**7.3 I-35 W Interstate Highway Bridge Collapse**

In August 2007, in Minneapolis, MN, at 6 pm in rush hour traffic, the I-35 W bridge across the Mississippi river collapsed taking with it 111 vehicles, killing 13 people, and injuring 145.

The bridge, **Figure 9**, constructed in 1967, was non-redundant and fracture critical, meaning if one member failed the entire bridge could collapse. The cause of the bridge failure was a gusset plate which tore along a line of rivets. It was determined the gusset plate was too thin. The failure was triggered by the additional weight of construction equipment parked on the bridge and rush hour traffic. In the previous years the bridge was identified as having deficiencies, to include the gusset plates.

In a paper by Salem et al. [9] the authors analyzed the cause of the I-35 collapse. The I-35 Bridge over the Mississippi River in Minneapolis, Minnesota catastrophically failed during the evening rush hour on August 1, 2007, collapsing into the river. In the years prior to the collapse, several reports cited problems with the bridge structure.

The author's research analytically investigated the cause of the collapse using the Applied Element Method. The bridge was modeled using construction drawings, with relevant structural details and loadings. Structural details included the steel

**Figure 8.** *Collapsed pedestrian bridge Miami, FL. CC BY-SA 3.0.*

*Perspective Chapter: Bridge Deterioration and Failures DOI: http://dx.doi.org/10.5772/intechopen.109927*

**Figure 9.** *I-35 W Mississippi River Bridge collapse. CC BY-SA 3.0.*

truss, gusset plates, concrete slabs, concrete piers, while structural loading included traffic and construction. AEM provided the cause of collapse of the I35-W Bridge. The cause of collapse was found to be the failure of the gusset plates at connections L11 and U10, which well agreed with the field investigations of the collapsed bridge. The under-designed thickness of the plates, their corrosion, and over loading due to traffic and construction loads at time of collapse were the reasons for the bridge collapse [9].

*Failure analysis:* The cause of the collapse was a single ½" gusset plate failing along a line of rivets. There were a number of contributing factors that came together leading to the bridge failure: design flaws, inadequate design review, inadequate inspection, MnDot policies not being followed, poor information flow, the organizational structure not addressing bridge conditions and safety. All these factors combined led to the bridge collapsing. It is noteworthy to note the AEM program used by the authors with the model of the bridge's construction drawings and structural details and loadings predicted the failure of the bridge exactly at gusset plate L11 and U10.
