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Hansen R.C.,Consulting Engineer
Antem 2002 - International Symposium on Antenna Technology and Applied Electromagnetics, Conference Proceedings | Year: 2017

Scan Element Pattern, SEP, (formerly active element pattern1) was developed circa 1960 by Allen [1], Oliner [2], Hannan [3], Stark [4], and others, to provide phased array gain behavior versus scan angles. It's utility for decades has been to give insight and results on the scan performance of various elements and lattices. A common measurement procedure terminates all elements in the array, with the excited center element connected to a gain measurement setup. As early as the Lincoln Lab reports [1] it was recognized that the impedance seen in the measurement procedure was not the Scan Impedance (SI), (impedance seen when all elements are excited with the proper amplitude and phase), due to the passive mutual couplings. In Allen's derivation the textbook definition of gain was used; Scan Impedance mismatch was not included. Hannan did include mismatch, but his formulas were based on 'intuitive reasoning'. Clearly his SEP proportional to cos θ is only approximate; it fails for large scan angles. Allen derives SEP for the center element excited case under the assumption that the isolated element pattern is equal to the element pattern in the array with all elements terminated. With this assumption it can be shown that transmit SEP (single element excited) equals receive SEP, with impedance determined in both cases with all elements excited. For single mode elements such as dipoles this assumption is very good; almost nothing will affect the shape of current on a thin dipole. However for more complex elements the element pattern with other elements terminated is not equal to the isolated element pattern. © 2002 ANTEM.

Thompson M.K.,KAIST | Thompson J.M.,Consulting Engineer
Scanning | Year: 2010

This work discusses some of the benefits, techniques, challenges, and considerations associated with the incorporation of measured surfaces in finite element (FE) models including how much surface data to measure and import into the model, the shape of the surface geometry to create, the presence and effect of surface layers and impurities, the required mesh density for rough surfaces, the nature of the element formulations and material properties at small length scales, the differences between measurement and FE coordinate systems, the limitations and idealizations of the FE method, issues associated with boundary conditions and their ability to impose or prevent conformal contact, and issues associated with the size of the pinball region and the contact stiffness relative to the nature of the surface. It also describes some current and future research directions that can be used to validate and expand existing techniques and to improve our understanding of surface phenomena. © 2010 Wiley Periodicals, Inc.

Efraimiadou S.,Consulting Engineer | Hatzigeorgiou G.D.,Democritus University of Thrace | Beskos D.E.,University of Patras | Beskos D.E.,Academy of Athens
Earthquake Engineering and Structural Dynamics | Year: 2013

The effect of collision between adjacent reinforced concrete building frames under multiple earthquakes is investigated in this paper. The four planar frames and the nine different pairs of adjacent reinforced concrete structures of the first companion paper are also examined here, under five real seismic sequences. Such a sequence of earthquakes results in a significant damage accumulation in a structure because any rehabilitation action between any two successive seismic motions cannot be practically materialised because of lack of time. Various parameters are investigated, such as the maximum horizontal displacement of top floor, ductility of columns, permanent displacements and so on. Furthermore, four different separation gaps between the building frames are considered to determine their influence on the behaviour of these frames. It is concluded that in most of the cases, the seismic sequences appear to be detrimental in comparison with the single seismic events. © 2013 John Wiley & Sons, Ltd.

Efraimiadou S.,Consulting Engineer | Hatzigeorgiou G.D.,Democritus University of Thrace | Beskos D.E.,University of Patras | Beskos D.E.,Academy of Athens
Earthquake Engineering and Structural Dynamics | Year: 2013

The effect of different structures configurations on the collision between adjacent planar RC building frames subjected to strong earthquakes is examined in this paper. Two 5-storey and two 8-storey frames, regular or with setbacks, are combined together to produce nine different pairs of adjacent RC structures. These pairs of buildings are subjected to six strong ground motions that are absolutely compatible with the design process. Various parameters are investigated such as maximum displacements, permanent displacements, members' ductility and internal forces and interstorey drift ratios. It is concluded that the effect of collision of adjacent frames seems to be unfavourable for most of the cases and, therefore, the structural pounding phenomenon is rather detrimental than beneficial. © 2013 John Wiley & Sons, Ltd.

Hatzigeorgiou G.D.,Democritus University of Thrace | Kanapitsas G.,Consulting Engineer
Earthquake Engineering and Structural Dynamics | Year: 2013

SUMMARY: Fundamental period of vibration appears to be one of the most critical parameter for the seismic design of buildings because this period strongly affects the magnitude of seismic forces. In this paper, an empirical formula for estimating the fundamental period of reinforced concrete structures is recommended, on the basis of the vibration analysis of 20 different real building configurations. These structures have already been constructed in Greece, and they are analyzed by using in detail 3-D finite element models and modal eigenvalue analysis. These models take into account the presence of external and internal infill walls, which are usually ignored as nonstructural elements. This neglect leads to unreliable evaluation of period because the infill walls' contribution to the lateral stiffness and therefore to the fundamental period of vibration is also ignored. Furthermore, taking into account that the flexibility of soil elongates the fundamental period, the soil-structure interaction effect is also considered. To achieve a unique, simple, and effective empirical expression for the fundamental period of vibration, a comprehensive nonlinear regression analysis is applied for the datasets of buildings under consideration. This empirical expression is also compared with the similar expressions from the pertinent literature. © 2013 John Wiley & Sons, Ltd.

