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This paper presents the main theoretical foundation and innovation of winad load provisions for wind loads on components and cladding in the newly-revised Standard for Wind Loads on Roof Structures (JGJ/T 481-2019). Generally, by introducing the concept of peak wind pressure coefficients, a more reasonable and convenient wind load determination for roof components and cladding can be obtained for structural designers. Moreover, based on extensive wind tunnel test data of external wind pressures on components and cladding of typical roofs, the corresponding peak external wind pressure coefficients are proposed, with more specific wind load zones. Regarding those large-span curved roofs, innovative external wind pressure coefficient values on detailed roof zones are firstly presented. In addition, according to comparisons, it is seen that the roof zones in the Chinese standard are similar to those in the Canada wind load code. The resulting peak external wind pressure coefficients in corner, edge and interior zones reach the international advanced level. Finally, optional three methods to determine peak wind pressure coefficient are also clearly specified, which are applicable to cases with different wind pressure time history lengths. All the development and improvement of the standard provide necessary supplement and reference for the international and Chinese wind-resisting design.

More and more nuclear power plants are being constructed in China, while the nationwide intensity regions with tornado-resisting design speeds are not specified. With the development of tornado damage investigations, more records of tornado events have been accumulated, which makes it possible to establish the probability distribution model of tornado speed and predict the design wind speeds of nuclear power plants. This paper summarizes the derivation of probability distribution of tornado speed based on the parameters of mean occurrence rate, intensity rating, path length and width. The tornado events in China are introduced, while the geographical distribution of tornadoes is described. The mean occurrence rates for each local region with square of 1° longitude and latitude are obtained by moving average method. The records of tornado events, which experienced post-disaster investigations and scattered in research articles, dissertations and yearbooks, are collected and revaluated. Using the accepted tornado records, both the probability distribution of path area and the joint probability distribution between tornado speed and path area are established. The equivalent speeds corresponding to different annual exceedance probabilities are calculated. The suggestions of intensity regions for tornado-resisting design of NPPs in China are proposed. The uncertainties of design wind speeds are simulated by Monte Carlo simulation method. It is indicated that the most significant impact on the uncertainties of design speeds originates from the variation of equivalent speed.

Under the action of the same wind azimuth, the extreme values of the wind load effect components of building structures are generated in the along-wind, cross-wind, vertical, and torsional directions. In designing the wind-resistant structure, the extreme values of effect components need to be combined to determine the internal force envelope values of members. Complete quadratic combination (CQC) and Turkstra combination rules are often used to determine the combination value of extreme values of wind effect components. The extreme probability distribution expressions of the CQC, and the Turkstra and approximate rules, are derived. The simplified combination Equations and combination coefficients of the CQC and Turkstra approximate rules are proposed in this paper. We use the combination Equations and Monte Carlo simulation method to analyze the accuracy of Turkstra and its approximate rules. The results show that the combination extreme is associated with the correlation coefficients, mean values, ratios of standard deviations, and fluctuating extremes of effect components. The errors between Turkstra and its approximate rules are small when load effect components show a positive correlation. The errors are largest when the standard deviations of components are equal. Our research results provide a theoretical basis for the combination method of wind load effect components of building structures.

Slender structures placed close to each other could greatly magnify the dynamic response due to interference effects. This paper presents the results of experimental studies of the proximity interference induced vibration of two identical square prisms in a turbulent boundary layer to clarify its excitation mechanism. The upstream interfering prism was static, while the principal prism was dynamic and free to vibrate only in the crosswind direction. The divergent vibration behavior at the critical interfered location was examined in detail. Based on the time-resolved particle image velocimetry (TR-PIV) technique and unsteady pressure measurement, the vortex shedding process and corresponding pressure distribution of the dynamic principal prism were described by examining their correlation with the motion time histories. The biased gap flow between the two prisms was found to control the vibration of the dynamic principal prism. The interaction between the vortex shedding in the wake of the dynamic principal prism and the gap flow is dramatically intensified with increasing wind velocity. Such effects create a large fluctuating lift force on the dynamic principal prism at high reduced wind velocity, compared with measurement taken with two static prisms, which drives the prism to undergo a divergent crosswind response.

