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An effective approach to deal with the structural failures of transmission towers in tornadic events is to develop good structural health monitoring (SHM) systems for them. However, the strategy for SHM of transmission towers against tornados should be different from the conventional atmospheric boundary layer (ABL) winds oriented ones, as the non-stationary nature of the tornados significantly differentiates them from the ABL winds. To satisfy the need of obtaining the highly time-varying whole-field stress on the structure in the course of the tornadic event for effective SHM, an innovative transient tornadic load distribution identification method is proposed for use, which is based on the field structural mode shape measurement and dynamic finite-element (FE) model updating. Via a numerical case study, it is noted that good effectiveness is achieved for the new load distribution identification method. Employing the Modal Assurance Criteria based FE model updating technique, the new method has the advantage of being easily embraced in practical SHM systems. It is found that when the transient tornadic velocity profile to be identified is noticeably different from the mode shape of the structure without undertaking external loads, the identified load pattern is very accurate for the new approach. [ABSTRACT FROM AUTHOR]

Structural analyses of transmission towers against tornados, which are of vital practical significance in design and maintenance of the structures in regions suffering from the convective weather, were rarely reported by the wind engineering community up to today. To balance the computing efficiency and the simulation accuracy, numerical calculations based on Wen's tornadic velocity model are employed to analyze the tornado‐induced structural responses of a 131‐meter‐high free‐standing transmission tower in east China in this article. Results suggest that both the tornadic load and the structural response are noticeably greater in the lateral direction than in the longitudinal direction, and they are found to be highly nonstationary due to the traveling nature of the tornado. In addition, according to the present study, the transmission tower is not prone to the strength failure during the tornadic event and slight fatigue damages are accumulated on the tower body due to the tornadic action which can be timely warned using the structural health monitoring strategy based on field measurements of low‐order structural natural frequencies. Besides the points mentioned above, the innovations of the present research additionally include the following: (1) tornado‐induced structural responses and atmospheric boundary layer wind‐induced structural behaviors have been compared to provide conclusions of theoretical significance; (2) a novel fatigue damage assessment method based on the high‐circle fatigue damage accumulation theory has been applied to the analysis of tornado‐induced structural damage; (3) the structural configuration of a key joint on a main chord has been optimized against the tornado based on the advanced response surface optimization method. [ABSTRACT FROM AUTHOR]

For this paper, full-scale/model test comparisons to validate the traditional atmospheric boundary layer (ABL) wind-tunnel simulation technique performed until now by the wind engineering community are systematically reviewed. The engineering background includes some benchmark low-rise buildings specifically established for use in wind engineering research (the Aylesbury experimental buildings, the Texas Tech University experimental building, the Silsoe buildings, etc.), several high-rise buildings in North America and East Asia, long-span bridges, large-span structures, and cooling towers. These structures are of different geometries, are located in different wind environments, and are equipped with various transducers and anemometers. By summarizing the different articles in the literature, it is evident that notable discrepancies between the full-scale measurement and the model test results were observed in most full-scale/model test comparisons, which usually took certain forms: the mean and/or the peak negative pressures at the flow separation regions on buildings were underestimated in the wind tunnel; differences in the root-mean-square (rms) values of the acceleration samples between the full-scale measurements and the force balance model tests were non-negligible; the vertical vortex-induced vibration amplitudes of bridges measured using section models and aero-elastic models were much lower than those observed on the prototypes, etc. Most scholars subjectively inferred that inherent technical issues with the ABL wind tunnel simulation technique could be responsible for the observed full-scale/model test discrepancies, including the Reynolds number effects, the turbulent flow characteristics effects, and the non-stationarity effects. However, based on the authors' years of experience and after discussion with experienced researchers, it was found that some of the full-scale measurements performed in earlier research were inherently less accurate and deterministic than the wind tunnel experiments they were supposed to validate, which could also be a significant cause of the full-scale/model test discrepancies observed. It is suggested herein that future studies in this field should regard full-scale measurements only as benchmarks, and that future works should focus on synthesizing the results from different schools of physical experiments and formulating universal empirical models of high theoretical significance to properly validate future wind tunnel tests. [ABSTRACT FROM AUTHOR]

