Serviceability and Ultimate Safety Checks of SegmentalConcrete Bridges through N-M and M-V Interaction Domains

Abstract

In current engineering practice, safety checks on serviceability and determinations of ultimate limit states of segmental bridges built by cantilevering are generally performed, either considering separately the contributions of axial force N, bending moment M, and shear force V, or considering the interaction effects through approximate expressions supplied by building codes. During construction stages and service life, the interaction between internal forces can be of fundamental importance in establishing the actual degree of structural safety and, for this reason, a different philosophy for performing checks in segmental bridges is proposed in this paper, plotting N-M and M-V interaction domains for cracking, construction stages, and serviceability (elastic domains) as well as M-V interaction domains for ultimate limit states (failure domains). Delayed deformations as a result of creep are considered, as are bonded and unbonded prestressing. A model is developed for plotting bending-shear domains at the ultimate limit state, underlining the strength reduction that occurs in concrete sections with external prestressing versus beams with full internal prestressing. A numerical application on an actual segmental bridge built by cantilevering was performed to show the proposed methodology, based entirely on strength domains, for safety checks. The load and stress paths in the construction stages are highlighted by considering the effects of creep in concrete, whereas bending-shear interaction is evaluated in the two cases of fully bonded prestressing and partially unbonded prestressing. The results show that safety checks which are performed based on approximate assumptions and expressions that do not explicitly consider the interaction effects can lead to unsafe evaluations, and it also shows that the proposed methodology allows engineers to take into account simultaneously any aspect related to cross-sectional strength on serviceability and ultimate limit states.