Free-standing Tower Research Articles

Effects of aerodynamic damping on freestanding bridge tower under the joint action of wind and wave loads

This study uses a time-domain simulation to investigate the effect of aerodynamic damping on a freestanding bridge tower under the joint action of wind and wave loads. The physical model of the bridge tower, which has been tested in laboratory, is numerically reconstituted considering structural nonlinearities obtained from free oscillation tests. Random wind fields are generated using the harmonic superposition method, and the wind flow characteristics, such as mean wind velocity and turbulence intensity, are identified based on the data collected in the laboratory. The wave loads measured at the bottom of the foundation during the experimental model tests are used for the simulation. The dynamic responses of the tower under the joints action of wind and wave loads are successfully simulated. A clear reduction in structural vibration in the wave-controlled region is confirmed by simulation results. Further numerical investigation indicates that an increase in the mean wave velocity produces additional aerodynamic damping in the structural motion system, which significantly dampens the responses of the wave-induced vibration. A simple method for determining the dynamic responses of a bridge tower under the joint action of wind and wave loads, using the data obtained from wind- and wave-only cases, is proposed.

SP2.2.17The leaning tower of pasta: lessons in team performance and creativity from a core surgical training boot camp design challenge

Abstract Aims Unity of effort is an important component of strategic leadership and management theory associated with Core Surgical Training (CST) outcome. The aim was to determine the impact of team diversity on task completion: a creative design challenge, during CST Boot camp. Methods Attendees (n = 44) at a single Statutory Education Body’s CST Boot camp were stratified into teams related to specialty theme, and set a design challenge as described by Peter Skillman, to build the tallest free-standing tower out of spaghetti (20 pieces), tape (1 m), and string (1 m), with a marshmallow on top in 18 minutes. Primary outcome measure was tower height. Results Five teams (50%) completed the task with the tallest tower measuring 70cm (median 51, range 0-70). Median satisfaction with the simulation exercise was 4 (2-5) on a scale of zero to five, with five corresponding with highest satisfaction. Successful task completion was associated with team surgical specialty (p = 0.032), ethnicity ratio (p = 0.010,), and gender ratio (p = 0.003), respectively. On multivariable analysis, only team gender ratio was independently associated with tower height (HR 0.515, 95% CI 0.350 - 0.759, p = 0.001). Conclusion Modern leadership theory emphasises the important dynamic relationship between individual team members, the team, and task completion. General surgery themed teams with a gender mix were most successful in completing the design challenge; whether relative simulation performance predicts strategic organisational skill and career progression will be the next question.

Experimental study on dynamic effect of freestanding tower of sea-crossing bridge under wave load

There is a debate over whether the sea-crossing bridges undergo dynamic motions when exposed to wave loads. In order to verify the dynamic effect of the tower of sea-crossing bridge under wave load, an experimental study on dynamic effect of a freestanding tower of sea-crossing bridge is accomplished in this paper. Firstly, a test model for a typical bridge tower of pile group foundation under wave load is established by using a scale of 1:100. Secondly, a typical sea condition is designed for the response test of the bridge tower under wave load. The test results indicated that obvious vibration of top the tower occurs when the wave load period is close to the natural vibration period of the structure, and both displacement and base shear are amplified. The results in this paper will provide an important reference for whether the dynamic effect of wave load should be considered in the designs of bridge structure under wave load.

