Modernising a monument: The challenges of strengthening and widening a structurally deficient road bridge under live traffic

Abstract

The historic Port Weir Bridge over the Nidau‐Büren Canal in the Canton of Bern, Switzerland, was inaugurated in 1938. This multi‐purpose structure serves as an important road bridge, a mechanised weir, a lock for canal boats, as well as a hydroelectric power station. During inspections in 2018, severe concrete damage and reinforcement corrosion were observed on this protected structure. Immediate temporary reinforcement measures were required as the conformity factors for structural safety at numerous locations were significantly below the minimum requirements. A project specific traffic load model allowed the temporary strengthening works to be limited to a few critical elements, thereby allowing the bridge to be reopened for heavy traffic in 2019 and then fully rehabilitated between 2020 and 2022. The renovation project involved an innovative reinforced UHPFRC strengthening of the existing T‐beam superstructure and a widening of the deck to bring the lane widths up to modern standards. This paper outlines the safety measures and the UHPFRC strengthening concepts applied, as well as some of the key construction challenges associated with maintaining road traffic on the bridge and traffic in the canal lock below the bridge during the construction works. Additionally, the UHPFRC strengthening concept is demonstrated by means of a design example.

Updated load models for short‐span road bridges in the range of 2‐15 m

“…The structural safety level at numerous locations was significantly below the minimum requirements of the Swiss Norm SIA269/1 for Existing Structures. The short span load models outlined in this paper allowed the temporary strengthening works to be limited to just a few critical elements before full rehabilitation took place [17].…”