Search results

In order to improve the robustness of bare-steel and composite structures in fire, a novel axially and rotationally ductile connection has been proposed in this paper.

The component-based models of the bare-steel ductile connection and composite ductile connection have been proposed and incorporated into the software Vulcan to facilitate global frame analysis for performance-based structural fire engineering design. These component-based models are validated against detailed Abaqus FE models and experiments. A series of 2-D bare-steel frame models and 3-D composite frame models with ductile connections, idealised rigid and pinned connections, have been created using Vulcan to compare the fire performance of ductile connection with other connection types in bare-steel and composite structures.

The comparison results show that the proposed ductile connection can provide excellent ductility to accommodate the axial deformation of connected beam under fire conditions, thus reducing the axial forces generated in the connection and potentially preventing the premature brittle failure of the connection.

Compared with conventional connection types, the proposed ductile connection exhibits considerable deformability, and can potentially enhance the robustness of structures in fire.

This paper aims to propose a methodology to remove inherent implicit creep from the Eurocode 3 material model for steel and to present a creep-free analysis on simply supported steel members.

Most of the available material models of steel are based on transient coupon tests, which inherently include creep strain associated with particular heating rates and load ratios.

The creep-free analysis aims to reveal the influence of implicit creep by investigating the behaviour of simply supported steel beams and columns exposed to various heating regimes. The paper further evaluates the implicit consideration of creep in the Eurocode 3 steel material model.

A modified Eurocode 3 carbon steel material model for creep-free analysis is proposed for general structural fire engineering analysis.

This paper reports on the development of a general-purpose Eurocode-compliant component-based connection finite element for steel-to-steel joints in fire. The development begins by utilising the temperature-dependent connection component characteristics previously developed at the University of Sheffield to create a component-based connection finite element to model flush endplate connections. Subsequently the element was extended to a new connection type with high ductility, the reverse channel. The component models have been developed for the reverse channel under tension and compression. The element has been incorporated into the nonlinear global structural analysis program Vulcan, in which it has been used along with a static-dynamic formulation. The use of the element is illustrated by modelling a fire test at the University of Manchester in which reverse channel connections were used.

A component-based model for fin-plate connections has been developed to study the robustness of simple beam-to-column connections at elevated temperatures. The key aspect of this component method is the characterisation of the force-displacement properties of each active component at any temperature, represented by a non-linear "spring". The prescribed temperature-dependent characteristics of any given bolt row are governed by the failure mechanism of the weakest component, based on experimental and analytical findings. A major additional complication involves force reversal in components, which may occur because of temperature change, without any physical reversal of displacement. The Masing Rule has been adapted to incorporate this effect for particular force directions. To account for the bolt slip phases, force transitions between tension and compression take place only when positive contact between a bolt and the edge of its bolt hole is re-established. The results of high-temperature tests on connections have been used to substantiate the developed component model. The component-based connection model has also been used to study joint behaviour in structural sub-frame analyses. This approach will enable more valid performance-based assessment of the overall responses of connections, including their robustness, in design fire scenarios.

A static/dynamic version of the software Vulcan has recently been developed, in which the numerical singularity of a static analysis, induced by a local instability of a structure, for instance the buckling of a column, can be covered by switching to the explicit dynamic procedure. This version of Vulcan allows the post-buckling behaviour of a member to be traced, finding a re-stabilized state if it exists.

In this paper a study of the behaviour of steel columns in localised fires is presented. A simplified model is developed, taking into consideration the axial restraint of the column in fire. An axial elastic stiffness is used to represent restraint from the superstructure, and the full post-buckling behaviour is covered. Results obtained from the simplified model have been validated against previous numerical studies. A full-frame model has been created for comparison. The simplified model has been extended to investigate the effect of beam yielding on the column's restraint conditions. This is modelled by giving a bilinear force-displacement relationship to the spring element. The influence of the stiffness and strength ratios of beam to column on the behaviour of the column in a localised fire are investigated. This study indicates that, although the member interaction is complex in a frame in a localised fire, it may be possible to find a simple way to deal with this behaviour, and to determine not only the initial buckling temperature but also the possibilities of re-stabilization and progressive collapse.

Actual developments in numerical simulations of the structural behaviour in fire situation are focussed on taking into consideration the interaction of all structural members in a global numerical approach. Therefore it is necessary to model the load bearing behaviour of connections in detail. In this paper a detailed 3D numerical model of a bolted steel endplate connection taking into account nonlinearities, e.g. temperature dependent material, is presented. The simulation is validated by experimental tests conducted at the University of Sheffield in 2008. During some of the experimental tests, large deformations and fractures occurred. These phenomena are simulated with the numerical model as well.

Fire hazards and full-scale structural tests have provided evidence that the beam-column connections of building frames are the weakest structural elements, which are vulnerable to fracture in fire. Connection fractures may lead to extensive damage or even progressive collapse. However, current design methods for connections are solely based on ambient-temperature behaviour, the additional forces and rotations generated in fire are not taken into account. The Structural Fire Engineering Research Group of the University of Sheffield is involved in a European-collaborative project which concerns the behaviour and robustness in fire of practical connections to composite columns. This includes two natural fire tests in a full-scale composite structure in Veselí, the Czech Republic. The Sheffield team was responsible for predicting the structural behaviour in the tests before they were conducted. This assessment was conducted using the specialist structural fire engineering FEA program Vulcan. This paper reports the results of this predictive analysis.

A simple folding mechanism, which considers the contributions of internal unprotected beams and protected edge beams, has been proposed for isolated slab panels in fire conditions. The current study extends the mechanism to include the reinforcement in the slab as well as continuity across the protected edge beams. Structural failure of the panel depends on the applied loads, the relative beam sizes, their locations within the building, their arrangement in the slab panel, the panel's location and the severity of fire exposure. These factors are considered in the development of a number of collapse mechanisms for verification so they may eventually serve as an additional check within the Bailey-BRE design method, to make it more robust for routine design of composite floors in fire. Comparisons are made with the finite element software Vulcan and other design acceptance criteria.

Fire following an earthquake is an important factor causing damage to buildings and life-line structures. Therefore, besides satisfying structural design requirements for normal loads, such as dead and live loads including the seismic hazard, buildings should also be designed to withstand the fire following earthquakes for a certain minimum duration as required for a desired level of performance. The behavior of a particular reinforced concrete structure that was fire exposed after seismic action is presented in this paper. The seismic response of the structure is evaluated using a pushover analysis, while the displacement demand under the corresponding seismic event is determined using the recommendations implemented in Eurocode 8.