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Kopp G.A.,University of Western Ontario | Galsworthy J.K.,University of Western States | Galsworthy J.K.,Rowan Williams Davies and Irwin Inc. | Oh J.H.,University of Western Ontario
Journal of Structural Engineering | Year: 2010

Wind tunnel tests of open-frame, low-rise buildings were carried out to determine the drag (base shear) and bracing loads in the direction normal to the frames (parallel to the ridge). In total, 18 configurations were examined in an open country terrain at a scale of 1:100. The worst wind angles for all configurations are between 0°-40° with 20°-30° typically yielding slightly higher loads, 0° being parallel to the ridge. The largest load coefficients are observed for the smallest frame buildings, consistent with observations for enclosed buildings, which is due to three-dimensional (edge) effects. The solidity ratio has a clear effect on the load coefficients with higher coefficients for lower solidity, similar to the behavior observed on lattice frames or trussed towers. However, when these coefficients are multiplied by the solidity ratio, so that they can be directly compared to enclosed building coefficients, it is clear that the total load increases monotonically with solid area. Bracing was observed to take up to 75% of the total drag load. An empirical model was developed for obtaining design loads. © 2010 ASCE. Source

Delgado-Fernandez I.,University of Ulster | Jackson D.W.T.,University of Ulster | Cooper J.A.G.,University of Ulster | Baas A.C.W.,Kings College London | And 2 more authors.
Journal of Coastal Research | Year: 2011

Studies of the role of secondary airflow effects demonstrate the importance of offshore flows in dune growth and maintenance. Turbulent processes at the lee side of aeolian dunes have previously been only qualitatively described. The recent incorporation of ultrasonic anemometers, capable of measuring the three components of the wind vector, allows quantification of flow patterns in complex areas such as the lee side of dunes. This paper presents measurements taken with an array of ultrasonic anemometers during an offshore wind event at Magilligan Point, Northern Ireland, where flow separation and reversal associated to offshore winds has been previously reported. A simple analysis using the raw u and w components of the wind was conducted to extract quantitative information on the location of turbulent zones along a dune-beach profile. Results indicate sharp differences between the relation of u and w with distance downwind from the dune crest, which in turn can be used to identify turbulent zones. Variations in wind velocity and direction at the dune crest did not result in changes in the location of turbulent zones at the beach surface, suggesting that turbulent structures are significantly constant in time. A quantitative model based on actual field data and using previous conceptual descriptions as a guide is presented to identify turbulent zones at the beach surface under offshore winds. Source

Love J.S.,Rowan Williams Davies and Irwin Inc. | Tait M.J.,McMaster University
Journal of Structural Engineering (United States) | Year: 2015

In traditional tuned liquid damper (TLD) installations, TLD tank(s) are tuned to a single optimal frequency as determined by well-known dynamic vibration absorber theory. A multiple tuned liquid damper (MTLD) is created when the sloshing frequencies are distributed over a range near the structural frequency. In this paper, an equivalent mechanical model for a structure-MTLD system is developed. A third-order nonlinear multimodal model is employed to assess nonlinear fluid affects and serve as independent model verification. To the authors' knowledge, this is the first time the nonlinear energy dissipation associated with damping screens and the nonlinear coupling amongst sloshing modes has been considered for MTLD systems. MTLD systems consisting of one (traditional TLD), two, and three tanks are used to reduce the resonant response of a single degree of freedom structure. The MTLD provides structural control that is superior to a traditional TLD. The MTLD is less sensitive to the structural excitation amplitude, which enables the device performance to be maintained at low amplitude excitations associated with common wind events. The MTLD is also shown to be more robust to changes to the structure's natural frequency than the traditional TLD. Since many TLD installations require multiple tanks to satisfy space restrictions, the findings of this paper are highly relevant to structural engineering. This paper shows that by slightly altering the fluid depth of each tank, improved structural control performance can be achieved at little additional cost. © 2015 American Society of Civil Engineers. Source

Mara T.G.,University of Western Ontario | Hong H.P.,University of Western Ontario | Lee C.S.,University of Western Ontario | Lee C.S.,Rowan Williams Davies and Irwin Inc. | Ho T.C.E.,University of Western Ontario
Wind and Structures, An International Journal | Year: 2016

The wind velocity profile over the height of a structure in high intensity wind (HIW) events, such as downbursts, differs from that associated with atmospheric boundary layer (ABL) winds. Current design codes for lattice transmission structures contain only limited advice on the treatment of HIW effects, and structural design is carried out using wind loadprofiles and response factors derived for ABL winds. The present study assesses the load-deformation curve (capacity curve) of a transmission tower under modeled downburst wind loading, and compares it with that obtained for an ABL wind loading profile. The analysis considers nonlinear inelastic response under simulated downburst wind fields. The capacity curve is represented using the relationship between the base shear and the maximum tip displacement. The results indicate that the capacity curve remainsrelatively consistent between different downburst scenarios and an ABL loading profile. The use of the capacity curve avoids the difficulty associated with defining a reference wind speed and corresponding wind profile that are adequate and applicable fordownburst and ABL winds, thereby allowing a direct comparison of response under synoptic and downburst events. Uncertainty propagation analysis is carried out to evaluate the tower capacity by considering the uncertainty in material properties and geometric variables. The results indicated the coefficient of variation of the tower capacity is small compared to those associated with extreme wind speeds. Copyright © 2016 Techno-Press, Ltd. Source

Tajima Y.,University of Tokyo | Yasuda T.,Kyoto University | Pacheco B.M.,University of the Philippines at Diliman | Cruz E.C.,University of the Philippines at Diliman | And 10 more authors.
Coastal Engineering Journal | Year: 2014

Japan Society of Civil Engineers (JSCE) and Philippine Institute of Civil Engineers (PICE) jointly collaborated to carry out the field survey on severe storm surge disasters caused by Typhoon Haiyan/Yolanda from 12 December to 16 December, 2013 in Leyte and Samar. Based on interviews with local residents, the joint survey team obtained measured inundation and run-up heights at almost 80 different locations along the coast and also at more than 70 locations inside the cities of Tacloban and Palo. Clear contrast of inundation characteristics was observed especially among east coast of Eastern Samar, inner and southern parts of San Pedro Bay. While inner part of San Pedro bay, as was expected, showed relatively high inundation heights, east coast of Leyte also had comparably high inundation heights even outside the San Pedro Bay. It should also be highlighted that surprisingly high inundation heights were observed along the east coast of Eastern Samar, which faces to the Pacific Ocean with deep Philippine Trench. This paper aims to report primary results obtained through the first joint field survey of JSCE and PICE. © 2014 World Scientific Publishing Company and Japan Society of Civil Engineers. Source

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