Chinese Load Code Research Articles

An improved Chinese load code method for the evaluation of wind‐induced base shear force on base‐isolated buildings

An improved Chinese load code method for the evaluation of wind‐induced base shear force on base‐isolated buildings

Wind load investigation of self-supported lattice transmission tower based on wind tunnel tests

Through a series of wind tunnel tests on a self-supported lattice transmission tower model, the wind loads on the tower were investigated in this paper. According to similarity laws, the scaled tower model was designed and fabricated, and the atmospheric boundary layer wind field of Category-B specified in Chinese load code was simulated in the wind tunnel laboratory. Based on the aeroelastic wind tunnel tests and the high frequency force balance tests, the dynamic vibrations, the nondimensional wind force coefficients and the generalized power spectral densities (PSDs) of dynamic wind forces were analyzed and discussed. For the convenient application, the empirical formulas of the generalized PSDs of dynamic wind forces were established and the nonlinear mode shape correction was introduced, which were verified via comparison between the aeroelastic tests and the calculated dynamic responses of tower top. It is indicated that the unfavorable wind attack angles may happen around θ = [15° 30°] and θ = [60° 75°] for this type of tower; the generalized PSDs of wind forces are unimodal in shape, and the corresponding effective bandwidths and the nondimensional frequencies of peaks vary with the wind attack angle θ, especially those of the cross-wind forces are larger than those of the along-wind forces obviously; the established empirical formulas of the generalized PSDs of dynamic wind forces and the derived nonlinear mode shape correction factor are applicable.

Field measurements of snowdrift characteristics on reduced scale building roofs based on the size effect study

Unbalanced snow distribution, which leads to an excessive snow load in a local area, is one of the main reasons for building collapses. The formation of uneven snowdrifts is closely related to the shape of the building as it seriously affects the turbulent structure and drifting snow process. Unfortunately, the design codes of different countries for applying snow load on building structures cannot give a clear explanation because of the discrepancies between them. Therefore, a series of reduced scale field measurements of snowdrifts on roofs were conducted to clarify such discrepancies. Firstly, the size effect of model scaling was investigated by observing snowdrifts around two models with a scale ratio of 1/2. The results show that the size effect has little influence on the snowdrift pattern on the premise of satisfying the similarity criterion. Thereafter, the snowdrift characteristics of two-level roofed and gable roofed buildings were explored and analyzed through the comparison with different national load codes and collapsed building cases. Overall, the provisions of the Chinese load code differ from the measurement results, which leads to an underestimation of roof snow load. ISO 4355 and Canadian NBC codes could give a better prediction of the snow load by comparison.

Reliability-based investigation into the duration of load effect for the design of timber structures based on Chinese standard

The duration of load effect is a widespread phenomenon that timber structural members will experience certain decrease in strength under long-term service, which should be properly considered during the design of timber structures to ensure the lifetime structural safety. This paper presents a series of reliability-based investigations into the duration of load factor for the Chinese standard of timber structures. Firstly, the load models including dead load, live load and snow load were set up, and the main features of the load models were validated according to the requirements in Chinese load code. Then, the Foschi and Yao’s damage accumulation model was calibrated with long-term experimental data, and the calibrated duration of load model was validated by comparing the cumulative failure probability with different intensities and durations of sustained load. Based on the validated load models and the damage accumulation model, the short-term and long-term reliability was calculated using JC method and Monte Carlo simulation, respectively. Finally, recommended values of the duration of load factors were obtained under different loading conditions, including dead loads only, dead loads plus live loads, and dead loads plus snow loads. The presented research aims to provide technical basis for the determination of duration of load factors for the design of timber structures, therefore ensuring the structural safety of timber structures under long-term service.

