In-Situ Test on Fatigue Characteristics of Top-Mounted Dividable Pile-Board Subgrade for High-Speed Railway

To simulate the fatigue characteristics of the pile-board structure under long-term dynamic load, using the in-situ dynamic testing system DTS-1, the forced vibration loading was repeated one million times at different cross-sections of the pile-board structure for high-speed railway. The dynamic deformation, permanent deformation and dynamic stress of main reinforcements were measured. The test results show that the dynamic responses of the pile-board structure almost did not vary with the forced vibration times under the simulated trainload. After one million times of forced vibration, the permanent deformations of the midspan section of intermediate span and midspan section of side span were 0.7 mm and 0. 6 mm, respectively, and there was no accumulative plastic deformation at the bearing section of intermediate span.

A new bracing system for improvement of seismic performance of steel jacket type offshore platforms with float-over-deck

In this paper, the seismic response of a newly designed steel jacket offshore platform with a float over deck （FOD） system in the Persian Gulf was investigated through incremental dynamic analysis. Comparison of incremental dynamic analysis results for both directions of the platform shows that the lateral strength of the platform in the float over direction is less than its lateral strength in other direction. Dynamic characteristics measurement of a scale model of platform was also performed using forced vibration tests. From experimental measurement of the scaled model, it was observed that dynamic characteristic of the platform is different in the float over direction compared to the other direction. Therefore, a new offshore installed bracing system for the float over direction was proposed for improvement of seismic performance of this type of platform. Finally, the structure with the modified system was assessed using the probabilistic seismic assessment method as well as experimental measurement of its dynamic characteristics. It was observed that the proposed offshore installed bracing system improves the performance of platforms subjected to strong ground motion.

Time-domain and frequency-domain approaches to identification of bridge flutter derivatives

Flutter derivatives are essential for flutter analysis of long-span bridges,and they are generally identified from the vibration testing data of a sectional model suspended in a wind tunnel.Making use of the forced vibration testing data of three sectional models,namely,a thin-plate model,a nearly streamlined model,and a bluff-body model,a comparative study was made to identify the flutter derivatives of each model by using a time-domain method and a frequency-domain method.It was shown that all the flutter derivatives of the thin-plate model identified with the frequency-domain method and time-domain method,respectively,agree very well.Moreover,some of the flutter derivatives of each of the other two models identified with the two methods deviate to some extent.More precisely,the frequency-domain method usually results in smooth curves of the flutter derivatives.The formulation of time-domain method makes the identification results of flutter derivatives relatively sensitive to the signal phase lag between vibration state vector and aerodynamic forces and also prone to be disturbed by noise and nonlinearity.