Concrete Filled Tubular Research Articles

A review on the performance of concrete filled tubular columns under axial compression: Emphasis on geometrical parameters and various concrete infills and encasings

SummaryThis paper summarizes the literature available on the behavior of concrete‐filled steel tubular (CFST) columns to evaluate the effect of geometrical properties such as shape of cross‐section, diameter‐to‐thickness ratio, and length‐to‐diameter ratio of CFST columns under axial loading. Then, the impact of different material composition for core concrete and encasing material is concluded for columns under axial loading. The performance of CFST is evaluated in terms of failure modes, ductility, stiffness, and axial compressive strength. For encasing tube, carbon steel, stainless steel, and aluminum are studied while for core, various concretes such as Normal (NSC) and high strength concrete (HSC), light weight concrete (LWC), recycled aggregate concrete (RAC), expansive concrete (EC), rubber crumb concrete(RuCC), and steel slag concrete (SSC) are covered for review in this paper. Material limitations as provided by various codes for design of composite structures is also mentioned for both tube and core concrete. Failure modes of concrete‐filled tubular(CFT) columns are most affected by geometric properties columns while materials used for concrete and encasing tube do not cause much difference. Though, ductility, axial compressive strength, and stiffness are affected by both geometric and material properties.

Axial loading mechanism analyses and evaluation methods of CCFT short columns with gap defects

The gap defect has proved to be a common quality issue in concrete-filled tubular (CFT) structures, which offers distinct unfavourable effects on their mechanics properties. To determine out the guidelines of gap defect affecting the axial loading performance of circular CFT (CCFT) short columns, this paper develops an array of refined numerical models of the axially-compressed CCFT short columns with spherical-cap gaps (CCFT-SG) and circumferential gaps (CCFT-CG), whose accuracy is verified by existing experiments. The typical axial force versus longitudinal displacement (N-Δ) curves, the contact stress, the longitudinal stress distribution and the failure modes are respectively given focus to reveal the intrinsic axial loading mechanism of the CCFT short columns, taking the existence of the gap defect into consideration. Based on these analyses, various design methods using confinement regionalization and circumferential expansion thoughts are proposed and adopted to evaluate the load bearing capacities of the axially-compressed CCFT-SG and CCFT-CG short columns. The results declare that the appearance of the gap defects dramatically weakens or delays the contact behaviour between the infilled concrete and the hollow tube, which accelerates the local bulging of the tube, reduces the longitudinal stress of the core concrete, and therefore the axial resistance of the CCFT short column is distinctly influenced. The design approaches delivered in this paper can assess the axial resistances of the CCFT short columns with gap defects accurately according to the test validation. The research may provide a theoretical basis and a reliable way for evaluating and treating the actual CFT structures with gap defects.

Behaviour of double-sleeve TubeBolt moment connections in CFT columns under cyclic loading

This research proposes a connection utilising a new blind bolt called TubeBolt to connect I-beams to concrete-filled tubular (CFT) columns. The aim of this study is to resolve the common problems of bolted connections in CFT columns such as column face deformation, bolt elongation, bolt sliding, and low flexural capacity. Tests were carried out on six half-scale specimens exposed to cyclic loading. The experiments were carried out on specimens with TubeBolts or EHB bolts. Different parameters such as hysteretic response, energy dissipation and ductility, failure modes, rotation and stiffness were extensively examined in this paper. Also, the effects of bolt types, bolt grades, and twin stiffener plates were studied on the structural response of the new connections. Test results demonstrated that the connections significantly reduce the above-mentioned problems, exhibit higher energy dissipation and ductility, and lead to a sizable hysteretic loop area. The connection with TubeBolt has higher capacity and stiffness and can avoid severe column face deformations compared to EHB bolts. It was found that using the TubeBolt with a higher bolt grade and twin stiffener plates can prevent brittle failure in the welded zone of the beam-extended endplate. Most importantly, connections with the TubeBolt meet the ductility and seismic design requirements for moment-resisting frames.