Equivalent uniform live loads under transit vehicles for floor slab of long-span urban transportation hubs

ABSTRACT Rapid development of long-span urban transportation hubs arouses higher requirements of structural design methods. However, the current design codes do not give effective provisions of the equivalent uniform live load for long-span transportation hubs. A revised equivalent uniform live load is developed by considering the aspect (length-to-width) ratio of the one-way slab system for the urban transportation hubs. The most unfavorable loading positions of the bus tires are determined, and the equivalent uniform live load is computed by using the Chinese Load Code. The structural response under equivalent uniform live load is further compared to that under actual load, then the original equation of the equivalent uniform live load with the Chinese Load Code is revised by considering the aspect ratio of one-way slab. An actual engineering computation of equivalent uniform live load is carried out. The results reveal that the calculation methods of the Chinese Load Code cannot reflect the force transmission characteristics of the small-area tire load on the one-way slab. The structural responses under the revised equivalent uniform load are in good agreement with that under the actual load. The revised calculation method is suitable for most areas in this urban transportation hub and similar structures.

Investigation on passive simulation method and factors influencing the type-C-terrain wind profile of a structural wind-resistant moving-vehicle tester

Wind-profile simulation is fundamental to structural wind engineering. The transiting test method is used to test the wind-resistance performance of structures via vehicle-driving wind. Herein, we establish a novel method of simulating the wind profile of Commonwealth Advisory Aeronautical Research Council (CAARC) high-rise building standard model type-C-terrain by using flat plates through a transiting test method. Effects of several factors (i.e., the distance between flat plates and Pitot tubes, the length of flat plates along the wind direction, the distance between adjacent flat plates, the number of flat plates, and the vehicle speed) on the simulation results of type-C-terrain wind profiles were investigated. The results confirm the feasibility of applying a transiting test method to simulate wind profiles. The vehicle speed is 72 km/h (20 m/s). When the distance between the flat plates and the Pitot tubes is properly adjusted from 300 mm to 340 mm, the length of the flat plates along the wind direction is 200 or 300 mm. The results well agree with the wind-profile curves corresponding to the type-C-terrain in Chinese Load Code GB 50009-2012. Overall, this study provides a novel method of simulating type-C-terrain wind profiles.

Wind-resistant design and equivalent static wind load of base-isolated tall building: A case study

More base-isolated tall buildings have been constructed in earthquake- and wind-prone regions in recent years. However, less work has been done on the wind-resistant design of base-isolated tall buildings including the design of isolation system and the modeling of equivalent static wind load (ESWL), especially from the perspective of Chinese load code. This study presents a comprehensive investigation on the alongwind response of base-isolated tall building with a to-be-built tall building as an example. The dynamic wind loads specified in both Chinese and Japanese codes are used and compared. The influences of the stiffness and additional damping of the isolation layer on the modal characteristics of the base-isolated tall building are studied. The alongwind responses of fixed-base and base-isolated buildings are compared. The modeling of ESWL of base-isolated tall building is discussed. Finally, a parametric study is conducted to investigate the influence of the isolation layer stiffness and additional damping on the wind-induced response of the base-isolated building. A scheme of choosing the appropriate stiffness and additional damping is proposed for reducing the base shear force. These discussions and results will provide meaningful guidance to the wind-resistant design of base-isolated tall buildings, especially in China.

Wind tunnel simulation of wind flows with the characteristics of thousand-meter high ABL

The accurate simulation of wind flow in the boundary layer wind tunnel is very important for the relevant research on the environmental and structural wind engineering. Due to the earth's rotation, an Ekman spiral shaped wind direction profile would be generated, which is a common phenomenon in the thousand-meter high atmospheric boundary layer (ABL). However, the simulation of wind direction was overlooked in previous studies. In this study, based on the objectives of wind profiles determined by the field measurement, two twisted wind flows (TWFs) with the characteristics of thousand-meter high ABL are successfully simulated using the modified passive simulation technology, i.e. a combination of a self-developed vane system and the traditional passive simulation facilities. In the two TWFs, the wind speed profiles follow the power-law. The maximum wind twist angles are 24.2° and 14.7° respectively, and the variations of wind directions follow the Ekman spiral. The turbulence intensities fluctuate within the stipulations in Chinese Load Code, indicating that the results obtained in the wind tunnel test are reasonable. The power spectra of wind speed show good agreement with the von Karman spectrum. In order to evaluate the effect of TWF, the simulation of multi targets equivalent straight wind flow (SWF) is achieved. Then, the effect of TWF on the wind loads of megatall building is discussed so as to illustrate the importance of accurate simulation of wind flow. It is found that due to the existence of wind twist angle, for any specified wind direction, the wind force that acts on a thousand-meter high building is no longer a specific value, but varies with the total wind twist angle.

