Research On Interference Effect Of Double Chimneys And Its Wind-resistant Design Method

Under the action of wind load,chimney structure can produce significant wind-induced vibration,easily collapse and damage,causing huge human and economic losses.In recent years,there appear multiple chimneys in many new large-scale power plants,especially double chimneys.Because of the relatively dense arrangement of chimneys,the interference effect is obvious.However,the interaction effect between two chimneys in Chinese Load code for the design of building structures is not clear enough,and the design method of wind resistance is not perfect enough.More importantly,because of the large displacement of the tall chimney structure under wind load,the coupling effect between its vibration and flow field will occur,which will produce additional aerodynamic force.This phenomenon is called aeroelastic effect or aeroelastic phenomenon.However,the Load code for the design of building structures do not consider aeroelastic effect.Because of the above imperfections in the wind-resistant design of double chimneys,the wind pressure distribution,base wind force and displacement of single and double chimneys were obtained by means of rigid model pressure measurement test(RMPMT)and aeroelastic model vibration measurement wind tunnel test(AMVMT).By comparing the differences between single and double chimneys,the interference effect of double chimneys was deeply analyzed.At the same time,the wind-induced displacement obtained by rigid pressure test data(DORMPMT)and that directly obtained by aeroelastic model vibration measurement test(DOAMVMT)were compared,and the aeroelastic effect of chimney structure was explored.Finally,the wind-resistant design method considering the interference effect of double chimneys was proposed in accordance with the relevant regulations of the Load code for the design of building structures in China,which could be used as a reference for designers.The main work included the following aspects:(1)Through the rigid model pressure test of single and double chimneys,the influence of interference effect of double chimneys on average wind load,fluctuating wind load,extreme wind load and combined wind load was studied and analyzed.The rigid interference factor of wind load force was calculated.It was found that when the interfering chimney is located in the range of 15 ~30 degrees in front of the principal chimney obliquely,there existed significant wind amplification effect.In order to facilitate engineering application,contour maps of rigid interference factor of wind load force were drawn.(2)A multi-degree-of-freedom aeroelastic model was used to carry out wind tunnel tests on single and double chimneys,and the displacement response of the chimney’s apex considering the aeroelastic effect was obtained.The aeroelastic effect of single chimney and double chimney was studied by comparing the DOAMVMT and DORMPMT.An aeroelastic factor was defined directly as the ratio of the DOAMVMT and DORMPMT in order to show the comprehensive influence of aerodynamic damping,stiffness and mass,and an intuitive reflection of the aeroelastic effect of chimney structure.It was found that the displacement response would be magnified in the critical wind speed.(3)Based on the test results of AMVMT,the displacements of the single and double chimneys’ apex were compared respectively,the aeroelastic interference factor of double chimneys was defined,and the relationship between the factor and the reduced wind speed was explored.It is found that the aeroelastic interference effect in the case of spacing 2D was significantly different from that in other case,where D is the average diameter of chimney.Based on the research results of some scholars,the causes of aeroelastic interference can be attributed to the narrow gap effect and the coordinated fluctuation of two chimney vortices.(4)The most disadvantageous rigid interference factor and aeroelastic interference factor were calculated.Based on the calculation method of design wind load in the Load code for the design of building structures in China,the calculation method of the design wind load of double chimneys was established by introducing the correction of interference factor.Finally,the rationality of this method was verified by an engineering example.