Steel-concrete Hybrid Research Articles

Computational Study of Steel–Concrete Hybrid Wind Turbine Tower Seismic Performance

ABSTRACT The seismic capacity of wind turbine support towers is of significant concern as wind power provides an increasing proportion of the world’s electricity supply. This study presents a computational study on the seismic performance of steel-concrete hybrid towers (SCHTs). The equations that govern the tower-free vibration responses are derived based on Euler-Bernoulli beam theory. The modal results are used in the response spectrum analysis to evaluate the higher-mode effects in the SCHTs. Then, a cantilever beam model capable of capturing the joint opening and closing was developed for structural analyses and calibrated against finite element models. Finally, dynamic time history analyses were conducted for different SCHTs under far-field (FF) and near-fault (NF) earthquakes. These analyses showed that the second mode of SCHTs is more significant for the shear force diagram. Dynamic amplification causes the mean peak base moment from the FF set and NF set to be 1.30–1.45 and 1.37–1.57, respectively, greater than the design spectrum using the same 5% damping.

Closed-Form Solution of Fundamental Frequency of Steel-Concrete Hybrid Wind Turbine Tower

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.

Investigation on shear behavior of studs and PBL shear connectors in steel-concrete hybrid bridge girder

Due to the excellent properties of concrete and steel, steel–concrete composite structures have a wide range of applications in civil engineering. The most common shear connectors are the stud and perfobond rib (PBL) shear connectors, and there are a lot of studies on the shear behavior of stud and PBL shear connectors, respectively. But fewer studies were conducted on the combined shear behavior of both. This research presents experimental and numerical studies on the shear behavior of stud and PBL shear connectors. Test results show that the primary failure of the specimens is that the studs were sheared off, accompanied by concrete damage. The number of rows of shear connectors and the diameter of the transverse rebar can significantly affect the shear capacity. In contrast, the concrete dowel diameter has a limited impact on the shear capacity. Based on the validated finite element (FE) analysis, the effects of concrete strength, perforated plate thickness, and stud diameter on the shear capacity were parametrically investigated. The test and FE analysis results are compared with the existing equations of stud and PBL shear connectors. A combination most consistent with test and FE analysis results with discrepancies less than 5% is suggested for predicting the shear capacity of stud and PBL shear connectors.

The mechanical behavior of a long-span steel-box girder during the hoisting process

A steel-concrete hybrid continuous rigid frame bridge was used for the Jiahua bridge. The span layout is 138 m + 252 m + 110 m. The steel box-girder, 90 m in length, was arranged in the middle of the mid-span. During the construction process of this bridge, the adopted method for the large steel box girder section is the whole lifting process, which is not common for this type of bridge. This study investigates the mechanical behavior of the steel-concrete joint through finite element analysis, aiming to understand the stress distributions of the long-span steel box girder in several integral hoisting conditions, which can be a reference to the construction of similar steel box bridges. The results show that the bottom plate stress of the mid-span section has a linear relationship with the lifting acceleration; the top plate stress of the mid-span section has a cubic nonlinear relationship with the lifting acceleration.

Influence of coupling ratio on seismic behavior of hybrid coupled partially encased composite wall system

SummaryPartially encased composite (PEC) members are novel composite members that efficiently exploit the advantages of mechanical properties of concrete and steel. However, the application of PEC members is limited to low‐ and mid‐rise buildings. To overcome this limitation, a study was conducted to assess the seismic performance of a newly proposed steel–concrete hybrid coupled wall consisting of PEC wall piers coupled by means of steel beams. Parametric analysis was conducted to investigate the elastic coupling ratio (CRelastic) and the way of changing CRelastic on the seismic behavior of the hybrid coupled PEC wall. The results showed that the CRelastic was the main parameter that affected the seismic performance of the wall. The way of changing CRelastic had little influence on the trend of the energy dissipation capacity and strength reservation of the wall. The failure mode and the development of plastic hinges of the wall were also not affected by the way of changing CRelastic. Both too large and too small CRelastic were detrimental to the seismic performance of the wall. To form an ideal plastic hinge development mode and experience good seismic performance, it is suggested that the reasonable range of CRelastic for the wall was 60%–70%.

