Conventional Reinforced Concrete Columns Research Articles

Self-centering capacity of RC columns with smart plastic hinges of martensitic NiTi SMA bars

The objective of this study was to examine the self-centering capacity of reinforced concrete (RC) columns with martensitic shape memory alloy (SMA) bars in the plastic hinge region. To achieve this, three RC columns were prepared: one was conventional and the other two had SMA bars in the plastic hinge zone. The columns had a diameter of 400 mm, height of 1400 mm, and aspect ratio of 3.5. The 400 mm long SMA bars were connected to the steel rebars using specially devised couplers. A cyclic lateral load was applied at the top of the columns, and the lateral displacements along the height of the columns and the corresponding forces were measured during cyclic lateral loading. The strain in the SMA bars was also measured. The RC column with SMA bars exhibited a plastic hinge around the couplers, thus concrete damage from cracking was concentrated at this site. This was completely different from the failure mode of the conventional RC column. The SMA bars in the column were in an elastic state, whereas the steel rebars yielded inside the couplers. The RC column with SMA bars exhibited excellent self-centering capacity, and its displacement recovery ratio was approximately 95% at a drift of 5%. However, its energy-dissipation capacity was lower than that of the conventional RC column. The equivalent damping ratio of the RC column with SMA bars was approximately 3% after 1.75% drift. It is conjectured that the excellent self-centering of the RC column with SMA bars was caused by the elastic behavior of the martensitic SMA bars.

Mechanical Behaviour Evaluation of Full Iron Tailings Concrete Columns under Large Eccentric Short-Term Loading

In this study, full iron tailings concrete (FITC) was created using iron tailings from a tailings pond in Qian'an, China. Iron tailings account for 86.8% of the total mass of solid raw materials in the FITC. To enable large-scale use of FITC, a comprehensive investigation of the structural behaviour of full-iron tailing-reinforced concrete (FITRC) specimens is warranted. Therefore, eight rectangular reinforced concrete (RC) columns with conventional reinforced concrete (CRC) as a control were tested to investigate the effects of section dimensions, initial eccentricities, and concrete strengths, on the structural behaviour of FITRC columns under large eccentric short-term loading. The experimental and analytical results indicated that the sectional strain of the FITRC columns satisfied the plane-section assumption under short-term loading, and the lateral deflection curve agreed well with the half-sinusoidal curve. In addition, the FITRC columns exhibited a slightly lower cracking load and lower ultimate load capacity than the CRC columns, and the crack widths were larger than those of the CRC columns. The reduction in the load capacity observed in the FITRC was within the permissible range stated in the design code, thereby satisfying the code requirements. The deformation coefficients of the FITRC and CRC columns were identical, and the cracking and ultimate loads calculated according to the current code and theories were in good agreement with the measured results.

Deformation ability of precast concrete columns reinforced with steel-FRP composite bars (SFCBs) based on the DIC method

A steel-fiber reinforced polymer (FRP) composite bar (SFCB) is a novel reinforcement composed of an inner steel bar and outer continuous FRP. Moreover, SFCBs have excellent corrosion resistance and stable positive post-yield stiffness and can be used to control structural damage. However, the relatively small fracture strain of the outer FRP may limit the deformation ability of the concrete members reinforced with SFCBs. Bundled reinforcement can weaken the interfacial adhesion to improve the structural deformation capacity and reduce the connections of the reinforced precast structures to enhance the construction efficiency and quality. In this paper, a quasistatic test of six concrete columns was conducted, and the deformation of the column foot was observed by the digital image correlation (DIC) method to investigate the effects of the reinforcement type (steel bar and SFCB), the number of bars in each bundle (1, 2, and 3), and the construction method (cast-in-place, general precast, and precast with full-length grouting) on the deformation capacity. The crack spacing of the precast concrete column reinforced with single-bar SFCBs increased by approximately 10% compared to the precast reinforced concrete (RC) column, and the crack spacing decreased with an increasing number of bars within each bundle. The proportion of the lateral displacement caused by rigid body rotation due to strain penetration of the longitudinal reinforcement at the precast column foot in total lateral drift was approximately 35%; the smaller growth rate of residual rotation in concrete columns reinforced with SFCBs produced a superior post-disaster resetting ability. The curvature distribution range of columns reinforced with SFCBs was wider and more uniform than that of RC columns. Overall, the utilization of SFCBs as longitudinal reinforcement improved the equivalent plastic hinge length by approximately 120% compared with RC columns, thus greatly reducing the curvature requirement of the column bottom. Moreover, the bundled reinforcement reduced the growth rate of plasticity. The precast specimen with full-length grouting altered the failure mode and achieved a considerable deformation capacity with the longest equivalent plastic hinge length of approximately 435 mm, which is 2.77 times that of the conventional RC column.

