Comparativo das perdas de protensão em viga BT-72 empregando concreto convencional e de ultra-alto desempenho

Abstract

Pre-stressed concrete is a consolidated technology in civil engineering, essential for spanning large spans in infrastructure projects. However, its design is critically affected by the loss of pre-stressing force over time. Various alternatives are being researched to minimize these losses, including the use of Ultra-High-Performance Concrete (UHPC). Thus, this study is justified given the absence of specific Brazilian standards for this material. The objective of the work was to compare the pre-stressing losses in a pre-tensioned girder of the PCI BT-72 model, using Conventional Concrete (CC) of 40 MPa and UHPC of 150 MPa. The methodology consisted of evaluating the initial, immediate, and progressive losses for a 35-meter span girder, using electronic spreadsheets based on the criteria of the ABNT NBR 6118 standard and, for UHPC, on formulations from the literature and the French standard NF P18-710. The results demonstrated that progressive losses were decisive for the project's feasibility, reaching 24.75% in the CC and only 9.08% in the final design with UHPC. Back-analysis confirmed that the conventional concrete girder proved to be technically unfeasible, with the final pre-stressing force falling below the necessary minimum, while the UHPC girder, after resizing, was the only solution that proved to be safe and reliable. It is concluded that the high dimensional stability of UHPC, mainly in controlling creep and shrinkage, is the decisive factor for the viability and safety of high-performance pre-stressed structures.