Dynamical analysis of a 40 m span precast posttensioned concrete girder during lifting operations

Abstract

AbstractCranes are employed to lift precast concrete girders during their construction. Presently, there is no recommendation for operational velocities during girder assemblage, particularly for long elements; simultaneously, several accidents have been reported during the transitory phase of girder motion. Since this mechanical problem has been examined in technical literature using a static approach, the present research study aims to investigate the dynamical behavior of a long, prestressed concrete girder by determining critical operational velocities according to crane movements. Prestressing cables' eccentricity and lifting loop position deviation were accounted for in 3D finite element simulations of a 40 m span precast prestressed concrete girder. Transient nonlinear analyses to obtain stresses and deflections were performed, so as to account for the large deformation behavior of the motion. A frequency domain approach was employed to analyze the time history results using the girder's natural frequencies obtained by modal analysis. The finite element model was developed to simulate upward, downward, and lateral girder movements. The most significant displacements and stresses were observed in the highest girder acceleration peaks, amplified by eccentricities. Safety against cracking and subsequent failure during vertical and lateral movements was ensured for crane operating accelerations of 0.02 g (v = 20 cm/s) and 0.007 g (v = 7 cm/s), respectively. Compared with the usual static analysis, for the critical case investigated, the inertial effect intensified the tensile stresses by 27 times, increased the compressive stresses by 11%, and increased the girder deflection by 3 times.