Concrete Tower Research Articles

Life cycle assessment of ultra-tall wind turbine towers comparing concrete additive manufacturing to conventional manufacturing

Wind power is a quickly growing renewable energy resource within the continental United States and is expected to continue increasing as more wind farms are installed onshore and offshore. As a part of this growth, larger turbines benefit from economies of scale from taller towers. However, the development of ultra-tall wind turbine towers is hindered by transportation restrictions which limit the diameter and weight of the prefabricated tower sections. One proposed solution to this problem is to employ concrete additive manufacturing to build ultra-tall wind turbine towers on-site. To evaluate the potential environmental impacts of this approach, this study performed a life cycle assessment comparing four prototype 7.5-MW wind turbine towers designed with a height of 140 m: a conventional tubular steel tower assembled using bolted connections, two 3D printed concrete towers additively manufactured on-site with normal-strength (35 MPa) or high-strength (78 MPa) concrete, and a 3D cast concrete tower with normal strength (35 MPa) concrete cast into concrete formworks additively manufactured with high-strength (78 MPa) concrete. The 3D cast concrete tower segments are manufactured off-site and assembled on-site. The life cycle assessment examined the impacts of differences in materials inventory, structural designs, manufacturing methods, maintenance schedules, and end-of-life options for the four towers. The results indicate that the material production stage dominates, contributing over 92% of the total CO2 emissions and 67–93% of the energy consumption of the four towers. Compared with the steel tower, the normal-strength 3D printed concrete tower has 23% lower total life cycle CO2 emissions but 29% higher energy consumption; the high-strength 3D printed concrete tower has 16% higher life cycle CO2 emissions and 64% higher energy consumption. Parametric studies were also conducted to examine the effects of cement content by weight, distance from the concrete plant to the tower construction site, the number of tower sections, rated tower life, and tower end-of-life recycling rate. The results indicate that reducing cement content in 3D printed concrete such as by incorporating waste or recycled materials can significantly reduce the life cycle environmental impacts of ultra-tall turbine towers.

Health monitoring of ultra high fiber performance reinforced concrete communication tower using machine learning algorithms

Within the last decades, the needed for communication towers has accelerated with the requirements for effective communication, especially for radio, radar, and television. The complexity configuration of the tower and limit access to the structure body especially inner part of the tower with hollow section is led the health monitoring of tower as the main challenging issue to maintenance during its function. The change of natural frequencies can be considered as one of the prevalent damage detection methods in structural assessment procedures. Therefore, the main aim of present research is to develop health monitoring system for Ultra High Fiber Performance Reinforced Concrete (UHPFRC) communication tower based on frequency domain response. Since the frequency data of tower is mostly noisy and interpreting of frequency in different modes in variant case of tower damage. The hybrid algorithm based on the Adaboost, Bagging and RUSBoost algorithms are implemented to identify the damage in the UHPFRC communication tower using frequency domain data. The training samples for the algorithm are obtained from a finite element simulation and full-scale experiment testing is also performed to generate the testing samples. The finite element simulation dynamic frequency results are verified through conducting a full-scale experimental test on 30 m height UHPFRC communication tower. For this propose, frequency Response Functions (FRF’s), for healthy and damaged structures were obtained by exciting of tower by an impact hammer and the acceleration response recorded by three accelerometers sensors attached in suitable positions. The developed hybrid algorithm to identifying the damage is tested and verified by considering the part of tower segments 2–3 and conducting experimental testing on the healthy structure as well as a damaged structure which caused using dynamic actuator. The testing results proved the accuracy of the developed optimized hybrid algorithm to identify damage in the tower structure in variant condition.

