Fire Resistance of Concrete Filled Box Columns

• Main Authors: JIANG,YI-JING, 江依瑾
• Other Authors: TANG,CHAO-WEI
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/5y7yyq

碩士 === 正修科技大學 === 營建工程研究所 === 103 === Concrete filled box columns (CFBC) typically consist of rectangular or square hollow structural sections filled with concrete. Compared with bare steel or reinforced concrete columns, CFBC have several structural and constructional benefits, such as high strength and fire resistance, large stiffness and ductility, large energy absorption capacity, restraint on local buckling of the steel box provided by the infill concrete core, omission of formwork and thus reducing the construction cost and time. As a result, CFBC have been widely used as primary axial load carrying members in high rise buildings, bridges and offshore structures. To promote the applications of CFBC in Taiwan, this study aims to explore the fire resistance of CFBC. Two groups of full-size experiments were carried out to consider the effect of type of concrete infilling (plain and reinforced) on the fire resistance (i.e., time to failure) of CFBC. The control group was a steel box filled withplain concrete, while the experimental group was consisted of a steel box filled withfiberconcrete and two steel boxes filled withfiber reinforced concrete. The columns had square cross-sections and were filled with different concretes. The width of the square columns was 400 mm and the wall thickness was 12 mm. All columns were 3060 mm long. No external fire-proofing was provided for the steel. Each of the CFBC had end plates welded to them in order to transfer the load, and end stiffeners were also introduced to ensure that end conditions did not affect the failure resistance of thermal load. Besides, the furnace, concrete and steel temperatures as well as the axial deformations were recorded until failure of the column. On the other hand, the temperature from the specimen’s surface to the inner central core was measured with type K thermocouples located at different depths in four sections of the column. During the whole test, the columns were subjected to a constant compressive load. This load was controlled by a load cell of 19.6 MN, located on the head of the piston of a jack. The applied load corresponded to 27%-28% of the design value of buckling resistance of the columns at room temperature, respectively. Thermal load was applied on the columns in form of CNS 12514 time-temperature curve in a natural gas-fired large-scale laboratory furnace until the set experiment termination conditionwas reached. The current failure criterion specified in CNS 12514 is adopted in this study, which is based on the amount of contraction and the rate of contraction. For the columns under consideration, these criteria correspond to a maximum contraction of 30.6 mm and a rate of contraction of 9.18 mm/min.