High-frequency force balance technique for tall buildings: a critical review and some new insights

Chen, Xinzhong,Kwon, Dae-Kun,Kareem, Ahsan Techno-Press 2014 Wind and Structures, An International Journal (WAS Vol.18 No.4

The high frequency force balance (HFFB) technique provides convenient measurements of integrated forces on rigid building models in terms of base bending moments and torque and/or base shear forces. These base moments or forces are then used to approximately estimate the generalized forces of building fundamental modes with mode shape corrections. This paper presents an analysis framework for coupled dynamic response of tall buildings with HFFB technique. The empirical mode shape corrections for generalized forces with coupled mode shapes are validated using measurements of synchronous pressures on a square building surface from a wind tunnel. An alternative approach for estimating the mean and background response components directly using HFFB measurements without mode shape corrections is introduced with a discussion on higher mode contributions. The uncertainty in the mode shape corrections and its influence on predicted responses of buildings with both uncoupled and coupled modal shapes are examined. Furthermore, this paper presents a comparison of aerodynamic base moment spectra with available data sets for various tall building configurations. Finally, e-technology aspects in conjunction with HFFB technique such as web-based on-line analysis framework for buildings with uncoupled mode shapes used in NALD (NatHaz Aerodynamic Loads Database) is discussed, which facilitates the use of HFFB data for preliminary design stages of tall buildings subject to wind loads.

High-frequency force balance technique for tall buildings: a critical review and some new insights

Xinzhong Chen,권대건,Ahsan Kareem 한국풍공학회 2014 한국풍공학회지 Vol.18 No.4

The high frequency force balance (HFFB) technique provides convenient measurements of integrated forces on rigid building models in terms of base bending moments and torque and/or base shear forces. These base moments or forces are then used to approximately estimate the generalized forces of building fundamental modes with mode shape corrections. This paper presents an analysis framework for coupled dynamic response of tall buildings with HFFB technique. The empirical mode shape corrections for generalized forces with coupled mode shapes are validated using measurements of synchronous pressures on a square building surface from a wind tunnel. An alternative approach for estimating the mean and background response components directly using HFFB measurements without mode shape corrections is introduced with a discussion on higher mode contributions. The uncertainty in the mode shape corrections and its influence on predicted responses of buildings with both uncoupled and coupled modal shapes are examined. Furthermore, this paper presents a comparison of aerodynamic base moment spectra with available data sets for various tall building configurations. Finally, e-technology aspects in conjunction with HFFB technique such as web-based on-line analysis framework for buildings with uncoupled mode shapes used in NALD (NatHaz Aerodynamic Loads Database) is discussed, which facilitates the use of HFFB data for preliminary design stages of tall buildings subject to wind loads.

Enhancement of polyphenol content and antioxidant capacity of oat (Avena nuda L.) bran by cellulase treatment

Dongfang Chen,Junling Shi,Xinzhong Hu 한국응용생명화학회 2016 Applied Biological Chemistry (Appl Biol Chem) Vol.59 No.3

In this work, cellulase was used to treat with oat bran, and its effect on the total polyphenol content and phenolic profiles were investigated, with heating-only treatment as the control. Antioxidant capacity of the phenolic extracts from oat bran was assessed by scavenging of 2,2′-azinobis (3-ethylbenzothiazoline-6- sulphonic acid), 2, 2-diphenyl-1-picrylhydrazyl radical cation, the ferric reducing antioxidant power, and protein oxidative damage protection assays. As a result, cellulase treatment significantly increased the total phenolic content, total antioxidant capacity, and the ability on the protection of protein from oxidative damage of the oat bran compared with heating-only treatment. Furthermore, cellulase treatment significantly increased availability of most phenolic compounds, except of gallic acid, such as caffeic acid by 97 % (5.33 vs. 10.51 μg g−1), vanillin by 28 % (3.32 vs. 4.24 μg g−1), p-coumaric acid by 105 % (5.55 vs. 11.35 μg g−1), and ferulic acid by 914 % (12.33 vs. 124.03 μg g−1). However, heating-only treatment had no significant influence on the five detected phenolic compounds. Therefore, the study revealed that cellulase treatment would produce polyphenol-rich oat products with increased antioxidant activity.

Improved modeling of equivalent static loads on wind turbine towers

Gong, Kuangmin,Chen, Xinzhong Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.20 No.5

This study presents a dynamic response analysis of operational and parked wind turbines in order to gain better understanding of the roles of wind loads on turbine blades and tower in the generation of turbine response. The results show that the wind load on the tower has a negligible effect on the blade responses of both operational and parked turbines. Its effect on the tower response is also negligible for operational turbine, but is significant for parked turbine. The tower extreme responses due to the wind loads on blades and tower of parked turbine can be estimated separately and then combined for the estimation of total tower extreme response. In current wind turbine design practice, the tower extreme response due to the wind loads on blades is often represented as a static response under an equivalent static load in terms of a concentrated force and a moment at the tower top. This study presents an improved equivalent static load model with additional distributed inertial force on tower, and introduces the square-root-of-sum-square combination rule, which is shown to provide a better prediction of tower extreme response.

