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The gas-tight joining between yttrium-stabilised semi-closed zirconia ceramic tube and 06Cr19Ni10 stainless steel tube was achieved by using a self-made Ag–27Cu–4Ti paste filler material, where the...

In this paper, the seismic performance of a prefabricated frame structure with a local outsource steel tube bolted column–column connect is evaluated from the perspective of seismic vulnerability theory. Firstly, a simplified model of the prefabricated frame structure was constructed and validated by experiments. Then, a six-story prefabricated reinforced concrete frame structure (PRCS) and a cast-in-situ reinforced concrete frame structure (CRCS) were designed as examples to get the increment dynamic analysis (IDA) of the structure under 12 ground motions, and the two-parameter damage model was used as the structural requirement index. As a traditional structural requirement index-the maximum inter-storey drift angle cannot accurately describe the mechanism of structural damage. Therefore, two types of damage models are compared and analyzed. In addition, in order to evaluate the damage of frame structure effectively, a new damage index weighted combination method is proposed, and its feasibility is verified. Finally, the IDA curve and vulnerability curve with Kunnath two-parameter damage model and the maximum inter-story displacement angle as the requirement index are drawn. The results show that the two-parameter damage model is more accurate than the maximum inter-storey drift angle model in evaluating the seismic performance of the PRCS and CRCS. It shows that the maximum inter-story displacement angle model can overestimate the collapse resistance of the PRCS by 60.7% on average, and the collapse resistance of the CRCS by 75.67% on average. The seismic performance of the CRCS is better than that of the PRCS as the seismic intensity increases. Although the seismic performance of fabricated columns is similar to that of cast-in-place columns, there is still a certain gap in the seismic performance of frame structures.

The thermal conductivity of hydrogen and its mixtures is a key parameter for its production, storage, and application; however, thermal conductivities at high temperatures and pressures are rarely measured due to gas leakage. A system based on the short-hot-wire method is developed here to measure the thermal conductivity of H2/CO2 binary mixtures at 323.15–620.05 K and 2.14–9.37 MPa. A double sealing device consisting of a steel tube filled with magnesium oxide powder and a tension nut was designed and used to seal the electrical wires and prevent gas leakage. A relatively low uncertainty of 2.254% for the thermal conductivity was achieved due to the high accuracy of the measurement system. The calculation results from two theoretical models are compared with the measurement results with good consistency.

Cold tube drawing is a metal forming process that enable to manufacturers to produce high precision tubes. The dimensions of the tube are reduced by drawing it through a conical converging die with or without inner tool. There are four types of tube cold drawing process. Their difference relies on the technique used for inner diameter calibration. Therefore, the main objective was determining the difference in development of crystallographic texture and stress-strain state between drawing with the fixed plug and hollow sinking process. The input feedstock (with E235 steel grade) after the recrystallizing anneal was cold drawn (drawing with the fixed plug, hollow sinking) by one drawing passes. Electron BackScatter Diffraction (EBSD) analysis was used to evaluate the changes of grain structure and texture connected with tubes manufacturing. The stress-strain state in the tube material during drawing was calculated using DEFORM-3D software and the crystallographic orientation with respect to the cylindrical reference frame (Z-direction = drawing direction). A significant difference in stress-strain state between drawing with the fixed plug and hollow sinking process was recorded in radial direction.

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.

Concrete-filled steel tube (CFST) columns are a composite member which mainly consists of steel tube infilled with concrete that are increasingly being used as load-carrying members these days. In construction industry, CFST columns are being preferred for the development of tall buildings and long-span bridges. This paper presents an experimental investigation on concrete-filled steel tube (CFST) columns which were post heated and were subjected to axial loading. The thickness of the casing steel was 4 mm and 5 mm and diameter was 100 mm, 125 mm and 150 mm and were infilled with concrete of grade M30 which were used in the present study. This study also represents the behavior of CFST columns for two cooling regimes (annealing and quenching) after exposure to elevated temperatures of 600 °C and 800 °C. The results obtained from experimental analysis were compared to each other in terms of load-deformation pattern, ultimate load capacity, residual strength index, secant stiffness and ductility index. The test results showed that as compared with water quenching, annealing is slightly better for post fire cooling of CFST columns. Also, the results obtained by the experimental investigation were compared with each other on the basis of two cooling regimes.

