尽管现有多种钢箱梁计算模型，板壳/实体单元模型太复杂不便于工程应用，而简化模型无法准确描述任意支撑与荷载条件下箱梁实际变形与受力状态。本课题通过叠加板件刚性位移和局部变形来描述大跨度扁平钢箱梁空间位移；基于结构力学理论和数值方法，确定加劲构件的约束刚度，导出单位宽度横向框架条带变形微分方程，确定变形解析解待定常数与梁段位移参数间的关系；建立反映板件与加劲构件变形相互影响的一维梁段有限元模型；提出考虑残余应力及塑性区发展影响的箱梁板件局部变形重构方法以及梁段弹塑性割线刚度列式方法；提出初始几何缺陷影响下板件与加劲构件局部屈曲耦合分析方法以及局部与整体相关屈曲分析的梁段初应力方法。基于上述研究成果，编制扁平钢箱梁高效数值模拟程序；通过数值算例与模型试验，修正理论模型和分析软件。本课题旨在揭示箱梁板件及加劲构件变形与内力分配机理，提出大跨度扁平钢箱梁受力全过程精细化、高效分析的一维有限元方法。

Although to date many theoretical models are available for analyzing thin-walled steel box girder, none of them are of general interests to fit all practical needs: shell/solid element models are too mathematical intensive and time consuming to fulfill routine design tasks,whereas most simplified or semi-analytical methods though implemented with low costs can not accurately capture the deformational and load-bearing behaviour of box girder under arbitrary support and load conditions. As a result, the present investigation starts from regarding the spatial deformation of the box girder as a combination of rigid displacements and local deformations of each slab component; The restraint stiffness parameters of stiffening members will be determined by the method of structural mechanics or numerical analysis, and its effects on the local deformation of stiffened slab are taken into account by deriving the differential equations for the transverse elementary strip of unit width and the undetermined constants involved are specified as functions of displacement parameters of a typical box girder segment. Therefore, an one-dimensional finite segment model is putforward that can predict the interactions among different deformation modes of slab components and stiffening members. The effects of residual stresses and inelastic zone expansion on structural behavior are considered by reformulating the local deformations of inelastic slab components, and meanwhile an explicit elasto-plastic stiffness matrix for the extened beam model is established. In the presence of initial imperfections, the interactions between local buckling modes of slabs and stiffening members are properly simulated and an initial stress approach based on the proposed extended beam segment formulation shall be developed to reliably account for the phenomenon of local-overall interaction buckling. Based on the foregoing research results, a computer program will be written for an efficient numerical simulation of the complex multiple interaction behavior of flat steel box girder. The theoretical model and numerical procedures are subject to error checking and necessary revisions through numerical validations and scaled model tests.This investigation aims to discover the complex mechanism of deformation and internal force distribution within slab components and stiffening members and to present an one-dimensional finite element formulation for a refined, yet computational efficient modeling of the complex full-range behavior of the long-span flat steel box girder.