Phase II: Chulitna River Bridge Structurally Health Monitoring

This study is phase 2 of a two phase research project. In Phase 1 a structural health monitoring system (SHMS) was installed on the Chulitna River Bridge. This bridge is 790 feet long, 42 foot 2 inches wide and has 5 spans. As part of that effort, three loaded dump trucks were used to conduct seventeen static and dynamic loadings on the structure. In addition to studying the bridge using SHMS, two ambient free vibration tests were conducted a year apart by. In 1993, the deck on this 1970 five span bridge was widened from 34-feet to a 42 foot 2 inch concrete deck. Increased load was accounted for by strengthening two variable depth exterior girders and converting interior stringers to interior truss girders. Construction documents for the upgrade called for stage construction. At the time of this study, the bridge had five bearings that were not in contact with the superstructure. Feasibility of using Structural Health Monitoring Systems (SHMS) for Alaska Highway Bridges was examined. Also, SHMS data for the load tests of Phase 1 were used to calibrate a three-dimensional model (FEM) to predict response and conduct a 2014 Operating Load Rating.LIST OF FIGURES ....................................................................................................................... iv LIST OF TABLES ........................................................................................................................ vii DISCLAIMER .............................................................................................................................. ix EXECUTIVE SUMMARY............................................................................................................. 1 CHAPTER 1.0 INTRODUCTION................................................................................................. 3 1.1 History .............................................................................................................................. 3 1.2 Bridge Details ................................................................................................................... 3 1.3 Phase 1 Research Study.................................................................................................... 5 1.4 Phase 2 Research Study.................................................................................................... 5 CHAPTER 2.0 LOAD RATING.................................................................................................... 7 2.1 General ............................................................................................................................. 7 2.2 Operating Load Rating ................................................................................................... 10 2.2.1 Investigation with updated calibrated finite element model, FEM (as-is condition) ............................................................................................................................. 11 2.2.2 Model 1 – Four members (A, B, C, and D) removed ............................................. 11 2.2.3 Model 2 – Five members (A, B, C, D, and E) removed ......................................... 11 2.2.4 Other alternative operating load ratings. ................................................................. 12 CHAPTER 3.0 CALIBRATED FINITE ELEMENT MODEL ................................................... 32 CHAPTER 4.0 PROPOSED ALASKA BRIDGE MONITORING SYSTEM ............................ 34 4.1 General ........................................................................................................................... 34 4.2 Selecting SHMS for Alaska ........................................................................................... 35 4.3 New Bridges (Proposed Monitoring Systems) ............................................................... 36 4.4 Existing Bridges (Proposed Monitoring Systems) ......................................................... 36 4.5 All Bridges (Proposed Monitoring Systems) ................................................................. 36 CHAPTER 5.0 CONCLUSIONS................................................................................................. 39 5.1 Phase 1 (Previous Study)................................................................................................ 39 5.1.1 Gravity load testing ................................................................................................. 39 5.1.2 Ambient testing (2012 tests were Phase 1; 2013 tests were Phase 2) ..................... 40 5.2 Phase 2 (Current Study) ................................................................................................. 40 5.2.1 Outcome 1 – Finite element model ......................................................................... 41 5.2.2 Outcome 2 – Structural evaluation and load rating ................................................ 41 5.2.3 Outcome 3 – LRFR HL-93 live load stresses for the critical members .................. 41 APPENDIX A – SIMPLE ACCURACY TEST............................................................................ 44 APPENDIX B – LONGITUDINAL BEHAVIOR TEST ............................................................. 47 APPENDIX C – MODEL IMPROVEMENTS (LONGITUDINAL DIRECTION) .................... 50 APPENDIX D – TRANSVERSE BEHAVIOR PRIOR TO MODEL MODIFICATIONS.......... 52 APPENDIX E – MODEL IMPROVEMENTS (TRANSVERSE DIRECTION)......................... 57 APPENDIX F – CORRELATION BETWEEN CALIBRATED MODEL AND EXPERIMENTAL DATA............................................................................................................. 61 APPENDIX G – CALIBRATED FINITE ELEMENT MODEL ................................................. 63 APPENDIX H – SENSOR LAYOUT .......................................................................................... 66 APPENDIX I – LOAD TESTING................................................................................................ 69 APPENDIX J – A FUTURISTIC APPROACH TO CALIBRATING A FINITE ELEMENT MODEL ........................................................................................................................................ 8

