| With the development of economy and progress of science and technology, lots ofbeautiful and innovative spatial structures have been built. Such long-span roofstructures are widely used in various large public buildings due to their exquisiteshapes and favorable performance. However, these structures, with the characteristicsof light mass, high flexibility and slight damping, are sensitive to wind loads, and thewind loads generally govern the design of these structures. In addition, suddenopening of doors and windows would result in an increase of internal pressure, whichwould be a major threaten to the roof structures. According to wind disaster surveys,the wind damages to roof structures, in a large degree, are caused by the combinedresults of internal and external pressures. At present, the mechanism of generating theinternal pressure changes is still not fully clear, and only the internal pressurecoefficients in nominal sealing or opening condition are provided in current domesticand international load codes for the wind-resistant design. Hence, further research onthe effect of wind-induced internal pressures on the wind loads on roof structures isrequired, which is also a hotspot in wind engineering.Based on the investigation of wind tunnel tests for fish-shaped roof structures interrain category A specified in the Chinese load code and typhoon wind field, it wasfound that the fluctuating pressure coefficients on the eaves and cantilevered roofswere larger than those on other areas of the roof. Obvious wind load differences forthe roof structures existed under different turbulence intensity conditions, the windloads under the typhoon wind field were greater than those in terrain category A.Besides the conventional norm for the assessment of design wind loads, it wassuggested that wind tunnel test in typhoon wind field was necessary when designingstructures are located in typhoon-prone areas, especially those with complicatedshapes.Based on the wind tunnel test of rigid model of Jilin Railway Station, the wind loaddistribution characteristics were presented and discussed. It was found that negativepressures (suctions) occurred on the eaves, cantilevered roof and the bulge part of theroof on the main station building. The turbulence characteristics of flow in lower partwere more obvious and the flow was easily affected by the surrounding topography.Therefore, the interference effect of the surrounding buildings on the lift coefficients of the platform awning of the station was more significant. Since stronger negativewind pressures were observed in the burbling zone of the roof, and the probabilitydistribution of wind pressure stretched away in the negative pressure area, so it wassuggested that different peak factors should be taken in the different areas of the roofwith different turbulence intensity levels, such as3.0-4.0would be appropriate for theintensive turbulence intensity area while2.5-3.0for the lower one.On comparison of the data of the wind tunnel test for the Kunming Railway (South)Station and those specified by the local load code, it was discovered that the shapecoefficients of the most areas of the main station building matched those specified bythe code when the fa ade entrance was enclosed, while the coefficients on the eavesand the cantilevered roof were distinctly greater than the specified ones. The shapecoefficients on the roof when there were openings were larger than those specified bythe load code with enclosed condition. The probability density function of fluctuatingwind pressure in the marginal area of the main station buildings and the platformawnings of the station shows obvious characteristics of Non-Gaussian, especially inits negative tail.The transfer equation of the internal pressure of roof structure with wall-openingconditions was deduced, and the additive damping effect of the internal pressure bythe opening in the leeward wall was also presented and discussed. Moreover, severalrelated factors were investigated, such as the variation tendency of the orificedamping with different opening areas, internal volume of structure, wind speed andwind pressure height coefficient of the opening. The relations between the openingrate of facade wall and the Helmholtz resonance of the opening structure were alsodiscussed.The assessment of internal and external pressure on long-span roof structuresinvolves several factors such as internal volume, opening area of wall, openinglocations and height-to-span were investigated by the wind tunnel tests of rigidmodels. It was observed from the Power Spectral Density (PSD) of internalfluctuating wind pressure that the spectra included not only the energy component ofatmospheric turbulence, but also the turbulence caused by the opening features. Thetheoretical estimation formula of the internal pressure under multiple wall openingsconditions was deduced, and a comparison between the experimental data and thetheoretical estimated values was also made.The analysis of wind-induced responses of long-span roofs indicated that thenatural frequencies of the roof structures play a significant role on the wind-induced responses, but little influence by the opening ratio. The comparison between the gustresponse coefficients calculated from traditional method and displacement gust factorcalculated by objective-probability method indicated that the traditional methodwould underestimate the response caused by fluctuating pressure where influencedmore by fluctuating wind, and it is not safe enough for the structural design.In this study, the combination of wind tunnel tests and theoretical analysis wereadopted to investigate the wind effects and wind-induced internal pressures of roofstructures with wall-openings. The outputs of this study are expected to providevaluable information and reference for the wind-resistant design of roof structures andthe revision of wind load codes in the future. |
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