The inclined six-roll tube straightener is an important equipment for the finishing line. It can not only straighten the steel pipe, but also finish the ovality of the cross section. In the actual straightening process, the cross section of the tube is prone to deform, that is, the roundness is not good. The flattening displacement is an important parameter to control cross-section forming of tube. According to the established mechanical model, the analytical calculation equations of the flattening force and the flattening displacement were derived using the energy method. Based on the finite element simulation data, the ratios of the finite element results of the flattening force to the analytical ones were fitted. The correlation coefficient after fitting is greater than 99%, and the fitting effect is excellent. The flattening experiment was carried out on tubes of different materials and different specifications, and the setting method of the optimal flattening displacement during straightening process was obtained. In the actual straightening process, using this flattening displacement, the ovality of straightened steel tube is less than 0.3%. Therefore, the proposed method can provide a reference for the flattening displacement in the actual straightening process.

Fiber-reinforced polymers (FRPs) are being widely used in the structural engineering because of their superior performance over conventional materials such as higher tensile strength, high corrosion resistance, electromagnetic resistance, good durability and light weight. The literature is deficient in the nonlinear finite element analysis (NLFEA) and theoretical predictions of FRP-confined concrete columns. The aim of the present work is to explore the structural performance of steel-tube FRP confined concrete (STC) columns under axial concentric loading. A NLFEA model of STC columns was simulated using ABAQUS which was then, calibrated for different material and geometric models of concrete, steel tube and FRP material using the experimental results from literature. The predictions of proposed NLFEA model were in close agreement with the previous experimental measurements. An extensive parametric study was performed to examine the effects of various parameters of STC columns. Furthermore, a large database of axial strength of 543 confined concrete compression members was developed from the previous researches to propose an empirical model that predicts the ultimate axial strength of STC columns accurately.

We investigated erosion-corrosion (E-C) and its mitigation on the internal surface of the expansion segment of N80 steel tube in a loop system using array electrode technique, weight-loss measurement, computational-fluid-dynamics simulation, and surface characterization techniques. The results show that high E-C rates can occur at locations where there is a high flow velocity and/or a strong impact from sand particles, which results in different E-C rates at various locations. Consequently, it can be expected that localized corrosion often occurs in such segments. The E-C rate at each location in the expansion segment can be significantly mitigated with an imidazoline derivative inhibitor, as the resulting inhibitor layer significantly impedes the electrochemical reaction rate. However, we found that this inhibitor layer could not effectively reduce the difference in the erosion rates at different locations on the internal surface of the expansion segment. This means that localized corrosion can still occur at the expansion segment despite the presence of the inhibitor.

The present construction industry requirement is more economical and speedy building the use of Light Gauge steel column infill with concrete that satisfies the excellent strength and improves ductility. Among the various infill materials, Nano SiO2 concrete is gaining attention in the composite column. The present work aims to investigate the comparative structural behavior of different Light gauge steel columns subjected to concentric loading. Light gauge steel rectangular hollow columns, plain and Nano SiO2 Concrete In-filled light gauge steel rectangular columns were considered for this research. The light gauge steel column dimension used for the experimental investigation is 80 mm × 40 mm size with 1.5 m length and 1.2 mm thickness. The ratio of width to thickness considered for the study is 66.67. Three different rectangular columns structural behavior such as load vs. axial shortening, deflection, strain characterization, and failure modes were studied from the experimental results under linear and non-linear stages. Further, the strength capacity obtained from the experiments is compared with theoretical strength derived from codes such as EC4, ACI, and BS5400. Results showed that a nano SiO2 in-filled concrete column enhances both strength and ductility, under axial load. The buckling resistance of nano SiO2 concrete in-filled steel columns was 4% higher than the plain concrete in-filled steel columns. The strength of plain concrete in-filled steel columns was 2.2 times more than the hollow steel column.

Tests and numerical simulation of rectangular recycled aggregate concrete filled steel tube (RACFST) stub columns under concentric compression are carried out. Eighteen specimens, including 12 RACFST specimens and 6 concrete filled steel tube (CFST) specimens as reference, with varied width-to-thickness ratio ( B / t ), depth-to-width ratio ( β ) and recycled coarse aggregate replacement ratio ( r ) are tested. The test results show that rectangular RACFST stub column specimens have similar failure pattern as their counterparts. However, the bearing capacity and the composite elastic modulus of RACFST specimens are lower than those of CFST ones while they both decrease with higher r . Moreover, the specimens with larger B / t and β possess a smaller ductility index. Numerical simulation of rectangular RACFST stub columns under concentric compression is executed using a finite element analysis (FEA) model developed based on the ABAQUS software, and the predicted results are verified by the experimental observations. The mechanism of concentrically loaded rectangular RACFST stub columns is further revealed by the FEA model. Finally, simplified formulae for the bearing capacity of rectangular RACFST stub columns are proposed, with the comparison between simplified and experimental results showing that the simplified model is a good predictor.

