Study On The Wind-environment And Wind Loads Of The Long-span Continuous Rigid Frame Bridge With Tall Piers In Mountainous Areas

With the entering of expressway into mountainous area, there are more and more long-span continuous rigid frame bridges with tall piers, and wind load and internal force of wind load have gradually become the major factors of this kind of bridge design. However, on the one hand, the existing research results on bridge wind environment are conducted on flat plain, yet mountainous area has more complicated terrain and the part wind environment has more influential factors. Therefore, the wind characteristic in mountainous area is very different from that in plain. The in-depth research on wind environment of bridge site is the prerequisite of bridge wind-resistant design in mountainous area. On the other hand, existing research results on wind resistance of bridge are targeted at long-span suspension bridges or cable-stayed bridges. The wind resistance research on long-span continuous rigid frame bridges with tall piers is not sufficient. Based on a typical actual engineering San-shui-he Bridge with span of 98+5×185+98 m and maximum high pier of 180m as background, research on bridge site wind environment in mountainous area and wind effect of long-span continuous rigid frame bridge with tall piers were conducted on the basis of existing researches in this thesis. The main research results are as follows:By different sample interval, extreme wind speed distribution possibility and wind speed sample sorting methods from existing research, the calculation formulas to determine basic wind speed were deduced in consideration of joint probability distribution of wind speed and direction. Through the statistical analysis of the wind speed and wind direction observational data in continuous 34 years of weather station around the bridge site, the different basic wind speed gained by different methods were given and compared in the paper. The results show that the traditional analytical method, which does not distinguish wind direction, overestimates the basic wind speed. The basic wind speed of the current code recommendation is overestimated too much. The basic wind speed deduction should take joint probability distribution of wind speed and direction into consideration, and the shorter sample interval is the more economic and reasonable it is.A large scale digital terrain model including the bridge site and nearby weather stations was established in the paper. On the digital model, the bridge site wind environment was studied, and the results of it were compared with that of physical wind tunnel trail. A method to estimate the bridge design standard wind speed through the basic wind speed of weather station by CFD (computational fluid dynamics) technology was proposed, and be used to calculate the design standard wind speed of San-shui-he Bridge. The results show that the wind profiles of the numerical wind tunnel have a certain deviation with the physical wind tunnel results, yet the consistence of the two's overall tendency is good. The complicated terrain of bridge site in mountainous area has great interference influence on the wind field. The wind profiles in different wind direction and different location have great variation, and part of them cannot meet the power exponent change laws. When coming wind is in consistent with valley direction, the wind profile of the bridge piers in down watercourse are close to that of B type terrain in codes. The bridge design standard wind speed at the same location might have great variation in different wind direction, and its distribution along the bridge length would be uneven even in the same wind direction.The aerostatic coefficients of different bridge cross sections under various wind attack angles or directions and the situation with or without guardrails were studied by CFD. The results were compared with that of physical wind tunnel trail, and the change laws of the aerostatic coefficients with different influential factors were summarized. On this bases, the aerodynamic interference mechanism of double width bridge was explored, and the effects of different interference factors on aerostatic coefficients of the bridge in up and down stream were summarized. The results show that the aerostatic coefficients gained by CFD have high accuracy in upstream bridge resistance coefficient and relatively larger error in downstream bridge resistance coefficient and lift coefficient and torque coefficient of bridge in up and down stream. However, the overall results are in good agreement with the physical wind tunnel test results. For resistance coefficients, the effect of coming wind to upstream bridges is strong push, and to downstream bridges is relatively weak suction. It is affected small by wind attack angle, and becomes bigger with increase of the girder section's height, and be affected largely by guardrail. Lift coefficients in up and down stream and torque coefficients will change with the influence of the wind attack angle (or wind direction), dimension of section, guardrail and other factors. The aerodynamic interference effect has great impact on double width downstream bridge. On the whole, the change rule of interference effect with wind attack angle is not very clear, but increase with the decrease of the gap and increase with the growth of the structure sizes. The aerodynamic interference effect has certain impact on upstream bridge, but the impact is relatively small.The differences of transverse wind load calculation about long-span continuous rigid frame bridges with tall piers in foreign and domestic standards were quantitatively analyzed and compared, and were further compared with buffeting analytical results by a numeric example. Based on the characteristic of tall pier continuous rigid frame bridge and its first model out-of-plane, considering average wind effects and background responses of fluctuating wind and its resonant responses as well, a practical analytical formulas was proposed in this paper, which aimed at calculating the equivalent wind loads of transverse bending moment and shear force of pier-bottom on continuous rigid frame bridge with tall piers. By two examples, the accuracy and applicability of simplified method were tested. Comparative analysis show that, because the fundamental frequency of the long-span continuous rigid frame bridge with tall piers is low, the resonant response effects should not be neglored. The wind load calculated using present code was generally underestimated due to the neglect of the resonant response effects. The wind loads on pier of high pier bridges, extra high pier bridges in particular, is very large, which impact on pier bottom internal force could even surpass the girder wind loads. It should be paid sufficient attention in design of these kinds of bridges.