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Reliable column–column connection contributes to a reduction in waste materials and enables structures to be demountable after their service life. This paper demonstrates the feasibility of using a bolted-flange connection with concrete-filled steel tube (CFST) columns subjected to axial compression load. Compression capacity, ductility, axial stiffness and toughness, as well as failure modes are discussed. The specimens are grouped into two categories: group I—connection without stiffeners and group II—connections supported by stiffeners. Three thicknesses of 2, 4 and 6 mm were used to manufacture the bolted flanges and stiffeners. The results showed that the proposed connection was effective to avoid a reduction in compression capacity. The various thicknesses of bolted flanges in group I specimens had a slight influence on the axial stiffness value and that influence was doubled in group II specimens. The stiffeners played a significant role in the toughness value and this was reduced with a reduction in the thickness of the stiffeners. In addition, an improvement in ductility was noticeable in stiffened specimens. Consequently, it can be inferred that bolted-flange joints have the potential to produce reliable and economical designs for CFST columns.

For more than two decades, the construction technique using concrete filled steel tube (CFST) has been widespread throughout the world. Indeed, it has been demonstrated that the use of normal or high strength concrete, confined in a steel tube of circular shape can considerably improve its ductility as well as its load capacity, owing to the combination of the qualities of the two constituent materials; these tubes have an effortless execution, indeed, the concrete used in the CFST does not require formwork nor reinforcement, a durability of the two materials as well as a good behavior to fire, which was the effect desired at the origin of their elaboration. In this paper, we study the axial compression behavior of short circular steel tubes filled with concrete; their modelling will be performed using the ABAQUS/Standard calculation program. In order to accurately determine their behavior, we have created different models. Indeed, these tubes will be modeled in order to simulate different plastic state behaviours, namely a perfect elasto-plastic state, an elasto-plastic state with multilinear strain hardening and a third elasto-plastic behavior with strain hardening proposed by Tao et al. The tested columns consist of circular hollow sections which are designated in the literature as Concrete Filled Steel Tube (CFST), for which we vary the diameters, heights as well as the wall thicknesses, and which we fill with concrete of different qualities. The compressive behavior, including ultimate loads, confinement, load-deflection relationship and failure modes, was obtained from numerical models and compared with experimental and theoretical results based on Eurocode 4. All these results showed a good agreement and a satisfactory correlation, allowing us to assume that a correct modelling can be sufficient to simulate the behavior of CFST.

This paper presents the experimental and numerical studies in the investigation of the concentrated compressive behaviors of cold-formed steel-foam concrete composite wall. The failure modes, load–displacement curves, and load–strain curves of the specimens were obtained from the experiments. The infilled specimen failed due to distortional buckling of the end stud and cracking of the concrete near the corner of the wall. The strength of the high strength cold-formed steel was not being fully utilized. A finite element model was established by ABAQUS software and validated by the test results to investigate the effect of the concrete strength, steel strength, the spacing between stud openings, and the thickness of the concrete protective layer on the behaviors of the composite wall. The results indicate that the improvement of concrete strength has the most obvious effect on the bearing capacity of the composite wall, while the changes in steel strength, concrete cover thickness, and hole spacing have limited effects.

Pendulum impact tests were conducted on a reinforced concrete (RC) frame column and four RC free-standing columns. The effects of the axial compression ratio and reinforcement ratio on the impact resistance of the columns were compared using the dynamic time curves of framed and freestanding columns under impact. The test results show that for the same impact load, although the presence of axial loads can play a positive role (e.g., reducing the residual displacement), it may lead to more severe local damage. In addition, compared with free-standing columns, frame columns can be considered as a protective structure because of their greater lateral stiffness and stronger crashworthiness. The corresponding finite element models are developed, and the influence of the axial loads on the cross-section force responses under impact excitation was deeply explored. Axial loads can significantly affect the distribution of moment, shear force, and damage to the column.

High strength aluminum alloy members can be used if the required cross-sections are larger than those obtainable by extrusion. The application range of the current design codes for aluminum structures is limited for normal-strength material and whether high-strength members can be designed with the existed buckling curves is examined. Fourteen H-section columns made from 7075-T6 were tested under axial compression. The effects of the different material properties and imperfections on the flexural buckling behavior of normal- and high-strength columns were analyzed numerically. The column curves in European, Chinese and American specifications can predict flexural buckling resistance of such columns safely with an average underestimation of 13%, 12% and 8%, respectively. Eighty-one column buckling tests available in the literature performed on extruded sections made of aluminum alloy with the yield stress between 388 MPa and 557 MPa were collected and analyzed. Finally, a new flexural buckling curve was suggested for the estimation of flexural-buckling resistance of high-strength extruded members.

Refereed/Peer-reviewed Fibre-reinforced polymer (FRP) bar-reinforced concrete (RC) columns (FRP-RC columns) have become increasingly popular since they are durable against harsh environmental attacks. For a reliable and cost-effective design of FRP-RC columns, it is essential to gain an in-depth understanding on the compressive behaviour of FRP spiral-confined concrete and the role of FRP longitudinal bars in resisting the axial stresses in the columns. Although extensive studies have been carried out on FRP-RC columns, few studies have been conducted to clarify the axial compressive behaviour of each component (i.e., FRP spiral-confined concrete and FRP longitudinal reinforcing bar). To this end, an experimental study was conducted to explore the compressive behaviour of FRP spiral-confined concrete in FRP-RC columns with and without longitudinal reinforcing FRP bars under axial compression. The contribution of the FRP bars in the FRP-RC columns is also investigated. The key variables of the experimental study include the spiral pitch and the diameter of FRP longitudinal bars. Test results show that the FRP spiral-confined concrete in FRP-RC columns exhibits a bilinear axial stress–strain behaviour. The threshold of sufficient confinement ratio of FRP spiral-confined concrete is 0.12, which is larger than that of the FRP jacket-confined concrete documented in the literature. The axial load carried by the FRP bars with a diameter of 16 mm (corresponding to a reinforcement ratio of 4.6%) accounts for 25% ∼ 35% of the total axial load in the column at the ultimate state, while the contribution of the FRP bars is significantly reduced with the decrease in the bar diameter. The value of the tensile elastic modulus of the longitudinal FPR bars should be reduced when estimating their axial load contribution to the FRP-RC columns. The axial load–strain behaviour of FRP-RC columns can be well predicted by the existing model with some modifications.