A probability-based analysis of wind speed distribution and related structural response in southeast China

According to the Chinese Load Code, the wind load for the structural design is based on the T-year return period of the annual maximum 10-min average wind speed. Therefore, determining the accurate regional annual maximum 10-min average wind speed, distribution is extremely important and essential. In this article, a new approach named generalised unified probability plotting (GUPP) method is proposed to parametrically analyse the regional wind speed distribution. The historical data of wind speed from 1953 to 2015 at southeast coastal city Xiamen, the distribution and parameters of the average 10-min annual maximum wind speeds are obtained. From the analysis results, the annual maximum 10-min average wind speed can be best modelled by the Pearson-III distribution among several distributions examined in the study, including the Gumbel distribution which underlies the Chinese Load Code. To further determine the significance of the updated wind speed distribution (namely the Pearson III), the wind-induced pressures at different story-levels of a high-rise building in Xiamen is examined relative to the Code-recommended distribution. Results show that the wind pressures corresponding to the Chinese Load Code is much higher than those of the Pearson-III. The difference is significant and may induce unreasonably high wind loads for design.AbbreviationsGuppGeneralised Unified Probability Plot; CDF: Cumulative Distribution Function; PDF: Probability Density Function; QQ Plot: Quantile-Quantile Plot; RMS: Root Mean Square; K–S: Kolmogorov–Smirnov

Research on reliability of steel roof structures subjected to snow loads at representative sites in China

An appropriate probabilistic description of snow loads is important in reliability analysis. Probability distributions for annual maximum ground snow loads are studied in detail in this paper based on the samples of snow loads on the ground, which are simulated by a snowmelt model. Then, selection of probability distribution function and parameter estimation method for ground snow loads is found to have a great influence on reliability assessment results. The reliability of members of steel roof structures subjected to snow load at four representative sites in China is investigated. The reliability indices of studied roofs are found not to be enough to reach the target value 3.2. The possible reason is that characteristic value of snow loads on the ground specified in Chinese load code is not conservative and the partial factor 1.4 for snow loads on roofs is not enough. To ensure designed roofs subjected to extreme snow loads a target reliability index 3.2, large partial factors for snow load that varies with COV of ground snow loads are expected to be used.

Extreme snow hazard and ground snow load for China

The ground snow load is used as the reference snow load to estimate the design snow load on roofs. The ground snow load is recommended in Chinese load code for the design of building structures in the applicable jurisdiction; this load needs to be updated regularly by integrating new available snow measurements and new analysis techniques. This study is concentrated on the estimation of extreme snow depth and ground snow load and on snow hazard mapping in China by using historical snow measurement data. A probabilistic model of the snowpack bulk density was developed. For the extreme value analysis of annual maximum snow depth, both the at-site analysis and region of influence approach were applied. Also, several commonly used probabilistic models and distribution fitting methods were considered for the extreme value analysis. For the annual maximum snow depth, it was identified from the at-site analysis results that the number of sites where the lognormal distribution is preferred is greater than that where the Gumbel distribution is preferred. The 50-year return period value obtained from the ROI approach is insensitive to whether the three-parameter lognormal distribution or the generalized extreme value distribution is adopted. Maps of annual maximum snow depth and ground snow load were developed. Comparison of the estimated ground snow load to that recommended in the design code was presented, and potential updating to the ground snow load in the design code was suggested.

