Tying capacity of web cleat connections in fire,Part 2: Development of component-based model

The companion paper has reported the results from a test programme in which web cleat connections were subjected to various combinations of shear, tying and moment actions at elevated temperatures. These tests showed that web cleat connections have very good tying resistance and rotational capacity, mainly due to the large deformation of which the web cleats are capable. In this paper a mechanical model is developed to predict the behaviour of web cleats subjected to tying forces. This model considers the formation of four plastic hinges on each angle and the effect of the angles opening in enhancing their resistance. It is capable of representing the action of the angles in component-based models for web cleat connections, in which algorithms for other components, including bolts in tension, bolts in double shear and holes in bearing, are already available. Failure criteria determined from the tests have been introduced into the models for components such as web cleats and bolts in double shear. This enables the component-based assembly to predict the occurrence and the sequence of connection failure. The behaviour of the connection predicted by the component-based model shows good correlation with the test results, which indicates that the developed model can be adopted in structural frame analysis to consider connection failure.     

Behaviour of composite cellular steel — Concrete beams at elevated temperatures

The behaviour of composite cellular floor beams is becoming important as such members are increasingly used in multistorey buildings. In the event of fire, this issue becomes increasingly critical, particularly for exposed steelwork. In a fire situation, a composite beam has a much higher perimeter area exposed to fire in its lower web-flange section than in the upper web-flange section, and so the temperature distribution across a composite beam is usually non-uniform. The reduction in fire of the strength and stiffness of the material properties of the perforated steel beam, as well as differential thermal expansion, therefore becomes an important influence on the overall behaviour of the composite beam. The objective of this research is to enhance the level of understanding of the generic behaviour of composite cellular floor beams in fire conditions. In this paper, three-dimensional nonlinear finite element models of composite cellular floor beams have been developed, taking into consideration the influence of the changes in material properties with temperature. Experimental data from furnace tests on cellular composite floor beams obtained from previous research work has been used to validate the FE models. An analytical model based on existing design guides is also presented in this paper. It is concluded that finite element analysis results are in good agreement with the experimental data, and all the failure modes have been accurately predicted. The proposed simplified analytical methods show reasonable agreement with the test and FE results, and are always conservative.     

Component modelling of flexible end-plate connections in fire

This paper describes a component-based model for simulating the behaviour of flexible end-plate connections between beams and columns in steel framed structures in fire conditions. In this method, a simple steel connection was split into a number of active components for which mechanical properties are represented by non-linear springs. The behaviour of a steel connection is then determined by assembling the individual behaviour for each active component into a spring model. The component model presented in this paper is capable of predicting the behaviour of steel connections under varied loading conditions. It is also capable of predicting the tying resistance and critical components of failure for steel connections in fire. Compared with experimental test data, a good correlation with the simplified model has been achieved and this method, combined with finite element modelling, may be used to examine the performance of simple steel connections in fire conditions.     

Influence of sketch types on distributed design team work

Product development is a collaborative activity more often than ever carried out by distributed design teams. It is critical to determine how sketches are used in such environments in order to improve the design process. Sketches produced by students participating in a collaborative design project of three European Universities are classified according to the intention of the designer when producing a sketch, the level of detail shown in the sketch and the phase when the sketch was produced. The adapted classification system used in this paper helps to analyse type of sketches with most variety of ideas. Furthermore, this paper reviews which type of sketches offers the most potential to be further developed. Results show that persuasive sketches offer the broadest range of ideas since they are produced as a combination of ideas from brainstorming sessions. Shared sketches help to achieve consensus in decision-making since the sketches are most likely to be produced by the entire group rather than individually.     