The axial compression performance and design method of web-stiffened stud walls (with and without perforations) may be clearly distinguished from that of un-stiffened stud walls. The objective of this paper is to investigate the axial behavior of web-stiffened stud walls, and to provide a design method for these walls. A total of 10 cold-formed thin-walled steel stud walls—including different cross-sections, sheathing material, and web holes, were tested by being subjected to axial compression. The performance of different cross-sections, sheathing types, and perforated and non-perforated stud wall samples are discussed. A simplified finite element model of the walls is established and verified against the experimental results. Further, various parameter analyses are carried out to study the influence of the height, width, and spacing of the web holes. Finally, on the basis of the ultimate strength data obtained from the experimental and numerical results, an extension is proposed to the existing Direct Strength Method (DSM)—which uses elastic buckling loads provided by sheathing bracing—to enhance the ultimate strength of the un-stiffened stud walls. The results of this study explicitly show that the current use of the DSM overestimates the strengths of web-stiffened stud walls because local-distortional interactive buckling is not taken into account. Hence, two proposed methods, both of which consider the interaction of local and distortional buckling, are used to calculate the nominal axial strength of web-stiffened stud walls. A comparison of the calculation results with the numerical results demonstrates that the proposed method that is based on AS/NZS 4600:2018 is relatively accurate.

The stress–strain characteristics of reinforced masonry (RM) under axial compression should be correctly understood to effectively analyse and design RM elements. However, past studies have overlooked this aspect and mainly focused on assessing the stress–strain behaviour of grouted or confined masonry. An experimental programme was executed in this research by constructing and testing RM wallettes under uniaxial compression to understand the stress–strain behaviour of RM. The effects of grout strength and lateral restrainer configurations on the compression behaviour were also studied. The experimental outcome revealed that the grout plays a major role in the axial capacity of the RM, while change in the configurations of the lateral restraining reinforcement did not significantly affect the axial capacities and axial stress–strain behaviour of RM wallettes. The predictability of the axial capacity of the RM wallettes were validated through the expressions given in the three masonry design standards. It was observed that all considered standards conservatively predicted the axial capacity of the RM. Moreover, the applicability of the existing analytical models in the literature for the RM were verified against the experimental data and an improved stress–strain model is proposed in this research.

Precast shear wall (PSW) have been widely used in structure construction. The connection of the precast part plays an important role in the seismic performance of the PSW. To improve the seismic performance and satisfy various important requirements of the PSW, this paper develops a new bolt-plate connection joint assembled by the high strength bolt with embedded steel plate in the PSW. Experimental study of four shear wall specimens, including one cast-in-situ integral specimen and three PSW specimens with different axial compression ratio, was conducted to investigate the seismic performance of the proposed bolt-plate connection joint under low cyclic loading. The key indexes including horizontal load-lateral displacement curve, skeleton curve, stiffness degradation, strain distribution of connecting device and steel bar are investigated. Results shows that the PSW with the proposed bolt-plate connection joint performed similar failure mode compared to that of the cast-in-situ shear wall (CISSW). The loading-carrying capacity of the PSW with the proposed bolt-plate connection joint is nearly equivalent to that of the CISSW. Note that the proposed connection joint can effectively improve the plastic deformation capacity of the PSW and also enhance the seismic performance and satisfy construction.

This paper presents an experimental study on the axial performance of square/rectangular concrete-filled steel tubular (CFST) columns. A total of 34 specimens, classified as four groups, were fabricated and tested under uniaxial compression. The failure modes, axial stress–strain curves, ultimate axial stress, and ductility were analysed in detail considering the effect of the steel ratio, steel fibre addition, concrete type, cross-section type, and size of the specimens. Further, the confinement index ( ξ ) and strength index (SI) was discussed. The obtained findings revealed that the ultimate axial stress of CFST columns was increased by increasing the thickness of the steel tube and adding steel fibres to the concrete mixture. When the steel ratio, steel tube thickness, and specimen height were the same, the type of cross-section (the square and the rectangular section) exhibited an insignificant effect on the axial stress–strain of the CFST column. Finally, a formula was proposed to estimate the ultimate axial stress of both square and rectangular CFST columns, with the concrete core strength ranging from 70 MPa to 150 MPa.

A novel type of welded corrugated steel tube-concrete-flat steel tube composite structural column was proposed, and the axial compressive behavior of this column type was evaluated by testing of 14 short column specimens. The test parameters included hollow ratios, inner tube diameter-thickness ratios, and concrete strength and reinforcement ratios. The test results indicated that the outer corrugated steel tube could provide good hoop confinement to the core concrete. The welded corrugated steel tube-concrete-flat steel tube composite structural columns failed with serious extrusion of the wave crests and inward buckling of the inner steel tubes. The effects of the test parameters on the failure modes, strength, and ductility and strain responses were also discussed. Moreover, some existing design models for concrete-filled double skin tubular (CFDST) columns were assessed based on the test results available in literature and this study, and new models for CFDST columns and welded corrugated steel tube-concrete-flat steel tube columns were proposed. The proposed analytical models were found to be in good agreement with both the test results of the specimens with outer flat steel tubes and corrugated steel tubes under axial compression.

