Study Of The Interfacial Shear Strength And Rib-to-deck Welded Joint Fatigue Of Orthotropic Steel Bridge Decks

Orthotropic steel bridge deck is an innovative bridge deck system composed of steel deck,longitudinal ribs welded on the steel deck and the floor beams perpendicular to it.Pavement of 50~80 mm is laid on the bridge deck.The orthotropic steel deck with traditional asphalt pavement is prone to problems of pavement damage and fatigue crack of welded joints.The new Steel-UHPC composite bridge deck structure provides a new design to solve the above problems.In the analysis of interfacial shear strength between the pavement and the steel deck,most of researchers evaluate the shear strength of stud connectors for composite bridge deck based on load spectrum of standard trucks.The effect of overloaded trucks has been ignored.The rib-to-deck welded joints under tension and compression cyclic loading dominated by compressive stress are easily to induce fatigue crack.At present,there is no accepted crack growth rate model that accurately accounts for the effects of compressive stress in tensile-compressive cyclic loading.According to above issues,the following studies are conducted in this thesis.(1)Shear strength evaluation of the stud in Steel-UHPC composite bridge deck.The interlaminar shear stress between the UHPC pavement and the steel plate of orthotropic steel deck in the new Steel-UHPC lightweight composite bridge deck is computed,and the shear strength of stud connectors in the Steel-UHPC composite bridge deck is evaluated.The influence of various wheel loading conditions and overloaded trucks are studied.The results show that the maximum interlaminar transverse shear stress under the action of overloaded trucks exceeds corresponding shear strength limit of stud in the Steel-UHPC composite bridge deck,which could result in shear failure of the studs.(2)The experiments of fatigue crack growth rate of Q345 steel under tension and compression cyclic loading.The driving effect of compressive stress in cyclic loading on fatigue crack growth is verified based on rationally designed fatigue crack growth rate test of Q345 steel.The crack growth rate model that can reasonably describe the influence of compressive stress in cyclic loading is preliminarily explored by evaluating the common models of fatigue crack growth rate.The experimental results show that the compressive stress in cyclic loading has a great driving effect on fatigue crack growth.It can be preliminarily concluded that the crack tip reverse plastic zone model can give more reasonable results for fatigue crack growth accounting for the effect of compressive stress.(3)Fatigue analysis of rib-to-deck welded joints of orthotropic steel deck based on 3D fracture mechanics model.The local 3D fracture mechanics model of rib-to-deck welded joints is established by using an improved Schwartz-Neuman alte-rnating method.And the fatigue crack growth under tension and compression cyclic loading is computed by using the crack growth rate model based on the crack tip reverse plastic zone model.The fatigue life of rib-to-deck welded joints is evaluated based on the load spectrum conditions of overloaded multi-axle trucks.Results show that the fatigue life of rib-to-deck welded joints is about 20 years if evaluating fatigue life conservatively by only taking into account of the fatigue damage caused by heavily overloaded five-axle and six-axle trucks,which is far less than the design life of the bridge.The effects of overloaded trucks on the stud shear strength and the rib-to-deck joint fatigue life of orthotropic steel bridge decks are studied,and the crack growth rate model that can reasonably describe the influence of compressive stress in cyclic loading is preliminarily explored.The study presented in this thesis can provide the basis for the safety design of orthotropic steel bridge decks and for a more accurate crack growth rate model that can consider the influence of compressive stress in cyclic loading.