High-strength Concrete Columns Research Articles

Creep of reinforced high‐strength concrete‐containing industrial by‐products silica fume and slag

AbstractThis study aimed to examine the creep of reinforced high‐strength concrete (HSC) containing industrial byproducts, silica fume (SF), and slag (SL). In total, 36 HSC specimens were prepared and tested for creep. Three specimens were used for the plain HSC creep test, 6 specimens were used for the reinforced HSC creep test, and 27 specimens were used for companion shrinkage tests. The applicability of existing creep models in predicting the creep of HSC containing SF and SL were evaluated. In addition, the effect of compressive strength and reinforcement ratio on reinforced HSC was investigated. Moreover, a new procedure to calculate the creep of reinforced HSC columns, based on the modified creep model and an existing creep recovery model, was developed. Finally, a parametric analysis was conducted to investigate the effects of compressive strength, reinforcement ratio, stress–strength ratio, loading age, and volume–surface ratio on reinforced HSC.

Investigation on Hysteretic Behavior of Embedded PVC Pipe Confined Reinforced High Strength Concrete Columns.

To study the seismic performance of embedded polyvinyl chloride (PVC) pipe confined reinforced high-strength concrete (PVC-RHC) columns, five specimens are designed for cyclic loading test, which include three PVC-RHC column specimens, an embedded circle steel tube confined reinforced high-strength concrete (CST-RHC) column specimen, and a reinforced high-strength concrete (RHC) column specimen. The failure mechanism and morphology are revealed by experiments. The influences of PVC pipe diameter, axial compression ratio, and concrete strength on seismic performance indexes are analyzed. The research results indicate thhe following: all specimens displayed shear baroclinic failure. Compared with RHC specimens, the hysteretic curves of the PVC-RHC specimen and CST-RHC specimen were fuller; furthermore, their energy dissipation capacity, deformation, and ductility were more beneficial. With the increase of the diameter–length ratio and axial pressure, the energy dissipation capacity and deformation capacity of PVC-RHC specimens decreased. The shear bearing capacity of the PVC-RHC specimen calculated with “concrete structure design code” (GB 50010-2010) was smaller than the test results by 25%, showing an excessive safety margin. Thus, according to the failure mechanism of the PVC-RHC specimen, a new calculation formula of shear bearing capacity is deduced, which is in good agreement with the experimental results.

Force-displacement behavior of limited ductile high-strength RC columns under bidirectional earthquake actions

This paper endeavors to enhance the understanding of the non-linear force-displacement hysteretic behavior of reinforced concrete (RC) columns subjected to bidirectional earthquake actions with different loading paths and magnitudes of lateral displacement in the two axes. RC column testing in literature has traditionally been focused towards the unidirectional testing of both normal and high strength concrete columns or the bidirectional testing of normal strength concrete columns only. This study will address this important knowledge gap by experimentally investigating the biaxial lateral capacity of high-strength RC columns with limited ductile detailing. The results of this experimental study and other previous studies are also used to develop a simplified model for predicting the non-linear backbone force-displacement behavior of RC columns. The paper will firstly present the six full-scale column specimens, the test setup, and the loading procedure. The test results will then be presented and analyzed. Three different bidirectional loading protocols were adopted to study the effects of loading history. The important effects of axial load ratio on the collapse behavior (i.e. maximum drift) are also examined in detail. The paper will conclude with an overview of the proposed backbone model for predicting the force-drift behavior of RC columns subjected to bidirectional loading.

EXPERIMENTAL STUDY ON FIRE RESISTANCE OF 200-300 MPA HIGH STRENGTH CONCRETE WITH SYNTHETIC FIBER AND STEEL FIBER

High strength concrete columns are largely used for high-rise reinforced concrete buildings. Such concrete with low water to cement ratio has a dense structure and may experience explosive cover spalling when subjected to fire. The decrease of column cross-section could cause the steel reinforcements exposed to a high temperature at an early stage, and consequently, reduce the load-carrying capacity of the column. For 80 – 150MPa high strength concrete, we developed a method of suppressing the spalling behavior by adding a small number of synthetic fibers in 2000. Moreover, in 2009, we applied hybrid fibers of synthetic fibers and steel fibers to 120 – 200MPa high strength concrete. It is now common knowledge that adding both synthetic and steel fibers is indispensable for improving the fire resistance of the concrete with compressive strength more than 150MPa. However, there is a lack of study concerning the effects of fiber content and fiber geometry. This study carried out several heating tests on 200 – 300MPa high strength concrete using the ISO834 standard fire curve, in which various fiber types and fiber contents were considered. The effects of fiber type, fiber content, and geometry of both synthetic fiber and steel fiber on spalling depth were discussed. The following conclusions can be derived from this study.

