Strength Steel Tubes Research Articles

Effects of galvanization on the mechanical properties of high and ultra‐high strength steel tubes

AbstractA widely used corrosion protection technique for steel structures is hot‐dip galvanizing. This method increases the life of steel structures and reduces maintenance costs. In this technique, steel elements are cleansed through caustic cleaning, rinsing, pickling, and dipping in flux solutions. After cleaning, components are dipped in molten zinc until a protective layer is formed. The galvanizing procedure and its effects on structural mild steel materials have been studied. However, the effects of galvanizing on mechanical properties of high and ultra‐high‐strength steels (HSS and UHSS) have received limited attention. This mechanical investigation is vital since UHSS, and HSS steels are sensitive to heating and cooling cycles, and their mechanical behavior may change when exposed to high‐temperature during hot‐dip galvanizing. To this end, an experimental program was designed and carried out to find out the mechanical behavior of standard coupons taken from UHSS and HSS tubes after galvanizing. HSS and UHSS tubes were cleansed and dipped in a molten zinc bath (460 °C) for 3.0 and 10.0 minutes. For comparison, a mild steel tube with the same dimensions was also galvanized by dipping in zinc for 10.0 minutes. After galvanizing, dog‐bones and short tubes were cut out from the tubes for standard tensile and compressive tests, respectively. The tests revealed that the ultimate tensile strength of HSS and UHSS tubes decreased noticeably while the changes in their yield strengths were not significant. These changes were more significant for longer molten zinc bath dipping times. For HSS and mild steel specimens, the heat exposure had a similar effect as normalizing or annealing done after casting steel. For mild steel, normalizing or annealing increases yield, and ultimate strength and the same thing happened here. It was shown how the observed behaviors and changes were related to the grade of steel materials and their manufacturing process. Finally, optical microscopy was conducted to inspect the micro‐scale properties of the zinc layer. Microscopic results show that under the same zinc dipping time the zinc layer thickness on UHSS and HSS is almost double of that on mild steel which can increase the lifespan of the galvanized parts while decreasing the adhesion of the zinc layer to the steel base.

Fire resistance of thin-walled steel tube confined reinforced concrete middle-length columns: Test and numerical simulation

Steel tube confined reinforced concrete (STCRC) column is a new type of composite compressive member. In recent years, the structural performance of the STCRC columns has been widely studied to promote its application, and this paper presents experimental and numerical studies on the fire-resistance behaviour of the middle-length members. Parameters, including thickness of steel tube, loading mode (axial or eccentric), and load ratio, were considered in the tests. Moreover, the furnace temperature, column temperature, axial displacement, lateral displacement, and applied load were recorded during the tests, and the failure pattern was obtained after the tests. The finite element model (FEM) was developed by ABAQUS and validated against the test results. Through parametric analyses, the effects from eccentric ratio, load ratio, cross-section diameter, material strength, the thickness of steel tube, and reinforcement ratio on the fire resistance of the middle-length STCRC columns were further studied. It was found that increasing the section diameter, concrete strength, yield strength of reinforcement, and reinforcement ratio would enhance the fire resistance of the columns. However, increasing eccentricity, yield strength of steel tube, thickness of steel tube, and load ratio would reduce the fire resistance of the columns.

Experimental and analytical investigation on fire resistance of circular tubed steel reinforced concrete medium-long columns

This paper presents experimental and numerical studies on the fire-resistance behavior of the circular tubed steel reinforced concrete (CTSRC) medium-long column. Parameters, including steel thickness, loading mode (axial or eccentric), and load ratio, were considered in the tests. Moreover, the furnace temperature, column temperature, axial displacement, lateral displacement, and applied load were recorded during the tests, and the failure pattern was obtained after the tests. The test results showed that when the load ratio increased from 0.4 to 0.6, it would lead to an approximately 37%–54% decrease in failure time. Moreover, when the specimen was loaded with an eccentricity ratio (e/D) of 12.5%, the failure time would be 17%–39% less than that of the axially loaded specimen. The finite element model (FEM) was developed by ABAQUS and validated against the test results. Furthermore, through parametric analyses, more parameters, such as cross-sectional diameter, material strength, and length to diameter ratio, were studied. It was found that the fire resistance increased with the cross-sectional diameter, concrete strength, yield strength of the H-steel, and the steel ratio of the H-steel, whereas it decreased with the eccentricity ratio, yield strength of steel tube, steel ratio of the steel tube, and load ratio. Based on the experimental and numerical results, a simplified design method for predicting the fire resistance of CTSRC columns under ISO-834 standard fire was proposed. The design method was proved to have a good agreement with numerical analyses and test results within a specific application range.

