High-strength Concrete Columns Research Articles

Combined nomograms for calculating the bearing capacity and reinforcement of high-strength and normal concrete RC columns

PurposeThis paper aims to obtain a calculation method by hand without iteration.Design/methodology/approachThis paper adopts strains as known quantities to solve the internal forces and deformations of the section, simplifies the deflection curve of the column and obtains nomograms that can calculate the bearing capacity and reinforcement of circular reinforced concrete (RC) columns by hand.FindingsNomograms include five variables: mechanical reinforcement ratio, relative normal force, dimensionless bending moment, slenderness ratio and ultimate dimensionless curvature. Nomograms corresponding to all classes of concrete have been drawn, and their dimensionless form makes them widely applicable. The calculation results of nomograms are compared and analysed with numerical calculation results, and the difference is within 5%, meeting the engineering requirements.Originality/valueCalculating the bearing capacity of compression bending components requires considering second-order effects. Therefore, the calculation of the bearing capacity of circular RC columns requires iterative calculation, as it includes dual nonlinearity of material and geometry, and the two are coupled with each other. To calculate the bearing capacity of the section adopting ordinary concrete, it is necessary to solve the transcendental equation iteratively. For high-strength concrete, it can only be solved by numerical integration. A fast calculation method by hand is proposed in this paper.

Numerical simulation investigation on the seismic performance of high-strength concrete columns reinforced with PVA fibers and HTRB630 steel bars

Numerical simulation investigation on the seismic performance of high-strength concrete columns reinforced with PVA fibers and HTRB630 steel bars

Mechanical performances of thin-walled high-strength concrete-filled steel tube square columns with high-strength reinforced cages under biaxial eccentric compression

In the current research that both steel tube and concrete use high-strength materials, there are few studies on the small wall thickness of steel tube exceeding the standard. In order to make full use of the mechanical properties of high-strength steel and enhance its restraint ability on concrete, this paper designs a steel cage dominated by transverse steel bars. A total of 15 square high-strength steel tube high-strength concrete medium-long column test pieces are tested and studied. The main parameters of the specimens are slenderness ratio, loading eccentricity and the form of internal steel reinforcement cage. After the loading test, according to the test results, the failure mode of the specimen is obtained and the mechanical properties of middle-long concrete-filled steel tubular columns are analyzed. The research results show that the ultra-thin high-strength steel pipe can restrain concrete well, but with the increase of eccentricity, its restraint capacity is slightly insufficient; the built-in steel cage can slow down the bulging of the specimen and help the steel pipe to further strengthen the restraint on concrete, but the steel cage as an indirect constraint cannot avoid the final bulging damage. Due to the existing formula overestimating the effect of ultra-thin steel tubes, this paper proposes a calculation formula for the axial compression of thin-walled high-strength concrete-filled steel tubes with steel cage short columns. Based on this method, the bearing capacity of medium-long columns under biaxial eccentric compression is calculated with good accuracy.

Investigation on Seismic Behavior of Prestressed Steel Strand Composite Reinforced High-Strength Concrete Column

To study the seismic performance of high-strength concrete columns reinforced with prestressed steel strands, five column specimens were designed and tested with varying parameters, such as axial compression ratio (0.2, 0.35, 0.5) and diameter of steel strands (9.5 mm, 11.1 mm, 12.7 mm), under low-cyclic reversed loading. The failure modes, hysteretic curves, stiffness degradation, ductility, and energy dissipation capacity of the prestressed steel strand-reinforced concrete columns were observed and recorded. The test results show that the failure mode of the prestressed steel strand-reinforced concrete columns is obvious bending failure. Within a certain range of axial compression ratio, the initial stiffness and load-bearing capacity of the specimens increase with the increase in axial compression ratio, but the plastic deformation capacity decreases. Within a certain range of steel strand diameter, the initial stiffness and load-bearing capacity of the specimens also increase with the increase in steel strand diameter, but the ductility coefficient first increases and then decreases. In addition, the seismic performance of prestressed steel strand-reinforced concrete columns was analyzed by the finite element method using DIANA software, and the results were compared with the test results. It was found that the hysteretic curve and stiffness degradation curve obtained from the finite element model are in good agreement with the test results, and the finite element model can accurately study the seismic performance of this type of column. Finally, based on the finite element model, the influence of different parameters on the mechanical properties of the column was discussed.