In the Urban Boundary Layer (UBL), the vertical structure is generally divided into four layers, namely urban canopy (UC), roughness sublayer (RS), inertial sublayer (IS) and mixing layer (ML), respectively. Full-scale wind speed spectra of a five-year time series in different layers are used to investigate the spectral characteristic in UBL. Due to the similar spectral characteristics in IS and ML, these two layers are combined into a single layer, namely, IS & ML. The results show peaks at a frequency of about 1 year−1 and 1 day−1, and a “gap” in the mesoscale in the horizontal wind speed spectrum at 47 m. It matches well with the spectra in other classical studies. In three layers, the spectra show different characteristic and distribution of spectral energy. For horizontal spectrum, the mesoscale spectral energy of the layer with higher altitude is obviously larger. With the increase of the height, the “gap” becomes flat and finally be filled in IS & ML. For vertical spectrum, the characteristics of spectra in the UC and RS are similar, and a diurnal peak can be found. In IS & ML, the proportion of spectral energy in the macroscale obviously increases, and the diurnal peak disappears.

The estimation of peak wind effects is an important issue in the structural and cladding design. The wind load effects such as wind pressures show the non-Gaussianity. In estimating the peak value of non-Gaussian wind load effects, a series of methods such as the global maxima method, the block maxima method and the translation process method have been developed. Among them, moment-based Hermite polynomial model (HPM) is becoming a popular approach due to its straightforwardness and accuracy. However, it is desired to improve this approach in terms of the easier use and better accuracy. In current study, the hybrid of analytical and empirical (or semi-analytical) formula based on HPM has been developed to estimate the mean of peak wind pressures and peak wind pressures at various percentiles. In this formula, HPM coefficients are determined by Winterstein’s analytical formula and related modification coefficients in the semi-analytical formula are fitted and validated based on long wind tunnel data of four building models. Results show that the proposed formula performs well under different sampling frequencies and wind tunnel data. Due to the easier use and better accuracy, the proposed formula is expected to be more appropriate for engineers.

Mode selection and modal coupling analysis are important to estimate wind-induced structural response of long-span roof structures. This article presents a framework for predicting wind-induced structural response of long-span roof structures based on modal analysis. This framework first identifies the dominant modes according to the correlation between the mode shape and the wind load spatial distribution on the structure as well as a proposed “modal participation coefficient.” Second, the concept of modal strain energy is introduced and a modal coupling coefficient is defined, based on which the dominant coupling modes are determined. A modified square root of the sum of the squares methodology is then developed to account for the modal coupling effects of the background and the resonant response components. The total responses can be obtained by combining the contributions of the dominant coupling modes and the square root of the sum of the squares results from the dominant modes. This avoids the use of the computation expensive complete quadratic combination method. Finally, an illustrative example of wind-induced response analysis of the China National Stadium roof structure is provided to demonstrate the effectiveness of the proposed framework.

A comprehensive wind tunnel experimental study for 4∶12-sloped hip roofs of L- and T-shaped low buildings was carried out in a simulated open terrain exposure to examine wind load character...

The extreme value of non-Gaussian wind pressure coefficients is usually estimated by fitting the probability density function (PDF) of maximum or minimum values while a large number of observations except the peak values in the measured samples are discarded. The implicit or explicit translation between non-Gaussian and Gaussian histories can also be utilized to estimate the extreme value of non-Gaussian wind pressure coefficients while the randomness of aerodynamic effect is not taken into account. The Hermite moment models are summarized and applied to formulate the PDF of non-Gaussian peak factors which is expressed as the joint PDF (JPDF) of the shape parameters of the Hermite moment model and the PDF of the translated Gaussian peak factors. After the variations of mean, standard deviation and non-Gaussian peak factor are considered, an innovative and analytical PDF formula of extreme wind pressure coefficients for multiple samples, which is expressed as a function of the JPDF of mean, standard deviation and the PDF of non-Gaussian peak factor, is presented in this paper. The theoretical developments are applied to establish the PDF and cumulative density function (CDF) of the negative peak wind pressure coefficients with multiple samples. It is verified that the analytical probability distribution model is a reasonable model to estimate the peak pressure coefficients.

The characteristics of cladding and structural loads for 4:12-sloped hip-roofed low-rise buildings with rectangular, L- and T-shaped plans are examined, based on wind tunnel data and three-dimensional linear computational models. Regarding cladding loads, the rectangular gable roof incurs more considerable local suction, compared with the rectangular hip roof. However, due to building plan configurations, intense suction and positive pressure are distinctly distributed on roofs and walls around building re-entrant corners of hip-roofed non-rectangular buildings. Considering structural loads, very high pressures act on the gable-roofed end frame, compared with those on the corresponding hip-roofed frames. Furthermore, the building plan impact on structural load patterns varying with wind directions and on most critical values is clear. Particularly, the most critical structural loads acting on intermediate and penultimate frames of wings of L-shaped hip-roofed buildings and side wings of T-shaped cases, show a 25% maximum increase. However, regarding the central wings of T-shaped buildings, results generally fall within the same range with those of the rectangular and L-shaped buildings. In addition, the structural connections and boundary conditions significantly influence structural load magnitudes and distribution shapes. Finally, the effect of horizontal aspect ratios on both cladding and structural loads is found to be minimal.

