Influences Of The U-rib To Diaphram Structure Details On Fatigue Properties Of Orthotropic Steel Bridge Deck

The orthotropic steel decks have become very widely used in construction of long span bridges such as suspensionbridges and cable stayed bridges. The increasing employment of the orthotropic steel deck system is due to its advantages such as (1) light weight compared with that of concrete decks, (2) guarantee of high quality by controlling its fabrication procedures at manufacturers,(3) convenience for in-situ assembling process which leads to reduction of construction period and cost, (4)aesthetic appearance provided by slender external shapes,etc. Furthermore, development of new steel materials and improvement in welding skills widens its application fields.On the contrary,the orthotropic steel deck system has the complicated sructural configuration consisting of a thin steel deck plate incorporated with longiudinal U-ribs and transverse cross-beams,and it accordingly makes the stress states in the connection details complicaed.For the complicated configuration and the welding residual stress concentration,some certain details are prone to fatigue,which may influence the stress condition of the whole deck system.In this thesis,I focus my study on a certain detail that are most likely to damaged by fatigue-the rib to diaphragm connection.In the thesis,the following aspects are investigated:(1) The history of the orthotropic steel deck was introduced, and domestic and overseas development in both theories and welding skills in recent years are summarized.(2) The achievement of fatigue test focusing on the rib to diaphragm connection was expounded.Aiming the major places of fatigue crack taking around the rib to diaphragm connction, such as cracks parallel to the rib to diaphragm weld, transverse cracks on the diaphragm,longitudinal cracks immediately beneath the weld toe on the ribs,the mechaisim of the cracks were analyzed.(3)To improve the fatigue properties of orthotropic steel deck and study the component of the in-plane and out-plane stress,the finite element models of certain U-ribs and diaphragm shapes based on an as-built bridge were established,and the calculating results can be a strong reference to the future design of the orthotropic steel deck.(4) When obtaining the result of the percentages of the in-plane and out-plane stress of the ribs and the diapgragms, some measurment will be considered to strengthen the local stiffness in design of the rib-to-diaphragm configurations, including the welding of a trapezoidalor curved bulkhead into the rib,a inside stiffener welded to the rib,etc.On the basis, the influences of the thickness of the deck,the ribs,the diaphragms and the bulkhead are studied.