Search

Steel–concrete hybrid towers have been proposed for onshore tall wind turbine tower installations. Their bottom sections are built with concrete and top sections with steel. The primary advantages of such hybrid towers include construction using low-cost durable material and avoidance of transport barriers associated with all-steel towers. In this study, a set of design constraints governing the geometry of hybrid towers was proposed to determine the optimal combination of concrete and steel sections. The primary constraint in tower design involves avoiding resonance because a resonant response can significantly damage the tower and trigger turbine fault conditions. A sensitivity analysis was conducted to explore the correlation between the natural frequency and geometry of a tower. The results demonstrated that an increase in the proportion of concrete can lead to a pronounced effect on the first modal frequency of taller towers. Additionally, geometric optimisation was performed on a 160 m tall tower. This resulted in a 12.7% reduction in the total cost compared with that of the initial design.

With the development of wind power energy, the steel-concrete hybrid tower has been gradually popularized as the onshore tall wind turbine tower. To avoid the resonant response that brings violent damage to the wind turbine tower, the fundamental frequency of the hybrid tower must be carefully analyzed. This study develops a closed-form solution of the fundamental frequency of the hybrid tower, where the abrupt changes of cross-section and material properties, the effect of prestressing, and the mass and rotary inertia of the wind turbine are taken into account. It provides an effective way to obtain the fundamental frequency in the preliminary design of the hybrid tower. The effectiveness of the proposed solution is validated by comparing it with the results of finite element analysis, showing good agreement. By using the proposed solution, a parametric analysis is conducted to investigate the variation rules of the fundamental frequency to the design parameters. It indicates that with the variation of the proportion of the concrete/steel segments, the correlations between the fundamental frequency and the design parameters also change significantly. The parametric analysis conducted herein may provide instructive guidelines to adjust the parameters in the preliminary design of the hybrid tower.

Carbon fiber reinforced polymer confined concrete-filled steel tube (CFRP-CFST) columns are having promising utilization in offshore structures, which are usually subjected to the combination of axial forces, bending moments, and torsional moments. This paper thus presents a finite element (FE) study on CFRP-CFST columns under combined compression-bending-torsion load. The comprehensive FE modelling was established and then validated by the experimental data. Analysis of typical failure modes, load-deformation relations and full-range behavior was performed based on the FE simulation. Meanwhile, parametric analysis was conducted to reveal the sensitive parameters as well as their influence on the structural behavior and ultimate capacity of CFRP-CFST columns. Finally, correlation relations which can reasonably characterize the coupled ultimate capacity of columns were obtained and validated. Correspondingly, simplified design formulae for predicting the ultimate capacity correlation of CFRP-CFST columns under compression-bending-torsion load were proposed.

In this article, three hot-rolled steel combined short columns and a pure steel short column under eccentric load were tested. The failure modes and load–displacement curves of the specimens under eccentric load were reported. A finite element model was developed and validated against the experimental results, and good agreement was achieved in terms of failure modes, bearing capacity and load–displacement curves. Upon validation, a series of finite element models were employed for the parameter analysis over the parameter of concrete strength (30–120 MPa) and steel strength (235–420 MPa). The finite element parameters analysis results showed that the steel strength has limited effect on the reduction coefficient (1 + η) of the ultimate bearing capacity of specimens, whereas the reduction coefficient (1 + η) of the ultimate bearing capacity of specimens decreases gradually as concrete strength increases. Based on the finite element parameter analysis results, the N–M correlation curve and a simplified design method for the reduction coefficient (1 + η) of the ultimate bearing capacity of hot-rolled steel combined short columns under eccentric load are proposed. Good agreement is achieved between the design method and finite element analysis results, and the prediction of the design method is accurate and consistent.

