Avaliação da segurança durante o içamento de vigas pré-moldadas

Abstract

In the current civil construction scenario, the quest for cost reduction tends to optimize the procedure and material involved in the dimensioning of strucutral elements in reinforced concrete, resulting in slender cross section sections with better mechanical efficiency. However, long and slender beams are more prone to the phenomenon of lateral instability during transiente phases, such as lifting. The objective of this work is to analyse the equations present in the technical literature to evaluate the safety of elements during the suspension phase, to perform numerical simulation in order to quantify the equilibrium rotation, as well as to analyze the influence of the several parameters inherent to the constructive process of pre-cast elements and the lifting phase, such as initial lateral eccentricity, deviation in the positioning of the loops, lenght of the cantilevers, protension and use of a rigid element between the beam and the lifting cable. The analyses carried out, including a case study for a real problem in a beam during lifting, show the need for an adequate design definition of the study variables, since the recommendations of the normative codes are still ineffective to guarantee the safety of this phase transitional period. The results show that positional deviations of the lifting loop, even in compliance with the PCI (2011) recommendation, can generate variation in the maximum tensile stress of up to 30%, as well as in the existence of initial lateral eccentricity, rigid body rotation for static balance can vary by 62%, even if different regulatory codes are pleased. The knowledge of these execution deviations becomes even more necessary to maintain the stability of the elemento when the lifting is perfomed without or with small cantilever, since these generate stabilizing effect able to reduce the interferences generated by the initial imperfection.