Lisa Choe

Fundamental Behavior of Steel Beam-Columns and Columns under Fire Loading: Experimental Evaluation

This paper presents the results of experimental investigations conducted to determine the fundamental behavior of steel members under fire loading. A total of eleven full-scale steel members were tested under combined thermal and structural loading. First, five A992 steel beam-columns (W10×68) were tested to determine their fundamental moment-curvature responses at elevated temperatures and different axial load levels. The experimental approach involved the use of radiant heating and control equipment to apply the thermal loading, and close-range photogrammetry combined with digital image processing techniques to measure the deformations (curvature) in the heated zone. Next, six A992 steel wide-flange (W8×35 and W14×53) columns were tested to determine their inelastic buckling behavior and axial load-displacement responses at elevated temperatures. A self-reacting test frame was designed to subject the column specimens to axial loading and heating. The thermal loading was applied by using the same type of...

Steel Columns Subjected to Thermal Gradients from Fire Loading: Experimental Evaluation

AbstractThis paper presents the behavior of axially loaded steel columns subjected to thermal gradients through their cross sections. Experimental tests were conducted on full-scale wide-flange steel columns with W8×35 and W14×53 sections made from standard grade 50 steel. The experimental investigations confirmed that variations in fire protection thickness had significant influence on the thermal gradient developing through the steel cross section. Thermal gradient along the flanges caused bowing of column specimens toward the hotter side. Thermal bowing introduced second-order moments and adversely affected stability, leading to failure of column specimens by inelastic flexural column buckling. The experimental behavior and results were compared with those obtained from detailed nonlinear finite-element analyses of the tested specimens. These nonlinear finite-element models utilized standard (temperature-dependent) material properties, and reasonably predicted the axial load-temperature-deformation beh...

Behavior of Steel Columns under Fire Loading

This paper presents the behavior of A992 wide flange steel columns under fire loading. Experimental tests were conducted to investigate the structural-thermal response of steel columns subjected to axial loads and elevated temperatures. Two identical W14X53 specimens were tested under (i) non-standard fire loading to determine the axial load capacity at elevated temperature and (ii) standard fire loading to determine the buckling temperature of the axially loaded steel column. For the non-standard fire test (Test I), the monotonically increasing axial load was imposed on the steel column under steady-state heating condition. For the standard fire test (Test II), the steel column carrying the sustained axial load was tested under transient heating condition. The structural-thermal responses of steel columns observed in Test I and Test II were compared including column end rotations, lateral and axial displacements, and steel temperatures. The measured column buckling behaviors were also compared to those obtained by 3D finite element analyses. The results indicated that the end rotations and displacements of the steel column before buckling were affected by the sequence of applied loading. Both Test I and Test II provided the similar prediction of axial load capacity and buckling temperature of the steel columns.

Section Characterization of Wide-Flange Steel Sections Subjected to Combined Thermal and Mechanical Loading

AbstractThe NIST Building and Fire Research Laboratory developed 29 recommendations for research based on the findings from the investigation of the World Trade Center (WTC). This paper discusses the results of a collaborative research effort conducted to address recommendation R9.1 from that report, namely to “Develop and validate analytical tools, guidelines, and test methods necessary to evaluate the fundamental behavior and fire performance of components and the structure as a whole system.” Specifically, it describes the development of a closed-form analytical model to represent moment-curvature-thrust-temperature (M-Φ-P-T) behavior of steel beam-columns in strong or weak-axis bending. The model considers uniform temperature distributions through the cross sections, and it is developed from parametric studies using a fiber-based analytical approach calibrated to experimental and finite-element results. The section-constitutive model was developed to provide a computationally efficient alternative to ...

Experimental Investigation of Steel Beam-Columns Under Fire Loading

This paper presents the experimental investigation of steel beam-columns under fire loading. Experimental tests have been planned to examine the fundamental behavior of steel beam-columns. Test specimens were sequentially subjected to: (i) constant axial loading, (ii) thermal loading on the plastic hinge region followed by ASTM E119 timetemperature (T-t) curve, and (iii) monotonically increasing flexural loading. The experimental approaches involved the use of: (a) innovative radiant heating and control equipment to apply thermal loading instead of using a conventional furnace and (b) digital image processing technique incorporated with close- range photogrammetry to measure the deformation and curvature over the heated region. The measured axial forcemoment-curvature-temperature (P-M-Φ-T) responses of the steel members were compared to those obtained by 3D finite element models and analyses.

Evaluation of Prestressed Concrete I-Girder Bridge Design Software with NCHRP Process 12-50

NCHRP Process 12-50 was used to evaluate and verify prestressed concrete bridge design software commonly used in Indiana. A test bed of 40 bridge structures was developed with input from practicing engineers and Indiana Department of Transportation (INDOT) specialists. The test bed included 20 simple-span and 20 multispan bridges. The primary parameters were bridge span, girder spacing, section type, strand pattern (straight or draped), and concrete strength. The remaining parameters were held constant with practical or consensus values provided by engineers or the INDOT bridge design manual. The section types included were AASHTO Types II, III, and IV and Indiana modified Bulb-Tee beams (54–78 in. deep). An indigenous computer program, PURDUE PSBD, was developed to implement the bridge design calculations specified in the AASHTO LRFD Bridge Design Specifications, which are currently endorsed by the INDOT bridge design manual. Both CONSPAN (the most common bridge design software in Indiana) and PURDUE PSBD generated calculation results for the complete test bed of bridges. The output from both computer programs was compared to identify assumptions and discrepancies from the AASHTO LRFD specifications. These comparisons indicated excellent agreement between the results from both programs for (a) concrete stresses and deflections at service-level loads, (b) nominal flexural strength, (c) nominal shear strength, and (d) initial camber and deflections. The test bed of bridge structures and the PURDUE PSBD program developed in this research are recommended for evaluating and verifying other bridge design software.