This paper proposes a simplified multi‐linear model of a shear force‐deformation relationship for concrete‐filled square steel tube short to slender beam‐columns. To evaluate the behavior of short to slender beam‐columns with a single model, the column member is divided into elasto‐plastic part and an elastic part. For the elasto‐plastic part, the deformation at each point is calculated based on the bending moment‐curvature relation model proposed by the author and by employing a newly proposed evaluation formula for curvature magnification. Predictions from the model are found to agree approximately with the experimental results up to large deformations.

Concrete-filled steel tube (CFST) columns are increasingly used in different structures owing to their excellent load carrying capacity provided by the interaction between the concrete core and steel tube. However, there is lack of information on the design and prediction of the behavior of CFST columns with rubberized concrete core when they are exposed to elevated temperature. This paper presents a study on the axial compressive behavior of short CFST columns containing steel fiber and tire rubber particles exposed to elevated temperatures. To this effect, steel fibers were added at two volume fractions of 1% and 1.5% and tire rubber particles were added as fine aggregate at two replacement ratios of 5% and 10% to the concrete core. CFST columns were exposed to four temperatures of 20 (as control), 250, 500 and 750 °C, and then axial compression tests were conducted on them. The experimental test results show that an increase in the exposure temperature to 500 °C does not have a significant influence on the compressive strength of CFST columns, whereas an increased temperature to 750 °C results in a significant decrease (34%) in the compressive strength of the columns. It is also found that an increase in the exposure temperature, steel fiber volume fraction and rubber replacement ratio lead to an increase in the axial and lateral strain corresponding to the compressive strength of CFST columns. It is shown that the predictions of the compressive strength and axial stress–strain relationship by the proposed model are in good agreement with the tests results of both unheated and post-heated CFSTs.

The flexural behavior of concrete-encased CFST box members is presented in this paper. Twelve bending tests were conducted to evaluate the influence of section size, steel tube diameter and bending direction on the performance of the concrete-encased CFST box beams. The test results were also discussed, including the observed failure patterns and developments of concrete cracks during the whole loading procedure. A numerical model was then developed to investigate the flexural behavior of the composite beams. The study of the full-range analysis, load transfer mechanism and stress distribution was carried out. Then the parametric studies were performed based on the FEA modeling. Finally, a simplified method for predicting the stiffness and flexural strength of the concrete-encased CFST box beams was presented.

In this study, three specimens of Warren truss girders composite with concrete deck slab were tested experimentally under a central monotonic load to study the effect of the existence of concrete inside the chords. The load capacity, deflection, slip between the concrete slab and steel tube, and failure modes were reported. Both chords were filled with concrete to the first specimen, only the lower chord was filled with concrete and the upper chord remained hollow to the second specimen and both chords were kept hollow in the third specimen. The result indicated that the existence of concrete inside the chords has a significant effect on the load capacity, failure pattern, and the slip. The steel tubes of the upper chord filled by concrete prevent surface plasticity failure of the upper chord under loading and increase the ultimate load by 6.68 %. Also, filling the lower chord with concrete prevents the surface plasticity failure in the supports zone and caused an increase in the ultimate load by 39.59 %. The slip at the end of the specimen of two chords filled with concrete is less by 71% than the end slip of specimen of hollow top chord and higher by 46.8 % than the specimen of two hollow chords.

Concrete-filled steel tube (CFST) columns are increasingly used in the construction of high-rise buildings which require high strength and large working space especially at lower stories. As compared to reinforced concrete columns, existence of the exterior steel tube not only bears a portion of axial load but also most importantly provides confinement to the infill concrete.with the confinement provided by the steel tube, axial strength of the infill concrete can be largely enhanced.this paper presents the investigation effect of impact load on concrete-filled steel tube columns under fire by numerical simulations using ABAQUS software.the results indicate that the CFST sections with larger confinement factor ξ=1.23 behaved in a very ductile manner under lateral impact. And the sections with smaller confinement factor ξ=0.44 generally behaved in a brittle mechanism.

