Strengthening of a railway arch bridge from 1854

Abstract

This paper presents the inspection of the condition and the design for strengthening of an existing railway arch bridge constructed in 1854. The original arch bridge is constructed with 5 layers of bricks in the arch and granite blocks in the foundation on top of an arrangement of frame made of timber and carried by piles. From the inspection it was concluded that the bricks in the arch was damaged due to freeze-thaw. It was also concluded that the timber structure in the foundation was rotten. The bridge is crossing a small creek. The environment is very sensitive. The access to the construction site is passing through landscape subject to preservation. The strengthening project included the arrangement of a new reinforced concrete arch. The arch was anchored with glued reinforcement bonded to the existing brick arch. The reinforcement and formwork was placed above the creek without disturbing the fauna in the water. The concrete was pumped into a form under the existing arch. After curing of the concrete arch, the strengthening of the foundation was initiated. It was planned to construct a bottom slab under the creek, which was able to carry the new concrete arch. In order to get access for the construction work the creek water was pumped through pipes suspended under the top of the new concrete arch. The procedures to handle the very delicate situation of replacing the foundation, while the bridge was in operation, and also protecting the environment is described in detail in the presentation. The process included high speed concrete curing, working processes under extreme narrow conditions and a very tight schedule.