The buckling-restrained braces (BRBs) are widely applied in reinforced concrete frames (RCFs) to improve their performance under seismic loading. A procedure for designing such structures based on stiffness ratios was developed. The stiffness ratio was assumed to decrease gradually from the bottom story to the roof. The intermediate stiffness ratios were defined by linear interpolation. A step-by-step design procedure was presented. Three structures with 5, 10, and 15 stories were designed using the procedure and considering three seismic intensity levels. Linear time analysis showed that the stiffness ratio reduced along structural height had no significant effect on the inter-story drift ratio (IDR) of low-rise structures. The nonlinear time history analysis was performed to assess the structural seismic performance. On the basis of the analytical results in terms of the elastic and inelastic IDRs, reinforcements, hysteretic energy ratios of BRBs and structural damage, recommended range of stiffness ratios are proposed for various structures and design seismic intensities.

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

This paper presents a time-varying model-based method for estimating earthquake-induced displacement responses of building structures using limited acceleration data. First, a time-varying ...

Concrete-filled steel tube (CFST) columns have been widely used in the construction industry because of their excellent compression capacity and torsion resistance. Regarding traditional CFST columns, the H-CFST column with an additional H-section steel member embedded in the core concrete provides improved fire and compression resistance. In this study, the seismic performance of nine H-CFST columns under cyclic torsional and compression–cyclic torsional loads was experimentally analysed. In the experiments, the failure mode, torque versus torsional angle hysteresis, torque versus torsional angle skeleton, torsional stiffness degradation, and energy dissipation capacity were determined. The hysteretic curves of the H-CFST columns under torsion were relatively plump in shape and exhibited no ‘pinching’ phenomenon, and the torsional stiffness of the H-CFST columns under unloading and reverse loading was approximately equal to the initial torsional stiffness. In addition, the applied compression had remarkable effects on the torsional capacity, torsional ductility, torsional stiffness, and hysteretic loop energy dissipation of the H-CFST columns. The shear capacities of the steel and concrete under normal stress or combined normal and shear stress were determined based on the latest theories and test results. Moreover, design method for the determination of the torsional capacity of H-CFST columns under compressive torsion is proposed based on the test results, and the theoretical contribution ratio of the H-section steel, steel tube, and concrete in the H-CFST columns to the torsional capacity was determined.

Under the action of complex earthquake loads, the elastic-plastic local buckling of a concrete-filled steel tubular column will most likely occur in the steel tube, which is difficult to be simulated using the traditional fiber beam-column finite element model. In this paper, 30 steel specimens with two strength grades, Q235 and LYP160, were prepared and tested considering various cyclic loading paths to obtain the hysteretic stress-strain relations and the elastic-plastic buckling behavior of steel material, aiming to develop an effective uniaxial constitutive model of steel material considering elastic-plastic buckling. Based on the available Legeron Model, Gomes and Appleton Model (GA Model), and Dhakal and Maekawa Model (DM Model) for determining the stress-strain relation of steel material considering the elastic-plastic buckling behavior, a comparison analysis was made between the test results and the predicted results. It is found that the buckling behavior of the steel in compression after yielding cannot be simulated well by Legeron Model; the compressive buckling stress and compressive strength of the steel with buckling behavior predicted by GA Model agrees well with the test results; and the unloading stiffness of the steel in tension and compression can be well predicted by DM Model.

Carbon fibre reinforced polymer material has many advantages, including high strength, light weight and good durability, resulting in good performance when it is used in concrete structures; however, the construction procedures of concrete columns confined by a CFRP tube are very complicated, leading to a relatively high cost. Therefore, CFRP-steel composite tubed concrete columns are suitable for application in concrete structures because of their excellent mechanical properties and convenient construction. In this paper, the axial static mechanical behaviour of circular CFRP-steel composite tubed concrete stub columns was investigated, including an experimental study and a theoretical analysis. Based on investigation of the strain efficiency of CFRP material, the calculation methods for the axial ultimate loading capacity of circular CFRP-steel composite tubed concrete stub columns were compared, and recommendations for practical design were provided.