This study is aimed at addressing the experimental and theoretical investigation of the compressive behavior of steel reinforced concrete (SRC) composite columns containing steel fibers considering the stirrups’ confinement effects. Variables used to fabricate and evaluate the performance of the steel reinforced fibrous concrete (SRFC) columns include the steel profile shape (both H -shaped and C -shaped), volume fraction of steel fibers ( 0 , 0.75 , and 1.25 % ), and spacing of stirrups ( 40 , 65 , and 130 m m ). In total, 36 short column specimens were fabricated and such parameters as the axial bearing capacity, compressive stress–strain curves, ductility, peak strain and toughness were investigated through the axial compression test. According to the results, the axial bearing capacity of concrete-confined steel columns was affected by the steel shape inside; the axial bearing capacity of H -shaped cross-section columns was more - due to their more confinement - than that of C -shaped ones. Although adding, and increasing the percentage of, steel fibers increased the columns’ axial bearing capacity slightly (up to 6 % ), their ductility and energy absorption improved significantly. Increasing the spacing of stirrups from 40 to 130 m m not only resulted in a 12 % reduction in the axial bearing capacity, but also reduced the contribution of the composite action of both H - and C -shaped profiles by more than 70 % . Finally, as predicting the SRC column strength is important, relationships presented by ACIITG , A S 3600 , C S A - A 23 , E N 1994 , J G J 138 , and N Z S 3101 for the prediction of the axial bearing capacity were thoroughly studied and showed that all had ignored the confinement effects. Considering the latter, this study modified the relationships, corrected the predicted results and compared them with both the experimental results of this study as well as those of other researchers’ which showed a good correlation between the results.

The concrete-filled wide rectangular steel tubular (CFWRST) column is attracting more and more attention in engineering practice. The aspect ratio of CFWRST section is normally 2.0–3.0, which exceeds the limitation in existing studies, being less than 2.0. The finite element (FE) analysis has been widely used in investigating behavior of the concrete-filled rectangular steel tubular (CFRST) columns, where many parameters need to be calibrated using test results. This paper presents an investigation on behavior of CFWRST stub columns under axial compression using ABAQUS. On the basis of original constitutive model for confined concrete, the constitutive model for simulating CFWRST stub columns is presented, in which the involved parameters are calibrated using existing test results. The proposed model is verified to be suitable for simulating CFWRST stub columns, and it is considered to be capable of well extending the application range of the original model in CFRST columns with large aspect ratios. Subsequently, a total of 330 CFWRST columns are analyzed to investigate the effects of key factors on the behavior of CFWRST stub columns. Finally, based on the analyses, the limitation of width-to-thickness ratio of steel tube in CFWRST stub columns is presented, and solutions are also proposed for the ultimate axial load of CFWRST columns.

According to the statistics of relevant departments, the total area of various existing buildings in China is at least 10 billion m2, of which about one-third of the houses have reached the design life and the safety reserve is insufficient. It is not economical to demolish these houses and rebuild them, and the benefits of new buildings are far less than those of extending the service life of old buildings through reinforcement. Therefore, reinforcement technology is increasingly indispensable. Currently varying methods for the prestressed reinforcement of concrete columns are developed, but they are generally not practical. Strengthening concrete columns with prestressed semicircular steel plate is a new prestressed strengthening technology. In this article, the experimental study on the axial compression of a reinforced concrete circular section short column strengthened with prestressed semicircular steel plate is carried out by combining experimental and numerical simulation methods, and the calculation formula of the bearing capacity of the reinforced short column is established by finite element analysis.

This paper reports on an investigation into the influence of an expansive admixture (EA) and fly ash (FA) on the axial compressive behaviour of concrete-filled glass-fibre-reinforced polymer (GFRP) tube columns. The effect of EA and FA on the compressive strength and restrained expansion ratio was studied for two concrete strength grades, and optimised mixtures of expansive FA concrete were selected. It was found that the desired concrete strength and maximum expansion was obtained with 12% substitution of EA and 10% substitution of FA. For this study, 12 concrete-filled GFRP tube columns of circular cross-section were designed and fabricated considering parameters including the GFRP tube thickness, EA content, FA dosage and concrete strength. Their axial compressive behaviour was investigated through their failure modes, load-carrying capacity, ultimate stress and stress–strain curves. The results showed that increases in the thickness of the GFRP tube and EA content can enhance the axial compressive strength of concrete-filled GFRP tube columns. The theoretical ultimate load results showed good agreement with the experimental data.

An innovative glass fiber reinforced polymer (GFRP) closed-type winding (GFRP-CW) tie was developed to eliminate the bond slip failure and make full use of the tensile strength of ties compared with conventional pultruded fiber reinforced polymer (FRP) rod ties. Although better confinement effect of GFRP-CW ties, however after spalling of concrete cover, the compressive longitudinal FRP bars in the plastic hinge regions of columns are most likely to crush or buckle. External FRP jackets can effectively restraint damage to concrete cover. Against this background, a novel FRP-reinforced concrete column confined with external FRP jackets and the internal GFRP-CW ties were proposed to prevent the FRP bars from premature buckling or crushing. In this article, twelve square new columns were constructed and tested to characterize the axial compressive behavior. The test parameters included FRP wrapping type (GFRP or carbon fiber reinforced polymer (CFRP)), FRP wrapping layers, and spacing of ties. Test results confirmed that FRP-reinforced concrete columns with external FRP jackets had significantly larger ductile behavior and exhibited higher load-carrying capacity than their counterparts FRP-reinforced concrete columns due to the contribution of longitudinal GFRP bars and the concrete cover. The test results also suggested reasonable spacing of ties and layers of GFRP jackets for an expected moderate confinement behavior.

