Investigation On Reasonable Reduction On Wind Load Of Large-span Flat Roofs

The correlation of fluctuating wind pressure varies with different location and distance,which certainly makes it necessary to consider the wind loading reduction.The load specifications of Chinese code and Japanese code take into account the reduction over considered area on the enclosure structures.However,when considering the reduction of wind load on enclosure structures,the Chinese load code has no detailed regulations on building type,building size,roof angle and roof sub-region,etc.In the traditional large-span roof model in wind tunnel tests,due to the limitation of experimental conditions,it is impossible to place very dense pressure measurement points on the surface of the large-span roof model to obtain the actual distribution of wind loads.Therefore,it is necessary to reasonably consider the reduction in design wind loading on large-span roof structure.Based on the expression of the coherence function of fluctuating wind pressure on the large-span flat roof,the aerodynamic admittance function was derived and presented.Then,the quartic integral expression of the aerodynamic admittance function is reduced to the double integral by the substitution.Finally,the moving average method for wind loading reduction on large-span flat roof was provided after matching the cut-off frequency of the aerodynamic admittance to that of the moving average filter.In this paper,wind tunnel test of a flat-roof museum building is carried out,and the wind pressure time history of a typical region of the roof surface is selected.Then the rationality of the present method was verified by using the pressure data from the wind tunnel tests.The research shows that,compared to the code method,the statistical method based on wind tunnel test data is more acceptable for calculating the most critical wind pressure on large-span flat roof;while with the increase of roof span,the wind loading reduction of a flat roof under the most critical scenario tends to be stable.Based on the Uematsu’s study,the CFD simulation of the circular large-span flat roof is carried out.In addition,Large Eddy Simulation with dynamic subgrid scale model is selected to investigate the turbulent flow around the structure.And the wind pressure time history of a typical region of the roof surface is selected.Then the rationality of the present method was verified by using the pressure data from the numerical simulation.The research shows that,the RFG method based on inlet boundary condition of RANS is difficult to generate self-sustained wind profiles in Large Eddy Simulation;the wind loading reduction characteristic area of enclosure structure should avoid severe changes in location and area of the wind pressure gradient on the roof.The present method can provide a useful way to reasonably determine the most critical wind loading on large-span flat roof structures.