Seismic performance of precast frame with UHPC composite beams and HSC columns under cyclic loadings

This research investigates the seismic performance of precast frame with ultra-high performance concrete (UHPC) composite beams and high-strength concrete (HSC) columns. An experimental study was conducted on two frame specimens with 1/2-scale, three-story, and two-bay: a precast UHPC-HSC composite frame (UHPC-HSC frame) and a fully cast-in-place concrete frame (RC frame). The precast UHPC-HSC frame consists of composite beams with precast U-shaped UHPC permanent beam formworks and cast-in-place beam cores, precast HSC columns, and cast-in-place UHPC connections. The results indicate that both frames exhibit a mixed sidesway mechanism with beam hinges dominating. The UHPC-HSC frame demonstrates better structural integrity and experiences smaller structural damage, making it more suitable for rapid repair after earthquakes. The hysteresis curves of both frames are plump. The load-carrying capacity of the UHPC-HSC frame is 15.78% higher than that of the RC frame. The UHPC-HSC frame exhibits better ductility and deformation capacity compared to the RC frame. The whole and interstory ductility coefficients of both frames are greater than 3.49. The energy dissipation capacity of the UHPC-HSC frame is superior to that of the RC frame. At θ = 4.5%, the cumulative energy dissipation value of the UHPC-HSC frame is 18.66% higher than that of the RC frame. The research results can provide a reference for the engineering application of precast UHPC-HSC frame with UHPC composite beams and HSC columns.

Experimental study of a new type of high-strength monolithic square-section concrete columns with spiral stirrups

Experimental study of a new type of high-strength monolithic square-section concrete columns with spiral stirrups

Stiffness-based stress–strain model of FRP-confined high-strength and ultra-high strength concrete column with various corner radii

This study introduces a unified design-oriented stress–strain model tailored for fiber-reinforced polymer (FRP)-confined high-strength concrete (HSC) with diverse cross-sectional shapes. The proposed stress–strain model incorporates more suitable mathematical forms, incorporating post-peak axial stiffnesses as crucial parameters, thereby enabling the model to accurately capture the three types of post-peak stress–strain behavior observed in FRP-confined HSC: strain-hardening, strain softening, and strain softening recovering to strain hardening. This variation in post-peak axial stiffness arises due to insufficient FRP confinement at the initial peak strength point, as well as changes in the confinement stiffness ratio stemming from the altered dilation behavior of FRP-confined HSC during the post-peak stage. To address the nonuniform effects of FRP confinement, the concept of effective confinement rigidity was defined, unifying the behavior of FRP-confined circular and square HSC. Additionally, the model incorporates the ultimate condition and the characteristic point on the post-peak branch, representing the change in FRP confinement stiffness, to establish the stress–strain model for FRP-confined HSC. The model parameters were evaluated using available experimental results, and the stress–strain curves derived from the proposed model were compared with existing models in the literature, revealing the proposed model's accuracy and rationality.

Experimental Study on the Damping Performance of High-Strength Concrete Columns with Different Section Sizes

In this paper, structural columns with cross-section sizes of 100[Formula: see text]mm × 100[Formula: see text]mm, 75[Formula: see text]mm × 150[Formula: see text]mm, and 85[Formula: see text]mm × 121[Formula: see text]mm are designed based on the same notional size of member. The acceleration signals of each column at axial compression ratio of 0.1, 0.2 and 0.3 were obtained by impact hammering. The corresponding frequency and damping ratio are obtained by half power wideband method. Based on the statistical method, the variation rules of acceleration signal characteristics, frequency characteristics and damping characteristics in different thickness directions under different axial compression ratios were analyzed. The correlation between frequency and damping ratio in different thickness directions with different axial compression ratios is discussed. The results show that under the same axial compression ratio, the damping ratio and frequency tend to decrease with the increase of the thickness in the tapping direction. Under the same thickness, the frequency decreases with the increase of the axial compression ratio. The damping ratio of the column decreases with increasing stress ratio when the thickness in the knocking direction is less than 100[Formula: see text]mm. The damping ratio of the column increases with the increasing stress ratio when the thickness in the knocking direction is equal to 100[Formula: see text]mm. The damping ratio of the column increases slightly with the increasing stress ratio when the thickness in the knocking direction is greater than 100[Formula: see text]mm. By fitting the discrete data, the frequency variation range is 229.65–511.07[Formula: see text]Hz, and the range of the damping ratio variation is 0.1–0.5%.

