Analysis Of Creep Effect Of Continuous Double Composite Box-girder Bridge By Pre-jacking Method

Continuous double steel and concrete composite beam is a new structural system developed on the basis of common steel and concrete composite beam.Controlling concrete slab crack width in a continuous double composite beam is a significant content in the bridge construction process.Jacking-up and landing bearing supports method is applied to a double composite girder bridge construction and its structural mechanical behaviors in the whole process will be simulated in this paper.By using of User Programmable Features and ANSYS Parametric Design Language,the commercial FEM software ANSYS was further developed.The exponential model of concrete creep and the implicit solution of concrete creep equation under the action of variable stress were introduced into ANSYS,to realize the concrete creep effect analysis of double composite continuous box-girder bridges constructed by pre-jacking method.In addition,combined with the engineering practice,the section form of double composite beam in negative moment region has made the corresponding changes.At the same time,Through the beam element,Midas respectively are stablished two kinds of considering concrete creep and does not consider steel-concrete double composite continuous beam finite element model,to analyse the creep effect.A three span(45 m+60 m+45 m)continuous double composite beam is taken as an example to discuss whether the proposed method is feasible for improving stress level of top concrete slab and the influence of concrete creep on the prestressing effect of the pre-jacking method by finite element analysis,and the results of modeling with different units were analyzed.The main construction phases are:(1)Steel beam connection and erection;(2)Concrete placement in the bottom concrete slab of the negative moment regions;(3)Pre-jacking the inner bearing supports;(4)Concrete placement in the top concrete slab of the positive moment regions;(5)Concrete placement in the top concrete slab of the negative moment regions;(6)Dropping the inner bearing supports after concrete hardening;(7)Bridge deck pavement.The results show that it is improved that the stress state of the top concrete slab in the negative moment regions by pre-jacking method,The effect of prestressing is greatly affected by pre-jacking value.Due to the effect of concrete creep,the deflection of the steel-concrete double composite continuous beam will increase,and the creep of the concrete also causes the stress redistribution of the concrete and the steel beam.In addition the concrete creep will cause tensile stress in the negative moment regions of the composite beam,which will reduce the compressive stress in the top concrete slab.The effect of prestressing is affected by pre-jacking method.