Design Method Of Fully Fully Precast Steel-ultra High Performance Concrete Lightweight Composite Bridge

With the continuous development of society,compared with the traditional bridge construction,the prefabricated bridge structure,which can ach ieve rapid construction,is more suitable for modern bridge construction.Traditional prefabricated bridges mainly include prefabricated concrete bridges and partially prefabricated steel-concrete composite bridges.Among them,prefabricated concrete bridges are simple in structure,transparent in stress,low in cost,and convenient in erection,so they are widely used in bridge construction.However,due to weak strength and durability problems,they are easy to cracking and corrosion.For steel-concrete composite bridges,the upper concrete slabs sustain compression,and the lower steel beams sustain tension,and the structural stress is more reasonable than concrete bridges.In recent years,with the decrease of steel price,more attention has been paid to partially prefabricated steel-concrete composite bridges.Compared with the steel bridges,the steel consumption of steel-concrete composite bridges is greatly reduced;compared with the concrete bridge,the concrete consumption of steel-concrete composite bridges is dramatically decreased,which effectively reduces the structural weight and beam height,and the steel-concrete composite bridge is a very preferred bridge scheme in the area with high clearance requirements.Therefore,in view of the above problems of traditional prefabricated concrete bridge,combined with the advantages of traditional steel-concrete composite bridge,this paper proposed a new type of bridge-the fully precast lightweight steel-ultra-high performance concrete composite bridge(SU-LWCB).SU-LWCB replace the traditional ordinary concrete panels with ultra-high performance UHPC panels,and the UHPC panels and steel girders are prefabricated integrally in the prefabricated factory,which can significantly achieve the structural integration.Due to the lightweight of the steel-UHPC composite beam element,it can easily transport and hoisted integrally.During the construction,only the joints need to be poured on-site,the existing construction equipment and technology can be used.There is little interference with the traffic environment,and the construction efficiency is high,which is very suitable for modern bridge construction.For prefabricated bridge structure,the joint is the focus of the design,and also the weak link of the prefabricated bridge structure.Traditional treatment usually brings additional design,construction,and durability problems.Therefore,this paper also proposed the connections between girders and panels,which are suitable for SU-LWCB.The connections have low construction difficulty and no need to weld on site.It is a convenient,fast,and very suitable joint form for the modern prefabricated bridge construction.Based on the SU-LWCB system,the following researches were carried out:(1)The design concept and calculation method of the SU-LWCB system were shown based on a 4× 25 m fully prefabricated steel-UHPC lightweight composite continuous beam bridge.The advantages of the SU-LWCB system in technology and economic performance were described in detail compared with the prestressed concrete small box girder and conventional steel-concrete composite girder with the same span.Meanwhile,the paper put forward the joints between girders and panels,which are suitable for the SU-LWCB system,and compares them with the traditional joint forms.Finally,the shrinkage performances of UHPC structure within or without reinforcement were discussed,and compared with the shrinkage prediction formula in the existing literature and standards,the shrinkage pred iction model suitable for UHPC panel was obtained;(2)The proposed girder-to-girder joint was further optimized,and the large-scale model test of the negative moment region of the SU-LWCB system was carried out to verify the mechanical properties.Simult aneously,the fatigue performance of the proposed joint was evaluated,and the prediction formula of the maximum crack width applicable for the joint interface was proposed.The deflection calculation formula considering the tensile stiffness of UHPC panel,and the simplified calculation method of the bearing capacity of the negative moment region were also proposed;(3)Based on the previous literature,the mechanical properties of steel-UHPC composite beams under the positive moment are analyzed through t heoretical,and FEM works.A more accurate modified plastic calculation method of ultimate bending capacity was proposed.Based on the principle of equal ultimate bearing capacity,the concrete panel of the conventional steel-concrete composite bridge was replaced by UHPC panel,and the equivalent section heights were obtained,which can be used for design;(4)Based on the track-separation model,the fitting parameters of bending-tension and shear-compression behaviors of the UHPC interface were obtained.The parameters were used to simulate the UHPC joint test,and show that the model can fit the test results well;(5)This paper puts forward standardized design suggestions for the SU-LWCB system,including bending and shear capacity,overall stability,an d fatigue performance calculation methods in the ultimate limit state;the calculation methods of crack width and deformation in the serviceable limit state were also introduced.The design of the UHPC panel along the transverse direction was discussed.Th e preliminary design suggestions for SU-LWCB with the spans of 20-50 m were given.