Influence of near-field ground motions and their equivalent pulses on nonlinear seismic response of intake-outlet towers and predicting based on artificial neural networks

Near-fault earthquakes with forward-directivity effects contain high energy and large amplitude velocity pulses. The nearby structures can be severely damaged by such pulses. This paper studies nonlinear seismic response of reinforced concrete intake-outlet towers subjected to forward-directivity near-field earthquake ground motions and their equivalent pulses. It also compares the responses under non-forward-directivity as well as far-field earthquakes. For this purpose, 72 forward-directivity near-field earthquakes, 120 non-forward-directivity near-field records, and 132 far-field records are selected to obtain statistically-scattered and reliable results. The tower-water-foundation interaction is considered in all analyses. The displacement, dissipated energy, tensile and compressive damage of the tower are determined employing detailed finite element simulation, and the obtained responses are thoroughly discussed. Additionally, an artificial neural network model is proposed to predict displacement and tensile damage of the intake tower. The results reveal that the mean seismic demand parameters of the tower under the forward-directivity and non-forward-directivity earthquakes are 3.8 and 2.7 times of those from the far-field earthquake, respectively.

An efficient model for solar radiation induced top displacement of steel-concrete composite bridge towers

The temperature effect caused by solar radiation significantly influences the stress state of bridges. Especially for ultra-high bridge towers, considerable deformation induced by solar radiation affects the safety of the structures. This research is conducted to evaluate the temperature deformation of a steel–concrete composite bridge tower where a sliding saddle is adopted. First, the temperature distribution pattern of the structure is analyzed. Second, based on the temperature distribution, an efficient model which can be applied to the long-term calculation is established, aiming at directly calculating the deformation results. Then, an outdoor experiment study is carried out to verify the temperature distribution and the results of sectional curvature. Finally, the efficient model is applied to calculate the annual bidirectional deformation. This method realizes the long-term temperature effect evaluation of the structure before construction, and the results can be referred to as guidance for the analysis of related types of structures.

Influence of system changes on closely spaced modes of a large-scale concrete tower for the application to structural health monitoring

AbstractConcrete steel towers are increasingly being used for onshore wind turbines. The lower part consists of separated segmented concrete rings connected with dry joints. Due to slight deviations from the axisymmetric cross-section, closely spaced modes occur. Therefore, the influences of small system changes on closely spaced modes, particularly the mode shapes, should be investigated to enable reliable vibration-based monitoring. In this context, the influence of imperfections due to the waviness of the dry joints requires attention. As no acceleration measurements on concrete towers considering small system changes have been performed so far, this has not yet been investigated. Therefore, an experiment is carried out using a large-scale laboratory model of a prestressed concrete segment tower. The system modifications are introduced by changing the preload. This changes the influence of imperfections of the surfaces of the horizontal dry joints, estimated by measuring strain and displacement at the lowest joint. An increasing preload causes the first two pairs of bending modes to move closer together. This enables to study the effect of the closeness of natural frequencies on the related mode shapes based on the same structure. Thus, the known effects of increasing uncertainty of the alignment and a rotation of the mode shape in the mode subspace with closer natural frequencies can be shown experimentally. In this work, the operational modal analysis (OMA) methods Bayesian-OMA (BAYOMA) and Stochastic Subspace Identification (SSI) are used. Local imperfections can significantly affect modal parameters, so these should be considered for vibration-based monitoring.

Three-Dimensional Temperature Field Simulation and Analysis of a Concrete Bridge Tower Considering the Influence of Sunshine Shadow

This paper forms a set of three-dimensional temperature field simulation methods considering the influence of sunshine shadow based on the DFLUX subroutine and FILM subroutine interface provided by the Abaqus platform to simulate the three-dimensional temperature field of concrete bridge towers and study its distribution law. The results show that the method has high accuracy for shadow recognition and temperature field calculation. The maximum difference between the shadow recognition results and the theoretical calculation value was only 19.1 mm, and the maximum difference between the simulated temperature and the measured temperature was 3.3 °C. The results of analyzing the temperature field of the concrete bridge tower using this algorithm show that the temperature difference between the opposite external surface of the tower column can reach 11.6 °C, which is significantly greater than the recommended temperature difference value of 5 °C in the specifications. For the concrete bridge tower, in the thickness direction of the tower wall, the temperature change was obvious only at a range of 0.3 m from the external surface of the tower wall, and the temperature change in the remaining range was small. In addition, the temperature gradient distribution of the sunshine temperature field in the direction of wall thickness conformed to the exponential function T(x) = T0e−αx + C. Additionally, the data fitting results indicate that using the temperature data at a distance of 0.8 m from the external surface as the calculation parameter in the function can achieve the ideal fitting result.

