| Long span cable-supported bridges are rapidly increasing nowadays not only in number but also in the length of central-span because of their inherent economical and technical advantages. However, these long span bridges are very flexible and lightly damped and vulnerable to wind-induced vibration. In particular, during the erection, long span bridge deck lacks continuity from pylon to pylon and its rigidity is much lower than that of a completed bridge. Serious buffeting vibration has been observed from a few long span cable-supported bridges during construction. Reviews of the existing literature, however, show that few studies have examined the suppression of lateral and torsional vibration of long span bridges. This thesis thus focuses on the development and application of novel tuned liquid column dampers for suppressing lateral and torsional vibration of long span cable-supported bridges during construction and at completion stage.; The frequency of STLCD or MTLCD depends solely on the length of liquid column, which imposes certain restrictions on its application to long span bridges. Multiple pressurized tuned liquid column dampers (MPTLCD) are thus studied to facilitate lateral and torsional vibration reduction of bridges and to improve the sensitivity under mistuning. The MPTLCD container is sealed with an air chamber at its two ends. The frequency tuning can be adjusted by manipulating static pressure inside the air chamber while the length of liquid column is fixed. To control vibration of bridges with high natural frequency, the MPTLCD with a longer liquid column length can be used to replace the STLCD or MTLCD with a shorter liquid column length. However, for a long span cable-supported bridge during construction, its very low natural frequency may require a STLCD or a MTLCD with very long liquid column length, which may not be possible in practice. Moreover, natural frequencies of a long span bridge vary during its construction stage. Hence, tuned liquid column dampers with adaptive frequency tuning capacity are developed for suppressing lateral and torsional vibration of bridges using a semi-active control technology. The natural frequency of the semiactive tuned liquid column dampers (SATLCD) studied herein can be adjusted by active control of air pressures at the two chambers of a PTLCD. |
