Performance Evaluation of Reinforced Concrete Bridge Columns after Fire Exposure

摘要

Columns are the most critical components for the overall stability of a bridge. In many bridge fire cases, it is very easy to determine which fire exposed columns are no longer functional. However, in special cases, a fire may last long enough to cause damage but not long enough to cause complete failure of the column. In fact, the damage may be undetectable by visual inspection, and a fire damaged column may appear the same as an intact one. Officials are in need of a simple and cost effective damage detection method which enables them to make quick decisions regarding the closure of a bridge with columns exposed to fire. Two one-fifth scale reinforced concrete (RC) bridge column specimens were designed in compliance with AASHTO specifications and subjected to two significant durations of extreme fire exposure at a fire testing facility. One specimen was subject to 1-hour of extreme temperature reaching 1285 degrees Fahrenheit, while the other was subjected to more than 2-hours of exposure at 1440 degrees Fahrenheit. Both of these durations cause significant damage to the concrete material but have very little visual indication. After the fire experiments, the columns were returned to the Next-Generation Multihazard Resilient Infrastructure Laboratory (NGMRIL) of the University of Connecticut where system identification and residual axial capacity tests were conducted on the undamaged and damaged columns. Modal analyses of both fire damaged columns as well as an undamaged column were conducted, and the residual axial capacities of the damaged columns were obtained using a 400 kip loading frame. The capacity of damaged columns was compared with the axial capacity of the benchmark column. Possible methodologies for determining the residual capacities of fire damaged bridge columns are developed based on these experimental observations.