A comprehensive FE model for slender HSC columns under biaxial eccentric loads

A finite element (FE) model for analyzing slender reinforced high-strength concrete (HSC) columns under biaxial eccentric loading is formulated in terms of the Euler-Bernoulli theory. The cross section of columns is divided into discrete concrete and reinforcing steel fibers so as to account for varied material properties over the section. The interaction between axial and bending fields is introduced in the FE formulation so as to take the large-displacement or P-delta effects into consideration. The proposed model aims to be simple, user-friendly, and capable of simulating the full-range inelastic behavior of reinforced HSC slender columns. The nonlinear model is calibrated against the experimental data for slender column specimens available in the technical literature. By using the proposed model, a numerical study is carried out on pin-ended slender HSC square columns under axial compression and biaxial bending, with investigation variables including the load eccentricity and eccentricity angle. The calibrated model is expected to provide a valuable tool for more efficiently designing HSC columns.

Seismic behaviour of concrete columns with high-strength stirrups

The seismic behaviour of reinforced concrete (RC) columns made from high-strength materials was investigated experimentally. Six high-strength concrete specimen columns (1:4 scale), which included three with high-strength stirrups (HSSs) and three with normal-strength stirrups (NSSs), were tested under a combination of high axial and reversed cyclic loads. The effects of stirrup strength and the ratio of transverse reinforcement on the cracking patterns, hysteretic response, strength, stiffness, ductility, energy dissipation and strain of transverse reinforcement were studied. The results indicate that good seismic behaviour of an RC column subjected to high axial compression can be obtained by using a well-shaped stirrup. Stirrup strength had little effect on the lateral bearing capacity. However, the ductility was significantly modified by improving the stirrup strength. When loaded with a large lateral displacement, the strength reduction of NSS specimens was more severe than that of those with HSSs, and increasing the stirrup strength had little effect on the stiffness reduction. The ductility and energy dissipation of specimens with HSSs were superior to those with NSSs. When the ultimate displacement was reached, the core concrete could be effectively restrained by HSSs.

Behaviour of short CFRP-steel composite tubed reinforced normal and high strength concrete columns under eccentric compression

The use of steel tubed reinforced concrete (STRC) column maximizes the confinement effectiveness of steel tube as the steel tube is disconnected at the beam-column joint. However, for high-strength and high performance concrete, the confinement from the steel tube would be limited. Also, certain measures need to be implemented to prevent the corrosion of steel tube. Carbon fibre reinforced polymer (CFRP) has the advantages of high strength-to-weight ratio and good corrosion resistance. However, the complicated construction procedures and relatively brittle post-peak behaviour limit its application to new concrete buildings. The combination of CFRP and STRC column is a good alternative to solve the concerning problems. This study experimentally investigated the behaviour of CFRP-steel composite tubed reinforced concrete (C-STRC) columns under eccentric compression. The observed failure modes, load-deformation curves, and load-stress curves of the steel tube and longitudinal reinforcing bars are presented. The test results show that the load capacity and deformability of the C-STRC columns with normal concrete strength are enhanced due to the use of CFRP and steel tube. The plastic stress distribution method was employed to analyse the axial load versus moment interaction curves and the results were found to be generally in good agreement with the test ones.

Numerical analysis study on seismic behavior of resilient high strength concrete columns reinforced by ultra-high-strength bars

To make concrete columns with drift-hardening behavior and small residual deformation, a simple method is proposed. The method is the use of ultra-high-strength (UHS) PC wire strands as longitudinal reinforcements of concrete columns. The effectiveness of the method has been verified by experiments. The purpose of this paper is to present an analytical method for simulating seismic behavior of resilient high-strength concrete columns reinforced by PC strands, based on reliable constitutive laws of the PC strands and the concrete. Five square concrete columns with the cross-section of 250mm × 250mm, the height of 1000 mm, the shear span ratio of 2.0, the axial load ratio of 0.25 and compressive cubic strength of 95 MPa were fabricated and tested. The experimental results were compared with the results predicted by the analytical method. Comparisons indicate that the proposed method can predict the development trend and feature points of the envelop curve of the columns until large deformation. Comparisons also indicate that the calculated flexural capacities by the proposed method show very good agreement with the test results. Utilizing the proposed method and the current design code, which are used to evaluate the ultimate flexure and shear capacities, respectively, can give a reasonable evaluation of the failure mode of concrete columns.

