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SUMMARY This paper presents the motivation and the mathematics required for the introduction of Bayesian structural reliability theory into the process of evaluating and strengthening any tall building located in the Los Angeles region. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This issue is the 2009 Special Issue of the journal developed by the Los Angeles Tall Buildings Design Council. The papers noted in this issue are all exceptional papers selected by the council. [ABSTRACT FROM AUTHOR]

SUMMARY This paper presents a methodology in wind design including in a scientific way the benefits of using dampers and of performing a nonlinear dynamic analysis of tall concrete buildings that are being evaluated and strengthened. It is developed for tall buildings in the Los Angeles region but is without geographic bounds. The uses of equations of structural reliability form this scientific basis. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY This paper addresses the topic of evaluating and strengthening a tall building in the Los Angeles region. Failure is characterized by the reliability index in terms that can be readily understood by structural engineers with only a basic knowledge of probability theory. The presented formulation requires the structural engineer to believe that the assumption of a normal or log-normal probability density function for capacity and demand is acceptable for the evaluation and strengthening of a tall building in the Los Angeles region. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper concentrates on investigating the seismic behaviours of vertically irregular steel special moment frame (SMF) buildings by comparison with the regular counterpart. All buildings in this study were assumed to be located in Los Angeles, and subjected to 20 earthquake ground motions with a seismic hazard level of 2% probability of exceedance in 50 years. The beam-column connections of the buildings were modelled to consider the panel zone deformation. In addition, a ductile connection model accompanied by strength degradation was incorporated to the analysis programme in an effort to obtain more accurate response results. Three types of irregularities (mass, stiffness and strength irregularity) specified as vertical irregularities in the IBC 2000 provisions were imposed to the original building. Nonlinear static and dynamic analyses were performed, and the confidence levels of which the performance objective will be satisfied were calculated as well. The effects of different irregularity types and levels on the seismic behaviours of the buildings were investigated and discussed in terms of the height-wise distribution of storey drifts, maximum storey drift demands, global collapse storey drift capacities and confidence levels. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY The architectural expressions for many modern buildings require creative and unconventional structural solutions. Columns must be taller, beams must span further, the structure must be more slender, elements must be curved, structural framing must be sloped and connections must deviate from conventional orthogonal fit-up. Although the technology exists to analyze and design responsive structural systems, prescriptive code requirements oftentimes hinder the implementation of those technologies. Although not a 'tall building' by traditional definition, the Tom Bradley International Terminal (TBIT) Modernization Program at Los Angeles International Airport (LAX) provides an appropriate case study in the implementation of unconventional structural geometry subject to code requirements that prescribe contrasting conventional geometry, which is a familiar challenge for many tall buildings. The architectural expression for the LAX TBIT Modernization Program required the use of long-span steel Special Moment Frames with non-orthogonal moment connections between the beams and columns. The beams were sloped, some were sloped and curved and some of the columns were sloped. The reduced beam section (RBS) moment connection was selected for the project. ANSI/AISC 358, Prequalified Connections for Special and Intermediate Steel Moment Frames for Seismic Applications, provides prequalification limits for using an RBS connection. Those limits do not address non-orthogonal moment connections. ANSI/AISC 358 implicitly limits connections to orthogonal geometry; hence, non-orthogonal moment connections are not prequalified for use in seismic applications. This paper describes the structure and the cyclic testing program that was implemented to qualify the proposed non-orthogonal RBS connections in accordance with ANSI/AISC 341, Seismic Provisions for Structural Steel Buildings, Appendix S for use on the LAX TBIT Modernization Project. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Three of the tall buildings that members of the Los Angeles Tall Buildings Structural Design Council visited after the 27 February 2010 Chilean moment magnitude 8.8 earthquake were reviewed. The three buildings discussed in this paper are located in the Greater Concepción area in the Biobió Region (Region VIII) of Chile. Two of the buildings (Bosquemar and Olas) are located on the west side of the Bio-Bio River in San Pedro de La Paz, while the third building (Pedro de Valdivia) is located on the east side of the river south of the downtown area of the city of Concepción. The tower at Bosquemar was the most thoroughly investigated, although the observations from the damage at all three structures offer important insight that can be applied to current and future earthquake engineering practice. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper summarizes the first phase of research on the relative safety of buildings in Los Angeles. At this phase, the behaviour of two 20-storey buildings designed according to UBC-1994 provisions and subjected to simulated and recorded/scaled ground motions that represent a rare seismic event is investigated. The seismic event considered in this study is a magnitude 7.15 ground motion initiated in the blind thrust Puente Hills fault system. The effect of beam to column connections detailing on seismic demands is also investigated by developing two models for each building: one with pre-Northridge connection assumptions and the other with post-Northridge ones. In all models, the effects of gravity load carrying system and slab are neglected for simplicity. It is concluded that simulated ground motions representing the magnitude 7.15 earthquake impose higher seismic demands compared with recorded/scaled motions that represent a similar event to the extent that in the high-slip region of the fault, the behaviour of the 20-storey building with post-Northridge connection can be deemed unacceptable. [ABSTRACT FROM AUTHOR]