Racking Performance of Long Steel-frame Shear Walls

The response of cold-formed steel-frame shear walls to lateral forces is the focus of the paper. Results are presented for monotonic and cyclic tests of sixteen full-size shear walls with and without openings. Walls of five configurations with sheathing area ratio ranging from 1.0 to 0.3 were tested. The specimens were 12-m (40-ft.) long and 2.4-m (8-ft.) high with 11-mm (7/16-in.) oriented strandboard (OSB) sheathing. One specimen had additional 13-mm (0.5-in.) gypsum wallboard sheathing. All specimens were tested in horizontal position with no dead load applied in the plane of the wall. Resistance of walls was compared with predictions of the perforated shear wall design method. During monotonic and cyclic tests, steel-frame walls failed in a stepwise manner due to bending of framing elements and head pull-through of sheathing screws. No fatigue of mechanical connections was observed. Cyclic loading did not affect elastic performance of the walls but significantly reduced their deformation capacity. Fully-sheathed walls were significantly stiffer and stronger but significantly less ductile than walls with openings. Gypsum sheathing was additive to the stiffness and strength of fully-sheathed walls during monotonic tests. Predictions of the perforated shear wall method appeared to be conservative at all levels of loading when overturning anchors are present at the ends of the wall specimen

Window Characterization at 1550 nm

Author Institution: Los Alamos National LaboratoryAuthor Institution: Sandia National LaboratoriesSlides presented at the Heterodyne Velocimeter Workshop held at Lawrence Livermore National Laboratory, Livermore, California, July 20-21, 2006

Response Analysis of Wood Structures Under Natural Hazard Dynamic Loads

The basic requirements needed for response analysis of wood structures against natural hazards are reviewed. A method for stochastic dynamic analysis of wood structures, which allows investigations into their performance and safety under natural hazards such as earthquakes and severe winds, is presented. To illustrate the method, earthquake ground motions are modeled as a stochastic process with Gaussian white noise properties. A single-degree-of-freedom wood structural system is modeled by a hysteretic constitutive law that produces a smoothly varying hysteresis. It models previously observed behavior of wood joints and structural systems, namely, (1) nonlinear, inelastic behavior, (2) stiffness degradation, (3) strength degradation, and (4) pinching. The constitutive law takes into account the experimentally observed dependence of wood joints' response to the input and response at an earlier time (known as memory). Hysteresis shapes produced by the proposed model compare favorably with common wood joints. The hysteresis model can produce a wide variety of hysteresis shapes, degradations, and pinching behavior to model a whole gamut of possible combinations of materials and joint configurations in wood construction. The nonstationary response statistics of a single-degree-of-freedom wood building subjected to white noise excitations are obtained by Monte Carlo simulation and stochastic equivalent linearization. The latter is shown to give a reasonably accurate prediction of the system's response statistics, which may be used in calculating design response values. The method of analysis is general and may be used to study the response of various kinds of structural systems, including multi-degree-of-freedom systems, as long as appropriate structural models are available and appropriate hysteresis model parameters for these systems are known

Trajectories through semantic spaces in schizophrenia and the relationship to ripple bursts

Human cognition is underpinned by structured internal representations that encode relationships between entities in the world (cognitive maps). Clinical features of schizophrenia-from thought disorder to delusions-are proposed to reflect disorganization in such conceptual representations. Schizophrenia is also linked to abnormalities in neural processes that support cognitive map representations, including hippocampal replay and high-frequency ripple oscillations. Here, we report a computational assay of semantically guided conceptual sampling and exploit this to test a hypothesis that people with schizophrenia (PScz) exhibit abnormalities in semantically guided cognition that relate to hippocampal replay and ripples. Fifty-two participants [26 PScz (13 unmedicated) and 26 age-, gender-, and intelligence quotient (IQ)-matched nonclinical controls] completed a category- and letter-verbal fluency task, followed by a magnetoencephalography (MEG) scan involving a separate sequence-learning task. We used a pretrained word embedding model of semantic similarity, coupled to a computational model of word selection, to quantify the degree to which each participant's verbal behavior was guided by semantic similarity. Using MEG, we indexed neural replay and ripple power in a post-task rest session. Across all participants, word selection was strongly influenced by semantic similarity. The strength of this influence showed sensitivity to task demands (category > letter fluency) and predicted performance. In line with our hypothesis, the influence of semantic similarity on behavior was reduced in schizophrenia relative to controls, predicted negative psychotic symptoms, and correlated with an MEG signature of hippocampal ripple power (but not replay). The findings bridge a gap between phenomenological and neurocomputational accounts of schizophrenia