SEISMIC PERFORMANCE OF PREFABRICATED CORE STEEL TUBE REINFORCED CONCRETE COLUMNS

AbstractPrefabricated assembly accelerates the building construction process. A primary concern related to prefabricated assembly is the increased fragility of the connection between precast members compared to cast‐in‐situ members. On the other hand, core steel tube reinforced concrete (CSTRC) columns are increasingly being used in high‐rise structures to provide effective axial and lateral force resistance. This study proposes a prefabricated core steel tube reinforced concrete (PCSTRC) column which capitalizes on both the strength of the CSTRC column and the advantages of precast manufacturing, as shown in Fig. 1. The connection is designed to guarantee the integrity of the whole column. Two full‐scale PCSTRC columns with varying axial loads and two controlled specimens, namely a monolithic CSTRC column and a conventional reinforced concrete (RC) column, were fabricated and tested under quasi‐static cyclic loading in order to investigate their seismic performance. The test results demonstrate that all the columns experienced typical flexure‐controlled failure, while the PCSTRC columns suffered less visual damage than the monolithic controlled specimens. The PCSTRC column performed satisfactorily in terms of strength, stiffness, ductility, and general hysteretic behavior and had significantly greater load‐carrying and energy dissipation capacities than the conventional RC column. In addition, there were no apparent differences between the capacities of the CSTRC and PCSTRC columns. As axial load increased, the deformation capacity of the PCSTRC column decreased. Overall, the proposed prefabricated composite column demonstrates good seismic performance and can be considered for use in building construction.

Cyclic loading test for reinforced concrete columns strengthened with high-strength engineered cementitious composite jacket

This paper intends to investigate the enhancing effect of high-strength engineered cementitious composite (HS-ECC) jacket on the seismic performance of reinforced concrete (RC) column subjected to cyclic loading. Totally eighteen column specimens were prepared, including conventional RC columns, high-performance mortar (HPM), high-strength fiber-reinforced concrete (HSFRC), and HS-ECC jacketed columns. The effect of different strengthening materials, axial compression ratio (0.2, 0.3, and 0.4), scheme of HS-ECC jacket (strengthening height, cast-in-place or prefabricate), and stirrup spacing on the hysteresis characteristics of the RC columns were explored. Three typical failure modes can be observed depending on different strengthening materials, including shear failure mode, flexural failure mode, and multiple cracking mode. The test results indicate that fiber-reinforced concrete jacketed columns exhibited both high bearing capacity and superior ductility under different axial compression ratios. In particular, HS-ECC jacketed full-column possesses the best overall performance. Under the axial compression ratio of 0.2, the ductility value and the accumulated energy absorption of the HS-ECC jacketed column were improved by 67.7% and 394.8%, respectively, compared with ith conventional RC column. The superior ductility and saturated cracking behavior of HS-ECC ensure jacketed columns have higher damage tolerance and crack closure ability. Compared with HPM and HSFRC jacketed columns, the ultimate displacement of HS-ECC jacketed column was improved by 113.4% and 26.5%, respectively. The accumulated energy dissipation was 866.6% and 111.7% higher than that of HPM and HSFRC jacketed columns. Additionally, the increase in strengthening height could significantly enhance the seismic performance of HS-ECC jacketed columns. In terms of the strengthening scheme, the deformation capacity of cast-in-place HS-ECC jacketed column was better than that of column strengthened by prefabricate HS-ECC slab.

