Strength and Deformation Properties of Steel Frames under Fire Conditions

Abstract

Steel structures are not fire resistant; this has long been reflected in the requirement for some form of fire protection to steel work used in buildings. Fire protection is a significant component of the total construction cost of a steel structure, up to 30% has been reached in some cases. To reduce the fire protection cost and at the same time not to lower the fire safety level of the structure, researches on the behavior of steel structures under fire conditions have been conducted worldwide over the past two decades and great achievements have been made, especially in the development of analytical and computation methods for the determination of the strength and deformation behavior of steel structures. Based on finite element analysis, a secant stiffness method suitable for the analysis of the strength and deformation properties of two-dimensional multistory steel frames in fire is presented. The method includes the effects of geometric and material nonlinearity, the non-uniform temperature distribution, and the gradual penetration of yield across the section and the spread of inelastic zone along each member. And also, a computer program for the calculation of the deformation-temperature (time) history and the collapse load at a specified temperature state or critical temperature at a specified load level is developed. The validity of the method is checked by a comparison with fire test results on steel frames.