Development of a structural health monitoring system for bridges and components

This dissertation summarizes the development of an autonomous, continuous structural health monitoring (SHM) system that can be used to monitor typical girder bridges. The developed system features two key uses. First, the system can be integrated into an active bridge management system that tracks usage and structural changes. Second, the system helps bridge owners to identify overload occurrence, vehicle collision to the structure, damage and deterioration.;The primary objective of this research was to develop a SHM system that could be used to monitor typical girder bridges for detecting and identifying overload occurrence, vehicle collision to the structure, changes in structural behavior, identification of damage and deterioration, and for tracking usage. These specific needs were established to give owners the tools to better manage bridge assets and were accomplished by completing three distinct work tasks.;The first task involved developing bridge-specific live load structural analysis software, BEC Analysis. Like many analysis software packages, the fundamental algorithm was based upon classic beam theory and the direct stiffness method structural analysis. BEC Analysis can be used for (1) analyzing beams or girders under moving loads, (2) computing absolute maximums in each span or at a specific location, and (3) generating envelopes of maximum moments and strains.;The second task involved developing the field data collection and analysis software that integrates with select data acquisition hardware. The software was designed to automatically collect, process, and evaluate the measured response of a bridge. Its use may allow bridge owners to quantitatively monitor a bridge for potential damage as well as gradual change in behavior. Significant effort was given to developing algorithms that include temperature compensation and fundamental sound data reduction and data mining techniques.;After the development of the SHM system was completed, the system was tested and implemented on a highway bridge to demonstrate and verify its general usage. The system was validated and several observations were given concerning the overall bridge performance during the brief monitoring period

Sustainability of Concrete as A Civil Engineering Material

With increasing concern about the environment, energy consumption, climate change, and depletion of natural resources, the importance of sustainability has become mainstream among engineering and scientific communities. Concrete infrastructure is superbly durable and comes with a myriad of benefits. Yet, the production of concrete is energy intensive and represents a substantial portion of air pollution. Largely due to cement manufacturing, concrete represents 7% of greenhouse gas emissions globally and 1% in the United States. Focusing on sector-specific emissions in the United States., this paper outlines the environmental concerns of concrete production and discusses the forefront of research in reducing these effects including innovations in cement manufacturing, alternative clinker technologies, and carbon capture use and storage. Also discussed are various approaches and efforts in concrete recycling and incorporation of industrial wastes and supplementary cementitious materials into concrete. Finally, this study reviews the role of civil engineering design at various scales in the sustainability of concrete infrastructure

Lexical differentiation in language production and comprehension

This paper presents the results of three experiments that explore the breadth of the relevant discourse context in language production and comprehension. Previous evidence from language production suggests the relevant context is quite broad, based on findings that speakers differentiate new discourse referents from similar referents discussed in past contexts (Van Der Wege, 2009). Experiment 1 replicated and extended this “lexical differentiation” effect by demonstrating that speakers used two different mechanisms, modification, and the use of subordinate level nouns, to differentiate current from past referents. In Experiments 2 and 3, we examine whether addressees expect speakers to differentiate. The results of these experiments showed no evidence of an expectation for differentiation, for either lexically differentiated modified expressions (Experiment 2), nor for subordinate level nouns (Experiment 3). Taken together, the present findings suggest that the breadth of relevant discourse context differs across language production and comprehension. Speakers show more sensitivity to things they have said before, possibly due to better knowledge of the relevant context. In contrast, listeners have the task of inferring what the speaker believes is the relevant context; this inferential process may be more error-prone

Mechanisms of conversation: audience design and memory

It is well established that conversational partners jointly establish brief labels for repeatedly mentioned entities. When speaking to a new partner who is unfamiliar with the labels, speakers use longer expressions to facilitate understanding. How this process of audience design scales up to conversations among three or more individuals is unknown. Further, while memory is thought to play an essential role in audience design, the link between memory for language and language use is not well explored. This dissertation consists of two parts that examine these two issues. In Chapter 2, I propose, and test, potential hypotheses regarding how speakers design referring expressions in multiparty conversation. The results of four experiments help to elucidate the mechanisms that support audience design in multiparty conversation. In Chapter 3, I explore the memory contributions to the referential phenomenon of lexical differentiation, aiming to understand the relationship between memory for discourse referents in dialogue and referential form. The results of three experiments provide insights into how memory for the discourse history guides language use during conversation. Taken together, these findings allow us to better understand the mechanisms of audience design and the interplay between language use and memory in conversation

Room temperature near-ultraviolet emission from In-rich InGaN/GaN multiple quantum wells

We grew In-rich InGaNGaN multiple quantum wells (MQWs) using growth interruption (GI) by metalorganic chemical vapor deposition. The quality of overgrown InGaNGaN QW layers in MQWs was largely affected by the crystalline quality and interfacial abruptness of the underlying QW layer. Introduction of 10 s GI was very effective in improving the crystalline quality and interfacial abruptness of InGaN QW layers, and we grew a ten periods of 1-nm -thick In-rich InGaNGaN MQW with 10 s GI and obtained a strong near-ultraviolet (UV) emission (~390 nm) at room temperature. We believe that use of less than 1-nm -thick In-rich InGaN MQW can be a candidate for near-UV source, which might replace the conventional low-indium content (<10%), thicker InGaN QW layer.open313

Investigation of Field Corrosion Performance and Bond/Development Length of Galvanized Reinforcing Steel