The mechanical properties of CFRP-confined rectangular concrete-filled stainless steel tube (CFSST) stub columns under axial compression were experimentally studied. A total of 28 specimens (7 groups) were fabricated for the axial compression test to study the influences of length-to-width ratio, CFRP constraint coefficient, and the thickness of stainless steel tube on the axial compression behavior. The specimen failure modes, the stress development of stainless steel tube and CFRP wrap, and the load-strain ratio curves in the loading process were obtained. Meanwhile, the relationship between axial and transverse deformations of each specimen was analyzed through the typical relative load-strain ratio curves. A bearing capacity prediction method was proposed based on the twin-shear strength theory, combining the limit equilibrium state of the CFRP-confined CFSST stub column under axial compression. The prediction method was calibrated by the test data in this study and other literature. The results show that the prediction method is of high accuracy.

Global wood resources have been in short supply for a long time, whereas corn straw resources are abundant. To effectively alleviate the shortage of wood resources and the harm caused by straw burning, this paper developed corn straw biomass integrated material substitute wood materials. Corn straw biomass integrated material is a new type of material produced by a new reorganization and integration process of corn straw, which can replace wood as a structural material in construction engineering. In this paper, the mechanical properties of the axial compression components of the three integrated methods of parallel texture integration, vertical texture integration, and combination texture integration of corn straw biomass integrated material are studied. Through experimental research on the corn straw biomass integrated material, the failure modes and bearing capacity of different integration methods are compared. The straw fiber characteristics of the failure surface of the axial compression component are observed on a mesoscopic scale. The axial compression failure mechanism is then analyzed and determined, and the optimal integrated method for the axial compression component of corn straw biomass integrated material is proposed. Strong theoretical support is provided for further research and application of corn straw biomass integrated material structural components, and a reliable reference for research on new sustainable biomass building materials is given.

In this study, an experiment was conducted to investigate the bearing behaviour of an external double-layered (EDL) flange connection under axial compression. The initial geometric imperfection of the flange plates was measured before the experiment to evaluate its effect on the compression capacity. Furthermore, finite element analysis was conducted and its results were compared with the experimental results. The initial imperfection was observed to be strongly related to the mechanical properties of the EDL flange connection. Moreover, stresses at symmetrical positions of the end plates and stiffened plates were asymmetrical, and most of the stiffened plates fully yielded in their sections adjacent to the end plates. On the basis of the initial imperfection measurements, three basic imperfection modes were proposed for the end plate. Finite element models considering these modes could predict the experimental results well. The load distribution coefficients of a stiffened plate and an end plate were obtained by considering the initial imperfection, and they are presented here along with practical design methods for the two components.

In recent years, the concrete-filled wide rectangular steel tubular (CFWRST) columns, whose cross-sectional width-to-depth ratio exceeds 2.0, is widely utilized in medium- and high-rise buildings. The global buckling behavior of CFWRST columns is of great concern in practical projects due to the multi-story fabrication and erection. In this paper, the stability performance of CFWRST columns is investigated. A refined finite element (FE) model is established for numerical simulation, and the ultimate resistances, load-displacement curves and failure modes obtained from FE models are compared with previous test results to verify the validity of the FE model. Main factors, including geometric dimensions, steel tube thickness, steel strength and concrete strength, are studied through parametric analysis. By comparing the typical equations specified in several existing design codes with a large number of numerical simulation results, it is found that Australian code (AS2327-2017), American code (AISC360-2016) and European code (EC4-2004) fail to predict the ultimate resistance of slender CFWRST columns under axial compression, and about half of the prediction results lead to unsafe designs. Meanwhile, the solutions of Chinese codes (GB50936-2014 and GB50017-2017) could conservatively predict the behavior of CFWRST columns within the deviation of 10% for most numerical results. Thus, these two codes are considered to provide valuable references for designing the CFWRST columns in practice.

The exposure of reinforced concrete (RC) columns to elevated temperatures is detrimental to its axial capacity and stiffness. Selecting the proper strengthening technique to repair heat-damaged RC columns is critical to ensure that the axial capacity and stiffness are restored. This paper examines the performance of different strengthening schemes using carbon fiber reinforced polymer (CFRP) jackets and near-surface mounted (NSM) steel bars in repairing circular and square RC columns damaged due to the exposure to high elevated temperature. The tested columns were divided into three categories, un-heated and un-strengthened columns, post-heated and un-strengthened columns, and post-heated and strengthened columns. The heated columns were exposed to 600 °C for 3 h. Two strengthening schemes were evaluated. The first strengthening scheme consisted of unidirectional CFRP strips in combination with NSM steel bars. The second scheme consisted of strengthening with unidirectional CFRP strips only. All the columns were tested under axial compression until failure. The test results showed that exposure to elevated temperatures caused a reduction in the load-carrying capacity of 38% in circular columns and 29% in square columns. Both strengthening schemes were effective in restoring and exceeding (by approximately 16%) the initial load-carrying capacity of heat-damaged RC columns. The use of CFRP strips in combination with NSM steel bars was more effective in restoring the initial stiffness of the post-heated columns compared to using CFRP strips alone. The initial stiffness recovery was more pronounced in circular columns compared to square columns. Circular columns exhibited 15% higher initial stiffness when compared to the control columns before heat-exposure. For square columns, the initial stiffness was equivalent to the initial stiffness of the control RC columns before heat-exposure.

A new type of concrete-filled steel tube (CFST) structural member is proposed by replacing the central portion of the infilled concrete with a stone prism. The mechanical behavior of the stone prism encased concrete-filled steel tube (SCFST) members under axial compression was studied through experimental testing. A total of twenty-four stub columns, including eighteen SCFST specimens and six CFST specimens, were subjected to axial compression until failure occurred. The primary parameters considered were the size of the stone prism (s = 75 mm, 100 mm or 125 mm), wall-thickness of the steel tube (t = 6.0 mm, 8.0 mm or 12.0 mm), and concrete strength (fcu = 62.3 MPa or 107.0 MPa). Test results demonstrated the composite actions between the three parts of the member, which significantly enhanced the load-carrying capacity of the SCFST column. The effect of the parameters on the failure mechanism, load-carrying capacity, load versus deformation response, and ductility of the SCFST specimens was researched. Meanwhile, the experimentally obtained axial compressive strength of each SCFST specimen was compared with predicted strengths obtained by adopting the formulae from currently available design codes for conventional CFST columns. These design codes could not precisely predict the load-carrying capacity of SCFST stub columns, and an improved model was proposed.

