Assessment of the behaviour factor for the seismic design of reinforced concrete structural walls according to SANS 10160 : part 4
Date
2008-12
Authors
Spathelf, Christian Alexander
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
The South African code for the design loading of building structures, namely SABS
0160 (1989), was revised with the requirements for seismic design prescribed in SANS
10160: Part 4: Seismic actions and general requirements for buildings. SANS 10160:
Part 4 incorporates the seismic design provisions of several seismic codes of practice,
however, the influence of the value prescribed for the behaviour factor has not been
established with regard to South African conditions.
The behaviour factor is used by most seismic design codes to account for the energy
dissipating effects of plastification in structural systems when subjected to earthquake
ground motion, to reduce the elastically determined forces to be designed for. However,
a considerable difference is observed in the values of the behaviour factor prescribed for
the design of reinforced concrete walls between the leading international seismic codes.
The aim of this study is to assess the value of the behaviour factor prescribed in SANS
10160: Part 4 for reinforced concrete structural walls under the influence of South
African seismic conditions and code requirements.
A method of quantifying the value of the behaviour factor was developed and
implemented in the study by Ceccotti (2008). This method entails estimation of the
maximum analytical behaviour factor as the ratio of seismic intensity at failure of the
structure to the seismic intensity prescribed by the design code. Such a method is
adopted for this study where the lateral force resisting systems of six-, eight- and tenstorey
buildings are investigated with nonlinear static analysis to quantify the maximum
computationally-determined value of the behaviour factor.
Firstly, it is observed that it is possible to quantify the value of the behaviour factor
through the use of a computational study. The nonlinear static method of analysis is
shown to provide reliable results in the estimation of the behaviour factor for a sixstorey
building, however, does not perform well for taller buildings. Further investigation with the use of dynamic time-history analysis is proposed to evaluate the
influence of the factors identified in this study.
The behaviour of structural walls, designed for reduced forces with the prescribed
behaviour factor of 5.0, exhibits high yield strengths and resists the design seismic
action entirely elastically. This high strength is found to be due to the
reliability/redundancy factor prescribed by SANS 10160: Part 4 and because of the high
values of structural overstrength. Similar studies observed high values of structural
overstrength for buildings designed for low seismic intensity, which were shown to
result from the fact that the resistance required to gravity loading became more critical
than the seismic loads in the design of the structural system.
This study identifies several factors that influence the value of the behaviour factor,
such as the number of walls in the lateral force resisting system; the number of storeys
of the buildings; available displacement ductility of the structural system; and the
ground type designed for.
Description
Thesis (MScEng (Civil Engineering))--Stellenbosch University, 2008.
Keywords
Earthquake resistant design, Sans 10160, Reinforced concrete construction, Structural design, Dissertations -- Civil engineering, Theses -- Civil engineering