PSI - Issue 64

Cedric Eisermann et al. / Procedia Structural Integrity 64 (2024) 1224–1231 Eisermann et al./ Structural Integrity Procedia 00 (2019) 000–000

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The adjustment factor accounts for case-specific target reliability level β and the coefficient of variation for permanent actions V G , and is calculated using the following formula: = , ′′ . ′ ∙ 1 − ′′ ′ ′ 1 − ′ ′ (5) The equation designates parameters for new structures with ′ and for existing structures with ′′ . The sensitivity factor and the model uncertainty factor are considered invariant for new and existing structures and are the same as for DVM. According to fib Bulletin 80, ′ = 0.1 can be assumed for new structures. This proposed coefficient of variation for new structures is consistent with the assumed model uncertainty factor of 1.07. The coefficient of variation for existing structures can be calculated using equation 3. When comparing the two methods, the APFM is usually considered to be the simpler, more robust approach with respect to practical applications, as it requires fewer probabilistic parameters for the adjustment process and provides a higher degree of subjectivity, as discussed in Orcesi et al. (2021). However, the DVM is able to incorporate more case-specific information and can therefore deliver more accurate results for partial factors. The results may differ significantly from those of the APFM if a different probabilistic model for variable actions is used in relation to the suggestion of fib Bulletin 80. On the other hand, the results for the partial factors of material properties and permanent loads are similar between the two models (Gino et al. 2020). 3. Case Study: the Nibelungen Bridge Worms 3.1. The bridge The Nibelungen Bridge is a prestressed concrete bridge in southwestern Germany. It spans the Rhine and connects the cities of Worms and Bürstadt as part of the B47 road. Built in 1953, the Nibelungen Bridge is one of the oldest cantilever-constructed bridges in the world. The river bridge is 335 m long and consists of three main spans of 101.63 + 114.22 + 104.25m (Fig. 1.). Each main span is composed of two cantilevered beams, that were erected in 3m sections from the piers and are connected in the middle by vertically prestressed Gerber joints. A shorter span, measuring 23.22 m, serves as a counterweight for the cantilever of the first main span.

Fig. 1: Side view of the Nibelungen Bridge

The superstructure consists of two box girders that are connected by a deck slab. The height of the superstructure varies between 6.5 m at the pier clamp and 2.5 m at the Gerber joint, see Fig. 2. The bottom slab thickness of the box girder was designed to follow the flow of forces, decreasing from 1.55 m at the pier to 0.15 m at the joint (Fig. 2). The superstructure was longitudinally, transversely and vertically post-tensioned using 26mm diameter Dywidag bar tendons.