Warner J.,Consulting Engineer
Geotechnical Special Publication | Year: 2012

Faulty concrete in a new 3-meter- (10-foot-) thick, heavily reinforced foundation for a power plant required construction to stop. Pressure grouting was selected as the most effective remedial method as appropriate grout hole testing could supplement the investigation findings and, if systematically performed, both identify the faulty conditions and verify their correction. A regular grid of grout holes was drilled, pressure tested, and categorized for further treatment. Depending upon the water test results, the holes were pressure grouted, vacuum grouted, or simply tremie filled with a pre-blended ultrafine cementitious grout. Secondary and tertiary holes were added to the work where behavior of the primary holes left doubt as to the resulting conditions. The repaired foundation was accepted by the design engineer and owner, after virtual no-take in successive grout holes and further verification core holes indicated all substantial voids had been filled. © 2012 American Society of Civil Engineers.

Cox D.W.,Consulting Engineer
Geotechnical Engineering for Infrastructure and Development - Proceedings of the XVI European Conference on Soil Mechanics and Geotechnical Engineering, ECSMGE 2015 | Year: 2015

Precise videogrammetry is a survey and monitoring technique for recording the precise position and movement of multiple points on structures in the short or long term. One or more video cameras are mounted on survey instruments, recording through the lens along a precisely known optical axis defined by the cross hairs. The results are merged in real time. The simplest and most effective applications are in levelling and verticality but any instrument gauge result can be recorded optically and there have been wide applications. Targets are not generally required and distant or remote points can be recorded without access. The accuracy is that of the instruments used, with enhancement depending on the optical or electronic magnification. The methods and some typical case histories are described, including 10 years monitoring of subsidence failure, 3D dynamic load deflection measurements for a large travelling crane, and a level survey before tunneling under a London terminus. © The authors and ICE Publishing: All rights reserved, 2015.

Belletti B.,University of Parma | Damoni C.,University of Parma | Gasperi A.,Consulting Engineer
Engineering Structures | Year: 2013

In the current paper the seismic performance of a regular multi-storey precast reinforced concrete structural wall building vertically connected with ordinary reinforcement is investigated. The structural walls have different cross section shapes (rectangular, "U", "L" and "C"). Some of the construction details of the structural joints connecting the precast walls horizontally and vertically are briefly described. Different modeling approaches for pushover analyses, from lower to higher levels of accuracy, have been applied in order to investigate the applicability of the calculation methods adopted to the study of buildings having non-rectangular structural walls. In particular the building has been analyzed with a shell model, implemented by the authors and denoted PARC model, a fiber-element model and a lumped-plasticity model, implemented by the authors and denoted LPA. The results obtained with the three models in terms of seismic response of the building proved to be consistent to each other. Hence, for this particular case, the lumped plasticity model presented, that can be simply applicable in the daily design practice, gave reliable results. © 2013 Elsevier Ltd.

Rhodes C.W.,Consulting Engineer
IEEE Transactions on Consumer Electronics | Year: 2010

Interference to DTV reception from signals in the 88-108 MHz FM broadcast band has been observed since the end of analog TV broadcasting in June, 2009. This interference is generated in the front-end (tuner) of the affected receiver. This paper describes the non-linear mechanisms in the receiver by which FMI to DTV reception takes place. The author has tested 15 models of NTIA approved DTV down-converters measuring the increase in DTV received signal power required as a function of the power of local offair FM signals in his laboratory. He has also tested "amplified indoor antennas" and found their performance was seriously impaired by FMI. This work was carried out as unsponsored research1. © 2006 IEEE.

Nazir C.P.,Consulting Engineer
Renewable and Sustainable Energy Reviews | Year: 2014

In a world where fossil fuel prices are subject to steep price hikes and where green house emissions are endangering the planet, dependence on non-renewable energy sources becomes more urgent. In this paper a technical feasibility and economic viability study of a new technology that utilizes hydroelectric power to tap the oceans enormous energy reserve is presented. Called the Offshore Hydroelectric Plant, such an installation has an underwater powerhouse, the water from the turbines being discharged into a tail race sump (TRS). Power is generated when suitable head is created between the TRS and the sea, by leading the water out and allowing it to flow into giant troughs located in a vertical elevator building. Here, hoists raise the troughs carrying the excess water and empty them into an overhead tank (OHT). Water from the OHT is carried by penstocks to another powerhouse located at sea level. The plant utilizes the existing technologies of tidal plants, vertical ship lifts, and pumped storage schemes. Well-developed technologies of the offshore oil industry are utilized in fabricating the structures on shore, and towing them to location. An example demonstrates that a 104 MW plant could produce 569 GWh annually. Project investment costs are approximately $ 432 million and Levelized Electricity Costs $0.055/kWh. © 2014 Elsevier Ltd.

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