Study On The Directionality Of Wind Load And Wind Effect Of Saddle Roof

For a given building orientation,the different flow directions make the wind load and wind effect of the building structure directional.When the directionality is not considered,the wind load or wind effect may be overestimated,resulting in a conservative calculation result.For the calculation of design wind load in the load code of China(GB5009-2012),the directional problem is not considered.It uses the maximum wind speed and the most unfavorable wind load or wind load effect coefficient in the whole wind direction to determine the design value of the wind load and wind load effect.In order to obtain more economical and reasonable structural design scheme,and provide reference for future structural wind resistance design optimization,it is necessary to consider the directionality of wind load and wind load effect in the process of structural wind resistance design.As one of the most common structural forms used in industrial and civil buildings,the large-span roof structure has the characteristics of large volume and high cost.Considering the directional problem can effectively reduce its construction cost and save economy.In this paper,the directionality of the wind load and wind effect about saddle roof is systematically studied.The main contents include the following aspects:(1)The current theoretical research methods of directionality of the wind load or wind effect are introduced.Different methods have different conditions when considering randomness and correlation between wind speeds in all directions.These factors will affect the accuracy of directional research results.In this paper,the merits and drawbacks of various methods are compared and analyzed.Finally,the theoretical research method considering both directionality and randomness is selected to analyze the directionality of the wind load and wind effect of structure.(2)Based on the theoretical research method considering both directionality and randomness,this paper studies the directional characteristics of the extreme wind load and extreme wind effect on a large-span saddle roof under different flow directions and also different building orientations,for which synoptic scale strong wind climate is assumed to be considered.And the differences of directionality in wind-resistant design codes of the United States,Japan and New Zealand are discussed.It is further found that there are potential safety hazards in wind-resistant design of structure about three kinds of codes in synoptic scale strong wind climate in China.(3)Integrating the characteristics of the directional regulations in different codes,the method of calculating the design wind load and wind effect under the condition that the wind effect in each direction is independent of each other is proposed.In synoptic scale strong wind climate in China,the correlation of extreme wind speeds in all directions is weak,even tends to be independent of each other.Under the conditions,the design values of the wind load or wind effect determined by the proposed method are more economical than those without considering directionality.At the same time,through the analysis of the Sector-by-Sector method,it is found that the wind load or wind effect value determined by the proposed method is always larger than its estimated value,thus ensuring that the structural wind-resistant design is safe.(4)Taking wind load of cladding structure and wind effect of main structure about saddle roof as examples,the effectiveness of the proposed method is verified by using wind speed information of Beijing,Jinan and Harbin in synoptic scale strong wind climate.At this time,the ratio of the wind load and wind effect estimated value to the designed value of the proposed method is about 0.9 to 1,and the corresponding ratio calculated when the directionality is not considered is about 0.5 to 0.9.In summary,this paper suggests that the method of calculating wind effects considering the independence of wind effects of each direction be used as an alternative to determine the design values of extreme wind load and wind effect in synoptic scale strong wind climate in China.