Keywords: concrete-filled steel tube, steel frame, fire resistance, finite element method.

With the wide application of concrete-filled steel tubes (CFST) in building structures, it becomes increasingly important for engineers to have a better understanding of the behaviour of integral CFST framed structures in fire conditions. This will eventually lead to an economical and scientific fire-proof design of the structures. Significant research work has been done on the bearing capacity of CFST members in or after fires, and some simplified formulae that can be used in practice have been suggested [1,2,3,4,5]. However, for integral structure systems subjected to extensive loadings including fire loadings, the structural behaviour is usually far more complex than that can be described by simple formulae. Moreover, a CFST column is considered to be exposed to all-around fire when its fire resistance is studied. But in some situations, a CFST column is exposed to one-sided fire, such as a column to be joined with a fire division wall. When a CFST column is exposed to a one-sided fire, the axial expansion of column over the cross-section is non-uniform. It leads to the initial bending of the column to which direction is point to fire.

In this paper, non-linear finite element method is used to simulate the behaviour of integral CFST tubular framed structures in fire conditions. The mechanics parameters, the bilinear constitutive law of steel and constitutive law of concrete with a nonlinear ascending phase and a linear descending phase in Eurocode were used [6]. Before using this software, we had verified the dependability of it by comparison with the test in reference [5]. The framed structures are constructed with circular CFST columns and steel beams with I-sections. The structural responses of the structures, including critical temperature and fire-resisting time limit are obtained for ISO-834 standard fire. Parametric studies on some of the dominating parameters are carried out to show their influence on the capacity of the framed structures in fire conditions.

Based on the analyses above, the following suggestions and recommendations are presented for possible adoption in future construction and design of these structures.

1. The type of exposure to fire is an important factor of fire resistance of CFST column because it might lead to initial bending and change bending direction.
2. The support of column can change the distribution of internal force and restrain the initial bending. It's also an important factor to affect fire resistance of CFST column. Besides, the load of steel frame also determines the final direction of bending when the column is exposed to one-sided fire. In the next work we should continue to do is to find out the equilibrium value of the load with initial expansion bending. Then we can get critical value of different type of bending.
3. Comparing with a single CFST column, the fire resistance of columns in the frame is increased because of redistribution of internal force in frame and the restraint from vertical support. But displacements of columns in frame are bigger than that of single column and the effect of displacements of columns on other beams and columns should be investigated in the future.

1

Y.C. Wang, "The effects of structural continuity on the fire resistance of concrete filled columns in non-sway frames", Journal of Constructional Steel Research, 50, 177-197, 1999. doi:10.1016/S0143-974X(98)00245-4

2

X.X. Zha, "FE analysis of fire resistance of concrete filled CHS columns", Journal of Constructional Steel Research 59, 769-779, 2003. doi:10.1016/S0143-974X(02)00059-7

3

T.T. Lie, D.C. Dtringer, "Calculation of the Fire Resistance of Steel Hollow Structure Section Columns Filled with Plain Concrete", Can.J.Civ.Eng.21, 382-385, 1994.

4

Han L.H., Yao G.H., "Behaviour of concrete-filled hollow structural steel columns with preload on the steel tubes", Journal of Constructional Steel Research 59 (12) 1455-1475. doi:10.1016/S0143-974X(03)00102-0

5

T.T. Lie, Chabot, "Experimental studies on the fire resistance of hollow steel columns filled with plain concrete", NRC-CNRC Internal Report, No.611, Ottawa, Canada.

6

Eurocode 4, "Design of composite steel and concrete structures-part1-2: general rules-structural fire design", ENV1994-1-2;1994, European Committee for Standardization, Brussels.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £135 +P&P)