Non-linear analysis of eccentric compression of steel and steel fiber reinforced high strength concrete column

To improve the ductility of high-strength concrete and enhance the ductility and load-bearing capacity of steel reinforced high-strength concrete (SRHSC) columns, steel fibers were added to SRHSC to prepare steel and steel fiber reinforced high-strength concrete (SSFRHSC) columns. In order to study the eccentric compression of SSFRHSC columns, based on the experimental study of the eccentric compression of SSFRHSC columns, finite element model specimens of SSFRHSC eccentric columns were established using ABAQUS software, and the accuracy of the model was verified by combining the test results. On the basis of the experiments, the parameters such as steel fiber volume rate, concrete strength and eccentricity distance were further changed to extend the study. The results show that: with the increase of the volume rate of steel fiber from 0.5 % to 3 % and the concrete strength from C40 to C90, the ultimate bearing capacity of the specimen increases by 40.81 % and 58.69 % respectively; at the same time, when the eccentric distance increases from 0 mm to 100 mm, the ultimate bearing capacity of the specimen decreases by 66.76 %, and when the eccentric distance When the eccentricity distance was increased from 0 mm-40 mm to 60 mm-100 mm, the structural damage form changed from brittle damage to ductile damage.

A new approach for the strength interaction diagram of FRP strengthened square steel reinforced high strength concrete columns

AbstractThis paper proposed a new approach for the strength interaction diagram (N‐M diagram) of FRP strengthened square steel reinforced high strength concrete (SSRHSC) column, considering the influence of the applied load eccentricity on the ultimate conditions of FRP strengthened high‐strength concrete (HSC). The analytical model for the strength interaction diagram of FRP strengthened SSRHSC (FRPS‐SSRHSC) columns, which incorporated the stress–strain models of constitutive materials into the rectangular stress block (RSB) method, was developed and verified against test data. The strength interaction diagrams of FRPS‐SSRHSC columns developed based on the proposed analytical model matched well with the test results, while the strength interaction diagrams developed using available design codes overestimated the experimental strength interaction diagrams. The effect of confinement ratio and longitudinal FRP strengthening on the strength interaction diagrams was examined via parametric analyses. It was found that longitudinal strengthening had a negligible influence on the axial load and bending moment when the axial load was applied at a small eccentricity but had a substantial influence when the axial load was applied at a large eccentricity.

Probabilistic curvature-and-drift limit states predictive models of high-strength bridge columns

This study presents the derivation of closed-form component limit state expressions for high-strength concrete columns reinforced with high-strength steel bars (HSC-HSSB) from an extensive database through the moment–curvature analysis approach. Initially, sensitivity analysis was conducted to investigate the regularity of the parameters (section size, axial-load ratio, longitudinal reinforcement ratio, stirrup reinforcement ratio, concrete compressive strength, and yield strength of longitudinal reinforcement) on the curvature limit state. The approach being convenient, massive samples were obtained in a short time, therefore, 6^7(279936) levels were generated to derive the predictive expressions of curvature and moment limit states by using the logarithm linearity model. Subsequently, based on the cross-section expressions, the drift displacement and shear force limit states predictive expressions were derived and verified by experimental studies, and these limit states were predicted with high precision. Moreover, after considering the uncertainty of material and section size, the curvature and drift displacement of the HSC-HSSB column exhibited a lognormal distribution, and the useful suggested standard deviations (βc) in different limit states were proposed for practical application of fragility curves to assess the vulnerability of bridge columns to earthquakes.

Calibrated Design of High Strength Composite Columns

AbstractWhat does the general design method, described in EN 1994‐1‐1, mean in practice for the construction industry? Even though this method requires additional efforts, it provides improved design accuracy. High strength and high slenderness concrete filled steel tube composite columns with a solid steel core inside have undoubtable benefits. However, application of such columns requires the use of a general method of design and special knowledge not fully covered by Eurocodes.In order to utilize the general design method for ATLANT® Strong composite columns, Peikko has conducted an extensive development program. During the program, multiple tests were conducted on materials and the columns itself. The test results were used to calibrate models of Finite Element Analysis (ABAQUS), which allowed to investigate the behaviour of those columns even more extensively. Eventually, the general design method was implemented and calibrated, allowing reliable and optimized design.The paper contains an overview of ATLANT® Strong composite columns behaviour, the extensive testing program and calibration process to reach the optimal design of such columns. Additionally practical specifics, challenges and benefits are discussed.