When examining the history of wind engineering, it is evident that many full-scale/model test comparisons have found noticeable differences between the results. Although understanding the causes of these differences is important for practical purposes, limited numerical and experimental conditions have often resulted in subjective explanations for full-scale/model test comparisons without scientific validation. To address this issue, this article suggests the use of the computational fluid dynamics technique or the multiple-fan actively controlled wind tunnel technique to quantitatively reveal the adverse effects that impact the reliability of the traditional atmospheric boundary layer wind tunnel tests for a large cooling tower, including not only the widely acknowledged influences (Reynolds number effects and turbulent flow characteristics effects) but also the non-stationarity effects that have potential influences. Established on the novel proposition, a new research scheme for future full-scale/model test wind effects comparisons for large cooling towers has been formulated based on the numerical or physical simulations of the sinusoidal flow fields. Using the Pengcheng cooling tower as a case study, the research recognized the very significant impact of Reynolds number effects, the non-stationarity effects that cannot be ignored, and the negligible effects of turbulent flow characteristics. [ABSTRACT FROM AUTHOR]

According to a previous study, a concrete bridge bearing vehicles traveling at lower speeds suffers from more severe apparent damage compared to one bearing vehicles traveling at higher speeds. The authors of the study subjectively inferred that the observed phenomenon is due to different vehicle load-holding durations for different vehicle speeds. However, this interpretation is not true for bridges with a smooth road surface. Based on an engineering case study of Renyihe Bridge (a concrete rigid-frame continuous highway bridge with spans of 80 m + 4 × 145 m + 80 m), this article reveals via numerical simulations that with the increase in road surface roughness, the resonant responses of the bridge are significantly amplified for cases of low vehicle speed, which can well explain the phenomenon observed by the aforementioned study. Field experiments undertaken on Renyihe Bridge further reveal the related mechanism. These experiments reveal that the frequency of the vehicle excitation for a bridge with sufficient road surface roughness might be closer to the low-order natural frequencies of a bridge with a decrease in vehicle speed. Therefore, the resonant responses are supposed to be more significantly amplified in cases of low vehicle speed after an increase in road surface roughness. [ABSTRACT FROM AUTHOR]

To rigorously evaluate the health of a steel bridge subjected to vehicle-induced fatigue, both a detailed numerical model and effective fatigue analysis methods are needed. In this paper, the process for establishing the structural health monitoring (SHM)-oriented finite element (FE) model and assessing the vehicle-induced fatigue damage is presented for a large, specially shaped steel arch bridge. First, the bridge is meticulously modeled using multiple FEs to facilitate the exploration of the local structural behavior. Second, manual tuning and model updating are conducted according to the modal parameters measured at the bridge's location. Since the numerical model comprises a large number of FEs, two surrogate-model-based methods are employed to update the model. Third, the established models are validated by using them to predict the structure's mode shapes and the actual structural behavior for the case in which the whole bridge is subjected to static vehicle loads. Fourth, using the numerical model, a new fatigue analysis method based on the high-circle fatigue damage accumulation theory is employed to further analyze the vehicle-induced fatigue damage to the bridge. The results indicate that manual tuning and model updating are indispensable for SHM-oriented FE models with erroneous configurations, and one surrogate-model-based model updating method is effective. In addition, it is shown that the fatigue analysis method based on the high-circle fatigue damage accumulation theory is applicable to real-world engineering cases. [ABSTRACT FROM AUTHOR]

