Wind tunnel testing to study turbulent wind field effect on wind load and wind-induced response of TV tower

Television towers have a complex aerodynamic shape and low damping characteristics. As such, the wind load and the wind induction response are key factors in their design and maintenance. To study these two parameters of high‐rise TV towers, a wind tunnel force test was conducted at a height of 280 m using the Foshan TV tower as a model. The TV tower model was divided into seven detachable sections. Three wind fields with different turbulence intensities were simulated in the wind tunnel, corresponding to different sections, and lateral force tests were performed on each section using a high‐frequency dynamic balance. The experimental results were used to calculate the wind‐induced response when considering the modal (first three‐order) coupled response and were compared with the wind‐induced response calculated using the complete quadratic combination (CQC) method. The results revealed that equivalent static wind loads (ESQL) and CQC calculation methods were used in this study, and a higher degree of coincidence was observed, which may be useful in engineering practice.

Long-span roof structures with multiple vibration modes may undergo coupled motions when exposed to spatiotemporally varying dynamic wind loads. This article presents a framework for the analysis of coupled wind-induced responses and equivalent static wind loads on long-span roof structures. This framework takes into account the inter-modal coupling of modal response components and cross correlation between the background and resonance. The load–response–correlation method is widely used for the background equivalent static wind loads of rigid structures. Also, the concept of load–response–correlation was extended for the correct estimation of equivalent static wind loads by considering the correlation between the load and exact total responses. However, there is no detailed study for the correct estimation of equivalent static wind loads on the component of background, resonance, and their cross response using load–response–correlation method. In this article, a consistent load–response–correlation method for equivalent static wind loads is presented in a unified framework which contains the background, resonance, and modal coupling. First, the accuracy of wind-induced responses is ensured by considering the modal coupling. Meanwhile, the efficiency is improved by decomposing the covariance matrix of the generalized resuming forces. Second, several effects of the wind-induced responses are discussed in detail, such as the effect of the modal coupling, the effect of the modal participations to resonant responses, and the effect of the cross correlation between the background and resonance. Finally, the proposed equivalent static wind loads are represented by the composition of the external wind loads and inertial forces, which are both the most probable load distributions. Accordingly, the equivalent static wind load distribution and the responses by equivalent static wind loads are reasonable.

Under the action of the fluctuating wind load, the low frequency part produces background response to the structures, while the high frequency part produces resonance response to the structures. In structural design, equivalent static wind load is usually used to equate the fluctuating wind load. Although there are various methods of evaluating the equivalent static wind load, they did not consider the correlation between modal responses or considered them insufficiently. Therefore, in this paper, the correlation between modal response is considered to evaluate the equivalent static wind load, the displacement response is decomposed by proper orthogonal decomposition (POD) method, the correlation between modal displacement is removed, the equivalent static wind load is expressed in the form of displacement mode, and then the correlation between modal response is fully considered in the extreme value combination. This paper combines the equivalent static wind loads in order to make the wind resistance design more reasonable for high‐rise buildings. First, the formulas of equivalent static wind loads expressed by displacement modes of background and resonant response are deduced based on modal decomposition and POD method. Second, the combination formulas of square‐root‐of‐sum‐square (SRSS) and complete‐quadratic‐combination (CQC) rules for the equivalent static wind loads considering the mean wind loads are proposed. Both the linear combination formula of SRSS for the equivalent static wind load and the weighting factor expressions of background and resonance equivalent static wind load are given. Third, the accuracy and validity of the formulas of equivalent static wind load are verified by a wind tunnel pressure test of a high‐rise building. Finally, the simplified combination coefficient formulas for the equivalent static wind loads are proposed, and the combination of the high‐rise building base's fluctuating equivalent static wind loads of along‐wind direction, across‐wind direction, and torsional direction is analyzed.

