Test Research And Fine Analysis On The Wind-resistant And Vibration-control Performance Of Suspension Catwalk

Catwalk of suspension bridge is the scaffold at high altitude erected as the sidewalk for constructor and machines. With long span and low stiffness catwalk is sensitive to dynamic forces. Large displacements induced by wind and walking constructors can lead to torsion, drumming and dispersing of cable wires, which has bad effects on the performances of cables. The torsional collapse of catwalk can result in the danger of constructor and machines. Along with the construction of suspension bridges spanning over sea and connecting islands, more and more long-span catwalks under bad construction conditions have appeared. So it is obviously significant to study wind-resistant and vibration-control performance and develop effective relative techniques for catwalks.Characteristics of reaction to wind for catwalk are comprehensively studied in this dissertation. The wind tunnel tests are conducted to study the vortex produced by the side cover and bottom cover of catwalks. It is verified that the vortex-induced vibration of catwalks can be avoided if the wind penetration rate of side cover is more than 70%. The wind penetration rate of bottom cover has no influence on this conclusion. The test method and conclusion can help to study the similar structure that allows wind penetrating. The gallop vibration cannot happen to catwalks according to the characteristics of lift force and resistant force tested through wind tunnel tests.Nonlinear analysis is performed by FEM method using sectional model tests results. According to the inner force and displacement of catwalk rope exposed to the wind load, it is indicated that near the critical wind velocity for torsional collapse the stress of the catwalk rope begins to lack because of upward air lifting, and then the resisting force of catwalk is less than the air moment. This is the cause of torsional collapse for catwalk. Nonlinear analyses are conducted for catwalk with the vibration control conformations including storm ropes, horizontal ropes, stay ropes and outside ropes. The displacements and critical wind velocity for torsional collapse are also calculated to compare the vibration control effects. Based on these conclusions the conformations above can be installed on catwalks by designers.The human-induced lateral vibrations on catwalks are analyzed in this dissertation. By comparing to vortex-induced vibration for bridges it is indicated that human-induced lateral vibration has a self-excited nature. With reference to the research of human-induced lateral vibration on footbridges the methods are amended to be suitable for analyzing this vibration on catwalks. The analysis leads to an equation for predicting critical number of pedestrians and needed damp for catwalk to avoid synchronized excitation. The lateral displacement of catwalks with a certain number of pedestrians can also be estimated through the analysis.Connecting rope is a simple and effect method for increasing the damp of catwalks. The vibration control effects of connectiong ropes are influenced by natural vibration frequency, damp, mass and connecting position. Vibration tests are conducted to study the relationship between damp increasing level and the factors above. Considering vibration control effects and construction practice, the angle between connecting rope and catwalk longitudinal axis should be between 40°and 50°. The mass of connecting rope should be one percent of the catwalk mass. The natural vibration frequency of connecting rope and catwalk should be similar to the largest extent. The vibration control effects get better with the damp of connecting rope increasing.