In reinforced concrete systems, ensuring that a good bond between the concrete and the embedded reinforcing steel is critical to long-term structural performance. Without good bond between the two, the system simply cannot behave as intended. The bond strength of reinforcing bars is a complex interaction between localized deformations, chemical adhesion, and other factors. Coating of reinforcing bars, although sometimes debated, has been commonly found to be an effective way to delay the initiation of corrosion in reinforced concrete systems. For many years, the standard practice has been to coat reinforcing steel with an epoxy coating, which provides a barrier between the steel and the corrosive elements of water, air, and chloride ions. Recently, there has been an industry-led effort to use galvanizing to provide the protective barrier commonly provided by traditional epoxy coatings. However, as with any new structural product, questions exist regarding both the structural performance and corrosion resistance of the system. In the fall of 2013, Buchanan County, Iowa constructed a demonstration bridge in which the steel girders and all internal reinforcing steel were galvanized. The work completed in this project sought to understand the structural performance of galvanized reinforcing steel as compared to epoxy-coated steel and to initiate a long-term corrosion monitoring program. This work consisted of a series of controlled laboratory tests and the installation of a corrosion monitoring system that can be observed for years in the future. The results of this work indicate there is no appreciable difference between the bond strength of epoxy-coated reinforcing steel and galvanized reinforcing steel. Although some differences were observed, no notable difference in either peak load, slip, or failure mode could be identified. Additionally, a long-term monitoring system was installed in this Buchanan County bridge and, to date, no corrosion activity has been identified

Synthesis and characterization of Na03RhO206H2O - a semiconductor with a weak ferromagnetic component

We have prepared the oxyhydrate Na03RhO206H2O by extracting Na+ cations from NaRhO2 and intercalating water molecules using an aqueous solution of Na2S2O8. Synchrotron X-ray powder diffraction, thermogravimetric analysis (TGA), and energy-dispersive x-ray analysis (EDX) reveal that a non-stoichiometric Na03(H2O)06 network separates layers of edge-sharing RhO6 octahedra containing Rh3+(4d6, S=0) and Rh4+ (4d5, S=1/2). The resistivities of NaRhO2 and Na03RhO206H2O (T < 300) reveal insulating and semi-conducting behavior with activation gaps of 134 meV and 7.8 meV, respectively. Both Na03RhO206H2O and NaRhO2 show paramagnetism at room temperature, however, the sodium-deficient sample exhibits simultaneously a weak but experimentally reproducible ferromagnetic component. Both samples exhibit a temperature-independent Pauli paramagnetism, for NaRhO2 at T > 50 K and for Na03RhO206H2O at T > 25 K. The relative magnitudes of the temperature-independent magnetic susceptibilities, that of the oxide sample being half that of the oxyhydrate, is consistent with a higher density of thermally accessible electron states at the Fermi level in the hydrated sample. At low temperatures the magnetic moments rise sharply, providing evidence of localized and weakl -ordered electronic spins.Comment: 15 fages 5 figures Solid State Communications in prin

Evaluation of Steel Bridges, Volumes I & II

This report is divided into two volumes. Volume I summarizes a structural health monitoring (SHM) system that was developed for the Iowa DOT to remotely and continuously monitor fatigue critical bridges (FCB) to aid in the detection of crack formation. The developed FCB SHM system enables bridge owners to remotely monitor FCB for gradual or sudden damage formation. The SHM system utilizes fiber bragg grating (FBG) fiber optic sensors (FOSs) to measure strains at critical locations. The strain-based SHM system is trained with measured performance data to identify typical bridge response when subjected to ambient traffic loads, and that knowledge is used to evaluate newly collected data. At specified intervals, the SHM system autonomously generates evaluation reports that summarize the current behavior of the bridge. The evaluation reports are collected and distributed to the bridge owner for interpretation and decision making. This volume (Volume II) summarizes the development and demonstration of an autonomous, continuous SHM system that can be used to monitor typical girder bridges. The developed SHM system can be grouped into two main categories: an office component and a field component. The office component is a structural analysis software program that can be used to generate thresholds which are used for identifying isolated events. The field component includes hardware and field monitoring software which performs data processing and evaluation. The hardware system consists of sensors, data acquisition equipment, and a communication system backbone. The field monitoring software has been developed such that, once started, it will operate autonomously with minimal user interaction. In general, the SHM system features two key uses. First, the system can be integrated into an active bridge management system that tracks usage and structural changes. Second, the system helps owners to identify damage and deterioration

Chromatin and transcriptional signatures for Nodal signaling during endoderm formation in hESCs

AbstractThe first stages of embryonic differentiation are driven by signaling pathways hardwired to induce particular fates. Endoderm commitment is controlled by the TGF-β superfamily member, Nodal, which utilizes the transcription factors, SMAD2/3, SMAD4 and FOXH1, to drive target gene expression. While the role of Nodal is well defined within the context of endoderm commitment, mechanistically it is unknown how this signal interacts with chromatin on a genome wide scale to trigger downstream responses. To elucidate the Nodal transcriptional network that governs endoderm formation, we used ChIP-seq to identify genomic targets for SMAD2/3, SMAD3, SMAD4, FOXH1 and the active and repressive chromatin marks, H3K4me3 and H3K27me3, in human embryonic stem cells (hESCs) and derived endoderm. We demonstrate that while SMAD2/3, SMAD4 and FOXH1 associate with DNA in a highly dynamic fashion, there is an optimal bivalent signature at 32 gene loci for driving endoderm commitment. Initially, this signature is marked by both H3K4me3 and H3K27me3 as a very broad bivalent domain in hESCs. Within the first 24h, SMAD2/3 accumulation coincides with H3K27me3 reduction so that these loci become monovalent marked by H3K4me3. JMJD3, a histone demethylase, is simultaneously recruited to these promoters, suggesting a conservation of mechanism at multiple promoters genome-wide. The correlation between SMAD2/3 binding, monovalent formation and transcriptional activation suggests a mechanism by which SMAD proteins coordinate with chromatin at critical promoters to drive endoderm specification