A new type of composite insulated concrete sandwich (ICS) wall is proposed. The wall consists of a three-dimensional spatial steel wire mesh skeleton, insulating core material and inner and outer c...

Intrinsically, lightweight aggregate concrete (LWAC) suffers from the low compressive strength and deformation capacity. This restricts the use of LWAC mainly to non-structural applications. Several studies have highlighted the potential of synthetic fiber-reinforced polymer (FRP) jackets for improving the substandard properties of the LWAC. However, the high costs associated with FRP jackets are generally a concern. This study identifies hemp fiber-reinforced rope polymer (FRRP) wraps as a potential alternative to the synthetic FRP jackets. The salient features of hemp FRRP include its low cost and easy availability. Therefore, the main question that needs to be answered is: can hemp FRRP strengthen LWAC as a low-cost alternative to synthetic FRP jackets? To quantitatively explain the effects of lightweight aggregates on concrete compressive strength, 24 concrete cylinders were tested in three groups. Group 1, 2, and 3 cylinders comprised 0, 50, and 100% of lightweight aggregates as natural aggregate replacements. The peak stress of the concrete was reduced by 34% and 49% in the presence of 50% and 100% lightweight aggregates, respectively. It was concluded that a single layer of hemp FRRP on Group 2 cylinders (i.e., 50% aggregate replacement) was sufficient to enhance the peak stress to the same level as that of the control cylinder in Group 1 (i.e., fabricated using natural aggregates only). At the same time, it took two layers of external FRRP on Group 3 cylinders to achieve the same strength. A positive correlation between the peak stress of the LWAC and the number of hemp FRRP layers was observed. Nonetheless, Group 1 and 3 cylinders formed the upper and lower bounds in terms of peak stress for the same level of confinement. Further to the interest, three layers of hemp FRRP shifted brittle compressive stress–strain response to a bi-linear response for all amounts of lightweight aggregates. Several existing analytical peak stress models were assessed in predicting the experimental results. From the results, it was inferred that none of these models predicted the compressive strength of all three groups of cylinders consistently.

A novel composite structural member, UHPC-encased concrete-filled steel tubular (UC-CFST) column, is proposed in this study to address the shortcomings of the ordinary concrete-encased CFST (OC-CFST) columns. A total of 22 specimens subjected to axial compression loading were tested, including nine UC-CFST stub columns, nine OC-CFST stub columns, and four CFST stub columns. The experimental results showed that the encasing UHPC of UC-CFST columns was less damaged than the encasing ordinary concrete of OC-CFST columns and did not spall when the UHPC was crushed. The UC-CFST stub columns reached their ultimate load-bearing capacity when the encasing UHPC attained the peak compressive strain, which was much greater than that of the OC-CFST stub columns. Compared to the OC-CFST stub columns, the ultimate load-bearing capacity of UC-CFST stub columns improved markedly by 75%–289% and the compressive stiffness increased by 22%–49%, while the ductility decreased by about 50% on average. Furthermore, increasing the area ratio of the encased CFST in the UC-CFST stub columns was unfavorable for the compressive stiffness and load-ultimate bearing capacity. Finally, by comparing the different calculation methods for ultimate load-bearing capacity of OC-CFST columns recommended by Chinese standard CECS 188, American standard AISC 360, Japanese standard AIJ-SRC, and European standard Eurocode 4, it was found that the calculation methods applicable to OC-CFST columns would underestimate the ultimate load-bearing capacity of UC-CFST columns to varying degrees. Thus, a modified calculation formula based on the CECS 188 standard was proposed for accurate prediction of the ultimate load-bearing capacity of the UC-CFST stub columns.

This study investigated the axial behaviour of precast concrete panels with hollow composite reinforcing systems (CRSs). These systems were provided to create voids, reduce the concrete and the self-weight of the panels. Thirteen specimens representing the unit width of a precast concrete panel were prepared and tested under concentric axial compression to investigate the effects of CRS spacing and slenderness ratio. From the experimental results, introducing the hollow core did not affect the stiffness of the panels due to the relatively small area of the hollow core at the middle of the section, while the axial capacity was reduced by 11%. On the other hand, the CRS increased the axial strength capacity and stiffness of the hollow panels by 70% and 71%, respectively as it provided additional reinforcement and stabilised the concrete core. Furthermore, narrower CRS spacing provided better structural performance than wider spacing due to the higher efficiency of the CRS and its flanges in holding together the cracked concrete. Moreover, the axial stiffness provided by the CRS prevented the global buckling failure of slender panels. Finally, a theoretical model was developed to predict axial load capacity by considering the contribution of the CRS and slenderness of the panels. Refereed/Peer-reviewed

Buried depth is an important physical factor that affects the seismic performance of underground structures yet remains scarcely considered in existing seismic design. This paper aims to determine the influence of buried depth variation on the seismic capacity of underground subway stations in the framework of performance-based seismic design with particular focus on the influence on the inter-storey drift ratio limit. A brief introduction is presented to determine the performance level of subway station structures based on the pushover method. The influence of buried depth on the seismic performance index (inter-storey drift ratio) of subway station structures is investigated, as well as its influence on the shear distribution and failure mode of the key structural component, that is the middle column. It is found that the inter-storey drift ratio limit generally decreases with increasing buried depth and the station ductility worsens. The failure mode of the middle column changes from large eccentric compression to small eccentric compression with increasing buried depth owing to increased axial compression. The results are applied to estimate an optimum buried depth that improves the overall safety of subway station structures.

