Fatigue Properties Study Of Orthotropic Steel Bridge Decks

At present, the orthotropic steel deck plates have been widely used in large-spanhighway bridges. But the fatigue cracking phenomenon in the welding connection oflongitudinal ribs, panels, and diaphragms is prominent; especially the position ofarc-shaped cutouts on diaphragms with the intersection of longitudinal ribs is moreserious, while there are different approaches in dealing with it in engineeringpractices and different countries’ specifications. In this paper, the fatigue propertiesof the diaphragm on steel deck are studied with static parameter analysis and fracturemechanics methods. And then, the arc-shaped cutout is optimized to offer somereference for future designers. The main research contents and results are as follows:（1） The development process, application, and mechanical characteristics of theorthotropic steel deck plates are elaborated, while the researches involved in steelbridge panel structure optimization and fatigue problems at home and abroad arereviewed.（2） The instances and causes of fatigue cracking on orthotropic steel deck platesat home and abroad are summed up, while the problem of fatigue cracking on steeldeck diaphragm is analyzed specifically. And then, the method of fatigue in steelstructures is elaborated in detail.（3） For the study of fatigue loading, the most unfavorable loading mode andstress concentration point location, on the basis of four kinds of arc-shaped cutout, anumerical spatial analytical model of deck plate is set up after comprehensive surveysof different countries’ specifications and engineering practice. Further more, the hotspot stress calculation method has been analyzed to determine the calculation of thehot spot stress and geometric stress concentration factor.（4） A comparative analysis of hot spot stress and stress concentration effects onthe adge of four kinds of arc-shaped cutout, considering the spacing and thickness ofdiaphragms, the rib high and the gap of cutouts, is studied. The results show that thehot spot stresses and geometric stress concentration factor of the spots closely relatedto the fatigue properties presented significant correlation to the various sizeparameters for the four kinds of arc-shaped cutout. On the basis of the aforementionedstudy, an optimized analysis of forms for arc-shaped cutout on diaphragms is carriedout, and a rational form of arc-shaped cutout which shows good stress distribution is recommended.（5） By applying the fracture mechanics, the feasibility and finite element methodfor stress intensity factor of crack on the edge of the arc-shaped cutout are studied.Then, a comparative analysis on stress intensity factor of crack-tip for the four kindsof arc-shaped cutout is presented. The results show that the cutout form HM₄0hasthe best fatigue performance. Finally, considering the change of the radiu and gap ofcutouts, a further optimization for the form of arc-shaped cutout recommended inChapter3is prensented, and a final optimized form of arc-shaped cutout isrecommended.