Dynamic load allowance (DLA) is a key factor for evaluating the structural condition of bridges; however, insufficient research has been performed regarding the characteristics of DLA in concrete-filled steel tube (CFST) arch bridges. To address this issue, based on an actual CFST arch bridge, the DLA characteristics of bridges are investigated numerically in this study. First, aiming at different structural components, such as the arch rib, main girder, and suspenders, the DLA values obtained at various locations of different structural components are compared in detail, and then the changing regulations of the DLA, considering the influence of different vehicle speeds and various extents of pavement roughness, are summarized and analyzed. Additionally, the relationship between the different DLAs obtained by using the different response indices, that is, displacement, bending moment, and axis force of structure, is investigated. Finally, some conclusions that are significantly beneficial for evaluating or detecting the condition of CFST arch bridges are drawn.

In this study, the seismic behavior factor of steel–concrete composite buildings was examined. For this purpose, 5-, 10-, 15- and 20-story composite moment-resisting frame (CMRF) buildings having concrete-filled steel tube columns and composite beams were designed at medium ductility (DCM) and high ductility (DCH) levels as per the regulations of Eurocode 8. Examined DCM structures were designed for a PGA of 0.2 g while DCH structures were designed for a PGA of 0.4 g. SeismoStruct software was utilized in the design and performance assessment of the case study structures. Nonlinear static pushover and incremental dynamic analyses were used. In the pushover analysis, the uniform and triangular load distributions were adopted while 12 earthquake ground motions were employed in the dynamic analysis. The effect of ductility levels and number of stories on the seismic behavior of CMRFs was studied using the results of the nonlinear analysis. To this, the variation in the lateral response, global yielding value, code-based behavior factor and component, and dynamic behavior factor were presented for CMRF structures with DCM and DCH. It was observed that the behavior factor of all CMRFs exhibited well above the design assumptions, especially DCM class CMRFs.

The bond-slip behaviors of self-stressing steel slag concrete filled steel tubes (SSSSCFST) are investigated by carrying out the push-out tests. The influence of thickness to diameter ratio, confining parameter and expansion ratio of steel slag concrete (SSC) on bond-slip performance are analyzed. Investigations of the failure modes of each specimen indicate that the shear failure of the bond interface dominates the failure of the specimen. Further, three stages of the load-slip relationship curve of bond slip was observed, i.e., the loading stage, descending section and constant load section. In the loading section, with the increase in thickness to diameter ratio or confining parameter, the interface bonding force of specimen improves firstly and then decreases. Besides, the interfacial bond strength increases with enhancement of the expansion ratio. In the descending section, the interfacial bonding force raises with improvement of diameter-thickness ratio, while decreases as the confining parameter and expansion ratio increase. Moreover, the influence of considered parameters on the ultimate interface bond load is analyzed. Finally, a theoretical model for the bond-slip behaviors of SSSSCFST is proposed by accounting for the non-uniform distribution of interface bond strength. It indicates that the theoretical model can well capture the main features that are exhibited during the whole process of push-out test.

The quasi-static experiments and finite element analysis of three groups of special-shaped concrete-filled steel tube (SCFST) column chevron braced frames (two groups of eccentrically braced frames and one group of concentrically braced frame) were carried out. The differences of quasi-static mechanical properties between the three groups frame were compared. The damage mechanism of the concentrically and eccentrically braced frames was significantly different, and the eccentrically braced frame could significantly improve the energy-dissipation ability and ductility. When the single limb of columns was connected by double-steel-plate, the stiffness of eccentrically braced structure could be improved around 10.4% and showed better energy-dissipation capacity. The finite element simulation was built on the basis of experiments, and parametric analysis was examined. The analysis results showed that section forms of the SCFST column and the thickness of brace have significant impacts on the quasi-static properties of such type of structure.

Circular concrete-filled steel tubular columns (CFST) with an inner bamboo culm, by replacing the internal steel tube of concrete-filled double skin steel tubular (CFDST) columns with a structural bamboo culm, promote the use of natural materials with lower cost and lighter weight. This type of composite column is expected to integrate the advantages of all the three kinds of materials. Twenty-two circular stub columns including 12 CFST with an inner bamboo culm, 3 CFST columns, 4 CFDST columns and 3 hollow CFST columns were tested under axial compression. The test parameters include the bamboo culm thickness, the bamboo culm diameter and the diameter to thickness ratio of the external steel tubes. Test results indicated that the columns with an inner bamboo culm had excellent ductility. Furthermore, the columns with an inner bamboo culm showed strain-hardening behaviour after an initial decline in its axial load-displacement curve, but the inner bamboo culm contributed mildly to the ultimate load. Finally, a unified formula was proposed to predict the load-carrying capacities of all the four types of composite columns.

