Experimental Investigation on the Nonlinear Coupled Flutter Motion of a Typical Flat ClosedBox Bridge Deck The nonlinear postflutter instabilities were experimentally investigated through twodegreeoffreedom sectional model tests on a typical flat closedbox bridge deck (widthtodepth ratio 9.14). Laser displacement sensors and piezoelectric force balances were used in the synchronous measurement of dynamic displacement and aerodynamic force. Beyond linear flutter boundary, the sectional model exhibited heavetorsion coupled limit cycle oscillation (LCOs) with an unrestricted increase of stable amplitudes with reduced velocity. The postcritical LCOs vibrated in a complex mode with amplitudedependent mode modulus and phase angle. Obvious heaving static deformation was found to be coupled with the largeamplitude postcritical LCOs, for which classical quasisteady theory was not applicable. The aerodynamic torsional moment and lift during postcritical LCOs were measured through a novel windtunnel technique by 4 piezoelectric force balances. The measured force signals were found to contain significantly higherorder components. The energy evolution mechanism during postcritical LCOs was revealed via the hysteresis loops of the measured force signals.

Dynamic Responses of a Metro TrainBridge System under TrainBraking: Field Measurements and Data Analysis This paper focuses on the dynamic responses of a metro trainxe2x80x93bridge system under trainbraking. Experiments were performed on the elevated Metro Line 21 of Guangzhou (China). A continuous, threespan, rigidframe bridge (42 m  65 m  42 m) and a standard Btype metro train were selected. The acceleration signals were measured at the centerpoints of the main span and one sidespan, and the acceleration signals of the car body and the bogie frame were measured simultaneously. The trainxe2x80x93bridge systemxe2x80x99s vibration characteristics and any correlations with time and frequency were investigated. The Choixe2x80x93Williams distribution method and wavelet coherence were introduced to analyze the obtained acceleration signals of the metro trainxe2x80x93bridge system. The results showed that the Choixe2x80x93Williams distribution provided a more explicit understanding of the timexe2x80x93frequency domain. The correlations between different parts of the bridge and the trainxe2x80x93bridge system under braking conditions were revealed. The present study provides a series of measured dynamic responses of the metro trainxe2x80x93bridge system under trainbraking, which could be used as a reference in further investigations.