NLFEA of Sulfate-Damaged Circular CFT Steel Columns Confined with CFRP Composites and Subjected to Axial and Cyclic Lateral Loads

It is rather costly and difficult to experimentally evaluate the performance of concrete-filled tubular (CFT) circular steel columns exposed to combined axial and cyclic lateral loads. This research paper uses the nonlinear finite element (NLFEA) technique to assess the influence of using carbon-fiber-reinforced polymer (CFRP) laminates on the structural response and failure mode of damaged-by-sulfate CFT circular steel columns. At the beginning, twenty-one CFT circular steel column models were devised and checked for soundness using the findings of previously conducted research. Next, the models were broadened to investigate how the models’ behavior was influenced by the CFRP number of layers and the level of sulfate damage. For experimental purposes, the numbers of CFRP layers were set to be zero, five, six, seven, eight, nine, and ten, while there were three levels of sulfate damage, namely: level 0 (undamaged), level 1 (73 days), and level 2 (123 days). Some of the models were left unconfined with CFRP wraps for comparison. The CFRP confinement was at the end of the models due to its importance regarding the models’ capacity of lateral load. The columns’ ends were confined to prevent the models from outward local buckling, which led to higher strength, bigger net drift, and enhanced energy dissipation. The NLFEA models were then appropriately modified and adjusted in accordance with credible previously conducted experimental research; after which, a parametric study was performed to investigate how the models’ behavior was affected by the number of CFRP layers and the level of axial load. The study found that the CFT circular steel column models’ performance significantly enhanced when the models were wrapped with five to ten CFRP layers. It must be mentioned, though, that using eight, nine, and ten CFRP layers gave almost similar results. In addition, the NLFEA results revealed that when the damaged-by-sulfate models were repaired externally with CFRP wraps, there was an improvement in the models’ cyclic behavior, as they showed a raise in the load capacity, an enhancement in the horizontal displacement, a greater displacement ductility, better energy dissipation, and little deterioration in secant stiffness. The study found that using wraps of CFRP proved a great efficiency with the change in the sulfate damage level.

Tensile behaviour of innovative one-sided bolts in concrete-filled steel tubular connections

This paper investigated the tensile pull-out responses of an innovative one-sided bolt in the application of the concrete-filled tubular (CFT) connection. The one-sided bolt allows a simplified installation process through the ellipse bolt head compared to existing ones. Five anchorage configurations were proposed and examined experimentally to evaluate their contributions to the stiffness and tensile capacity of the one-sided bolt connections in the concrete-filled steel tubes. It was observed that with a properly designed anchorage system, concrete cone could be developed in the concrete infill, resulting in the improved stiffness and tensile capacity of the connection. The optimal anchorage configuration was determined based on three criteria, namely stiffness, tensile capacity and ease of fabrication. Finite element (FE) analyses on the tensile pull-out response of five anchorage configurations achieved a good agreement with the experimental results. Using the validated FE modelling technique, parametric studies were performed using the optimal anchorage configurations with bolt diameters of 12 mm and 16 mm to investigate the effects of concrete grade, embedment depth, bolt grade and tube slenderness. It was observed that the change in parameters significantly influences the overall connection behaviour and strength.

A study on self-curing self-compacting concrete filled steel columns subjected to axial compression