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

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

Assessment of high-strength concrete encased steel composite columns subject to axial compression

This paper investigates the axial load capacity of concrete encased steel composite stub columns with high strength concrete and steel materials. A total of 14 column specimens with varying material strengths and different steel section shapes were tested under concentric compression load. The test results revealed that the design methods in EN 1994-1-1 and JGJ 138-2016 overestimate the axial load capacity of high strength concrete encased steel columns. Adding a small percentage of steel fiber in the high strength concrete was found to improve the compression resistance of the composite section. A new test database consisting of 51 partially encased composite sections and 82 fully encased composite sections was established, covering a wide range of section geometric and material grades. Parametric study was then carried out to assess current design methods in predicting the axial capacity of such composite columns with respect to material strengths, steel contribution ratio, reinforcement ratio, section slenderness ratio, confined concrete area ratio, and concrete confinement efficiency. The effectiveness of concrete confinement in partially encased composite column was evaluated and a simplified method was proposed to compute the enhanced concrete strength based on regression analysis. For fully concrete encased composite columns, a concrete strength reduction factor was proposed to be used with EN 1994-1-1 to predict the compression resistance. Design recommendation was made considering the early cover spalling of high strength concrete and the material compatibility between steel and concrete in composite column design.

High-Strength Concrete Circular Columns with TRC-TSR Dual Internal Confinement

The standard requirements for transverse steel reinforcement (TSR) confinement in reinforced-concrete (RC) columns are mainly to provide the following: ductile behavior, minimum axial load capacity of the column’s core, and prevention of longitudinal bars buckling. It is well-known that the passive confinement due the TSR action is less effective in high-strength concrete (HSC) compared to normal-strength concrete (NSC). Therefore, the TSR amounts required by the standards for HSC columns are high, and in some cases, especially in the lower stories columns of high-rise buildings, are impractical. This paper presents a new construction method using textile-reinforced concrete (TRC) as internal confinement together with reduced TSR amounts. Moreover, comparison of the proposed method with RC columns casted in fiber-reinforced polymer (FRP) stay-in-place forms as additional external confinement, is presented. Eleven large-scale column specimens were tested under axial compression. The results give an insight on the application feasibility of the proposed construction method. It is shown that the TRC-TSR dual internal confinement action can be an option to reduce the standard required TSR amounts while maintaining similar levels of ductile behavior.

Behavior of high strength concrete encased steel composite stub columns with C130 concrete and S690 steel

This paper presents an experimental program that studies the structural behaviour of high strength Concrete Encased Steel (CES) composite columns. The structural performance under compression, including the damage pattern, load-carrying capacity, post-peak ductility, and load-displacement response is experimentally investigated. A total of 14 specimens were tested under concentric compression. The parameters studied in this program include concrete compressive strength, steel yield strength, stirrup spacing, incorporation of steel fiber, as well as the shape of the structural steel section. To evaluate the material compatibility between high strength concrete and high strength steel, two concrete grades (C90, C130) and two steel grades (S500, S690) were used to prepare the test specimens. In addition, 0.5% volume fraction of steel fiber was added in concrete mix to minimize the inherent brittleness of high strength concrete. The comparison between test results and analytical predictions reveals the inability of existing design codes to estimate high strength CES columns, unless steel fiber and dense reinforcement are used in combination. The effect of material strength, steel fibers, volumetric ratios of hoop reinforcement, and shape of steel section on both strength and ductility of CES columns was assessed through a comprehensive parametric study. The analysis of test results demonstrates that steel contribution ratio plays a dominant role in the ductility, whereas increasing hoop reinforcement ratio and adding steel fiber has negligible effect. Finally, a simplified formula is proposed to evaluate ductility of high strength CES columns.

