| As an important structural form of steel bridge decks,orthotropic steel decks(OSDs)are widely applied because of their advantages,such as light self-weight,high strength and short construction period.However,OSD bridges usually develop two types of problems with prolonged service time: frequent damage of the asphalt pavement and fatigue cracking of the steel deck.These issues seriously affect the safe use of OSD bridges.To fundamentally solve the above problems,the author’s team proposed a new composite deck system for OSD bridges.The new composite deck is composed of an OSD and a thin ultra-high performance concrete(UHPC)layer with high crack strength and low shrinkage.The two components are connected by stud shear connectors and the new composite deck is also referred to as the “light weight composite deck(LWCD).In the preliminary research,the author’s team has carried out in-depth research on the mechanical properties,fatigue property and other properties of the LWCD and applied the LWCD in girder bridges,arch bridges,cable-stayed bridges and self-anchored suspension bridges.While the research on the ground-anchored suspension bridges using the LWCD is still dificient.Therefore,this thesis carried research on the property of three long-span flexible suspension bridges using the LWCD:(1)To comprehensively study the influence of the thickness of the STC laye r,the thickness of the diaphragm and the spacing of the stud shear connectors on the fatigue property of the LWCD are warranted.The analysis results can serve as a provide reference to further optimize the design of the LWCD.Based on a real bridge,a ser ial local finite element(FE)model was built to calculate the fatigue stress range of the typical fatigue-prone cracking details of the steel bridge deck under different combinations of the three parameters.Based on the basis of the FE analysis,the nominal stress of each fatigue-prone detail was obtained,and the following observations were obtained: First,the lightweight composite bridge deck structure could strongly enhance the local stiffness of the steel bridge deck,but its contribution to the global stiffness of the bridge deck is limited;Second,The lightweight composite bridge deck under different design parameters had more influence on the stress amplitude of rib-to-deck plate joints than that of other details and the stress range reduction is about 51%-91%.The floor beam detail in the r ib-floor beam weld joints was the cracking control detail;Third,increasing the thickness of the floor beams could improve the cracking details at the U-rib-to-diaphragm connection and butt weld at the U-rib lower edge,and the stress range reduction is about 20%–29%;Fourth,reducing the spacing of the stud shear connectors could obviously decrease the stress range of the U-rib-diaphragm welded joints and the arc cutouts in floor beams,and the stress range decreases by 22.01%–27.96%.Fifth,in the FE analysis,7 of the 12 LWCD schemes could satisfy the fatigue strength design requirements and only one scheme,whose stress amplitude of all of typical fatigue-prone details is below their CAFLs,would never crack theoretically.(2)The Second Dongting Lake Br idge is the first kilometer-level long-span flexible bridge using the Light-weight composite deck(LWCD).During the construction of the UHPC,the UHPC layer of the bridge was cast in-situ through 12 times.To avoid the UHPC from cracking in construction,water tanks were placed on the bridge deck prior to casting and water was bled to balance the dead load in casting.To obtain the strain in UHPC during construction,over twenty strain gauges were installed to the bridge deck of this bridge.Based on the test data,the following conclusions are obtained:(1)In the complex curing environment and stress environment,the UHPC of the long-span flexible bridge still have good shrinkage properties.The shrinkage basically completed during curing and did not increase a lot after curing.(2)The basic trend of the shrinkage of UHPC along longitudinal direction is similar to the shrinkage of the model test: The shrinkage increases slowly during natural curing.When the steam curing starts,the shrinkage increases rapidly and achieve the maximum soon.After the steam curing,the longitudinal shrinkage reduces to about 0 ?? and its final value is in the range of-50~50 ??.The maximum of the logitudinal shrinkage is over 120?? larger than that of the model test.(3)The transverse shinkage of the UHPC layer increases slowly during natural curing,which is similar to the longitudinal shrinkage of the UHPC layer.But after steam curing starts,the trnsverse strain of the UHPC layer increases rapidly.The maximum value of the trnsverse strain is in the range of 50~120 ?? which is 33%~53% of the maximum longitudinal shrinkage of the UHPC layer.The trend of the transverse strain of the UHPC layer is contrary to that of the longitudinal shrinkage of the UHPC layer.After the steam curing,the transverse strain of the UHPC layer reduces to about 0?? and its final value is-20~-100??.(3)To solve frequent damage of the asphalt pa vement and fatigue cracking of the steel deck of Yichang Yangtze River Bridge,this thesis proposed two kinds,seven types of LWCD strengthening schemes.The first kind of schemes need to repair the fatigue cracking of the steel deck(scheme 1-A,45mmUHPC+35mmSMA;scheme 1-B,45mmUHPC+10mmTPO;scheme 1-C,50mmUHPC+35mmSMA;scheme 1-D,50mmUHPC+10mmTPO);while the second kind of schemes do not need(scheme 2-A,55mmUHPC+35mmSMA;scheme 2-B,55mmUHPC+10mmTPO;scheme 2-C,50mmUHPC+10mmTPO).Based on the integration finite analysis of those schemes,conclusions are as follows:(1)Except for the scheme 2-A(55mmUHPC+35mmSMA),other schemes all can be applied to strengthen the cracking steel bridge deck o f Yichang Yangtze River Bridge.(2)Among the six feasible schemes,when increases of the dead weight of stiffened girder are-1.3%~9.9%,the increases of peak stress of steel girder are-0.8%~0.9%.(3)The maximum tensile stress of the UHPC layer decreases with the increase of the asphalt thickness,while increase with the increase of the thickness of the UHPC layer.(4)The deflection of the stiffening girder under vehicle loads decreases because that the stiffness of the steel girder increases after using the LWCD,and this improvement increases with the increase of the UHPC thickness.The maximum stresses of the main cable,suspender,tower of the new scheme increase with the increase of the weight of the deck system. |
