14 Chapter 2 LITERATURE REVIEW2.1 General Considerable research has been conducted on the behaviour ofsteel moment resisting frames, buckling restrained braced frames andoptimization techniques for minimum weight design under seismicground excitation. Because of the rapid evolution of codes, much ofthis research is not necessarily consistent with modern constructiondetailing; however, many of the fundamental observations from theseinvestigations are relevant to an assessment of modern design andanalysis procedures. The available collection of literature extends overseveral decades and is rapidly growing. As such, it cannot adequatelybe summarized in a brief chapter. Instead, an overview of majorreferences is provided here along with useful citations to previousworks that contain detailed reviews of related literature. Theliterature review in this chapter is separated below into threecategories:(i)optimization of steel frames, which examines referencesthat describe the optimum design of framed/braced steel structures ofrecent earthquakes (1978– 1995) in the United States, Mexico, Japanand India.(ii) Moment resisting frames: which discusses the previousworks on moment resisting braced frames relevant to seismicapplications and (iii) buckling restrained braced frames: whichdiscusses previous experimental and analytical works on buckling
15restrained braced frames relevant to seismic applications. Considerable literature also exists on numerical modelling ofbuckling restrained braces, anticipation of performance and behaviourof various configurations of braced-frame/framed systems, andsensitivity of behaviour to various ground motion and structuralcharacteristics. This literature will not be reviewed in this chapter, butrather distributed throughout the remainder of the report where theseparticular topics are considered.2.1 Optimization of Steel Frames “Optimization techniques play an important role in structuraldesign, the very purpose of which is to find the best solutions fromwhich a designer or a decision maker can derive a maximum benefitfrom the available resources” Structural designers have used optimization techniques for theseismic design of buildings; however, they have been generally limitedto static analyses which are not as accurate at modelling true seismicresponse as non-linear time history analysis. Because in staticanalysis seismic force simply distributes to joints and causes abuilding to fail in its first mode shape. Several researchers have usedoptimization procedures and linear and non-linear static analyses forthe design of reinforced concrete and steel moment framed buildings[Ganzerli, et al. (2000); Zou, et al. (2007); and Liu, et al. (2003)].
16 As taller buildings may experience more complicated modalresponses, static analysis may be inappropriate to model their failure.Researchers have recently coupled non-linear time history analysiswith the optimization algorithm although with relatively simplemodels. For example, Lagaros, et al. (2006) investigated optimizeddesigns of a steel moment frame and Ohsaki, et al. (2007) used non-linear response history analysis and a multi-objective procedure tominimize structural volume and maximize plastic energy dissipationat the collapse state for a steel moment frame. Balling, et al. (2009)optimized shorter BRBF brace sizes under a suite of earthquakes andcompared results with designs obtained from the equivalent lateralforce procedure. All of these studies were performed on relatively simplestructures where computational demand is comparatively low.Oxborrow (2009) and Yeates (2010) began the exploration of tall BRBFoptimization using non-linear time history analysis and the geneticalgorithm. As a structure increases in complexity and height theresponse becomes more complicated, and as more members areallowed to change in an optimization, the design search spaceincreases exponentially. Do Dai Thang, and Min-Se Koo et al. (2009) presented a paperin which, optimum cost design of steel box girder bridge is carried
17out 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 paperproposed new penalty functions which have better convergenceproperties, as compared to the commonly used exterior and interiorpenalty functions. They applied the old and new exterior and interiorpenalty functions in conjunction with the steepest descent method tothree-bar truss and ten-bar truss and compared the results. It wasshown that the convergence speed and accuracy of the result wereimproved. In order to be able to predict and control the inelastic behaviourunder 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 ofsteel 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 fordiscrete minimal weight design of steel planar frames with semi-rigidbeam-to-column connections. It was revealed that the results ofdiscrete minimal weight design are highly affected by the appliedconnection modelling method.