In-situ testing and model updating of a long-span cable-stayed railway bridge with hybrid girders subjected to a running train

This study investigates the dynamic responses of a long-span cable-stayed railway bridge with steel–concrete hybrid girders in different train load scenarios. The investigated scenarios included driving and braking of running trains. The bridge was instrumented with different types of sensors to measure strains, displacements, and accelerations during train load testing. Based on the measurement results, this study evaluated the effects of train speed on the vertical and transverse accelerations, impact factor, derailment coefficient, and wheel unloading rate, which are critical parameters that affect safety and riding comfort. Assessment results revealed that the bridge had adequate dynamic behavior to ensure safe operation and riding comfort of the train. Based on test data, a finite element model was developed, and a finite element model updating framework was proposed to improve the prediction accuracy. This study provides real-life test data and an assessment tool for promoting design and evaluation of cable-stayed railway bridges.

Hybrid Wind Turbine Towers Optimization with a Parallel Updated Particle Swarm Algorithm

The prestressed concrete–steel hybrid (PCSH) wind turbine tower, characterized by replacing the lower part of the traditional full-height steel tube wind turbine tower with a prestressed concrete (PC) segment, provides a potential alterative solution to transport difficulties and risks associated with traditional steel towers in mountainous areas. This paper proposes an optimization approach with a parallel updated particle swarm optimization (PUPSO) algorithm which aims at minimizing the objective function of the levelized cost of energy (LCOE) of the PCSH wind turbine towers in a life cycle perspective which represents the direct investments, labor costs, machinery costs, and the maintenance costs. Based on the constraints required by relevant specifications and industry standards, the geometry of a PCSH wind turbine tower for a 2 MW wind turbine is optimized using the proposed approach. The dimensions of the PCSH wind turbine tower are treated as optimization variables in the PUPSO algorithm. Results show that the optimized PCSH wind turbine tower can be an economic alternative for wind farms with lower LCOE requirements. In addition, compared with the traditional particle swarm optimization (PSO) algorithm and UPSO algorithm, the proposed PUPSO algorithm can enhance the optimization computation efficiency by about 60–110%.

Compressive behavior of large-size square PEN FRP-concrete-steel hybrid multi-tube concrete columns

Fiber-reinforced polymer (FRP)-concrete-steel hybrid multi-tube concrete column (MTCC) is a new type of composite column and comprises a number of steel inner tubes, an FRP external tube and concrete fillings for the space inside all the tubes. This paper presents a series of experimental tests on four large-size square PEN (polyethylene naphthalate) FRP-MTCCs, of which the PEN fibers were extracted from recycled plastic bottles. The parameters of interest include the FRP thickness and the steel tube configuration. The experimental results showed that the large-size square MTCCs with PEN FRP exhibited excellent ductility due to the effective confinement provided by PEN FRP jacket and steel tubes. A prediction method for the square PEN FRP-MTCCs has been developed in the present study to consider the unique characteristics of the column and is able to produce reasonable predictions for the experimental results. This study serves to present an innovative alternative in an environmentally friendly way that can replace the conventional bridge piers in coastal and salina regions.

Geometric optimisation analysis of Steel–Concrete hybrid wind turbine towers

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.

Experimental investigation on the seismic behaviour of innovative self-centring precast steel-concrete hybrid frames

An innovative self-centring precast steel-concrete hybrid (SPH) frame was proposed. The proposed SPH frame was assembled with reinforced concrete (RC) columns and prefabricated steel-concrete hybrid (PH) beams using steel end plates and high-strength bolts. The RC columns consisted of a traditional RC section and an unbonded post-tensioned (PT) screw-thread steel (STS) bar, and the PH beam was composed of two steel beam ends, a prefabricated RC beam unit and four unbonded PT strands. The self-centring ability of the structure system was mainly provided by the PT steel reinforcements; the energy dissipation capacity was mainly provided by the bolted web friction devices (WFDs) applied to the beam and the plastic deformation of the steel beam ends. To examine the seismic behaviour of this innovative structural system, cyclic tests were conducted on two SPH frames and one non-prestressed precast steel-concrete hybrid (NPH) frame. By analysing failure modes, hysteretic loops, skeleton curves, energy dissipation, displacement ductility ratios, stiffness degradation and the relative self-centring efficiency (RSE), the effects of the initial prestress, the pretorque of the high-strength bolts at the WFDs and the construction measure at the column base were thoroughly assessed. The test results indicated that the proposed noncontact oil jack prestressing technique used in the PH beams was reliable; during the testing process, gap opening and closing could be clearly observed at the interfaces between the RC beam unit and the steel beam end; the SPH frames exhibited better self-centring and energy consumption capabilities than the NPH frame; and the SPH frame exhibited a typical two-stage cyclic behaviour, namely, a self-centring stage and an energy consumption stage. In the self-centring stage (before the drift ratio of 2.0%), the SPH frame could effectively control residual deformation, and the RSE remained at approximately 85%; in the energy consumption stage (after the drift ratio of 2.0%), the SPH frame could effectively consume the absorbed energy. Based on the test results, a moment calculation method, which could distinguish the gap opening in the PH beam, was proposed, and the calculated results agreed well with the experimental results.

