Tubular Members Research Articles

Strengthening Behavior of Rectangular Stainless Steel Tube Beams Filled with Recycled Concrete Using Flat CFRP Sheets

Recently, the adoption of recycled concrete instead of normal concrete as infill material in tubular stainless steel members has received great attention from researchers regarding environmental improvement. However, the flexural behavior of recycled concrete-filled stainless steel tube (RCFSST) beams that have been repaired/strengthened using carbon fiber-reinforced polymer (CFRP) sheets via a partial-wrapping scheme has not yet been investigated, and is required for a variety of reasons, as with any conventional structural member. Therefore, this study experimentally tested six specimens for investigating the effects of using varied recycled aggregate content (0%, 50%, and 100%) in infill concrete material of stainless steel tube beams strengthened with CFRP sheets. Additionally, several finite element RCFSST models were built and analyzed to numerically investigate the effects of further parameters, such as the varied width-to-thickness ratios and yield strengths. Generally, the results showed that using 100% recycled aggregates in infill concrete material reduced the RCFSST beam’s bending capacity by about 15% when compared to the corresponding control specimen (0% recycled aggregate), with little difference in the failure mode behavior. Pre-damaged RCFSST beam capacity showed significant improvement (43.6%) when strengthened with three CFRP layers. The RCFST model with a lower w/t ratio showed better-strengthening performance than those with a higher ratio, where, the models with w/t ratios equal to 15 and 48 achieved a bending capacity improvement equal to about 18% and 35%, respectively, as an example. Furthermore, the results obtained from the current study are well compared by those predicted using the existing analytical methods.

Numerical investigation and design of P-M interaction capacity of CFRP-jacketed hexagonal CFST short beam-columns

Hexagonal Concrete-Filled Steel Tubular (H-CFST) members are now widely recognized by engineers. A serious concern with these columns is the local buckling of thin-walled steel tubes, which Carbon Fiber-Reinforced Polymer (CFRP) sheets offer considerable help in eliminating this troublesome condition. The objective of this study is to evaluate the structural performance of short H-CFST columns stiffened by CFRP strips through nonlinear analysis and numerical simulation. First, the finite element (FE) models were validated against the previous test results, and a close agreement was achieved. Next, an organized parametric study was carried out to investigate the influence of a collection of vital parameters on the strength of the columns. The ultimate eccentric loads of the columns were computed, and the results were plotted as load-moment (P-M) interaction diagrams. The confining contact stress methodology between the steel tube and the concrete infill was in depth discussed, and it was found that the stress concentration is greater in CFRP-jacketed H-CFST columns than in bare ones, and its value is greatest in the corners. Based on the parametric study within the considered geometric and material ranges, using CFRP sheets effectively improves the confinement effect of steel tubes to the core concrete and enhances the strength of the columns by up to 35%. However, by using fully-wrapped CFRP layers, the columns could handle a maximum of 55% more load-carrying capacity. Finally, a modified design formula based on a unified theory was suggested to estimate the ultimate load and bending moment capacity of H-CFST short columns under eccentric loading.

Design of cold-formed high strength steel square and rectangular hollow section beam–columns

Cold-formed high strength steel (CFHSS) square and rectangular hollow section (SHS and RHS) beam–columns were investigated in this study with an objective to evaluate the applicability of existing design rules given in American, Australian and European codes for SHS and RHS beam–columns of S700, S900 and S1100 steel grades, and subsequently, provide economical and reliable design rule for CFHSS SHS and RHS beam–columns. A comprehensive numerical investigation was performed in this study, where the values of flat width-to-thickness ratio of the tubular sections ranged from 7.5 to 96. The constitutive model developed for CFHSS tubular members was used in the numerical investigation. Global and local geometric imperfections were also included in the numerical models. In total, 465 data were compared with the nominal capacities predicted from American, Australian and European codes, including 390 numerical data obtained in this investigation. The safety levels of design rules given in these standards were examined by performing a reliability analysis. It has been demonstrated that the current design rules given in the American, Australian and European codes provide conservative predictions. A modified design method based on the recommendations given in European code was proposed in this study. Overall, it has been proved that the proposed design rule provides accurate and reliable predictions for the design of cold-formed S700, S900 and S1100 steel grades SHS and RHS beam–columns.

