Seismic behaviour of self centring braced frame buildings with reusable hysteretic damping brace

Structural systems designed with conventional seismic design approach dissipate seismic energy by
incurring ductile inelastic response in selected regions. Such a seismic design strategy may not be
appealing from a life cycle cost perspective, especially for high seismic regions, where costly repairs
are often required after moderate earthquakes. After the 1994 Northridge earthquakes, growing
interests are given to a more logical seismic design approach, which involves energy dissipation
through supplemental damping system or fuse-type energy-dissipating devices. In such systems, the
main structural system is intended to have little or no damage while supplemental damping devices
are designed directly for energy dissipation and can be replaced if damaged during earthquakes.
Examples of such energy dissipation devices include friction damper, buckling-restrained brace
and many other types of passive or active structural control devices [1].
Buckling-restrained braces (BRB), which are capable of yielding in both tension and compression,
have been developed to overcome the buckling problem of conventional braces in concentrically
braced frames [2, 3]. BRB frame has been used extensively for seismic applications in Japan
after the 1995 Kobe earthquake and is also gaining popularity in the United States after the 1994
Northridge earthquake. BRB frames are desirable for seismic design and rehabilitation for their
superior ductile performance. Non-linear dynamic analyses by Sabelli et al. [2] have shown that
the behaviour of BRB frames is comparable and often better than that associated with conventional
concentrically braced frames and moment frames. However, several potential problems such as
tendency of BRBs to yield under frequent earthquakes have been identified for BRB frame by
a few researchers [2, 4]. Costly repair after moderately strong earthquakes might be necessary
due to these problems. For example, large residual displacements may exist in a BRB frame
after moderate earthquakes, necessitating closure of the building while costly repairs are being
carried out.
Recently, an alternative seismic resisting system with self-centring hysteretic behaviours has
received considerable interests (e.g. [5–7]). A flag-shaped hysteresis loop is typical of such selfcentring
systems with energy dissipation capability. Self-centring systems have the ability to control
damage and to reduce (or even eliminate) residual structural deformation. This is important since
residual structural deformation is emphasized as a fundamental complementary parameter in the
evaluation of structural (and non-structural) damage in the performance-based seismic design and
assessment approach [8].
Although several self-centring structural systems using post-tensioned high strength steel bars
or tendons have been proposed [5, 6, 9], special metals such as superelastic shape memory alloys
(SMA) possess a self-centring hysteretic behaviour which can be utilized to construct self-centring
braced frame systems. However, without pre-tensioning, superelastic SMA would most likely
remain linearly elastic and thus no energy dissipation would occur under frequent earthquakes.
SMA-based energy dissipation devices have recently attracted a great attention from civil engineering
researchers for seismic response control applications (e.g. [10–17]). Hodgson and Krumme [10]
proposed a SMA damping device with a centre-tapped configuration, in which the superelastic
wires are loaded to the middle of its superelastic strain limit when the device is constructed. This
centre-tapped configuration allows the device to dissipate energy in both push and pull directions.
Dolce et al. [13] tested Nitinol-based devices with full re-centring and good energy dissipation
capabilities. The kernel component of such a device consists of two groups of Nitinol wire loops—a
re-centring group of Nitinol wires with pre-strain and an energy-dissipating group of pre-tensioned
superelastic Nitinol wires, which are mounted on two concentric tubes. Their full-scale brace,
which was designed for a maximum force of 200 kN and has a double flag-shaped hysteretic
loop, can be used as a bracing element in framed structures. The ability of these SMA braces to
control the seismic response of RC framed structures was assessed through shaking table tests of a
1
3.3 -scale, 3-storey, two-bay RC plane frame, which was designed for low seismicity and low ductility
[14]. Their experimental results have shown that the SMA braces can provide performances
at least comparable to those provided by steel braces, while having an additional self-centring
feature.
This paper presents a special hysteretic damping device termed reusable hysteretic damping
brace (RHDB) with inherent self-centring behaviour and enhanced energy dissipation capacity.
A new type of self-centring braced frame system can be established by combining the concepts
of braced frames and self-centring system using RHDB. A seismic performance study of steel
concentrically braced frames with RHDBs, which is based on non-linear time history analysis of
RHDB frames, is the focus of this paper. The non-linear dynamic analysis involves a 3-storey and
6-storey concentrically braced frames subjected to design basis earthquake and frequent earthquake
ground motions for California.
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