Research on the Wind Tunnel Force Balance Tests of Long-Span Closed Coal Trestle

Structures with long span and high flexibility are very sensitive to the wind forces, so it is necessary to study on the wind effects on such structures. In this paper, based on section model wind tunnel high-frequency force balance tests, two horizontal base bending moments and shear forces of the typical supporting columns as well trestle bridge deck of the closed coal trestle under different wind directions were measured. The shape coefficients and their variations with the wind directions of the typical supporting columns as well trestle bridge deck were calculated then analyzed by the mean values of base forces. The experimental values of the shape coefficients were compared with those in the Chinese Load Code, the results shown that both were in good agreement, which verified the reliability of the test, which also illustrated that wind-resistant design of the coal trestle in accordance with the Code was reasonable. Based on analysis of the variances of base forces between overall model with and without surrounding buildings, influences of surroundings buildings were studied. Interference factors were proposed which provided the basis for the base forces checking and wind-resistant design of the long-span closed coal trestle structures.

Wind Resistance Research and Wind Tunnel Test of Large-Span Roof Based on Yancheng Financial Center

A large number of buildings with large-span or complex-shape have come to the fore in recent years. To these structures, wind load tends to be control load in the structural design. Shape coefficient of wind load which Chinese load code for the design of building structures can provide is extremely limited due to complex-shape of long-span space structures, therefore carrying our related study is of great practical significance. Yancheng Financial Center model is established in this paper based on ETABS software. The acquired date in the use of wind tunnel test is to simulate wind load which is on the structure and to analysis stress distribution of critical element in order to ensure safety and applicability of structures. This paper mainly covers wind tunnel test, equivalent static wind load, and wind-induced response, etc.

Structural Design of Shanghai Tower for Wind Loads

Nearby Jin Mao tower and the World Financial Center, the 632-meter, 121-story mixed-use Shanghai tower will be the tallest super tall tower in the new Lujiazui Finance and Trade Zone of Shanghai. Due to the super tall height, curved façade and spiraling form of the Shanghai tower project, wind is the dominant lateral load and governed many aspects of the structural design. To precisely determine the design wind loads, a detailed wind climate study was conducted. The influences of typhoon events and typhoon profiles were considered in the wind climate study. Due to its long structural period, the across-wind load of the Shanghai tower project is prominent. Aerodynamic optimization studies were conducted to reduce the correlation of vortex shedding along the building height, and thus reduce the across-wind building response. The optimization results show that the across wind load can be effectively reduced with certain building configuration. Detailed wind tunnel studies, including HFFB and HFPI studies, high Reynolds number tests and aeroelastic model tests, were conducted to accurately capture the wind load on the building. The wind load parameters, such as the Shape factor, Strouhal number and the terrain type, were obtained and derived from the wind tunnel studies. The wind load and wind induced structural responses obtained from the wind tunnel studies were then compared with those calculated based on Chinese load code. The design criteria for the ultimate limit check and serviceability limit check of Shanghai tower for wind loads were discussed. Finally, the building vibration under wind load and the related human comfort problem is addressed. Different human comfort criteria are compared and the building acceleration results from both the wind tunnel tests and code-based calculation are discussed.

Across‐wind dynamic response of high‐rise building under wind action with interference effects from one and two tall buildings

AbstractSystematic studies on the across‐wind dynamic interference effects on two and three tall buildings are presented in this paper. It is found that surrounding and upstream interfering building(s) can significantly affect the across‐wind load on the interfered principal building. Generally speaking, two interfering buildings can cause more adverse dynamic effects on the principal building than a single one does. The results show that the maximum interference factor (IF) among three buildings increases 80% over that between two buildings in terrain category B which has been defined in Chinese load code for design of building structures; a noticeable difference of 29% of IF is also observed in terrain category D. Vortex shedding from the upstream buildings can lead to vortex‐induced resonance, resulting in excessive across‐wind loads on the downstream building. Although interference effects in terrain category D are much smaller than those in exposure category B, the maximum IF is found to be 1·83 in the case of three buildings with the same size in terrain category D and 2·27 in other configurations. Copyright © 2007 John Wiley & Sons, Ltd.