research work

1. 14
Chapter 2
LITERATURE REVIEW
2.1 General
Considerable research has been conducted on the behaviour of
steel moment resisting frames, buckling restrained braced frames and
optimization techniques for minimum weight design under seismic
ground excitation. Because of the rapid evolution of codes, much of
this research is not necessarily consistent with modern construction
detailing; however, many of the fundamental observations from these
investigations are relevant to an assessment of modern design and
analysis procedures. The available collection of literature extends over
several decades and is rapidly growing. As such, it cannot adequately
be summarized in a brief chapter. Instead, an overview of major
references is provided here along with useful citations to previous
works that contain detailed reviews of related literature. The
literature review in this chapter is separated below into three
categories:(i)optimization of steel frames, which examines references
that describe the optimum design of framed/braced steel structures of
recent earthquakes (1978– 1995) in the United States, Mexico, Japan
and India.(ii) Moment resisting frames: which discusses the previous
works on moment resisting braced frames relevant to seismic
applications and (iii) buckling restrained braced frames: which
discusses previous experimental and analytical works on buckling

2. 15
restrained braced frames relevant to seismic applications.
Considerable literature also exists on numerical modelling of
buckling restrained braces, anticipation of performance and behaviour
of various configurations of braced-frame/framed systems, and
sensitivity of behaviour to various ground motion and structural
characteristics. This literature will not be reviewed in this chapter, but
rather distributed throughout the remainder of the report where these
particular topics are considered.
2.1 Optimization of Steel Frames
“Optimization techniques play an important role in structural
design, the very purpose of which is to find the best solutions from
which a designer or a decision maker can derive a maximum benefit
from the available resources”
Structural designers have used optimization techniques for the
seismic design of buildings; however, they have been generally limited
to static analyses which are not as accurate at modelling true seismic
response as non-linear time history analysis. Because in static
analysis seismic force simply distributes to joints and causes a
building to fail in its first mode shape. Several researchers have used
optimization procedures and linear and non-linear static analyses for
the design of reinforced concrete and steel moment framed buildings
[Ganzerli, et al. (2000); Zou, et al. (2007); and Liu, et al. (2003)].

3. 16
As taller buildings may experience more complicated modal
responses, static analysis may be inappropriate to model their failure.
Researchers have recently coupled non-linear time history analysis
with the optimization algorithm although with relatively simple
models. For example, Lagaros, et al. (2006) investigated optimized
designs of a steel moment frame and Ohsaki, et al. (2007) used non-
linear response history analysis and a multi-objective procedure to
minimize structural volume and maximize plastic energy dissipation
at the collapse state for a steel moment frame. Balling, et al. (2009)
optimized shorter BRBF brace sizes under a suite of earthquakes and
compared results with designs obtained from the equivalent lateral
force procedure.
All of these studies were performed on relatively simple
structures where computational demand is comparatively low.
Oxborrow (2009) and Yeates (2010) began the exploration of tall BRBF
optimization using non-linear time history analysis and the genetic
algorithm. As a structure increases in complexity and height the
response becomes more complicated, and as more members are
allowed to change in an optimization, the design search space
increases exponentially.
Do Dai Thang, and Min-Se Koo et al. (2009) presented a paper
in which, optimum cost design of steel box girder bridge is carried

4. 17
out by varying plate thickness for different spans, uniform loading,
and two types of closed rectangular and open trapezoidal sections.
A. Joghataie and M. Takalloozadeh (2009), in their paper
proposed new penalty functions which have better convergence
properties, as compared to the commonly used exterior and interior
penalty functions. They applied the old and new exterior and interior
penalty functions in conjunction with the steepest descent method to
three-bar truss and ten-bar truss and compared the results. It was
shown that the convergence speed and accuracy of the result were
improved.
In order to be able to predict and control the inelastic behaviour
under seismic loading and to determine the corresponding load factor,
the design of steel MRF is studied by A. Kaveh and B. Dadfar (2008).
They concluded that In spite of some preliminary beliefs, the design of
steel MRFs, according to weak beam strong column rule is not simple.
In most current methods; based on the elastic design of structures,
the structure is not often optimally designed.
A Csébfalvi and G. Csébfalvi proposed a genetic algorithm for
discrete minimal weight design of steel planar frames with semi-rigid
beam-to-column connections. It was revealed that the results of
discrete minimal weight design are highly affected by the applied
connection modelling method.

