Keywords: fire, high strength concrete, column, temperature distribution, spalling, cross sectional area, finite element analysis.

High strength concrete (HSC) structures subject to fire exhibit severe structural damage not only because of the degradation of the mechanical material properties at high temperature but also because of spalling. The degradation of mechanical material properties is temperature dependent, and temperature distributions are highly related to spalling. Also, it is known that spalling and temperature distributions are affected by many factors, such as concrete strength, cover thickness, reinforcing bar ratio and spalling resistant techniques [1,2].

In this paper, the effect of cross sectional areas of high strength concrete (HSC) columns at elevated temperatures is investigated. Toward this goal, experimental and analytical studies are performed on short HSC columns subjected to fire. For the experimental studies, HSC columns having a compressive strength of 50MPa are fabricated. All columns are in length of 1500mm, and the cross sections are varied from 350mm x 350mm, 450mm x 450mm, and 550mm x 550mm. The temperature in the chamber is controlled to a ISO834 time-temperature curve for three hours. During the heating, temperature distributions at different locations inside the HSC columns are measured from the thermocouples. To measure the amount of spalling, losses of cross sectional area are calculated by measuring the spalling depth at every 50mm height from the side surfaces of the fire damaged columns. Also the weight of the columns before and after the fire tests are measured in order to calculate the weight loss from fire damaged columns.

In order to verify the experimental results and to perform parametric studies, finite element models are generated using the commercial finite element software, ABAQUS version 6.10-3. Three-dimensional models with different kinds of cross sectional area are generated same as the columns tested experimentally. The models are composed of concrete and steel reinforcement. Both parts are modelled using eight node linear brick elements, in addition temperature dependent concrete, steel thermal material properties, and the spalling effect are included.

Based on the results, the following conclusions can be drawn: 1) Cross sectional areas have significant effects on the thermal behaviour of high strength concrete columns subject to elevated temperature. 2) The column with the largest cross sectional area shows the highest temperature distribution and spalling. 3) The temperature distributions of the HSC columns can be predicted using the proposed analytical methods considering temperature dependent thermal material properties and spalling. 4) The proposed analytical methods are validated by comparing with the experimental results and show good agreement.

1

Y.S. Shin, J.E. Park, J.Y. Mun, H.S. Kim, "Experimental studies on the effect of various design parameters on thermal behavior of high strength concrete columns under high temperatures", Korea Concrete Institute, 23(3), 385-392, 2011. doi:10.4334/JKCI.2011.23.3.377

2

H.S. Kim, J.Y. Mun, J.E. Park, Y.S. Shin, "Structural capacity evaluation of high strength concrete short columns with various design parameters under high temperatures", Korea Concrete Institute, 23(5), 637-645, 2011. doi:10.4334/JKCI.2011.23.5.637

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