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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Wind and Structures
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Volume 4, Issue 6 - Dec 2001
Volume 4, Issue 5 - Oct 2001
Volume 4, Issue 4 - Aug 2001
Volume 4, Issue 3 - Jun 2001
Volume 4, Issue 2 - Apr 2001
Volume 4, Issue 1 - Feb 2001
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A deformable section model for the dynamics of suspension bridges -Part I : Model and linear response
Sepe, Vincenzo ; Augusti, Giuliano ;
Wind and Structures, volume 4, issue 1, 2001, Pages 1~18
DOI : 10.12989/was.2001.4.1.001
The classical two-degree-of-freedom (2-d-o-f) "sectional model" is currently used to study the dynamics of suspension bridges. Taking into account the first pair of vertical and torsional modes of the bridge, it describes well global oscillations caused by wind actions on the deck and yields very useful information on the overall behaviour and the aerodynamic and aeroelastic response, but does not consider relative oscillation between main cables and deck. The possibility of taking into account these relative oscillations, that can become significant for very long span bridges, is the main purpose of the 4-d-o-f model, proposed by the Authors in previous papers and fully developed here. Longitudinal deformability of the hangers (assumed linear elastic in tension and unable to react in compression) and external loading on the cables are taken into account: thus not only global oscillations, but also relative oscillations between cables and deck can be described. When the hangers go slack, large nonlinear oscillations are possible; if the hangers remain taut, the oscillations are small and essentially linear. This paper describes the model proposed for small and large oscillations, and investigates in detail the limit condition for linear response under harmonic actions on the cables (e.g., like those that could be generated by vortex shedding). These results are sufficient to state that, with geometric and mechanical parameters in a range corresponding to realistic cases of large span suspension bridges, large relative oscillations between main cables and deck cannot be excluded, and therefore should not be neglected in the design. Forthcoming papers will investigate more general cases of loading and dynamic response of the model.
On the use of tuned mass dampers to suppress vortex shedding induced vibrations
Strommen, Einar ; Hjorth-Hansen, Erik ;
Wind and Structures, volume 4, issue 1, 2001, Pages 19~30
DOI : 10.12989/was.2001.4.1.019
This paper concerns computational response predictions when a tuned mass damper is intended to be used for the suppression of vortex shedding induced vibrations of e.g., a bridge deck. A general frequency domain theory is presented and its application is exemplified on a suspension bridge (where vortex shedding vibrations have been observed and where such an installation is a possible solution). Relevant load data are taken from previous wind tunnel tests. In particular, the displacement response statistics of the tuned mass damper as well as the bridge deck are obtained from time domain simulations, showing that after the installation of a TMD peak factors between three and four should be expected.
Modelling the dispersion of a tracer gas in the wake of an isolated low-rise building
Quinn, A.D. ; Wilson, M. ; Reynolds, A.M. ; Couling, S.B. ; Hoxey, R.P. ;
Wind and Structures, volume 4, issue 1, 2001, Pages 31~44
DOI : 10.12989/was.2001.4.1.031
Mean concentrations of ammonia gas released as a tracer from an isolated low-rise building have been measured and predicted. Predictions were calculated using computational fluid dynamics (CFD) and two dispersion models: a diffusion model and a Lagrangian particle tracking technique. Explicit account was taken of the natural variation of wind direction by a technique based on the weighted summation of individual steady state wind direction results according to the probability density function of the wind direction. The results indicated that at distances >3 building heights downstream the weighted predictions from either model are satisfactory but that in the near wake the diffusion model is less successful. Weighted solutions give significantly improved predictions over unweighted results. Lack of plume spread is identified as the main cause of inaccuracies in predictions and this is linked to inadequate resolution of flow features and mixing in the CFD model. Further work on non-steady state simulation of wake flows for dispersion studies is recommended.
Unbalanced wind buffeting effects on bridges during double cantilever erection stages
Mendes, Pedro A. ; Branco, Fernando A. ;
Wind and Structures, volume 4, issue 1, 2001, Pages 45~62
DOI : 10.12989/was.2001.4.1.045
This paper is focused on the torsional effects that are induced on bridge piers by unbalanced wind buffeting on the deck during double cantilever erection stages. The case of decks with variable cross section is considered in particular as this characteristic is typical of most frame bridges that are built by the cantilever method. The procedure outlined in the paper is basically an application of the method that Dyrbye and Hansen (1996) have illustrated for decks with constant cross section. This format was chosen because it is suitable for design purposes and may easily be implemented in structural codes. As a complement, the correspondence with the format that is adopted in the Canadian code (NBCC 1990) for the gust factor is established, which might be useful to bridge designers used to the North-American approach to the gust effects on structures. Only alongwind turbulence and horizontal movements of the deck are considered. The combination of torsional and bending effects is also discussed and it is illustrated with an example of application.
Experimental test on bridge jointed twin-towered buildings to stochastic wind loads
Ni, Z.H. ; He, C.K. ; Xie, Z.N. ; Shi, B.Q. ; Chen, D.J. ;
Wind and Structures, volume 4, issue 1, 2001, Pages 63~72
DOI : 10.12989/was.2001.4.1.063
This paper presents results of a study on wind loads and wind induced dynamic response of bridge jointed twin-towered buildings. Utilizing the high-frequency force balance technique, the drag and moment coefficients measured in wind tunnel tests, and the maximum acceleration rms values on the top floor of towers, are analyzed to examine the influence of building`s plan shapes and of intervals between towers. The alongwind, acrosswind and torsional modal force spectra are investigated for generic bridge jointed twin-towered building models which cover twin squares, twin rhombuses, twin triangles, twin triangles with sharp corners cut off, twin rectangles and individual rectangle with the same outline aspect ratio as the twin rectangles. The analysis of the statistical correlation among three components of the aerodynamic force corroborated that the correlation between acrosswind and torsional forces is significant for bridge jointed twin-towered buildings.
Characteristics of wind loads on roof cladding and fixings
Ginger, J.D. ;
Wind and Structures, volume 4, issue 1, 2001, Pages 73~84
DOI : 10.12989/was.2001.4.1.073
Analysis of pressures measured on the roof of the full-scale Texas Tech building and a 1/50 scale model of a typical house showed that the pressure fluctuations on cladding fastener and cladding-truss connection tributary areas have similar characteristics. The probability density functions of pressure fluctuations on these areas are negatively skewed from Gaussian, with pressure peak factors less than -5.5. The fluctuating pressure energy is mostly contained at full-scale frequencies of up to about 0.6 Hz. Pressure coefficients,
and local pressure factors,
given in the Australian wind load standard AS1170.2 are generally satisfactory, except for some small cladding fastener tributary areas near the edges.