Axial compressive behavior on steel tube-retrofitted circular RC short columns with grout under preload

Steel tubes are widely used in strengthening reinforced concrete (RC) columns. However, in engineering construction, the effect of preload on the original RC column on the performance of strengthened RC column has not mostly considered. Therefore this paper tests five circular short columns under axial compression—three steel tube-strengthened RC columns with preload, one strengthened RC column with no preload, and one normal RC-to study compressive performance of steel tube-retrofitted circular RC short columns under various preload levels. Moreover, the verified finite element numerical model is established using ABAQUS software to stimulate the behavior of the retrofitted columns. The extended parametric studies is conducted based on the thickness of steel tube, yield strength of steel tube, and strength of grout under preload, in addition to preload level itself. A practical design method is proposed and compared with four existing design codes to predict the axial compressive ultimate strength of the retrofitted column under preload.

Behaviour and design of prefabricated CFST stub columns with PCC connections under compression

This paper investigates the compressive behaviour of prefabricated concrete-filled steel tube (CFST) columns with prefabricated column–column (PCC) connections. The innovative PCC connections are designed using conventional structural bolts instead of expensive blind bolts to connect two prefabricated CFST columns, simplifying the construction process and rendering the construction cost-effective. The compressive behaviour of prefabricated CFST columns with or without PCC connections has been investigated numerically. Parametric studies have been conducted to investigate the effect of different parameters of PCC connections, including connection configurations, horizontal and vertical stiffeners of connections, diameter of the coupling bolt, steel tube thickness, yield strength of steel tube, and compression strength of concrete, on the compressive behaviour of CFST columns with PCC connections. The prefabricated CSFT columns with the developed PCC connections are able to achieve similar compressive strengths that are achieved by the CFST columns without connections. Therefore, the developed PCC connections can be used to construct prefabricated CFST columns for the prefabricated steel–concrete composite structures.

Buckling strength of steel tube for lifting telescopic wind steel tower

A telescopic pole for wind energy production with low environmental impact and its lifting system for a 60–250 kW turbine and a height of 30 m have been designed and manufactured. The tower, was raised and lowered by automation or by remote control, that allows one to differentiate the presence of the generator within the landscape over time. The jacking systems acting on the legs had a combination of holes (on the legs) and pegs actuated by hydraulic pistons. The aim of the paper was the experimental and the analytical verification of the stability condition of the steel piston as a lifting system of the prototype. An experimental investigation was carried out on small-scale specimens to examine the influence of lateral restraints constituted by external steel tubes and transverse devices to increase the buckling load and to ensure a stability condition during the elevation operation of the telescopic steel pole. Finally, the experimental results were numerically validated. The original contribution of the paper to research was the design of lifting system of telescopic wind tower though a steel piston with transverse stiffeners.

Size effect prediction on axial compression strength of circular CFST columns

Based on size effect law of plain concrete, a size-dependent analytical model for axially loaded CFST column was developed by considering the influence of confinement on size effect. The proposed model can make a similar forecasting precision for CFST specimens in different size ranges, and it was efficient to predict the size effect of axial compression strength, therefore it was used here to conduct the parametric analysis on size effect of CFST column. The analysis results indicated that the size effect of axial compression strength was connected with the confinement level apart from the specimen size. As the steel ratio of the specimen or yield strength of steel tube increased, size effect of axial compression strength tended to become less obvious. Conversely, the size effect was more obvious as the concrete strength increased. Based on parametric analysis, a formula was developed to predict the size effect of axial compression strength for CFST specimens by considering the specimen size and the influence of confinement factor.

