Fundamental behavior and stability of CFT columns under fire loading
Abstract
This dissertation presents: (a) experimental and analytical research of the fundamental behavior of concrete filled steel (CFT) members under elevated temperatures from fire loading, and (b) its use to investigate the stability of CFT columns under standard fire loading. The experimental investigations were conducted using an innovative experimental technique to determine the moment-curvature-temperature (M-&phis;-T) behavior of CFT beam-columns subjected to axial, flexural, and thermal loading. The testing technique involved the use of radiation-based heating units and digital imaging systems to measure deformations at elevated temperatures. Thirteen CFT beam-columns specimens were tested and the experimental results included the M-&phis;-T responses of the plastic hinges. 3D finite element models and fiber-based section models were developed and calibrated for predicting the M-&phis;-T behavior of the tested CFT beam-column specimens. These models provide significant insight and predict the behavior of the specimens with reasonable accuracy. The stability behavior of CFT columns under fire loading was investigated using a simple analytical approach, which was developed by modifying Newmark’s method for inelastic buckling analysis to include: (a) the effects of elevated temperatures and (b) section fiber models (of M-&phis;-T responses) at the station points. The analytical approach was used to predict the standard fire behavior and stability of several CFT columns tested by researchers around the world. The analytical predictions were verified by comparing them with: (a) experimental results and (b) analytical results predicted using 3D finite element models. The comparisons indicated that the simple analytical approach could predict the standard fire behavior of CFT columns with reasonable accuracy. The experimental approach for determining the fundamental behavior of structural members under fire loading is recommended for future research. The fiber-based section model for predicting the fundamental behavior of members under fire loading is also recommended for future development of modeling techniques. The simple analytical approach for predicting column stability under fire loading is recommended for future research focusing on the effects of various loading, restraint, and fire parameters on column inelastic behavior and stability under standard or realistic fire loading.
Degree
Ph.D.
Advisors
Varma, Purdue University.
Subject Area
Civil engineering
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