LETTERS TO THE EDITORS
Expanding on the Collapse
To the Editors:
The interesting article, "The Collapse of the Kinzua
Viaduct" by Thomas Leech (July-August), shows in Figure 7 the
roller bearings referred to in the text as providing a means to
relieve thermal stresses within the towers. Although Leech notes
that these metal roller bearing assemblies corroded and never served
their intended function, it would appear that any lateral motion
they would have permitted would also have put shear stresses on the
bolts that ultimately failed. Therefore, from looking at the
artist's drawing, not actual engineering drawings, it seems that
this feature of the bridge design was flawed from the outset, and
perhaps was a major factor in the eventual collapse.
Leslie E. Matson
Roseburg, Oregon
Mr. Leech responds:
The artist's sketch was intended to highlight the location of the
fractured collar coupling assembly and resulting separation failure
within the anchor bolt system, perhaps at the expense of other
important features of the original design. The 1901 engineering
drawing, shown at right, indicates holes elongated in the direction
of intended lateral movement, to permit the structure to literally
move back and forth in the lateral direction while the anchor bolts
remain stationary. It is interesting to note that while the original
design permitted lateral expansion, it did not permit longitudinal
expansion, which potentially was much greater based on the locations
of the various wind locks within the structure. This restriction
likely directly contributed to the fatigue fracture of the collar
coupling assemblies.