Axial compression performance of thin-walled T-shaped concrete filled steel tubular columns under constant high temperature: Experimental and numerical study

This study investigates the effects of temperature and stiffener on the axial compression performance of thin-walled T-shaped concrete filled steel tubular (CFST) stub columns. Eight CFST columns with and without stiffener were fabricated and exposed to different elevated temperatures, then tested for axial compressive performance. The complete load-displacement curve of the specimens under axial compression, the failure pattern after test and the failure characteristics of concrete core are also discussed. The finite element analysis is then developed to establish the calculation model of temperature field and axial pressure field of thin-walled T-shaped concrete filled steel tubular stub columns with stiffeners at constant high temperature. The FE model presents a highly agreement with experimental data in term of load-displacement behavior, which enable to further investigate stress distribution and failure mechanism of the columns. In addition, parametric study is conducted showing that temperature, thickness of steel tube, yield strength of steel tube and compressive strength of concrete are the key factors in contributing to axial compressive performance of the CFST stub columns. Finally, to provide reference for practical application of engineering, a simplified calculation formula for ultimate bearing capacity and axial compression stiffness of CFST stub columns were obtained via the regression analysis based on results from the experimental and numerical analysis. The result shows that the relative errors between results calculated from simplified formulae and from FE models are within 10%, which indicates that the proposed formulae are able to provide the theoretical reference for the practical engineering applications.

Post-earthquake fire performance of square concrete-filled steel tube columns

Abstract It has been shown that fire disaster normally occurs following an earthquake disaster, which might cause even more serious losses than the earthquake itself. This study investigates the post-earthquake fire performance of concrete-filled steel tube (CFST) columns. The experimental programme contains two parts - quasi-static tests and fire tests. During the quasi-static tests, the square CFST columns were loaded under constant compressive force and cyclic horizontal force, until reaching different degrees of seismic damage. Afterwards, the pre-damaged columns were loaded under a constant axial compression ratio (i.e. ratio of the applied compressive load to its bearing capacity) of 0.3 at elevated temperatures. The fire resistance time and failure modes of these pre-damaged CFST columns were reported. Finite element (FE) models were developed and validated against the test results; a total of 48 numerical results were generated in the parametric study using the validated model. In the parametric study, the influence of key parameters including the thickness of steel tube, the yield strength of steel tube, the axial compression ratio and pre-damage degrees on the fire resistance of square CFST columns were analysed. The experimental and numerical results are used to propose design rules for the fire performance of square CFST columns with different degrees of seismic damage.

Galvanic corrosion induced localized defects and resulting strength reduction of circular steel tubes under axial compression: An experimental study

Corrosion-induced durability has become a critical issue for aging spatial structures using steel tubes as primary load-carrying structural components. Tremendous efforts have been made in predicting the ultimate strength of steel tubes under axial compression but understanding corrosion-induced buckling remains a challenge due to uncertainty of localized defects. To experimentally investigate the effect of localized corrosion on steel tubes, a modified galvanic method was developed to generate predefined corroded defects at targeted locations. A total of 24 tubes with different slenderness ratios were produced with various localized corroded defects, and then axially compressed to obtain ultimate strengths. Our experiments showed that the galvanic method could efficiently generate localized defects that could change the direction of buckling and significantly lower the ultimate strength of tubes. Further, the corrosion depth has the largest effect on the residual capacity of the tubes among three geometric characteristics of corroded patches. The influence of circumferential corrosion size is greater than that of longitudinal corrosion size due to the deviation of section centroid. From a practical perspective, our experiments indicate that the ultimate strengths of steel tubes can be lower than those estimated by both US and Chinese codes when the localized corrosion ratio exceeds 15%. Thus, the localized corrosion should be checked regularly during the maintenance routine such that buckling-induced failure can be avoided in advance.

