Experimental Study Of Wind Load And Wind-induced Response On Large Outdoor Single-column Billboards

As an important advertising carrier,the applications of large-scale outdoor single column-supported billboards are more and more widely.They are a typical vulnerable structure under the disastrous wind,and are usually built around the urban,rural area and along railways,highways,so their strong wind-induced damage is not uncommon.It will bring up very serious impact on the main traffic thoroughfare once they collapse or generate debris due to strong wind.So it is urgent to carry out the research of wind-induced response of billboards.Although the design of billboards has made great progress so far,the present code that calculates the wind loads of billboards just simply follows the method of single-plate sign in Load Code for the Design of Building Structures.For the "V-shape" two-and three-plate billboard,due to its unique aerodynamic shape and the soft dynamic characteristics,and belonging to single column-supported cantilever system,it is necessary to make further study of wind loading on this billboard structure and of consequence of wind induced vibration response.This paper includes the following points:(1)Giving the wind loads on these two typical billboards with rigid column based on pressure measurement experiment and obtaining the PSD of along-and across-wind force and torque.A suggested formula of along-wind and torsional PSD were Prosposed according to the most unfavourable configuration.(2)Based on the in-depth study of the structure of two-and three-plate billboards,the structural parameters of these two billboards with typical size were selected,and then their aero-elastic models were made.Structural dynamic characteristics and aerodynamic damping ratio under wind-induced vibration were identified effectively.(3)The force and torque coefficients at the column's bottom of billboard as well as the eccentricity of torque under different angles of wind incidence were calculated and analyzed by force-balance technique,and compared with the results of rigid model pressure measurements test,and also wind-induced vibration response spectrum of force at the column's bottom was analyzed detailedly.Back to prototype of billborads,analyses aiming at the stress at the column's bottom were given and the contribution of every stress component to the failure of column was discussed.(4)The translational displacement in along-wind,across-wind and torsional angle along vertical axis of the billboard were obtained by using displacement sensor under different configurations.And the PSD of displacements in three directions were given.(5)Based on quasi-steady theory,simplifying the along-wind motion of billboards as a wind-induced buffeting mechanics model to calculate the along-wind response and the measured response by force-balance shows that the method is effective.The torsional response of the structure can be calculated by input torsional load that calculated by fitting the torque spectrum in pressure measurements test of rigid model.(6)From the perspective of structural design,and taking prototype of billboards into consideration,the simplified calculation method of torsional response of billboard was proposed according to the analyses of unfavourable configurations.