Dae Kun Kwon

Peak Factors for Non-Gaussian Load Effects Revisited

The estimation of the extreme of non-Gaussian load effects for design applications has often been treated tacitly by invoking a conventional peak factor on the basis of Gaussian processes. This assumption breaks down when the loading process exhibits non-Gaussianity, in which a conventional peak factor yields relatively nonconservative estimates because of failure to include long tail regions inherent to non-Gaussian processes. To realistically capture the salient characteristics of non-Gaussian load effects and incorporate these in the estimates of their extremes, this study examines the peak factor for non-Gaussian processes, which can be used for estimating the expected value of the positive and negative extremes of non-Gaussian load effects. The efficacy of previously introduced analytical expressions for the peak factor of non-Gaussian processes on the basis of a moment-based Hermite model is evaluated and the variance of the estimates in standard deviation is derived. In addition, some improvements ...

Efficacy of Averaging Interval for Nonstationary Winds

AbstractIn comparison with atmospheric boundary-layer winds, which are generally regarded as stationary, windstorms such as hurricanes and thunderstorms/downbursts have strong nonstationary features characterized by rapid changes in wind speed and direction. The averaging interval associated with turbulent wind characteristics in boundary-layer winds is typically varied between 10 min and 1 h. A fixed averaging interval (FAI), which uses a constant mean to isolate the fluctuating wind component, has been effective in characterizing boundary-layer winds; however, the question remains as to whether the user-defined interval is appropriate for nonstationary winds. To address this concern, a variable averaging interval (VAI) scheme is proposed. For better understanding of the characteristics of nonstationary winds, traditional FAI methods are compared with alternative FAI approaches that use time-varying means and the proposed VAI approaches. In addition, the definitions for gust factor, turbulence intensity,...

SmartSync: An Integrated Real-Time Structural Health Monitoring and Structural Identification System for Tall Buildings

AbstractThis study introduces a unique prototype system for structural health monitoring (SHM), SmartSync, which uses the building’s existing Internet backbone as a system of virtual instrumentation cables to permit modular and largely plug-and-play deployments. Within this framework, data streams from distributed heterogeneous sensors are pushed through network interfaces in real time and seamlessly synchronized and aggregated by a centralized server, which performs basic data acquisition, event triggering, and database management while also providing an interface for data visualization and analysis that can be securely accessed. The system enables a scalable approach to monitoring tall and complex structures that can readily interface a variety of sensors and data formats (analog and digital) and can even accommodate variable sampling rates. This study overviews the SmartSync system, its installation/operation in the world’s tallest building, Burj Khalifa, and proof-of-concept in triggering under dual e...

Performance-Based Design of High-Rise Buildings for Occupant Comfort

AbstractThis paper introduces a framework for the performance-based design (PBD) of high-rise buildings with respect to the occupant comfort performance objective. The performance is expressed in terms of the probability—conditional on the wind event intensity—that the fraction of the building occupants on one floor that perceive the motion is greater than a chosen threshold value. The framework is fully probabilistic, and numerous uncertainties affecting both the structural response and the human perception threshold are considered in the assessment of the exceedance probability. In addition, a new database-enabled online analysis module based on the proposed PBD framework [Performance-Based Data-Enabled Design module for Occupant Comfort (PBDED-OC)] is presented. The PBDED-OC allows the assessment of the occupant comfort performance of a tall building by taking advantage of databases of high-frequency base balance measurements or by adopting specific user-supplied wind tunnel data and is envisaged to be...

Full-Scale Validation of the Wind-Induced Response of Tall Buildings: Updated Findings from the Chicago Monitoring Project

While high-rise construction serves as one of the most challenging projects undertaken by society each year, tall buildings are one of the few constructed facilities whose design relies solely upon analytical and scaled models, which, though based upon fundamental mechanics and years of research and experience, have yet to be systematically validated in full-scale. In response to this deficiency, a full-scale monitoring project was initiated through the combined efforts of members of academe (University of Notre Dame), practicing design firms (Skidmore, Owings & Merrill LLP, Chicago) and commercial testing laboratories (Boundary Layer Wind Tunnel Laboratory, University of Western Ontario, Canada). The objective of this program is to monitor the full-scale response of some representative tall building structures and compare their actual performance to the predictions from wind tunnel testing and finite element computer models used in their design. As such, this program offers the opportunity to refine the design state-of-the-art based on any discrepancies revealed. As part of this full-scale evaluation, in-situ periods and damping ratios over a range of response amplitudes are being ascertained, which will prove vital for expanding the existing databases of full-scale dynamic properties. This paper presents a brief overview of the program.

