforced concrete (RC) columns strengthened with externally wrapped steel plates was introduced in this paper. In order to study the bearing capacity and seismic performance of circular RC columns after strengthening, a formula for calculating the bearing capacity of circular RC columns strengthened with externally wrapped steel plates was derived, with reference to theCode for Design of Strengthening Concrete Structure. Through ABAQUS software, the vertical monotone static loading analysis and the horizontal low-cyclic reversed loading analysis were carried out, respectively, before and after the strengthening of the full-size RC columns in this project. The results showed that the bearing capacity of the normal section of the RC column after strengthening was about 80% higher than that before strengthening, and the results of FEM software were in accord with the calculation results of theoretical formula to some degree. Under horizontal low-cyclic reversed loading, the columns after strengthening had both plumper hysteresis curves and higher ductility factors and equivalent viscous damping coefficient than those before strengthening, indicating the energy dissipation capacity, plastic deformation capacity, and seismic performance of the RC columns after strengthening were all obviously improved.

A numerical method for improving seismic resistance of concrete based on its meso-scale damage mechanisms

In this study, reliable image-based meso-scale damage evolution simulation of concrete can be executed by considering its heterogeneous meso-components. Meso-scale damage evolution of concrete with different meso-components are simulated and analyzed here, which can be used to optimize seismic resistance of concrete. As a case study, seismic damage process of a reinforced concrete (RC) column with different meso-component parameters are simulated. From the simulation results, it can be seen that improvement of the properties of interfacial transition zone (ITZ) can significantly improve the seismic performance of RC columns. The established reliable damage evolution simulation of concrete can supply a useful numerical tool to study the method for improving seismic performance of RC column such as optimizing concrete’s meso-model parameters.

Prediction for lateral deformation capacity of corroded reinforced concrete columns

SummaryThe deformation capacities of columns, which are the main lateral force‐resisting elements of reinforced concrete (RC) structures, have been the subject of great interest with the development of performance/displacement‐based seismic design. However, deterioration due to chloride‐induced corrosion causes a significant reduction in the seismic performance of RC columns. Although numerous investigations have focused on the deformation capacity of columns with corroded rebars and various strengthening measures have been proposed, little attention was paid to evaluating the contribution of each deformation component to the tip displacement under corrosion (i.e., bending, shear, and longitudinal bar slip at the column footing), which plays an important role in investigating and explaining the failure mechanisms of columns. This paper presents a computational prediction model to estimate the deformation capacity of RC columns with corroded rebars, and the contributions of bending and bar slip at the column footing are mainly considered in this model due to the negligible contribution of the shear deformation component for columns subjected to flexural failure mode. The calculation results obtained by the prediction model are compared with the quasistatic test results of both noncorroded and corroded RC columns. It turns out that the prediction model simulates the deformation capacity of RC columns with corroded rebars reasonably well considering its simplicity and computational efficiency, and it can be used for time‐variant capacity estimates for the lifetime seismic design and fragility assessment of RC columns exposed to corrosion.

Quasi-static tests of RC columns under variable axial forces and rotations

The behaviour of reinforced-concrete (RC) elements subjected to axial force and rotation variations in conjunction with lateral displacement variation is considered a highly important topic, but only a few experimental studies investigating this topic have been performed. In this paper, five full-scale RC rectangular columns were tested by quasi-static testing (QST) to investigate the effects of large variation axial forces and rotations on the seismic behaviour of columns. Furthermore, the effects of variable axial forces and rotations on the seismic performance of RC columns in terms of the failure modes, hysteretic loops, skeleton curves, ductility factors, stiffness degradations and energy dissipations are presented and analysed. Based on the QST results, the axial force and rotation variations have significant effect on the seismic behaviour of RC columns. Generally, the variable axial forces and rotations may cause a distinct asymmetrical failure phenomenon in the specimens and reduce the lateral strength and ductility factor. Thus, RC columns should be well designed to account for the adverse effects of variable axial forces and rotations.