FINITE ELEMENT ANALYSIS FOR 3-D FRAME STRUCTURES UNDER COMBINED ACTIONS OF GEOMETRIC NONLINEARITY AND CREEP

In analysis of long-span or tall flexible concrete structures, geometric nonlinearity and creep are two important factors, which have usually been taken into consideration separately. However, the coupling of the two factors is of special concern for more accurate calculation. In the present study, based on the co-rotational coordinate method for geometrically nonlinear analysis and the initial strain method for concrete creep, the equilibrium equations for a proposed 3-D beam element was developed, considering both the geometrical nonlinearity and initial strains under the co-rotational coordinate system. By using the principle of static equilibrium, the equilibrium equations were transformed into the global coordinate system and a detailed flow chart of the algorithm was given. Taking into consideration of the effect of creep, the geometrically nonlinear analysis for a concrete tower of a long-span cable-stayed bridge with a hybrid girder was performed for illustration purposes. Results demonstrated that both the internal forces and displacement of the tower when considering the coupling of creep and geometrical nonlinearity were greater than the summation of the results when the two factors were considered separately. It is suggested that the coupling of geometrical nonlinearity and creep is essential for the analysis of large span or tall flexible concrete structures.