S. Pampanin
Department of Civil Engineering, University of Canterbury,
Christchurch, New Zealand
D.K. Bull and J.P. Jensen
Holmes Consulting Group, New Zealand
Department of Civil Engineering, University of Canterbury,
Christchurch, New Zealand
Presented at New Zealand
Society for Earthquake Engineering Annual Conference (NZSEE07),
New Zealand,
2007.
In the recent past a number of issues regarding the seismic performance
of typical existing hollowcore floor systems have been raised. The most
concerning of these is the vulnerability to loss of vertical support of the
floor system at the end floor to seating beam connection. This vulnerability
arises due to incompatibilities between the floor system and intrinsic
deformations of the neighbouring seismic frames.
In a previous contribution by the authors (Jensen et al 2006), a
conceptual retrofit strategy for existing hollowcore seating connections was
proposed. This paper provides an experimental validation of that strategy
through quasi-static cyclic testing of alternative seating connection configurations,
adopting varying seating lengths.
In general, unfavourable performance was exhibited by the existing
seating connections, resulting in loss of vertical support of the hollowcore
unit. In contrast, when additional seating and selective weakening retrofit
approaches were implemented, a higher level of seismic performance leading to
collapse prevention was achieved. In conclusion, issues and uncertainties
associated with the evaluation of the likely failure mechanism, as well as the
definition of an appropriate retrofit intervention are discussed.
Post-earthquake reconnaissance and experimental investigations have
identified a number of uncertainties regarding the seismic performance of
suspended precast hollowcore floor systems when coupled with ductile seismic
frame systems (Norton et al., 1994; Iverson and Hawkins, 1994; Holmes and
Somers, 1995; Herlihy, 1999; Bull and Matthews, 2003; Liew, 2004; Matthews,
2004). These uncertainties are associated with the structural detailing and
resulting behaviour of the connections between the floor and frame systems
around the floor perimeter. The foremost of these uncertainties is maintaining
vertical support of the one-way floor system at the end floor to seating beam
connection during a seismic event.
References
Lindsay, R. A. Mander, J. B. & Bull, D. K.
2004. Experiments on the Seismic Performance of Hollow-Core Floor Systems in
Precast Concrete Buildings. 13th World Conference on Earthquake Engineering.
Matthews, J. Bull, D.K. & Mander, J.B.
2003. Hollowcore floor slab performance following a severe earthquake. Concrete
Structures in Seismic Regions FIB 2003 Symposium.
Matthews, J. 2004. Hollow-core floor slab
performance following a severe earthquake: PhD Thesis, University of Canterbury.
MacPherson, C. J. Mander, J. B. & Bull, D.
K. 2005. Reinforced Concrete Seating Details of Hollowcore Floor Systems. 2005 New Zealand
Society of Earthquake Engineering Conference, Paper 24.
Technical Advisory Group of Precast Flooring
Systems (TAG). 2002. The Seismic Performance of Flooring Systems - Executive
Summary. SESOC Journal, vol. 15, no. 2, pp. 26-43.
Norton, J. A. King, A. B. Bull, D. K. Chapman,
H. E. McVerry, G. H. Larkin, T. J. & Spring, K. C. 1994. 'Northridge
Earthquake Reconnaissance Report'. Bulletin of the NZNSEE, vol. 27, no. 4.
NZS3101:1995 2004, Amendment No.3 to 1995 Standard (NZS3101). Standards New Zealand, Wellington, NZ.
Bull, D. K. & Matthews, J. G. 2003. Proof
of Concept Tests for Hollow-core Floor Unit Connections, University
of Canterbury, Christchurch.
Herlihy, M.D. 1999. Precast concrete floor
support and diaphragm action, PhD Thesis, Department of Civil Engineering, University of Canterbury,
Christchurch, New Zealand.
Fenwick, R., Deam, B. & Bull, D. K. 2005.
Failure Modes of Hollowcore Flooring Units, SESOC Journal, vol. 17, no. 1, pp.
52-70.
Holmes, W.T and Somers, P. 1995. Northridge
Earthquake of January 17, 1994, Reconnaissance Report Vol. 2, Earthquake
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Structures during Northridge Earthquake. PCI Journal, March-April, Vol. 39, No.
2.
Ireland, M.G. Pampanin,
S. Bull D.K. 2006. Concept and Implementation of a Selective Weakening Approach
for the Seismic Retrofit of R.C buildings. 2006 New Zealand Society of Earthquake
Engineering Conference.
Liew, H. Y. 2004. Performance of hollowcore
floor seating connection details: Masters Thesis, University of Canterbury.
Jensen, J.P. Bull, D.K. Pampanin, S. 2006.
Conceptual Retrofit Strategy for Existing Hollowcore Seating Connections. 2006 New Zealand
Society of Earthquake Engineering Conference.
Excellent Article, very informative :)
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