Physical Testing Campaign Facilitating Validation of Welded Steel Structures by Non-Linear Finite Element Analysis

Abstract Non-linear finite element (FE) analysis is a powerful tool for determination of ultimate capacities of steel components. To produce reliable predictions of structural strength, it is of fundamental importance that non-linear finite element analyses are based on a validated methodology. This paper focuses on physical test campaigns, which are designed with the purpose of providing an experimental foundation for calibrated and validated non-linear finite element assessments of plated components, which form part of typical offshore structures. The experimental work discussed in the current paper is a continuation of the experiments of tubular members and joints, which were carried out by Maersk Oil in the late nineties. The objective is that the two-test campaigns together shall allow for development of a non-linear finite element methodology with calibrated failure criteria providing either characteristic or mean level of capacity/response for the main details in typical offshore structures. This paper particularly focuses on the testing campaign completed in 2017 which forms the basis for the calibration of the failure criteria covering plated sections.

Dynamic responses and residual capacity of high-strength CFST members subjected to axial impact

Impact is one of the main accidental actions that should be considered; high-strength concrete-filled steel tubular (HSCFST) members are mainly served as the main piers of high-rise buildings, large-span bridges, and defense structures. Hence, this study systematically investigated dynamic responses and residual capacity of HSCFST members subjected to axial impact. A total of six square HSCFST columns were tested, including testing groups with high-strength steel Q690 and a control group using normal-strength steel Q355. Results showed that as the impact energy increased, the local buckling of the steel tube became more severe, and the impact force, time duration, maximum axial displacement, and residual deformation were also enlarged; the residual capacity and residual rate were reduced. High-strength steel significantly improves the axial impact resistance and residual capacity. However, the increment of residual capacity by using high-strength steel was relatively small owing to the severe local buckling of steel tubes. Furthermore, the application range of developed equations for predicting maximum displacement of CFST members subjected to axial impact has been extended to high-strength steels (i.e., up to Q690), and together with the axial displacement limits (i.e., 1/100 L), these equations can be employed as a simplified method for anti-impact design.

Numerical investigations on flexural behavior of I-shaped CFRP-encased high-strength square concrete filled steel tubes

To enhance the mechanical properties of high-strength concrete-filled high-strength steel tubular (HSCFHST) members, a new type of composite structure is proposed in which an I-shaped CFRP is encased inside the HSCFHST member. The objective of this research is to improve the theoretical foundation for HSCFHST members by analyzing the flexural behavior of inner I-shaped CFRP on HSCFHST members. HSCFHST members' nonlinear finite element models is created using ABAQUS and confirmed by comparing simulation and test data. It is subjected to pure bending stresses. The flexural behavior of the HSCFHST members are examined with respect to failure mode, complete curve, moment sharing ratio, longitudinal and contact stresses in steel tubes and concrete. Additionally, material interaction mechanisms among three components are investigated to explore the range of restraint between the components. To assess a substance's effect and structural parameters on the flexural behavior of the members, including different combinations of the three types of materials, steel's yield strength, concrete's compressive strength, and the ratio of steel. The findings demonstrate that the steel tube's restraint of the concrete is mostly concentrated at its corners on the tensile side. The HSCFHST member's deformation capacity and stiffness were both increased by the usage of the CFRP encased in the member, which also decreased the height of the central axis' upward movement. The flexural load capacity is largely affected by the steel ratio, which also has an impact on steel strength.

CFRP repair effectiveness on compressed steel tubular members with circular cutout

Welding procedures for repairing corroded tubular structures are commonly used; however, composite material repairs are becoming popular since they do not use heat sources that might cause accidents. This paper provides a detailed description of the CFRP patch repair application in steel tubular members with a circular perforation originated from a prolonged corrosion process. The results of experimental tests on mid-scale unrepaired damaged and repaired steel tubes are reported. The predictions of the maximum loads recovered from a proposed numerical model lie close to the experimental observed values, justifying its usage for analysis of repaired tubular structures with circular cutouts when subjected to axial compression. Compared to unrepaired perforated tubes, the experimental results demonstrate a substantial strength recovery for repaired tubes. The value of this research for the oil and gas industry is that it demonstrates the feasibility of this kind of repair, which means reduced risk to the production unit and a shorter repair period.

Optimization of the Cross-Member Thickness and its Effect of Torsional Rigidity

According to the tadpole design, the vehicle will have two wheels up front and one wheel in the back. Because it is a perfect fit between the motorcycle and automobile categories, the vehicle must adhere to both motorcycle and automobile laws. The purpose of this project is to design a full-scale chassis concept based on modern and future requirements and regulations. In addition to this, the chassis should have a reasonable price without sacrificing the overall quality of the design. It was estimated that cross-members with a thickness of 200 mm were the best option for increasing the chassis torsional rigidity, and the basis of the chassis is constructed out of frames. It was observed that the C-shaped side members on the chassis were not as robust as the tubular truss side members when subjected to the vertical stresses.