5. 18
Stanislovas Kalanta1, Juozas, et al, in their paper, considered
the optimal design problems of the elastic and elastic-plastic bars. The
mathematical models of the problems, including the structural
requirements of the strength, stiffness and stability, are formulated in
the terms of finite element method. The stated nonlinear optimization
problems are solved by the iterative method, structures. These
problems are formulated as nonlinear discrete optimization problems
Yasuyuki Nagano and T. Okamoto, et al, presented this paper;
the purpose of this paper is to show the practical applicability of a
new optimum design method by the authors to an actual high-rise
building structure with hysteretic dampers. They concluded that it
possible to save structural cost and reduce computational cost than
the conventional seismic resistant design method, including iterative
dynamic response analysis.
2.2 Moment Resisting Frames
E. Kalkan and S. K. Kunnath(2004) revealed in their study that
the suitability of using unique modal combinations to determine
lateral load configurations that best approximate the inter-story
demands in multi-storey moment resisting frame buildings subjected
to seismic loads.
Akshay Gupta and Helmut Krawinkler (1999), in their Report

6. 19
No. 132, sponsored by the SAC Joint Venture considered MRFs
emphasized on behaviour assessment and quantification of global and
local force and deformation demands for different hazard levels
Krishnan et al. (2006) studied the responses of tall steel
moment frame buildings in scenario magnitude 7.9 earthquakes on
the southern San Andreas Fault. This work used three-dimensional,
nonlinear finite element models of an existing eighteen-story moment
frame building as is, and redesigned to satisfy the 1997 Uniform
Building Code. The authors found that the simulated responses of the
original building indicate the potential for significant damage
throughout the San Fernando and Los Angeles basins. The redesigned
building fared better, but still showed significant deformation in some
areas. The rupture on the southern San Andreas that propagated
north-to-south induced much larger building responses than the
rupture that propagated south-to-north.
Thomas Heaton, et al. (2007) simulates the response of 6 and
20-story steel moment-resisting frame buildings (US 1994. UBC) for
ground motions recorded in the 2003 Tokachi-oki earthquake. They
consider buildings with both perfect welds and also with brittle welds
similar to those observed in the 1994 Northridge earthquake. Their
simulations show that the long-period ground motions recorded in
the near-source regions of the 2003 Tokachi-oki earthquake would
have caused large inter-story drifts in flexible steel moment-resisting

7. 20
frame buildings designed according to the US 1994.UBC.
2.3 Buckling Restrained Braced Frames
Takanori OYA, Takashi Fukazawa, et al (2009), in their paper
introduced the applications of a new type BRB to various structures.
The brace has two buckling restraining parts (steel mortar planks),
clipping a core plate being under axial forces. These parts are welded
together and restrain the core plate of plastic behaviour, avoiding the
out-of-plane deformation and the buckling.
Saif Hussain and Paul Van Benschoten provide in their paper
an overall understanding of the system along with a case study of a
recent project in the City of Los Angeles. The paper includes material
on BRBF background and development, the various issues related to
code provisions, agency approvals, analysis, and design, detailing as
well as construction and erection challenges.
Qiang Xie (2005) presents in his paper a summary of buckling-
restrained braces (BRBs). BRBs show the same load deformation
behaviour in both compression and tension and higher energy
absorption capacity with easy adjustability of both stiffness and
strength. Because of its good seismic behaviour, construction
feasibility, and easy-replacement, BRBs become popular in high-rise
steel buildings in Asia, especially in Japan in the past few years.
Applications for both new high-rise steel buildings and the seismic

