Simple Approach for Performance-Based Fire Safety Design of Circular CFT Columns in Lage Enclosure

Abstract

ABSTRACT:The usage of concrete filled steel tubular (CFT) columns in large space buildings is increasing. Flashover is unlikely to happen in a large enclosure and the localized fire model is preferable to model the fire environment in a large enclosure fire. This paper proposed a simple approach to evaluate the fire resistance of circular CFT columns in localized fires. Simple model was provided to calculate the column temperatures in a localized fire. The concept of equivalent fire severity or time equivalent was used to correlate the localized fires with the standard fire. The simple model used in the Chinese code was used to calculate the load capacity of the circular CFT columns subjected to the equivalent standard fire exposure. The proposed approach, by correlating real fires with the standard fire, only includes heat transfer analysis and avoids the complex structural analysis, which provides an easy and efficient way for performance-based fire safety design. A case study is also provided to demonstrate the application of the approach. INTRODUCTIONConcrete-filled steel tubular (CFT) columns have many advantages, including high load carrying capacity, fast construction, small cross-section, and high fire resistance. These attractions have enabled CFT columns to be used in many large space, and high-rise buildings [1].Traditionally, the fire resistance of CFT columns is determined by a standard fire resistance test conducted on an isolated member subjected to a specified heating such as ASTM E119, ISO834. The standard fire resistance test is time consuming and expensive, and the dimension of the test specimen is limited by the size of the furnace. As an alternative to the test method, calculation approaches are also developed to assess the fire resistance of CFT columns [1][2][3][4][5]. Lie and Chabot [2] developed a mathematical model to calculate the temperatures and fire resistance of circular CFT columns. In the model, the cross-section area of the column was subdivided into a number of concentric layers to calculate the column temperatures, and a finite difference method was applied to solve the heat transfer equations. The strength and stiffness was calculated by subdividing the cross-section area into a number of annular elements. The representative temperature of an element was taken as the average temperature of the layer in which the element was located. In the Eurocode EC4-1-2 [3], a simple model is provided in the Annex H to calculate the fire resistance of CFT columns by subdividing the cross-section area into several elements and respectively calculate the strength and stiffness accordingly. Kodur [4] proposed a simplified equation based on the results of parameter studies supported by an experimental program on circular and square CFT columns under fire. The equation is widely used in North America, and it directly provides the fire

Fire Resistance of Steel Tubular Columns Infilled With Ultra-High Strength Concrete

“…The temperatures, stresses and strains at the centre of each element are assumed to be representative of those of the entire element. Furthermore, it is assumed that the steel and the concrete had the same temperature, t, at the interface (Song et al [26]; Wang et al [27]). Mesh convergence studies have been performed to study the sensitivity of the mesh size on the predicted results.…”