Load Rating Assessment of Three Slab-Span Bridges Over Shingle Creek

(c) 1036194Three slab-span bridges crossing Shingle Creek in Brooklyn Center, Minnesota, have poor American Association of State Highway and Transportation Officials (AASHTO) load rating factors for certain truck configurations. Characterization of load distribution is useful for determining the load rating of bridges, but results in the literature have shown that the AASHTO code results in conservative load rating factors. The focus of this study was to determine if the load rating of the three concrete slab-span bridges was conservative and could be improved using results from live load testing and finite element analysis. Field testing used a suite of instrumentation that included displacement transducers, strain gauges, accelerometers, and tiltmeters. A three-dimensional solid-element finite element model was used to determine an expected range of behaviors and corroborate the field data regarding how load distributed when placed near and away from a barrier. In addition, a method for developing a simple plate model of slab span bridges was developed considering in-situ material properties and effects of secondary elements such as barriers. Results indicated that the AASHTO load rating was conservative, and an improved rating factor could be obtained considering the field test data and computational modeling results

Real-Time Wireless Data Acquisition for Structural Health Monitoring and Control

Wireless smart sensor networks have become an attractive alternative to traditional wired sensor systems in order to reduce implementation costs of structural health monitoring systems. The onboard sensing, computation, and communication capabilities of smart wireless sensors have been successfully leveraged in numerous monitoring applications. However, the current data acquisition schemes, which completely acquire data remotely prior to processing, limit the applications of wireless smart sensors (e.g., for real-time visualization of the structural response). While real-time data acquisition strategies have been explored, challenges of implementing highthroughput real-time data acquisition over larger network sizes still remain due to operating system limitations, tight timing requirements, sharing of transmission bandwidth and unreliable wireless radio communication. This report presents the implementation of real-time wireless data acquisition on the Imote2 platform. The challenges presented by hardware and software limitations are addressed in the application design. The framework is then expanded for highthroughput applications that necessitate larger networks sizes with higher sampling rates. Two approaches are implemented and evaluated based on network size, associated sampling rate, and data delivery reliability. Ultimately, the communication and processing protocol allows for nearreal- time sensing of 108 channels across 27 nodes with minimal data loss.published or submitted for publicationnot peer reviewe

Characterization of Wireless Smart Sensor Performance

A critical aspect of using wireless sensors for structural health monitoring is communication performance. Unlike wired systems, data transfer is less reliable between wireless sensor nodes due to data loss. While reliable communication protocols are typically used to reduce data loss, this increase in communication can drain already limited power resources. This report provides an experimental investigation of the wireless communication characteristics of the Imote2 smart sensor platform; the presentation is tailored towards the end user, e.g., application engineers and researchers. Following a qualitative discussion of wireless communication and packet delivery, a quantitative characterization of wireless communication capabilities of the Imote2 platform is provided, including an assessment of onboard and external antenna performance. Herein, the external antenna was found to significantly outperform the onboard antenna in both transmission and reception reliability. However, the built environment, including building materials and other wireless networks, can significantly reduce reception rate and thus increase packet loss. Finally, implications of these results for a full-scale implementation are presented.published or submitted for publicatio

Smart wireless control of civil structures

Structural control techniques are an alternative approach to protect structures from natural hazards that continue to plague our nation’s infrastructure. Due to their onboard sensing, communication, and computational capabilities, wireless smart sensors, which have become popular for structural health monitoring applications, are an attractive option for implementing structural control systems. However, wireless smart sensors pose unique challenges, such as communication latency and unreliable communication, which make common centralized control systems over wireless networks less feasible. Previous research has implemented wireless structural control using decentralized approaches on semi-active control systems; however, these implementations are less sensitive to the challenges related to wireless structural control, because semi-active control systems are inherently stable. On the other hand, wireless active control systems require the entire control system, from hardware selection to control design, to deal with these challenges to limit delays and error and to ensure a stable system. Therefore, this research addresses all the elements of wireless active control design to overcome these challenges. Low- latency data acquisition and actuation hardware tailored for control limits any inherent delay due to the sensing and control components. Real-time wireless data acquisition and control strategies are implemented within the existing software framework. The approach for digital control design preserves stability and control performance in the presence of delays and at slow sampling rates. The wireless control system is validated on an actively controlled multi-story, small-scale test structure suitable for different levels of control decentralization. The result of this research is the realization of a decentralized wireless active structural control system that overcomes the challenges posed by wireless smart sensors to realize their potential for structural control.Financial support for this research was provided in part by the National Science Foundation under NSF Grants No. CMS- 0600433, CMMI-0928886, and CNS-1035773. The first author was supported by the National Science Foundation Graduate Fellows Program, Illinois Distinguished Fellowship, and Carver Trust Fellowship. FOpe