Practical artificial neural network tool for predicting the axial compression capacity of circular concrete-filled steel tube columns with ultra-high-strength concrete

This paper aims to develop a practical artificial neural network tool for predicting the axial compression capacity of circular concrete-filled steel tube columns with ultra-high-strength concrete. For this purpose, a nonlinear finite element analysis of circular concrete-filled steel tube columns with ultra-high-strength concrete was conducted and verified with experiments in the literature. Accordingly, a database of 768 finite element models was generated to use for developing the artificial neural network models. In this regard, the column length, the diameter of steel tube, the thickness of steel tube, yield and ultimate strength of steel tube, and compressive strength of concrete were considered as the input variables while the axial compression capacity was considered as an output variable. The performance of the proposed artificial neural network model was compared with the current structural design codes including AS/NZS 5100.6, Eurocode 4, AISC, and GB 50936. The comparative study indicated that the proposed artificial neural network model achieved a superior prediction compared to others. Ultimately, a graphical user interface tool was developed based on the proposed artificial neural network model to predict the axial compression capacity of circular concrete-filled steel tube columns with ultra-high-strength concrete for practical engineering design. • The proposed ANN model can accurately predict the axial compression capacity of CCFST columns with UHSC. • The proposed ANN model shows more accuracy than four notable existing design code formulas. • A GUI tool is developed based on the proposed ANN model for practical engineering design.

Performance analysis and bearing capacity calculation on circular concrete-filled double steel tubular stub columns under axial compression

Concrete-filled double steel tubular (CFDST) columns have been proposed in recent years. This paper presents the performance analysis and a new bearing capacity calculation method of circular CFDST stub columns under axial compression. In order to establish accurate finite element (FE) model, various constitutive models for both the concrete infill and steel tubes are analyzed and compared with experimental results in FE analysis, and the suitable constitutive models for sandwich concrete, core concrete and steel tube are proposed in the FE model developed. Based on the validated numerical model, the variation of confining stress between steel tube and concrete is analyzed in detail. In addition, parametric studies are conducted to investigate the effects of concrete strength, external tube thickness, inner tube thickness, diameter ratio of inner tube to external tube and yield strength of steel tube on the axial compressive performance of circular CFDST stub columns. A new simplified formula based on the confining pressure is proposed to evaluate the ultimate bearing capacity of the circular CFDST stub columns. Based on the comparisons with experimental results and numerical simulation results, it is shown that the proposed formulae for the circular CFDST stub columns appear to be satisfactory.

Nonlinear analysis of circular concrete-filled steel tube columns under eccentric loading

In this paper, the mechanical behaviours of circular concrete-filled steel tube (CFST) columns were numerically investigated with the Abaqus/standard solver software. Based on the analysis of contact stress between the core concrete and the steel tube, it was found that the contact stress was non-uniformly distributed for CFST columns under eccentric loading, which is quite different from CFST columns under axial loading. A new concrete constitutive model, which considered the influence of eccentricity and depicted all loading stages, was developed. Existing experimental results were employed to validate the proposed constitutive model. It is concluded that the current model proposed in this paper is accurate in simulating the eccentric behaviour of CFST columns. Parameter study was also conducted to examine the effect of steel tube ratio (αs), yield strength of steel tube (fty) and compression strength of core concrete (fccu) on the mechanical behaviours of the CFST column under eccentric loading.

Performance evaluation of recycled aggregate concrete-filled steel tubes under different loading conditions: Database analysis and modelling

