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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.

Dynamic Messaging Signs (DMS) and Rural Intersection Conflict Warning Signs (RICWS) are roadside signs that feature much larger and heavier signs than are typically placed on their respective support systems. The excess weight and size of these signs; in conjunction with their breakaway support systems; introduces vibration problems not seen in the past. The AASHTO 2015 LRFD Specification for Structural Supports for Highway Signs; Luminaires; and Traffic Signals (SLTS) does not yet address vibration design for these nontraditional roadside signs. DMS and RICWS were instrumented in the field and numerically modeled to explore their wind-induced behavior. A dynamic numerical model was validated with experimental field data and used to evaluate the fatigue life of the DMS support system instrumented in the field. The resulting fatigue life differed significantly from the equivalent static pressure analysis prescribed in the AASHTO specification. The fatigue life of the DMS instrumented in the field was conservatively estimated to be 23.8 years. Based on data collected from a RICWS instrumented in the field and experiments done on a scaled model of the RICWS at the St. Anthony Falls Laboratory; vortex shedding was identified as the predominant wind phenomena acting on the RICWS structure. Three modifications were proposed to reduce the impacts of vortex shedding. The investigation of these newer sign types highlights the importance of considering the impact of dynamic behavior and vortex shedding on the structural design.

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.

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.

Three 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.