© 2020 Institution of Structural Engineers Concrete-filled steel tube (CFST) has been widely used in civil engineering. Numerous studies have shown that concrete-filled double-skin steel tube (CFDST) columns exhibit satisfactory mechanical properties under various loading conditions. Furthermore, ultra-high performance fiber-reinforced concrete (UHPFRC) has been developed as a prominent representative of new construction materials. This study investigates the residual bearing capacities of 10 concrete-filled steel tube specimens (three CFST columns and seven CFDST columns) after impact loading. The investigated parameters include the steel ratio, the concrete type, the section form, axial load ratio, the impact energy and the presence/absence of impact load. The results demonstrate that, when the inner steel tube thicknesses are identical, increasing the steel ratio from 0.296 to 0.467 (the outer steel tube thickness increases from 5 mm to 8 mm) can effectively improve the residual performance. For the non-impacted specimens, the bearing capacity of the CFDST columns is increased by 47.1% as the concrete type is changed from NSC to UHPFRC. For the impacted specimens, due to the influence of the test setup and other reasons, the concrete type has only a slight influence on the residual performance of CFDST columns; however, it has a substantial influence on the residual performance of the CFST columns. Furthermore, with the concrete type in the CFST columns changing from NSC to UHPFRC, the residual performance of CFST columns can be significantly enhanced.

This paper presents a review on rubberized concrete mixes and their properties such as strength, ductility, sound and water absorption, in addition to acid and sulphate resistance. Moreover, it discusses a review about using rubberized concrete in structural elements and its effect on ultimate compressive strength and ductility. Rubberized concrete mixes exhibit lower strength than ordinary concrete mixes. On the other hand, rubberized concrete has higher ductility and energy dissipation behaviour. Rubberized concrete with its lightweight showed a high resistance to freeze-thaw and sulphate and acid attacks in comparison with ordinary concrete. The most common structural member is Rubberized Concrete Filled Steel Tubes (RuCFST). In addition to the aforementioned merits of rubberized concrete, the confining effect of the steel tube recoups the reduction in concrete compressive strength caused by rubber inclusion. Limited researches concerned in strengthening and repairing of deficient Concrete Filled Steel Tubes (CFST) with different types of Fibre Reinforced Polymers (FRP). There is noticeable effect of using these FRP materials on RuCFST sections, ultimate strength and ductility

The steel fiber reinforced concrete (SFRC) shear wall with concrete filled steel tube (CFST) columns is an innovative composite structure. In order to calculate the shear strength of SFRC shear wall with CFST columns, the softened strut and tie model (SSTM) of SFRC shear wall with CFST columns was proposed based on the analysis of shear mechanism of SFRC shear wall with CFST columns. The SSTM was composed of diagonal, horizontal, and vertical mechanisms, in which the contributions of concrete, reinforcement, and steel fiber to the shear strength of SFRC web of shear wall were identified. The shear capacities of 24 shear walls were calculated and compared with the available test results, and reasonable agreement was obtained. The results also showed that the steel fibers distributed randomly in concrete could be treated as longitudinal and transverse reinforcement in the shear strength analysis of SFRC web, and the SSTM was reasonable and useful to analyze and predict the shear strength of SFRC shear wall with CFST columns.

In a concrete-filled steel tube (CFST), dry shrinkage and creep produce a circumferential gap between the inner concrete core column and outer steel tube that is increased by harsh weather in cold ...

Three-dimensional nonlinear finite element (FEA) is developed to predict the experimental behaviour of concrete filled square steel tubular member. The FEA is conducted to determine moment carrying capacity at ultimate load for simple beam. The concrete-steel interface model is the important parameter affecting the result of FEA simulation. Based on the experimentalresult, there is a local buckling near the loading contact point. To investigate the local buckling phenomenon, concrete-steel interface model is studied by using contact analysis between concrete and steel elements, by using rigid bar element (rbe2 element) and by using interface elements. The geometrical non-linearity, material non-linearity, loading, boundary conditions is the same for all analysis models. To account for all of these properties, FEA model by means MSC Marc Mentat software is developed. The proposed model can predict the ultimate strength with difference only 5-30%. The collapse modes by FEA model are also compared. Based on the numerical analysis, it can be seen that the local buckling is clearly shown in the FEA model with the concrete and steel interface by using interface elements.