18 Stanislovas Kalanta1, Juozas, et al, in their paper, consideredthe optimal design problems of the elastic and elastic-plastic bars. Themathematical models of the problems, including the structuralrequirements of the strength, stiffness and stability, are formulated inthe terms of finite element method. The stated nonlinear optimizationproblems are solved by the iterative method, structures. Theseproblems 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 anew optimum design method by the authors to an actual high-risebuilding structure with hysteretic dampers. They concluded that itpossible to save structural cost and reduce computational cost thanthe conventional seismic resistant design method, including iterativedynamic response analysis.2.2 Moment Resisting Frames E. Kalkan and S. K. Kunnath(2004) revealed in their study thatthe suitability of using unique modal combinations to determinelateral load configurations that best approximate the inter-storydemands in multi-storey moment resisting frame buildings subjectedto seismic loads. Akshay Gupta and Helmut Krawinkler (1999), in their Report
19No. 132, sponsored by the SAC Joint Venture considered MRFsemphasized on behaviour assessment and quantification of global andlocal force and deformation demands for different hazard levels Krishnan et al. (2006) studied the responses of tall steelmoment frame buildings in scenario magnitude 7.9 earthquakes onthe southern San Andreas Fault. This work used three-dimensional,nonlinear finite element models of an existing eighteen-story momentframe building as is, and redesigned to satisfy the 1997 UniformBuilding Code. The authors found that the simulated responses of theoriginal building indicate the potential for significant damagethroughout the San Fernando and Los Angeles basins. The redesignedbuilding fared better, but still showed significant deformation in someareas. The rupture on the southern San Andreas that propagatednorth-to-south induced much larger building responses than therupture that propagated south-to-north. Thomas Heaton, et al. (2007) simulates the response of 6 and20-story steel moment-resisting frame buildings (US 1994. UBC) forground motions recorded in the 2003 Tokachi-oki earthquake. Theyconsider buildings with both perfect welds and also with brittle weldssimilar to those observed in the 1994 Northridge earthquake. Theirsimulations show that the long-period ground motions recorded inthe near-source regions of the 2003 Tokachi-oki earthquake wouldhave caused large inter-story drifts in flexible steel moment-resisting
20frame buildings designed according to the US 1994.UBC.2.3 Buckling Restrained Braced Frames Takanori OYA, Takashi Fukazawa, et al (2009), in their paperintroduced 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 weldedtogether and restrain the core plate of plastic behaviour, avoiding theout-of-plane deformation and the buckling. Saif Hussain and Paul Van Benschoten provide in their paperan overall understanding of the system along with a case study of arecent project in the City of Los Angeles. The paper includes materialon BRBF background and development, the various issues related tocode provisions, agency approvals, analysis, and design, detailing aswell as construction and erection challenges. Qiang Xie (2005) presents in his paper a summary of buckling-restrained braces (BRBs). BRBs show the same load deformationbehaviour in both compression and tension and higher energyabsorption capacity with easy adjustability of both stiffness andstrength. Because of its good seismic behaviour, constructionfeasibility, and easy-replacement, BRBs become popular in high-risesteel buildings in Asia, especially in Japan in the past few years.Applications for both new high-rise steel buildings and the seismic
21retrofitting of existing buildings show good prospects of using BRBs. Cameron Black and Nicos Makris (2003) presented test resultsof unbounded buckling restrained braces from a comprehensiveexperimental program together with a mathematical model thatapproximates their hysteretic behaviour. It is concluded that theplastic torsional buckling of the inner core was the most critical modewith a factor of safety of 1.25. Bradly B. Coy (2003) presents in his thesis work, the connectiondesign and testing of a BRBF. Recommendations are given regardingimplementation of the connection design and follow-up tasks andprojects. Edison Ochaoa Escudero (2003), in his thesis presentedcomparative parametric study on normal and buckling restrainedbraces in building frames. It was concluded that buckling restrainedbraces were more cost effective. Rafael Sabelli and Walterio López (2004), in their paper, presentedthe efficiency of BRBs in absorbing seismic energy. It was concludedthat frames using BRBs can be designed as an effective and efficientseismic-load-resisting system. Using the Recommended Provisionsdeveloped by AISC and SEAOC, engineers can design a system withperformance that is more than adequate for building-code
22requirements. Watanabe et al. (1988). A set of five specimens was tested toinvestigate the stiffness, strength, and buckling resistance of braceswith 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 thatwas coated to prevent the transfer of axial force from the steel to theconcrete encasement, and polystyrol was used to allow for Poisson’sexpansion to occur freely under compression. Each brace wasmounted diagonally in a frame and an actuator was used to impose acyclic horizontal displacement on the frame. The following conclusionswere drawn from the results: 1) In cases where the Pe/Py is greater than 1.0, the brace did notexhibit any buckling failures, resulting in a stable hysteresis. 2) In cases where the Pe/Py is less than 1.0, the braces buckledwhen the axial load on the brace approached Pe, resulting in a sharpdecrease in yield strength when subjected to compressive loads. 3) With proper design for buckling-restraint, the stiffness of thebrace can be determined based on the yield strength of the core alone.In order to prevent global buckling of the brace, the Pe/Py ratioshould be at least 1.5. Clark et al. (2000). In a study to support the first installation ofbuckling-restrained braced frames in the United States, severalnonlinear analyses were conducted along with large-scale experiments
23in the laboratory at the University of California Berkeley. The resultsof this study were used to design the lateral force-resisting system inthe Plant and Environmental Sciences Building at the University ofCalifornia Davis. A three-story building from the SAC Steel Project was used as aprototype for the nonlinear analysis, and the performance of the BRBFlateral system was compared with that of Special Moment-ResistingFrame (SMRF) system. Under the assumption that the BRBFperforms similar to an Eccentrically-Braced Frame (EBF), theequivalent static lateral force method found in the 1994 UniformBuilding Code (UBC) was used to design BRBF system, whereas theSMRF was designed to meet specific drift control requirementsspecified in the code. As a result, the weight of the steel required forthe 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 CentroNorth-South, 1952 Taft East-West and 1995 Kobe North-South. Both static and dynamic analyses showed that the BRBF systemhad lower yield strength but higher stiffness than the SMRF. As seenin Figure 1.1 the yield strength of the BRBF, which was calledUnbonded Brace Frame (UBF), was approximately 50% of the yieldstrength of SMRF. The over strength in SMRF is largely a result of thedrift control limits imposed by the design code.
24 Lagaros, et al. (2006) investigated optimized designs of a steelmoment frame considering both linear analysis methods andnonlinear time history analysis.