Fatigue Safety And Design Study Of Through And Half-through Arch Bridges' Suspender

After the 19th century, through-arch bridges and half-through arch bridges with suspenders developed rapidly. The suspenders are important force transmission components to through-arch bridges and half-through arch bridges, which have characteristics of small size, multiple component parts, sensitive to many factors such as corrosion and fatigue, and the operation state of suspenders and its components is fairly complex. It works normally or not, affects the operation safety and lifetime of the whole bridge. However, the current bridge design theory has not kept pace with the development of the bridge, there is no uniform and scientific standard for design criterion of the suspender, the service injury, safety criteria, life prediction, removal and replacement scheme and so on, and most of the past engineering practice is based on the subjective judgment of the designers. In addition, the bridge designers paid little attention to the force of suspenders. They usually adopt a safety factor to control its maximum stress in the design, but ignored the control of fatigue and corrosion problems. As to the factors affecting fatigue of suspenders and its changes law, there are almost no comprehensive and systematic researches, so the suspenders'breakage occurred frequently.Therefore, on the basis of referring and summarizing the having achievements and present status, this article takes a certain through tied arch bridge as the background. And the static and dynamic characteristics of suspenders, structural design factors impacting suspender fatigue and the fail safety conditions of suspenders were calculated and analyzed. The main contents and conclusions are as follows:(1) Static and dynamic analysis of suspenders. Through the static characteristics analysis of suspenders in simple and continuous bridge deck system under the dead and live load, and also combining the consideration of fail safety, we conclude that simple bridge deck system is not conducive to suspender fatigue.(2) We use dynamic time history response of uniform speed moving loads to simulate vehicles crossing the bridge, and use transient dynamic response of impact loads to analyze the vehicle bump, which shows that: suspenders have obvious dynamic effect, and dynamic effect is proportional to the vehicle speed; the shorter suspender has stronger dynamic effect, and calculated dynamic magnification factor of short suspender under high-speed is greater than the value in the code. Thus, a separate dynamic checking of short suspender should be conducted in the design as possible.(3) From the perspective of structural design, we analyze and compare the factors that affect the suspender fatigue under load, including the location of suspenders, spacing of the suspender, distance from limitrophe suspender to skewback, the area of the suspender, rise-span ratio, stiffness ratio of arch and beam and so on, and obtain structural design methods that are conducive to improve suspender fatigue.(4) By discussing the current design criteria and fatigue design methods of suspender, we think that the current design can not guarantee the security of suspender in service, and we should establish an appropriate design theory and method as soon as possible. This thesis puts forward the checking method and thought of suspender fail safety conditions. Through the fail safety checking calculation of a bridge model's suspenders, we find that part of suspender failure may not lead to chain reaction of collapse.