Long-term Experimental Study On Prestressed Steel-concrete Composite Continuous Box Beams

In the past 20 years,national and international scholars have also done a series of research on steel concrete composite beams,but on the whole focus on simple structure,while the section form is often an ?-shaped cross section,the research of multi span composite box girder is not enough,especially in the long term mechanical properties.The structural behavior of composite beams under long-term load is more complex,the analysis of how concrete shrinkage and creep influences the research on long term deformation and the stress of composite continuous beam section are in the stage of theoretical analysis.Most of literatures are mainly aimed at the T type composite beam,but still lack of theories and practice on the study of the continuous box girder.In order to study the steel-concrete composite continuous box girder in loading shrinkage and creep and prestressing force performance of long term,combining with the Hunan Province Natural Science Fund Project "the shrinkage and creep of steel-concrete composite continuous box girder bridge under long-term load effect" project,made three pieces of steel-concrete composite continuous box the beam(of which one pieces of ordinary composite beams,two pieces of prestressed composite beams),the load test of 360 day.The main contents and conclusions of this paper are as follows:(1)This paper has a detailed introduction of the development history of bridge construction nationally and internationally of steel-concrete composite and scholars of scientific research on beams,then further expounds the basic theory of creep and shrinkage of concrete,the calculation method of the effect of shrinkage,and creep of steel-concrete composite structure.(2)We set up a series of actions for this model,such as program design,model making,measuring point layout and long-term loading,and then tested the deflection of the model,the concrete strain,the reaction force of the support and the relative sliding time,to draw the concrete conclusion as follows:(a)Prestress,will reduce the composite continuous beam deflection and additional deflection of short-term growth,and the larger the prestress,the more obvious decrease effect.(b)The additional deflection of prestressed composite continuous beam growth than ordinary composite continuous beam,negative moment area of concrete slab cracking ordinary composite continuous beams will decrease the strain release the creep effect,cause the additional deflection of prestressed composite growth than Liang Man;(c)a force along the bearing section due to prestress to the middle support section transfer,resulting in the intermediate support force at any time increases,the reaction of support at any time decreases.That prestressed composite continuous beam linear arrangement on the redistribution of internal force.Louder;(3)Finally,according to the internal force redistribution and according to age adjusted effective modulus method on the deflection,concrete strain and anti stress at any time of the theoretical calculation,and analyzes the effects of shrinkage and creep to the additional deflection and concrete strain development law,the comparative results are highly consistent.