A new, side-mounted, steel beam-and-post bridge rail was designed, crash tested, and evaluated according to safety performance guidelines included in the American Association of State Highway and Transportation Officials Manual for Assessing Safety Hardware (MASH) for Test Level 4 (TL-4). The new bridge rail system was designed to be compatible with multiple bridge decks, including cast-in-place concrete slabs and prestressed box beams. Additionally, the bridge rail was designed to remain crashworthy after roadway overlays up to 3 in. thick. The bridge rail was designed and optimized based on strength, installation cost, weight per foot, and constructability. The new bridge rail consisted of three rectangular steel tube rails supported by standard steel cross section, W6 × 15 steel posts spaced at 8 ft on-center. The upper rail was a 12 × 4 × ¼ in. hollow structural section (HSS) steel tube, and the lower two rails were 8 × 6 × ¼ in. HSS steel tubes. The top mounting heights for the upper, middle, and lower rails were 39 in., 32 in., and 20 in. above the surface of the deck, respectively. A new, side-mounted, post-to-deck connection was also developed that incorporated HSS steel spacer tubes that offset the posts 6 in. from the bridge deck and aligned the face of the bridge rail with the edge of the deck. Thus, the traversable width of the bridge was maximized. Three full-scale crash tests corresponding to the MASH TL-4 testing matrix were performed on the new bridge rail. All three crash tests successfully contained and redirected the vehicles and satisfied all MASH evaluation criteria.

In order to study the compression behavior of rectangular steel reinforced concrete columns with built-in steel tubes under different eccentric loads, three 1/10 scale specimens were designed and monotonic loading tests were carried out on them. The dimensions, steel bars and steel tube of the three specimens were the same except for the location of the loading point. The eccentricity ratios of the three specimens were 0, 0.25 and 0.5, respectively. The failure modes, load-bearing capacity and displacement characteristics of the test specimens were analyzed. According to the Chinese code, the load-bearing capacity calculation principles and methods of steel reinforced concrete columns with built-in steel tube were investigated for the comparison. The study shows that the peak vertical loads of specimens decrease and the corresponding vertical and horizontal peak displacement increase as the eccentricity increases. The load-bearing capacity calculation results from Chinese code are slightly smaller than the test result because of the unconsidered sleeve effect of the internal steel tube. The errors between them are small, and the calculation methods are beneficial to ensure the structural safety.

Concrete sandwiched double steel tubular (CSDST) columns have improved ductility under cyclic loads. Two CSDST columns are investigated in this paper (1) CSDST-CS with Circular outer tube and Square inner tube and (2) CSDST-CC with Circular outer tube and Circular inner tube. The confinement of concrete between the annular spaces of the inner and outer tubes is very important for their behaviour. To the authors’ knowledge, the literature is scarce on a validated concrete confinement model for CSDST. In this paper, the concrete confinement mechanism in CSDST columns is explained based on thick-walled cylinder theory and a semi-analytical equation is developed. Hollowness ratio of the cross-section, width to thickness ratio of the outer steel tube, strength of the outer steel tube and sandwiched concrete strength are identified as the main parameters influencing the confinement effect in CSDST. The proposed equation is extended to CSDST-CS with inner square tube approximated as an equivalent circular tube. This assumption is validated by conducting tests on short column specimens under axial compression. With outer tubes being the same, concrete confinement effect in CSDST-CS, CSDST-CC and concrete filled steel tubular column (CFST) are 18%, 20% and 30%, respectively. This study has demonstrated that the presence of double steel tubes does not improve the concrete confinement in CSDST compared to CFST. Further, this study presents a modification to the design equations of EN 1994-1-2 2005-1-1 (Eurocode 4: Design of composite steel and concrete structures Part 1–1: General rules and rules for buildings. European Committee for Standardization, Brussels, 2004) for CFST columns to CSDST stub columns by incorporating the effect of hollowness.

In recent years, a large number of studies have been carried out to investigate the behaviours of concrete filled double skin steel tube (CFDST) members due to its increasing popularity in the construction industry. This project aims to study on ultra-high performance concrete filled double-skin tubes subjected to blast loading with cross section being square for both inner and outer steel tubes using ANSYS software. It is evident that the proposed CFDST column was able to withstand a large blast load without failure so that it has the potential to be used in high-value buildings as well as critical infrastructures. The steel tubes and concrete work together well and integrity of steel concrete interface is maintained. Steel tubes in inner and outer can acts as permanent formwork and primary reinforcement. ANSYS results shows that the CFDA column can withstand applied blast load.

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.

