Investigation and Control of VIVs with Multi-Lock-in Regions on Wide Flat Box Girders

On the preliminary designing of a wide flat box girder with the slenderness ratio 12, vertical and torsional vortex-induced vibrations (VIV) are observed in wind tunnel tests. More than one lock-in region, which are defined as “multi-lock-in regions,” are recorded. Therefore, suspicions should be aroused regarding the viewpoint that wide box girders are aerodynamic friendly. As the three nascent vortexes originating at the pedestrian guardrails and inspection rails shed to near-wake through different pathways with different frequencies, the mechanisms of VIVs and multi-lock-in regions are analyzed to be determined by the inappropriate subsidiary structures. A hybrid method combining Large Eddy Simulation (LES) with experimental results is introduced to study the flow-structure interactions (FSI) when undergoing VIVs; the vortex mode of torsional VIV on wide flat box girders is defined as “4/2S,” which is different from any other known ones. Based on the mechanism of VIV, a new approach by increasing ventilation rate of the pedestrian guardrails is proved to be effective in suppressing vertical and torsional VIVs, and it is more feasible than other control schemes. Then, the control mechanisms are deeper investigated by analyzing the evolution of vortex mode and FSI using Hybrid-LES method

Bridge deck aerodynamics: A case study in full-scale

PhD thesis in Mechanical and Structural Engineering and Materials ScienceOne of the key aspects of bridge deck aerodynamics is the transformation of the incident wind flow into fluctuating surface pressures around a bridge deck. The atmospheric turbulence generates fluctuating loads on bridge decks, i.e. the buffeting wind action. The state-of-the-art knowledge about bridge deck aerodynamics, as well as the bases for the design of long-span bridges, relies primarily on wind-tunnel testing. By contrast, full-scale studies concentrating on the surface pressure distributions around bridge girders are rare. The central thrust of this work is to develop an experimental setup to investigate the aerodynamics of a closed-box girder bridge deck in full-scale. A bespoke pressure measuring system is designed and developed to monitor wind-induced surface pressures around three chords of the Lysefjord Bridge in Norway, previously instrumented by a number of wind and vibration sensors. The one- and two-point statistics of the undisturbed turbulence are simultaneously measured, thereby facilitating the study of the spatial structure of the gust loading in the atmosphere. The experimental setup is aided by 3D sonic anemometers placed within the disturbed flow regions, upstream of the bridge deck nose and in the near wake. The overall distortion of the atmospheric turbulence induced by the bridge deck body is examined, as well as the related vortex shedding process. In particular, the flow in the near-wake region of the bridge deck is investigated, in both model- and full-scale. For skewed incident winds, the near-wake flow exhibits highly three-dimensional features, including a significant axial flow on the leeward side of the full-scale bridge deck. Also, the frequency-dependent energy redistribution within the near wake is examined with emphasis on wavelengths associated with the periodic formation of vortex structures. The Strouhal number associated with the deck cross-section studied is found to be similar in both full- and model-scale. The turbulence level in the inflow is found to impact significantly the value of the non-dimensional vortex shedding frequency in full-scale. Specifically, the higher the turbulence intensity, the higher the Strouhal number. Lastly, the “anatomy” of the vortex shedding process is described based on the surface pressure measurements undertaken on the trailing edges of the deck. Investigating the gust loading generation in full-scale is central to this research. Fluctuating drag, lift and twisting moment are estimated on three chord-wise strips, based on a limited number of pressure sensing points. The analysis of the monitored surface pressures underpins the limits of the strip assumption in modelling the correlation along the bridge span of the lift and moment. Specifically, the span-wise coherence of the turbulence-driven lift and moment is observed to be higher than the span-wise coherence of the incident vertical velocity fluctuations. This result, which is deemed original given its full-scale framework, is in an overall agreement with the wind tunnel studies focusing on the gust loading on motionless section models of closedbox girder bridge decks. Also, a pronounced amplification of the vertical velocity fluctuations is observed upstream of the bridge deck nose, thereby providing a link between the undisturbed turbulence and the resulting gust loading on the deck. Keywords: Bridge deck aerodynamics, Full-scale, Wind turbulence, Nearwake flow, Wind buffeting, Surface pressure measurement

Fatigue Resistance and Reliability of High Mast Illumination Poles (HMIPs) with Pre-Existing Cracks: Final Report

0-6829High mast illumination poles (HMIPs) are used throughout Texas and the U.S. to provide lighting along highways and at interchanges. Texas currently has about 5000 HMIPs, varying in height from 100 to 175 ft. Failures of HMIPs have been reported in several states, attributed to failures at the shaft-to-base plate connection. No collapses of HMIPs have been reported in Texas. However, recent studies have shown that many galvanized HMIPs in Texas have pre-existing cracks at their shaft-to-base plate connection, most likely caused by the galvanization process before the poles were placed in service. Previous research has also shown that pre-existing cracks may significantly reduce the fatigue life of galvanized HMIPs. The Texas Department of Transportation (TxDOT) has identified three major issues/concerns with respect to HMIPs with pre-existing cracks: the lack of reliable experimental data about the fatigue life of pre-cracked HMIP base-connection details; the significant uncertainty regarding the natural wind response of HMIPs to the various major wind environments in Texas (much of this uncertainty is related to the lack of measured data from comprehensive field studies); and, due to this lack of data, the \u2018safe/serviceable\u2019 life of in-service TxDOT HMIPs with pre-existing cracks cannot be reliably predicted. The main goal of this research project was to generate data and information to support a probabilistic-based assessment of the remaining life of HMIPs with pre-existing cracks. The research included extensive laboratory fatigue testing of HMIPs with pre-existing cracks, field monitoring of in-service HMIPs at five locations across Texas, and the development of a reliability based framework to assess the safety of in-service HMIPs with pre-existing cracks. The results of this study show a wide range in the predicted lives of HMIPs with pre-existing cracks at different locations throughout the state. Based on a probability of failure of 5 percent, the predicted fatigue life at a number of locations analyzed throughout the state showed predicted lives varying from approximately 30 years to over 300 years. The variation in predicted lives is mainly affected by differing wind characteristics at each location