A concrete and steel beam weighing more than 85 tons came crashing off a semi-truck on the heavily traveled Marquam Bridge spanning the Willamette River just south of downtown. This happened Tuesday afternoon, shutting down northbound Interstate 5 in the heart of Portland. It started with a semi-truck overturning on the Marquam Bridge. The truck was carrying a concrete I-beam intended for the Portland-Milwaukie Light Rail Transit Project. That falling beam crushed a nearby car. That car then caught fire.