For vehicle parking areas, in multi-storey buildings and bridge piers, composite tubular columns have been considered as a better solution. The cold-formed steel and concrete combination is notable, because of the benefits of inherent material properties of both the materials. Concrete filled tubular (CFT) columns is in-filled with concrete having single tubes or concentric double tubes leaving the core as hollow. Moreover, for the design of such composite columns a specific design code is yet to be released in India. Henceforth, this experimental research intends to study the structural behaviour of CFT columns, consisting steel tube in terms of load- deflection graph, ultimate load carrying capacity, confinement of concrete and ductility. The structural use of a unique Self-Curing and Self-Compacting Concrete (SCSCC) using 10% granite saw dust waste and 25% fly ash as partial replacement to cement was confirmed. The experimental results are compared with computer modelling analysis done using ABAQUS for a better understanding of the column specimen's behaviour. Based on experimental studies percentage of super plasticizer and Super Absorbent Polymer (SAP) is determined as 1.3% & 0.3% respectively. The variation between experimental and analytical results is minimum and is due to minor material defects in steel sections. In this present experimental study three different cross sections namely: (i) cylindrical (ii) rectangular and (iii) square cross sections with 500 mm length and 2 mm thickness was used. Secondly a parametric study was conducted for 3 different lengths and 3 thickness which also showed that the performance of square cross sections was effective irrespective of the lengths. The load carrying capability of columns with increased steel section thickness is seen to be greater for the same length of column. When compared to cylindrical sections, rectangular and square sections show a significant reduction in load carrying capability as the thickness of the steel section is reduced. These changes in load carrying capacity are mainly due to the shape factor. The main advantage of the CFST column is that it has a better ultimate strength than a regular column due to the concrete confinement. This increased strength due to confinement is higher in cylindrical specimens.

Modified confinement model for monotonic axial behavior of concrete-filled tubular columns

Concrete-filled tubular (CFT) columns exhibit higher axial resistance and better displacement ductility as compared to the conventional reinforced concrete members. The performance of CFT members may be influenced by many geometric and material parameters. This study presents an experimental study on twenty-two CFT column specimens subjected to monotonic axial compressive loading until their failure. The main parameters varied in the test specimens were the grade of concrete, slenderness i.e., length-to-depth (L/D) ratios, and tube compactness i.e., depth-to-thickness (D/t) ratios. The L/D ratios were varied in the range of 3–10 for two different values of D/t ratios (i.e., 13 and 26). The performance of CFT columns was evaluated in terms of the peak axial strength, ductility, and post-peak resistance. Test results showed that as the grade of concrete was increased, the peak axial resistance was improved. Further, the increase in the L/D ratios resulted in a steeper degradation in the post-peak stiffness of the CFT columns. An analytical investigation was also conducted to predict the axial strengths using the available confinement models and various design codes. The D/t ratios were varied in the range of 10–120, whereas the L/D ratio was varied between 3 and 48 in the analytical study. Based on both experimental and analytical investigations, a modified confinement model has been proposed to predict the peak axial strength as well as the post-peak axial resistance of CFT columns. The proposed model includes the effects of material grades, tube compactness ratio, and column slenderness ratio.

Effect of bolted shear connectors on the axial load-bending moment interaction capacity of CFT columns

In Concrete-Filled Tubular (CFT) columns under the influence of compressive loading, an omnilateral confinement pressure is exerted upon the concrete core which leads to increase in the strength, stiffness, and ductility of the column. This paper investigates the influence of bolted shear connectors on the behavior of circular and square CFT columns. Also, a comparison is made between the interactional axial load-bending moment (P–M) curves obtained from the numerical analyses and the P–M relationships put forth by different design standards. For this purpose, 18 circular and 9 square CFT columns, categorized into six groups, are subjected to eccentric compressive loading. The investigated parameters include concrete compressive strength, diameter of the steel tube, load eccentricity, and the presence of bolted shear connector. In most cases, the presence of bolted shear connectors in the column causes strength and ductility to increase, leading to an improvement in the axial load-bending moment (P–M) interaction. The employment of bolted shear connectors at 12.5 cm to 25 cm intervals results in a minimum of 5% and a maximum of 45% increase in the strength of the column.