Development of effective XGB model to predict the Axial Load Capacity of circular CFST columns

The Axial Load Capacity (ALC) of Concrete-Filled Steel Tubular (CFST) structural members is regarded as one of the most crucial technical factors for the design of these composite structures. This work proposes the development and application of the Extreme Gradient Boosting (XGB) model to forecast the ALC of circular CFST structural components using the affecting input parameters, namely column diameter, steel tube thickness, column length, steel yield strength, and concrete compressive strength. A dataset of 2073 experimental results from the literature was used for the model development. The performance of the XGB model was evaluated using statistical criteria such as Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Coefficient of Determination (R2), and Mean Absolute Percentage Error (MAPE). The five-fold cross-validation technique and Monte Carlo simulation method were used to evaluate the model's performance. The results show good performance of the XGB model (R2 = 0.999, RMSE = 242.757 kN, MAE = 157.045 kN, and MAPE = 0.057) in predicting the circular CFST’s ALC.

Development of effective XGB model to predict the Axial Load Capacity of circular CFST columns

The Axial Load Capacity (ALC) of Concrete-Filled Steel Tubular (CFST) structural members is regarded as one of the most crucial technical factors for the design of these composite structures. This work proposes the development and application of the Extreme Gradient Boosting (XGB) model to forecast the ALC of circular CFST structural components using the affecting input parameters, namely column diameter, steel tube thickness, column length, steel yield strength, and concrete compressive strength. A dataset of 2073 experimental results from the literature was used for the model development. The performance of the XGB model was evaluated using statistical criteria such as Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Coefficient of Determination (R2), and Mean Absolute Percentage Error (MAPE). The five-fold cross-validation technique and Monte Carlo simulation method were used to evaluate the model's performance. The results show good performance of the XGB model (R2 = 0.999, RMSE = 242.757 kN, MAE = 157.045 kN, and MAPE = 0.057) in predicting the circular CFST’s ALC.

Development of effective XGB model to predict the Axial Load Capacity of circular CFST columns

The Axial Load Capacity (ALC) of Concrete-Filled Steel Tubular (CFST) structural members is regarded as one of the most crucial technical factors for the design of these composite structures. This work proposes the development and application of the Extreme Gradient Boosting (XGB) model to forecast the ALC of circular CFST structural components using the affecting input parameters, namely column diameter, steel tube thickness, column length, steel yield strength, and concrete compressive strength. A dataset of 2073 experimental results from the literature was used for the model development. The performance of the XGB model was evaluated using statistical criteria such as Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Coefficient of Determination (R2), and Mean Absolute Percentage Error (MAPE). The five-fold cross-validation technique and Monte Carlo simulation method were used to evaluate the model's performance. The results show good performance of the XGB model (R2 = 0.999, RMSE = 242.757 kN, MAE = 157.045 kN, and MAPE = 0.057) in predicting the circular CFST’s ALC.

Flexural performance of circular concrete‐filled double steel tubular members: Testing, modeling, and strength predictions

AbstractThis paper presents experimental and numerical investigations on circular concrete‐filled double steel tubular (CFDST) members under flexural load. Seven specimens including five CFDST specimens were tested and the test parameters included the effects of concrete compressive strength, the thickness of the steel tubes, and the diameter ratio on their flexural performance. The final failure modes, moment (M)‐curvature (ϕ) curves, deflection curves of specimens, and distributions of section longitudinal strains were analyzed and reported in this study. A nonlinear finite element model (FEM) was then developed for the CFDST members. After successful validation in ultimate strengths and failure modes, parametric studies were performed by using the verified FEM. A simple formula for calculating the flexural capacity of CFDST members was proposed and compared against several design codes to investigate the design accuracy. Based on this study, it was found that the CFDST members exhibit ductile behavior under flexural load. Increasing the steel area, particularly for the outer tube improved the flexural capacities of the members. Furthermore, the existing design codes were found to be remarkably underestimating the moment capacities of CFDST members whereas the design formula proposed can predict the ultimate flexural capacity with reasonable accuracy.