In order to study the mechanical behavior of steel tube confined reinforced concrete (STRC) columns under combined compression-bending-torsion, an experimental investigation was conducted. The load–deformation hysteretic curves and the strain distribution law of steel tubes under pure torsion, bending-torsion and compression-bending-torsion loads were obtained. Results show that a ‘pinch’ effect appeared in the load–deformation hysteretic curves of STRC under pure torsion and bending-torsion loads, however, this was not noticeable for specimens under compression-bending-torsion load. When the axial compression ratio was relatively small, STRC columns under compression-bending-torsion load showed higher bending capacity and torsion capacity than that under bending-torsion load, as well as good energy dissipation capacity. Furthermore, the strain of the steel tube increased linearly with the load, and the corresponding stress was always below the yield strength. Based on the test results, the enhancement of the bending and torsion capacities of reinforced concrete columns caused by steel tubes, and the reduction of the bending capacity of STRC columns caused by torque were analyzed.

This paper proposes the concept of resilient friction beams (RFBs) and investigates how RFBs can be economically implemented in moment-resisting frames (MFs) to improve seismic performance . The RFBs mainly consist of two T-shaped beams and four cap plates, resulting in a cost-effective configuration that employs less steel than previous self-centring beam designs. The mechanics of the RFB are first explained, and the equations predicting its responses are given. Two numerical methods are presented for modelling RFBs. The results from a finite element model (FEM) confirmed the sliding behaviour of the RFBs. Then a simplified spring model was created for performing nonlinear dynamic analysis. Finally, a set of steel framed buildings with different heights were designed and computationally subjected to two seismic levels of ground motions. The results suggest that residual interstory drift , peak base shears and peak absolute accelerations can be effectively limited by providing RFBs at the lower storeys.

Experimental investigation was conducted on large-section extruded aluminum alloy columns of I-section and rectangular hollow section (RHS). Altogether seven columns with different slenderness ratios were comprised. The failure modes and stability resistance as well as load-displacement responses were identified. It was found that all tested specimens failed in flexural buckling. An extensive parametric analysis on 180 specimens was carried out with general FEA software ANSYS to evaluate the reliability level of the current design specifications including American aluminum design manual, Eurocode 9 and Chinese code GB 50429. The design stability resistance advised by Eurocode 9 and Chinese code GB 50429 is conservative, while that of American aluminum design manual slightly overestimates the practical stability resistance. Based on the parametric analysis results, a new design method was proposed to improve the design accuracy.

Tapered Concrete-Filled Double Skin Steel Tubular (CFDST) columns have been commonly used in structures. To report further information, it is necessary to perform more studies on the structural behaviour of tapered CFDST columns, especially for those with high hollow ratios. This paper thus conducted an investigation on the tapered CFDST stub columns under axial compression. Specimens with varied tapered angle, hollow ratio and tubes' thickness were tested, and then typical failure modes, load versus displacement relations as well as strain development were revealed. Validated finite element models were given to further analyse the columns' structural mechanisms including the stress distributions, the interaction between the steel tubes and the sandwiched concrete, and the influence of main parameters. The ultimate strength of specimens was calculated tentatively using the methods in the existing design guidelines, and their accuracy and applicability for the tapered CFDST stub columns with high hollow ratios were preliminarily evaluated. A simplified method was suggested to predict the ultimate strength based on one of the guidelines, and the predictions show reasonable agreement with the test results.

The compressive buckling behaviour of extruded aluminium alloy I-section columns with fixed-pinned end conditions has been experimentally and numerically investigated in this study. A total of 11 column tests, involving two heat-treated aluminium alloys – 6061-T6 and 6063-T5, were carried out to acquire the compressive buckling strengths. Prior to the column tests, material properties of the two aluminium alloys were determined from tensile coupon tests, while the initial local and global geometric imperfections were separately measured by means of experimental techniques. By using the ABAQUS software package, finite element (FE) models that could account for material non-linearity and initial geometric imperfections were developed. The FE models were further validated against the test results, enabling reliable simulation of the compressive buckling behaviour of the tested columns with fixed-pinned end conditions. Based on the obtained test and numerical results, the calculation methods in the current design standards, including the European, Chinese, American and Australian/New Zealand specifications, were all assessed. It was shown that the design provisions in all the four standards provided relatively conservative strength predictions, especially for the aluminium alloys with more pronounced strain hardening capacity.

