Study Of Wind Induced Response And Equivalent Wind Load Of Large Span Roofs

The long span, light deadweight, low natural vibration frequency, close vibration modes distribution etc are the characteristics of large span roof structures, so it should consider multi-mode participant and the modal coupling effect in wind induced vibration response analysis. Moreover, as the characteristics of complex structure and multi-mode participant, different nodes can't completely synchronized during vibration, it is not clear of the wind-induced response control objects. Correspondingly, the equivalent static wind load (ESWL) should be take into account the more control objects. At present, considering above features, there are many analysis methods of wind induced response and ESWL for large span roofs, each method has its calculation characteristic and application condition. In this paper, takes the National Stadium roof and 2008 Olympic Tennis center cantilevered roof as engineering background, the key issues that wind-resistant design practice of large span roof structure are studied through calculating analysis and theoretical derivation, mainly works as following:1.It systematically summarizes and compares the wind induced response and ESWL analysis methods of large span roof structures which are widely researched in current wind engineering fields, and points out the problems, advantages, disadvantages, application conditions of each method. At the same time, it identifies the key issues of wind-resistant design of large span roofs. Based on these methods, calculating the wind induced response and ESWL of the National Stadium roof and 2008 Olympic Tennis center cantilevered roof, and do a analysis and comparison for the calculation results. On the basis of this, for these two types of typical large span roof structures, the valuable reference advice which properly select wind-induced dynamic response analysis method and ESWL analysis method for engineering design staffs are proposed.2.It points out the main factors which impact the contributions of different modes to wind-induced dynamic response of large span roofs:(1) the correlation of modal spatial distribution and fluctuant wind load distribution on the structure; (2) the proximity of the fluctuant wind load main frequency and modal natural frequency. According to the two factors, the idea which select the dominant modes of wind-induced dynamic response is established. Considering the wind load distribution uncertainty on large span roof structures, it is proposed to select wind load strongly correlated higher frequency modes through the lower frequency modes which are significient contribution to wind-induced dynamic response. Furthermore, simplifying the modal response covariance matrix, the modal participant coefficient is constructed, which is used to select dominant modes of wind-induced dynamic analysis. It effectively solve the key matters of selecting dominant modes in large span roof structures wind-resistant design.3.The relationship between CQC(Complete Quadratic Combination) and SRSS(Square Root of Sum of Squares) is analyzed. It makes a simple analysis for the modal coupling part of background and resonate response of different modes, and their simplified expression are obtained. On the basis of this, introducing the concept of modal strain energy, the background response modal coupling coefficient and resonate response modal coupling coefficient are defined. According to these modal coupling coefficients, the coupling magnitude of background and resonant response for different modes can be conveniently estimated. Therefore a standard for the identification of dominant-coupling modals can be established. The total wind induced background and resonant response can be obtained by the superposition of dominant-coupling modals and SRSS results of each dominant modals. The example analysis results illustrate that the method not only avoid the complicated CQC calculation but also take into account the modal coupling effect, can meet the requirements of large span roof structures wind-resistant design.4.As the characteristic of multi-objects should be considered in calculating ESWL of large span roof structures, this thesis presents an new description of ESWL based on the strain energy which induced by static wind load is equal to the fluctuating wind load. The strain energy is obtained by the product of fluctuant wind load on each nodes and the peak displacement response on each nodes which induced by fluctuant wind loads. Based on this idea, the background response ESWL expression is deduced. The example analysis results illustrate that the proposed method could be used to determine the background response ESWL perfectly, the ESWL not only take into account the multi-objects of response but also have a clear physical meaning, and is suitable for engineering application.