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FUNDAMENTAL BEHAVIOR OF CFT BEAM-COLUMNS UNDER FIRE LOADING

FUNDAMENTAL BEHAVIOR OF CFT BEAM-COLUMNS UNDER FIRE LOADING. Amit H. Varma, Sandgo Hong Purdue University 2005 ASCE Structures Congress New York City, NY. Findings for CFTs with Insulation.

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FUNDAMENTAL BEHAVIOR OF CFT BEAM-COLUMNS UNDER FIRE LOADING

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  1. FUNDAMENTAL BEHAVIOR OF CFT BEAM-COLUMNS UNDER FIRE LOADING Amit H. Varma, Sandgo Hong Purdue University 2005 ASCE Structures Congress New York City, NY

  2. Findings for CFTs with Insulation • The insulation thickness becomes the most important parameter influencing P-M-f-T behavior and strength (P-M) under elevated temperatures from fire loading. • As expected, CFTs with b/t =48 have greater increase in moment capacity with increase in axial load (below the balance point). This continues to be true at elevated temperatures also. • The tube width (b) and width-to-thickness (b/t) ratio do not have significant influence on the P-M-f-T behavior of CFTs at elevated temperatures from fire loading

  3. EXPERIMENTAL INVESTIGATIONS • Experimental investigations will focus on measuring the P-M-f-T response of CFT segments. Parameters included in the experimental studies are: • Tube width (b) and b/t ratio • Concrete strength f’c • Axial load level • Heating (surface temperature) • Insulation thickness and type • Experimental test matrix is currently being finalized using results of preliminary investigations

  4. CFT TEST SETUP • The test-setup will be similar to those used for measuring P-M-f response of beam-column specimens at ambient temperature • It will be a cantilever column with axial force and lateral load applied at the top (free) end and the bottom end clamped. A custom-built portable furnace will be placed to surround the plastic hinge region. It will subject the surface to the selected T-t curve. • Thus, the specimen plastic hinge region will be subjected to P, M, and T. • The deformations of the plastic hinge region will be measured using close-range photogrammetry and digital image processing techniques.

  5. FURNACE DESCRIPTION • The portable furnace consists of ceramic fiber radiant heaters. Four such panel heaters are assembled to form a box around the hinge region. • Heaters have wattage density of 2.5 kW/ft2. Can provide surface temperature approaching 1200oC. They use radiant heating which is efficient and economic

  6. FURNACE T-t CONTROL • Radiant heaters are fully controllable. Specify control surface T-t curve and the heater will provide it. • For example, in the experiment below, we are controlling steel surface T-t curve under the insulation. • The insulation surface T-t curve can also be directly controlled. This experiment is in progress.

  7. FURNACE T-t CONTROL • In this experiment we are directly controlling the steel surface T-t curve without insulation to follow the ASTM E119 gas T-t curve.

  8. DEFORMATION MEASUREMENTS • The deformation (or movement) of any point on the specimen surface can be measured using close-range photogrammetry and digital image processing fundamentals. • For example, the thermal expansion was measured as shown below.

  9. TEMPERATURE MEASUREMENTS • Thermocouples bonded to steel and embedded in concrete to measure temperatures

  10. EXPERIMENTAL INVESTIGATIONS • Will be conducted this year. Results to be presented at next ASCE Structures Congress. • Acknowledgments • National Science Foundation - funding • Purdue University • Dr. Jim Bethel – photogrammetry • Jarupat Srisa-Ard - student

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