一级入轨大型液体捆绑火箭全箭模态特性研究

Structural vibration modes of large clustered liquid launch vehicles are important criteria for attitude stability design,POGO stability design and structural dynamic load calculation.As the first large one-stage-to-orbit clustered liquid launch vehicle of China,LM-5B has unique structural modal properties which are different from other launch vehicles at home and abroad because of its special structural scheme.Hence,it was necessary to study the structural modal properties for LM-5B.In this paper,ground modal tests for the whole vehicle were conducted to verify and modify the finite-element model of LM-5B,then the structural modal properties were obtained via simulation during flight time,providing significant input for the development of the vehicle.

Mode-based equivalent multi-degree-of-freedom system for one-dimensional viscoelastic response analysis of layered soil deposit

Discrete models such as the lumped parameter model and the finite element model are widely used in the solution of soil amplification of earthquakes. However, neither of the models will accurately estimate the natural frequencies of soil deposit, nor simulate a damping of frequency independence. This research develops a new discrete model for onedimensional viscoelastic response analysis of layered soil deposit based on the mode equivalence method. The new discrete model is a one-dimensional equivalent multi-degree-of-freedom（MDOF） system characterized by a series of concentrated masses, springs and dashpots with a special configuration. The dynamic response of the equivalent MDOF system is analytically derived and the physical parameters are formulated in terms of modal properties. The equivalent MDOF system is verified through a comparison of amplification functions with the available theoretical solutions. The appropriate number of degrees of freedom（DOFs） in the equivalent MDOF system is estimated. A comparative study of the equivalent MDOF system with the existing discrete models is performed. It is shown that the proposed equivalent MDOF system can exactly present the natural frequencies and the hysteretic damping of soil deposits and provide more accurate results with fewer DOFs.

Performance-based seismic assessment of a historical masonry arch bridge:Effect of pulse-like excitations

Seismic analysis of historical masonry bridges is important for authorities in all countries hosting such cultural heritage assets.The masonry arch bridge investigated in this study was built during the Roman period and is on the island of Rhodes,in Greece.Fifteen seismic records were considered and categorized as far-field,pulse-like nearfield,and non-pulse-like near-field.The earthquake excitations were scaled to a target spectrum,and nonlinear timehistory analyses were performed in the transverse direction.The performance levels were introduced based on the pushover curve,and the post-earthquake damage state of the bridge was examined.According to the results,pulse-like near-field events are more damaging than non-pulse-like near-field ground motions.Additionally the bridge is more vulnerable to far-field excitations than near-field events.Furthermore,the structure will suffer extensive post-earthquake damage and must be retrofitted.