聚焦波浪对哑铃型跨海桥梁围堰作用的试验研究

Experimental study of focused wave actions on dumbbell-shaped sea-crossing bridge cofferdam

台风引起的巨浪将严重威胁跨海桥梁施工期围堰的安全,台风波浪较普通规则波浪具有周期更长、波高更大特点,正好符合聚焦波浪的特征。为更好地指导跨海桥梁围堰抵抗极端台风浪设计,开展聚焦波浪与哑铃型桥梁围堰相互作用的波浪水槽试验研究,探讨围堰吃水深度、聚焦波最大波幅、入射角度对测点波面位移及波浪力的影响。其中,分析结果表明,围堰吃水深度及入射角度的变化对测点波面位移的影响不大。随着吃水深度增加,垂直波浪传播方向的有效投影面积增大,围堰顺波向波浪力明显增大。由于波浪能量沿水深衰减,底部浮托力随之减小。随着入射角度增加,有效投影面积增大使得围堰顺波向波浪力非线性增大,而围堰底部浮托力则变化较为平缓。当入射角度和波幅均较大时,围堰顺波向和垂向浮托力的正、负向幅值差异均较大,呈现较明显的不对称性,若按对称受力设计施工方案可能偏危险。与同波幅的聚焦波浪相比,长波条件下若按线性波考虑作用于结构的波浪力将偏不安全,实际跨海桥梁工程设计时有必要按聚焦波浪考虑台风波浪作用。

Great wave triggered by typhoon may present severe danger to the construction safety of sea-crossing bridge cofferdam. Compared with regular wave, typhoon-induced wave has characteristics of longer periods and greater wave heights, which just coincide with those of focused wave. To better guide the design of the cofferdam's resistance to the extreme typhoon-induced wave, a wave flume experimental study of the interaction between focused wave and bridge cofferdam is conducted. In the study, the influences of the cofferdam draught, maximum wave amplitude and incident wave angles of focused wave on wave elevation and wave force are discussed. The results show that changes of the cofferdam draught and incident wave angles have little influence on wave elevation. With the cofferdam draught increasing, effective projection areas of transverse wave-propagation directions increase, longitudinal wave force increases largely. Besides, as a result of wave energy attenuation with water depth, uplift force at the bottom decreases. With the increase of wave incident angles, the expansion of effective projection areas causes that the longitudinal wave force increases nonlinearly, while the uplift force at the bottom changes smoothly. When incident wave angles and wave amplitudes are relatively large, there are comparatively remarkable differences between positive and negative amplitude values of the longitudinal and transverse wave force. What's more, the longitudinal and transverse wave force would present significant asymmetry, resulting in a relatively dangerous construction design if it's based on symmetrical force. Compared with focused waves of the same wave amplitude, regular wave force is much more dangerous especially with longer period condition. Thus it's necessary to consider the focused waves as the typhoon- induced wave for the actual sea-crossing bridge engineering.