Search

Summary: High‐rise buildings are an efficient solution to meet the housing challenges of global urbanization that is happening at an incredible pace. Code‐based seismic design philosophies are aimed at achieving collapse‐prevention under major earthquakes, implying extensive structural damage associated with important losses. A number of high‐performance systems have been investigated for enhancing the resilience of high‐rise buildings whose design is especially challenging due to higher‐mode effects even when a flexural mechanism is formed at the base of the structure. To this end, this paper proposes a new concept consisting of a three‐dimensional uncoupled rocking and shear mechanism system for high‐rise buildings where reinforced concrete (RC) core walls are used as the lateral‐force‐resisting system. The proposed system provides a dual‐mechanism at the base that independently limits both overturning moments (OTMs) and shear forces and thus more effectively mitigates higher‐mode effects. The characteristic mechanics of the proposed system are first studied through an idealized model. A physical embodiment is then designed, detailed, and validated through advanced models and extensive nonlinear dynamic analyses. A 42‐story RC core‐wall building that is located in Los Angeles and was studied as part of the PEER Tall Buildings Initiative is used as a reference structure in this study. Results confirmed that the proposed system eliminates damage at the base of the walls and minimizes the inelastic demands over the height of the building. In a general sense, the proposed concept provides a framework in which the intended dual mechanism can be implemented to a wider range of high‐rise structures. [ABSTRACT FROM AUTHOR]

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]

The scarcity of strong ground motion records presents a challenge for making reliable performance assessments of tall buildings whose seismic design is controlled by large‐magnitude and close‐distance earthquakes. This challenge can be addressed using broadband ground‐motion simulation methods to generate records with site‐specific characteristics of large‐magnitude events. In this paper, simulated site‐specific earthquake seismograms, developed through a related project that was organized through the Southern California Earthquake Center (SCEC) Ground Motion Simulation Validation (GMSV) Technical Activity Group, are used for nonlinear response history analyses of two archetype tall buildings for sites in San Francisco, Los Angeles, and San Bernardino. The SCEC GMSV team created the seismograms using the Broadband Platform (BBP) simulations for five site‐specific earthquake scenarios. The two buildings are evaluated using nonlinear dynamic analyses under comparable record suites selected from the simulated BBP catalog and recorded motions from the NGA‐West database. The collapse risks and structural response demands (maximum story drift ratio, peak floor acceleration, and maximum story shear) under the BBP and NGA suites are compared. In general, this study finds that use of the BBP simulations resolves concerns about estimation biases in structural response analysis which are caused by ground motion scaling, unrealistic spectral shapes, and overconservative spectral variations. While there are remaining concerns that strong coherence in some kinematic fault rupture models may lead to an overestimation of velocity pulse effects in the BBP simulations, the simulations are shown to generally yield realistic pulse‐like features of near‐fault ground motion records. [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]

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]

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]