Experimental and Analytical Study on the Axial Behavior of Circular High-Strength Concrete Columns with Hybrid Carbon Fibers and Steel Confinement System

This paper describes a work that examines a new solution to the problem that arises from the relatively high amount of transverse reinforcement required in HSC columns. It presents an alternative to common transverse steel reinforcement, a dual system comprising steel ties and a carbon-fiber mesh (CFM) applied internally together with steel ties. The behavior of the proposed system was examined in this work in a series of twelve laboratory tests of circular stub column specimens. The experiments performed in this work focused on the columns’ load and displacement capacities. The tests were planned with the aid of an analytical model that was originally developed for a hybrid system of external fiber-reinforced polymer (FRP) sheets and internal steel, and was adapted for the current system. An analysis of the results shows that for a given amount of conventional transverse steel, the application of the carbon-fiber meshes adds efficiency to the rebar confinement system, in terms of both the load bearing capacity and the ductility, and for specimens with the hybrid confinement system, the higher the carbon fiber amount the larger the ductility improvement. Furthermore, fair to good agreement was observed between the model and the measured stress–strain curves, especially those of the peak stresses. Based on the above findings and the added benefit of fire resistance, the hybrid method appears to be promising for confining HSC columns.

Seismic Behavior of High-Strength Recycled Aggregate Concrete Columns with High-Strength Reinforcement

ABSTRACT This study investigated the seismic performance of high-strength recycled aggregate concrete (RAC) columns with high-strength reinforcement under cyclic loading. Five full-scale columns were carried out, and the results revealed that the lateral loading capacity of RAC column was slightly lower than that of natural aggregate concrete column. Increasing the axial load, the lateral loading capacity of RAC columns increased significantly. Increasing the concrete strength under the same axial load, the lateral loading capacity was slightly increased. Based on the test results, a numerical simulation model was established. Finally, a flexural capacity calculation model and an N–M curve calculation model are proposed.

Compressive behavior of FRP-confined cruciform steel-reinforced normal- and high-strength concrete columns

Fiber-reinforced polymer (FRP)-confined steel-reinforced concrete column (FCSRC), which consists of an external FRP tube and a steel-reinforced concrete (SRC) core, have been proposed to avoid the brittleness of SRCs. Capitalizing on the benefits of FRP-confine concrete, it is expected that full strength capacities of high-strength materials (i.e., high-strength concrete and high-strength steel) in FCSRCs can be exploited. Axial compression tests on FCSRCs with different strengths of concrete and steel were conducted in this study. A cruciform steel was adopted in FCSRCs. The parameters investigated in this study included the concrete strength, the steel strength and the FRP tube thickness. The test results demonstrated that the excellent performance of FCSRCs. Compared with normal-strength cross-shaped steel, the high-strength cruciform steel delays the development of hoop strains in the FRP tube for FCSRCs with normal-strength concrete. Additionally, the ultimate axial load of FCSRCs is generally larger than the direct summation of those of the steel section and FRP-confined concrete section (i.e., CFFT), demonstrating that the interaction between the three components (concrete, steel profile and FRP tube) in FCSRCs are in a benificial manner.

Cyclic Compressive Behavior and Load-Strain Model of FRP-ECC-HSC Composite Columns

An innovative composite column, which consists of a high strength concrete (HSC) core, engineered cementitious composites (ECC) ring, and fiber-reinforced polymer (FRP) tube, has recently been developed and subjected to monotonic axial compression testing by the authors. In this study, the cyclic compressive behavior of this proposed FRP-ECC-HSC composite column was examined. Test parameters, including HSC core strength, FRP tube thickness, and ECC ring thickness, were investigated. Typical failure modes, dilation behavior, and axial load versus axial strain behavior were discussed and analyzed. It was found that the FRP-ECC-HSC composite columns exhibited improved deformability, compared with the counterpart traditional FRP-confined HSC columns, with the ultimate axial compressive strain increased by 0.7%–69.1% for the tested specimens. Meanwhile, the ultimate axial strain for cyclically loaded specimens is larger than that for monotonically loaded specimens in general, indicating a delayed column failure. Cyclic axial load-axial strain models, including the envelope model, unloading and reloading models, plastic strain equation, and stress deterioration equation, were proposed to predict the cyclic compressive behavior of the tested specimens. The proposed model was verified with the test results and exhibited good performance.

