Assessment of minimum vertical reinforcement limits for RC walls
DOI:
https://doi.org/10.5459/bnzsee.46.2.88-96Abstract
During the 2010/2011 Canterbury earthquakes, several reinforced concrete (RC) walls in multi-storey buildings formed a single crack in the plastic hinge region as opposed to distributed cracking. In several cases the crack width that was required to accommodate the inelastic displacement of the building resulted in fracture of the vertical reinforcing steel. This type of failure is characteristic of RC members with low reinforcement contents, where the area of reinforcing steel is insufficient to develop the tension force required to form secondary cracks in the surrounding concrete. The minimum vertical reinforcement in RC walls was increased in NZS 3101:2006 with the equation for the minimum vertical reinforcement in beams also adopted for walls, despite differences in reinforcement arrangement and loading. A series of moment-curvature analyses were conducted for an example RC wall based on the Gallery Apartments building in Christchurch. The analysis results indicated that even when the NZS 3101:2006 minimum vertical reinforcement limit was satisfied for a known concrete strength, the wall was still susceptible to sudden failure unless a significant axial load was applied. Additionally, current equations for minimum reinforcement based on a sectional analysis approach do not adequately address the issues related to crack control and distribution of inelastic deformations in ductile walls.
References
ACI 363R-84. (1984), State of the art report on high-strength concrete. Farmington Hills, MI, American Concrete Institute.
Bažant, Z.P. (1984), Size Effect in Blunt Fracture: Concrete, Rock, Metal, Journal of Engineering Mechanics, Vol. 110(4), 518-535.
Bentz, E. and Collins, M.P. (2001), Response-2000, University of Toronto.
Bull, D. (2012), The performance of concrete structures in the Canterbury earthquakes: Lessons for concrete buildings, Structural Engineers Association of California (SEAOC) Convention, Santa Fe, NM.
Canterbury Earthquakes Royal Commission. (2012), Final report: Volume 2: The performance of Christchurch CBD buildings, http://canterbury.royalcommission.govt.nz/Commission-Reports, Wellington, New Zealand.
Carpinter, A. (1989), Size Effects on Strength, Toughness, and Ductility, Journal of Engineering Mechanics, Vol. 115(7), 1375-1392.
Dai, H. (2012), An investigation of ductile design of slender concrete structural walls, ME thesis, Iowa State University, Ames, IA.
Fédération Internationale du Béton (fib). (2012), Model Code 2010 - Final draft, Volume 2. fib Bulletin No. 66, Lausanne, Switzerland.
Fenwick, R. and Dhakal, R.P. (2007), Material strain limits for seismic design of concrete structures, Journal of the Structural Engineering Society New Zealand (SESOC), Vol. 20(1), 14-28.
Fenwick, R.C. (1988), The behaviour of soffit slabs in concrete box girder bridges. Report No. 445, Dept. of Civil Engineering, University of Auckland, Auckland, New Zealand.
Fenwick, R.C. and Dickinson, A.R. (1987), The flexural behaviour of lightly reinforced concrete beams and slabs. Report No. 435, Dept. of Civil Engineering, University of Auckland, Auckland, New Zealand.
Holmes Solutions. (2011), Material testing in buildings of interest: Gallery Apartments, Westpac Centre and IRD building, http://canterbury.royalcommission.govt.nz/documents-by-key/20111129.1351, Report prepared for the Canturbury Earthquakes Royal Commission.
Kam, W.Y., Pampanin, S. and Elwood, K.J. (2011), Seismic performance of reinforced concrete buildings in the 22 Feburary Christchurch (Lyttelton) earthquake, Bulletin of the New Zealand Society for Earthquake Engineering, Vol 44(4) 239-278. DOI: https://doi.org/10.5459/bnzsee.44.4.239-278
Mander, J.B., Priestley, M.J.N. and Park, R. (1988), Theoretical stress-strain model for confined concrete, Journal of Structural Engineering, Vol. 114(8), 1804-1826.
Mindess, S., Young, J.F. and Darwin, D. (2003), Concrete. Prentice Hall, Upper Saddle River, NJ.
NZS 3101:2006. Concrete Structures Standard. Wellington, New Zealand, Standards New Zealand: 646.
Park, R. and Paulay, T. (1975), Reinforced concrete structures. John Wiley and Sons, New York. DOI: https://doi.org/10.1002/9780470172834
Paulay, T. and Priestley, M.J.N. (1992), Seismic design of reinforced concrete and masonry buildings. John Wiley and Sons Inc., New York. DOI: https://doi.org/10.1002/9780470172841
Smith, P. and England, V. (2012), Independent assessment on earthquake performance of Gallery Apartments - 62 Gloucester Street, http://canterbury.royalcommission.govt.nz/documents-by-key/20120217.3188, Report prepared for the Canturbury Earthquakes Royal Commission.
Structural Engineering Society of New Zealand (SESOC). (2011a), Practice note - Design of conventional structural systems following Canterbury earthquakes, http://canterbury.royalcommission.govt.nz/documents-by-key/20111221.1908, Report prepared for the Canterbury Earthquakes Royal Commission
Structural Engineering Society of New Zealand (SESOC). (2011b), Preliminary observations from Christchurch earthquakes. http://canterbury.royalcommission.govt.nz/documents-by-key/20111205.1533, Report prepared for the Canturbury Earthquakes Royal Commission
Wang, C.-K., Salmon, C.G. and Pincheira, J.A. (2007), Reinforced concrete design. John Wiley & Sons, Hoboken, NJ.
Wight, J.K. and MacGregor, J.G. (2009), Reinforced concrete: mechanics and design. Prentice Hall, Upper Saddle River, N.J.
Wood, S.L. (1989), Minimum tensile reinforcement requirements in walls, ACI Structural Journal, Vol. 86(5), 582-591.
Wood, S.L., Stark, R. and Greer, S.A. (1991), Collapse of eight-story RC building during 1985 Chile earthquake, Journal of Structural Engineering, Vol. 117(2), 600-619.
