Published February 23, 2019
Graduate Students: Reza Imani
Principal Investigator: Michel Bruneau
Co-Principal Investigator: Gilberto Mosqueda
Project Completion Date: 08-21-2014
The main goal in this project was to study the behavior of Concrete-Filled Double-Skin Tube (CFDST) columns subjected to fire following earthquake scenarios. For this purpose, the behavior of CFDST columns with various degrees of simulated seismic damage was examined under the standard ASTM E119 (ASTM 2012) fire, using both experimental and numerical approaches. Moreover, to get a preliminary understanding of the reverse scenario (i.e., a post-fire earthquake), the effect of fire on the seismic capacity of a CFDST column was also experimentally studied.
Experimental studies were conducted to examine the behavior of concrete filled double-skin tube (CFDST) columns exposed to fire after being subjected to simulated seismic loads. The experiments were conducted in two separate phases, consisting of the quasi-static cyclic tests followed by fire tests. Three nominally identical column specimens were constructed for these studies. One of the specimens was directly tested under fire to quantify its resistance in an undamaged condition. The other two specimens were first subjected to quasi-static cyclic lateral loads, imposing varying degrees of lateral drift to simulate two different seismic events with moderate and high damage levels before being exposed to fire. Both of the specimens were pushed to the maximum drift of 6-6.5% with different residual drifts of 1.4% and 3.9% for moderate and high damage levels, respectively.
The undamaged and damaged columns were then subjected to the same fire tests following the standard ASTM E119 (ASTM 2012) temperature-time curve while sustaining an axial load until the column failed due to global buckling. Local buckling of the tubes was also observed in the specimens due to the thermal expansion and separation from the concrete. Overall, the results showed marginal differences in the fire resistance of the three specimens, providing evidence for the resilient performance of these columns under post-earthquake fire scenarios. An additional quasi-static cyclic loading test was conducted on the specimen that had been exposed to fire without any prior damage, to investigate the behavior of the column subjected to seismic loads after the fire test. Again, differences in behavior were modest, except for a 5.7% drop in strength attributed to permanent degradation in material properties due to the fire test.
In addition to the experimental studies, detailed finite element analyses were conducted using ABAQUS and LS-DYNA to simulate the behavior of CFDST columns subjected to post-earthquake fires. The models were shown to be capable of replicating the experimental results with sufficient accuracy. A simplified step by step analytical procedure was proposed for calculation of the axial load capacity of CFDST columns subjected to fire. The procedure was defined based on an analytical solution to the heat transfer problem and calculation of axial load capacity using the fire-modified material properties. A number of design recommendations, based on the knowledge gained from the experimental and analytical studies, were proposed for CFDST columns subjected to fire.
This work was supported by MCEER, University at Buffalo.