Wind-induced vibrations and suppression measures of the Hong Kong-Zhuhai-Macao Bridge

A series of wind tunnel tests, including 1:50 sectional model tests, 1:50 free-standing bridge tower tests and 1:70 full-bridge aeroelastic model tests were carried out to systematically investigate the aerodynamic performance of the Hong Kong-Zhuhai-Macao Bridge (HZMB). The test result indicates that there are three wind-resistant safety issues the HZMB encounters, including unacceptable low flutter critical wind speed, vertical vortex-induced vibration (VIV) of the main girder and galloping of the bridge tower in across-wind direction. Wind-induced vibration of HZMB can be effectively suppressed by the application of aerodynamic and mechanical measures. Acceptable flutter critical wind speed is achieved by optimizing the main girder form (before: large cantilever steel box girder, after: streamlined steel box girder) and cable type (before: central cable, after: double cable); The installations of wind fairing, guide plates and increasing structural damping are proved to be useful in suppressing the VIV of the HZMB; The galloping can be effectively suppressed by optimizing the interior angle on the windward side of the bridge tower. The present works provide scientific basis and guidance for wind resistance design of the HZMB.

Predicting single freestanding transmission tower time history response during complex wind input through a convolutional neural network based surrogate model

As the steel towers in the power system are vulnerable to intensive wind loads, it is essential to understand their dynamics response to estimate its potential failure. Conventional structural analysis methods like the finite element analysis or the field test are either computational heavy or cost expensive. Thus, this paper proposes a machine learning approach based on convolutional neural network (CNN) to predict the time history response of the transmission tower during the complex wind input. By preprocessing the time history of wind load and the tower’s dynamic response, a well-developed CNN can capture the time and spatial correlation of the wind load successfully and provide high accuracy results. CNN configuration, window size selection, and training data scale are carefully discussed to optimize the CNN design to maximize the prediction accuracy as well as minimize its computational time. Finally, to evaluate the performance of the surrogate model, the accuracy of the optimal CNN is tested in predicting the time history response of the transmission tower under 15 m/s to 70 m/s wind speed. The effectiveness of the CNN surrogate model is validated through a fragility model development, and its robustness is investigated using two wind inputs generated from a random wind profile and a random wind spectrum.

The Leaning Tower of Pasta: Lessons in Team Performance and Creativity From a Core Surgical Training Boot Camp Design Challenge

Unity of effort is an important component of strategic leadership and management theory associated with Core Surgical Training (CST) outcome. The aim was to determine the impact of team diversity on task completion: a creative design challenge, during CST Boot camp. Attendees (n = 44) at a single Statutory Education Body's CST Boot camp were stratified into teams related to specialty theme, and set a design challenge as described by Peter Skillman, to build the tallest free-standing tower out of spaghetti (20 pieces), tape (1 m), and string (1 m), with a marshmallow on top in 18 minutes. Primary outcome measure was tower height. Five teams (50%) completed the task with the tallest tower measuring 70 cm (median 51, range 0-70). Median satisfaction with the simulation exercise was 4 (2-5) on a scale of 0 to 5, with 5 corresponding with highest satisfaction. Successful task completion was associated with team surgical specialty (p = 0.032), ethnicity ratio (p = 0.010,), and gender ratio (p = 0.003), respectively. On multivariable analysis, only team gender ratio was independently associated with tower height (Hazard ratio 0.515, 95% confidence interval 0.350-0.759, p = 0.001). Modern leadership theory emphasizes the important dynamic relationship between individual team members, the team, and task completion. General surgery themed teams with a gender mix were most successful in completing the design challenge; whether relative simulation performance predicts strategic organizational skill and career progression will be the next question.

Calculational model for first-mode eigenfrequency of a semi-guy-wired vertical-axis wind turbine tower

A simple model for accounting for tower mass when estimating the first-mode eigenfrequency of a semi-guy-wired tower has been derived. This extends previous work where an analytical model of the semi-guy-wired tower of a 200-kW vertical-axis wind turbine was developed. The model was primarily used to estimate the eigenfrequencies as a result of adding guy wires to a free-standing tower (thus creating a semi-guy-wired setup). However, a weakness with the model was that the tower mass was accounted for in a rough way that essentially ignored the guy wires, which gave a larger-than-necessary error. In this work, an effective top mass, that takes into account the tower mass and the constraints from the guy wires, is derived to achieve a higher accuracy when estimating the first-mode eigenfrequency. This, together with the earlier models, gives a more complete method to estimate the eigenfrequencies for a semi-guy-wired wind turbine.