Seismic response analysis of steel–concrete hybrid wind turbine tower

The steel–concrete hybrid wind turbine tower is characterized by the concrete tubular segment at the lower part and the traditional steel tubular segment at the upper part. Because of the great change of mass and stiffness along the height of the tower at the connection of steel segment and concrete segment, its dynamic responses under seismic ground motions are significantly different from those of the traditional steel tubular wind turbine tower. Two detailed finite element models of a full steel tubular tower and a steel–concrete hybrid tower for 2.0 MW wind turbine built in the same wind farm are, respectively, developed by using the finite element software ABAQUS. The response spectrum method is applied to analyze the seismic action effects of these two towers under three different ground types. Three groups of ground motions corresponding to three ground types are used to analyze the dynamic response of the steel–concrete hybrid tower by the nonlinear time history method. The numerical results show that the seismic action effect by the response spectrum method is lower than those by the nonlinear time history method. And then it can be concluded that the response spectrum method is not suitable for calculating the seismic action effects of the steel–concrete hybrid tower directly and the time history analyses should be a necessary supplement for its seismic design. The first three modes have obvious contributions on the dynamic response of the steel–concrete hybrid tower.

Behavior and modelling of FRP-concrete-steel hybrid double-skin tubular columns under repeated unloading/reloading cycles

Fiber-reinforced polymer (FRP)-concrete-steel hybrid double-skin tubular columns (hybrid DSTCs) consist of an outer FRP tube, an inner steel tube and a concrete infill between the two tubes. Extensive research has been conducted on the monotonic behavior of hybrid DSTCs, but only a limited number of studies have examined their behavior under cyclic axial compression. In particular, no systematic experimental study has been conducted on hybrid DSTCs under repeated unloading/reloading cycles. This paper first presents a systematic experimental study on hybrid DSTCs under two types of loading schemes: (a) a single unloading/reloading cycle to evaluate the relationship between the unloading strain and the plastic strain; (b) repeated unloading/reloading cycles to investigate the effect of loading history. In the present study, hybrid DSTCs were prepared using filament-wound FRP tubes of a relatively large scale (up to 300 mm in diameter), and the experimental program covered a wide range of concrete strengths (from 40.9 MPa to 104.4 MPa). The systematic experimental study with extensive instrumentation allowed the cyclic stress-strain behavior of the concrete in hybrid DSTCs to be examined in detail, clarifying the cumulative effect of the loading history on both the stress deterioration and the plastic strain of the concrete. This paper also presents a detailed comparison between the test results and the predictions of an existing cyclic stress-strain model for FRP-confined concrete in solid columns, in terms of the repeated unloading/reloading cycles. The cyclic stress-strain model is shown to provide reasonably accurate predictions, and thus can be used together with a monotonic stress-stress model for the concrete in hybrid DSTCs to predict the complete cyclic stress-strain curve of such concrete.

Circular fibre-reinforced polymer (FRP)-concrete-steel hybrid multitube concrete columns: Compressive behaviour

This paper presents a study on circular fibre-reinforced polymer (FRP)-concrete-steel hybrid multitube concrete columns (MTCCs), which consists of an outer FRP tube, a number of inner small steel tubes to form a “steel wall” and concrete filled in the remaining spaces. The advantages of MTCCs include excellent axial load and deformation capacities, ease of construction, elimination/mitigation of difficulties in transporting and installing large steel tubes, and possibility of optimising the arrangement of the small steel tubes to improve structural performance. A total of 7 pairs of MTCCs, 4 pairs of concrete-filled FRP tubes (CFFTs), 4 pairs of concrete-filled steel walls (CFSWs) and 3 pairs of concrete-filled steel tubes (CFSTs) were tested in the present study, with the investigated parameters covering the thickness of FRP tube, the number and type of steel inner tubes, the type of concrete and status of the steel inner tubes. The test results lead to an in-depth understanding of the behaviour of MTCCs under axial compression. Furthermore, a comparison between the test results and predictions by a model previously proposed by the authors shows that the model can reasonably well predict the axial load–strain behaviour of MTCCs but largely underestimates the ultimate strain of the specimen. This model may be used for conservative design, while further investigation is needed for the development of a more accurate model.

