Strengthening of a city center tunnel with concrete screw anchors under special boundary conditions

Johannes Lechner, Jürgen Feix, Robert Hertle

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

3 Scopus citations

Abstract

The Altstadtring-Tunnel is one of the essential east-west traffic routes in the city center of Munich and was constructed in the late 1960s. Segment 34 of the tunnel was built directly underneath the existing Prince-Carl-Palais, a historic building from 1804. Therefore 15 pre-stressed concrete girders with an effective depth of 3.5 m and a maximum span of up to 30 m were built which now form the tunnel roof slab. These girders were pre-stressed with steel nowadays well known for stress corrosion cracking. A recalculation of the slab showed that no ductile failure can be guaranteed in case of a progressive rupture of the tendons. Therefore, a concept for strengthening the slab was developed using concrete screw anchors as post installed bending and shear reinforcement. The concrete screw anchors are normally installed as anchoring elements in cracked and non-cracked concrete and are available with diameters up to 22 mm. Developing this concept further, it is straight forward to use these anchoring elements as post-installed reinforcement in existing concrete structures. This new strengthening system was developed at the University of Innsbruck in the last few years and can fulfill the special requirements of this project, such as installation of the strengthening system from underneath the tunnel slab during ongoing use of the structure. High strength steel with diameters of up to 63.5 mm will be used as post-installed bending reinforcement covered with a new shotcrete layer on the underside of the tunnel slab. In total 59.3 tons of new flexural reinforcement and 7199 concrete screws for strengthening the shear capacity of the girders will be used to ensure a ductile failure of the tunnel slab. The on-site work started in March 2019 and is expected to take two years to complete.

Original languageEnglish
Title of host publication20th Congress of IABSE, New York City 2019
Subtitle of host publicationThe Evolving Metropolis - Report
PublisherInternational Association for Bridge and Structural Engineering (IABSE)
Pages1493-1502
Number of pages10
ISBN (Electronic)9783857481659
StatePublished - 2019
Event20th IABSE Congress, New York City 2019: The Evolving Metropolis - New York City, United States
Duration: 4 Sep 20196 Sep 2019

Publication series

Name20th Congress of IABSE, New York City 2019: The Evolving Metropolis - Report

Conference

Conference20th IABSE Congress, New York City 2019: The Evolving Metropolis
Country/TerritoryUnited States
CityNew York City
Period4/09/196/09/19

Keywords

  • Concrete screw anchors
  • Post-installed bending reinforcement
  • Post-installed shear reinforcement
  • Strengthening of concrete structures

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