Minimum vertical reinforcement in RC walls
Theoretical requirements for low and high ductility demands
DOI:
https://doi.org/10.5459/bnzsee.50.4.471-481Abstract
Recent earthquakes and research have shown that the minimum vertical reinforcement requirements in current concrete standards are insufficient to ensure well distributed cracking occurs in ductile reinforced concrete (RC) walls. To address the deficiencies of existing requirements, new theory was proposed to calculate the minimum distributed and end zone vertical reinforcement required for RC walls to meet current performance expectations. The distributed vertical reinforcement requirement was intended to prevent non-ductile behaviour for walls with low ductility demands, and was derived based on the requirement that nominal flexural strength must exceed the cracking moment capacity. The vertical reinforcement required in the ends of the wall was intended to ensure that well distributed secondary cracks form in the plastic hinge region of walls with high ductility demands, and was derived to ensure that the concrete tensile strength could be overcome by the tensile demands imposed when the vertical reinforcement in the ends of the wall yields. The proposed requirements considered the key parameters that influence the behaviour of walls with minimum vertical reinforcement. In addition, the proposed formulas were compared with current minimum vertical reinforcement limits from different concrete design standards by considering the margin of safety between cracking and nominal flexural strength and the secondary cracking behaviour. The deficiencies of the existing requirements were demonstrated and the proposed requirements were proved to be superior for walls with both low and high ductility demands.
References
Paulay T and Priestley MJN (1992). “Seismic design of reinforced concrete and masonry buildings”. New York: John Wiley & Sons, Inc. DOI: https://doi.org/10.1002/9780470172841
Kam WY, Pampanin S and Elwood K (2011). “Seismic performance of reinforced concrete buildings in the 22 February Christchurch (Lyttelton) earthquake”. Bulletin of the New Zealand Society for Earthquake Engineering, 44(4): 239-278. DOI: https://doi.org/10.5459/bnzsee.44.4.239-278
Sritharan S, Beyer K, Henry RS, Chai YH, Kowalsky M and Bull D (2014). “Understanding poor seismic performance of concrete walls and design implications”. Earthquake Spectra, 30(1): 307-334. DOI: https://doi.org/10.1193/021713EQS036M
Lu Y, Henry RS, Gultom G and Ma QT (2017). “Cyclic Testing of Reinforced Concrete Walls with Distributed Minimum Vertical Reinforcement”. Journal of Structural Engineering, 143(5):10.1061/(asce)st.1943-541x.0001723.
Lu Y and Henry RS (2017). “Numerical Modelling of Reinforced Concrete Walls with Minimum Vertical Reinforcement”. Engineering Structures, 143: 330-345.
Lu Y (2017). “Seismic design of lightly reinforced concrete walls”. PhD Thesis, Department of Civil and Environmental Engineering, University of Auckland, Auckland, NZ.
Henry RS (2013). “Assessment of minimum vertical reinforcement limits for RC walls”. Bulletin of the New Zealand Society for Earthquake Engineering, 46(2): 88-96. DOI: https://doi.org/10.5459/bnzsee.46.2.88-96
Standards New Zealand (2006). “NZS 3101:2006 Concrete Structures Standard (Amendment 2)”. Wellington, NZ.
Standards New Zealand (2017). “NZS 3101:2006 Concrete Structures Standard (Amendment 3)”. Wellington, NZ.
American Concrete Institute (2014). “ACI 318-14, Building Code Requirements for Structural Concrete (ACI 318-14) and Commentary”. Farmington Hills, Michigan.
European Committee for Standardization (2006). “Eurocode 8: Design of Structures for Earthquake Resistance”. Brussels, Belgium.
Canadian Standards Association (2014). “Standard CSA-A23.3-14 Design of Concrete Structures”. Toronto, Canada.
China Architecture & Building (2010). “GB 50010-2010, Code for Design of Concrete Structures”. China Architecture & Building Press: Beijing.
Puranam A and Pujol S (2017). “Minimum Flexural Reinforcement in Reinforced Concrete Walls”. 16th World Conference on Earthquake Engineering (16WCEE), Santiago, Chile.
Fédération Internationale du Béton (fib) (2013). “fib Model Code for Concrete Structures 2010”. Ernst & Sohn: Lausanne, Switzerland.
Cook D, Fenwick R and Russell A (2014). “Amendment 3 to NZS 3101”. The New Zealand Concrete Industry Conference, Taupo, New Zealand.
