The concrete box-girders bridges have their webs subjected to a combination of shear force and transverse bending moments, which may reach important values. The purpose of this paper is to introduce a new design approach including the Ultimate Limit State due to fatigue. An experimental investigation was undertaken with the purpose of verifying the validity of the newly developed approach. The following failure modes were considered: excessive plastic deformation of the stirrups, crushing of the compressed struts and rupture of the stirrups due to fatigue The experimental results showed good agreement with those results predicted by the proposed approach Furthermore, the tests 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 connection between the web and the bottom flange, and not at the corner of the stirrups.
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