Study On Wind Loads Of A Long Span Cantilevered Building In A Non-ideal Mountain Area

Long span cantilever structure is sensitive to wind load because of its long span and long cantilever.Previously,the wind load research on large-span cantilever structures is mostly based on the flat wind field.The wind load research on the large-span cantilever structure under the complex wind field in mountainous areas is still scarce.If the wind load research conclusion of long-span cantilevered structures based on flat wind field is directly adopted for structural design,it is bound to produce large errors.Therefore,wind tunnel test,CFD numerical simulation and finite element analysis method are used to study the wind field characteristics of non-ideal shape mountains and the wind load characteristics of large-span cantilever structures located on mountain cliffs.And the advices of the wind pressure value of the long span cantilever structure and the optimization of the cross-section about wind load are obtained.At the same time,the wind-induced response characteristics of the large-span cantilever structure in the mountain are obtained.The main research work and conclusions of this paper include:(1)Through wind tunnel test and CFD numerical simulation of the non-ideal shape mountain,the wind field rule of the windward face of such mountain was studied.The study found that,for the average wind speed,the maximum wind speed amplification effect appears at the top of the cliff,and the negative acceleration effect occurs at the position below one-half of the mountain slope.However,the wind speed amplification effect at the top of the mountain is smaller than the common mountain.For the near-surface turbulence intensity,the turbulent intensity at the top of the cliff reaches a maximum of 42.7%in the lateral wind direction,and is similar to the turbulence of the incoming flow under both windward and leeward conditions;the power spectrum of the pulsating wind speed is affected by the mountain,the power spectrum Both the high and low frequencies will change.For the simplified model of such mountain numerical simulation,it is necessary to accurately simulate the slope of the cliff and the opening angle of the concave cliff,and other parts can be simplified.(2)the influence of non-ideal shape mountain on the shape coefficient of large-span roof,the average wind pressure coefficient of large-span cantilever structure and the lift coefficient was studied was studied through the rigid model pressure-measuring wind tunnel test.It is found that,for large-span roofs in mountainous areas,the maximum local wind pressure coefficient occurs in the windward eaves and corners.And the overall shape coefficient of the roof was close to zero on the lee side with mountain cover.For the large-span cantilever structure in the mountainous region,due to the influence of the mountain,the structure is subject to a great lifting force in the downwind direction and downward pressure in the crosswind direction,which is an adverse working condition for the structure design.(3)Based on the time-history data of wind pressure on building surface obtained from wind tunnel test,the wind-induced vibration response of large cantilever structure in mountain area was analyzed,and the influence of wind direction angle,basic wind pressure and turbulence intensity on vertical wind-induced acceleration of structure was studied.It is found that the vertical wind-induced acceleration of the long-span cantilever structure is greatly affected by the non-ideal shape of the mountain,and the amplitude of the vertical wind-induced acceleration reaches its maximum when the wind direction is sideways.The longer the cantilever length,the larger the amplitude of the vertical wind vibration acceleration of the structure.The greater the basic wind pressure,the larger the amplitude of the vertical wind vibration acceleration of the structure.The stronger the turbulence intensity,the larger the amplitude of the vertical wind vibration acceleration of the structure.The vertical wind-induced acceleration amplitude of the structure under the wind field of class B landform is larger than that of the uniform flow field.The maximum increase amplitude reaches 0.68 m/s~2,and the average increase amplitude is0.14 m/s~2.(4)Aiming at the problem that the vertical wind-induced acceleration amplitude of the structure does not meet the requirements of human comfort,CFD numerical simulation method was used to study the optimization performance of the cantilevered skywalk and cliff hotel wind load with the section angle treatment measures of chamfering and rounding.The results show that the chamfering and rounding treatment of the section can effectively reduce the lift coefficient of the cliff hotel.When the chamfering rate is 15%,the lift coefficient is reduced by about 30%,and the optimization effect of the chamfering is better than that of rounding.It is recommended to optimize the building section in the actual project to reduce the lift coefficient of the building and reduce the vertical acceleration amplitude of the wind vibration.