Dimensionamento das almas de pontes celulares.

Abstract

Box-girders have received a growing attention in the field of prestressed concrete bridges. The modern trend is to build wider unicellular bridges, which leads to a considerable increase in the transverse bending moment acting mainly in their webs. These are subjected to a combination of shear force and transverse bending moments, which may reach important values. The purpose of this thesis is to introduce a new design approach of box-girder webs, including the Ultimate Limit State due to fatigue. This design approach is derived from a critical analysis of the current criteria. The different criteria for the design of box-girder webs are analyzed and compared by means of shear-bending moment interaction diagrams as an attempt to identify the more realistic one. An experimental investigation has been undertaken with the purpose of verifying the validity of the new developed approach. The following failure modes have been considered: crushing of the compressed struts, excessive plastic deformation of the stirrups and rupture of the stirrups due to fatigue. The experimental results have shown good agreement with those predicted by the proposed approach. Furthermore, the tests have revealed new aspects of the fatigue behavior: the rupture of the stirrups due to fatigue occurred in stages, one at a time in a gradual manner. In all cases the failure took place near the top face of the lower flange and not at the corner of the stirrups.

Concepção de tabuleiros curvos e estaiados.

“…Conforme exemplificado por Gaspar (2003), nas seções celulares simétricas, com o carregamento contido no plano longitudinal de simetria, as tensões de cisalhamento são nulas neste mesmo eixo de simetria (Figura 6.15). Portanto, este fato permite considerar a seção como se ela fosse aberta.…”

“…Em outras palavras, a solução deste problema é obtida pela superposição dos efeitos da solução da seção aberta, submetida a uma carga P, que passa pelo centro de cisalhamento e provoca as tensões i, e dos efeitos do fluxo de torção q0, que provoca tensões 0 = q0/e, decorrente da torção ΔT dada por P vezes a distância entre CA e CF na direção horizontal, como indica a Figura 6.16 (GASPAR, 2003).…”