Andrew H. Buchanan
Professor, Department of Civil and Natural
Resources Engineering, University of Canterbury, Christchurch,
New Zealand
Peter J. Moss
Associate Professor, Department of Civil and
Natural Resources Engineering, University
of Canterbury, Christchurch, New Zealand
Rajesh P. Dhakal
Senior Lecturer, Department of Civil and
Natural Resources Engineering, University
of Canterbury, Christchurch, New Zealand
Jeremy Chang
Assistant Lecturer, Department of Civil and
Natural Resources Engineering, University
of Canterbury, Christchurch, New Zealand
Proceedings of the 5th
International Conference on Structures in Fire (SiF’08).
Previous studies have shown that the fire performance of hollowcore
units is significantly affected by the end support conditions, but it has not
been clear how the fire resistance of the overall floor system can be improved
by providing side supports. The previous studies used beam grillage and shell
elements to separately model the hollowcore units and the topping concrete slab
using the platform of the non-linear finite element program SAFIR. The
modelling method required a lot of computational resources and is not ideal to
model a large floor area. This paper describes the effect of the side supports
and the aspect ratio of the floor on the predicted fire resistance. It also
compares the efficiencies of shell elements and short beam elements for finite
element modelling of the topping concrete in fire conditions. The results show
that integrating the topping concrete slab into the beam grillages reduces the
complexity of the model and also provides satisfactory results. Side supports
can increase the fire performance of hollowcore floor slabs provided that the
spacing of the side supports does not greatly exceed the span length.
Precast, prestressed hollowcore concrete floors are very popular in
multi-storey buildings because of their excellent structural performance in
ambient conditions, high quality control and low on-site labour costs. Hollowcore
concrete floors are designed as one-way slab systems, with the units sitting
side-by-side, spanning between supporting walls or beams. Most hollowcore
concrete floors have in-situ reinforced concrete topping. Structural behaviour
of hollowcore concrete floors is dominated by action parallel to the units and
their prestressing strands. Two-way action can sometimes occur in such slab
systems, resulting from transverse structural behaviour of the topping
concrete, depending on the vertical supports parallel to the hollowcore units.
The fire resistance of hollowcore concrete slab has not been outlined
specifically in Eurocode 2. However, Eurocode 2 provides separate measures for
the fire resistance of flat slabs and solid slabs. The tabulated data in Eurocode
2 relate the fire resistance of a flat slab or of a one way solid slab to the
slab thickness and the axis distance of the reinforcements to the surface; they
also associate the fire resistance of a two-way solid slab to the aspect ratio
which serves as an additional parameter. The British Standard BS EN1168
“Precast Concrete Products – Hollow Core Slabs” suggests that the fire
resistance of hollowcore concrete floors follows the table for flat slabs which
does not include the effect of the vertical supports parallel to the hollowcore
units. The New Zealand Standard NZS 3101 “The Design of Concrete Structures”,
however, suggests the fire resistance of hollowcore concrete floors follows the
table for solid slabs, which considers the influence of the two-way effect.
References
BSI, Precast Concrete Products – Hollow core
Slabs, BS EN1168, British Standards Institution, London, 1995.
EC3. Eurocode 3: Design of Steel Structures.
PrEN 1993-1-2: General rules – Structural fire design. Brussels: CEN; 2002.
SNZ, The Design of Concrete Structures, NZS
3101, Standards New Zealand,
Wellington,
2006.
Chang J. Computer Simulation of Hollowcore
Concrete Floor systems Exposed to Fire. PhD Thesis, Christchurch:
University of Canterbury; 2007.
Firth Stresscrete & Stahlton Flooring,
Precast Concrete Manual 2007, Firth Stresscrete, Porirua, 2007.
fib. Résistance au Cisaillement de Dalles
Alvéolées Précontraintes. Belgium:
Studiecommissie SSTC; 1998.
Fellinger, JHH. Shear and Anchorage
Behaviour of Fire Exposed Hollowcore Slabs, DUP Science, the Netherlands,
2004.
BEF. Hollow Core Slabs and Fire –
Documentation on Shear Capacity, Birch & Krogboe A/S, Denmark, 2005.
Fib. Résistance au Cisaillement de Dalles
Alvéolées Précontraintes, Studiecommmissie SSTC, University of Liège, Belgium,
1998.
Chang, J., Buchanan, AH, Dhakal, RP. &
Moss, PJ, “Hollowcore concrete slab exposed to fire”, Fire and Materials,
Online ISSN: 1099-1018, 2008.
Franssen, JM., Kodur, VKR. & Mason, J.
User’s Manual for SAFIR2001 Free: A Computer Program for Analysis of Structures
at Elevated Temperature Conditions, University of Liège, Belgium, 2002.
EC2. Eurocode 2: Design of Concrete
Structures. PrEN 1992-1-2: General rules – Structural fire design, Brussels: CEN; 2002.
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