Análise da influência da variação da excentricidade de cordoalhas engraxadas no comportamento estrutural de lajes lisas protendidas

Abstract

The correct positioning of the tendons in the assembly and execution of prestressed concrete slabs is essential for the structural system to present the real behavior in place as designed, without changes in the stresses acting on the structure, avoiding the appearance of pathological manifestations, such as unforeseen cracks, excessive vertical displacements, reduced load capacity or even the collapse of the structure, in more extreme cases. In this study, four distinct architectural models were dimensioned, in the structural system of flat slabs in post-tensioned concrete, with unboned tendons, and later variations in vertical eccentricities were inserted, and thus, to analyze the new pre-compression stresses, stresses on the lower and upper faces, vertical displacements, load balancing and passive reinforcement of the slabs. At the end of the work, it can be seen that the reduction of vertical eccentricities on the lower face of the slab, provided greater losses of stresses applied by prestressing, in relation to the modification of the eccentricities of the upper face, showing decreases in load balancing, increases in displacements vertical and normal tensile stresses on the slab faces, mainly, exceeding the normative limits of ABNT NBR 6118:2014 for the maximum allowable stresses in the position on the columns, on the upper face. Bearing in mind that, the values of the analyzed criteria, remained in compliance with the specified limits, the maximum increase in the values of overlayings, in relation to the eccentricities of the tendons on the faces of the slabs, is 16,7 %.