n August 2022, a transport tanker carrying a highly flammable liquid crashed into the south approach barriers at the Sikanni Chief River Bridge resulting in a full closure of the Alaska Highway (Highway 97) in northern BC. The fire generated intense heat that resulted in extensive structural damage and brought forward severe concerns for weakening of the bridge load carrying members. As a critical link to Northern Canada and then to Alaska, USA, there was extreme pressure to get this highway safely re-opened as quickly as possible. An emergency response was initiated immediately with a rapid damage assessment that enabled light vehicle traffic to be restored shortly after the incident. The emergency response and structural assessment continued until full unrestricted truck traffic was restored on the bridge. While the primary focus was forensic review and structural evaluation of the residual load carrying capacity, several concurrent bridge engineering teams were mobilized to work in parallel, developing contingency plans that were on hand in case the structural evaluation demonstrated insufficient capacity for truck traffic. Concurrent teams completed forensic review; load testing; structural evaluation for load carrying capacity of the bridge in its damaged state; detour crossing planning; fibre-reinforced polymer strengthening of fire damaged concrete girders; and external strengthening of fire damaged superstructure.
For the structural evaluation of the residual load carrying capacity, destructive and non-destructive testing was performed along with petrographic examination of the concrete core samples to determine heat profiles throughout the reinforced concrete bridge deck and within the prestressed concrete girders. Prestressing strands, mild reinforcing steel, steel drainpipe, and concrete cores were all extracted from the fire damaged zones for laboratory testing. Material strengths were adjusted for heat profiles determined from the petrographic examination and were then used for structural evaluation of the residual capacity for the bridge in its damaged state. Load testing results were used to validate a 3D Finite Element Model of the bridge to accurately determine structural demands. The structural evaluation and load testing determined that the bridge has sufficient residual capacity in its damaged state for unrestricted truck traffic as per the Canadian Highway Bridge Design Code (CHBDC), CSA S6-19, and the bridge was re-opened to full legal truck traffic 24 days following the incident in a single lane alternating traffic configuration.
This paper highlights key lessons learned from this project with respect to responding to a major fire incident and assessing heat damaged structures in terms of what to triage and prioritize in the response.
