On Wednesday, Aug. 1, 2007, at 6:05 p.m. (during evening rush hour), the I-35W bridge across the Mississippi River in Minneapolis collapsed, killing 13 people and injuring 145. At the time of the collapse, repair work was in progress on the deck of the bridge, resulting in an additional 287 tons of construction material and equipment being on the bridge deck. This paper will present an analysis of a simple but similar bridge structure, using only Newton's second law. This analysis can give some insights into the cause of the collapse. This paper is the third of a series on bridge collapses, the first two being on the Tacoma Narrows Bridge and the Nimitz Freeway.