This paper presents a set of data mining analyses on the structural performance of recycled aggregate concrete-filled steel tubes (RACFSTs) conducted using grey relational evaluation and Back-Propagation (BP) neural networks. A comprehensive experimental database containing the results of 20 flexural, 105 compressive and 85 lateral cyclic loading tests of RACFSTs manufactured using conventional recycled aggregates (RAs) (i.e., sieve grading varying from 5 mm to 31.5 mm) and demolished concrete lumps (i.e., sieve grading varying from 50 mm to 300 mm) were compiled through a critical literature review. The influential experimental variables identified through the review of the literature, namely the geometric ratios (i.e., steel tube diameter-to-wall thickness ratio and length-to-diameter ratio), steel tube strength grade, effective water-to-cement ratio, RA content and axial load ratio were selected as the input parameters to evaluate their influence on the structural performance (i.e., load carrying capacity, stiffness, peak strain, ductility and energy dissipation) of RACFST beams and columns. The results of the grey sensitivity analysis indicate that the effective water-to-cement ratio, steel tube strength grade, and steel tube diameter-to-wall thickness ratio and length-to-diameter ratio are in general the most influential set of parameters on the structural performance of RACFSTs, respectively; whereas, the overall performance of RACFSTs is less sensitivity to the RA content when compared with other parameters. It can also be seen from the results that the RA content influence on the seismic performance of RACFSTs is larger when conventional RAs are used in concrete mixes instead of demolished concrete lumps. To extend the parametric range of the experimental database, BP neural networks were employed to estimate the load carrying capacity of RACFSTs, and the results demonstrate that this machine learning algorithm can simulate the effect of RA content on the load carrying capacity of RACFSTs. Based on the extended database, two simple expressions were proposed to model the RA content influence on the axial and lateral load carrying capacities of RACFST columns.

Experimental and Analytical Behavior of Square CFDST Column Blind Bolted to Steel Beam Connections

In recent years, steel or composite beam-column connections adopting blind fasteners have drawn increasing praise due to the rapid development of assembled steel structures. However, limited researches have paid attention to the experimental and analytical behavior of concrete filled double-skin steel tube (CFDST) column blind bolted joints. For investigating the structural performance and seismic behavior of this type of connection, cyclic tests on blind bolted joints to square CFDST columns were carried out to explore the effects of column hollow ratio and end plate type. Finite element analytical modelling of the semi-rigid joint was performed considering complex contact interactions and material models. Good agreement between the test and analytical results was observed in terms of the failure modes and the hysteretic behavior. Substantial parametric analyses were conducted on typical CFDST column connections to observe the influence of parameters including strength of steel tube, column hollow ratio and bolt pretension force. Furthermore, certain constructional measures commonly employed in engineering practice were also discussed. It was concluded that the CFDST column blind bolted to the steel beam joint has favorable seismic behavior and is feasible for application in high-intensity earthquake regions.

Numerical Analysis and Axial Bearing Capacity of Composite Columns with Recycled Aggregate Concrete-Filled Steel Tube and Profile Steel

The axial compressive behavior of composite columns with recycled aggregate concrete (RAC)-filled steel tube and profile steel was examined through numerical investigations. The constitutive models of the RAC material, profile steel, and steel tube were assigned to respective elements in the columns. The experimental results were used to verify the finite element (FE) model. Results indicated that the FE model accurately predicts the deformation, stress, and load–strain curves of the columns. Then, the effects of RAC strength, steel tube strength, profile steel strength, profile steel ratio, and diameter-to-thickness ratio on the axial compressive behavior of the columns were evaluated through a parametric study. The increase in RAC strength, steel tube strength, and profile steel strength significantly affected the axial bearing capacities of the columns. However, deformation ability and ductility decreased gradually as the RAC strength and steel strength increased. The increase in the diameter-to-thickness ratio had a negative effect on the axial bearing capacities of the long columns. Based on the experimental research, FE analysis, and ultimate analysis method, a formula for the axial bearing capacity of the composite columns was proposed. The validity of the proposed formula was verified through the comparison of the results. The research conclusions can provide a reference for the design of composite columns.

Ultimate torsional capacity of steel tube confined reinforced concrete columns

Based on two quasi-static experiments of steel tube confined reinforced concrete columns (STRC) under pure torsion load, detailed finite element (FE) simulation and theoretical derivation of the corresponding calculation methods were conducted in this paper. FE models of STRC specimens under pure torsion were established using the finite element software ABAQUS, the feasibility of which was then validated against the testing results in terms of both ultimate torsional capacity and failure modes. Comprehensive parametric analysis was presented, including the yield strength of steel tube, the thickness of steel tube, the dimension of cross-section, the strength of concrete, the yield strength of longitudinal reinforcement, the ratio of longitudinal reinforcement, the yield strength and the ratio of stirrup, to investigate the influence on the torsional capacity of STRC columns with important structural factors. It can be found from the parametric analysis results that, the thickness of steel tube, the dimension of cross-section and the ratio of longitudinal reinforcement are the most important parameters for the torsional capacity of STRC. Based on the results parametric analysis, an accurate and simplified calculation method for the ultimate torsional capacity of STRC columns under pure torsion was proposed.

