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EP/I031553/1 - Modelling Localized Fracture in Composite Floors at Elevated Temperatures

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Dr Z Huang EP/I031553/1 - Modelling Localized Fracture in Composite Floors at Elevated Temperatures

Principal Investigator - Sch of Engineering and Design, Brunel University

Scheme

Standard Research

Research Areas

Performance and Inspection of Mechanical Structures and Systems Performance and Inspection of Mechanical Structures and Systems

Structural Engineering Structural Engineering

Start Date

02/2012

End Date

05/2015

Value

£290,201

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Grant Description

Summary and Description of the grant

Steel-framed structures, particularly of composite construction, are widely used in the UK for multi-storey buildings. The fire resistance of composite structures has therefore become of major concern to designers. In the most recent design codes, notably Eurocodes 1, 3 and 4, fire is treated as one of the basic design limit states for structures, which is in itself a major step forward in philosophy from the previous emphasis on prescriptive requirements for fire protection. A range of design procedures at different levels of complexity and conservatism allows designers to move away from prescriptive requirements towards appropriate performance-based concepts. Fire resistance of structural elements is defined according to up to three criteria: (1) Structural Stability; (2) Integrity; (3) Insulation. Failure occurs when any one of these is violated. The first of these applies to all types of elements; the other two apply only to separating elements such as floor slabs and walls. Over the past decade a significant amount of research has developed numerical models of the structural behaviour of composite slabs in fire conditions. These are all based on a continuum approach in which local concrete failure is represented by smeared cracking. These models can predict the global behaviour of concrete slabs subject to large deflection with reasonable accuracy, at least until fracture begins to dominate. However, they cannot predict localized failures due to individual large cracks through the slab thickness. It is clear that when this type of crack forms the criterion of structural integrity is violated, although stability may still be maintained. It is therefore important to develop a robust numerical procedure with which both structural stability and integrity can be assessed, so that a meaningful failure definition can be identified by the analysis. Performance-based designs may therefore currently have to rely on arbitrary and inappropriate limiting deflection criteria, such as the span/30 , span/20 and limiting deflection rate criteria used in Eurocode 1 Part 1-2 and BS476 to control furnace testing. These deflection criteria have very little scientific basis, and are generally assumed to have been developed empirically to protect short-span furnaces under standard fire conditions. This arbitrary element significantly undermines the power of the performance-based design method. It is the objective of the proposed research to tackle this important and difficult issue. The direct aim of the project is to develop a practical and robust numerical procedure to model localized fracture of reinforced concrete slabs at high temperatures. The layered reinforced concrete slab elements will consist of three components, representing the plain concrete slabs, reinforcing steel bars and the bond characteristics between concrete and reinforcement. The model should have the ability to assess both the structural stability and the integrity of floor slabs, in order to identify meaningful fire resistance failure points, and should be suitable for direct employment in structural fire engineering design of composite and concrete buildings. For the first time this procedure will enable designers to assess fire resistance of a building directly on the basis of both the structural stability and integrity criteria. This would dramatically change structural fire engineering design practice, in which arbitrary limiting deflections, of either span/30 or span/20, are currently used by consulting engineers.

Structured Data / Microdata


Grant Event Details:
Name: Modelling Localized Fracture in Composite Floors at Elevated Temperatures - EP/I031553/1
Start Date: 2012-02-01T00:00:00+00:00
End Date: 2015-05-31T00:00:00+00:00

Organization: Brunel University

Description: Steel-framed structures, particularly of composite construction, are widely used in the UK for multi-storey buildings. The fire resistance of composite structures has therefore become of major concern to designers. In the most recent design codes, notably ...