Experimental evaluation of the shear capacity of perfobond strips with steel fiber-reinforced mortar in narrow joint structures

Appropriate transfer of the shear force of a perfobond strip used as a shear connector in steel concrete hybrid structures depends on the restraining effect around the strip, and hence, the arrangement of the surrounding reinforcements is very important to improve the restraining effect. However, when the perfobond strip is arranged in narrow joint structures and when the rapid construction is also required, reinforcements are undesirable on the site. An alternate method to improve the restraining effect around the perfobond strip is to use steel fiber-reinforced mortar (SFRM). This study aims to evaluate appropriately the shear capacity of a perfobond strip with SFRM without surrounding reinforcements for narrow joint structures. Assuming these conditions, pull-out tests were conducted, and the data obtained were considered along with the results of push-out tests conducted in the previous study of the authors. Based on the results of both test series, the impacts of various factors on the shear capacity of the perfobond strip was analyzed comprehensively. The results showed that the shear capacity of a perfobond strip with SFRM increases with the perforation diameter, SFRM compressive strength, volume content of steel fibers in the mortar, and dimensions of the mortar block around the perfobond strip. Moreover, the plasticization of the perfobond steel plate and the difference in boundary conditions between the push-out and pull-out tests also affect the shear capacity of the perfobond strip. An equation was proposed for evaluating the shear capacity of the perfobond strip with SFRM without any surrounding reinforcements for narrow joint structures. The shear capacity obtained using the proposed equation has high correlation with the experimental value for both push-out and pull-out specimens.

Research on Construction Control of Semi Hybrid Steel-concrete Comoposite Cable-stayed Bridge

Hong-shui river especially big bridge is a kind of semi hybrid steel-concrete comoposite cable-stayed bridge. The erection of Guizhou side span adopt the incremental launching construction method, which was composite beam; The erection of midspan adopt cable-stayed buckled method, which was composite beam; The erection of Guangxi side span adopt support frame casting in situ construction method, which was concrete π type girder. The paper focus on the characteristics of the asymmetrical structure forma and asymmetric construction method of Hong-shui river especially big bridge, discussing the key contents of construction monitoring, which can offer reference and consulting for related engineering.

Shear behavior of a perfobond strip with steel fiber-reinforced mortar in a condition without surrounding reinforcements

To sufficiently transmit the shear force of a perfobond strip shear connector in steel–concrete hybrid structures, the arrangement of the surrounding reinforcements is essential to improve the restraining effect around the perfobond strip. However, in cases of joint structures with small dimensions and rush work on site, because the arrangement of reinforcements in the joint is challenging, steel fiber-reinforced mortar (SFRM) can be used along with a perfobond strip to improve the restraining effect around the perfobond strip. This study investigates the shear behavior of a perfobond strip that uses SFRM without surrounding reinforcements. Push-out tests were conducted focusing on the effect of steel fibers inside the SFRM, SFRM compressive strength, perforation diameter, and dimensions of the mortar block around the perfobond strip. Findings of the study confirmed that the steel fibers inside the mortar contribute to the restraining effect around the perfobond strip, thus preventing a rapid drop in the shear force beyond the shear capacity of the perfobond strip. The shear capacity of the perfobond strip combined with SFRM increased with the perforation diameter, SFRM compressive strength, and dimensions of the mortar block around the perfobond strip. Several shear capacity evaluation equations proposed in previous studies are not applicable for evaluating the shear capacity of the perfobond strip that uses SFRM without surrounding reinforcements. Here, the shear capacity of the perfobond strip can be evaluated by considering the correlation between the experimental parameters of this study, but more test data are required.

