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Measuring the dynamic displacements of a structure provides a comprehensive understanding of the structure, especially when subjected to different types of dynamic loading (i.e., wind, traffic, impact loads, blast loads, etc.). Despite their usefulness, direct displacement measurements are typically not collected due to the cumbersome logistical issues of sensor placement and maintenance and the impracticality of instrumenting contact-based sensors across all significant structures. In this context, this study proposes a novel dual stereovision technique to measure the dynamic displacement of structures using a portable, noncontact measurement system that involves an uncrewed aerial system (UAS) and four optical cameras. One pair of cameras tracks the three-component (x , y , and z) motion of a region of interest (ROI) on a structure with respect to the UAS system, and the other pair of cameras measure the six degrees of freedom motion (6-DOF) (both rotational and translational motion) of the UAS system by tracking a stationary reference. The motion of the UAS is then compensated for to recover the true dynamic displacement of the ROI. The proposed dual stereovision technique realizes simultaneous measurement of all three components of displacements of the structure and 6-DOF of UAS motion through a mathematically elegant process. The unique dual stereovision technique allows flexibility in choosing a global reference coordinate system, greatly enhancing the feasibility of applying the new technology in various field environments. This new technique has overcome the major challenge of significant UAS motions in full-scale applications. Furthermore, this technique relies on natural features and eliminates the requirement of artificial targets on the structure, permitting applications to difficult-to-access structures. [ABSTRACT FROM AUTHOR]

Measuring the dynamics of vibrating cables in situ can be challenging using traditional contact-based sensors (e.g., accelerometer). This work proposes a novel computer vision–based technique using a portable unmanned aerial system (UAS) (also referred to as drones) sensing platform to enable the measurement of the dynamic displacements of a cable in a unique blast-loading experiment where other types of sensing may be impractical. The proposed technique utilizes one optical camera equipped on a UAS to record the dynamic displacement of the blast-loaded cable and measure the drift of the UAS as it hovers. Artificial targets attached to the cable are not required because the technique proves effective when tracking natural features inherent in the cable. This makes the proposed technique versatile and convenient for field implementation. This technique also allows simultaneous displacement measurement at multiple points along the cable across the entire field of view of the camera. The natural frequency, damping, and mode shape are successfully identified from the measured cable displacement time histories. Measuring the vibration of a cable is challenging with traditional techniques. A novel technique is proposed to use only one camera attached to a drone to measure the vibration of a cable directly. However, because the drone hovers in the air, there is inherent drift of the drone. The drone's drift is measured with respect to a stationary target using the camera and compensated for to measure the true motion of the cable. To test the proposed technique, a blast was detonated close to the cable to produce vibration in the cable, and the drone hovered above the cable to record its movements. Because the actual movement of the cable is unknown, finite-element simulations were performed to provide a basis for validating the proposed technique. The natural frequency of the finite-element model is compared with that obtained from the measured vibration of the cable. A good agreement was achieved with a 2.1% difference between the simulated and measured natural frequencies. [ABSTRACT FROM AUTHOR]

Nonstructural damage to the cladding and façades systems caused by excessive wind pressure and debris impact is the primary damage to urban high/midrise buildings after hurricanes. This paper focuses on the assessment of damage to urban buildings envelopes due to windborne debris while leaving the wind pressure-induced damage outside the scope. The existing building envelope damage assessment models for urban high/mid-rise buildings often neglect the geometry of building clusters or simply assume a homogeneous configuration, which can introduce errors and uncertainties for urban building clusters with varying geometries and layouts. In this context, this paper proposes a new fragility modeling approach for urban buildings envelopes, which explicitly considers geometric configurations of urban buildings, to improve the accuracy of risk assessment for urban buildings. To develop such a fragility model, first, a physical model of debris impact on building envelopes is established, considering the configuration of the surrounding buildings. Then the fragility function is rigorously formulated by propagating the uncertainties from hurricane wind hazard, local urban wind field, the resistance of the envelope component, as well as debris size, location and generation. Reduced-order modeling and Monte Carlo simulation are employed to construct fragility surfaces. An illustrative example is presented to validate the proposed physical model of debris impact and demonstrate the implementation of the proposed fragility modeling approach. [ABSTRACT FROM AUTHOR]

Coastal cities in the east and southeast regions of the US have seen significant population growth and economic development in the last 2 decades. As a result, urban infrastructure, populations, and economies are becoming increasingly vulnerable to hurricane-driven hazards. Criteria for wind design in national standards are intended specifically for the design and performance assessment of individual buildings and other facilities for life safety. They are not adequate for assessing community resilience because hurricane winds are spatially nonuniform. Although scenario-based approaches to representing hurricane demands are more useful in community performance assessment because the distinct features of various hurricane scenarios and their impact on a community can be captured, they are not tied to a specific hazard level. This study introduces a new method for systematically identifying a set of hurricane scenarios corresponding to a stipulated return period (RP) for resilience assessment of coastal communities using a deaggregation approach, which establishes a connection that has not existed previously between hurricane scenarios and the building regulatory process. A community patterned after Miami, Florida, was used to demonstrate the proposed hazard deaggregation and damage analysis. Hurricane scenario events that are dominant contributors to the stipulated RP events, coupled with fragility models of engineered buildings, were used to identify building damage patterns and form an improved basis for risk-informed decision making. [ABSTRACT FROM AUTHOR]

Interpolation can be used to up-sample a sparsely recorded or simulated data set. Ideal interpolation models such as a Nyquist-bandlimited filter in the frequency domain and sinc function in the time domain are difficult to implement. Previous researchers proposed an interpolation scheme that interpolates data faithfully and preserves the spectral features of the original data. This approach has one possible limitation that the interpolated data may not pass through the original data points exactly. This technical note provides a modification of this scheme to ensure the interpolated data capture the original data points. [ABSTRACT FROM AUTHOR]

This 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 excitations (wind and earthquake). [ABSTRACT FROM AUTHOR]

This study proposes a generalized wind loading chain to describe a complete relationship among wind, force, and response induced by nonstationary wind events such as tropical storms or downbursts to complement the Davenport wind loading chain. In the proposed chain, nonstationary winds are represented as a nonstationary model in terms of the time-varying mean and nonstationary fluctuating wind components similar to a stationary model involving the mean and stationary fluctuating wind components in the Davenport's stationary wind loading chain. Specifically, the five chain components of the fluctuating wind in the Davenport's chain such as gustiness of wind, aerodynamic transfer/admittance, aerodynamic force, structural transfer/admittance, and response statistics are recast as time-dependent counterparts in the time-frequency domain to capture nonstationary winds effects on structures. These components are formulated using the evolutionary power spectral density (EPSD) as a form of time-frequency representation that captures salient features of nonstationary tropical storm and downburst winds. As an alternative, a wavelet-based representation is also offered. A numerical example demonstrates the estimation of nonstationary response using the proposed generalized chain. For possible codification of nonstationary wind effects on structures, a preliminary examination suggests that the extreme nonstationary response computed by the generalized chain may be conveniently meshed with the gust front factor or its generalized version frameworks. This may facilitate a rapid shift in the current design approach from stationary to nonstationary winds. [ABSTRACT FROM AUTHOR]