A novel damage classification method based on wavelet packet transform and statistical analysis is developed in this study for structural health monitoring. The response signal of a structure under an impact load is normalized and then decomposed into wavelet packet components. Energies of these wavelet packet components are then calculated to obtain the energy distribution. Statistical similarity comparison based on an F-test is used to classify the structure from changes in the wavelet packet energy distribution. A statistical indicator is developed to describe the damage extent of the structure. This approach is applied to the test results from simply supported reinforced concrete beams in the laboratory. Cases with single and two damages are created from static loading, and accelerations of the structure from under impact loads are analyzed. Results show that the method can be used with no reference baseline measurement and model for the damage monitoring and assessment of the structure with alarms at a specified significance level.

The wind velocity spectra at Beijing Meteorological Tower are calculated using Hilbert-Huang transform and Fourier transform, respectively. A innovative model of wind velocity spectrum, which is accordant with the characteristics in both the inertial subrange and the large eddies range, is presented in this paper. The method of least squares is adopted to obtain the parameters in the model. Then the differences between the FFT spectrum and the HHT spectrum are compared. It is indicated that the values of the HHT spectrum in the energy containing range are slightly larger than those of the FFT spectrum while the values of the HHT spectrum in both inertial subrange and dissipation subrange are very close to that of Fourier spectrum. It is concluded that the HHT spectrum describes elaborately and accurately the spectrum values in the low frequencies and the fitted wind velocity model provides a reference for reconstructing the near-ground wind field of Beijing city in wind tunnel test and for numerical simulation.

This study presents two hybrid methods, the full combination method and the simplified expression, for evaluating the fatigue life of linear structures with uncertain-but-bounded parameters subjected to stochastic excitations. First, approximate expressions of the spectral moments and spectral bandwidth parameters are derived based on the improved interval analysis via extra unitary interval and the interval Taylor expansion. Then, the lower and upper bounds of the interval expected fatigue damage rate and fatigue life are evaluated by fully or properly combining the two bounds of the spectral moments and spectral bandwidth parameters by the Tovo–Benasciutti method. Through the numerical study, the full combination method is recommended for the accurate assessment of the interval fatigue life, and the simplified expression is recommended for rapid evaluation of the two bounds of the interval fatigue life using the explicit expression. Finally, three numerical examples are adopted to illustrate the accuracy and efficiency of the proposed methods via comparison of the present results with the exact ones.

There are two models in use today to analyze structural responses when subjected to earthquake ground motions, the Displacement Input Model (DIM) and the Acceleration Input Model (AIM). The time steps used in direct integration methods for these models are analyzed to examine the suitability of DIM. Numerical results are presented and show that the time-step for DIM is about the same as for AIM, and achieves the same accuracy. This is contrary to previous research that reported that there are several sources of numerical errors associated with the direct application of earthquake displacement loading, and a very small time step is required to define the displacement record and to integrate the dynamic equilibrium equation. It is shown in this paper that DIM is as accurate and suitable as, if not more than, AIM for analyzing the response of a structure to uniformly distributed and spatially varying ground motions.

Both the lowerand higher-order Hermite moment models of softening processes and the model of hardening process are derived. The monotonic limits are found numerically; therefore it is convenient to judge directly the order of the Hermite model from the skewness and kurtosis. To overcome the systematic errors existed in the lower-order Hermite models, the iterative procedures to increase the transformation precision and the corresponding stoppage criteria are presented. Then the non-Gaussian peak factor is produced after the Gaussian peak factor is calculated and substituted into the Hermite model. The reduced and closed-form formulae of nonGaussian peak factor are discussed and compared with the numerically exact solutions, in which Winterstein’s formulae overestimates the non-Gaussian peak factor and the bandwidth parameter related to the 4-order spectrum moment should not be introduced.

The two characteristics of near-fault ground motions, i.e., the forward directivity effect and permanent displacement effect, result in long period and large velocity pulse in the velocity time history and large step pulse in the displacement time history. Considering the two effects, a simple expression of continuous function for equivalent velocity pulse time history is presented in this paper. The equivalent pulse model, in which the pulse period, peak velocity and pulse shape are described by five parameters, is highly advantageous to fit and simulate the pulse-type velocity time history. The equivalent pulse model comprises only one low-frequency component while the high-frequency component of a pulse-type earthquake record cannot be considered. Based on 28 records of 11 earthquakes, the pulse frequency of pulse-type records is generally less than 1 Hz. Therefore the low-frequency component and high-frequency component are simulated respectively and combined them together to generate a pulse-type ground motion.