Finite element (FE) model updating can guarantee the accuracy of the numerical analyses for civil structures. However, two deficiencies currently exist with the traditional FE model updating technique based on the measurements of modal parameters and/or the static structural responses of the built structure with respect to its reference information insufficiency and its non-unique solution generally obtained, hampering its extensive use. It becomes the goal of the whole engineering community to introduce new effective methods for the civil structural FE model update. To this end, an innovative FE model updating method using data from construction monitoring is proposed in this article. With regard to its theoretical novelty, the new method transforms the complicated multi-variable optimization mathematical problem with the traditional FE model updating technique into many simple single-variable parameter identification problems. Under the engineering background of Huangsha Harbor Bridge, a three-span concrete continuous box girder bridge constructed utilizing the symmetric cantilever casting method, the effectiveness and the efficiency of the new model updating practice were validated. It is demonstrated using quantitative data that the abundant data measured on Huangsha Harbor Bridge in construction stages can enhance the reference information for the more accurate FE model updating of the structure, and the uncertain parameters with the initial FE model of Huangsha Harbor Bridge can be progressively and easily identified for the proposed model updating method using many single-variable linear regression models, instead of one complicated multi-variable mathematical or numerical model employed by the traditional model updating approaches, which generally leads to non-unique solutions rendered by normal optimization algorithms. [ABSTRACT FROM AUTHOR]

To protect large cooling towers against strong winds, wind tunnel model tests have traditionally been undertaken. As typical circular cylindrical structures, simulations of high Reynolds number (Re) effects are indispensable on scale models of large cooling towers to validate the truthfulness of test results. However, two issues currently exist that hinder the effectiveness of high Re effects simulation: (1) the mean wind pressure distribution at high Re is usually utilized as the sole simulation target, and the simulation results are not typically checked for other dynamic wind effects that are equally important; and (2) it is not clear whether the wind effects obtained and generalized by other researchers for small-sized cooling towers can be used as simulation targets for large cooling towers. In light of these issues, a new method for the simulation of high Re effects that takes into account real simulated dynamic wind effects is proposed in this study and compared with the traditional simulation method, which only considers the simulation of the mean wind pressure distribution. By comparing the wind effects measured on a 167 m-high large cooling tower with those obtained on small-sized cooling towers, the irrationality of treating the wind effects measured on small-sized cooling towers as high Re effects simulation targets for large cooling towers is demonstrated. With these findings, future model tests are expected to reproduce more realistic wind effects on large cooling towers. [ABSTRACT FROM AUTHOR]

A new research scheme for a full-scale/model test comparison is proposed for effectively validating the wind tunnel pressure measurement technique in this article. With the new research scheme and using quantifiable data, future full-scale/model test comparisons are expected to reasonably disclose the main problem with the traditional atmospheric boundary layer wind tunnel pressure measurement technique with regard to the Reynolds number (Re) effects, the aero-elastic effects and the flow characteristic effects. Based on the engineering background of the Peng-cheng cooling tower, it was quantified by using the new research scheme that the average relative errors of the mean wind pressure coefficients are 52.39%, 1.87% and 35.91% for the Re effects, the aero-elastic effects and the flow characteristic effects, respectively. In view of the fluctuating wind pressure coefficients, the average relative errors are 97.58%, 21.14% and 20.20% for the Re effects, the aero-elastic effects and the flow characteristic effects, respectively. These suggest that Re effects are extremely significant for pressure measurement model tests of circular cylindrical structures, and flow characteristic effects are noticeable too. They should be mitigated using effective approaches, i.e., increasing the model surface roughness and placing the actively controlled devices at the beginning of the wind tunnel's working section, respectively. Additionally, the key field measurement technique adopted (i.e., the calculation of the reference static pressure) and details of manufacturing the aero-elastic pressure measurement model for the present study are also expounded in the article for reference. [ABSTRACT FROM AUTHOR]

This paper investigates the efficiency of three surrogate model-based dynamic finite element model updating methods, the response surface, the support vector regression, and the radial basis function neural network, using the engineering background of the Tsing Ma Bridge tower. The influences of two different sampling methods (central composite design sampling and Box–Behnken design sampling) on the model updating results are also assessed. It was deduced that the impact of the surrogate model type on the updating results is not significant. More precisely, the models updated using the response surface method and the support vector regression method are similar in terms of reproducing the dynamic characteristics of the physical truth. However, the effects of the employed sampling method on the model updating results are significant as the model updating quality using the central composite design sampling method is higher than that using the Box–Behnken design sampling method in some considered cases. [ABSTRACT FROM AUTHOR]