Dynamic Analysis of a Large Freestanding Rock Tower (Castleton Tower, Utah)

AbstractWe acquired a unique ambient vibration dataset from Castleton Tower, a 120 m high bedrock monolith located near Moab, Utah, to resolve dynamic and material properties of the landform. We identified the first two resonant modes at 0.8 and 1.0 Hz, which consist of mutually perpendicular, linearly polarized horizontal ground motion at the top of the tower. Damping ratios for these modes were low at ∼1%. We successfully reproduced field data in 3D numerical eigenfrequency simulation implementing a Young’s modulus of 7 GPa, a value ∼30% lower than measured on core samples. Our analysis confirms that modal deformation at the first resonant frequencies closely resembles that of a cantilever beam. The outcome is that with basic estimates of geometry and material properties, the resonant frequencies of other freestanding rock monoliths can be estimated a priori. Such estimates are crucial to evaluate the response of rock towers to external vibration inputs.

Current Observation Results of Downward Negative Flashes at Tokyo Skytree From 2012 to 2018

Direct observation of lightning current is a fundamental approach to evaluating lightning parameters, which are among the most basic factors for the lightning protection design of various grounded objects. However, for a tall grounded structure, upward lightning flashes initiated from the top of the structure have usually been observed, and the direct observation results of downward flashes have been limited. We developed and installed a pair of Rogowski coils at Tokyo Skytree, which is a 634-m-high freestanding broadcasting tower in Japan (35.71°N, 139.81°E), and have conducted direct observation of lightning flashes striking the tower. As of November 2018, 70 lightning flashes striking the tower, 26 downward and 44 upward, have been observed since the end of February 2012. In this paper, we focus on the downward negative flashes that occurred at the tower for seven years from 2012 to 2018 and report on the observed results of typical waveform parameters of lightning stroke currents in comparison with other observed results on downward negative flashes.

System identification of the suspension tower of Runyang Bridge based on ambient vibration tests

A series of field vibration tests are conducted on the Runyang Suspension Bridge during both the construction and operational stages. The purpose of this study is devoted to the analysis of the dynamic characteristics of the suspension tower. After the tower was erected, an array of accelerometers was deployed to study the evolution of its modal parameters during the construction process. Dynamic tests were first performed under the freestanding tower condition and then under the tower-cable condition after the superstructure was installed. Based on the identified modal parameters, the effect of the pile-soil-structure interaction on dynamic characteristics of the suspension tower is investigated. Moreover, the stiffness of the pile foundation is successfully identified using a probabilistic finite model updating method. Furthermore, challenges of identifying the dynamic properties of the tower from the coupled responses of the tower-cable system are discussed in detail. It\'s found that compared with the identified results from the freestanding tower, the longitudinal and torsional natural frequencies of the tower in the tower-cable system have changed significantly, while the lateral mode frequencies change slightly. The identified modal results from measurements by the structural health monitoring system further confirmed that the vibrations of the bridge subsystems (i.e., the tower, the suspended deck and the main cable) are strongly coupled with one another.

Experimental study on the dynamic responses of a freestanding bridge tower subjected to coupled actions of wind and wave loads

This work presents an experimental investigation of the dynamic responses of a freestanding bridge tower model under coupled wave and wind actions. A test model with a geometric scaling of 1:100 was manufactured, and the test was performed in a wind tunnel and wave flume. The dynamic responses of the test model were measured under three cases of wind, wave and wind-wave coupled actions. The displacement, acceleration and bending moment were analyzed for the model with different wind speeds and wave exposures. The test results indicated that the coupled wind-wave effects are clear for lower wind speed with regular waves when the wave period is in the resonant region of the structures. When the wave period is far from the resonant frequency of the structure or the wind speed is much higher, the coupled wind-wave action does not significantly affect the dynamic responses of the bridge tower.

