Effect of Heating and Cooling on Axially Restrained RC Columns with Special-Shaped Cross Section

Abstract

This paper describes the performance of 12 axially restrained RC columns (four for each type of cross section, i.e., +-, T-and L-shaped cross section) under fire conditions that were recently finished in South China University of Technology. The main objective of the paper is to investigate the effect of axial restraint on RC columns during both expanding and contracting phases. The RC columns were all initially concentrically loaded and subjected to ISO834 standard fire on all sides. Axial restraints were imposed at the top of the columns to simulate the restraining effect of the rest of the whole frame. Different degrees of axial restraint were obtained by varying the length of the restraining beam. The boundary conditions of the columns were considered as fixed-fixed for all tests. It is found that restrained RC columns behave quite differently to isolated ones. No typical 'runaway' failure of isolated RC columns was observed in the fire test. Finally, the finite element software, SAFIR, is employed to conduct a numerical analysis of the tests.

Effect of Transient Creep Strain Model on the Behavior of Concrete Columns Subjected to Heating and Cooling

“…It should be noted that no creep is explicitly considered in these relationships for steel reinforcement, which is an important assumption as the creep of the steel reinforcement is known to have an effect on stress and strain state in reinforced concrete frames when temperature in reinforcement bars exceeds 400°C [21,22], as is the case here. The axial restraint stiffness remains unchanged during the simulations, which can be justified by the fact that the maximum displacement at the center of the restraining beam is only about 13 mm [14]. The deformation behavior and the evolution of the axial load for the eight experiments can be observed in Figure 6.…”

“…Implicit models such as the EC2 model have limitations that, even though they were not considered as significant when following a prescriptive design, could lead to inappropriate results when a performance-based design including the cooling phase is performed. To highlight the difference in the structural response obtained using implicit or explicit models, a series of experimental fire tests performed at South China University of Technology [14] has been numerically modeled using the nonlinear software SAFIR [15]. Two different concrete models were used for comparison: on the one hand, the current EC2 model, and on the other hand, a new formulation of the EC2 model that contains an explicit term for transient creep strain.…”

“…A series of experimental fire tests made at South China University of Technology on axially restrained concrete columns, described by Wu et al [14], was simulated using the nonlinear finite element software SAFIR [15]. The experimental data were compared with the computed results obtained respectively with the EC2 concrete model and the ETC concrete model.…”

“…Thermal parameters for concrete and steel recommended by EC2 were used in the heat transfer analysis by SAFIR. Note that, in the original paper presenting the test, the thermal analysis of the tests has been performed using the thermal parameters from the EC2 and the software SAFIR and the simulations showed good agreement with the measured temperatures in the section [14]. For the structural analysis, initial eccentricity of 3 mm was introduced as it is the same value used by Wu to perform the numerical simulation of its tests.…”

Experimental research on the fire performance of a special cross-shaped composite column with a high-strength concrete-filled steel tubular core

“…In the past decade, research has been concentrated on the fire performance of normal RC columns (Al-Salloum et al, 2016; Hwang et al, 2016; Raut and Kodur, 2011; Wu et al, 2010) or steel and composite columns (Abbas et al, 2017; Espinos et al, 2014; Won et al, 2016). In contrast, the research studies on the fire performance of specially shaped columns are limited.…”