The Guangzhou New TV Tower with a height of about 610 m is presently the tallest TV tower in the world. Wind loads and wind effects are the key factors dictating the design of the structure. A wind-resistance study on the tower has thus been made. The entire tower was divided into 19 sections and models for each section were individually wind tunnel tested using the high-frequency balance technique in specially simulated turbulent wind fields. Descriptions of the sectional tower models, the experimental method and the test results are presented in the paper. The test results were then made use of in computing wind induced responses, including tower displacements, accelerations and internal forces, taking modal coupling effects into account. The whipping effects of the antenna on the responses, especially on accelerations were quantified, can be found. The equivalent static wind loads acting on the structure are also provided in the paper.

A method of assessing equivalent static wind loads that can represent all the real ultimate states of a high-rise building and towering structure has still not been fully determined in wind engineering. Based on random vibration theory, the wind-induced response and equivalent static wind loading of high-rise buildings and towering structures are investigated using the vibration decomposition method. Firstly, the structural wind-induced mean response, background response, resonant response and background and resonant coupled response are studied in the time and frequency domains. Secondly, a new gust load factor (GLF) assessment method suitable for wind-induced displacement, bending moment and shear force response at any height of the structure is proposed, and a typical high-rise building is used as an example for comparison with the previous research results, in order to verify the effectiveness of the method in this paper. The results show the following: for high-rise buildings and towering structures, the percentage of the coupled components in the total pulsation response is less than 2%, and the influence can be ignored; the GLF based on bending moment (MGLF) and the GLF based on shear force (QGLF) increase significantly with height, and the traditional GLF methods underestimate the maximum wind effects.

Wind resistant size optimization of geometrically nonlinear lattice structures using a modified optimality criterion method

Wind pressure measurements were carried out for dome roofs with different rise–span ratios (f/L = 1/4,1/6,1/8) in a boundary wind tunnel. A parametric study was conducted to investigate the influences of wind loading and structural parameters on the wind-induced response and the universal equivalent static wind loads (ESWLs) of single-layer reticular dome shells, including the span, rise–span ratio, roof mass and the mean wind velocity. Results show that the rise–span ratio has a significant influence on the wind pressure distribution of the roof. High suction appears at the top of the roof with a larger rise–span ratio f/L = 1/4, and it appears at the top and leading edge when f/L is 1/6 or 1/8. Many vibration modes should be included to analyze the wind-induced response of dome roof structures, and this makes it very difficult to analyze the ESWL. The resonant response is larger than the background response. A method to calculate the universal ESWL for the building code is proposed for easy understanding by practicing engineers. Based on the distribution characteristics of the ESWL, simple fundamental vectors are constructed to recalculate the universal ESWL. This method is employed to divide the dome roof into four zones, and it also means that four fundamental vectors are used to evaluate the ESWL. Simplified expressions of universal ESWL in these four roof zones are proposed for the engineering design. All nodal displacements and structural member stresses under the universal ESWL agree well with actual peak responses.

A new methodology based on the results of wind tunnel tests was proposed in order to obtain the wind-induced responses and equivalent static wind loads(ESWLs) of a high-rise building which has complicated shape and is under the aerodynamic interference of other buildings.The resultant forces on layers of the high-rise building were calculated based on the wind pressures measured simultaneously from wind tunnel tests.Based on the simplified layer model,a methodology to obtain the wind-induced responses and ESWLs accounting for different responses was developed in the frequency domain.Then the developed methodology was applied to a high-rise building to show how it works.Results show that the displacements of the building are contributed mainly by the first vibrating mode,whereas the accelerations are contributed by first several vibrating modes.The displacements and accelerations calculated in the frequency domain match well with those calculated in the time domain.Three ESWLs accounting for the displacement on the top of the building,the base shear and the base moment are almost the same for this building.The accumulated value of ESWLs can be used to determine the most unfavorable wind direction.

