Estudo analítico do tombamento de vigas pré-moldadas sobre almofadas de apoio

Abstract

The handling of long and slender precast prestressed concrete beams deserves study and attention due to the risks of lateral instability. During the lifting phase and after positioning the beam in the structure, these structural elements, which have low lateral flexural stiffness, require verification of the safety for handling by the designers. Therefore, this work aims to propose an analytical model for parametric analysis of beams already positioned in their definitive location, when the connections have not yet been made, considering the geometry of the cross-section, physical characteristics of the materials as well as geometric imperfections. Nonlinear analytical solutions are proposed to determine the loading of precast beams on elastomeric support devices. It is worth mentioning that no analytical formulation available in the literature that considers the initial rotation of the beam as an imperfection in the study of equilibrium. A numerical model developed in the ANSYS software program is used for comparison with the analytical results. Finally, a parametric analysis is performed to verify the behavior of the structure as a function of the variability of specific parameters such as initial eccentricity, initial beam rotation, concrete strength, dimensions of the bearing pads, the prestressing force and cross-section of the beam. The results show that the proposed equations allow to characterize the non-linear behavior after the peak of the beam and to consider both the eccentricity and the initial rotation. The parametric analysis evidenced the significant influence of the geometric properties of the beam, such as cross-section, eccentricity, and initial rotation, among other parameters, on the stability of the beam. The rotational stiffness of the support and the section stiffness were the factors of most significant influence on the rollover load. The camber due to the prestressing force resulted in an insignificant decrease in the critical load. For the analyzed cases, the rollover load had an average reduction up to 7% due to the presence of initial eccentricity and 9% due to the consideration of initial rotation, an average reduction between 42% and 62% due to the decrease in the rotational stiffness of the support, 33% and 41% due to the reduction of the beam top flange length, 29% and 48% for the increase in section height for the beams BT-63 and BT-72 compared to the BT-54, respectively. Regarding the critical rollover angle, the analyses show that the initial eccentricity and the initial rotation cause significant increases in their values, reaching an increase of 52% for the analyzed values of initial eccentricity and 47% for the values of initial rotation. The cracking angle is sensitive to variations in beam cross-sectional properties. In this way, lateral stiffness is the main parameter that governs the cracking of the beam. Finally, the shape of the cross-section and the quantification of geometric imperfections, such as eccentricity and initial rotation, are of paramount importance for stability analyzes.