Effect of construction method on shear lag in prestressed concrete box girders
Most of the previous researches conducted on shear lag of box girders were only concerned about simple types of structures, such as simply supported and cantilever beams. The structural systems concerned in these previous researches were considered as determined and unchangeable. In this paper, a finite element method considering shear lag and creep of concrete was presented to analyze the effect of dynamic construction process on shear lag in different types of concrete box-girder bridges. The shear lag effect of the three types of a two-span continuous concrete beam classified by construction methods was analyzed in detail according to construction process. Also, a three-span prestressed concrete box-girder bridge was analyzed according to the actual construction process. The shear lag coefficients and stresses on cross sections along the beam including shear lag were obtained. The different construction methods, the changes of structural system with the construction process, the changes of loading and boundary conditions with the construction process and time, the prestressing, and creep were all imitated in the calculations. From comparisons between the results for beams using different construction methods, useful conclusions were made.
Shear Lag in Shear/Core Walls
Shear lag occurs not only in bridge decks and framed tubes, but also in shear/core walls. However, there have been relatively few studies on shear lag in wall structures. Moreover, most existing theories neglect shear lag in the webs and, although they are acceptable for bridge decks that normally have flanges wider than webs, they may not be applicable to shear/core walls whose webs can be much wider than flanges. To study the shear lag phenomenon in wall structures, a parametric study using finite-element analysis is carried out. Unlike previous studies that neglected shear lag in the webs, many layers of elements are used for both the webs and flanges so that shear lag in the webs can also be taken into account. The results indicate that the shape of the longitudinal stress distribution in an individual web or flange panel is quite independent of the dimensions of the other panels. Based on this observation, design charts and empirical formulas for estimating the shear lag effects are developed for pra...
Effective Width of Steel Deck-Plates in Bridges
The problem of the effective width, which is encountered in the design of steel plate deck bridges, is presented and examined theoretically. The differential equation of the correlated plane state of loading in the deck-plate is obtained taking in consideration the effect of the mutually perpendicular stiffeners. A solution for the equation is given and the effective width is calculated. Formulas and tables of the effective width are presented for the case of sine-wave loading on the main girders. The behavior of the effective width of the steel deck-plate is presented showing that in addition to the usual factors governing the effective width of isotropic flanges, the ratio of the cross-sectional area of the longitudinal stiffeners to the cross-sectional area of the skin-plate has a significant effect.