Finite-element modelling of concrete-filled steel tube columns wrapped with CFRP

Experimental evaluation of the structural behaviour of concrete-filled tubular (CFT) circular steel columns under the combined effects of axial and cyclic lateral loads is costly and challenging. This study provides a non-linear finite-element analysis (FEA) of 21 models of CFT circular steel columns wrapped with several carbon-fibre-reinforced polymer (CFRP) composite layers at the end region, which represents the critical location in terms of lateral load capacity. The intent is to confine the column end to avoid outward local buckling of the column and thus develop high strength, larger net drift and more energy dissipation. The non-linear FEA models were properly calibrated and validated with reputable experimental results; a parametric study was then conducted to assess the influence of the number of CFRP layers and axial load level on CFT circular steel column performance. Also, it was found that the column axial load level significantly affects the CFT circular steel column behaviour under lateral loading, behaviour improved as the axial load level increased. It takes a parametric investigation, in terms of strengthening system, and the findings of this study provide a useful guideline and methodology for similar strengthening of CFT steel columns.

Influence of compressive load on concrete filled steel tubular column with variable thickness

The concrete-filled tubular (CFT) structure consists of high strength, favourable ductility, fire resistance and huge energy absorption. The cost and time of construction can be reduced as there is no shuttering required for CFT columns. The confinement outcome of CFT column possesses higher stiffness as compared to hollow steel tube columns. In this article, testing is administered on twelve specimens of natural and artificial sand M25 grade CFT columns with a ratio of diameter to variable tube thickness (D/t of 27.72, 22.18 and 18.48). The twelve CFT columns have been tested under axial compression. The behaviour of CFT columns has been studied in terms of axial load-carrying capacity, deflection and buckling effects and compared the behaviour with numerical results determined using Eurocode 4 and AISC 360-10. The performance of CFT columns increased, as the thickness of tube increased with the effective confinement. The experimental and the numerical results of CFT columns have been validated by using ANSYS 14.5. The axial load-carrying capacity of an artificial sand CFT specimen has been improved significantly. Therefore, the natural sand could be replaced with artificial sand for CFT columns.

Experimental Investigation on Behavior of Rectangular Concrete-Filled Tubular Columns Considering Diaphragms.

Concrete-filled tubular (CFT) columns have been widely used as structural members because CFT columns synergize the advantages of steel and concrete resulting in high strength, high ductility, and large energy dissipation capacity. Numerous studies have been performed to understand the behavior of CFT columns. However, the behavior of CFT columns remains uncertain due to their inelastic behavior and uncertain confinement effects, especially when failure occurs. In addition, diaphragms, which are generally installed, make it more complicated to understand the behavior of CFT columns. The purpose of this study is to investigate the effects of the diaphragms on the failure behavior of the CFT columns. To this end, eighteen rectangular CFT columns were tested with five different loading cases. The experimental results suggest that the size of the diaphragm has significant effects on the compressive strength and toughness of the CFT columns. In order to facilitate the proper composite actions of steel and concrete, the size of a diaphragm has to be at least three-quarters of the cross-sectional area.

Cumulative Component Damages on Collapse Capacity of Ductile Steel and CFT Moment Resisting Frames under Over-design Ground Motions

ABSTRACT Great earthquakes are likely to generate ground motions larger than those considered in design codes (over-design ground motions) and hence leading to a seismic demand that causes severe damages of structural components in general high-rise steel moment-resisting frames (SMRFs). Overall seismic behavior of high-rise SMRFs may be significantly affected by the local failure of members. This paper focuses on the margins of deterioration and collapse of 40-story SMRFs and the equivalent MRFs with concrete-filled tubular (CFT) columns considering the strength deterioration effect in constitutive models designed by current building standards. The input long-period ground motions are synthetic earthquake waves with flat velocity spectral shape. Deterioration and collapse criteria of models based on the peak ground motion velocity are estimated by performing the incremental dynamic analysis (IDA). The results indicate that the collapse mechanism was formed in the lower stories of high-rise SMRFs under the very rare earthquake. The strength and stiffness deterioration significantly amplified the damage extent and the influence degree depends on the sectional compactness of components. And the MRF with concrete-filled tubular (CFT) columns has a higher collapse margin against overall collapse compared with SMRFs.