Investigation on the performance of reinforced concrete columns jacketed by conventional concrete and geopolymer concrete

The objective of this investigation is to experimentally study the behaviour of reinforced concrete (RC) columns strengthened using RC and geopolymer concrete (GPC) jacketing by subjecting them to axial loading. The experimental results were analytically validated by the finite element model (FEM). For this investigation, six columns of M25-grade conventional concrete were subjected to more than 75% of the ultimate load. Then three columns were jacketed by using M40-grade RC and another three columns were jacketed by using M40-grade GPC. The interfacial behaviour of the conventional RC column and jacketed GPC columns was studied and compared. The 3D linear and FEM was employed to measure the effect of conventional RC and GPC-jacketed columns under increasing load by considering the concrete damage plasticity (CDP) and elastoplastic models with isotropic hardening. The validation against the experimental results confirmed 90% accuracy of the analytical model.

Experimental and Numerical Investigation of the Seismic Performance of Bridge Columns with High-Strength Reinforcement and Concrete

Despite the numerous advantages high-strength reinforcement (HSR) and high-strength concrete (HSC) offer over conventional materials, the practical use of these materials for bridge column design in seismic zones has somewhat been limited. This is due to the insufficient research data and guidelines for the seismic design of bridges using HSC and HSR and the lack of a reliable analytical model. Therefore, to address this issue and promote the application of HSR and HSC, this paper investigates high-strength bridge columns’ seismic performance experimentally and numerically. Six large-scale reinforced concrete (RC) bridge columns and one multi-column bent frame were tested under a quasi-static cyclic loading with constant axial compression. The primary design parameters were axial load ratio, longitudinal and transverse reinforcement yield strength, and transverse reinforcement spacing. The failure pattern of high-strength columns was similar to conventional RC columns and satisfied the requirements for seismic design in terms of failure mode, hysteresis behavior, ductility, and energy dissipation capacity. The experimental ductility values of the high-strength columns were satisfactory and capable of meeting the ductility demand of most codes. Furthermore, a numerical model was built using the OpenSees program to predict the seismic performance of the specimens and then verified by comparing them with the test results of 12 columns. The numerical model’s results were in good agreement with the experimental results. The results suggested that numerical modeling techniques commonly used for normal strength concrete (NSC) columns can be used for HSC bridge columns by incorporating a proper material model.

Simplified plasticity damage model for large rupture strain (LRS) FRP-confined concrete

Large rupture strain (LRS) fiber-reinforced polymers (FRP) composites with an elongation greater than 5% offer an attractive solution for seismic strengthening of reinforced concrete (RC) columns. For a quick and reliable design of LRS FRP-strengthened RC columns, this paper presents a simplified plasticity damage model for LRS FRP-confined concrete under cyclic axial compression. This model consists of two parts: (a) a recent monotonic LRS FRP-confined concrete model developed by the authors’ group as an envelope curve and (b) a simplified linear plasticity damage cyclic rule for predicting unloading and reloading paths. To solve the cyclic model deviation induced by concrete softening under a large axial strain, a pseudo-plastic strain was proposed, based on which the damage degradation of FRP-confined concrete can be quantified. The model comparisons show that although the proposed model sacrificed some precision when directly applied for the cyclic axial compressive behavior of FRP-confined concrete, it can give similarly accurate predictions as a complex model does for the behavior of conventional or LRS FRP-jacketed RC columns under a combined axial load and cyclic lateral load. Thus, this simplified plasticity damage model serves as a promising basic model for simulation of the seismic performance of FRP-strengthened structures.

Effects of the Replacement Length of Concrete with ECC on the Cyclic Behavior of Reinforced Concrete Columns.

This paper presents an experimental investigation on the effects of the replacement length of concrete with engineered cementitious composites (ECC) on the cyclic behavior of a reinforced concrete (RC) column. A conventional RC column specimen and two RC composite columns designed with ECC were fabricated. To investigate the cyclic behavior of each specimen, a series of cyclic loading tests was performed under a reversed cyclic loading condition with a constant axial load. Test results showed that ECC columns exhibited higher cyclic behavior in terms of load carrying capacity, ductility, and energy dissipation capacity compared to the RC column. It was also found that when applying ECC to the column specimen with a length of 3.6d or more, the energy dissipation capacity was greatly increased.

