Keywords: explosion, fire, rate-dependent, shell element, local buckling, steel frame.

In recent decades, researchers have proposed a number of approaches to assess the resistance of structures under fire. These approaches include the simplified calculation method, the plastic analysis method, the Rankine approach, efficient plastic hinge methods, and the finite element approaches. All these approaches described above vary in their applicability and degree of sophistication; however, they cannot be applied to situations in which the fire is a direct consequence of an explosion, as permanent structural deformation caused by the explosion can reduce the fire resistance of the structure.

The overall stability of structures under the combined actions of explosion and fire has become a concern in addressing the issues on building safety arising from "extreme events". The short duration of explosion loading implies that the material is strain-rates dependent, i.e., high strain rate will increase the yield strength of steel. On the other hand, fire loading is associated with elevated temperatures which cause thermal strains and lead to significant deterioration in the material properties of steel. Izzuddin et al. [1] proposed an integrated analysis method using beam element for explosion and fire analysis of steel structures. Their method allows the elastic elements to be refined and re-meshed to account for elasto-plastic effects in the members. Liew and Chen [2] proposed an inelastic transient analysis using beam element to study the effect of explosion-induced deformations and plasticity on frame stability and the subsequently effect of fire on the overall stability of the structure.

It is often convenient and economical to model large steel framework using beam element. The use of one element per member is sufficiently accurate to model the nonlinear inelastic behaviour of 3-D frame structures. However, under blast loading, the yield strength of steel will increase due to the high strain-rate effect, and the steel cross-sections are more vulnerable to local buckling, which can not be predicted by the beam element approach. The beam element approach adopts the assumption of plane section remaining plane after deformation. Hence the material nonlinearity induced by high shear cannot be modelled correctly. This will inevitably over-predict the explosion-resistance of steel frame structures.

The pressure on structure caused by explosion, the elevated temperature in the structural members caused by fire, and the response of the structure are interrelated in nature. In coupled analyses, the blast and fire prediction programs are simultaneously linked with a structural response program to account for the pressure and fire that arise due to motion and failure of the structure. Coupled solutions of fluid dynamics, heat transfer and structural response (where the fluid and heat transfer solutions are obtained interactively with the structure solution) can provide more accurate predictions, however they require the use of huge computational resources and are very costly to implement. In this research, the structure is analyzed under predefined explosion and fire loads. Although coupled analyses are not adopted at present, the current research forms the basis for further studies, in which the explosion and fire analyses may be coupled. In this paper, a mixed element approach, implemented using ABAQUS, is adopted to achieve a realistic modelling of the overall framework subjected to localized explosion and fire. Beam element is used to model frame members that are not directly subjected to explosion and fire, and shell element for frame members directly subjected to explosion and fire. The influences of blast loading on the fire resistance of a column and a 3-storey steel frame are studied.

1

B.A. Izzuddin, L. Song, A.S. Elnashi, P.J. Dowling, "An integrated adaptive environment for fire and explosion analysis of steel frames - Part II: verification and application", J. Constr. Steel Res., 53, 87-111, 2000. doi:10.1016/S0143-974X(99)00041-3

2

J.Y.R. Liew, H. Chen, "Inelastic transient analysis of steel frames subjected to explosion and fire", Research Report CE10/02, Department of Civil Engineering, National University of Singapore, 2002.

3

H. Chen, J.Y.R. Liew, "Explosion and fire analysis of steel frames", Proceedings of the Second International Conference on Structural Stability and Dynamics, December 16-18, 2002, Singapore. doi:10.1142/9789812776228_0101

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 £123 +P&P)