Predicting of tall building response to non-stationary winds using multiple wind speed samples

Guoqing Huang,Xinzhong Chen,Haili Liao,Mingshui Li 한국풍공학회 2013 한국풍공학회지 Vol.17 No.2

Non-stationary extreme winds such as thunderstorm downbursts are responsible for many structural damages. This research presents a time domain approach for estimating along-wind load effects on tall buildings using multiple wind speed time history samples, which are simulated from evolutionary power spectra density (EPSD) functions of non-stationary wind fluctuations using the method developed by the authors’ earlier research. The influence of transient wind loads on various responses including time-varying mean, root-mean-square value and peak factor is also studied. Furthermore, a simplified model is proposed to describe the non-stationary wind fluctuation as a uniformly modulated process with a modulation function following the time-varying mean. Finally, the probabilistic extreme response and peak factor are quantified based on the up-crossing theory of non-stationary process. As compared to the time domain response analysis using limited samples of wind record, usually one sample, the analysis using multiple samples presented in this study will provide more statistical information of responses. The time domain simulation also facilitates consideration of nonlinearities of structural and wind load characteristics over previous frequency domain analysis.

Improved modeling of equivalent static loads on wind turbine towers

Kuangmin Gong,Xinzhong Chen 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.20 No.5

This study presents a dynamic response analysis of operational and parked wind turbines in order to gain better understanding of the roles of wind loads on turbine blades and tower in the generation of turbine response. The results show that the wind load on the tower has a negligible effect on the blade responses of both operational and parked turbines. Its effect on the tower response is also negligible for operational turbine, but is significant for parked turbine. The tower extreme responses due to the wind loads on blades and tower of parked turbine can be estimated separately and then combined for the estimation of total tower extreme response. In current wind turbine design practice, the tower extreme response due to the wind loads on blades is often represented as a static response under an equivalent static load in terms of a concentrated force and a moment at the tower top. This study presents an improved equivalent static load model with additional distributed inertial force on tower, and introduces the square-root-of-sum-square combination rule, which is shown to provide a better prediction of tower extreme response.

Predicting of tall building response to non-stationary winds using multiple wind speed samples

Huang, Guoqing,Chen, Xinzhong,Liao, Haili,Li, Mingshui Techno-Press 2013 Wind and Structures, An International Journal (WAS Vol.17 No.2

Non-stationary extreme winds such as thunderstorm downbursts are responsible for many structural damages. This research presents a time domain approach for estimating along-wind load effects on tall buildings using multiple wind speed time history samples, which are simulated from evolutionary power spectra density (EPSD) functions of non-stationary wind fluctuations using the method developed by the authors' earlier research. The influence of transient wind loads on various responses including time-varying mean, root-mean-square value and peak factor is also studied. Furthermore, a simplified model is proposed to describe the non-stationary wind fluctuation as a uniformly modulated process with a modulation function following the time-varying mean. Finally, the probabilistic extreme response and peak factor are quantified based on the up-crossing theory of non-stationary process. As compared to the time domain response analysis using limited samples of wind record, usually one sample, the analysis using multiple samples presented in this study will provide more statistical information of responses. The time domain simulation also facilitates consideration of nonlinearities of structural and wind load characteristics over previous frequency domain analysis.

POD Analysis for modeling wind pressures and wind effects of a cylindrical shell roof

Fanghui Li,Xinzhong Chen 한국풍공학회 2020 Wind and Structures, An International Journal (WAS Vol.30 No.6

This paper presents a study on the effectiveness of the proper orthogonal decomposition (POD) technique for reconstruction of wind pressure field as applied to a cylindrical shell roof based on simultaneously measured wind pressure data. The influence of wind loading mode truncation on the statistics of dynamic pressures and wind load effects are investigated. The results showed that truncation of higher wind loading modes can have more noticeable influence on the maximum and minimum pressures that the standard derivation (STD) values. The truncation primarily affects the high-frequency content of the pressures. Estimation of background response using wind loading modes is more effective than the use of traditional structural modal analysis.

Wind load characteristics of large billboard structures with two-plate and three-plate configurations

Dahai Wang,Xinzhong Chen,Jie Li,Hao Cheng 한국풍공학회 2016 Wind and Structures, An International Journal (WAS Vol.22 No.6

This paper presents a wind tunnel study of wind loads of the large billboard structures with two-plate and three-plate configurations. Synchronous dynamic pressures on the surfaces of plates are measured, and the characteristics of local pressures, integrated forces on each individual plate and on the overall structures are investigated. The influences of wind direction and plate configuration on wind load characteristics, and the contributions of overall crosswind load and torque to the stress responses are examined. The results showed that the wind load characteristics of windward plate in both two- and three-plate configurations are very similar. The contribution of overall crosswind load makes the total resultant force from both alongwind and crosswind loads less sensitive to wind direction in the case of three-plate configuration. The overall torque is lower than the value specified in current codes and standards, and its contribution is less significant in both two-plate and three-plate configurations.

Wind load characteristics of large billboard structures with two-plate and three-plate configurations

Wang, Dahai,Chen, Xinzhong,Li, Jie,Cheng, Hao Techno-Press 2016 Wind and Structures, An International Journal (WAS Vol.22 No.6

This paper presents a wind tunnel study of wind loads of the large billboard structures with two-plate and three-plate configurations. Synchronous dynamic pressures on the surfaces of plates are measured, and the characteristics of local pressures, integrated forces on each individual plate and on the overall structures are investigated. The influences of wind direction and plate configuration on wind load characteristics, and the contributions of overall crosswind load and torque to the stress responses are examined. The results showed that the wind load characteristics of windward plate in both two- and three-plate configurations are very similar. The contribution of overall crosswind load makes the total resultant force from both alongwind and crosswind loads less sensitive to wind direction in the case of three-plate configuration. The overall torque is lower than the value specified in current codes and standards, and its contribution is less significant in both two-plate and three-plate configurations.