Prediction model on compressive strength of recycled aggregate concrete filled steel tube columns

The design of composite members consisting of a tubular column and in-filled conventional concrete has been available and well-defined in the provisions. However, for steel tube members filled with recycled aggregate concrete, there aren't any other special requirements in the current provisions. In this study, the experimental test results are used to model and evaluate the ultimate strength of axially loaded recycled aggregate concrete filled steel tube columns. The test specimens has a length to diameter ratio ranging from 2.0 to 3.5, indicating that they are the stub column and not failing in overall buckling. The proposed model was derived based the technique of gene expression programming. The database utilized contains a total of 97 test results. The predictor variable employed to generate the model are outer diameter, thickness and yield strength of steel tube, length of the column, recycled coarse aggregate replacement ratio, and concrete compressive strength. The experimental data and associated analytical model are examined by four widely used design codes of ACI, Eurocode 4, AIJ, and DL/T. A sensitivity statistical analysis is further conducted to assess the contributions of each parameter affecting the axial capacity. The outcome indicates that the developed model gives reasonable predictions of the axial capacity of recycled aggregate concrete filled circular steel tube stub columns compared to the existing expressions.

Axial compression capacity of circular CFST columns transversely strengthened by FRP

Fiber reinforced polymer (FRP) jackets have been recently used for strengthening purpose of concrete filled steel tube (CFST) composite columns and also for the suppression of outward local buckling that CFST columns may suffer. This study intends to investigate the axial compression capacity of circular CFST columns transversely strengthened by FRP. For this, an attempt has been made to implement gene expression programming (GEP) technique for the development of axial capacity of confined CFST prediction model. The database required for the derivation of the GEP model is based on the extensive experimental results of the FRP confined CFST columns tested in compression (92 test specimens). Moreover, these test specimens wrapped with the carbon or glass fiber sheets have different length to diameter ratios of 2.0–4.5. The input predictor variables used in the study are the properties of the FRP (the type, thickness and sheet wrap layers, tensile strength and elastic modulus of FRP), the steel tube (outer diameter, thickness, length and tensile strength of steel tube) and unconfined concrete (compressive strength of in-filled concrete). To verify the effectiveness of the model, the values from GEP were examined statistically against those of existing equations given by various researchers. After analyzing and comparing the proposed model with the existing formulas, it was found that the results obtained by GEP have significantly less errors and far more accurate.

Influence of unsteady pressure-flow conditions on strength of steel pipelines with volumetric defects reinforced by composite sleeves

Structural integrity and risk management have a wide interest because of its practical applications, such as oil and gas pipelines, piping systems under pressure in power stations, urban water, and heating networks. The main goal of this paper is twofold. Firstly, to estimate the unsteady pressureflow variations in a gas transmission grid within the framework of sequential data assimilation. This technique enables to determine accurately the maximum pressure at the localized defect on the pipeline by merging measurements that contain random errors into the inexact numerical flow model. For this purpose, a particle filter is used. The semi-discretization approach is applied to convert the nonisothermal flow model into an initial value problem of ordinary differential equations. The spatial discretization is based on a five-point, fourth-order finite difference approximation and the time marching was done using a diagonally implicit Runge-Kutta scheme. Secondly, to study the strength of steel tubes reinforced with composite sleeves containing localized part-wall thickness losses caused by corrosion while taking into consideration a safe operating pressure. For a steel thin-walled cylinder containing a wrap of fiberglass with epoxy resin, the burst pressure and sleeve thickness are determined. Finally, the repaired pipeline with a fiber-reinforced composite sleeve is investigated. The results enable operators to handle problems of corroded steel pipelines and develop effective repair activities during operation. For this reason, current research is important for the maintenance of underground steel networks.