ABSTRACT
This paper presents the NDT methods and instrumentation used for monitoring of a major crack that developed in the masonry pedestal of a tower of the Williamsburg Bridge. The paper will explain the factors which contributed to the cracking of the pedestal, as well as the reason for monitoring the crack and the tower.
Williamsburg Bridge is a suspension bridge located in New York City. It is a major crossing of the East River and it is vital to the traffic flow in and out of Manhattan.
Due to poor maintenance, the “pinned” link at the top of one of the side span towers “froze”, becoming a rigid connection between the tower and the deck. Consequently the longitudinal movements of the bridge deck induced significant horizontal forces at the top of the tower. As a result during the summer months of 1994 a wide crack developed on the entire west face of the tower’s masonry pedestal. The crack’s width varied in accordance with the horizontal movement of the bridge deck, due to the temperature variation of the bridge.
The bridge is a very important artery on which traffic must be maintained. Until a permanent repair or replacement of the “pinned” link on the top of the tower can be made, a monitoring program has been implemented.
The following are monitored:
the variation of the crack width, the variation of the stress in the steel structure portion of the tower, and tower verticality.
The following methods (procedure, instruments) are used:
electrical resistance strain gages for static and dynamic readings, dial gauge indicators, optical instrumentation
