Widening Design Method For Assembly Ttype Bridge

In recent years, with the rapid development of China’s economy and the trafficindustry, the flux of people and goods becomes more and more frequent; someexpressways in use need to be rebuilt and expanded, because the traffic volume ofthese expressways has been saturated or oversaturated to cause traffic jam, thus thematter of widening old bridges arises. Although a great deal of researching work hasbeen carried out on the reconstruction of bridges on expressways in both China andother countries and there are many successful examples, no specific notions have beenset down on some key technologies. And the matter of joint function of the newbridge and the old bridge in old bridge widening projects has caught much attention inacademic filed and among engineering technicians. Based on typical bridges onexpressways and aiming at problems appeared on the reconstruction and wideningwork of bridges, the paper carried out researches on many issues, such as wideningmethod of bridges, coupling stress analysis of old and new bridges afterreconstruction, concrete shrinkage and creep discrepancy influence of old and newbridges, the influence of the base’s uneven settlement on structures and the controllingmethod. And the following work has been completed:The paper systematically introduces the widening and linking methods ofexisting bridges, analyzes their advantages&disadvantages and thereby explains theadaptability of various widening and linking methods. Pursuant to the result acquiredand the structural characteristics of the projects, the paper brings forward a methodto calculate load transversal distribution of coupling bridges suitable for variouslinking methods. Combining ANSYS, a finite elements analyzing software, the paperanalyzes the capacity of widened bridges through analysis on load transversaltransferring rules and internal force deformation. In addition, the paper also analyzesall kinds of factors influencing load transversal distribution coefficients and thechange of transversal distribution coefficient of the old bridge’s main girder. Theresult shows that the deflection and internal force of inner side girders of old bridgesare greatly reduced after reconstruction under the influence of live load, and theinfluence of various linking methods on the capacity of the old bridge’s main girder istrivial.By simulating creep with CREEP materials in ANSYS software, the paper analyzes the postponed coupling time with finite element, simulates pre-stressingforce and concrete shrinkage strain with temperature load, and carries out shrinkageand creep analysis on assembled bridges after reconstruction. The result shows that:The age difference of concrete shrinkage and creep will cause deformation differenceof old and new bridges, internal force difference, as well as partial stress on theconnecting surface of old and new concrete; the influence of shrinkage and creep onthe internal force of new girders are notable, which causes transversal deformation ofwidened bridges; and further from the pivot section, more notable the shrinkage andcreep.The paper creates a finite elements model of assembled bridges reconstructedwith various linking styles with ANSYS software, researches the influence ofadditional internal force produced by the main girder and the influence of settlementdifference on widened bridge after base settlement of assembled bridge afterreconstruction, and brings forward the allowable deformation value of linking surfaceunder the joint function of live load and base settlement. In addition, according to themaximum bearable base settlement value of upper structures built with variouscoupling methods, the paper brings forward the concept of allowable value of newand old bridges’ base settlement. Through calculating base settlement with variouscalculation theories, the paper gets the settlement value of different bridges andcompares them with the allowable deformation value of upper structure settlement.On-spot measurement result and theoretical analysis result show that it is completelypossible to control base settlement difference within allowable scope.Research result of the paper has been applied into Xi’an—Lintong and Xi’an—Baoji expressways; the paper also offers design reference for widening assembledbridges in other expressways.