This paper presents an experimental study on the seismic behavior of PVC-CFRP confined reinforced concrete columns subjected to combined axial compression load and horizontal reversed cyclic loading. A total of six one-fourth scale PVC-CFRP confined reinforced concrete columns (PVC-CFRP) and two one-fourth scale PVC confined reinforced concrete columns (PVC) are fabricated. The flexural failure mode, which is characterized by the crushing of concrete and the yielding of longitudinal reinforcement, is found for all PVC-CFRP and PVC specimens. The effects of axial compression ratio and CFRP strip spacing on the secant stiffness, energy dissipation, etc. are investigated. The results show the secant stiffness decreases rapidly as the axial compression ratio increases, and the confining effect of the CFRP strip spacing on the secant stiffness evolution is more obvious for the specimen with higher axial compression ratio. The specimen with smaller CFRP strip spacing exhibits better energy dissipation capacity, and the strengthening effect of CFRP strips is more significant for the specimen with higher axial compression ratio. The effective CFRP strip spacing for the PVC-CFRP is suggested.

Elliptical concrete-filled stainless steel tubular (CFSST) columns are high-performance composite columns that have the enormous potentiality to be used in composite construction in the near future. However, to date, limited studies on the performance analysis of such columns under axial compression have been performed taking into account the accurate material laws of stainless steel and the confined concrete. This paper presents a mathematical model to investigate the axial performance of elliptical CFSST short columns. Accurate material laws of stainless steel and the confined concrete are incorporated in the numerical modeling to capture their true performance. Independent test results are utilized to validate the accuracy of the mathematical predictions. A parameter study is performed to study the important column parameters on their axial performance. The investigations of the accuracy of the existing design models for CFST columns in designing axially loaded elliptical CFSST columns are performed with the test and numerical predictions.

This paper presents the investigation on built-up cold-formed steel column sections strengthened with carbon fibre-reinforced polymer (CFRP). Here, box-shaped column sections were fabricated by screwing together with individual channels. Behaviour of twelve plain and twelve CFRP-strengthened box sections was studied under axial compression. Three lengths of 300 mm, 500 mm and 700 mm with section thickness of 0.6 mm, 0.75 mm and 1 mm were studied in the investigation. The cold-formed steel design procedure suggested by North American specification AISI S100-16 and Euro code 3 (EC3) provisions was applied and compared with the experimental results, which were in good agreement. The results also indicate that the proposed strengthening technique is effective in repair and increasing the load-carrying capacity of cold-formed steel built-up box column.

This paper presents an experimental and numerical investigation into the buckling behaviour of axially loaded cold-formed steel (CFS) zed and hat sections. In total, 12 experimental tests are reported, of those 6 tests are on CFS zed sections and the remaining 6 are on CFS hat sections. The failure modes, ultimate loads, and load–displacement curves of the specimens were reported and analyzed. The experiments revealed the deformation mechanism of both the zed and hat sections failing in distortional mode. Nonlinear finite element (FE) models are then described for both the zed and hat sections, which include material non-linearity and geometric imperfections. The validated finite element models were then used for the purpose of parametric studies comprising 140 models, which include 70 models each for CFS zed and hat sections. Ten different cross-sections were analyzed in the parametric study for both the zed and hat sections. The axial strengths obtained from the experimental tests and FE analysis were used to assess the performance of the current design guidelines as per the Direct Strength Method for both the zed and hat sections. From the comparison, it was found that the design strengths are un-conservative by 7% and 10% on average for CFS zed and hat sections, respectively. An improved design equation was therefore proposed for those CFS zed section columns, which failed by either distortional buckling or through a combination of distortional and global interactive buckling. The proposed equation gave a close comparison against FE results, being conservative to the FE results by only 3%. Reliability analysis was also performed to confirm the reliability of the proposed design equation.

The main aim of this paper is to investigate the postbuckling and buckling of functionally graded graphene-reinforced composite (FG-GRC) laminated cylindrical shells strengthened by stiffeners unde...

Typical effects of coarse and fine aggregates on the long-term properties of sea sand recycled aggregate concrete (SSRAC) are analyzed by a series of axial compression tests. Two different types of fine (coarse) aggregates are considered: sea sand and river sand (natural and recycled coarse aggregates). Variations in SSRAC properties at different ages are investigated. A novel test system is developed via axial compression experiments and the digital image correlation method to obtain the deformation field and crack development of concrete. Supportive results show that the compressive strength of SSRAC increase with decreasing recycled coarse aggregate replacement percentage and increasing sea sand chloride ion content. The elastic modulus of SSRAC increases with age. However, the Poisson’s ratio reduces after 2 years. Typical axial stress-strain curves of SSRAC vary with age. Generally, the effect of coarse aggregates on the axial deformation of SSRAC is clear; however, the deformation differences between coarse aggregate and cement mortar reduce by adopting sea sand. The aggregate type changes the crack characteristics and propagation of SSRAC. Finally, an analytical expression is suggested to construct the long-term stress-strain curve of SSRAC.