Experimental Investigation on Conventional Rebar RC Column with Non-Conventional Prefabricated Cage System

A new steel reinforcement is recommended in the name Prefabricated Cage System (PCS) in the column. PCS is a non-conventional prefabricated cage reinforcement system that allows for simpler, quicker and more durable construction which can be utilized in Reinforced Concrete (RC) columns to replace traditional longitudinal and transverse steel. Besides having alike or greater strength correlated with the traditional reinforcement given in columns, the PCS decreases the construction schedule time and reduces the overall construction expense. The PCSwas manufactured through punching or cutting hollow steel tubes or plates by perforation, and PCS costs are often almost equal to traditional rebar reinforcement. The construction time can be greatly decreased by using PCS. In this article, instead of two types of traditional rebar reinforcements, two types of perforations were used in PCS reinforcement. Comparative research was performedfor the columns under axial loading among the PCS reinforcement and the traditional rebar reinforcement. Test results showed that the axial load carrying capacity of PCSspecimens was comparable or superiorto that of conventional reinforced concrete columns.

Mechanical bar splices for incorporation in plastic hinge regions of RC members

Mechanical devices are incorporated in reinforced concrete (RC) structures in lieu of conventional lap splicing mainly to reduce bar congestion in joints. Mechanical bar splices, which are also referred to as bar couplers, might also be used to connect precast members to accelerate construction. Nevertheless, current codes prohibit the use of bar couplers in plastic hinge regions of RC special moment-resisting frames and RC bridge columns in high seismic zones preventing the use of couplers as precast connections. This may be because of a lack of systematic test data on the coupler performance, limited experimental studies on mechanically spliced RC members, and engineering precautions. All bar couplers available in the U.S. market were evaluated as part of this study and 10 products from six different manufacturers were identified as potential couplers to be used in precast members. New standard test methods for mechanical bar splices were developed and more than 160 bar couplers were tested under uniaxial monotonic and cyclic loading to failure to generate the first-of-its-kind systematic database of the coupler performance. Mechanical properties of these splices were established, and a coupler material model adopted from the literature was found to be viable in producing the splice stress–strain behavior. Furthermore, a parametric study was carried out to investigate the seismic performance of mechanically spliced bridge columns utilizing the verified coupler models. More than 240 pushover analyses were performed. It was found that mechanically spliced bridge columns may exhibit up to 43% lower displacement ductility capacity compared to conventional RC columns and the force capacity of these columns may be up to 10% higher than that for RC columns. Columns spliced with rigid and long couplers will show the lowest displacement capacities. Based on the research findings, a new standard testing method was prepared for seismic couplers and was submitted to the American Association of State Highway Transportation Officials (AASHTO) for possible adoption.

The Composite Steel Reinforced Concrete Column Under Axial and Seismic Loads: A Review

The composite steel reinforced concrete (SRC) columns with the form of partial or full encasement of the steel section in the reinforced concrete (RC) have attracted pervasive attention due to their advantages compared to the conventional RC columns. This paper aims to summarize the representative publications regarding the SRC columns. Firstly, the analytical studies of the SRC columns, including comparative studies between available codes to address the philosophy of design and the limits in the available codes of design, bond slip behavior, analytical confinement material models, and finite element analysis, are addressed. In addition, the discussion and summary of the axial behavior of the SRC columns and the important parameters affecting the axial behavior of these types of columns were included. It also attempts to cover the parameters affecting the seismic behavior of the SRC columns. Important progress has been made by the previous studies in the SRC columns under the axial load and the combination of axial and seismic loads, but they fundamentally focused on the columns with the simple arrangement of steel section, and a few attention was paid to the new type of SRC columns with rotated cross-shaped steel section whose webs coincide with the diagonal lines of the columns’ section. Due to the lack of study and the brittle failure of the columns with lightweight and high strength concrete, more studies should still be made to know the behavior of the SRC columns. The paper concludes with suggestions for the future studies to enhance the effectiveness of the SRC columns.

A new strengthening technique for increasing the load carrying capacity of rectangular reinforced concrete columns subjected to axial compressive loading