Monitoring foam expansion and the study of foaming kinetics during in-situ foam filling are essential to ensure a desirable quality of foam-filled profiles. In this current research, a novel technique is proposed for monitoring in-situ aluminum foam filling of hollow profiles. In this technique, instantaneous temperatures measured at various locations of the hollow profile being filled have been used to determine the foam expansion rate. Hence, the apparatus developed in this study is named as thermal expandometer. To demonstrate the usefulness of this thermal expandometer, aluminum foaming is performed inside a steel tube by heating the foaming precursor at different rates, and an analysis of the effect of heating rate on the foam expansion rate is presented.

This study deals with the influence of selected technological factors on hardness, surface quality and topography of substrates after 24 layers of NiCr plasma was self-peeled off. The paper also deals with frequency of self-peeling the layers and the SEM observation of the deposited layers and substrates. Presented procedures and experimental results demonstrate changes and resistance of individual materials after an application of 24 plasma coatings. Samples from materials duralumin, chromium steel and material with the coating Ni-Cu-Ni were tested. The least impact for surface changes of substrate had samples from chromium steel. For this reason, chromium steel samples were also tested and compared for self-peeling frequency with respect to the number of coating layers and angle of surface. The main objective of this work was to select material, angle of plasma spraying and surface cleanliness that will show the least change in hardness and roughness after multiple plasma spraying with respect to the longest life of the cover mask. Cover mask is necessary for covering required areas of steel tube that must not be affected by plasma spraying, for use in serial production.

Experimental studies about the flexural performance of channel steel tube slab (CSTS) structure subjected to concentrated loads were carried out, with considering various spacing of adjacent tubes, longitudinal spacing between the channel steel and missing tensile channel steel. A self-designed flexural device equipped with particle image velocimetry (PIV) technology was used to monitor continuous structure deformation and concrete cracking characteristics. In this study, the mechanism and performance of CSTS structure serving in underground engineering were analyzed, and a theoretical model for the bearing capacity of the CSTS structure was proposed. The results show that the failure mode of the test specimens exhibits ductile failure with an average ductility coefficient 2.52. The large shear strain of the concrete was obtained from PIV speckle contour, and it shows the same propagation trend compared with the main cracks appearing in the tests. In addition, the tensile channel steel along with decreasing the spacing of adjacent tubes can increase the bearing capacity of the specimens. The proposed theoretical model shows a reasonable prediction of the ultimate bearing capacity of specimens compared with the experimental results.

In the present study, an experimental research was conducted on square steel tube confined steel reinforced concrete column under eccentric load. The major parameters of the specimens included slenderness ratio, eccentricity ratio, and structural steel reinforced ratio. According to the tested results, the eccentricity ratio, from 0 to 0.55, significantly affects the structural bearing capacity. The slenderness ratio, from 3 to 8, and steel reinforced ratio, from 0.3 to 0.41, slightly affect the capacity. Furthermore, a numerical analysis program was developed, and the calculated results are well consistent with the experimental results. Also, the theoretical formula for eccentrically loaded columns was proposed based on numerical results.

Concrete-filled steel tube (CFST) has been widely applied in bridges due to its excellent structural and constructional performance. In CFST bridges, temperature action is not only an important but also a special load that must be considered in bridge design, construction and structural evaluation. This paper presents an overview on current researches of the temperature action and effect of CFST bridges. The historical and spatial characteristics as well as corresponding influencing factors of temperature distributions are summarized, and classifications of temperature actions are also reviewed. Results show that in-depth investigations of the contributions of temperature influencing factors can help to effectively reduce the adverse temperature effects on CFST bridges in the design stage. Due to the lack of long-term measurements and insufficient use of historical meteorological data, research on the representative value along with correlation analysis of CFST temperature actions and meteorological parameters have to be further carried out. In the meanwhile, a decomposition method of temperature distribution is proposed based on structural effects of CFST bridges in this paper. The decomposed temperature actions can be used for more accurate effect calculation than traditional temperature action classification method, especially for CFST truss bridges. At last, specific temperature action patterns still need to be investigated in some of the special problems, such as longitudinal temperature differences along the CFST arch rib and thermal debonding in the CFST interface. Further investigations are required on the accurate simulation of temperature distribution of CFST bridges considering the shading effects of components and terrain. Keywords: Bridge engineering, CFST bridge, Temperature action, Temperature effect, Thermal debonding

This paper studies the axial compressive behavior of square timber filled steel tube (TFST) stub columns. A total of twelve specimens, including bare timber columns, hollow steel tube columns, and TFST columns, are fabricated and tested. Test variables include the number of confining carbon fiber reinforced plastics (CFRP) layers and the timber condition (with or without knots). The failure modes, load versus deformation relationships, strain characteristics, ultimate strength, ductility, stiffness, and strength-to-weight performance are investigated. The confining effect of CFRP on TFST columns is also analyzed. Test results show that the TFST columns have higher strength and ductility compared with the hollow steel tube columns or the bare timber columns. The presence of knots reduces column strength and ductility. CFRP can increase the axial compressive strength of columns. TFST columns have good strength-to-weight performance, indicating that high strength values can be achieved using light TFST columns.