With constrained plates on both sides of steel coupling beam web, the continuous strengthening can be achieved in steel coupling beam subject to cyclic shear loading with web shear yielding failure. Compared to traditional steel coupling beam which sets stiffeners on the web, the local buckling of the new type of steel coupling beam with shear yielding will not occur, before the steel web reaches its ultimate shear strain, resulting in excellent energy dissipation capacity. Eight quasi-static tests on buckling constraint steel coupling beams with shear yielding had been carried out to study the impact of various constraint manners on seismic behavior of this type of steel coupling beam. Tests results showed that all the test specimens realized shear yielding and strengthening of bearing capacity, and major failure mode included weld joint fracture between flange and endplate and failure of constrained plate. Average over strength factor of the test specimens was 1.38, above 1.1, the minimum requirement of Code for Seismic Design of Building Structures. Among them, the over strength factor of test specimens which used 50 mm-thick reinforced concrete constrained plates and 25 mm-thick wooden constrained plates exceeded 1.5. Test specimens with different constraint methods showed similar yield shear strain. While test specimens without constrained plates showed the minimum ultimate shear strain, test specimens with 25 mm-thick wooden constrained plates showed the maximum, approaching the ultimate shear strain of the web’s steel in material property test.

This analysis was carried out based on the smeared crack model and plasticity damage model in general finite element program ABAQUS. Comparison and analysis were made on the key factors of concrete constitutive models that have effect on the static mechanical behavior of structural members. Then the mechanical behavior of reinforced concrete members and steel-concrete composite members under monotonic loading and cyclic loading were simulated using various concrete constitutive models. Both the smeared cracking model and the plasticity damage model could accurately simulate the macroscopic response of flexural concrete members or flexural composite members subjected to monotonic load, and the smeared cracking model was more accurate in simulating the cracking behavior of concrete, applicable for analyzing the stress situation of concrete during stress-strain space constantly changing after cracking. Besides, the plasticity damage model could be adopted to simulate the stress behavior of concrete structures or composite structures under the action of cyclic load. The two models could not accurately simulate the whole process of stress behavior of concrete in two-dimensional or three-dimensional stress state.

Under gravity and the horizontal earthquake load, the eccentric compression and torsion combined action will be produced in the piers of curved girder bridges and the main arch of arch bridge. In order to study the torsion behavior of concrete filled steel tube columns subjected to eccentric compression, tests were carried out on eight specimens of concrete filled steel tube column subjected to static pure torsion, cyclic pure torsion and eccentric compression-torsion cyclic load. The results of tests have indicated that, the hysteresis curve of concrete filled steel tube column subjected to torsion cyclic load was plump; no pinch phenomenon can be found; the damage and degradation degree of the strength and stiffness of specimens is lower; and high energy dissipation capacity can be achieved. The stiffness degradation of the specimens with square section subjected to eccentric compression-torsion cyclic load is more obvious. The eccentric compression has led to weaken of the energy dissipation capacity of the square section concrete filled steel tube column. Under the ultimate state, the wave angle of steel tube was affected by the eccentric compression.

In this paper, a new type of steel section is proposed comprising adjacent H-sections linked together by intermediate steel plates welded along their flanges. Experiments on three hot-rolled steel built-up H-sections and five columns infilled with concrete are conducted, with results showing that both variants having much better ductility compared to conventional columns (i.e. hollow section columns and concrete filled steel tube (CFST) columns). Experimental results showed that the bearing capacity of the built-up hot-rolled steel hollow section column improved by 45.1% to 55% after it was filled with concrete. A finite element software ABAQUS is used for parametric study. The newly developed finite element models were validated against test results in terms of failure modes and load-displacement curves. A total of 482 numerical results, 132 hot-rolled steel built-up section columns and 350 concrete-filled built-up section columns, have been generated. Based on the experimental and numerical results, the compressive behaviours of hot-rolled steel built-up section columns and concrete-filled built-up section columns are studied. A new design method for the compression capacity of these two types of columns is proposed. It is found that the newly proposed design method could provide accurate and consistent predictions – the mean value of experimental to predicted results are 0.963 for hollow section columns (with coefficient of variation being 0.061) and 1.04 for composite section columns (with coefficient of variation being 0.043).