8. 21
retrofitting of existing buildings show good prospects of using BRBs.
Cameron Black and Nicos Makris (2003) presented test results
of unbounded buckling restrained braces from a comprehensive
experimental program together with a mathematical model that
approximates their hysteretic behaviour. It is concluded that the
plastic torsional buckling of the inner core was the most critical mode
with a factor of safety of 1.25.
Bradly B. Coy (2003) presents in his thesis work, the connection
design and testing of a BRBF. Recommendations are given regarding
implementation of the connection design and follow-up tasks and
projects.
Edison Ochaoa Escudero (2003), in his thesis presented
comparative parametric study on normal and buckling restrained
braces in building frames. It was concluded that buckling restrained
braces were more cost effective.
Rafael Sabelli and Walterio López (2004), in their paper, presented
the efficiency of BRBs in absorbing seismic energy. It was concluded
that frames using BRBs can be designed as an effective and efficient
seismic-load-resisting system. Using the Recommended Provisions
developed by AISC and SEAOC, engineers can design a system with
performance that is more than adequate for building-code

9. 22
requirements.
Watanabe et al. (1988). A set of five specimens was tested to
investigate the stiffness, strength, and buckling resistance of braces
with varied ratios of tube buckling strength to core yield strength
(Pe/Py) from 0.55 to 3.82. The braces were designed using a core that
was coated to prevent the transfer of axial force from the steel to the
concrete encasement, and polystyrol was used to allow for Poisson’s
expansion to occur freely under compression. Each brace was
mounted diagonally in a frame and an actuator was used to impose a
cyclic horizontal displacement on the frame. The following conclusions
were drawn from the results:
1) In cases where the Pe/Py is greater than 1.0, the brace did not
exhibit any buckling failures, resulting in a stable hysteresis.
2) In cases where the Pe/Py is less than 1.0, the braces buckled
when the axial load on the brace approached Pe, resulting in a sharp
decrease in yield strength when subjected to compressive loads.
3) With proper design for buckling-restraint, the stiffness of the
brace can be determined based on the yield strength of the core alone.
In order to prevent global buckling of the brace, the Pe/Py ratio
should be at least 1.5.
Clark et al. (2000). In a study to support the first installation of
buckling-restrained braced frames in the United States, several
nonlinear analyses were conducted along with large-scale experiments

10. 23
in the laboratory at the University of California Berkeley. The results
of this study were used to design the lateral force-resisting system in
the Plant and Environmental Sciences Building at the University of
California Davis.
A three-story building from the SAC Steel Project was used as a
prototype for the nonlinear analysis, and the performance of the BRBF
lateral system was compared with that of Special Moment-Resisting
Frame (SMRF) system. Under the assumption that the BRBF
performs similar to an Eccentrically-Braced Frame (EBF), the
equivalent static lateral force method found in the 1994 Uniform
Building Code (UBC) was used to design BRBF system, whereas the
SMRF was designed to meet specific drift control requirements
specified in the code. As a result, the weight of the steel required for
the BRBF is 0.51 times the weight of steel required for the SMRF.
Each model was subjected to a static pushover analysis and time-
history analyses were conducted using the records of 1940 El Centro
North-South, 1952 Taft East-West and 1995 Kobe North-South.
Both static and dynamic analyses showed that the BRBF system
had lower yield strength but higher stiffness than the SMRF. As seen
in Figure 1.1 the yield strength of the BRBF, which was called
Unbonded Brace Frame (UBF), was approximately 50% of the yield
strength of SMRF. The over strength in SMRF is largely a result of the
drift control limits imposed by the design code.

11. 24
Lagaros, et al. (2006) investigated optimized designs of a steel
moment frame considering both linear analysis methods and
nonlinear time history analysis.