Date of Graduation

Summer 2016

Document Type

Honors Research Project

Degree Name

Bachelor of Science

Major

Civil Engineering

Research Sponsor

Dr. David Roke

Abstract

The AISC Steel Construction Manual covers structural steel design while at atmospheric and elevated temperatures. The manual does not, though, cover what happens to the steel after it has cooled from elevated temperatures. To fill in this knowledge gap, A36 steel was studied with respect to three main criteria: time, temperature, and cooling. Time was sub-divided into a standard burn (17-20min) and a prolonged burn (90min). Temperature was sub-divided into an average burn (600-800⁰F) and an extreme burn (>1200⁰F). To reach such temperatures, a forge was constructed and used during the burning process. Cooling was sub-divided into standard (air cooling) and rapid (water quenching) cooling. All possible combinations of time, temperature, and cooling were made in order to test all possible effects. No mechanical loading was used during any of the burns in order to only test the heterogeneous thermal effects. The prescribed burn combinations were performed on Charpy impact samples, compression slugs, and tensile coupons. The samples were then destructively tested in order to determine the principal stresses and the ductility of the samples after the burns. After testing, it was determined that while the standard burn is not ideal for the health of the structure, no immediate effects should be seen. For extreme burns though, depending on the length of time of the burn and the rate of the cooling, two main thermal effects will be almost immediately noticeable. Under rapid cooling conditions, brittle-strengthening will most likely be present; the degree of which depends on the duration of the exposure to the heat source. Without rapid cooling conditions, when the steel was exposed to the heat source for a long period of time, annealing will most likely be exhibited by the steel. Without rapid cooling conditions, when the steel was exposed to the heat source for a short period of time, no immediate effects should be seen. For seismic design, any adverse thermal effects could potentially be detrimental to the safety/stability of the structure. That is why it is recommended that after any fire event, the steel elements of the structure be inspected and retrofitted/replaced if it has been determined that brittle-strengthening or annealing has occurred. For structures not under immediate seismic threat, the urgency of the retrofit/replacement of the elements after inspection should be based on which thermal effect would most likely have occurred. Brittle-strengthening should be handled immediately, while annealing can be handled at a later, more convenient, time.

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