Recycled lump concrete (RLC) made with demolished concrete lumps (DCLs) and fresh concrete (FC) provides a solution for effective waste concrete recycling. To promote the development of precast RLC structures, this study tested a new type of connection for precast concrete columns: connecting the upper and the lower halves of columns with bent longitudinal reinforcements and structural adhesive. In this work the behavior of precast RLC columns with the new connection was studied under axial compression. The axial compressive strength of nine two-part columns was tested. The effects of the degree of bending in the longitudinal reinforcement, the replacement ratio of DCLs and the stirrup spacing were investigated. Tests showed that: (1) the failure mode of precast concrete columns is different from that of cast-in-place columns; (2) when the strength of the waste concrete is close to that of the fresh material, there is no significant difference in the axial compression performance of either precast or cast-in-place columns; (3) the bent longitudinal reinforcement causes the axial load bearing capacity of precast concrete columns to be 4.2%–12.3% lower than that of a similar cast-in-place column; (4) reducing the stirrup spacing has little effect on a precast column’s axial load bearing capacity and ductility; (5) when using Chinese and American codes to predict the axial load bearing capacity of the column, the predicted value should be multiplied by a reduction factor.

To study the residual performance of the welded hollow spherical joint after exposure to high temperatures. A total of 12 welded hollow spherical joint specimens are heated to six different preselected temperatures and subsequently air-cooled and water-cooled to the ambient temperature. Axial compressive tests are thereafter performed until the joints are damaged. The displacement characteristics, strain development, failure modes, stiffness, ductility, and load bearing capacity of specimens are investigated. The results show that the mechanical properties of spherical joints are considerably affected by the temperatures and cooling methods. Under the air-cooling condition, both the stiffness and compressive load of spherical joints decrease with an increase in the exposed temperature, and the ductility increases considerably. Under the water-cooling condition, the stiffness and ductility of spherical joints decrease with the increase in exposed temperature. The yield and ultimate loads decrease when the temperature is up to 500 °C and then gradually increase when the temperature exceeds 500 °C.

To investigate the effects of the height–thickness ratio (β) on the mechanical properties and stability coefficients ([Formula: see text]) of interlocking compressed earth block (ICEB) masonry members under axial compression, four groups of specimens with different β of 3.75, 6.75, 11.25, and 14.25 were tested, thereby assessing their stress process, failure mode, compressive strength, and in- and out-of-plane deformations. All the specimens underwent brittle failure under axial compression: the compressive strength was found to decrease in a range from 5.6% to 43% with increasing β, whereas the initial stacking defects and the in- and out-of-plane deformations increased. The specimens became less stable, and we noticed that the overall damage was caused by strength failure and not instability failures. Because the stability coefficient of ICEB-based masonry components cannot be calculated as those of more conventional brickwork, we combined our results with well-established masonry design guidelines and derived an interlocking improvement coefficient. Finally, we proposed a formula for calculating the axial compression stability coefficient of ICEB masonry that can provide a useful reference for subsequent research on ICEB walls.

Reinforced concrete (RC) walls subject to in-plane lateral loads are essentially subject to axial compression and tension forces in the respective end regions of the wall. The tension forces initially result in elastic tensile stresses in both the concrete and longitudinal reinforcement. Cracking occurs after the maximum tensile stress of the concrete has been exceeded and results in the reinforcement providing the sole tensile resistance at each crack location. The mechanical interlock between the reinforcement and concrete means that a portion of the tensile stress in the reinforcement at each crack is transferred back into the concrete between adjacent cracks. This mechanism stiffens the concrete in tension and is referred to as tension stiffening. This paper presents a generalised tension stiffening model developed for limited ductile (i.e. lightly confined) RC walls. However, it is also applicable for lightly confined RC elements generally. The model was validated against 14 boundary element prism specimens subject to cyclic loading, with very good correlation observed between the theoretical model and the experimental results. This model can easily be adopted into a sectional analysis procedure to account for tension stiffening in both the elastic and inelastic regions of response in an RC wall.

Timber infilled steel tubular (TIST) columns can be a promising alternative to the concrete infilled steel tubular (CIST) columns, particularly for the lightly loaded prefabricated structures, as timber is lighter and more sustainable material than the conventional concrete. However, limited research studies were dedicated to investigate the structural behaviour of TIST columns. Therefore, in this study an attempt has been made to investigate the parameters that influence the compressive behaviour and to develop appropriate design guidelines through finite element (FE) analyses of TIST columns. A three-dimensional FE modelling technique of TIST has been developed and validated with available experimental results. The developed model considered the steel tube induced confinement on the strength and orthotropic characteristics of timber as well as contact interaction between steel and timber. The validated modelling technique has been extended to parametrically (120 FE models) study the compressive behaviour of TIST columns varying parameters such as strength properties of steel and timber, thicknesses of steel tube, and cross-sectional shapes. The analyses reveal that the TIST columns can be used on par with CIST columns. The calculated strength and ductility indices reveal that the maximum strength and ductility enhancement up to 60% and 65% can be achieved with TIST. Further, the parametric analyses results have been used to verify suitable design formulations for TIST column, subsequently the design formations that are similar to CIST columns can consciously be extended to design the TIST columns.

Based on the reasonable determination of material constitutive relationship and interaction model between concrete and steel tube, a finite element model of T-shaped stiffened concrete-filled steel tube (TSCFST) stub column exposed to uniform fire was established, and model reliability was verified. Through the FE model, the working mechanism of the model in the whole process of loading was analyzed in detail. In the process of axial compression, the load distributions of steel tube and concrete, and the interaction between steel tube and concrete were discussed. This paper analyzed the effects of the main factors on residual bearing capacity of TSCFST stub columns, and put forward the calculation formula of the residual bearing capacity of TSCFST stub columns after uniform fire exposure.

High-strength concrete can effectively reduce the cross-sectional size, increase space usage, and cut material costs. To analyze the mechanical properties of high-strength concrete vertical members, various confinement models have been proposed to define the ties-confined concrete stress–strain relationship. However, most existing models are divided into ascending and descending segments. These are continuous but not derivable at the peak point, which does not facilitate numerical calculations. Moreover, these models have a large number of parameters that are mostly obtained based on the fitting of experimental data, which may also lead to the limited applicability of the models. In this study, existing confinement models for high-strength concrete under axial compression are reviewed, and the differences between the models are discussed. Based on the results of normal triaxial experiments on high-strength concrete and the test data from other studies on ties-confined concrete columns, the effective confinement coefficient and empirical formula of ties strain at the peak stress of confined concrete are proposed. A confinement model is proposed based on the continuous derivable function, and it is validated based on the available experimental data. Results show that the proposed model can reflect the stress–strain relationship of the test specimens more simply while keeping the basic accuracy with other models.