A cyberbased Data-Enabled Design framework for high-rise buildings driven by synchronously measured surface pressures

Abstract This study presents a new Data-Enabled Design Model for high-rise buildings driven by pressure datasets, DEDM-HRP, which seamlessly combines synchronous pressure measurement databases with a rigorous computational framework to offer convenient estimation of wind load effects on high-rise buildings for their preliminary design. To respond to the need for practical applications, DEDM-HRP employs a web-based on-the-fly framework designed with user-friendly/intuitive web interfaces for the assessment of wind-induced responses as well as equivalent static wind loads in the three principal response directions, for any incident wind angle of interest, with minimum added complications or requirements of knowledge of comprehensive background theories for its use.

SmartSync: An Integrated Real-Time Monitoring and SI System for Tall Buildings

This study introduces the SmartSync monitoring system, which utilizes the buildings existing network as “virtual” instrumentation cables. Given the reliability of modern networks and the comparatively low sampling rates required for structural monitoring, the issues of packet loss and synchronization often experienced in wireless systems are eliminated, as is the need for lengthy instrumentation cables that add to the cost and noise in wired systems. Instead this system offers a self-contained, “plug-and-play” module for scalable and rapidly deployable monitoring. Within this framework, data streams from distributed sensors are pushed through network interfaces in real-time and are seamlessly synchronized and integrated by a centralized server, which performs the functions of basic data acquisition, event triggering and data management and processing, while at the same time providing a powerful interface for data visualization. This study introduces the system and its installation during the construction of Burj Dubai (Burj Khalifa).

Performance Evaluation of Database-Enabled Design Frameworks for the Preliminary Design of Tall Buildings

AbstractDatabase-enabled design (DED) frameworks offer convenient meshing of wind-tunnel driven databases with state-of-the-art analysis methodologies for the design of low-rise to high-rise buildings. These procedures can serve as an alternative or supplementary tool to codes and standards. Despite their obvious advantages over simplified code-specified procedures, the response estimates obtained from these data-driven frameworks are by nature susceptible to the accuracy of both the analysis schemes employed within the procedure as well as the aerodynamic databases that are driven by different wind tunnels, instrumentations, and experimental techniques. To examine and quantify these potential sources of discrepancy, this paper attempts to evaluate the performance of various cyber-based DED frameworks that are currently used in the preliminary design of tall buildings. To this end, a systematic comparison is carried out among along-wind and across-wind response estimates of a typical building example usin...

A Cyber-Based Data-Enabled Virtual Organization for Wind Load Effects on Civil Infrastructures: VORTEX-Winds

Despite many advances in the area of wind effects on structures in recent decades, research has been traditionally conducted within limited resources scattered geographically. With the trend toward increasingly complex designs of civil infrastructure combined with the escalating potential for losses by extreme wind events, a new culture of research needs to be established based on innovative and collaborative solutions for better management of the impact of extreme wind events. To address this change, this paper presents a new paradigm of a multi-scale cyber based laboratory framework for the analysis/design, modeling and simulation of wind load effects based on an ongoing collaborative cyberinfrastructure based platform, VORTEX-Winds: Virtual Organization for Reducing the Toll of EXtreme Winds (https://vortex-winds.org), and discusses its current status since its inception in 2007 and ongoing developments. This collaborative framework as it evolves would enable a paradigm shift by offering advanced cyber-enabled modules (e-modules) for accelerating advances in research and education to achieve improved understanding and better modeling of wind effects on structures. Accordingly, it will enhance wind community’s analysis and design capabilities to address next generation challenges posed by wind. Through empowering those without computational or experimental resources, the e-modules will encompass a large set of subject areas and topics categorized as Database-enabled design, Full-scale/Field site data repository, Statistical/Stochastic toolboxes, Tele-experimentation, Uncertainty modeling, Damage assessment, and Computational platforms. This prototype will allow access to the individual e-module, while it is envisaged that next level of development in VORTEX-Winds will have the capability for an automated and integrated analysis/design through a nexus of e-modules. A highlight of the e-modules currently completed or in development is presented not only to show the efficacy of the framework to enhance and supplement the limitation of traditional off-line approaches, but also to describe architecture and features of e-modules to promote additional cyber-enabled data-driven developments in the field.