Numerical Investigation of Blast Performance of Plate-Reinforced Moment-Resisting Connection Using Large Concrete Filled Tubular Section

This paper presents a numerical study to investigate the blast performance of a plate-reinforced moment-resisting connection using a large concrete filled tubular (CFT) column with dimensions of 1000 × 1000 mm and a thickness of 40 mm. A steel H-section with dimensions of 700 × 300 × 13 × 24 mm is used for beam. The plate-reinforced large CFT connection is analyzed numerically using a finite element code to evaluate its blast resistance. The methodology of modeling the connection is validated based on a past experimental study and verified using an alternate finite element code. Five improvised explosive devices (IED) are considered as blast loadings. The blast resistance of the proposed connection against the IED attacks is investigated based on the design criteria specified in the U.S. government document, UFC 3-340-02, and in comparison to that of a widely used through-diaphragm moment connection. Local failure modes in the vicinity of the connections are also examined. Recommendation is provided for design practice.

Numerical Study on the Effect of Concrete Grade on the CFT Circular Column’s Behavior under Axial Load

Concrete-filled tubular (CFT) column improves the structure properties under different load pattern, so that it should be designed under two main load patterns (static and cyclic load) using current design method such as Finite Element Method (FEM) and analytical method (guideline equation). In this research, a CFT column with specific dimensions is modeled by using ABAQUS finite element software; the target of this study is to conduct a pushover analysis and also a hysteresis analysis under cyclic loading. Then, the concrete grade and percentage of column reinforcement were altered using the FEM, and eventually, compared with the results of analytical equations to measure the safety level of analytical equations. For this purpose, the CFT columns with C20, 30, 40 & 50 concrete cores were modeled with and without reinforcement, and the effect of concrete grade on the capacity of column was studied. In addition, MATLAB software was used to obtain beta index and load capacity design for the CFT column. The results demonstrated that the columns designed in accordance with the AISC have a good performance under the cyclic and static loading. The safety level of design equations ranged between 3 and 5, and the columns could resist higher loads (about 2.5-3.5 times) through the design by ABAQUS.

Behaviour of concrete-filled corrugated steel tubes under axial compression

Concrete-filled tubular (CFT) structures are exposed to increasingly complex environments with ever-broadening applications. Anticorrosion maintenance is generally difficult and expensive for established structures exposed to the air. Due to the superior corrosion resistance and the high lateral stiffness of the corrugated steel pipe (CSP), concrete-filled corrugated steel tube (CFCST) is proposed which has the similar working mechanism with the tube confined concrete columns. Such innovative composite member has advantages such as free of maintenance, ease of construction, high load-bearing capacity, good ductility and strong interlocking effect between CSP and concrete. In order to verify the load bearing reliability of concrete-filled corrugated steel tube (CFCST), twenty-one short columns including twelve CFCSTs were tested under axial compression. It was found that the CFCST is a tube confined concrete member and behaves slightly better than tubed-concrete columns. The strain and stress of CSP are discussed in detail to clarify the confinement effect. As well, solid nonlinear finite element models (FEM) were established to investigate the influence of key factors including geometries of CSP and strength of materials, which were summarized in the confinement index. Based on early studies on steel tube confined concrete and the parameter analysis in this paper, a suitable design method to predict the ultimate axial compressive load capacity for CFCST columns is proposed in this paper.

Test and Numerical Study on Monotonic Behavior of Complex CFT Column Joints

This paper presents a test and numerical investigation into the monotonic behavior of three different complex steel trusses to concrete‐filled tubular (CFT) column joints. Based on an engineering structure, 1 : 4 reduced‐scale specimens are manufactured and the three‐dimensional subassembly testing system is designed to apply the monotonic load. Test phenomena and load‐stress curves show that all three types of joints have a considerable load‐carrying capacity and joint rigidity. Finite element (FE) analysis is adopted, and the stress distribution shows good agreement with test data. Both test and FE results show that local buckling and yielding in the root region of steel truss are the main failure modes of test joints and the core area of the CFT column remains intact which are in accordance with the design conception of “strong column and weak beam.” Design conception of proposed overlap joint form is then investigated based on the FE model, and results show that the optimized overlap joint can effectively reduce the stress concentration in the adjacent steel tube and beam member when compared to the traditional N‐type overlap joint. Finally, the influence of the outer diaphragm on the stiffness of joint is analyzed. By comparing the end‐displacement of the beam member, conclusion can be obtained that the beam flange thickness is suggested to be chosen as the outer diaphragm thickness. The forms of three different proposed joints and their design conceptions can provide good guidance for designers and engineers.