Investigation of the strut‐and‐tie model of a single‐plane cable‐stayed bridge tower under vertical component of the cable force

AbstractThe design of reinforcement of concrete pylons in cable‐stayed bridges is a challenging task. Usually, only the influence of the strong horizontal component of the cable force is considered during the reinforcement design of the concrete tower, while the bursting forces caused by the vertical components of the cable forces are ignored. However, the latter is also an important factor for concrete cracking in bridge towers. In this paper, the concrete tower of a single cable plane cable‐stayed bridge is considered. The strut‐and‐tie model (STM) of the pylon wall subject to the vertical components of one single cable force was derived. Based on the minimum strain energy principle, an equation for predicting the bursting force was given. Then, the STMs of a concrete pylon with two cable forces with different vertical distances between cables were proposed. A series of equations for predicting the bursting force in different STMs were presented. The STMs of a concrete pylon with multiple cables were subsequently obtained from the STM for two cable forces. The analysis results show that the vertical distance between cables has a great influence on the STM configuration of the tower. When the cable distance is less than 0.7 times the width of the tower wall, the bursting force is larger than that when the cable distance is larger than 0.7 times the width of the tower wall. This study was expected to provide a reference in the design and applications of pylons of concrete cable‐stayed bridges.

Experiment study on temperature field and effect on steel-concrete composite bridge towers

Due to the significant difference in thermal parameters between steel and concrete, complex temperature-related problems exist in steel–concrete composite bridge towers. Especially for the bridge tower with a particular type of Steel-Box-CFST section, the temperature distribution shows unique characteristics. To ensure the safety and regular use of the structure, it is necessary to analyse the temperature distribution mode of the composite bridge tower under solar radiation and to provide a method of temperature simulation at different conditions. In this paper, an indoor experiment in which the loading mode can be manually controlled has been carried out to study the temperature time-history and distribution in different loading conditions. The interface void between steel and concrete in CFST has also been detected. The results show that the outer steel box can protect the inner CFST from the temperature effect caused by solar radiation. A finite element model has also been established and verified by the experiment, providing a feasible way to simulate the temperature field under solar radiation.

Study on fatigue performance of double cover plate through-core bolted joint of rectangular concrete-filled steel tube bundle wind turbine towers

Rectangular steel tube concrete bundle wind turbine towers is a new type of tower structure with high prefabrication, convenient installation, convenient transportation and good integrity.Based on the uniaxial tensile test and fatigue loading test of the double cover plate through-core bolted joint, the stress condition of the key connection parts of the structure is analyzed, the S-N curve of the joint under parameter expansion is summarized, and the Weibull distribution test is carried out for the fatigue life of the concrete inside the joint. Finally, the fatigue damage of the joint are analyzed. The results show that the failure mode of the double cover plate through-core bolted joint under fatigue loading is bolt shear; Through S-N curve fitting, the S-N curve expression and fatigue limit value of different types of joints are obtained. It is found that under the shear failure mode, the fatigue limit of different types of joints is higher than the limit value specified in GB50017–2017, EC3 and AISC-360; The fatigue life of concrete at different loading factors conforms to the two parameter Weibull distribution.The damage analysis of the joint through the high cycle fatigue damage model shows that the trend of a sharp increase in the damage rate of the joints in the late loading period can better explain the phenomenon of instantaneous fracture. The research results of this paper can provide reference for the analysis, research and application of wind turbine towers.