In this work, a new technique for the efficient confinement of reinforced concrete (RC) columns of rectangular cross-section is described and its effectiveness is assessed experimentally. This technique is based on the concept of applying strips of carbon fiber reinforced polymer (CFRP) wet layup sheets with a certain prestress level using a mechanical device. The influence of the cross-section aspect ratio of columns on the axial stress-strain response, strain field in the CFRP and strength increase provided by the different adopted strengthening configurations was investigated. All specimens had a height of 1100 mm, and three cross-sections were considered: 120 × 120 mm2, 240 × 120 mm2 and 480 × 120 mm2, representing cross-section aspect ratios (large/small edge) equal to 1, 2 and 4, respectively. Four types of columns were tested: conventional RC columns (reference columns), fully-wrapped columns, partially-wrapped columns, and columns strengthened according to the new technique. All columns were subjected to axial compression loading until failure. The experimental results show that the cross-section aspect ratio has a significant effect on the confinement effectiveness that CFRP strengthened systems can provide to RC columns of rectangular cross-section. The maximum axial strength and axial strain at the peak load of all columns significantly decrease when the cross-section aspect ratio increases. Based on the obtained experimental results, it is shown that the proposed technique is more efficient in terms of increasing the load carrying capacity of rectangular RC columns than CFRP-based conventional strengthening techniques.

Experimental study on reinforced concrete large‐eccentricity compressive column of basic magnesium sulfate cement concrete—in different curing conditions

Basic magnesium sulfate cement (BMS) has many advantages, such as early strength, high strength, resistance to water and corrosion resistance, and so on. In order to explore the difference in performance between BMS and conventional reinforced concrete (RC) large‐eccentric columns, the experiments of eight BMS concrete columns, including their deflection, cracking, yielding, ultimate moments, and failure modes are studied. The results show that large‐eccentric compression column of BMS concrete has 20% higher values of cracking load and the ultimate capacity compared with the conventional RC column. The curing relative humidity has no obvious effect on the eccentric compressive performance of BMS concrete columns. There is no obvious difference in the failure modes of BMS concrete columns and conventional columns under large‐eccentric compression. In addition, with the increase of the strength of BMS concrete, the cracking moment and the eccentric compressive capacity for BMS concrete columns can be improved. The general eccentric compressive theory and current code provisions for eccentric compressive column design are modified in order to be applicable to eccentric BMS concrete columns.

Probabilistic assessment of FRP-confined reinforced concrete columns

This paper presents a reliability study on reinforced concrete (RC) columns retrofitted by Fibre Reinforced Polymers (FRP) confinement. First, variability of the compressive resistance of FRP-confined RC columns considering uncertainty in the model error, material properties, section dimensions, FRP strain efficiency factor and minimum load eccentricity as well as any existing correlation among random variables was studied. Then, reliability of FRP-confined RC columns designed based on the ACI 440 and the fib bulletin 14 guidelines was investigated. Results showed that in order to achieve the target reliability used in design of conventional RC columns, resistance reduction factors of these guidelines require modification. For the design of FRP-confined RC columns, a resistance reduction factor of 0.85 for the ACI 440 guideline and a partial safety factor of 1.45 for the fib bulletin 14 are suggested.

An experimental investigation of innovative bridge columns with engineered cementitious composites and Cu–Al–Mn super-elastic alloys

Recent strong earthquakes have shown that reinforced concrete (RC) bridge columns constructed using conventional materials and techniques suffer from major damage and permanent deformations. The yielding of the longitudinal reinforcement as the main source of energy absorption, and cracking and spalling of concrete results in a dysfunctional bridge structure that does not support the post-disaster recovery efforts. This paper investigates the use of engineered cementitious composites (ECCs) and Cu–Al–Mn super-elastic alloys (SEAs) to improve the performance of bridge columns under seismic loads. A new column design is proposed, which is composed of a pre-fabricated ECC tube that encompasses the longitudinal and transverse steel reinforcement (rebar). The rebar in the plastic hinge region of the cantilever columns was totally or partially replaced with Cu–Al–Mn SEA bars. The tube was filled with conventional concrete after it was placed inside the rebar cage of the foundation. ECC exhibits superior tensile ductility, bonding with steel, energy absorption and shear resistance, in addition to lower permeability and reduced crack widths compared to conventional concrete. Cu–Al–Mn SEA bars are capable of recovering large inelastic deformations exceeding 12% strain. The proposed approach capitalizes on the deformability of ECC with reduced damage, and the energy absorption capacity of Cu–Al–Mn SEA bars without permanent deformation. A total of six column specimens were constructed and tested under simulated seismic loading. The number of rebars replaced with Cu–Al–Mn SEA bars, ECC mixture design, and the ratio of the concrete core area to total column cross-sectional area were the variables investigated in the test program. A comparison of the results indicated that the proposed concept with no Cu–Al–Mn SEA bars provides higher lateral strength, similar energy absorption and reduced damage compared to conventional RC columns; however, similar to a conventional column, it results in excessive permanent deformations. Using Cu–Al–Mn SEA bars in the proposed concept led to a lower lateral strength and energy absorption while the permanent deformations were reduced significantly (over 90%).

