the southernmost lug at the top of the first full angle block from the west end. He noted that the lugs atop the angle blocks on the bridge had, for some reason, been shaved down to from . This significantly weakened the ability of the lugs to transmit stress from the chord to the braces and counter-braces. According to his report, "The cast iron angle block at top of second set of braces had the south lug broken off close to the face, and the line of fracture disclosed an air hole extending over one half the entire section. ...[The] failure first began in the south truss, at the second panel point from the west abutment." The second full angle block "was so far impaired by an air hole as to be reduced in strength fully one half. ... At no other point were these lugs subjected to so great strain, except at the end casting and here they were heavily reinforced." This "defective detail" caused the collapse of the bridge. Conclusions by the railroad LS&MS president Amasa Stone categorically denied that there were any design or construction flaws. He initially blamed the bridge's collapse on the deraillment of one of the two locomotives pulling the train, or by a loose rail which caused the train's deraillment. The railroad also hypothesized that a tornado may have hit the bridge, causing it to come loose from the abutments. Although the LS&MS refused to accept responsibility for the disaster, it paid out more than $500,000 ($ in dollars) to victims and their families to quiet legal claims. Modern engineering analysis of the disaster Björn Åkesson, a civil engineer at Chalmers University of Technology in Sweden, has identified three proximate causes of the bridge collapse: (1) the failure of an angle block lug on the west end of the bridge due to fatigue (caused by bending and shear stress), (2) thrust stress from improperly fitting chords and diagonals, and (3) low temperatures, which caused the cast iron angle blocks to become brittle. The failure of the angle block caused the upper chord to buckle, and the bridge to collapse. The angle block The angle blocks were made of cast iron, which Åkesson says was appropriate, for the angle blocks were in compression. The vertical lugs atop the angle blocks in the upper chord of the bridge received shear stress, but this should have