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.
A finite element model to simulate long-term behavior of prestressed concrete girders
The development of a finite element model for time-dependent analysis of bonded prestressed concrete girders at service conditions is presented. The effects of creep and shrinkage of concrete and relaxation of steel tendons are taken into account. The concrete creep is modeled based on the Dirichlet series creep compliance with efficiency in simulating the stress history. In addition, the interaction between different time-dependent effects is fully considered in the numerical procedure. The numerical method is formulated based on the layered Euler-Bernoulli beam theory. In the constructed incremental equilibrium equations, the equivalent nodal load increments consist of four components contributed by external loads, concrete creep, concrete shrinkage and tendon relaxation, while the stiffness matrix is composed of the material and geometric stiffness matrices. Numerical examples show that the proposed model can well predict the long-term behavior of prestressed concrete beams, and that the time-dependent effects have important influence on the structural behavior.
Shear‐Lag Analysis of T‐, I‐, and Box Beams
Based on some rational assumptions, a harmonic shear‐lag analysis using plane stress elasticity for the stresses in flanges of simple or continuous beams with I‐, T‐ and box cross sections is developed, and it is accurate and convenient enough for a wide range of problems. Since harmonic analysis is used, convergence of the solution and the peak stresses in the flanges is studied in detail. An effective technique is presented to improve the convergence. The shear‐lag effect upon the longitudinal distribution of the stress resultants of a continuous beam with wide flanges is studied, and a general procedure to account for this effect is developed. To show the accuracy and applicability of the solution, typical numerical examples are presented, and the results compared with other solutions.