Development of a novel type of steel‐shell concrete composite tower

Development of a novel type of steel‐shell concrete composite tower

Boundaries

Boundaries Elena Croitoru (bio) Click for larger view View full resolution A countryside flâneuse in search of her deceased grandfather contemplates anchoring, wandering, and the small marks we leave on the world. How does one get to know a person who passed away? I thought about that while I flew from London to Bacau, a city close to where my now-retired parents lived for most of the summer. All I had left of my grandfather—the person I wanted to know more about—were a few monochrome photographs with scalloped edges displayed in a family album. My mother's descriptions of him were sparse because the paths to her memories closed up over the years. She called him good-natured and said he'd loved the land he'd owned and that he'd spent a lot of his life riding horses or walking—something that resonated with my childhood self. When I was three he passed away, and later his letters and notes were destroyed in a flood. ________ AFTER THE PLANE landed, a cab drove me away from Bacau's constellation of concrete tower blocks and from the bitter fumes of groaning buses, and into the land of vineyards, corn, and wheat crops. It was hot and the city was grinding itself up into dust and getting into our lungs. Once [End Page 8] we reached the quilted countryside, it seemed as though I was going back in time, to the years when my life wasn't as defined as it is now. I spent my long childhood summers doing one of two things: either reading in the cool front room of my grandparents' house, on top of a pile of itchy wool rugs hand-woven by my grandmother, or walking for kilometers on end and trying to get to the spectral blue peaks I saw in the distance. I didn't know at the time that my wish was quixotic because the Tarcau Mountains were too far away. My grandmother's friends saw me as a wild girl because I took long trips on my own. I didn't know at the time that I'd probably inherited this desire to walk from my grandfather. ________ FOR THE FIRST time in more than five years, I arrived in Măgirești, a village shaped like a fish spine with a bent tail. Time had shrunk its square, its restored medieval stone well, and its bodega, which still smelled of strong tuica, but it had not dulled the green of its hills. Located at the foot of the forested Oriental Carpathians, it is built on an intricate terrain on which God seems to have spent a lot of time. It's made up of verdant hillocks abundant in shrubs and medicinal herbs, streams that swallow paths after the springtime thaws, meadows, velvety hills studded with grazing sheep, stratified and shimmering escarpments, golden inselbergs and bottle-green ponds on which pieces of wood float like miniature boats. It's a chamomile- and hay-scented symphony of textures and colors, a facsimile of the Shangri-La and a liminal space neighboring the malachite-green mountainscapes topped with a blue sawblade horizon. The village adopts borderland characteristics. Fruit trees aren't confined to orchards, so one can find an assortment of sour cherry, green plum, Mirabelle plum, cornelian cherry, walnut, and Jonathan apple trees (bearing sharp and aromatic fruits) living together on the same hill, communicating underground through their roots, sometimes overseeing muscat grapevines. When I heard that there are more trees on earth than there are stars in the Milky Way, I thought that the count could have started in this village. ________ MY GRANDPARENTS HAD never moved away from this area. For people like them, who had experienced two world wars, living in the countryside must have seemed like a good life because they'd witnessed the destruction and bombings that people sometimes brought to one another and to their environment. My grandfather loved the land and understood that independence came from it. He strived for self-sufficiency; hence he became a merchant and accumulated hundreds of acres that included pastures, arable land, and forests. All this...

Reinforced Concrete Wind Turbine Towers: Damage Mode and Model Testing

This study investigates the complex load-bearing mechanism of the reinforced concrete tower of large wind turbines through a structural model test. MTS electro-hydraulic servo loading system was used to load two reinforced concrete tower models for the push-out test. The ultimate bearing capacity of the reinforced concrete tower was found to be 8.894 kN. The test findings revealed that the top of the tower is subjected to unilateral shear as the horizontal load increases. As a result, the concrete strain in the compression zone of the test piece increases to its highest level in the bottom plastic hinge area. The concrete in the compression zone is being crushed in the meantime. The reinforcement achieves its yield point and deforms within the range of plastic failure when subjected to extreme loads. The outcomes of this study serve as a foundation for the running of wind turbines in extreme conditions.