Feasibility of Vibration-Based Long-Term Bridge Monitoring Using the I-35W St. Anthony Falls Bridge

Vibration based structural health monitoring has become more common in recent years as the required data acquisition and analysis systems become more affordable to deploy. It has been proposed that by monitoring changes in the dynamic signature of a structure, primarily the natural frequency, one can detect damage. This approach to damage detection is made difficult by the fact that environmental factors, such as temperature, have been shown to cause variation in the dynamic signature in a structure, effectively masking those changes due to damage. For future vibration based structural health monitoring systems to be effective, the relationship between environmental factors and natural frequency must be understood such that variation in the dynamic signature due to environmental noise can be removed. A monitoring system on the I-35W St. Anthony Falls Bridge, which crosses the Mississippi River in Minneapolis, MN, has been collecting vibration and temperature data since the structures opening in 2008. This provides a uniquely large data set, in a climate that sees extreme variation in temperature, to test the relationship between the dynamic signature of a concrete structure and temperature. A system identification routine utilizing NExT-ERA/DC is proposed to effectively analyze this large data set, and the relationship between structural temperature and natural frequency is investigated.Gaebler, Karl O.; Shield, Carol K.; Linderman, Lauren E.. (2017). Feasibility of Vibration-Based Long-Term Bridge Monitoring Using the I-35W St. Anthony Falls Bridge. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/185540

Displacement Monitoring of I-35W Saint Anthony Falls Bridge with Current Vibration-Based System

Since the opening of the I-35W Saint Anthony Falls Bridge in 2008, over 500 sensors have been collecting data to better understand the behavior of post-tensioned concrete box girder structures. Recent research in the accelerometers installed on the bridge indicates they can be effectively used in a vibration-based structural health monitoring system, but previous studies have shown that natural frequency alone may not be sufficient to determine the performance of the structure. Vertical displacements were believed to be a simpler performance measure as direct comparisons can be made with design calculations and maintenance guidelines. To avoid the shortcomings of conventional displacement measurement options, this study focuses on using the currently installed accelerometers to estimate the vertical displacements of the southbound bridge. The proposed technique utilizes up-to-date modal parameters within a dual Kalman filter to estimate the vertical displacements of the structure from noisy acceleration measurements. When applied to the I-35W Saint Anthony Falls Bridge, it was found that the dual Kalman filter approach captures only dynamic displacements due to relatively slow loading (e.g., traffic loading and thermal loading) and the corresponding low-frequency static displacements are likely too small for GPS measurements due to the high stiffness of the structure

Ten-Year Review of Monitoring System on I-35W Saint Anthony Falls Bridge

The I-35W St. Anthony Falls bridge was highly instrumented with over 500 sensors to verify design assumptions, serve as a testbed to examine bridge sensing techniques, and evaluate the effectiveness of different bridge monitoring strategies. The instrumentation deployed on the bridge to investigate the structural behavior included vibrating wire strain gages (VWSGs), thermistors, fiber optic sensors (SOFO), resistance strain gages, linear potentiometers, accelerometers, and corrosion monitoring sensors. This report documented the successes and challenges of the monitoring program over the first ten years of the bridge’s life. In particular, the effectiveness of different strain measurement techniques and sensor distributions were addressed. Previous investigations of temperature-dependent and time-dependent behavior were also expanded with the larger data set to better understand the behavior of post-tensioned concrete box girder structures with the potential to impact future designs

Aerodynamics of highway sign structures: from laboratory tests and field monitoring to structural design guidelines

Field- and model-scale experiments were conducted to quantitatively assess the effects of wind loading on Rural Intersection Conflict Warning System (RICWS) highway sign structures. A field-scale RICWS was instrumented with acceleration and linear displacement sensors to monitor unsteady loads, dynamics, and displacement of the sign under various wind events classified by cup and vane wind velocity measurements. To complement the field-scale results, tests on a 1:18-scale model were conducted under controlled laboratory conditions in the St. Anthony Falls Laboratory towing tank and wind tunnel facilities. Aerodynamic effects on the sign structure were identified through analysis of the mean and oscillating drag and lift forces. Vortices periodically shed by the structure induced forces at a frequency governed by the Strouhal number. The shedding frequency overlapped with the estimated natural frequency during strong wind events, leading to possible resonance. Amplified oscillations were additionally observed when the wind direction was parallel to the structure, possibly due to an aeroelastic instability. The findings highlight the relevance of aerodynamic effects on roadside signs or similar complex planar geometries under unsteady wind loading.Heisel, Michael; Daugherty, Carly; Finley, Nicole; Linderman, Lauren; Schillinger, Dominik; French, Catherine E; Guala, Michele. (2020). Aerodynamics of highway sign structures: from laboratory tests and field monitoring to structural design guidelines. Retrieved from the University Digital Conservancy, 10.1061/(ASCE)ST.1943-541X.0002798