Bridges: I35-W Bridge

Case study: System

Static and dynamic monitoring

Project Description

Summary: On Aug. 1, 2007 the I-35W Bridge over the Mississippi River in Minneapolis collapsed. The new bridge was opened 11.5 months later. Several vibrating wire and fiber optic sensors were installed in the new bridge.

Clients: Flatiron/Manson

Place: Minneapolis (MN) (USA)

Period: 2008 - 2008

Installation: Smartec

Structure's short description: The new I35-W bridge has five traffic lanes going each direction (the old collapsed bridge had only three lanes going each way) and it is designed to accomodate light rail transit in the future. If LRT is incorporated in the bridge, traffic lanes will be reduced from 10 to 8 and the two lanes along the center of the bridge will be converted to LRT tracks. Pier Shape : The pier shape is reflective curves with the dominant curve shaping along the length of the bridge, tapering from 30' to 11' to 30'. (11' depth at the center of the main span over the river). This pier shape is about the form and tying a continuous curve directly into the superstructure, while framing the river. The proportions reflect strength and elegance in their unique design. Two main piers features observation platforms curved along the river's edge. The superstructure concrete box girder is a closed shape with inclined walls and smooth surfaces of continuous flat planes. The appearance underneath is a sweeping form with the shape and concrete material creating a visually clean and quiet space below the bridge. Global View : A functional sculptural bridge reflecting a series of modern arch forms softly set into the context of the site to maximize openness, light and green space, while focusing on the river. River span sweeps 504' in a parabolic curve of graceful proportions. The pier shape of Concept A creates reflection of curved forms with continuous movement into the bridge superstructure. Strength and elegance combine for a 70' tall pier.

Aim of monitoring: A lot of sensors embedded or mounted to the bridge provide information to engineers about the structural behavior of the bridge. In particular Roctest vibrating wire sensors and Smartec SOFO sensors measure how the bridge is resisting to loads and the temperature of concrete. Additional Senscore corrosion sensors measure the chloride penetration in concrete.

Number of sensor: 12

Main Results: N/A

The dimensions of the new I-35 bridge

Bridge cross-section

The old I-35 bridge, collapsen on 01.08.2007

One of the 12 SOFO sensors installed in the new bridge

Junction boxes inside the main span of the South bound

Bibliography:

Overview of 40 Bridge Structural Health Monitoring Projects , Daniele Inaudi, International Bridge Conference, IBC 2010: June 15?17, 2009, Pittsburgh, USA, 2009

Structural Health Monitoring System for the new I-35W St Anthony Falls Bridge , Daniele Inaudi, Martijn Bolster, Ren?Deblois, Cathy French, Alan Phipps, Josh Sebasky, Kevin Western, 4th International Conference on Structural Health Monitoring on Intelligent Infrastructure (SHMII-4) 2009, 22-24 July 2009, Zurich, Switzerland, 2009