- PURPOSE The purpose of this Notice is to alert personnel of the Federal
Highway Administration (FHWA) and State highway agencies of a welded detail
which is potentially fracture critical.
- In instances where structural members intersect, bridges have been constructed
that pass one more components of one member through one or more components
of the other in order to provide
continuity through the intersection.
- This type of connection requires that one component be slotted to receive
the other. If these slots closely approximate the size of the member passing
through the slot, sharp corners can occur at plate edges, providing high stress
concentrations. Where the member or component passing through the slot is welded
to close the gap, additional stress concentrations are imposed by shrinkage
of a highly restrained weld around the periphery of the slot. There is added
difficulty in providing a satisfactory weld at the corners of the slot. In
the instance where either the member being slotted or the member passing through
the slot is in a tension area, the potential for fracture is greater than a
Category E detail.
- If continuity of one member through another is required and cannot be avoided by placement of one member on top, it is recommended the slotted detail to contain no sharp or reentrant corners and that no
welding be done to close the slot. A bolted connection (sketch attached) shows one possible alternate if this type of connection cannot be avoided.
- Each State should be alerted by this Notice to identify and locate these
highly restrained details in existing structures. Retrofit action to avoid
possible fracture should be considered. Such action should consider careful
weld removal or a combination of drilling holes and slotting material to remove
the stress concentrations, depending upon the particular detail.
H. A. Lindberg
Associate Administrator for Engineering and Traffic Operations
Attachment: Section A-A
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