Modeling of cable vibration effects of cable-stayed bridges

The analysis of dynamic responses of cable-stayed bridges subjected to wind and earthquake loads generally considers only the motions of the bridge deck and pylons.The influence of the stay cable vibration on the responses of the bridge is either ignored or considered by approximate procedures.The transverse vibration of the stay cables,which can be significant in some cases,are usually neglected in previous research.In the present study,a new three-node cable element has been developed to model the transverse motions of the cables.The interactions between the cable behavior and the other parts of the bridge superstructure are considered by the concept of dynamic stiffness.The nonlinear effect of the cable caused by its self-weight is included in the formulation.Numerical examples are presented to demonstrate the accuracy and efficiency of the proposed model. The impact of cable vibration behavior on the dynamic characteristics of cable-stayed bridges is discussed.

Aerodynamic stability evolution tendency of suspension bridges with spans from 1000 to 5000 m

Aerodynamic instability owing to aerostatic and flutter-related failures is a significant concern in the wind-resistant design of long-span suspension bridges.Based on the dynamic characteristics of suspension bridges with spans ranging from 888 to 1991 m,we proposed fitted equations for increasing spans and base frequencies.Finite element models of suspension bridges with increasing span from 1000 to 5000 m were constructed.The structural parameters were optimized to follow the fitted tendencies.To analyze the aerodynamic instability,streamlined single-box section(SBS),lattice truss section(LTS),narrow slotted section(NSS),and wide slotted section(WSS)were considered.We performed three-dimensional(3-D)full-mode flutter analysis and nonlinear aerostatic instability analysis.The flutter critical wind speed continuously decreases with span growth,showing an unlimited approaching phenomenon.Regarding aerostatic instability,the instability wind speed decreases with span to approximately 3000 m,and increases when the span is in the range of 3000 to 5000 m.Minimum aerostatic instability wind speed with SBS or LTS girder would be lower than observed maximal gust wind speed,indicating the probability of aerostatic instability.This study proposes that suspension bridge with span approximately 3000 m should be focused on both aerostatic instability and flutter,and more aerodynamic configuration optimistic optimizations for flutter are essential for super long-span suspension bridges with spans longer than 3000 m.