This paper presents the results of an experimental study of sea sand recycled concrete filled circular steel tubes (SSRCFSs) under axial compression. The mechanical behaviours of axially loaded SSRCFSs were investigated. Two different parameters were considered: sea sand chloride ion (Cl−) content and recycled coarse aggregate (RCA) replacement percentage. Typical influences of sea sand Cl− and RCA contents on the bearing capacity, deformation and load–deformation curve of SSRCFS were studied. The test results showed that the typical failure mode of the SSRCFSs was similar to that of ordinary concrete filled steel tubes. The axial load–deformation curves of the SSRCFSs could be divided into elastic, plastic growth, declining and steady stages. It was found that the bearing capacity of SSRCFSs increased with decreasing RCA replacement percentage. The effect of sea sand Cl− content on the mechanical behaviour of the SSRCFSs decreased with an increase in RCA replacement percentage. The peak strain of the specimen could be enhanced due to the low modulus of the RCA, but this improvement decreased with increasing sea sand Cl− content. Finally, numerical expressions were developed to obtain the peak load and load–deformation curve of the SSRCFSs. The calculated results were in line with the experimental data.

Collision of structure of a vehicle is not limited to the axial direction but it can occur laterally. The purpose of this paper is to present a study of the energy absorption behavior of different length of the circular mild steel tube under lateral crushing. A ring/tube (length of 10 mm, 35 mm, and 60 mm), 60 mm diameter and 1.5 mm thickness is compressed quasi-statically. Maximum loading setup to Instron machine was 50 kN. The speed of compression is 5mm/min. Finite Element Analysis (FEA) it used to validate the experimental work to ensure of getting accurate results. Numerical results of energy absorption and collapse load showed respectively 96.52% and 94.36% agreement with experimental results. The theoretical results showed 14.37% deviation with experimental and 15.5% with numerical results. The specimen with 60 mm length leads to better energy absorption than the other specimens. The results obtained numerically and experimentally in addition to theoretically showed the energy absorbed and collapse load varies with the length of the tube.

Composite shear walls are widely used in high-rise buildings because of their high bearing capacity. To improve the bearing capacity of ordinary shear walls, restraining elements are usually installed at both boundaries or within the wall body. In this article, two different restraining elements, namely, a rectangular steel tube and a column-type reinforcement (the whole wall body was restrained by segmented stirrups and tied by diagonal bars), were applied to the boundary frame and wall body of the shear wall either jointly or separately. A new type of steel-concrete composite shear wall, referred to as a composite shear wall incorporating a concrete-filled steel tube boundary and column-type reinforced wall, was proposed. In addition, three specimens with different restraining elements, namely, a column-type reinforced shear wall, a concrete-filled steel tube boundary shear wall and an ordinary reinforced concrete shear wall, were presented for comparison. The influences of the two different restraining elements on the seismic performance and bearing capacity of the shear walls were analyzed from four perspectives of failure mode, hysteresis behavior, stiffness and residual deformation, and the equivalent lateral pressures of the two restraining elements were calculated. Based on the plane-section assumption, expressions for the crack, yield, peak and ultimate bearing capacities were derived, and the effects of the two restraining elements on the peak and ultimate bearing capacities were considered. The results show that these two restraining elements significantly improved the bearing capacity of the shear wall specimens, and the concrete-filled steel tube restraining element was more effective than the column-type reinforced restraining element. Finally, the calculated values of the bearing capacity of the four different restraining elements of the shear wall specimens proposed in this article were in good agreement with the experimental values.

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.

The shock-wave initiation of chemical reaction in pressed pellets of a stoichiometric mixture of Al and CuO powders in a steel tube was studied. The dynamics of the chemical transformations in the heterogeneous flow of reaction products of the mixture with dispersion of the pressed pellet material in the unloading wave was investigated. From the results of pyrometric measurements, the maximum brightness temperature of chemical reaction products was $$\approx$$ 3500 K.