Local and post-local buckling behavior of welded square high-strength steel tubes with concrete-infilled restraints

Concrete-filled high-strength steel tubular members gain increasing popularity as the building height and bridge span increase. The slender sections and higher stress levels, however, make the high-strength steel plates more susceptible to local buckling. This paper reports an experimental and numerical investigation on local and post-local buckling behavior of welded square high-strength steel tubes with concrete-infilled restraints. Sixteen high-strength steel tubes with nominal yield strengths of 460, 500, and 550 MPa with concrete-infilled restraints were tested. The experimental results reveal that the post-buckling reserve strength of steel tubes with slender sections increases with the increase in plate slenderness regardless of steel grade. A total of 168 numerical models were subsequently established using the verified finite element method. Based on the finite element analysis results, the slenderness limits and effective width formula were proposed for both high-strength and normal-strength steel tubes with concrete-infilled restraints. Available test data of steel-only-loaded concrete-filled steel tubular specimens constitutes an experimental database to evaluate the reliability of the existing slenderness limits and effective width formulas. The comparison result shows that GB 50936, AS/NZS 2327, and AISC 360-16 overestimate the slenderness limits, while Song et al. underestimate the slenderness limit excessively. The proposed slenderness limit (λpl = 0.500) is more consistent with the experimental results with a reasonable conservative level. The mean ratio of predicted post-buckling strengths by the proposed effective width formula to experimental results is 0.94, with a standard deviation of 0.073. The proposed slenderness limit and effective width formula provide a more accurate prediction and, therefore, are recommended in design.

Load capacity of concrete-filled steel tubular members with multilayer confinement subjected to coupled axial compression-bending and fire

The demands to increase bearing capacity of concrete-filled steel tubular (CFST) members and, thus, cross-sectional size of the members, have caused a series of practical issues, such as the difficulties in manufacturing steel tubes and low quality of concrete pouring. As a solution for these, concrete-filled steel tubular (CFST) members with stiffeners can be used. There is no compression-bending interactive equation for CFST members with multilayer confinement at high temperatures. This paper is mainly based on the compression-bending interactive equations of traditional CFST members recommended by Chinese standards at room temperatures, introduces the reduction factors of material strength and elastic modulus at high temperatures, and further extends the compression-bending interactive equations at room temperatures to high temperatures. To verify the validity of the unified formulae, the calculation results of the theoretical formulae are compared with the numerical and experimental results in this paper. The results of numerical simulation show that the two sets of proposed compression-bending interactive equations of CFST members with multilayer confinement are conservative. In general, the equation computing coefficient is proportional to the fire resistance time. In addition, the experimental results are in good agreement with the compression-bending interactive equation.

Axial Compression Test and Numerical Investigation of Concrete-Filled Double-Skin Elliptical Tubular Short Columns

To probe into the performance of concrete-filled double-skin elliptical steel tubular (CFDEST) members, this paper designs and conducts an experiment on CFDEST short columns imposed with axial pressure, and finite element (FE) models of the axially compressed CFDEST stub columns are established and verified by the test outcomes, taking the influences of elliptical cross-section and hollow ratio into account. The impressions of various parameters, such as hollow ratio, diameter-to-thickness ratio, aspect ratio and so on, on the load-bearing capacity, initial rigidity and ductility property were investigated systematically. Moreover, the typical failure modes, contact pressure and concrete longitudinal stress of the axially compressed CFDEST short column are revealed. In light of the findings acquired by the laboratory tests and numerical analyses, the calculation formulae for evaluating the axial compress capacity of the CFDEST short column are proposed by taking the impact of the sectional aspect ratio and hollow ratio into account. The results indicate that the failure morphologies of axially compressed CFDEST short columns mainly include outward local bulges of the outside EST, the inward bulges of the inside EST and the crushing of core concrete. The axial compress capacity of the CFDEST short column would increase with the decrease in the sectional hollow ratio and aspect ratio. The calculation method is proved to be an accurate and reliable approach to evaluate the axial compress capacity of the CFDEST short column.

Structural Integrity Assessment of Offshore Jackets Considering Proper Modeling of Buckling in Tubular Members—a Case Study of Resalat Jacket

Structural Integrity Assessment of Offshore Jackets Considering Proper Modeling of Buckling in Tubular Members—a Case Study of Resalat Jacket

Study on the Nonlinear Behavior and Factors Influencing the Axial Compression of High-Durability Fibrous Concrete Wrapped Steel Tube Composite Members.

