Study On The Wind Characteristic Parameters And Buffeting Response Of Long-span Steel Trussarch Bridge Of Mountainous Regions In Western China

Characterised by advantages such as a light structure, reasonable stress levels,convenient segmental assembly and construction, etc., steel trussed arch bridges havebeen widely constructed in mountainous areas with criss-cross gulleys in western China.To bridge these gulleys generally requires an arch spanning more than300m. Thelengthening of a span reduces the overall stiffness and damping ratio of such bridgesand increases the sensitivity to wind-loading. Therefore, wind-induced vibrationsignificantly influences bridge structures and their construction, particularly during thecantilever construction period before completion. However, the current Wind-resistantDesign Specification for Highway Bridges does not provide detailed specifications forthe wind-resistance of bridges in mountainous areas: this brings difficulties in thewind-resistant design of bridges in such areas. By applying the wind environment ofDaning River site as the research objective, this work observed the wind at the site andanalysed the wind field distribution law. According to the wind field characteristicsmeasured in situ and the suggested wind spectra in the Specification, the wind spectralparameters conforming to the site’s characteristics were fitted. Based on the windspectra at the site, the buffeting responses of a bridge structure in its completed state, atclosure, and at maximum cantilever during construction were studied and comparedwith the computational results based on the suggested wind spectra to verify theeffectiveness of the current Specification with regards its wind-resistance calculation forbridges in mountainous areas. The research encompassed the following aspects:1) By using the C#programming language, software for processing windcharacteristics found by observation and their analysis was developed in anMS-Windows Presentation Foundation (WPF) framework. The software couldsegmentally process data, automatically, quickly, and accurately calculate and analyseobserved wind data, and output final wind characteristic parameters and the actual windspeed spectra. By using this software, it became convenient and simple to processmassive amounts of measured data pertaining to the in situ wind field.2) The analysis of wind characteristic data revealed the distribution of the windfield at the bridge site in valley area of the Daning River. The variation of average windspeed at different heights at the site was not consistent with either the exponentialdistribution or logarithmic distribution provided by the Specification. For mountainous landforms in western China, the wind exhibited significant fluctuations. The horizontalturbulence intensity measured at a height of10m above the skewback was40%, andthat at90m was20%. The results indicated that the influence of large turbulence scalehave to be taken into account in the wind-resistant design of bridges in westernmountainous areas.3) By fitting the measured wind speed spectra at the bridge site with statisticalmethods, the wind spectra expressions for horizontal and vertical fluctuations wereobtained. The measured fluctuation wind speed spectra were different to thosesuggested in the Specification and showed much less energy at low-frequencies. Thisphenomenon directly influenced the contributions of low-frequent modes to thebuffeting resonant response.4) Based on ANSYS finite element analysis software, three finite element modelsfor the completed bridge, its closure, and the cantilever during construction of thebridge over the Daning River were established and their structural dynamiccharacteristics obtained. The buffeting responses of the bridge structure in these threestates were analysed using a self-compiled program based on the fitted wind spectra andthat suggested by the Specification, respectively.5) The results of buffeting response analysis indicated that the bridge underwent alarge lateral displacement and little vertical and torsional buffeting displacement whencompleted. In addition, the displacement at mid-span was apparently larger than that ateach end. The buffeting responses in the completed, and closure, states were mainlyinfluenced by the combined action of symmetric and asymmetric modes; while themaximum cantilever construction state was only affected by symmetric modes andshowed a larger buffeting response amplitude than that of the other two states. Moreover,instead of a lateral bending mode with torsion, the torsional buffeting in the maximumcantilever construction state was influenced by the symmetric torsional mode.6) The computation of buffeting in each state revealed that the computed values ofthe suggested wind spectra were larger than those actually fitted to site data: there werelarge differences in the horizontal direction, where the structure exhibited a lowerstiffness. Furthermore, the comparison of buffeting response spectra demonstrated thatthe two types of wind spectra contributed equally to the background response of thestructure and they had consistent order and distribution of resonant modes. However;the resonant response of the suggested wind spectra was larger, particularly forlow-frequency modes. The computational results also intimated that the provisions for calculating buffeting in the current Specification were able to guide the wind-resistantcomputation for large-span arch bridges in mountainous areas. However, theuniversality of the provisions has to be verified by further research.