Theoretical And Experimental Investigation Of Unbonded Prestressed Continuous Steel-Concrete Composite Beam

Steel-concrete composite structure is a new structure developed from basis of original steel structure and reinforced concrete structure.Compared with steel structure, steel-concrete composite structure can save steels,and increase rigidity,etc.Compared with reinforced concrete structure, steel-concrete composite structure has many advantages of reducing dead weight and structural dimension,etc.Since 20 century 80s, steel-concrete composite structure has become an important bridge supporting member in constructions such as high-rise building and bridge span structure in our country,and there will be more and more applications of steel-concrete composite structure.In order to obtain working performance of prestressed steel-concrete composite continuous beam under vertical load during tension stage and using stage,the laboratory test model of prestressed steel-concrete composite continuous beam is designed by summarizing present research results.A two-span test beam with 3 meters'span length is made,and then it is tested under vertical load during the whole process. States of strain and displacement of each part under each load grade are measured. Conclusions can be obtained as follows.Strain state of normal section of unbonded prestressed steel-concrete composite continuous beam,under monotonic load,basically corresponds to plane section assumption during elastic stage. Shear lag phenomenon existes on concrete roof of composite continuous beam. Shearing slip strain deviation on the interface between steel and concrete nearby action point of concentrated load is relatively large. And shearing slip strain deviation also increase nearby anchor ends of prestressed steel and turning points.The existence of shearing slip will have large influence on the composite effect between steel and concrete in continuous beam,and lead to the increase of member curvature and stress at upper and lower. Influence of shearing slip should be taken into full consideration in the process of designing.After applying prestress, bearing capacity and elastic range of composite structure improve a lot.but members still have excellent plastic property.Because of large elastic range of composite structure,it can infer that it can increase the span ability of composite continuous beam under the prerequisite for satisfying the use requirement. And it has a wide application prospect.In order to analyze the mechanical behavior of prestressed steel-concrete composite continuous beam in actual dimension, the large finite element software named ANSYS is used to establish finite element analysis model of the test beam,by summarizing the mechanical characteristics of the test beam during tensiling prestress stage and using stage, based on stress characteristics of the test beam,By the method of setting load step,the whole process of the test beam under prestressed and external loads is analyzed.Compared with test results,it shows that effective simulation test can be carried out to the finite element model of unbonded prestressed steel-concrete composite continuous beam established based on basic idea in this paper. The variation law of static response,such as shear lag effect and shearing slip of external prestressed concrete composite beam, deflection and curvature under monotonic load,is analyzed and calculated effectively.So the method reduces lots of experiments,saves substantial contribution,and provides a finite element model with certain use-value for numerical simulation research of composite beams in future.By summarizing the research results of shearing slip and data analysis of the test beam,the analytical expression of shearing slip strain deviation of steel-concrete composite continuous beam under concentrated load and uniform load is derived based on elastic theory.Results of shearing slip strain deviation under concentrated load is analyzed comparatively,by using the form of uniform load equivalent to concentrated force. The analysis shows that the analytical solution under each kind of loads is reasonable and believable. Shearing slip strain deviation of steel-concrete composite continuous beam under concentrated load reaches maximum value at concentrated force point and middle fulcrum.It means that the setion with the larger moment,the larger the Shearing slip strain deviation is.Calculated results of the stress at upper and lower of steel-concrete composite continuous beam is relatively small,based on the hypothesis of complete interaction.If calculation is carried out based on complete interaction,the results are unsafe.Therefore,the influence of shearing slip to steel-concrete composite continuous beam should be taken into consideration.In order to obtain practical formula of prestressed steel-concrete composite continuous beam under vertical load, according to characteristics of the interaction between steel beam and the vertical part of concrete roof along composite beam,a new composite beam element stiffness equation is obtained for the first time,based on contact theory.By comparing theoretical results and test results,it shows that the formula is reasonable and believable.Vertical distribution of static response along the beam,such as deflection of composite beam under vertical load,each part of stress and strain deviation between shear stress and shearing slip,can be calculated by using finite element solution of composite beam element.Each static response of prestressed steel-concrete composite continuous beam can be obtained at one time.By the basic idea of iterative method, the deformation behaviour of composite beam under prestressed tendon load is calculated.By comparing test results and calculation results, a conclusion is obtained.It is that static response of prestressed steel-concrete composite beam calculated by iterative method combined with composite beam element method is reliable and reasonable.Influence of various parameters on flexural behavior of composite beam is analyzed by iterative method combined with composite beam finite element method. Influence of static parameter which designers care about , such as thickness of concrete flange plate,detail dimensions of steel beam, diameter and number of studs,area of prestressed steel and tension control stress,on flexural behavior of composite continuous beam is obtained. Based on the characteristics of finite element method, composite beam element method is easily extended to flexural calculation of variable cross-section composite continuous beam and composite simply surpported beam.However, flexural calculation of variable cross-section composite continuous beam with considering shearing slip is not be found at present.