Thin-walled steel pipe concrete has better economic performance, but the problem of local buckling is more prominent with a thin-walled steel pipe; meanwhile, thin-walled steel pipe is more sensitive to the environment and the influence of rusting is more prominent. To solve the above problems, this paper proposes new spiral stiffened rib thin-walled steel pipe concrete laminated members to obtain better force and economic performance. Based on axial compression tests on five forms of composite members, this paper studies the nonlinear behavior of the axial compression of this new type of laminated member and the factors influencing it. The following conclusions are obtained. Under the constraint of the spiral ribs, the new composite member has good integrity and each part can ensure cooperative stress; the buckling of the steel pipe is well limited and the mechanical performance is significantly improved. Compared with ordinary thin-walled concrete-filled steel tubular members, the bearing capacity is increased by about 20% and the deformation ability is increased by more than 30%. The nonlinear behavior of the member in compression can be better achieved through finite element analysis. The parametric analysis shows that the pitch and the steel tube width-to-thickness ratio greatly influence the force behavior of the member. In contrast, the spiral rib width-to-thickness ratio and the external reinforcement only need to meet the structural requirements. Finally, based on the superposition theory, the proposed method of calculating the member's axial compressive load-bearing capacity is given and design suggestions are made. The results of this paper can provide some basis for the engineering application of this new combination member.

Buckling resistance of steel circular tubes strengthened by welding cover plates

Welding under service load generates welding-induced residual stresses and deflection, affecting the stability of compression members strengthened by welding cover plates notably. Hence, the associated stability check is more complicated than that of their unstrengthened counterparts. This paper is aimed to propose a stability design method for such strengthened circular tubular members. A model for the welding-induced residual stress is proposed, and its influence on member stability is evaluated through parametric FE analysis. Results show that, for hot-rolled circular tubes, the column curve used for buckling resistance calculation is reduced from column curve “a” prior to strengthening to column curves “b” and “c” after strengthening, depending on the thickness of strengthening plates. Formulas to predict the welding-induced deflection and equivalent residual imperfection are proposed and validated, and the influence of the equivalent residual imperfection on member stability is evaluated through parametric FE analysis to derive the resistance reduction factor, which is also related to normalised slenderness ratio. Having determined the column curve and resistance reduction factor, a stability design method for strengthened circular tubular members is proposed, which is demonstrated to be more accurate than that codified in Chinese code GB 51367. In addition, the service load-generated stress limit for safe and effective strengthening is put forward.

Crippling of cold-formed stainless steel circular tubular members under concentrated bearing loads

This study presents experimental, theoretical, and numerical investigations on the crippling behaviors of cold-formed stainless steel circular hollow sections (CHS) subjected to concentrated bearing loads. First, a total of twenty-four specimens, six for each loading condition, were tested under four typical loading conditions, namely the end-one-flange, interior-one-flange, end-two-flange and interior-two-flange. Thereafter, yield-line models were established based on the failure modes demonstrated by the tests, and preliminary equations for the crippling strength were derived. Subsequently, finite element models were developed and validated against the test results and used for parametric analysis. The coefficients in the preliminary equations were modified based on the results of the parametric analysis. Finally, a comparison between the test results and prediction of the proposed equations was performed, which indicated that the proposed equations provided accurate predictions for the crippling strengths of cold-formed stainless steel CHS.

A formula for estimating the buckling capacity of corroded tubular members

PurposeSeveral experimental and numerical studies were performed in the past to estimate buckling capacity of corroded tubular members. However, the effect of initial imperfections has not been properly considered in most of these earlier proposed formulas. Therefore, the main objective of this paper is to propose an accurate analytical formula to determine the buckling capacity of patched corroded tubular members.Design/methodology/approachTubular members with initial geometrical imperfections can be regarded as beam-columns because of the combination of axial load and bending moment. The proposed formula is derived for a rectangular corrosion patch. The proposed formula is verified with results from finite element analysis of corroded tubular members and experimental results. The formula is also applied to an existing offshore jacket structure to highlight its significance and applicability. It is found that the buckling capacity of jacket members in splash zone reduces significantly with ageing. This reduction is around 29 and 14% for the selected brace and leg member respectively, during the design life. Finally, it is concluded that corrosion reduces the buckling capacity significantly and the proposed formula can be easily applied by practicing engineers to give an accurate and slightly conservative estimate the remaining buckling capacity.FindingsThe main finding is the new formula which accurately and conservatively estimate the buckling capacity of corroded tubular members. The proposed formula considers the secondary effect of both initial geometrical imperfections and shifting of centroid because of corrosion.Originality/valueThe proposed new formula is unique and original in that it considers both secondary effects from geometrical imperfections, reduction of cross-section from corrosion wastage and shifting of centroid because of corrosion. Finally, it is concluded that corrosion reduces the buckling capacity significantly and the proposed formula can be easily applied by practicing engineers to conservatively estimate the remaining buckling capacity and verify if further, more advanced estimations are needed.