Design optimization of steel–concrete hybrid wind turbine tower based on improved genetic algorithm

SummaryThe steel–concrete hybrid wind turbine tower is characterized by the lower part of the traditional steel tubular tower replaced with the concrete segment. The lateral stiffness will be improved obviously, and then, the excessive vibration of the steel tower can be solved effectively. Based on the improved genetic algorithm, an optimization program is built to consider the influence of materials, labor, machinery, and transportation on the construction cost of a steel–concrete hybrid tower for a 2.0‐MW wind turbine with a hub height of 120 m, in which the initial height of the concrete segment is 32 m. During the optimization process, design requirements of relevant specifications and industry standards are used as the constraints. The optimization variables include the bottom and top diameters of the tower, the wall thickness of each segment, the height of the concrete segment, and the area of the prestressed steel strand. By comparing the results of construction cost and structural capacity before and after optimization, it can be found that the steel–concrete hybrid wind turbine tower after optimization has the better structural stiffness and lower construction cost. The proposed optimization program can meet the design requirements and significantly improve the economic performance of the tower.

Characterization and optimization of a steel beam to RC wall connection for use in innovative hybrid coupled wall systems

Steel-concrete hybrid solutions with replaceable fuses as coupling elements and appropriately detailed composite connections have shown their efficiency to design safe and easily repairable earthquake-resisting structures. In this general framework, the behavior of a possible steel to concrete composite connection to be used in a recently suggested Hybrid Coupled Wall (HCW) system, consisting of a reinforced concrete shear wall coupled with steel side columns via dissipative steel shear links, is studied in this paper. The steel shear links are bolted to a steel profile either partly embedded or passing through the RC wall. The connection zone is designed in such a way that the damage always occurs in the steel shear links (fuses) prior to any damage in the RC wall in general and in the connection zone in particular. The emphasis lies therefore on the characterization of a suitable “steel link + embedded composite connection within the RC wall” configuration and on the evaluation of an appropriate embedment length allowing the concentration of seismic damage to the replaceable steel links. To this purpose, two joint configurations are designed based on a capacity-based approach, namely “partly embedded” and “completely passing through” steel beam, and are examined through detailed FE analyses. A parametric study is carried out to provide sufficient insight into the system in terms of strength, stiffness and local bearing strength, in view of validating the proposed design procedure.

The development of composite bridges with corrugated steel webs in China

The prestressed concrete girder with corrugated steel webs is one of the most promising steel–concrete hybrid structures applied to highway and railway bridges, owing to its excellent mechanical properties and efficient material utilisation. Composite bridges with corrugated steel webs (CBCSWs) have undergone rapid development in China since 2005, resulting in remarkable technical progress in many aspects. A state-of-the-art review of CBCSWs in China is presented. Based on data collected for over 90 CBCSWs built in China during the years 2005–2018, characteristics relating to bridge span, structural type and construction methods are comprehensively analysed. Some mechanical issues regarding the design and construction of typical CBCSWs are elaborated to understand fully their structural performance and promote their development. Furthermore, a few representative CBCSWs are expounded in relation to their innovative structural design and construction techniques; their respective characteristics are highlighted. Finally, several conclusions are drawn and future research directions are predicted: the CBCSW is a competitive bridge solution when 80–200 m main spans are required; advanced materials, innovative structure types and advanced construction methods making good use of corrugated steel web are the source of its development. The experiences in this study can serve as a useful base for constructing more excellent and impressive CBCSWs.

Pseudo-dynamic and cyclic loading tests on a steel-concrete vertical hybrid structure

This paper presents the experimental investigations on the seismic performance of a peculiar steel-concrete vertical hybrid structural system referred to as steel truss-RC tubular column hybrid structure. It is typically applied as the supporting structural system to house air-cooled condensers in thermal power plants (TPPs). Firstly, pseudo-dynamic tests (PDTs) are performed on a scaled substructure to investigate the seismic performance of this hybrid structure under different hazard levels. The deformation performance, deterioration behavior and energy dissipation characteristics are analyzed. Then, a cyclic loading test is conducted after the final loading case of PDTs to verify the ultimate seismic resistant capacity of this hybrid structure. Finally, the failure mechanism is discussed through mechanical analysis based on the test results. The research results indicate that the steel truss-RC tubular column hybrid structure is an anti-seismic structural system with single-fortification line. RC tubular columns are the main energy dissipated components. The truss-to-column connections are the structural weak parts. In general, it has good ductile performance to satisfy the seismic design requirements in high-intensity earthquake regions.