ABSTRACT
The durability of reinforced concrete (RC) structures is influenced by uncertain service loads and material properties, which must be taken into account in service life-oriented structural design. The consideration of aleatory and epistemic uncertainties allows probabilistic service life predictions in the context of service life design, replacing the classical safety factors.
In the context of this article, the service life of a prestressed concrete bridge strengthened with a fiber reinforced concrete (FRC) layer is to be maximized. The L3378 bridge near Fulda-Lehnerz in Germany will be used as a reference structure. The bridge consists of four prefabricated prestressed RC girders with T-girder cross-section, supplemented by an RC layer and an additional FRC layer. The FRC layer is made of ultra-high-performance fiber reinforced concrete (UHPFRC) and is intended to increase the load-bearing capacity while also serving as a waterproofing layer.
For the optimization, finite element simulations are performed to determine the most sensitive parameters. The fiber orientation of the UHPFRC layer, the prestressing force and position, the bond between concrete and steel, and the material properties are investigated, and then the most sensitive parameters are applied as uncertain parameters for the maximization of the service life, while the cost of material is to be minimized. Although the reference structure is build new, the presented design approach is also applicable to the strengthening of existing structures to extend their service life. For this reason, the original design is finally compared with a conventional design without FRC layer in terms of failure probability considering stochastic live loads and polymorphic uncertainties.