As an important issue for establishing structural health monitoring–oriented finite element models for large steel pylons, identification of beam-end stiffness draws the attention of the engineering circle. Since the methods adopted by other researchers for parameter identification are impracticable, a beam-end stiffness identification method which combines in situ measurements for the structure's global dynamic properties with effective multi-variable optimization methods is utilized to improve the accuracy of established finite element models. A 131-m-high large transmission tower is employed as a case study to validate the method. In situ measurements for the tower's global dynamic characteristics are performed, and identifications of Young's modulus for 20 semi-rigid connections distributed along each of the tower's four main chords are undertaken utilizing three multi-variable optimization methods, that is, the first-order method, the subproblem approximation method, and the response surface method. Static numerical simulations on two detailed connection models prove that multiple uncertain parameters can be correctly and simultaneously identified when appropriate optimization techniques are chosen. Finally, the influence of beam-end stiffness identification on the structural health monitoring–oriented structural safety assessment is revealed by calculating the wind-induced dynamic structural responses for the single tower and the transmission tower-line system, which indicates that identification of the correct beam-end stiffness and updating the structural health monitoring–oriented finite element model are indispensable procedures for reliable structural health monitoring. [ABSTRACT FROM AUTHOR]

To excite sufficient vibrations of bridges for more effective modal experiments to take place, traveling vehicles were utilized in many bridge field inspection campaigns in history. However, the dynamics of a bridge subjected to the traveling vehicles are of changed resonant properties compared with those of the same structure with the ambient excitation in nature. Therefore, the field modal experiments employing vehicle excitations might unfavorably lead to shifted measurement results of low-order natural frequencies for long-span bridges of large mass. Using Xinjiang Bridge (a single-tower pre-stressed concrete cable-stayed bridge with spans 40m + 150m + 150m + 40m) as the engineering background, this paper validates this technical notion based on reliable physical experiments and numerical simulations and seeks a practical approach to deal with the issue. It is found that the maximum deviation between the low-order modal frequencies measured on Xinjiang Bridge for the vehicle excitation case and those measured for the ambient excitation case (the accurate values) reaches 0.65Hz, and the deviation between the lower limit of the usual vehicle excitation’s energy band and the modal frequency measured (factor 1) and the traveling vehicles’ speed (factor 2) are the two key factors influencing the modal frequency shifts. An empirical model to compensate for modal frequencies’ deviations is formulated considering the two key factors accordingly, which is of high-practical significance in future applications of the modal experiments using vehicle excitations to other long-span bridges. [ABSTRACT FROM AUTHOR]

Simultaneous identification of vehicle load and structural damage is an issue of practical significance in structural health monitoring and maintenance of in-service concrete bridges. However, most methods proposed in history to deal with this engineering issue are solely based on data from a single source of structural vibration response measurement, which are subjected to problems such as incomplete understanding of the structural health, the computational inefficiency and the easy failure of the monitoring system. To this end, this paper proposes a new method of synthesizing data generated from two different types of sensors (the strain gauges and the accelerometers) to simultaneously identify the vehicle load and the structural damage which is established on the theories of weigh-in-motion method based on the strain influence line. The new method, which is supposed to be able to well solve the problems with the traditional approaches disseminated to the profession, is formulated in a flowchart for use, and applied to the actual Renyihe Bridge (a concrete rigid-frame continuous highway bridge with spans of 80m + 4 × 145m + 80m) to validate its effectiveness. The results suggest that the new method is of high accuracy in use in low vehicle speed scenarios and superior to the traditional simultaneous identification approach based on unitary structural acceleration sensing. [ABSTRACT FROM AUTHOR]