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Austin, TX, United States

Rendon E.A.,Ensoft Inc. | Manuel L.,University of Texas at Austin
Wind Energy | Year: 2014

Accurate prediction of long-term 'characteristic' loads associated with an ultimate limit state for design of a 5-MW bottom-supported offshore wind turbine is the focus of this study. Specifically, we focus on predicting the long-term fore-aft tower bending moment at the mudline and the out-of-plane bending moment at the blade root of a monopile-supported shallow-water offshore wind turbine. We employ alternative probabilistic predictions of long-term loads using inverse reliability procedures in establishing the characteristic loads for design. Because load variability depends on the environmental conditions (defining the wind speed and wave height), we show that long-term predictions that explicitly account for such load variability are more accurate, especially for environmental states associated with above-rated wind speeds and associated wave heights. Copyright © 2012 John Wiley & Sons, Ltd. Copyright © 2012 John Wiley & Sons, Ltd.

Burkett T.B.,Fugro | Gilbert R.B.,University of Texas at Austin | Simpson R.C.,Loadtest United States | Wooley J.A.,Balcones Geotechnical PLLC | And 2 more authors.
Geotechnical Special Publication | Year: 2015

An investigation into the load-settlement behavior of two drilled shafts, founded in shale, is presented. The motivation for this research is to advance the understanding on how drilled shafts react under loading in stiff clays and shales. The objective of this study is to improve the understanding of axial capacities for rock-socketed shafts in hard clays and shales. In order to achieve this objective, the research team measured the strengths within the subsurface material at the test site, estimated the unit side shear and unit end bearing of the shale-shaft interaction by running two axial load tests using the patented Osterberg-Cell (O-Cell) loading technique, and compared the results to the current design methods that are used to predict the axial capacity of drilled shafts. The results of the study concluded that the current methods for estimating unit end bearing developed by the Texas Department of Transportation (TxDOT) and the Federal Highway Administration (FHWA) provide fairly accurate predictions when compared to the measured information However, it was discovered that the measured ultimate side resistance steadily decreased nearing the tip of the shaft. A limited amount of information is currently available for load tests performed in soils with Texas Cone Penetration (TCP) values harder than 2-in per 100 blows. The results presented herein demonstrate the effectiveness of the current design methods for drilled shafts and the non-uniformity of side resistance within one- to two-diameters of the shaft tip. © ASCE 2015.

Vasquez L.F.G.,Ensoft Inc. | Maniar D.R.,Stress Engineering Inc. | Tassoulas J.L.,University of Texas at Austin
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2010

We outline the development of a computational procedure for finite-element analysis of suction-caisson behavior, highlighting its unique features and capabilities. The procedure is based on a description of clayey soil as a two-phase medium: a water-filled porous solid. Nonlinear behavior of the solid phase is represented by means of a bounding-surface plasticity model. An algorithm is developed for frictional contact in terms of effective normal stress. Furthermore, a special remeshing scheme is introduced facilitating the simulation of the installation process, tracking the caisson penetration path and avoiding numerical complications in the vicinity of the caisson-soil interfaces. To illustrate the use of the proposed computational procedure and examine its validity, complete simulations of available laboratory tests on model suction caissons are conducted. Results are presented and discussed for test-bed preparation (consolidation) followed by caisson installation by self-weight and suction, setup (reconsolidation), and axial pullout. The overall agreement between computations and measurements is good. Possible improvements are identified and recommendations are made regarding future studies. © 2010 ASCE.

Talley K.G.,Texas State University | Arrellaga J.,Ensoft Inc. | Breen J.E.,University of Texas at Austin
Journal of Structural Engineering (United States) | Year: 2014

The research program discussed in this paper included both experimental and computational investigations of structural capacity effects on bridge columns by simulating observed column damage. For the experimental research, scaled models of a column were constructed and fractured using stone-splitting wedges. This method was intended to create the worst-case scenario based on the observed damage in the field: cracks propagating through the core of the columns and effectively cleaving each column into four pieces. The finite-element software ATENA, which models cracking in reinforced concrete, was used for the computational modeling and a parametric study. The computer model was correlated to the experimental results and then used to predict capacities for a variety of deterioration levels. This parametric study was used to determine the critical crack width, which would reduce the capacity of the column to its design load. This predicted critical crack width gives the bridge owner another tool for the evaluation of concrete degradation. This paper focuses on the computational portion of the research. As such, this paper presents a method to mimic existing damage in a finite-element model that the practicing engineer could use in a structural assessment of existing conditions. © 2014 American Society of Civil Engineers.

Han Y.,Fluor Corporation | Wang S.-T.,Ensoft Inc.
Geotechnical Special Publication | Year: 2013

The advances on soil-pile-structure interaction are described in this study. The nonlinearity of soil is accounted for approximately by a boundary zone model, and the curves of stiffness and damping of the nonlinear soil-pile system are provided. The coupled horizontal and rocking vibration of an embedded foundation (including pile cap) is analyzed by four parameters rather than the traditional six parameters. The radiation damping is corrected based on many dynamic tests in the field. The effects of soil-pile-structure interaction on dynamic behaviour are examined based on an engineering case. Three conditions are considered: (1) the soil-pile-structure interaction is accounted for fully; (2) the soil-pile system is flexible, but the structure is assumed to be rigid; and (3) the structure is flexible, but the base foundation is assumed to be rigid. For practical applications, a tower structure supported on piled foundation was examined under seismic loads. The earthquake forces and response were calculated using the time history analysis and response spectrum analysis, and compared with those using the method of equivalent static loads. © 2013 American Society of Civil Engineers.

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