Axial compressive behavior of self-compacting micro-expansive high-strength concrete confined by glass fiber reinforced plastic tube

To solve the instability of the compression bars in the space truss composed of GFRP tubes, a composite column with high-strength concrete (HSC) confined by glass fiber-reinforced plastic (GFRP) tube was proposed. High-strength self-compacting micro-expansive concrete with a slump greater than 255 mm was produced under normal-temperature curing conditions and confined by GFRP tubes. A mechanical performance test of the GFRP-confined HSC short column under axial compression was performed. The effects of GFRP tube types, concrete expansion agent, constraint effect, ultimate load capacity, and failure mode of the composite structure were discussed and analyzed through the test. A model of the stress-strain response of the GFRP confined HSC column was proposed. The results show that the 45° fiber-wound GFRP tube has a significant restraining effect on the HSC. The stress-strain relationship increases quadratically in a linear fashion. When the composite column was damaged, the GFRP fiber was broken and the concrete was crushed. The ultimate strength was about 1.5 times that of unconstrained HSC columns, and the loading method has less influence on the results. The expansion agent has a significant effect on the deformation performance of the composite column, and its ultimate strain was about 1.4 times that of the composite column without expansion agent.

Behavior and design of eccentrically-loaded slender tubed steel-reinforced high-strength concrete columns

This study experimentally and numerically investigated the behavior of eccentrically-loaded slender circular tubed steel-reinforced concrete (CTSRC) columns filled with high-strength concrete (HSC). Six specimens with the HSC of 81.4 MPa were tested considering the length-to-diameter ratio and load eccentricity; and their effects on the failure phenomenon, bearing capacity, and ductility were evaluated. A three-dimensional finite element model was established and validated for further investigating the column behavior. The study results indicate that all specimens fail in a flexural failure mode and show good ductility; and the shear studs and circular steel tube are found to ensure the composite behavior of CTSRC columns. Besides, increasing the tube thickness contributes more to the improvement of column ductility than the load capacity and the steel shape yields before the peak load, indicating the full utilization of steel strength. Based on the parametric study, a design method considering the second-order effect and the influence of unequal load eccentricities at both column ends is proposed to assist designers to determine the load capacity of slender CTSRC columns.

Finite element modeling of square high-strength concrete short columns longitudinally reinforced with steel equal-angles under axial loading

Conventional steel bars in Reinforced Concrete (RC) square columns are utilized as longitudinal reinforcement and steel ties are utilized as transverse reinforcement for concrete confinement. The concrete confinement in RC columns with square section is less than that with circular section. Recently, Steel-Equal Angle (SEA) as longitudinal reinforcement has been investigated for square RC columns. The RC columns with SEA as longitudinal reinforcement exhibit higher strength and ductility than the RC columns with conventional steel bars as longitudinal reinforcement. However, experimental and computational investigations have been very limited on RC columns with SEA as longitudinal reinforcement. Existing studies investigated only the effects of lateral tie spacing on the performance of RC columns reinforced with SEA sections. However, the effects of the other important column parameters, such as the width and thickness of SEA sections, yield stress of SEA sections, and the concrete compressive strength, on the axial performance of RC columns reinforced with SEA sections have not been fully investigated yet. This study develops finite element (FE) models for quantifying the behavior of axially loaded square RC short concrete columns reinforced with SEA. The inelastic buckling of SEA cross-sections and the effects of concrete confinement are considered in the simulation. The accuracy of the FE analysis is verified using available test results. The influences of material and geometric properties on the compressive behavior of square RC short concrete columns incorporating SEA are studied. The results show that the model accurately estimates the behavior of square SEA reinforced concrete short columns. Moreover, the width of the SEA sections, the concrete compressive strength, and the lateral tie spacing have the most significant effects on the performance of SEA reinforced concrete columns subjected to axial loads.

Nonlinear inelastic analysis of eccentrically loaded square high-strength concrete short columns incorporating steel equal-angles

Steel-Equal Angle (SEA) has recently been utilized as longitudinal reinforcement in high-strength concrete columns to improve their strength and ductility. However, investigations have been very limited on the responses of eccentrically loaded SEA Reinforced Concrete (SEARC) columns. This paper presents the development of a computer simulation model based on fiber element discretization for determining the structural behavior of eccentrically loaded SEARC short columns. The inelastic buckling of SEA sections and the concrete confinement induced by SEA sections are explicitly taken into account. The modeling procedures are given for axial load moment-interaction curves and moment-curvature curves of SEARC columns. The accuracy of the developed fiber model is verified against the available test data. The performance of eccentrically loaded SEARC columns incorporating various design parameters is extensively investigated. It is shown that the developed computer simulation model captures well the experimentally measured responses of short SEARC columns and can be utilized in the analysis and design of such columns in practice. It has been found that the behavior of SERAC columns under eccentric loads is significantly influenced by the longitudinal steel ratio, the compressive strength of concrete, and the axial load level. The width of SEA sections and tie spacing considerably influence the ductility of the columns.