This paper presents the experimental results of concrete-encased-steel filled CFRP (carbon fiber reinforced polymer) tube (CSFCT) cylinders under monotonic axial compression. In this experiment, the prestress produced by the expansion agent was applied to the self-stressing concrete-encased-steel filled CFRP tube cylinders. The experimental parameters included the prestress, the layers of CFRP (1, 2, 3 layers) and the dimensions of section steel. It is aimed to investigate the influence of these parameters on the behavior of concrete-encased-steel filled CFRP tube cylinders under axial compression. Test results showed that compared with the non-prestressed test specimens, the application of prestress in self-stressing cylinders eliminates the stress lag of CFRP, makes the utilization ratio of CFRP higher, and improves the standard ultimate load, intercept load and inflection load. Meanwhile, the axial compression behavior of columns was improved with the increase of CFRP layers regardless of the prestress. The results also indicated that CFRP has more efficient confinement effect on small-cross sectional area section steel compared with large one. According to the test results, on the basis of the existing theoretical model, considering the influence of initial prestress and section steel, the calculation models of the inflection load and ultimate axial strain were modified. Finally, the stress-strain model of CSFCT cylinders with high accuracy was developed.

In this study, the co-effects of steel fibers and FRP confinement on the concrete behavior under the axial compression load are investigated. Thus, the experimental tests were conducted on 18 steel fiber-reinforced concrete (SFRC) specimens confined by FRP. Moreover, 24 existing experimental test results of FRP-confined specimens tested under axial compression are gathered to compile a reliable database for developing a mathematical model. In the conducted experimental tests, the concrete strength was varied as 26 MPa and 32.5 MPa and the steel fiber content was varied as 0.0%, 1.5%, and 3%. The specimens were confined with one and two layers of glass fiber reinforced polymer (GFRP) sheet. The experimental test results show that simultaneously using the steel fibers and FRP confinement in concrete not only significantly increases the peak strength and ultimate strain of concrete but also solves the issue of sudden failure in the FRP-confined concrete. The simulations confirm that the results of the proposed model are in good agreement with those of experimental tests.

Reactive powder concrete-filled steel tubes (RPCFSTs) have become an important research target in recent years. In engineering applications, RPCFSTs can provide superior vertical components for high-rise and tower buildings, thereby enabling developers to provide more floor space. However, this type of composite structure is prone to inelastic outward local buckling. The use of carbon fiber reinforced polymer (CFRP) wrapping to suppress such local buckling has shown great potential in limited test results. This paper presents experimental results concerning the axial compression of CFRP-confined reactive powder concrete-filled circular steel tubes (CF-RPCFSTs). We included 18 specimens in our experimental investigation, varying the number of CFRP layers, steel tube thickness, and RPC strength. According to our test results, CF-RPCFSTs exhibit compression shear failure and drum-shaped failure. The CFRP wrap can effectively enhance bearing capacity and postpone local buckling of the steel tube. In addition, three-layer CFRP-confined RPC-filled thin-wall steel tubes are suitable for engineering. We also propose a model to calculate the bearing capacity of CF-RPCFSTs. Compared to the existing model of CFRP-confined concrete-filled steel tubes, the results obtained using the proposed model are in good agreement with our experimental results.

For an in-depth understanding of the seismic behavior of shaped columns, a kind of T-shaped prefabricated special-shaped concrete-filled steel tubular with rectangular multi-cell columns was proposed in this paper. Furthermore, three specimens of full scale were designed and produced for low cyclic reversed loading and their failure morphology, hysteresis curve and P-Δ curve were obtained. The experimental results showed that the failure of the specimen was the bulking and cracking of the steel tube at the bottom of column along the loading axis, the powdery concrete dropped and finally the specimen failed to work. In addition, ABAQUS was used to perform finite element simulation on the three specimens in the experiment to verify the rationality and feasibility of the simulation. In this paper, by changing the axial compression ratio, concrete grade, steel grade, section height to thickness ratio and loading direction, the P-Δ curve, stiffness degradation, ductility and energy dissipation capacity of models under different parameters were analyzed for seismic performance. The simulation results showed that higher axial compression ratio leads to lower ultimate bearing capacity and ductility. With the increase of concrete grade, steel grade and section height to thickness ratio, the ultimate bearing capacity of the model increased but the ductility decreased. The shaped column specimens loaded in the 45° direction have higher bearing capacity, better ductility and seismic performance.

One effective method of reducing the cement content and carbon footprint so as to produce eco-concrete is to add limestone fines to replace an equal volume of cementitious paste. This method is herein applied to the concrete infill of concrete filled steel tubes (CFSTs). To study the properties of the eco-concrete so produced and the effects of using such eco-concrete on the axial performance of CFSTs, circular steel tubes infilled with such eco-concrete or conventional concrete had been tested under axial compression. The steel tubes were of grade S355 and had diameters ranging from 88.9 to 168.3 mm, whereas the concrete infills had water/cement ratio of 0.35–0.55, and limestone fines content by concrete volume of 8%. The results revealed that at same water/cement ratio, the eco-concrete generally had higher compressive strength and the CFSTs infilled with the eco-concrete had better axial performance. However, at same concrete strength level, the CFSTs infilled with the eco-concrete had similar axial performance. Lastly, the test results were compared with predictions by the existing design equations in various codes and it was found that the existing design equations may also be applied to CFSTs infilled with such eco-concrete.