Distinct replay signatures for prospective decision-making and memory preservation

Theories of neural replay propose that it supports a range of functions, most prominently planning and memory consolidation. Here, we test the hypothesis that distinct signatures of replay in the same task are related to model-based decision-making (“planning”) and memory preservation. We designed a reward learning task wherein participants utilized structure knowledge for model-based evaluation, while at the same time had to maintain knowledge of two independent and randomly alternating task environments. Using magnetoencephalography and multivariate analysis, we first identified temporally compressed sequential reactivation, or replay, both prior to choice and following reward feedback. Before choice, prospective replay strength was enhanced for the current task-relevant environment when a model-based planning strategy was beneficial. Following reward receipt, and consistent with a memory preservation role, replay for the alternative distal task environment was enhanced as a function of decreasing recency of experience with that environment. Critically, these planning and memory preservation relationships were selective to pre-choice and post-feedback periods, respectively. Our results provide support for key theoretical proposals regarding the functional role of replay and demonstrate that the relative strength of planning and memory-related signals are modulated by ongoing computational and task demands

Modelling the enigmatic Late Pliocene Glacial Event: Marine Isotope Stage M2

The Pliocene Epoch (5.2 to 2.58Ma) has often been targeted to investigate the nature ofwarmclimates. However, climate records for the Pliocene exhibit significant variability and show intervals that apparently experienced a cooler than modern climate. Marine Isotope Stage (MIS) M2 (~3.3 Ma) is a globally recognisable cooling event that disturbs an otherwise relatively (compared to present-day) warm background climate state. It remains unclear whether this event corresponds to significant ice sheet build-up in the Northern and Southern Hemisphere. Estimates of sea level for this interval vary, and range from modern values to estimates of 65 m sea level fall with respect to present day. Here we implement plausibleM2 ice sheet configurations into a coupled atmosphere–ocean climate model to test the hypothesis that larger-than-modern ice sheet configurations may have existed at M2. Climate model results are compared with proxy climate data available for M2 to assess the plausibility of each ice sheet configuration. Whilst the outcomes of our data/model comparisons are not in all cases straight forward to interpret, there is little indication that results from model simulations in which significant ice masses have been prescribed in the Northern Hemisphere are incompatible with proxy data from the North Atlantic, Northeast Arctic Russia, North Africa and the Southern Ocean. Therefore, our model results do not preclude thepossibilityof the existenceof larger icemasses duringM2 in the Northern or SouthernHemisphere. Specifically they are not able to discount the possibility of significant icemasses in the Northern Hemisphere during the M2 event, consistent with a global sea-level fall of between 40 m and 60 m. This study highlights the general need for more focused and coordinated data generation in the future to improve the coverage and consistency in proxy records for M2, which will allow these and future M2 sensitivity tests to be interrogated further

Large-scale features of Pliocene climate: results from the Pliocene Model Intercomparison Project

Climate and environments of the mid-Pliocene warm period (3.264 to 3.025 Ma) have been extensively studied. Whilst numerical models have shed light on the nature of climate at the time, uncertainties in their predictions have not been systematically examined. The Pliocene Model Intercomparison Project quantifies uncertainties in model outputs through a coordinated multi-model and multi-model/data intercomparison. Whilst commonalities in model outputs for the Pliocene are clearly evident, we show substantial variation in the sensitivity of models to the implementation of Pliocene boundary conditions. Models appear able to reproduce many regional changes in temperature reconstructed from geological proxies. However, data/model comparison highlights that models potentially underestimate polar amplification. To assert this conclusion with greater confidence, limitations in the time-averaged proxy data currently available must be addressed. Furthermore, sensitivity tests exploring the known unknowns in modelling Pliocene climate specifically relevant to the high latitudes are essential (e.g. palaeogeography, gateways, orbital forcing and trace gasses). Estimates of longer-term sensitivity to CO2 (also known as Earth System Sensitivity; ESS), support previous work suggesting that ESS is greater than Climate Sensitivity (CS), and suggest that the ratio of ESS to CS is between 1 and 2, with a "best" estimate of 1.5

Electrical Anomalies Observed During DC3

The primary scientific goals of DC3 involved improving our understanding of the chemical impacts of thunderstorms and their anvils. However, the Colorado domain provided opportunities to study other interesting phenomena, including the potential impacts of smoke ingestion on convection and thunderstorms, electrification processes in smoke plumes and pyrocumulonimbus clouds, and the production of sprites by unconventional thunderstorm