Due to the significant aerodynamic interference from sub-towers and surrounding tall buildings, the wind loads and dynamic responses on main tower of three-tower connected tall building typically change especially compared with those on the isolated single tall building. This paper addresses the wind load effects and equivalent static wind loads (ESWLs) of three-tower connected tall building based on measured synchronous surface pressures in a wind tunnel. The variations of the global shape coefficients and extremum wind loads of main tower structure with or without interference effect under different wind directions are studied, pointing out the deficiency of the traditional wind loads based on the load codes for the three-tower connected tall building. The ESWLs calculation method based on elastic restoring forces is proposed, which completely contains the quasi-static item, inertia item and the coupled effect between them. Then the wind-induced displacement and acceleration responses for main tower of three-tower connected tall building in the horizontal and torsional directions are investigated, subsequently the structural basal and floor ESWLs under different return periods, wind directions and damping ratios are studied. Finally, the action mechanism of interference effect on structural wind effects is investigated. Main conclusions can provide a sientific basis for the wind-resistant design of such three-tower connected tall building.

Estimation of wind load on supertall buildings using partial output measurements

Wind-induced response monitoring of large-span air-supported membrane structure coal-shed under the influence of typhoons

Transmission lines will significantly deviate from the initial location under wind loadings due to the strong geometric nonlinearity of the conductor. Ignoring the location updating (LU) effect can greatly reduce the modeling accuracy of wind load. This paper proposes a framework to quantify the influence of the LU effect on wind-induced responses and equivalent static wind load (ESWL), and emphasizes the need to consider this effect through systematic discussions. To facilitate the actual engineering design, a simplified method based on the rigid pendulum assumption is developed to modify the ESWL. The results indicate that the mean wind load is amplified by the LU effect, and the amplification effect becomes increasingly noteworthy with increasing basic wind speed. Conversely, the gust response factor is hardly affected. After considering the LU effect, the average component of various responses increases to varying degrees, particularly the horizontal tension and lateral reaction. The simplified method has a relative error of only -0.45% under the design condition and exhibits great robustness to the height difference. Compared with the methods recommended by various codes, the proposed method provides a more accurate estimation of ESWL, which helps to balance the contradiction between structural safety and construction cost.

Traditional gust load factor (GLF) method, inertial wind load (IWL) method and tri-component method (LRC+IWL) cannot accurately analyze the wind-induced responses of super-large cooling towers, so the real combination formulas of fluctuating wind-induced responses and equivalent static wind loads (ESWLSs) were derived based on structural dynamics and random vibration theory. The consistent coupled method (CCM) was presented to compensate the coupled term between background and resonant response. Taking the super-large cooling tower (H=215 m) of nuclear power plant in Jiangxi Province, China, which is the highest and largest in China, as the example, based on modified equivalent beam-net design method, the aero-elastic model for simultaneous pressure and vibration measurement of super-large cooling tower is firstly carried out. Then, combining wind tunnel test and CCM, the effects of self-excited force on the surface pressures and wind-induced responses are discussed, and the wind-induced response characteristics of background component, resonant component, coupled term between background and resonant response, fluctuating responses, and wind vibration coefficients are discussed. It can be concluded that wind-induced response mechanism must be understood to direct the wind resistant design for super-large cooling towers.

Gust response envelope approach to the equivalent static wind load for large-span grandstand roofs

Nowadays, the digital divide is one of the major issues facing the global community. Around 3 billion people worldwide are still not-connected or under-connected. In this article, we investigate the use of TV towers with multi user (MU) massive multiple input multiple output (mMIMO) techniques to offer connectivity in rural areas. Specifically, the coverage range is assessed for a MU mMIMO base station (BS) mounted on a high tower as a TV tower, and compared with a legacy mMIMO BS. The obtained results show that one high tower BS can cover an area at least 25 times larger than the area covered by a legacy BS. This is of high interest as recycling TV towers can enhance rural connectivity with low expenditures. We apply the proposed solution to a realistic case study in an Ethiopian rural area, based on population densities and locations of current BS and TV towers. Our study shows that a high number of people can be covered by existing TV towers. Non-technological challenges and additional possible solutions to enhance rural connectivity are also discussed.