An Analytical Study of Square CFT Columns in Bracing Connection Subjected to Axial Loading

This paper presents the behavior of square concrete-filled tubular (CFT) columns with different penetrating gusset plates under axial load. Load transfer mechanism in the CFT columns including load distribution between gusset plate and core concrete and composite action of the gusset plate and steel tube was investigated. Experimental results showed that the axial load can be transferred from the bottom edge, ribs, and the hole of the gusset plate to core concrete through the bearing mechanism. Adding ribs or a hole on the gusset plate can efficiently facilitate load transmission and improve the composite action. Numerical models were established to determine the distribution of axial forces among members in the square CFT column. Then, revised coefficients of elastic modulus for the square CFT column with the gusset plate were proposed.

Analytical study on innovative VHS-steel section stub CFT columns

Very high strength steel (VHS) is implemented in structures to increase their load carrying capacity. This paper deals with finite element analysis of fabricated very high strength steel square and triangular stub concrete filled tubular (CFT) columns. Innovative design by attaching steel tubes at vertices was considered for this investigation. VHS steel of nominal yield of 1350 MPa was employed as material for tubes and facet plates. Post-peak behavior and failure pattern were compared with the experimental results and a parametric study was conducted to check the load–deflection behavior of samples with variation in B/T ratio. Likewise, effect of change of material properties was observed. Increasing thickness of steel tubes by 2% led to the spike in elastic yield in both square and triangular sections of about 3%. Solid deformable elements used for modeling steel encasing instead of shell elements produced more approximate realistic failure patterns. Change in material properties from mild steel to high-strength steel exhibits increase in elastic yield. Comparison with experimental results in literature reveals fair congruence.

Pull-out performance of a novel anchor blind bolt (TubeBolt) for beam to concrete-filled tubular (CFT) column bolted connections

The utilisation of beam to concrete-filled tubular (CFT) column bolted construction remains limited due to the severe slippage of bolts, column surface deformation and low moment-resisting capacity. This study proposes a novel blind bolt, known as the TubeBolt, for beam to CFT column connections. Ten pull-out test specimens were evaluated under tensile monotonic loading. Bolt type, bolt diameter, end anchor member, hollow tube wall thickness and bolt hole diameter were varied for the test. The failure modes, anchorage performance, load-carrying capacity, strength, slippage and elongation of the bolts were analysed. The behaviour of the TubeBolt specimens was compared with that of the Extended Hollo-bolt specimens under the same condition. Experimental results indicated that the novel TubeBolt in concrete-filled tubes exhibited excellent anchorage performance, higher strength and less slip and elongation until the failure state was reached.

Effect of ultra-high strength steel on mitigation of non-ductile yielding of concrete-filled double-skin columns

Concrete-filled tubular (CFT) sections, and the most recent configuration of these sections, concrete-filled double-skin tubular (CFDST) sections, can provide high strength in structural construction. In this study, an innovative fabrication strategy is proposed to prohibit the non-ductile yielding of CFDST sections by applying ultra-high strength steel corner steel tubes. Hence, the static compressive behaviour of CFDST columns containing ultra-high strength steel tubes is experimentally investigated. The results are then compared with those for the same experiment conducted on a CFDST specimen with corner mild steel tubes. In addition, a numerical investigation is conducted to examine the effect of different parameters on promoting the ductility and compressive strength. In order to pave the way for utilizing CFDSTs with corner tubes in engineering practice, a simple analytical formulation is also proposed to predict the load-displacement relationship of these sections based on the experimental and numerical results.