A study of mechanical configuration optimisation in micro-systems

This paper shows that there are three main categories of factors that make the optimum mechanical design of micro-systems different from macro-systems: scale effects, a limited range of materials, and a limited range of production processes. The combined effect of these factors can make the optimum configuration of a micro-system potentially very different from that of the same system on a macro-scale. In particular, the use of flexible elements for hinges is much more feasible and desirable on a micro-scale.Notation a acceleration (m/s²) - A cross-sectional area (m²) - B magnetic flux [wb/m²] - b width [m] - C constant - d depth [m] - D drag [N] - E Young's modulus [N/m²] - E*= - f resonant frequency [Hz] - F _D drive force [N] - F _E electrostatic pulling force [N] - F emmisivity function - F _G geometric view factor - g gravitational constant [m/s²] - h _c convention heat transfer coefficient [W/m²K] - h height [m] - i current [A] - I _A second moment of area [m⁴] - I _I moment of inertia [kg m²] - J polar second moment of area [m⁴] - k stiffness [N/m] - K thermal conductivity [W/m K] - l length [m] - m mass [kg] - M moment [N m] - P load [N] - P _H Hertz contact pressure [N/m²] - P _C cylinder pressure [N/m²] - q heat transfer rate [W] - R, r radius [m] - Re Reynolds number - T, t temperature [K] - T _A atomic friction torque [N m] - T _D drive torque [N m] - T _F Coulomb friction torque [N m] - T _I inertial resistive torque [N m] - u velocity [m/s] - mean velocity [m/s] - V volume [m³] - V _e voltage [V] - x distance between electrodes [m] - y maximum distance to neutral axis [m] - angular acceleration [rad/s²] - _d thermal diffusivity [1/K] - rolling friction factor - P pressure difference [N/m²] - ₀ dialectric constant [F/m] - strain - dynamic viscosity [Pa s] - scale factor - _S coefficient of sliding friction - _R coefficient of rolling friction - _{1, 2} Poisson's ratio - density (kg/m³) - temperature rise [°C] - _B bending stress [N/m²] - _y yield strength [N/m²] - shear stress [N/m²] - reliability constant     

Optimal spectrum utilisation in cognitive radio networks based on processor sharing techniques

Cognitive radio networks have achieved higher efficiency in terms of spectrum usage; however they do not readily solve any competition for access among secondary users. Optimisation is applied to an underlay network to obtain the optimal solution for at least two secondary users operating simultaneously on the same channel. Performance measures are used as the target for optimisation. However, the objective function is difficult to obtain in closed form. For the performance measures, queueing theory, particularly weighted processor sharing techniques are employed to model the system dynamics and behaviour. Transmission power and the interference temperature limit are used to allocate weights to the secondary users. Queue length and waiting time functions obtained from the queuing models are used for optimisation. After establishing that the objective function can be considered to be pseudo‐convex, convex programming is then deployed to obtain the optimised solution. The results suggest that there is indeed an improvement in network performance after optimisation. The immediate benefits of such a system are firstly improved spectrum utilisation through adding multiple secondary users and secondly, through optimisation, higher performance that can be achieved by the secondary users.     

Formation of metastable wurtzite phase boron nitride by emulsion detonation synthesis

Emulsion detonation synthesis (EDS) is a newly developed process to synthesize nano‐sized ceramic powders based on the detonation of 2 water‐in‐oil emulsions. The process provides high pressure and temperature along with rapid quenching. In this work, we report the formation of wurtzite phase BN (w‐BN) for the first time by EDS process, using hexagonal BN (h‐BN) as the precursor. Characterization studies demonstrated the formation of w‐BN with sizes varying from nanometer to micrometer scale either embedded in or grown from h‐BN matrix. These findings provide a new avenue to synthesize metastable and superhard BN phases.     

Review

Richard Mabey, Home Country London: Century 1990 £14.95

A Tour of the Lakes in Cumberland. John Ruskin's Diary for 1830. James S. Dearden, (Ed.), with an Introduction by Van Akin Burd. Scolar Press, Aldershot, 1990.

The Landscape Vision of Paul Nash, Roger Cardinal. Reaktion Books, London, 1989. £9,95 paperback ISBN 0948462 02 7

M G R Cannell & M D Hooper, The Greenhouse Effect and Terrestrial Ecosystems of the UK London, HMSO, 1990. 56pp. £4.95

Amenity In Action, The Civic Trust Handbook of Community Initiatives compiled & edited by Deirdre Genet, Societies Development Officer, The Civic Trust (1989), (supported by the Shell Better Britain Campaign)

Sue Minter The Greatest Glass House: The rainforests recreated HMSO, 1990. £25.00     

Moment-rotation-temperature curves for semi-rigid joints

Although connections are known to have a very significant effect on the behaviour of steel and composite framed buildings in the event of fire, the cost of high temperature tests on the broad range of connections used in practice means that their influence is not well detailed in current design codes. The paucity of data also limits the effective use of numerical models developed to simulate the behaviour of complete structures at elevated temperature. This research describes a series of elevated temperature tests conducted on beam-to-column connections. This paper presents moment-rotation-temperature curves for a variety of connections.