Residual Axial Capacity Comparison of CFFT and RC Bridge Columns after Fire

The fire performance of protected concrete-filled fiber reinforced polymer (FRP) tube (CFFT) and conventional reinforced concrete (RC) bridge columns is studied through two phases of experimental research comprised of fire exposure and residual axial capacity tests. Two one-fifth scale CFFT columns and two one-fifth scale conventional RC columns having similar axial and flexural capacities were subjected to two durations of extreme temperature exposure. The CFFT columns were protected by the Tyfo® CFP fire protection system during the experiments. Subsequently, the post-fire robustness of the columns was quantified by measuring the residual axial capacity characteristics of each column. The protected CFFT columns exhibited superior axial strength and stiffness retention compared to the RC columns after fire exposure.

EXPERIMENTAL STUDY OF SEISMIC PERFORMANCES OF RC BRIDGE COLUMNS WITH CFST COLUMN EMBEDDED LNSIDE

To improve the seismic performances of reinforced concrete (RC) bridge columns and to prevent columns from shear failure and core concrete crushing, high strength concrete filled steel tube (CFST) is put into RC columns to form a new kind of composite column. Through cyclical loading tests, the seismic performances of four columns are studied. The first column tested is a conventional RC column, the second one is a bonded composite column, the third one is an unbonded composite column, and the fourth one is an unbonded composite column whose axial force is composed of only bone by its CFST column. The test results show that the CFST column can increase the flexural strength, displacement ductility and energy dissipation capacity, and decrease the residual displacement after undergoing large deformation. When the degree of bond between the steel tube and the outside concrete around the tube is reduced, the load-carrying capacity of the composite column decreases, but the ductility increases. When the axial force is only bone by the CFST column, the load-carrying capacity of the composite column decreases significantly, and the ductility increases markedly.

Seismic performance of modular columns made of concrete filled FRP tubes

In this study the effectiveness of a modular column without post-tensioning is evaluated for earthquake resistance. The segments of the modular columns are made of concrete-filled fiber reinforced polymer (FRP) tubes (CFFT) for providing additional flexural hinge confinement by FRP tube. The CFFT segments are manufactured by match cast method, having insert holes for longitudinal steel bars embedded in reinforced concrete (RC) foundation to penetrate. No tensioning is applied for the connection of the segments by considering the difficulty to install anchorage devices. The segments are bonded to each other by epoxy. Quasi-static cyclic loading tests of scale-down circular columns were carried out. The experimental results of the modular CFFT columns were compared with those of CFFT cast-in-place columns and conventional RC columns. The results showed that the seismic performance of the modular CFFT columns is superior to that of their RC counterparts and comparable to that of their CFFT cast-in-place counterparts. The proposed modular system can be easily installed and will provide rapid construction.

Numerical simulation of conventional RC columns under concentric loading

This paper aims to explore the correct prediction of stress–strain behavior and the determination of load ratio of conventional reinforced concrete (RC) columns subjected to concentric loading. Although there are numerous empirical confinement models are reported in the literature for the prediction of stress–strain response of the columns with conventional tie configuration under concentric loading, there is still an apparent need for the detailed analyses and more practical numerical models to provide further understanding of the stress–strain behavior. In this study, a comprehensive nonlinear finite element analysis (NLFEA) of square conventional RC columns under confining pressures has been performed improving the material parameters of Drucker–Prager criterion: cohesion and the internal friction. As in the previous companion paper of the author, these parameters were determined so that the Drucker–Prager failure cone approximates the whole compression meridian of the concrete up to the analytically predicted point of hydrostatic pressure obtained by making use of a realistic failure model. This crushing failure type model needs only the cylindrical compressive strength of concrete. As a result of this study, a new relation corresponding to the low levels of lateral pressure is also proposed for cohesion. A couple of experimental studies have also been presented here for the validation of the numerical method proposed in this work. The numerical analyses successfully reproduce the stress–strain behavior of 30 specimens tested by seven different researchers.