Experimental study of transition junctions in elevated steel silos

2004-2005 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Characteristics of wind pressures on large cantilevered roofs: Effect of roof inclination

Wind pressure distributions on both surfaces of a cantilevered roof are measured on a wind tunnel model. The investigation covers a down-sloping roof configuration at -5° roof angle and two up-sloping roof configurations of roof angles 5° and 10°. The results supplement an earlier study made on a horizontal roof. The wind pressure pattern on the upper surface of an up-sloping roof suggests that there exists a preferred mode of flow separation on that surface. The pattern shows two localized regions of high suction, which are separately located towards the two ends of the roof span. On the up-sloping roofs, this pressure pattern is observed in the time-averaged mean distribution as well as during the occurrence instant of a peak total uplifting force on the roof. On the horizontal roof, this particular pattern of flow separation is not obviously observed in the time-averaged mean wind pressure pattern but is revealed by the conditional sampling technique which captures the wind pressure distribution during the generation of a peak uplifting force on the roof. The wind pressure signals are analysed to study the characteristics of the total wind force on the roof and also the wind forces on individual roof surfaces. © 2002 Elsevier Science Ltd. All rights reserved.postprin

Structural behavior and design of large steel silos

2001-2002 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Occurence of peak lifting actions on a large horizontal cantilevered roof

Wind tunnel tests are performed on a rigid model of a horizontal grandstand roof. The objective is to investigate the generation mechanism of wind pressure and peak lifting actions on a large cantilevered roof. The roof model is 780 mm wide, 150 mm deep and is equipped with 78 pairs of pressure taps covering both roof surfaces. With an electronic pressure scanning system, wind pressures at these 156 taps are measured in a near-simultaneous manner. Time histories of the wind forces on both roof surfaces and of the net wind force on the entire roof are obtained from the simultaneous pressure signals. These force signals are analyzed statistically to investigate the mechanism of peak lift forces. The conditional sampling technique is used to extract the wind pressure pattern on the lower and upper roof surfaces when a large total uplift is occurring on the roof. It is found that the occurences of peak lift and peak moments on the roof are connected with large lifting actions on both roof surfaces. Differences between the conditionally sampled pressure pattern and the time-averaged mean pressure pattern are observed and discussed. A study is made on the overestimation of net roof pressure if it is assumed to be the worst combination of peak pressures simultaneously occuring on both roof surfaces. © 2002 Elsevier Science Ltd. All rights reserved.postprin

Wind-induced loading and dynamic responses of a row of tall buildings under strong interference

This paper studies wind-induced interference effects on a row of five square-plan tall buildings arranged in close proximity. Mean and fluctuating wind loads are measured on each building member and wind-induced dynamic responses of the building are estimated with the high-frequency force-balance technique. The modifications of building responses from interference over a practical range of reduced velocities are represented by an envelope interference factor. Wind tunnel experiments and response analysis are carried out under all possible angles of wind incidence, at four different building separation distances, and for two arrangement patterns of buildings in the row, that is the parallel and diamond patterns. It is found that building interference leads to amplified dynamic responses in many cases but reduction in responses also occurs at some wind incidence. For a building row of the parallel pattern, five distinct wind incidence sectors of different levels and mechanisms of interference effect can be identified. The largest values of envelope interference factors can reach 2.4 for the torsional responses. When the row of tall buildings is arranged in the diamond pattern, increase in wind excitation occurs at many wind angles due to a "wind catchment" effect. The interference factors have larger peak values, reaching 2.1 in the sway directions and above 4 in torsion. However, all large amplifications of building responses do not occur in the situations of peak resonant dynamic responses of the single isolated building. Thus, the design values of peak dynamic responses of a tall building are not significantly magnified when placed in a row. © 2011 Elsevier Ltd.postprin

Stability design rules for transition ringbeams in steel silos

2000-2001 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Robust optimization of multilayer conductors of HTS AC cable using PSO and perturbation analysis

For a High Temperature Superconducting (HTS) cable, a non-uniform AC current distribution among the multilayer conductors gives rise to increased AC losses. To get a uniform current distribution among the multilayer conductors, a constrained optimization model is constructed with continuous and discrete variables, such as the winding angle, radius and the winding direction of each layer. Under the constraints of the mechanical properties and critical current of the tape, the Particle Swarm Optimization (PSO) algorithm is employed for structural parameter optimization in both warm and cold dielectric type HTS cables. A uniform current distribution among layers is realized by optimizing the structural parameters. The perturbation analysis is employed to evaluate the parameters after optimization. It is found that the robust stabilizations are different among the various optimal results. The PSO is proved to be a more powerful tool than the Genetic Algorithm (GA) for structural parameter optimization. © 2006 IEEE

Transient simulation and analysis for saturated core high temperature superconducting fault current limiter

In this paper, the transient performance of a magnetic core fault current limiter (FCL) saturated by high temperature superconducting (HTS) dc bias winding is investigated by using both 3-D field-circuit coupled simulation and magnetic circuit analysis. A high voltage is induced on the dc HTS winding during the fault current state. The induced voltage is computed and a short circuit coil for the reduction of induced voltage is studied. The numerical computations are verified by the experiment results on an FCL prototype. © 2007 IEEE