Experimental study on the joint bearing behavior of segmented tower structures subjected to normal and bending shear loads

AbstractThis article deals with the analysis and evaluation of the structural behavior of segmented tower constructions in large‐scale experimental investigations. For this purpose, a tower model with dry horizontal joints on a scale of approximately 1:10 is constructed and loaded. The objective of these large‐scale investigations is to determine the load‐bearing behavior of concrete segment towers subjected to normal force (external prestressing), bending, shear force and torsion and to derive more efficient and realistic design models. The transfer of shear stresses between individual segments is ensured by frictional resistance in the horizontal joints due to prestressing. The current design models are based on plane flange surfaces at the top and bottom of the segments as well as their ideal circular ring shape. This assumes a constant normal stress distribution for the compression connection. Within the large‐scale experimental tests, findings for uneven force distribution in the horizontal joints due to prestressing and shear bending were obtained, that have a significant impact on the design models. However, for the evaluation of the results and the projection onto the real construction components, the scale effects must be urgently taken into account.

Buckling and free vibration analysis of non-prismatic columns using optimized shape functions and Rayleigh method

In this paper, optimized shape functions have been used in Rayleigh method to determine the critical buckling load and the fundamental natural frequency of non-prismatic steel-reinforced slender concrete columns. A range of admissible shape functions describing the mode shape in buckling as well as for the fundamental natural frequency of the column are considered and then an optimization strategy is developed to arrive at the optimum shape function. The results obtained from the present method based on the implementation of Rayleigh method through the concept of generalized coordinates are verified and validated by the finite element method. The application of the theory is demonstrated by two illustrative examples, both of which are steel-reinforced concrete towers that are representative of practical structures. Of particular significance is the duality between the free vibration and buckling problems which is captured and fruitfully exploited in the analysis. The effect of an additional mass located at the top of the tower is included in the investigation. Additionally, the impact of the creep behavior of the towers on results due to continuing lapse of time is critically examined and assessed. Finally, significant conclusions are drawn following the discussion of results.

Weld acoustic emission inspection of structural elements embedded in concrete.

After a catastrophic failure of the weld of the anchoring element of one cable in a stayed bridge, a non-destructive inspection was required to evaluate the weld condition of the 111 remaining anchoring elements to prevent future and similar failures. This examination was quite complicated since the anchoring elements are partially embedded in the reinforced concrete tower, and the weld is fully integrated into the concrete. Considering that direct access to the weld was not possible, acoustic emissions (AE) were a feasible alternative for these inspections. This study describes the inspection method, from laboratory tests simulating actual conditions for calibration to field tests for the method's tuning and evaluation. The AE inspection results are presented, and welds' condition is classified according to the acoustic energy, measured through a severity index and graded from a zonal intensity plot. Two structural elements were selected for concrete demolition to expose the weld for penetrant and ultrasonic inspections to correlate measurements of the actual condition of the welds and their defect size. Because of the analysis, welds are identified for immediate repair and the rest for AE monitoring to evaluate defect evolution through the increase of the severity index.