Construction aerodynamics of cable-stayed bridges for record spans: Stonecutters Bridge

This paper presents the extensive aerodynamic investigations conducted for the construction of the 1018m-main span Stonecutters Bridge. The emphasis is on the behaviour of the bridge structure during the erection stages, notably its response to vortex shedding, buffeting and divergent amplitude effects. A description is given of the principal aspects of the wind tunnel testing carried out, including section model testing, aeroelastic freestanding tower model testing on different erection heights, and aeroelastic bridge model testing to investigate the bridge erection stages. The engineering implications of the results are discussed. Wind tunnel testing on stay cables has also been carried out, with special reference to determining cable drag and the susceptibility to rain-wind induced oscillations. These investigations advanced general understanding of the behaviour of cable-stayed bridges during construction, and contributed significantly to the development of the erection method and sequence for the Stonecutters Bridge leading to the expeditious completion of this work.

Experimental investigation on a freestanding bridge tower under wind and wave loads

Long-span cross-strait bridges extending into deep-sea waters are exposed to complex marine environments. During the construction stage, the flexible freestanding bridge towers are more vulnerable to environmental loads imposed by wind and wave loads. This paper presents an experimental investigation on the dynamic responses of a 389-m-high freestanding bridge tower model in a test facility with a wind tunnel and a wave flume. An elastic bridge model with a geometric scale of 1:150 was designed based on Froude similarity and was tested under wind-only, wave-only and wind-wave combined conditions. The dynamic responses obtained from the tests indicate that large deformation under resonant sea states could be a structural challenge. The dominant role of the wind loads and the wave loads change according to the sea states. The joint wind and wave loads have complex effects on the dynamic responses of the structure, depending on the approaching direction angle and the fluid-induced vibration mechanisms of the waves and wind.

Comparison of Responses of Guyed and Freestanding Transmission Line Towers Under Conductor Breakage Loading

Cascades have been a prominent feature of many transmission line (TL) accidents around the world. During these events, a localized member failure changes the boundary conditions of the structural system, magnifying member loads over a considerable extension of the line. This results in the progressive failure of successive support structures. Phase conductor breakage is regarded as the most severe cascade triggering event, generating a shock wave that propagates through the conductor and induces large unbalanced longitudinal loads on the transmission line components. Under such an extreme loading event, nonlinear time-history dynamic analysis has to be employed to predict the response of the TL system. In the present work, an explicit dynamic analysis scheme is developed to predict the response of a multi-span TL section. The analysis includes all the main structural components of a TL section. This procedure was used to investigate the response of two types of suspension steel latticed towers, guyed and freestanding, subjected to conductor breakage loading. Results indicate the occurrence of peak dynamic loads (PDLs), that significantly increase the internal forces in system components, exceeding their design capacities, particularly in tower's members. The results also show that the guyed tower accommodates such a loading event more adequately than the freestanding tower.

Current distribution and transient magnetic fields in an observatory of TOKYO SKYTREE

TOKYO SKYTREE is the tallest free-standing antenna tower; whose height is 634m. However, the number of lightning strikes to a tall structure increases in proportion to the structure height. Therefore, it is important to establish lightning protection methods for facilities in and around such tall antenna tower.There is a possibility that comparatively large magnetic fields occur inside an observatory by the current flowing through steel columns composing the TOKYO SKYTREE. This paper presents simulation results of lightning current distribution and magnetic fields around the observatory. Simulated results are from the finite-difference time-domain (FDTD) method which is one of the most widely used numerical electromagnetic analysis methods. The knowledge of these current distribution characteristics and magnetic fields would be very useful for lightning protection of TOKYO SKYTREE.