Seismic behavior of normal-strength concrete-filled precast high-strength concrete centrifugal tube columns

This study reports the cyclic loading test results of normal-strength concrete-filled precast high-strength concrete centrifugal tube columns. Seven half-scale column specimens were tested under cyclic loads and axial compression loads to investigate their seismic behavior. The major parameters considered in the test included axial compression ratio, filled concrete strength, and volumetric stirrup ratio. The structural behavior of each specimen was investigated in terms of failure modes, hysteresis behavior, bearing capacity, dissipated energy, ductility, stiffness degradation, drift capacity, and strain profiles. Test results revealed that the concrete-filled precast high-strength concrete centrifugal tube column exhibited good integral behavior, and the failure modes of all columns were ductile flexural failures. Lower axial compression ratio and higher volumetric stirrup ratio resulted in more satisfactory ductile performance. In contrast, the filled concrete strength has a limited influence on the structural behavior of concrete-filled precast high-strength concrete centrifugal tube columns. Based on the limit analysis method, the calculation formula for the bending capacity of the concrete-filled precast high-strength concrete centrifugal tube column was developed, and the results predicted from the formulas were in good agreement with the experiment results.

Seismic resistance capacity of steel reinforced high-strength concrete columns with rectangular spiral stirrups

In this paper, several experimental investigations on seismic resistance capacity of steel reinforced high-strength concrete (SRHC) columns with rectangular spiral stirrups are presented. Tests were carried out on eleven SRHC columns with rectangular spiral stirrups and one comparative SRHC column with an ordinary stirrup arrangement under low reversed cyclic loading to investigate their failure patterns, characteristic loads and displacements, hysteresis loops, skeleton curves, inter-story drift ratios and ductility coefficients, energy dissipation capacities and stiffness degradation. Range analysis and variance analysis methods were used to analyze the data from the experiments. The results showed that the failure patterns of the test specimens changed from shear baroclinic failure to shear-bond and flexural failure, as the shear span ratio was increased. In addition, the shear span ratio is the main factor that had a significant effect on the carrying capacity of the test specimens. The carrying capacity of the SRHC specimens increased gradually, but their ductility decreased as the axial compression ratio was increased. The ductility coefficients of the SRHC specimens with the normal stirrup and the rectangular spiral stirrup were 3.01 and 3.27, respectively, indicating that the columns with the rectangular spiral stirrup had better deformation capacity. Furthermore, the inter-story drift ratios of all the columns with the rectangular spiral stirrup in elastic phase and elastic-plastic phase were in the range of 1/200 to 1/66 and 1/26 to 1/17, respectively, which are much larger than the limit value specified by the seismic design code. In addition, the SRHC columns with rectangular spiral stirrups exhibited plumper hysteresis curves and higher energy dissipation than the SRHC column with ordinary stirrup. Thus, the SRHC columns with rectangular spiral stirrups showed good seismic resistance capacity.

Evaluation and comparison of GFRP casing and CFRP sheets application on the behavior of circular reinforced concrete column made of high-strength concrete

This paper presents the results of axial compression testing on reinforced concrete columns (RCC) made with high-strength concrete (HSC) and confined by glass fiber-reinforced plastic (GFRP) casing and carbon fiber-reinforced polymer (CFRP). The major parameters evaluated in the experiments were the effects of GFRP casing, CFRP wrapping, and the number of CFRP layers. In this study, six cylindrical HSC-reinforced concrete columns (150 mm diameter and 600 mm height) were prepared and divided into two groups; with and without GFRP casing. In each group, one column was without CFRP, a column was wrapped with one CFRP layer, and another column with two CFRP layers. Concrete compressive strength was 63.1 MPa. All columns were tested under concentrated compression load. Results indicated that the utilization of CFRP wrapping and GFRP casing improved compression capacity and ductility of reinforced concrete columns. The addition of one and two CFRP layer wrapping increased compression capacity to an average of 10.2% and 24.8%, respectively; while the utilization of GFRP casing increased the compression capacity of the HSC columns by 3.38 times. These results indicate that although both CFRP wrapping and GFRP casing resulted in confinement, the GFRP casing has a higher effect on increased compression capacity.