THE ABILITY OF MODERN TECHNOLOGIES TO INFLUENCE THE NEUTRAL MODE OF ELECTRIC GRIDS

In this article, we consider the modes of neutrals of 0,38 to 750 kV networks. In any network with different voltage classes, the neutral point of a power transformer winding can operate both in isolated and deaf earthed mode. However, the choice of this mode depends on economic feasibility.
 The paper presents arguments and advantages of application of system with isolated and compensated neutral of networks with voltage classes 6–35 kV. For networks of these voltage classes various options of connecting arc suppression reactors with step and smooth regulation, as well as low and high impedance resistors in the neutral point of neutralizing transformer or zero sequence filter are considered. On the example of operation of electric networks of the Republic of Chuvashia for many decades it is emphasized that compensation of capacitive currents with arc suppression reactors is an effective and reliable way to protect not only substation electrical equipment from overvoltage, but also to ensure electrical safety of people and animals, as well as reinforced concrete towers from destruction.
 It is noted that the 6–35 kV networks in the future can be made with deaf earthed neutral. However, this will be possible under the condition that self-supporting insulated wires will be installed on overhead transmission lines instead of bare wires, and cross-linked polyethylene cables will be used on cable lines. It is emphasized that the introduction of work under voltage in 6-35 kV networks and digitalization of substations with the widespread introduction of microprocessor technology will accelerate the transition from a system with insulated (or compensated) neutral to a deaf earthed system. Nevertheless, the decision to switch from the insulated neutral system to a deaf earthed system will remain the prerogative of the design organization based on the specifics of the electrical equipment and the sphere of industrial activity.

Post-tensioned tendons for enhancing the seismic behaviour of base-isolated monopole transmission towers

The seismic performance of monopole transmission towers under the near-fault earthquake excitations are evaluated in this paper and some innovative solutions are presented to enhance their seismic behaviour. To this purpose, two benchmark concrete transmission towers are selected as case studies. The towers differ in the used materials, which are high-performance and ultra-high-performance concretes. In order to improve the tower performance under seismic actions, an isolation system with and without tendon elements are installed. The tendon gross-sectional area, effective length, and post-tensioning force are considered as three important factors, which affect the behavior of the structure equipped with isolation system. The tower top acceleration and displacement responses are evaluated and used to identify the optimal ranges of the above-mentioned design parameters. Accordingly, detailed finite element models are built in OpenSees environment in order to conduct non-linear time-history analyses under some near-fault ground motions. The results of the analyses show that the application of the isolation system may improve the displacement response of the tower, but it may cause an increase of the acceleration responses due to the impact of the isolators with their external boundary. In contrast, the addition of the tendon elements with proper characteristics improves the overall responses of the isolated towers.

Structural identification of tall buildings: a reinforced concrete structure as a case study

The present paper concerns an approach to the structural identification of tall buildings. The identification is based on a large number of experimental data obtained on a scaled model. The procedure consists in steps of system identification by means of a refined finite element model which is the base for the evaluation of a simplified one dimensional scheme. The parameters accuracy of this last one has been determined with reference to a refined schematization. The approach is model updating, based on the first three experimental natural frequencies and modes. The case study is a structure in Naples, made by two reinforced concrete towers, linked at the top by a steel girder with suspended storeys, while the foundation slab is based on a reinforced concrete piled group.

Investigation of the strut‐and‐tie model of a two‐plane cable‐stayed bridge tower under vertical component of the cable force

AbstractThe geometry and mechanical behavior of concrete bridge towers are complex. Hence, it is important to generate a rational mechanical analysis model for structural design. The method of strut‐and‐tie models (STMs) is an effective way to analyze disturbed regions (D‐regions) such as the anchorage zones of cables in bridge towers. This paper provides a detailed analysis of the elastic stress distribution on the bridge tower of a cable‐stayed bridge with two cable planes. The vertical component of the stay cable force was considered for the analysis. Additionally, two different STMs of the bridge tower were developed with the load path method using different horizontal spacings of the stay cables. Based on the minimum energy principle, the optimal STMs of the two different STMs were generated. A detailed calculation method for the configuration of the optimal STMs is presented. In the paper, computational expressions of the internal force for the tie members in the two STMs are also proposed. Overall, this study demonstrated the strong applicability of the proposed STMs for a bridge tower in a cable‐stayed bridge with two cable planes. This can be considered an effective simplified method in the structural design of bridge towers. Furthermore, the study established that the influence of the horizontal distance between stay cables on the mechanical response‐behavior of the structure should be considered in the design of concrete bridge towers.

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.