大跨度斜拉桥下击暴流风致振动响应实测

以苏通长江公路大桥为工程背景,针对该桥风致振动响应监测系统实测的一次下击暴流风与桥梁结构振动加速度响应实测数据,对该桥在一次雷暴天气下风速、风向及主梁振动响应进行研究.首先,对桥位处下击暴流实测风速、风向数据进行分析,获得了该桥主梁跨中、桥塔塔顶处下击暴流风的时变平均风与脉动风特性;然后,对下击暴流作用下主梁风致振动加速度响应数据进行分析.结果表明:在下击暴流作用下,该桥主梁与塔顶高度处风速发生了明显突变,持续时间约为10～24 min;主跨跨中主梁外侧边缘处下游、上游侧最大瞬时风速分别为32.4 m/s和27.3 m/s,南、北桥塔塔顶高度处最大瞬时风速分别达60.5 m/s和62.9 m/s.主梁高度处30 s时距湍流度约0.048～0.32,10 min时距湍流度约0.43～0.51;主梁下游与北塔处折减脉动风速符合高斯特性,其功率谱与Burlando等学者的实测结果吻合较好.主梁跨中附近(即NJ26D、NJ32D拉索锚固处)发生了较为明显的短时竖向与横桥向振动,相应加速度响应幅值分别为0.25 m/s2和0.10 m/s2,对应位移幅值分别为0.12 m与0.03 m;主梁竖向振动响应明显大于横桥向振动响应,主梁竖向振动主频为0.183 Hz,与主梁全桥一阶正对称竖弯振型频率0.174 Hz接近;横桥向振动主频为0.117 Hz,与主梁全桥一阶正对称侧弯振型频率0.0975 Hz接近.

Field Measurement of Wind-induced Vibration Response of Long-span Cable-stayed Bridge under Downburst

Taking Sutong Yangtze River Highway Bridge (STB) as an engineering background, a downburst wind and the vibration acceleration responses of the bridge structure were monitored based on the wind-induced vibration response monitoring system of the bridge. Furthermore, the wind speed and direction, vibration responses of the main girder under the thunderstorm were investigated. Firstly, the measured wind speed and wind direction data of the downburst wind at the bridge site were analyzed, the time-varying mean wind and fluctuating wind characteristics of the downburst at the mid-span of the main girder and the pylon tops were obtained. Then, the wind-induced vibration acceleration responses of the main girder under the downburst were analyzed. The research results show that the wind speeds at the main girder level and the pylon tops of the STB changes abruptly under downburst, which lasts approximately 10~24 minutes. The maximum instantaneous wind speeds at the leeward and windward side of the main girder in the middle of the main span of STB are 32.4 m/s and 27.3 m/s, respectively. Meanwhile, the maximum instantaneous wind speeds at the south and north pylon tops are 60.5 m/s and 62.9 m/s, respectively. The turbulence intensity for a time interval of 30 s at the main girder level is about 0.048~0.32, and the turbulence intensity for a time interval of 10 minutes is about 0.43~0.51. The reduced fluctuating wind speed at the downstream of the main girder and the north pylon conforms to Gaussian characteristics, and its power spectrum is in good agreement with the field measurement results by Burlando and other scholars. Obvious short-term vertical and horizontal vibration occurred near the middle of the main girder (that is, the anchorage of NJ26D and NJ32D cables), and the corresponding acceleration response amplitudes were 0.25 m/s2 and 0.10 m/s2, corresponding to the displacement amplitudes of 0.12 m and 0.03 m, respectively. The vertical vibration response of the main girder is obviously larger than the transverse vibration response. The predominant frequency of vertical vibration of the main girder is 0.183 Hz, which is close to the 1st symmetric vertical bending mode frequency 0.174 Hz of the main girder. And the predominant frequency of horizontal vibration is 0.117Hz, which is close to the 1st symmetry lateral bending mode frequency 0.097 5 Hz of the main girder.