Non-linear Analysis of Slender High Strength Concrete Column

This article shows the influence of axial force eccentricity on high strength concrete columns design. The behavior of columns made of normal, middle and high strength concrete with slenderness values between 20 and 60 under an eccentric axial force has been studied. Structural analysis has been developed by means of software which considers both geometrical and mechanical non-linearity. The sequence of points defined by increasing values of axial force and bending moment produced by eccentricity has been represented on the cross-section interaction diagram until failure for each tested column. Then, diagrams depicting the relationship between failure axial force and column's slenderness have been drawn. The loss of bearing capacity of the member for normal and middle strength columns when compared with the bearing capacity of their cross-section is more noticeable as axial force eccentricity assumes higher values. However, this situation reverses for high strength columns with high slenderness values. On the basis of results obtained, the accuracy level for the moment magnifier method was checked. Despite the good concordance in most of the cases, it was verified that the moment magnifier method leads to excessively tight results for high strength concrete columns with high slenderness values. In these specific cases, a coefficient which amends the column rigidity is proposed so as to obtain safer values.

Ductility and stiffness of slender confined reinforced high-strength concrete columns under monotonic axial load

This paper presents an investigation based on tests results of high-strength concrete (HSC) columns externally confined with post-tensioned steel straps, subjected to monotonic axial load. The parameters of the tests were eccentricity ratio (ei/es = 0, 1), load eccentricity (e = 25 mm, 50 mm), slenderness ratio (λ = 16, 24, 32) and confining volumetric ratio (ρv = 0.09, 0.25, 0.50). This paper is served as a continuation of a previous paper conducted by Ma et al. (2014b), which focuses on the ductility and stiffness analysis. The results show that the confinement of post-tensioned steel straps is beneficial to HSC columns but confining efficiency reduced drastically with the increase of column slenderness. Two ductility models were proposed to predict the ultimate ductility for slender confined HSC columns with the consideration of important parameters. The proposed models are simple and easy to apply but adequately accurate estimation is guaranteed. It is believed that the proposed ductility models can aid structural engineers in the designing a ductile structure especially in the seismic region. The confinement has no significant effect on the flexural stiffness of HSC columns.

Modeling cover spalling behavior in high strength reinforced concrete columns using a plasticity-fracture model

The cover spalling behavior in reinforced concrete (RC) columns can greatly affect the axial peak load carrying capacity. For RC columns with normal-strength concrete, the concrete cover still carries some load in the post-peak regime. However, for high-strength concrete, the concrete cover can spall prematurely, eliminating the cover capacity from the peak axial capacity of the column. The strength reduction due to premature cover spalling in high strength concrete columns may be recovered once confinement of the core increases and results in a second peak axial load. Hence, in nonlinear analysis a proper strategy is required to quantify any premature cover spalling for high- or very high-strength reinforced concrete columns. This paper discusses the strategies in modeling the concrete cover region spalling at the constitutive level. These strategies involve: (1) Adjusting the material properties for the concrete cover elements because of restrained shrinkage caused by the steel reinforcement; (2) Extending the plastic dilation rate into the tensile pressure region and adjusting the concrete dilatancy in presence of the tensile pressure; (3) Adding a tension cut-off failure surface to distinguish cracks caused by pure tensile stresses and concrete crushing (tensile splitting cracks) and (4) Assigning the cover spalling material properties only for cover elements outside the reinforcement cage or weak planes. To verify the proposed strategies, numerical validations against experimental published results are undertaken using a 3D-NLFEA finite element package. From the comparisons, it is shown that the proposed model is in good agreement with the experimental results and can accurately predict the location of the cover spalling in the load-deflection behavior.

Nominal axial and flexural strengths of high-strength concrete columns

The ACI building code is allowing for higher strength reinforcement and concrete compressive strengths. The nominal strength of high-strength concrete columns is over predicted by the current ACI 318 rectangular stress block and is increasingly unconservative as higher strength materials are used. Calibration of a rectangular stress block to address this condition leads to increased computational complexity. A triangular stress block, derived from the general shape of the stressstrain curve for high-strength concrete, provides a superior solution. The nominal flexural and axial strengths of 150 highstrength concrete columns tests are calculated using the proposed stress distribution and compared with the predicted strength using various design codes and proposals of other researchers. The proposed triangular stress model provides similar level of accuracy and conservativeness and is easily incorporated into current codes.

Compressive Behavior of Circular Tubed Steel-Reinforced High-Strength Concrete Short Columns

AbstractIn this paper, a total of 12 circular tubed steel-reinforced concrete (CTSRC) short columns with high-strength concrete are constructed and tested under axial compressive load. The main var...