Abstract
A finite element aerodynamic model that can be used to analyse flutter instability of long span bridges in the time domain is presented. This approach adopts a simplified quasi-steady formulation of the wind forces neglecting the vortex shedding effects. The governing equations used are effective only for reduced velocities V* sufficiently great: this is generally acceptable for long-span suspension bridges and, then, the dependence of the wind forces expressions of the flutter derivatives can be neglected. The procedure describes the mechanical response in an accurate way, taking into account the non-linear geometry effects (large displacements and large strains) and considering also the compressed locked coil strands instability. The time-dependence of the inertia force due to fluid structure interaction is not considered. The numerical examples are performed on the three-dimensional finite element model of the Great Belt East Bridge (DK). A mode frequency analysis is carried out to validate the model and the results showrngood agreement with the experimental measurements of the full bridge aeroelastic model in the wind tunnel tests. Significant parameters affecting bridge response are introduced and accurately investigated.rnrn
Key Words
flutter; FEM; aerodynamic.
Address
Universita di Padova, Padova, ItalyrnLADSEB-CNR Padova, Italy
Abstract
Seven hip roof building models for 10o, 15o, 20o, 25o, 30o, 35o and 40o roof pitch with large overhangs of 1.1 m were tested in a wind tunnel at the university of Roorkee, India to investigate wind pressure distributions over hip roofs for various roof pitch and wind direction. The results show that the roof pitch and wind direction do significantly affect the magnitude and distribution of the roof pressures. The 40o roof pitch has been found to experience the highest peak suctions at the roof corners amongst the seven hip roofs tested. Pressures on 15o, 20o and 30o hip roofs are comparable with those reported by Xu and Reardon (1998). Meecham et al. (1991) for 18.4o hip roof is compatible with 15o hip roof of the present study. Holmes
Key Words
low-rise building; hip roof; TTU building; gable roof; pressure coefficients
Address
Department of Civil Engineering, Aligarh Muslim University, Aligarh, IndiarnDepartment of Civil Engineering, University of Roorkee, Roorkee, India
Abstract
The wind flow over two-dimensional sinusoidal hilly obstacles with slope (the ratio of height to half width) of 0.5 has been investigated experimentally and numerically. Experiments for single and double sinusoidal hill models were carried out in a subsonic wind tunnel. The mean velocity profiles, turbulence statistics, and surface pressure distributions were measured at the Reynolds number based on the obstacle height(h=40 mm) of 2.6 104. The reattachment points behind the obstacles were determined using the oil-ink dot and tuft methods. The smoke-wire method was employed to visualize the flow structure qualitatively. The finite-volume-method and the SIMPLE-C algorithm with an orthogonal body-fitted grid were used for numerical simulation. Comparison of mean velocity profiles between the experiments and the numerical simulation shows a good agreement except for the separation region, however, the surface pressure data show almost similar distributions.
Key Words
hilly obstacle; numerical simulation; single hill; double hill; turbulence model; flow visualization.
Address
Pohang University of Science & Technology, San 31 Hyoja-Dong, 790-784, Pohang, Korea
Abstract
Wind-excited vibrations of slender structures can induce fatigue damage and cause structural failure without exceeding ultimate limit state. Unfortunately, the growing importance of this problem is coupled with an evident lack of simple calculation criteria. This paper proposes a mathematical method for evaluating the crosswind fatigue of slender vertical structures, which represents the dual formulation of a parallel method that the authors recently developed with regard to alongwind vibrations. It takes into account the probability distribution of the mean wind velocity at the structural site. The aerodynamic crosswind actions on the stationary structure are caused by the vortex shedding and by the lateral turbulence, both schematised by spectral models. The structural response in the small displacement regime is expressed in closed form by considering only the contribution of the first vibration mode. The stress cycle counting is based on a probabilistic method for narrow-band processes and leads to analytical formulae of the stress cycles histogram, of the accumulated damage and of the fatigue life. The extension of this procedure to take into account aeroelastic vibrations due to lock-in is carried out by means of ESDU method. The examples point out the great importance of vortex shedding and especially of lock-in concerning fatigue.
Abstract
The main purpose of this study is to discuss the design wind loads for the structural frames of single-layer latticed domes with long spans. First, wind pressures are measured simultaneously at many points on dome models in a wind tunnel. Then, the dynamic response of several models is analyzed in therntime domain, using the pressure data obtained from the wind tunnel experiment. The nodal displacements and the resultant member stresses are computed at each time step. The results indicate that the dome