SUMMARY The time is now for the nonlinear dynamic analysis of buildings for wind loads. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY This study utilized nonlinear response history analysis to compare the seismic demand on three variations of a 40-storey buckling-restrained braced frame designed for high seismic hazard in the Los Angeles region. The three designs were referred to as a 'code-based design', based on the 2006 International Building Code, a 'performance-based design', based on criteria published by the Los Angeles Tall Building Design Council (LATBSDC) and a 'performance-based design plus', based on newly developed criteria from The Pacific Earthquake Engineering Research Center (PEER). The response history analysis utilized spectrum-matched ground motions as well as simulated ground motions for the Puente Hills fault. The spectrum-matched motions were selected from the Next Generation Attenuation of Ground Motions (NGA) database, which is largely composed of recorded motions and scaled to five hazard levels. The simulated ground motions were broadband signals generated from a moment magnitude (Mw) 7.15 scenario rupture of the Puente Hills fault for two near fault regions and exhibit long period energy content that significantly exceeds the uniform hazard spectrum. Structural performance was assessed in terms of exceedance of a safe inter-storey drift ratio (IDR). It was seen that the simulated ground motions impose higher IDR demands on the structures than the spectrum-matched NGA ground motions. Furthermore, the number of instances of exceedance of a safe IDR, considered for this study as IDR = 0.03, is substantially higher for the simulated ground motions, pointing to the importance of considering such motions in the collapse prevention of tall buildings on a site-specific basis. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Simpson Gumpertz & Heger has prepared two prototypical designs for a 40-storey buckling-restrained braced steel-framed office building located at a generic site in Los Angeles, CA. One of these designs conforms in all respects, except height limits with the design criteria contained in the 2007 California Building Code and ASCE 7.05 Standard for Minimum Design Loads for Buildings and Other Structures. The second design has been conducted using a performance-based approach generally based on the criteria contained in guidelines published by the Los Angeles Tall Buildings Council. The performance-based design incorporates fewer bays of bracing and lighter members than the code-based design, but is intended to provide performance at least equivalent to that anticipated for code-designed buildings. The purpose of this work was to permit study of the performance capability of buildings designed to alternative criteria. This work was performed in support and under funding provided by the Pacific Earthquake Engineering Research Center's Tall Buildings Initiative. [ABSTRACT FROM AUTHOR]

Based on experience from the design of 20 concrete ductile core wall buildings using performance-based design concepts and a sample design for a high-rise concrete core wall building performed for the Los Angeles Tall Buildings Structural Design Council, several important issues to be considered before embarking on a detailed analysis have been identified. Nonlinear response history analysis for large, complicated structures can consume many hours of engineering effort. It is always advisable to understand as much as possible about the anticipated building behaviour before beginning this analysis. Performance objectives should be clearly identified for both frequent and maximum considered earthquakes. In particular, acceptable performance at serviceability levels should be understood, as current building codes do not provide much guidance. Factors such as anticipated demand on the lateral system, building height, soil type and seismic hazard should all be considered before running computer models, so appropriate cracking assumptions can be made. Even the design spectra themselves can be indicators of anticipated higher mode effects that may govern design. [ABSTRACT FROM AUTHOR]