IMPROVEMENT OF THE ELEMENT STIFFNESS MATRIX FOR NEW-OLD COMPOSITE CONCRETE BEAMS UNDER THE INFLUENCE OF SHRINKAGE AND CREEP

The shrinkage and the creep of concrete will lead to a stress redistribution in new-old composite concrete beams. The nonlinear differential equation for the composite beam is derived in terms of the deflection. By solving the differential equation, the displacement shape function, the stiffness shape function and the equivalent nodal load shape function are introduced. Finally, the improved element stiffness matrix and the equivalent nodal loads with the combination of the new concrete beams, the old concrete beam and the Goodman elastic intermediate layer, are obtained, which may serve as an effective way to calculate the internal force of the concrete under the influence of shrinkage and creep. An example is given to verify the analysis.