MULTIPLE LOADING EFFECTS ON WIND-INDUCED STATIC PERFORMANCE OF SUPER-LARGE COOLING TOWERS

Currently, four grouped 177 m super-large cooling towers, i.e. column-supported hyperboloidal shells, are to be constructed in a typical electric power plant in Southeast China. To this end, simultaneous pressure measurements on 1:200 rigid tower models are carried out in an atmospheric boundary layer (ABL) wind tunnel, aimed at accurately obtaining the external/internal cladding wind loads on these shells. The wind-induced static behavior of the cooling towers is analyzed by applying the wind loads acquired via the pressure model tests, using both linear elastic and nonlinear elastic finite element (FE) analyses. The corresponding responses (structural deformation, internal force and local buckling state) are compared with those obtained by the traditional design approach, focused on the effects of internal suction and external pressure distribution. Besides, the tower group interference effects are studied by comparing the results computed of a freestanding tower, with those of the tower groups during two different construction stages. The main findings about the loading effects on the static performance of the super-large cooling towers are helpful for improving the current Chinese Codes that govern the design of super-large cooling towers.

Analysis on Stability of the Short-Pylon Cable-Stayed Bridge

This thesis took the Changshan Bridge in Dalian Changhai county as an example and adopted the general finite element software ANSYS to simulate it. Analyzed the stability of the completed bridge and the single free-standing tower state, and studied the buckling of the main girder and the thin-walled pier.

Wind Tunnel Investigations for the Free Standing Tower of the Penang Second Bridge

The Penang Second Bridge is a new bridge under construction in Penang, Malaysia. The aerodynamic behavior of the bridge was one of the main concerns. This paper summarizes of the wind tunnel testing of the 1:40 scaled aeroelastic model testing for the free standing tower. The wind tunnel Investigations were carried out with the objective of verifying the detailed design of bridge towers through measurement of the buffeting response to turbulent wind, susceptibility to galloping instabilities and susceptibility to vortex shedding excitation in smooth oncoming flow.The test results show that explicit vortex-induced vibration was observed for the completed free standing tower, however it will not affect the safety of the tower, and the buffeting response of tower is within acceptable range under the designed wind speed.

Wind Tunnel Test and the Analysis of Buffeting Performance of Free-Standing Tower of Cable-Stayed Bridge under Yaw Wind

The buffeting performance of free-standing tower of JiangHai Navigation Channel Bridge, a cable-stayed bridge, under yaw wind is investigated by means of wind tunnel test of aeroelastic model. It is found that the variation of buffeting response of free-standing tower with wind yaw angle is not monotonous. The lateral buffeting response on the top of the free-standing tower reach their minimal values and maximal values at around 150°and 180°of wind yaw angle respectively and the longitudinal buffeting response attain their maximal values at around 90°of wind yaw angle. Also, at the 2/3 height of the tower the lateral buffeting response and torsional buffeting response get their minimal values at around 150°of wind yaw angle, and at around 180°achieve the maximal values. It is also seen that, the buffeting response changes with the wind speed at a conic curve approximately.

Progressive finite element model calibration of a long-span suspension bridge based on ambient vibration and static measurements

A two-phase model updating approach is presented to develop a baseline model for the Runyang Suspension Bridge (RSB), which is the longest bridge in China with a main span of 1490 m. In this approach, the model updating is divided into two phases of free-standing tower phase and full-bridge phase according to the construction procedure, so that the model updating of the long-span suspension bridge can be greatly simplified. The physical meaning of sensitivity and the penalty function concept is employed in the iterative calculation. The structural model is updated by modifying the parameters of design, and validated by structural natural vibration characteristics and static responses. The design parameters used for updating are bounded according to measured static results and engineering judgments. After ambient vibration measurements were carried out to obtain the eigenfrequencies, damping ratios and mode shapes of RSB based on the monitored acceleration records, the FE model is then updated by using the measurements come from field tests during construction of the bridge and after the completion of the bridge. The calibrated FE model is proved to have a good correlation with the static and dynamic measurements and is then used for the continuous structural health monitoring of the bridge.